Release Notes

2.8.0 (Upcoming)

Minor changes

  • Added support to set boundary metadata for SpatialSeries. (#524)

  • Added columns waveform_mean_index and waveform_sd_index to Units to make the waveform_mean and waveform_sd columns ragged. This allows for a different number of waveform means/SDs per unit which is useful when each unit is associated with a different number of electrodes and there is a waveform mean/SD for each electrode and unit. (#576)

2.7.0 (February 7, 2024)

Minor changes

  • Fixed typos in docstrings. (#560)

  • Deprecated ImagingRetinotopy neurodata type. (#565)

  • Modified OptogeneticSeries to allow 2D data, primarily in extensions of OptogeneticSeries. (#564)

  • Added optional stimulus_template column to IntracellularStimuliTable as part of the IntracellularRecordingsTable. (#545)

  • Added support for NWBDataInterface and DynamicTable in NWBFile.stimulus. (#559)

2.6.0 (January 17, 2023)

Minor changes

  • Added OnePhotonSeries. (#523)

  • Subject.age has a new optional attribute, reference, which can take a value of “birth” (default) or “gestational”. (#525)

  • Added “in seconds” to the doc of Units.spike_times. (#530)

2.5.0 (June 14, 2022)

Major changes

  • Shape of is more restrictive to prevent > 3 columns. (#510)

Minor changes

  • The elements x, y, z, imp and filtering are now optional instead of required. (#506)

  • Added an offset attribute to all TimeSeries objects to allow enhanced translation to scientific units. (#494)

  • Allowed NWBFile/stimulus/templates to contain Images objects. (#459)

  • Added new optional “order_of_images” dataset to Images that contains an ordered list of object references to Image objects stored in the same Images object. This dataset must be used if the images are referred to by index, e.g., from an IndexSeries object. Created new neurodata type ImageReferences which should be used for this dataset. (#459, #518, #519, #520)

  • Overhauled IndexSeries type (#459): - Fixed dtype of data dataset of IndexSeries (int32 -> uint32). - Updated unit attribute of data to have fixed value “N/A”. - Updated docstrings for the conversion, resolution, and offset attributes of data to indicate that these fields are not used. - Added link to an Images object, which contains an ordered collection of images. - Discouraged use of the indexed_timeseries link to an ImageSeries.

  • Updated TimeIntervals to use the new TimeSeriesReferenceVectorData type. This does not alter the overall structure of TimeIntervals in a major way aside from changing the value of the neurodata_type attribute in the file from VectorData to `TimeSeriesReferenceVectorData. This change replaces the existing TimeIntervals.timeseries column with a TimeSeriesReferenceVectorData type column of the same name and overall schema. This change facilitates creating common functionality around TimeSeriesReferenceVectorData. This change affects all existing TimeIntervals tables as part of the intervals/ group, i.e., intervals/epochs, intervals/trials, and intervals/invalid_times. (#486)

  • Clarified the doc string for the reference column of the electrodes table. (#498)

  • Added cell_id field to IntracellularElectrode. (#512)

2.4.0 (Aug. 11, 2021)

Major changes

  • Added new TimeSeriesReferenceVectorData type for referencing ranges of TimeSeries from a VectorData column (#470)

  • Integrated the intracellular electrophysiology experiment metadata table structure developed as part of the ndx-icephys-meta extension project with NWB (#470). This includes the following new types:

    • IntracellularRecordingsTable is an AlignedDynamicTable for managing individual intracellular recordings and to group together a stimulus and response from a single electrode recording. The table contains the following category tables:

      • IntracellularElectrodesTable; a DynamicTable for storing metadata about the IntracellularElectrode used

      • IntracellularStimuliTable; a DynamicTable for storing metadata about the recorded stimulus TimeSeries using the new TimeSeriesReferenceVectorData type to reference TimeSeries

      • IntracellularResponsesTable; a DynamicTable for storing metadata about the recorded response TimeSeries using the new TimeSeriesReferenceVectorData type to reference TimeSeries

    • SimultaneousRecordingsTable is a DynamicTable for grouping different intracellular recordings from the IntracellularRecordingsTable together that were recorded simultaneously from different electrodes and for storing metadata about simultaneous recordings

    • SequentialRecordingsTable is a DynamicTable for grouping different sequential recordings from the SimultaneousRecordingsTable together and storing metadata about sequential recordings

    • RepetitionsTable a DynamicTable for grouping different sequential intracellular recordings from the SequentialRecordingsTable together and storing metadata about repetitions

    • ExperimentalConditionsTable is a DynamicTable for grouping different intracellular recording repetitions from the RepetitionsTable together and storing metadata about experimental conditions

  • Added the new intracellular electrophysiology metadata tables to /general/intracellular_ephys as part of NWBFile (#470)


  • SweepTable has been deprecated in favor of the new intracellular electrophysiology metadata tables. Use of SweepTable is still possible but no longer recommended. (#470)

  • /general/intracellular_ephys/filtering has been deprecated in favor of IntracellularElectrode.filtering (#470)

Bug Fixes

  • Fixed incorrect dtype for electrodes table column “filtering” (float -> text) (#478)

  • Removed quantity: * from the type definitions of OptogeneticStimulusSite and ImagingPlane. This change improves clarity of the schema to follow best practices. It has no functional effect on the schema. (#472)

  • Updated ImageSeries to have its data dataset be required. Since ImageSeries is a TimeSeries and is required, should also be a required dataset. Otherwise this creates problems for inheritance and validation. If ImageSeries data are stored in an external file, then should be set to an empty 3D array. (#481)

2.3.0 (May 12, 2021)

  • Add optional waveforms column to the Units table.

  • Add optional strain field to Subject.

  • Add to DecompositionSeries an optional DynamicTableRegion called source_channels.

  • Add to ImageSeries an optional link to Device.

  • Add optional continuity field to TimeSeries.

  • Add optional filtering attribute to ElectricalSeries.

  • Clarify documentation for electrode impedance and filtering.

  • Add description of extra fields.

  • Set the stimulus_description for IZeroCurrentClamp to have the fixed value N/A.

  • Update hdmf-common-schema from 1.1.3 to version 1.5.0. - The HDMF-experimental namespace was added, which includes the ExternalResources and EnumData data types. Schema in the HDMF-experimental namespace are experimental and subject to breaking changes at any time. - Added experimental data type ExternalResources for storing ontology information / external resource references. - Added experimental data type EnumData to store data from a set of fixed values. - Changed dtype for datasets within CSRMatrix from ‘int’ to ‘uint’ and added missing data_type_inc: Container to the CSRMatrix type. - Added data type SimpleMultiContainer, a Container for storing other Container and Data objects together. - Added data type AlignedDynamicTable, a DynamicTable type with support for categories (or sub-headings) each described by a separate DynamicTable. - Fixed missing dtype for VectorIndex. - VectorIndex now extends VectorData instead of Index. - Removed unused and non-functional Index data type. - See for full release notes.

2.2.5 (May 29, 2020)

  • Add schema validation CI.

  • Fix incorrect dims and shape for ImagingPlane.origin_coords and ImagingPlane.grid_spacing, and fix incorrect dims for TwoPhotonSeries.field_of_view.

2.2.4 (April 14, 2020)

  • Fix typo in nwb.ophys.yaml that prevents proper parsing of the schema.

2.2.3 (April 13, 2020)

  • Move nested type definitions to root of YAML files. This does not functionally change the schema but simplifies parsing of the schema and extensions by APIs.

  • Make ImagingPlane.imaging_rate optional to handle cases where an imaging plane is associated with multiple time series with different rates.

  • Add release process documentation.

2.2.2 (March 2, 2020)

  • Fix shape and dims of for color images

  • Allow more than one OpticalChannel object in ImagingPlane

  • Update hdmf-common-schema to 1.1.3. This fixes missing ‘shape’ and ‘dims’ key for types VectorData, VectorIndex, and DynamicTableRegion.

  • Revert changes to nwb.retinotopy.yaml in 2.1.0 which break backward compatibility and were not supported by the APIs in any case. Changes will be revisited in a future version.

2.2.1 (January 14, 2020)

  • Fixed incorrect version numbers in nwb.file.yaml and hdmf-common-schema/common/namespace.yaml.

2.2.0 (January 6, 2020)

  • Moved common data structures such as Container and DynamicTable to hdmf-common-schema.

  • Added “channel_conversion” dataset to ElectricalSeries to represent per-channel conversion factors.

  • Added “sampling_rate” and “unit” attributes to “waveform_mean” and “waveform_sd” datasets/columns in Units table.

  • Added “description” and “manufacturer” attributes to Device.

  • Deprecated ImagingPlane “manifold” in favor of “origin_coords” and “grid_spacing”

  • Use “text” data type for all DynamicTable “colnames”. Previously, only ASCII was allowed.

  • Use “text” data type for electrode table columns “location” and “group_name”. Previously, only ASCII was allowed.

  • Added to description to make electrode x,y,z consistent with CCF reference.

  • Added “position” dataset with compound data type x,y,z in ElectrodeGroup.

  • Avoid enforcing “uint64” for sweep numbers for better compatibility. Use uint instead which is 32bit.

  • Set dtype for Image and its subtypes to numeric. (note: technically this breaks backwards compatibility, in the schema, but the pynwb API has always enforced that Images have a numeric type, and realistically we do not think users are storing strings in an Image dataset.)

  • Added “resolution” attribute to “spike_times” column of Units.

  • Changed the “quantity” key of attribute Units.resolution to “required” for schema language compliance.

  • Removed “required” key from dataset ImageSeries.field_of_view for schema language compliance.

  • Replaced “required” keys with “quantity” keys for ImagingPlane.origin_coords and ImagingPlane.grid_spacing for schema language compliance.

  • Refactored ImagingRetinotopy type to reduce redundancy.

  • Added “doc” key to ImagingRetinotopy.axis_2_power_map for schema language compliance.

  • Fixed makefiles for generating documentation on Windows.

  • Added optional “reference” column in “electrodes” table.

  • Changed dims of ImageSeries from (frame, y, x) to (frame, x, y) and (frame, z, y, x) to (frame, x, y, z) to be consistent with the dimension ordering in PlaneSegmentation.

  • Changed dims of Image from (y, x) to (x, y). (note: as far as we know, users of NWB 2.0 that use the Image type encode their data as (x, y)) to be consistent with the dimension ordering in ImageSeries.

  • Updated hdmf-common-schema to version 1.1.0 which includes:

    • The ‘colnames’ attribute of DynamicTable changed from data type ‘ascii’ to ‘text’.

    • Improved documentation and type docstrings.

2.1.0 (September 2019)

  • Improved documentation in “doc” attribute of many types

  • Removed “help” attribute

  • Removed static “description” attribute from some types

    • These were intended to be a “help” attribute, which has now been removed

    • For example, TimeIntervals dataset “start_time” attribute “description” had a fixed value that is now removed

  • Reordered keys

  • Added “dims” attribute for datasets where “shape” was specified without “dims”

    • The “dims” attribute describes the data along each dimension of the dataset and is helpful to provide alongside “shape”

    • For example, NWBFile dataset “keywords” has attribute “shape” has one entry: “null”. The attribute “dims” was added with one entry: “num_keywords”

  • Removed redundant specifications that are inherited from a parent type

  • ElectrodeGroup link “device”: optional -> required

  • Matched default and fixed values of datasets and attributes with the documentation and intended use

    • IZeroClampSeries dataset “bias_current” unspecified value -> fixed value 0.0

    • IZeroClampSeries dataset “bridge_balance” unspecified value -> fixed value 0.0

    • IZeroClampSeries dataset “capacitance_compensation” unspecified value -> fixed value 0.0

    • TimeSeries dataset “resolution” default value: 0.0 -> -1.0

    • ImagingRetinotopy dataset “axis_descriptions” attribute “shape”: null -> 2

    • DecompositionSeries dataset “data” attribute “unit” default value unspecified -> default value “no unit”

    • VoltageClampStimulusSeries, CurrentClampSeries, IZeroClampSeries attribute “unit” has fixed value “volts”

    • CurrentClampStimulusSeries, VoltageClampSeries, attribute “unit” has fixed value “amperes”

  • NWBFile dataset “experimenter” and “related_publications” change from scalar to 1-D, unlimited arrays

  • Standardized units to be plural, lower-case, SI units

    • TimeSeries dataset “starting_time” attribute “unit” fixed value: “Seconds” -> “seconds”

    • TimeSeries dataset “timestamps” attribute “unit” fixed value: “Seconds” -> “seconds”

    • ElectricalSeries dataset “data” attribute “unit” default value (previously optional): “volt” -> fixed value “volts”

    • SpikeEventSeries dataset “data” attribute “unit” default value (previously optional): “volt” -> fixed value “volts”

    • SpikeEventSeries dataset “timestamps” attribute “unit” fixed value (previously optional): “Seconds” -> fixed value “seconds”

    • EventDetection dataset “times” attribute “unit” default value: “Seconds” -> “seconds”

    • VoltageClampSeries dataset “capacitance_fast” attribute “unit” default value “Farad” -> fixed value “farads”

    • VoltageClampSeries dataset “capacitance_slow” attribute “unit” default value “Farad” -> fixed value “farads”

    • VoltageClampSeries dataset “resistance_comp_bandwidth” attribute “unit” default value “Hz” -> fixed value “hertz”

    • VoltageClampSeries dataset “resistance_comp_correction” attribute “unit” default value “percent” -> fixed value “percent”

    • VoltageClampSeries dataset “resistance_comp_prediction” attribute “unit” default value “percent” -> fixed value “percent”

    • VoltageClampSeries dataset “whole_cell_capacitance_comp” attribute “unit” default value “Farad” -> fixed value “farads”

    • VoltageClampSeries dataset “whole_cell_series_resistance_comp” attribute “unit” default value “Ohm” -> fixed value “ohms”

    • OptogeneticSeries dataset “data” attribute “unit” default value “watt” -> fixed value “watts”

    • ImagingPlane dataset “manifold” attribute “unit” default value “Meter” -> default value “meters”

    • see for details

  • Made Units table column “waveform_mean” and “waveform_sd” have shape num_units x num_samples x num_electrodes

  • Made CorrectedImageStack and ImagingRetinotopy inherit from the more specific NWBDataInterface instead of NWBContainer

  • Added a scratch space for saving arbitrary datasets to an NWBFile

    • NWB is cumbersome as a format for day-to-day work. There is a lot of overheard to save one-off analysis results to an NWB file. To save new datasets, a user has write an extension. This is a lot of work for a result that may just be tossed out.

    • “scratch” is now an optional top-level group under NWBFile that can hold NWBContainer groups and ScratchData datasets

    • The scratch space is explicitly for non-standardized data that is not intended for reuse by others. Standard NWB types, and extensions if required, should always be used for any data that you intend to share. As such, published data should not include scratch data and a user should be able to ignore any data stored in scratch to use a file.

    • See for details

  • Set the default value for the dataset “format” to “raw” and clarified the documentation for ImageSeries

  • Add required attribute object_id to all NWB Groups and Datasets with an assigned neurodata_type

Backwards compatibility: The PyNWB and MatNWB APIs can read 2.0 files with the 2.1 schema.

2.0.2 (June 2019)

2.0.1 (March 2019)

Change: Added doc and title descriptions for the individual source files included in the main namespace.

Reason: Enhance documentation of the namespace and facilitate presentation of types in autogenerated docs by making it easier to sort neurodata_types into meaningful categories (i.e., sections) with approbriate tiles and descriptions.

Backwards compatibility: No changes to the actual specification of the format are made. 2.0.1 is fully compatible with 2.0.0.

2.0.0 (January 2019)

Main release: November 2017 (Beta), November 2018 (RC), January 2019 (final)

Added new base data types: NWBContainer, NWBData, NWBDataInterface

Change: Added common base types for Groups, Datasets, and for Groups storing primary experiment data

Reason Collect common functionality and ease future evolution of the standard

Specific Changes

Support general data structures for data tables and vector data

Support row-based and column-based tables

Change: Add support for storing tabular data via row-based and column-based table structures.

Reason: Simplify storage of complex metadata. Simplify storage of dynamic and variable-length metadata.

Format Changes:

  • Row-based tables: are implemented via a change in the specification language through support for compound data types The advantage of row-based tables is that they 1) allow referencing of sets of rows via region-references to a single dataset (e.g., a set of electrodes), 2) make it easy to add rows by appending to a single dataset, 3) make it easy to read individual rows of a table (but require reading the full table to extract the data of a single column). Row-based tables are used to simplify, e.g., the organization of electrode-metadata in NWB 2 (see above). (See the specification language release notes for details about the addition of compound data types in the schema).

    • Referencing rows in a row-based tables: Subsets of rows can referenced directly via a region-reference to the row-based table. Subsets

    • Referencing columns in a row-based table: This is currently not directly supported, but could be implemented via a combination of an object-reference to the table and a list of the labels of columns.

  • Column-based tables: are implemented via the new neurodata_type DynamicTable. A DynamicTable is simplified-speaking just a collection of an arbitrary number of VectorData table column datasets (all with equal length) and a dataset storing row ids and a dataset storing column names. The advantage of the column-based store is that it 1) makes it easy to add new columns to the table without the need for extensions and 2) the column-based storage makes it easy to read individual columns efficiently (while reading full rows requires reading from multiple datasets). DynamicTable is used, e.g., to enhance storage of trial data. (See )

    • Referencing rows in column-based tables: As DynamicTable consist of multiple datasets (compared to row-based tables which consists of a single 1D dataset with a compound datatype) is not possible to reference a set of rows with a single region reference. To address this issue, NWB defines DynamicTableRegion (added later in PR634 (PyNWB)) dataset type, which stores a list of integer indices (row index) and also has an attribute table with the object reference to the corresponding DynamicTable.

    • Referencing columns in a columns-based table: As each column is a separate dataset, columns of a column-based DynamicTable can be directly references via links, object-references and region-references.

Enable efficient storage of large numbers of vector data elements

Change Introduce neurodata_types VectorData , VectorIndex, ElementIdentifiers

Reason To efficiently store spike data as part of UnitTimes a new, more efficient data structure was required. This builds the general, reusable types to define efficient data storage for large numbers of data vectors in efficient, consolidated arrays, which enable more efficient read, write, and search (see Improved storage of unit-based data).

Format Changes

  • VectorData : Data values from a series of data elements are concatenated into a single array. This allows all elements to be stored efficiently in a single data array.

  • VectorIndex : 1D dataset of exclusive stop-indices selecting subranges in VectorData. In addition, the target attribute stores an object reference to the corresponding VectorData dataset. With this we can efficiently access single sub-vectors associated with single elements from the VectorData collection. An alternative approach would be store region-references as part of the VectorIndex. We opted for stop-indices mainly because they are more space-efficient and are easier to use for introspection of index values than region references.

  • ElementIdentifiers : 1D array for storing unique identifiers for the elements in a VectorIndex.

See Improved storage of unit-based data for an illustration and specific example use in practice. See also I116 (nwb-schema) and PR382 (PyNWB) for further details.

Use new table and vector data structures to improve data organization

Improved organization of electrode metadata in /general/extracellular_ephys

Change: Consolidate metadata from related electrodes (e.g., from a single device) in a single location.

Example: Previous versions of the format specified in /general/extracellular_ephys for each electrode a group <electrode_group_X> that stores 3 text datasets with a description, device name, and location, respectively. The main /general/extracellular_ephys group then contained in addition the following datasets:

  • electrode_group text array describing for each electrode_group (implicitly referenced by index) which device (shank, probe, tetrode, etc.) was used,

  • electrode_map array with the x,y,z locations of each electrode

  • filtering, i.e., a single string describing the filtering for all electrodes (even though each electrode might be from different devices), and iv),

  • impedance, i.e., a single text array for impedance (i.e., the user has to know which format the string has, e.g., a float or a tuple of floats for impedance ranges).


  • Avoid explosion of the number of groups and datasets. For example, in the case of an ECoG grid with 128 channels one had to create 128 groups and corresponding datasets to store the required metadata about the electrodes using the original layout.

  • Simplify access to related metadata. E.g., access to metadata from all electrodes of a single device requires resolution of a potentially large number of implicit links and access to a large number of groups (one per electrode) and datasets.

  • Improve performance of metadata access operations. E.g., to access the location of all electrodes corresponding to a single recording in an <ElectricalSeries> in the original layout required iterating over a potentially large number of groups and datasets (one per electrode), hence, leading to a large number of small, independent read/write/seek operations, causing slow performance on common data accesses. Using the new layout, these kind of common data accesses can often be resolved via a single read/write

  • Ease maintenance, use, and development through consolidation of related metadata

Format Changes

  • Added specification of a new neurodata type <ElectrodeGroup> group. Each <ElectrodeGroup> contains the following datasets to describe the metadata of a set of related electrodes (e.g., all electrodes from a single device):

    • description : text dataset (for the group)

    • device: Soft link to the device in /general/devices/

    • location: Text description of the location of the device

  • Added table-like dataset electrodes that consolidates all electrode-specific metadata. This is a DynamicTable describing for each electrode:

    • id : a user-specified unique identifier

    • x, y, z : The floating point coordinate for the electrode

    • imp : the impedance of the channel

    • location : The location of channel within the subject e.g. brain region

    • filtering : Description of hardware filtering

    • group : Object reference to the ElectrodeGroup object

    • group_name : The name of the ElectrodeGroup

  • Updated /general/extracellular_ephys as follows:

    • Replaced /general/extracellular_ephys/<electrode_group_X> group (and all its contents) with the new <ElectrodeGroup>

    • Removed /general/extracellular_ephys/electrode_map dataset. This information is now stored in the ElectrodeTable.

    • Removed /general/extracellular_ephys/electrode_group dataset. This information is now stored in <ElectrodeGroup>/device.

    • Removed /general/extracellular_ephys/impedance This information is now stored in the ElectrodeTable.

    • Removed /general/extracellular_ephys/filtering This information is now stored in the ElectrodeTable.


In NWB 2.0Beta the refactor originally used a row-based table for the ElectrodeTable based on a compound data type as described in #I6 (new-schema), i.e., electrodes was a 1D compound dataset. This was later changed to a column-based DynamicTable (see Support row-based and column-based tables). The main reason for this later change was mainly to avoid the need for large numbers of user-extensions to add electrode metadata (see #I623 (PyNWB) and PR634 (PyNWB) for details.) This change also removed the optional description column as it can be added easily by the user to the DynamicTable if required.

Improved storage of lab-specific meta-data

Reason: Labs commonly have specific meta-data associated with sessions, and we need a good way to organize this within NWB.

Changes: The datatype LabMetaData has been added to the schema within /general so that an extension can be added to /general by inheriting from LabMetaData.

For further details see I19 (nwb-schema) and PR751 (PyNWB).

Improved storage of Spectral Analyses (Signal Decomposition)

Reason: Labs commonly use analyses that involve frequency decomposition or bandpass filtering of neural or behavioral data, and it is difficult to standardize this data and meta-data across labs.

Changes: A new datatype, DecompositionSeries has been introduced to offer a common interface for labs to exchange the result of time-frequency analysis. The new type offers a DynamicTable to allow users to flexibly add features of bands, and a place to directly link to the TimeSeries that was used.

For further details see #I46 (nwb-schema) and #PR764 (PyNWB)

Improved storage of Images


  • Improve consistency of schema: Previously there was a reference to Image from ImageSeries, however Image was not defined in the schema

  • Support different static image types

Changes: Image was added as a base type, and subtypes were defined: GrayscaleImage, RGBImage, and RGBAImage (The “A” in “RGBA” is for alpha, i.e., opacity).

Improved storage of ROIs


  • Improve efficiency: Similar to epochs, in NWB 1.x ROIs were stored as a single group per ROI. This structure is inefficient for storing large numbers of ROIs.

  • Make links explicit: The relationship of RoiResponseSeries to ROI objects was implicit (i.e. ROI was specified by a string), so one had to know a priori which ImageSegmentation and ImagingPlane was used to produce the ROIs.

  • Support 3D ROIs: Allow users to add 3D ROIs collected from a multi-plane image.

Changes: The main types for storing ROIs in NWB 2 are ImageSegmentation which stores 0 or more PlaneSegmentation. PlaneSegmentation is a DynamicTable for managing image segmentation results of a specific imaging plane. The ROIs are referenced by RoiResponseSeries which stores the ROI responses over an imaging plane. During the development of NWB 2 the management of ROIs has been improved several times. Here we outline the main changes (several of which were ultimately merged together in the PlaneSegmentation type).

  1. Added neurodata_type ImageMasks replacing ROI.img_mask (from NWB 1.x) with (a) a 3D dataset with shape [num_rois, num_x_pixels, num_y_pixels] (i.e. an array of planar image masks) or (b) a 4D dataset with shape [num_rois, num_x_pixels, num_y_pixels, num_z_pixels] (i.e. an array of volumetric image masks) ImageMasks was subsequently merged with PlaneSegmentation and is represented by the VectorData table column image_mask in the table.

  2. Added neurodata_type PixelMasks which replaces ROI.pix_mask/ROI.pix_mask_weight (from NWB 1.x) with a table that has columns “x”, “y”, and “weight” (i.e. combining ROI.pix_mask and ROI.pix_mask_weight into a single table). PixelMasks was subsequently merged with PlaneSegmentation and is represented by the VectorData dataset pixel__mask that is referenced from the table via the VectorIndex column pixel_mask_index.

  3. Added analogous neurodata_type VoxelMasks with a table that has columns “x”, “y”, “z”, and “weight” for 3D ROIs. VoxelMasks was subsequently merged with PlaneSegmentation and is represented by the VectorData dataset voxel_mask that is referenced from the table via the VectorIndex column voxel_mask_index.

  4. Added neurodata_type ROITable which defines a table for storing references to the image mask and pixel mask for each ROI (see item 1,2). The ROITable type was subsequently merged with the PlaneSegmentation type and as such does no longer appear as a separate type in the NWB 2 schema but PlaneSegmentation takes the function of ROITable.

  5. Added neurodata_type ROITableRegion for referencing a subset of elements in an ROITable. Subsequently ROITableRegion has been replaced by DynamicTableRegion as the ROITable changed to a DynamicTable and was merged with PlaneSegmentation (see 8.)

  6. Replaced RoiResponseSeries.roi_names with RoiResponseSeries.rois, which is a DynamicTableRegion into the PlaneSegmentation table of ROIs (see items 3,4). (Before ROITable was converted from a row-based to a column-based table, RoiResponseSeries.rois` had been changed to a ROITableRegion which was then subsequently changed to a corresponding DynamicTableRegion)

  7. Removed RoiResponseSeries.segmentation_interface. This information is available through RoiResponseSeries.rois (described above in 5.)

  8. Assigned neurodata_type PlaneSegmentation to the image_plan group in ImageSegmentation and updated it to use the ROITable, ImageMasks, PixelMasks, and :VoxelMasks (see items 1-4 above). Specifically, PlaneSegmentation has been changed to be a DynamicTable and ROITable, ImageMasks, PixelMasks, and VoxelMasks have been merged into the PlaneSegmentation table, resulting in the removal of the ROITable, ROITableRegion, ImageMasks, PixelMasks, and VoxelMasks types.

For additional details see also:

Improved storage of unit-based data

In NWB 1.0.x data about spike units was stored across a number of different neurodata_types, specifically UnitTimes, ClusterWaveforms, and Clustering. This structure had several critical shortcomings, which were addressed in three main phases during the development of NWB 2.

Problem 1: Efficiency: In NWB 1.x each unit was stored as a separate group unit_n containing the times and unit_description for unit with index n. In cases where users have a very large number of units, this was problematic with regard to performance. To address this challenge UnitTimes has been restructured in NWB 2 to use the new VectorData , VectorIndex, ElementIdentifiers data structures (see Enable efficient storage of large numbers of vector data elements).Specifically, NWB 2 replaced unit_n (from NWB 1.x, also referred to by neurodata_type SpikeUnit in NWB 2beta) groups in UnitTimes with the following data:

  • unit_ids : ElementIdentifiers dataset for storing unique ids for each element

  • spike_times_index: VectorIndex dataset with region references into the spike times dataset

  • spike_times: VectorData dataset storing the actual spike times data of all units in a single data array (for efficiency).

See also I116 (nwb-schema) and PR382 (PyNWB) for further details.

UnitTimes data structure overview

Fig. 1 Overview of the basic data structure for storing UnitTimes using the VectorData (spike_times), VectorIndex (spike_times_index), and ElementIdentifiers (unit_ids) data structures.

Problem 2: Dynamic Metadata: Users indicated that it was not easy to store user-defined metadata about units. To address this challenge, NWB 2 added an optional top-level group units/ (which was subsequently moved to /intervals/units) which is a DynamicTable with id and description columns and optional additional user-defined table columns. See PR597 on PyNWB for detailed code changes. See the PyNWB docs for a short tutorial on how to use unit metadata. See NWBFile Groups: /units for an overview of the unit schema.

Problem 3: Usability: Finally, users found that storing unit data was challenging due to the fact that the information was distributed across a number of different types. To address this challenge, NWB 2.0 integrates UnitTimes, ClusterWaveforms, and Clustering (deprecated) into the new column-based table units/ (i.e., intervals/units) (which still uses the optimized vector data storage to efficiently store spike times). See for discussions and I674 on PyNWB (and related I675 on PyNWB) and the pull request PR684 on PyNWB for detailed changes.

Together these changes have resulted in the following improved structure for storing unit data and metadata in NWB 2.0.

Spiking units data structure overview

Fig. 2 Overview of the data structure for storing spiking unit data and metadata in NWB 2.0.

In addition to spike_times, the units table includes the following optional columns:
  • obs_intervals: intervals indicating the time intervals over which this unit was recorded.

  • electrodes: range references to the electrodes table indicating which electrodes from which this unit was recorded.

  • electrode_group: may be used instead of electrodes if mutually exclusive electrode groups are sufficient.

  • waveform_mean: mean waveform across all recorded spikes.

  • waveform_sd: standard deviation from the mean across all recorded spikes.

Improved support for sweep-based information

Changes Added SweepTable type stored in /general/intracellular_ephys

Reason: In Icephys it is common to have sweeps (i.e., a group of PatchClampSeries belonging together, were up to two TimeSeries are from one electrode, including other TimeSeries not related to an electrode (aka TTL channels)). NWB 1.0.x did not support the concept of sweeps, so it was not possible to link different TimeSeries for sweeps. The goal of this change is to allow users to find the TimeSeries which are from one sweep without having to iterate over all present TimeSeries.

Format Changes Added neurodata_type SweepTable to /general/intracellular_ephys. SweepTable is a DynamicTable <sec-DynamicTable> storing for each sweep a the sweep_number and the series_index. The later is a VectorIndex pointing to a VectorData dataset describing belonging PatchClampSeries to the sweeps. See I499 (PyNWB) and PR701 (PyNWB) for further details.

Improved specification of reference time stamp(s)

To improve the specification of reference time, NWB adopts ISO8061 for storing datetimes and adds timestamps_reference_time as explicit zero for all timestamps in addition to the session_start_time.

Improve standardization of reference time specification using ISO8061

Changes: Modify session_start_time an file_create_date to enforce use of ISO 8601 datetime strings

Reason: Standardize the specification of timestamps to ensure consistent programmatic and human interpretation

Format Changes: Updated session_start_time and file_create_date to use dtype: isodatetime that was added as dedicated dtype to the specification language. For details see PR641 (PyNWB) and I50 (nwb-schema).

Improved specification of reference time

Change: Add field timestamps_reference_time, allowing users to explicitly specify a date and time corresponding to time zero for all timestamps in the nwb file.

Reason: Previously session_start_time served both as the indicator for the start time of a session as well as the global reference time for a file. Decoupling the two makes the global reference time explicit and enables users to use times relative to the session start as well as other reference time frames, e.g., using POSIX time. This also makes the specification easier to develop against, since this will explicitly specify the offset to obtain relative timestamps, eliminating the need for APIs to guess based on range.

Format Changes: Added top-level field timestamps_reference_time. See PR709 (PyNWB) and I49 (nwb-schema) for further details.

Improved storage of time intervals

Improved storage of epoch data

Change: Store epoch data as a table to improve efficiency, usability and extensibility.

Reason: In NWB 1.x Epochs are stored as a single group per Epoch. Within each Epoch, the index into each TimeSeries that the Epoch applies to was stored as a single group. This structure is inefficient for storing large numbers of Epochs.

Format Changes: In NWB 2 epochs are stored via a TimeIntervals table (i.e., a DynamicTable for storing time intervals) that is stored in the group /intervals/epochs. Over the course of the development of NWB 2 the epoch storage has been refined in several phases:

  • First, we create a new neurodata_type Epochs which was included in NWBFile as the group epochs. This simplified the extension of the epochs structure. /epochs at that point contained a compound (row-based) table with neurodata_type EpochTable that described the start/stop times, tags, and a region reference into the TimeSeriesIndex to identify the timeseries parts the epoch applies to. Note, the types Epochs, EpochTable and TimeSeriesIndex have been removed/superseded in subsequent changes. (See PR396 (PyNWB) and I119 (nwb-schema) ).

  • Later, an additional DynamicTable for storing dynamic metadata about epochs was then added to the Epochs neurodata_type to support storage of dynamic metadata about epochs without requiring users to create custom extensions (see PR536 (PyNWB)).

  • Subsequently the epoch table was then fully converted to a DynamicTable (see PR682 (PyNWB) and I664 (PyNWB))

  • Finally, the EpochTable was then moved to /intervals/epochs and the EpochTable type was replaced by the more general type TimeIntervals. This also led to removal of the Epochs type (see PR690 (PyNWB) and I683 (PyNWB))

Improved support for trial-based data

Change: Add dedicated concept for storing trial data.

Reason: Users indicated that it was not easy to store trial data in NWB 1.x.

Format Changes: Added optional group /intervals/trials/ which is a DynamicTable with id, start_time, and stop_time columns and optional additional user-defined table columns. See PR536 on PyNWB for detailed code changes. See the PyNWB docs for a short tutorial on how to use trials. See NWBFile Groups: /trials for an overview of the trial schema. Note: Originally trials was added a top-level group trials which was then later moved to /intervals/trials as part of the generalization of time interval storage as part of PR690 (PyNWB) .

Generalized storage of time interval

Change: Create general type TimeIntervals (which is a generalization of the previous EpochTable type) and create top-level group /intervals for organizing time interval data.

Reason: Previously all time interval data was stored in either epochs or trials. To facilitate reuse and extensibility this has been generalized to enable users to create arbitrary types of intervals in addition to the predefined types, i.e., epochs or trials.

Format Changes: See PR690 (PyNWB) and I683 (PyNWB) for details:

  • Renamed EpochTable type to the more general type TimeIntervals to facilitate reuse.

  • Created top-level group /intervals for organizing time interval data.

    • Moved /epochs to /intervals/epochs and reused the TimeIntervals type

    • Moved /trials to /intervals/trials and reused the TimeIntervals type

    • Allow users to add arbitrary TimeIntervals tables to /intervals

    • Add optional TimeIntervals object named invalid_times in ‘’/intervals``, which specifies time intervals that contain artifacts. See I224 (nwb-schema) and PR731 (PyNWB) for details.

Improved consistency, identifiably, and readability

Improved identifiably of objects

Change: All groups and datasets are now required to either have a unique name or a unique neurodata_type defined.

Reason: This greatly simplifies the unique identification of objects with variable names.

Format Changes: Defined missing neurodata_types for a number of objects, e.g.,:

  • Group /general/optophysiology/<imaging_plane_X> now has the neurodata type ImagingPlane

  • Group /general/intracellular_ephys/<electrode_X> now has the neurodata type IntracellularElectrode

  • Group /general/optogenetics/<site_X> now has the neurodata type StimulusSite

To enable identification of the type of objects, the neurodata_type is stored in HDF5 files as an attribute on the corresponding object (i.e., group or dataset). Also information about the namespace (e.g., the name and version) are stored as attributed to allow unique identification of the specification for storage objects.

Simplified extension of subject metadata

Specific Change: Assigned neurodata_type to /general/subject to enable extension of the subject container directly without having to extend NWBFile itself. (see and for details)

Reduce requirement for potentially empty groups

Change: Make several previously required fields optional

Reason: Reduce need for empty groups.

Format Changes: The following groups/datasets have been made optional:

  • /epochs : not all experiments may require epochs.

  • /general/optogenetics : not all experiments may use optogenetic data

  • device in IntracellularElectrode

Added missing metadata

Change: Add a few missing metadata attributes/datasets.

Reason: Ease data interpretation, improve format consistency, and enable storage of additional metadata

Format Changes:

  • /general/devices text dataset becomes group with neurodata type Device to enable storage of more complex and structured metadata about devices (rather than just a single string)

  • Added attribute unit=Seconds to <EventDetection>/times dataset to explicitly describe time units and improve human and programmatic data interpretation

  • Added filtering dataset to type <IntracellularElectrode> (i.e., /general/intracellular_ephys/<electrode_X>) to enable specification of per-electrode filtering data

  • Added default values for <TimeSeries>/description and <TimeSeries>/comments

Improved Consistency

Change: Rename objects, add missing objects, and refine types

Reason: Improve consistency in the naming of data objects that store similar types of information in different places and ensure that the same kind of information is available.

Format Changes:

  • Added missing help attribute for <BehavioralTimeSeries> to improve consistency with other types as well as human data interpretation

  • Renamed dataset image_plan_name in <ImageSegmentation> to image_plane to ensure consistency in naming with <TwoPhotonSeries>

  • Renamed dataset electrode_name in <PatchClampSeries> to electrode for consistency (and since the dataset is now a link, rather than a text name).

  • Renamed dataset electrode_idx in <FeatureExtraction> to electrode_group for consistency (and since the dataset is now a link to the <ElectrodeGroup>)

  • Renamed dataset electrode_idx in <ElectricalSeries> to electrode_group for consistency (and since the dataset is now a link to the <ElectrodeGroup>)

  • Changed imaging_rate field in ImagingPlane from text to float. See PR697 (PyNWB) and I136 (nwb-schema) for details

Added keywords field

Change: Added keywords fields to /general

Reason: Data archive and search tools often rely on user-defined keywords to facilitate discovery. This enables users to specify keywords for a file. (see PR620 (PyNWB))

Removed source field

Change: Remove required attribute source from all neurodata_types

Reason: In NWB 1.0.x the attribute source was defined as a free text entry intended for storage of provenance information. In practice, however, this attribute was often either ignored, contained no useful information, and/or was misused to encode custom metadata (that should have been defined via extensions).

Specific Change: Removed attribute source from the core base neurodata_types which effects a large number of the types throughout the NWB schema. For further details see PR695 (PyNWB))

Removed ancestry field

Change: Removed the explicit specification of ancestry as an attribute as part of the format specification

Reason: 1) avoid redundant information as the ancestry is encoded in the inheritance of types, 2) ease maintenance, and 3) avoid possible inconsistencies between the ancestry attribute and the true ancestry (i.e., inheritance hierarchy) as defined by the spec.

Note The new specification API as part of PyNWB/HDMF makes the ancestry still easily accessible to users. As the ancestry can be easily extracted from the spec, we currently do not write a separate ancestry attribute but this could be easily added if needed. (see also PR707 (PyNWB), I24 (nwb-schema))

Improved organization of processed and acquisition data

Improved organization of processed data

Change: Relaxed requirements and renamed and refined core types used for storage of processed data.

Reason: Ease user intuition and provide greater flexibility for users.

Specific Changes: The following changes have been made to the organization of processed data:

  • Module has been renamed to ProcessingModule to avoid possible confusion

    and to clarify its purpose. Also ProcessingModule may now contain any NWBDataInterface.

  • With NWBDataInterface now being a general base class of TimeSeries, this means that it is now possible to define data processing types that directly inherit from TimeSeries, which was not possible in NWB 1.x.

  • Interface has been renamed to NWBDataInterface to avoid confusion and ease intuition (see above)

  • All Interface types in the original format had fixed names. The fixed names have been replaced by specification of corresponding default names. This change enables storage of multiple instances of the same analysis type in the same ProcessingModule by allowing users to customize the name of the data processing types, whereas in version 1.0.x only a single instance of each analysis could be stored in a ProcessingModule due to the requirement for fixed names.

Simplified organization of acquisition data

Specific Changes:

  • /acquisition may now store any primary data defined via an NWBDataInterface type (not just TimeSeries).

  • /acquisition/timeseries and /acquisition/images have been removed

  • Created a new neurodata_type Images for storing a collection of images to replace acquisition/images and provide a more general container for use elsewhere in NWB (i.e., this is not meant to replace ImageSeries)

Other changes:

Improved governance and accessibility

Change: Updated release and documentation mechanisms for the NWB format specification

Reason: Improve governance, ease-of-use, extensibility, and accessibility of the NWB format specification

Specific Changes

  • The NWB format specification is now released in separate Git repository

  • Format specifications are released as YAML files (rather than via Python .py file included in the API)

  • Organized core types into a set of smaller YAML files to ease overview and maintenance

  • Converted all documentation documents to Sphinx reStructuredText to improve portability, maintainability, deployment, and public access

  • Sphinx documentation for the format are auto-generated from the YAML sources to ensure consistency between the specification and documentation

  • The PyNWB API now provides dedicated data structured to interact with NWB specifications, enabling users to programmatically access and generate format specifications

Specification language changes

Change: Numerous changes have been made to the specification language itself in NWB 2.0. Most changes to the specification language effect mainly how the format is specified, rather than the actual structure of the format. The changes that have implications on the format itself are described next. For an overview and discussion of the changes to the specification language see specification language release notes.

Specification of dataset dimensions

Change: Updated the specification of the dimensions of dataset

Reason: To simplify the specification of dimension of datasets and attribute

Format Changes:

  • The shape of various dataset is now specified explicitly for several datasets via the new shape key

  • The unit for values in a dataset are specified via an attribute on the dataset itself rather than via unit definitions in structs that are available only in the specification itself but not the format.

  • In some cases the length of a dimension was implicitly described by the length of structs describing the components of a dimension. This information is now explicitly described in the shape of a dataset.

Removed datasets defined via autogen

Change Support for autogen has been removed from the specification language. After review of all datasets that were produced via autogen it was decided that all autogen datasets should be removed from the format.

Reason The main reasons for removal of autogen dataset is to ease use and maintenance of NWB files by 1) avoiding redundant storage of information (i.e., improve normalization of data) and 2) avoiding dependencies between data (i.e., datasets having to be updated due to changes in other locations in a file).

Format Changes

  • Datasets/Attributes that have been removed due to redundant storage of the path of links stored in the same group:

    • IndexSeries/indexed_timeseries_path

    • RoiResponseSeries/segmentation_interface_path

    • ImageMaskSeries/masked_imageseries_path

    • ClusterWaveforms/clustering_interface_path

    • EventDetection/source_electricalseries_path

    • MotionCorrection/image_stack_name/original_path

    • NWBFile/epochs/epoch_X.links

  • Datasets//Attributes that have been removed because they stored only a list of groups/datasets (of a given type or property) in the current group.

    • Module.interfaces (now ProcessingModule)

    • ImageSegmentation/image_plane/roi_list

    • UnitTimes/unit_list

    • TimeSeries.extern_fields

    • TimeSeries.data_link

    • TimeSeries.timestamp_link

    • TimeSeries.missing_fields

  • Other datasets/attributes that have been removed to ease use and maintenance because the data stored is redundant and can be easily extracted from the file:

    • NWBFile/epochs.tags

    • TimeSeries/num_samples

    • Clustering/cluster_nums

Removed 'neurodata\_type=Custom'

Change The 'neurodata\_type=Custom' has been removed.

Reason All additions of data should be governed by extensions. Custom datasets can be identified based on the specification, i.e., any objects that are not part of the specification are custom.

1.0.x (09/2015 - 04/2017)

NWB 1.0.x has been deprecated. For documents relating to the 1.0.x schema please see

1.0.6, April 8, 2017

Minor fixes:

  • Modify <IntervalSeries>/ documentation to use html entities for < and >.

  • Fix indentation of unit attribute data_type, and conversion attribute description in /general/optophysiology/<imaging_plane_X>/manifold.

  • Fix typos in <AnnotationSeries>/ conversion, resolution and unit attributes.

  • Update documentation for IndexSeries to reflect more general usage.

  • Change to all numerical version number to remove warning message when installing using setuptools.

1.0.5i_beta, Dec 6, 2016

Removed some comments. Modify author string in info section.

1.0.5h_beta, Nov 30, 2016

Add dimensions to /acquisition/images/<image_X>

1.0.5g_beta, Oct 7, 2016

  • Replace group options: autogen: {"type": "create"} and "closed": True with "\_properties": {"create": True} and "\_properties": {"closed": True}. This was done to make the specification language more consistent by having these group properties specified in one place ("\_properties" dictionary).

1.0.5f_beta, Oct 3, 2016

  • Minor fixes to allow validation of schema using json-schema specification in file using utility check\

1.0.5e_beta, Sept 22, 2016

  • Moved definition of <Module>/ out of /processing group to allow creating subclasses of Module. This is useful for making custom Module types that specified required interfaces. Example of this is in python-api/examples/create\_scripts/ and the extension it uses (extensions/

  • Fixed malformed html in nwb\ documentation.

  • Changed html generated by doc\ to html5 and fixed so passes validation at

1.0.5d_beta, Sept 6, 2016

  • Changed ImageSeries img_mask dimensions to: "dimensions": ["num\_y","num\_x"] to match description.

1.0.5c_beta, Aug 17, 2016

  • Change IndexSeries to allow linking to any form of TimeSeries, not just an ImageSeries

1.0.5b_beta, Aug 16, 2016

  • Make 'manifold' and 'reference\_frame' (under /general/optophysiology) recommended rather than required.

  • In all cases, allow subclasses of a TimeSeries to fulfill validation requirements when an instance of TimeSeries is required.

  • Change unit attributes in VoltageClampSeries series datasets from required to recommended.

  • Remove 'const'=True from TimeSeries attributes in AnnotationSeries and IntervalSeries.

  • Allow the base TimeSeries class to store multi-dimensional arrays in 'data'. A user is expected to describe the contents of ‘data’ in the comments and/or description fields.

1.0.5a_beta, Aug 10, 2016

Expand class of Ids allowed in TimeSeries missing\_fields attribute to allow custom uses.

1.0.5_beta Aug 2016

  • Allow subclasses to be used for merges instead of base class (specified by 'merge+' in format specification file).

  • Use 'neurodata\_type=Custom' to flag additions that are not describe by a schema.

  • Exclude TimeSeries timestamps and starting time from under /stimulus/templates

1.0.4_beta June 2016

  • Generate documentation directly from format specification file.”

  • Change ImageSeries external\_file to an array.

  • Made TimeSeries description and comments recommended.

1.0.3 April, 2016

  • Renamed "ISI\_Retinotopy" to "ISIRetinotopy"

  • Change ImageSeries external\_file to an array. Added attribute starting\_frame.

  • Added IZeroClampSeries.

1.0.2 February, 2016

  • Fixed documentation error, updating 'neurodata\_version' to 'nwb\_version'

  • Created ISI\_Retinotopy interface

  • In ImageSegmentation module, moved pix\_mask::weight attribute to be its own dataset, named pix\_mask\_weight. Attribute proved inadequate for storing sufficiently large array data for some segments

  • Moved 'gain' field from Current/VoltageClampSeries to parent PatchClampSeries, due need of stimuli to sometimes store gain

  • Added Ken Harris to the Acknowledgements section

1.0.1 October 7th, 2015

  • Added 'required' field to tables in the documentation, to indicate if group/dataset/attribute is required, standard or optional

  • Obsoleted 'file\_create\_date' attribute 'modification\_time' and made file\_create\_date a text array

  • Removed 'resistance\_compensation' from CurrentClampSeries due being duplicate of another field

  • Upgraded TwoPhotonSeries::imaging\_plane to be a required value

  • Removed 'tags' attribute to group ‘epochs’ as it was fully redundant with the 'epoch/tags' dataset

  • Added text to the documentation stating that specified sizes for integer values are recommended sizes, while sizes for floats are minimum sizes

  • Added text to the documentation stating that, if the TimeSeries::data::resolution attribute value is unknown then store a NaN

  • Declaring the following groups as required (this was implicit before)


\_ images/

\_ timeseries/






\_ presentation/

\_ templates/

This is to ensure consistency between .nwb files, to provide a minimum expected structure, and to avoid confusion by having someone expect time series to be in places they’re not. I.e., if 'acquisition/timeseries' is not present, someone might reasonably expect that acquisition time series might reside in 'acquisition/'. It is also a subtle reminder about what the file is designed to store, a sort of built-in documentation. Subfolders in 'general/' are only to be included as needed. Scanning 'general/' should provide the user a quick idea what the experiment is about, so only domain-relevant subfolders should be present (e.g., 'optogenetics' and 'optophysiology'). There should always be a 'general/devices', but it doesn’t seem worth making it mandatory without making all subfolders mandatory here.

1.0.0 September 28th, 2015

  • Convert document to .html

  • TwoPhotonSeries::imaging\_plane was upgraded to mandatory to help enforce inclusion of important metadata in the file.