Allen Brain Observatory

Create an nwb file from Allen Brain Observatory data.

This example demostrates the basic functionality of several parts of the pynwb write API, centered around the optical physiology submodule (pynwb.ophys). We will use the allensdk as a read API, while leveraging the pynwb data model and write api to transform and write the data back to disk.

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from datetime import datetime
from dateutil.tz import tzlocal

from allensdk.core.brain_observatory_cache import BrainObservatoryCache
import allensdk.brain_observatory.stimulus_info as si

from pynwb import NWBFile, NWBHDF5IO, TimeSeries
from pynwb.ophys import OpticalChannel, DfOverF, ImageSegmentation
from pynwb.image import ImageSeries, IndexSeries
from pynwb.device import Device


# Settings:
ophys_experiment_id = 562095852
save_file_name = 'brain_observatory.nwb'

Let’s begin by downloading an Allen Institute Brain Observatory file. After we cache this file locally (approx. 450 MB), we can open data assets we wish to write into our NWB:N file. These include stimulus, acquisition, and processing data, as well as time “epochs” (intervals of interest)”.

boc = BrainObservatoryCache(manifest_file='manifest.json')
dataset = boc.get_ophys_experiment_data(ophys_experiment_id)
metadata = dataset.get_metadata()
cell_specimen_ids = dataset.get_cell_specimen_ids()
timestamps, dFF = dataset.get_dff_traces()
stimulus_list = [s for s in si.SESSION_STIMULUS_MAP[metadata['session_type']]
                 if s != 'spontaneous']
running_data, _ = dataset.get_running_speed()
trial_table = dataset.get_stimulus_table('master')
trial_table['start'] = timestamps[trial_table['start'].values]
trial_table['end'] = timestamps[trial_table['end'].values]
epoch_table = dataset.get_stimulus_epoch_table()
epoch_table['start'] = timestamps[epoch_table['start'].values]
epoch_table['end'] = timestamps[epoch_table['end'].values]

1) First, lets create a top-level “file” container object. All the other NWB:N data components will be stored hierarchically, relative to this container. The data won’t actually be written to the file system until the end of the script.

nwbfile = NWBFile(
    session_description='Allen Brain Observatory dataset',
    identifier=str(metadata['ophys_experiment_id']),
    session_start_time=metadata['session_start_time'],
    file_create_date=datetime.now(tzlocal())
)

2) Next, we add stimuli templates (one for each type of stimulus), and a data series that indexes these templates to describe what stimulus was being shown during the experiment.

for stimulus in stimulus_list:
    visual_stimulus_images = ImageSeries(
        name=stimulus,
        data=dataset.get_stimulus_template(stimulus),
        unit='NA',
        format='raw',
        timestamps=[0.0])
    image_index = IndexSeries(
        name=stimulus,
        data=dataset.get_stimulus_table(stimulus).frame.values,
        unit='NA',
        indexed_timeseries=visual_stimulus_images,
        timestamps=timestamps[dataset.get_stimulus_table(stimulus).start.values])
    nwbfile.add_stimulus_template(visual_stimulus_images)
    nwbfile.add_stimulus(image_index)

3) Besides the two-photon calcium image stack, the running speed of the animal was also recordered in this experiment. We can store this data as a TimeSeries, in the acquisition portion of the file.

running_speed = TimeSeries(
    name='running_speed',
    data=running_data,
    timestamps=timestamps,
    unit='cm/s')

nwbfile.add_acquisition(running_speed)

4) In NWB:N, an “epoch” is an interval of experiment time that can slice into a timeseries (for example running_speed, the one we just added). PyNWB uses an object-oriented approach to create links into these timeseries, so that data is not copied multiple times. Here, we extract the stimulus epochs (both fine and coarse-grained) from the Brain Observatory experiment using the allensdk.

for _, row in trial_table.iterrows():
    nwbfile.add_epoch(start_time=row.start,
                      stop_time=row.end,
                      timeseries=[running_speed],
                      tags='trials')

for _, row in epoch_table.iterrows():
    nwbfile.add_epoch(start_time=row.start,
                      stop_time=row.end,
                      timeseries=[running_speed],
                      tags='stimulus')

5) In the brain observatory, a two-photon microscope is used to acquire images of the calcium activity of neurons expressing a fluorescent protien indicator. Essentially the microscope captures picture (30 times a second) at a single depth in the visual cortex (the imaging plane). Let’s use pynwb to store the metadata associated with this hardware and experimental setup:

optical_channel = OpticalChannel(
    name='optical_channel',
    description='2P Optical Channel',
    emission_lambda=520.,
)

device = Device(metadata['device'])
nwbfile.add_device(device)

imaging_plane = nwbfile.create_imaging_plane(
    name='imaging_plane',
    optical_channel=optical_channel,
    description='Imaging plane ',
    device=device,
    excitation_lambda=float(metadata['excitation_lambda'].split(' ')[0]),
    imaging_rate=30.,
    indicator='GCaMP6f',
    location=metadata['targeted_structure'],
    conversion=1.0,
    unit='unknown',
    reference_frame='unknown',
)

The Allen Insitute does not include the raw imaging signal, as this data would make the file too large. Instead, these data are preprocessed, and a dF/F flourescence signal extracted for each region-of-interest (ROI). To store the chain of computations necessary to describe this data processing pipeline, pynwb provides a “processing module” with interfaces that simplify and standarize the process of adding the steps in this provenance chain to the file:

ophys_module = nwbfile.create_processing_module(
    name='ophys_module',
    description='Processing module for 2P calcium responses',
)

6) First, we add an image segmentation interface to the module. This interface implements a pre-defined schema and API that facilitates writing segmentation masks for ROI’s:

image_segmentation_interface = ImageSegmentation(
    name='image_segmentation')

ophys_module.add(image_segmentation_interface)

plane_segmentation = image_segmentation_interface.create_plane_segmentation(
    name='plane_segmentation',
    description='Segmentation for imaging plane',
    imaging_plane=imaging_plane)

for cell_specimen_id in cell_specimen_ids:
    curr_name = cell_specimen_id
    curr_image_mask = dataset.get_roi_mask_array([cell_specimen_id])[0]
    plane_segmentation.add_roi(id=curr_name, image_mask=curr_image_mask)

7) Next, we add a dF/F interface to the module. This allows us to write the dF/F timeseries data associated with each ROI.

dff_interface = DfOverF(name='dff_interface')
ophys_module.add(dff_interface)

rt_region = plane_segmentation.create_roi_table_region(
    description='segmented cells with cell_specimen_ids',
)

dFF_series = dff_interface.create_roi_response_series(
    name='df_over_f',
    data=dFF,
    unit='NA',
    rois=rt_region,
    timestamps=timestamps,
)

Now that we have created the data set, we can write the file to disk:

with NWBHDF5IO(save_file_name, mode='w') as io:
    io.write(nwbfile)

For good measure, lets read the data back in and see if everything went as planned:

with NWBHDF5IO(save_file_name, mode='r') as io:
    nwbfile_in = io.read()

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