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Evaluating deep transfer learning for whole-brain cognitive decoding

This README file contains the following sections:

Project description

This repository supplements our preprint:

Thomas, A. W., Lindenberger, U., Samek, W., Müller, K.-R. (2021). Evaluating deep transfer learning for whole-brain cognitive decoding. arXiv preprint arXiv:2111.01562

With this repository we provide access to two main packages (deeplight and hcprep; see below), which allow to easily apply the DeepLight framework to the task-fMRI data of the Human Connectome Project (HCP):

  • deeplight is a simple python package that provides easy access to two pre-trained DeepLight architectures (2D-DeepLight and 3D-DeepLight; see below), which are designed for cognitive decoding of whole-brain fMRI data. Both architecturs were pre-trained with the fMRI data of 400 individuals in six of the seven HCP experimental tasks (all tasks except for the working memory task, which we left out for testing purposes; click here for details on the HCP data).
  • hcprepis a simple python package that allows to easily download the HCP task-fMRI data in a preprocessed format via the Amazon Web Services (AWS) S3 storage system and to transform these data into the tensorflow records data format, which is optimised for the training of DL models with tensorflow.

Repository organization

├── poetry.lock         <- Overview of project dependencies
├── pyproject.toml      <- Details of installed dependencies
├── README.md           <- This README file
├── .gitignore          <- Specifies files ignored by git
|
├── scrips/
|    ├── decode.py      <- An example of how to decode fMRI data with `deeplight`
|    ├── download.py    <- An example of how to download the preprocessed HCP fMRI data with `hcprep`
|    ├── interpret.py   <- An example of how to interpret fMRI data with `deeplight`
|    └── preprocess.sh  <- An example of how to preprocess fMRI data with `hcprep`
|    └── train.py       <- An example of how to train with `deeplight`
|
└── src/
|    ├── deeplight/
|    |    └──           <- The `deeplight` package
|    ├── hcprep/
|    |    └──           <- The 'hcprep' package
|    ├── modules/
|    |    └──           <- The 'modules' package (a dependency of `deeplight`)
|    └── setup.py       <- Makes 'deeplight', `hcprep`, and `modules` pip-installable (pip install -e .)

Installation

deeplight and hcprep are written for python 3.6 and require a working python environment (we recommend pyenv for python version management).

To install the dependencies, first clone and switch to this repository:

git clone https://github.com/athms/evaluating-deeplight-transfer.git
cd evaluating-deeplight-transfer

This project manages python dependencies with python poetry. To install all required dependencies with poetry, run:

poetry install

To then also install deeplight and hcprep in your poetry environment, run:

cd src/
poetry run pip3 install -e .

Packages

HCPrep

hcprep provides basic functionality to download the preprocessed HCP task-fMRI data (see here for details on the preprocessing steps) and store these locally in the Brain Imaging Data Structure (BIDS) format.

To make the downloaded fMRI data usable for DL analyses with tensorflow, hcprep further provides basic data cleaning and preprocessing functionalities.

Getting data access: To download the HCP task-fMRI data, you will need AWS access to the HCP public data directory. A detailed instruction can be found here. Make sure to safely store the ACCESS_KEY and SECRET_KEY; they are required to access the data via the AWS S3 storage system.

AWS configuration: Setup your local AWS client (as described here) and add the following profile to '~/.aws/config'

[profile hcp]
region=eu-central-1

Choose the region based on your location.

TFR data storage: hcprep can store the preprocessed task-fMRI data locally in TFRecords format. In this format, each entry corresponds to an individual fMRI volume (i.e., TR) of the data with the following features:

  • volume: the flattened volume voxel activations with shape 91x109x91 (flattened over the X (91), Y (109), and Z (91) dimensions)
  • task_id, subject_id, run_id: numerical id of task, subject, and run
  • tr: TR of the volume in the experimental task
  • state: numerical label of the cognive state associated with the volume in its task (e.g., [0,1,2,3] for the four cognitive states of the working memory task)
  • onehot: one-hot encoding of the cognitive state across all HCP experimental tasks that are used for training (e.g., there are 20 cognitive tasks across the seven experimental tasks of the HCP; the four cognitive states of the working memory task could thus be mapped to the last four positions of the one-hot encoding, with indices [16: 0, 17: 1, 18: 2, 19: 3])

Basic descriptive information about the HCP task-fMRI data is provided in hcp.info.basics:

hcp_info = hcprep.info.basics()

Specifically, basics contains the following information:

  • tasks: names of all HCP experimental tasks ('EMOTION', 'GAMBLING', 'LANGUAGE', 'MOTOR', 'RELATIONAL', 'SOCIAL', 'WM')
  • subjects: dictionary containing 1000 subject IDs for each task
  • runs: run IDs ('LR', 'RL')
  • t_r: repetition time of the fMRI data in seconds (0.72)
  • states_per_task: dictionary containing the label of each cognitive state of each task
  • onehot_idx_per_task: index that is used to assign cognitive states of each task to the onehotencoding of the TFR-files across tasks (see onehot above)

For further details on the experimental tasks and their cognitive states, click here.

DeepLight

deeplight implements two DeepLight architectures ("2D" and "3D"; see our preprint for details), which can be accessed as deeplight.two (2D) and deeplight.three (3D).

Importantly, both DeepLight architectures operate on the level of individual whole-brain fMRI volumes (e.g., individual TRs).

2D-DeepLight: The whole-brain fMRI volume is first sliced into a sequence of axial 2D-images (from bottom-to-top). These images are passed to a DL model, consisting of a 2D-convolutional feature extractor as well as an LSTM unit and output layer. First, the 2D-convolutional feature extractor reduces the dimensionality of the axial brain images through a sequence of 2D-convolution layers. The resulting sequence of higher-level slice representations is then fed to a bi-directional LSTM, modeling the spatial dependencies of brain activity within and across brain slices. Lastly, 2D-DeepLight outputs a decoding decision about the cognitive state underlying the fMRI volume, through a softmax output layer with one output unit per cognitive state in the data.

3D-DeepLight: The whole-brain fMRI volume is passed to a 3D-convolutional feature extractor, consisting of a sequence of twelve 3D-convolution layers. The 3D-convolutional feature extractor directly projects the fMRI volume into a higher-level, but lower dimensional, representation of whole-brain activity, without the need of an LSTM unit. To make a decoding decision, 3D-DeepLight utilizes an output layer that is composed of a 1D- convolution and global average pooling layer as well as a softmax activation function. The 1D-convolution layer maps the higher-level representation of whole-brain activity of the 3D-convolutional feature extractor to one representation for each cognitive state in the data, while the global average pooling layer and softmax function then reduce these to a decoding decision.

To interpret the decoding decisions of the two DeepLight architectures, relating their decoding decisions to the fMRI data, deeplight makes use of the LRP technique. The LRP technique decomposes individual decoding decisions of a DL model into the contributions of the individual input features (here individual voxel activities) to these decisions.

Both deeplight architectures implement basic fit, decode, and interpret methods, next to other functionalities. For details on how to {train, decode, interpret} with deeplight, see the example scripts provided in scripts/.

For any further methdological details on the two DeepLight architectures and their training, see our preprint.

Please note that we currently recommend to run any applications of interpret with 2D-DeepLight on CPU instead of GPU, due to its high memory demand (assuming that your available CPU memory is larger than your available GPU memory). This switch can be made by setting the environment variable export CUDA_VISIBLE_DEVICES="". We are currently working on reducing the overall memory demand of interpret with 2D-DeepLight and will push a code update soon.

Modules

modules is a fork of the modules module from interprettensor, which deeplight uses to build the 2D-DeepLight architecture. Note that modules is licensed differently from the other python packages in this repository (see modules/LICENSE).

Basic usage

You can find a set of example python scripts in scripts/, which illustrate how to download and preprocess the task-fMRI data from the Human Connectome Project with hcprep and how to {train on, decode, interpret} fMRI data with the two DeepLight architectures of deeplight.

You can run individual scripts in your poetryenvironment with:

cd scripts/
poetry run python <SCRIPT NAME>