Scripts for the analysis of the fMRI data of "The Little Prince" project (Hale, Pallier)

Micipsa - Songsheng YING

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soshyng@gmail.com

Modified from Christophe Pallier's git which allows to perform fMRI encoding experiments with regressions.

Requirements:

• Python: pandas, nistats, nibabel, nilearn, statsmodels

Differences from the original git

1. Pythonize the original makefile and use class methods to build regressors from onsets, design matrices from regressors.
2. Use config files to define model parameters and model comparison settings.
3. File organization by model and modelComp.
4. Use Ridge regression as the default regression model instead of GLM.
5. Generates r2, MSE scores for whole models, no longer provides feature-wise contrast maps.
6. Large GridSearch with shrinkage: step-wise forward feature selection & alpha.

How to make it work

General guidelines

Three class interfaces are created in lib/utils to manage file paths (Env), model configuration and training (Model) and cross-model comparison (ModelComparison). In any case of non-clarity of the following text, please refer to the raw code.

Initiating the environment

1. Clone the original repo

2. Execute the following code from the root directory to create necessary folders

from lib import utils
env = utils.Env('./', <lingua>)

3. Load event onsets (generation of semantic onsets in another repo) into ./data/onsets/<lingua>, <lingua> in the Micipsa project should be set to fr.

4. Load normalized fMRI data file in ./data/fmri/<lingua>/<subject>/<run.nii.gz>

Creating regression models

1. Create model configurations in ./models/<lingua>/<model_name> by creating config.json. Examples are available in the existing repo.

2. In the configuration file, base_regressors will ask the model to look in onset folders with exact-name-matching onset files. E.g. rms will point to <run_id>_rms.csv

3. embedding files will sequentially point to a series of onset files. It contains three subfields, with dim an integer value, name_base serving as onset file-name filters, and regressors which takes either a list of onset feature names, or a string infer, which would look for onset file starting with name_base and ending with an integer ranging from 0 to dim. E.g. in rms-wrate-cwrate-sim100 model, a list of regressor names are passed. In rms-wrate-cwrate-asn200, <run_id>_<name_base><dim_range>.csv are consulted.

4. alpha takes a list, of which members can either be a number, or a dictionary composed of three mandatory keys: start, end and step, which would be inflated into a log range.

5. dimension is similar to alpha, but the ranges are linear.

6. orthonormalize indicates if regressor orthonormalization should be performed at the creation of design matrices. If this field is absent, the model would set the value to true by default.

Model manipulation pipeline

1. Create model python object

model = utils.Model('<model_name>', env)

2. Configure model with configuration file, or by default with config.json in the corresponding folder

model.config_model()

3. Convolute event onsets to obtain separate regressors (regressors are shared across models)

model.generate_regressors()

4. Merge regressors into design matrices in the model local folder, check model.orthonormalize and env.verbose. Verbose flag would print and generate design matrix analysis files.

model.generate_design_matrices()

5. Finally the regression! The code will perform 9 cross validations (as the recordings are divided into 9 blocks both in English and French experiment), leaving 1 run out as validation data and 8 as training data. Voxel models are considered as independent and a uniform brain masker will be applied to transform the 3d fMRI array into an 1d array. The regression will store run-wise validation scores with each combination of alpha and dimension.

model.generate_individual_results(core_number=-1, verbose=None, output_type=['r2', 'mse', 'r'])

6. Group averages can be calculated with the following code.

model.generate_group_results()

Model comparison pipeline

The results generated with ModelComparison class is not used in the master's thesis.

Model comparison configuration files are located at ./model_contrasts/<lingua>/<comparison_name>.