medicine-neuro 1.3

MEDICINE: Motion Estimation by DIstributional Contrastive Inference for NEurophysiology.

MEDiCINe: Motion Estimation by DIstributional Contrastive Inference for NEurophysioloy

Introduction

MEDiCINe is a method for estimating motion in neurophysiology data for spike sorting. See our publication for a complete description of the method and results. The general idea of MEDiCINe is to decompose neural activity data into two components:

• The motion of the brain relative to a probe in depth.
• An activity distribution of the brain along the probe.

These two components are jointly optimized via gradient descent to maximize the likelihood of a dataset of detected spikes extracted from a neural recording session. Here is a video of this optimization process in action:

The red curves on the left show the motion learned by the model, the heatmap on the right show the activity distribution learned by the model and the scatterplots show detected spikes (colored by amplitude). Below is a schematic of the model:

Usage

Getting Started

We recomend using a virtual environment (e.g. conda or pipenv) to manage dependencies. Once in a virtual environment, install MEDiCINe with:

pip install medicine-neuro

This will also install the necessary dependencies. Then you can run the demo script with

python -m medicine_demos.run_demo

This will run the demo script and display several figures showing the results. See medicine_demos/run_demo.py for more details.

SpikeInterface Integration

Once you have installed MEDiCINe, you can use it to do motion correction in a SpikeInterface data processing pipeline. SpikeInterface peak detection methods require the numba package ($ pip install numba). Here is an example SpikeInterface pipeline with peak extraction and motion correction using MEDiCINe motion estimation:

from pathlib import Path
from medicine import run as run_medicine
import numpy as np

from spikeinterface.core.node_pipeline import ExtractDenseWaveforms, run_node_pipeline
from spikeinterface.sortingcomponents.motion.motion_interpolation import InterpolateMotionRecording
from spikeinterface.sortingcomponents.motion import motion_utils
from spikeinterface.sortingcomponents.peak_detection import detect_peak_methods
from spikeinterface.sortingcomponents.peak_localization import localize_peak_methods

# SpikeInterface recording object you would like to do motion correction for
recording = ...

# Detect, extract, and localize peaks, such as with the following pipeline
node_detect = detect_peak_methods['locally_exclusive'](
  recording, detect_threshold=10)
node_extract = ExtractDenseWaveforms(
  recording, parents=[node_detect], ms_before=0.1, ms_after=0.3)
node_localize = localize_peak_methods['monopolar_triangulation'](
    recording, parents=[node_detect, node_extract], return_output=True)
peaks, peak_locations = run_node_pipeline(
  recording,
  [node_detect, node_extract, node_localize],
  dict(chunk_duration='1s', n_jobs=-1, progress_bar=True),
  job_name='detect_and_localize',
  squeeze_output=False,
)

# Create directory to store MEDiCINe outputs for this recording
medicine_output_dir = Path('path/to/medicine/output/directory')
medicine_output_dir.mkdir(parents=True, exist_ok=True)

# Run MEDiCINe to estimate motion
run_medicine.run_medicine(
  peak_amplitudes=peaks['amplitude'],
  peak_depths=peak_locations['y'],
  peak_times=peaks['sample_index'] / recording.get_sampling_frequency(),
  output_dir=medicine_output_dir,
)

# Load motion estimated by MEDiCINe
motion = np.load(medicine_output_dir / 'motion.npy')
time_bins = np.load(medicine_output_dir / 'time_bins.npy')
depth_bins = np.load(medicine_output_dir / 'depth_bins.npy')

# Use interpolation to correct for motion estimated by MEDiCINe
motion_object = motion_utils.Motion(
  displacement=motion,
  temporal_bins_s=time_bins,
  spatial_bins_um=depth_bins,
)
recording_motion_corrected = InterpolateMotionRecording(
  recording,
  motion_object,
  border_mode='force_extrapolate',
)

# Continue with spike sorting or other processing on recording_motion_corrected.
# If you run a spike sorter with built-in motion correction, you may want to
# turn off that motion correction. If you use the SpikeInterface sorter module,
# this would entail `sorters.run_sorter(do_correction=False, ...)`.

Kilosort Integration

To-Do.

Hyperparameters

Here are descriptions of all of the hyperparameters in the MEDiCINe method:

• motion_bound: Float, default 800. A bound on the maximum allowed absolute motion, namely the spread of the motion function output. Units are the same as units of spike depth (typically microns). The motion function is smoothed after application of this bound, so we recommend being liberal with the bound. In all of our recording sessions, the value 800 worked well. Adjusting this parameter is unlikely to improve results unless you have very large-magnitude motion.

• time_bin_size: Float, default 1. Temporal resolution of motion estimation, in the same units as the spike times (typically seconds). The motion array discretizes the total session duration into temporal bins of this size. Note that the actual motion is smoothed and interpolated, so while this temporal resolution limits the computational complexity of the motion function, it does not make the motion function itself a discrete or step-wise function. We find that 1 second is sufficient for all of our datasets. Increasing this improves runtime slightly. Adjusting this parameter is unlikely to improve results.

• time_kernel_width: Float, default 30. Width of the triangular smoothing kernel applied to the motion function, in the same units as the spike times (typically seconds). If you have very high-frequency motion, you may want to reduce this. If you observe over-fitting or have very low firing rates, you may want to increase this.

• activity_network_hidden_features: Tuple, default (256, 256). Hidden layer sizes for the activity network. Adjusting this is unlikely to improve results.

• num_depth_bins: Int, default 2. Number of depth bins for motion estimation. A value of 1 will enforce uniform (rigid) motion at all depths. Higher numbers allow more complex dependencies of motion on depth. We find that a value of 2 to be sufficient for all of our datasets. A value of 2 allows linear interpolation of motion between two independently fit motion functions at the extremes of the array.

• amplitude_threshold_quantile: Float in [-1, 1], default 0. Cutoff quantile for peak amplitudes. If 0, no cutoff is applied and all peaks are used. If > 0, then the smallest amplitude_threshold_quantile fraction of amplitudes are ignored. If < 0, then the largest amplitude_threshold_quantile fraction of amplitudes are ignored. See "raw_raster_and_amplitudes.png" output figure for a histogram of all amplitudes used by the model. Typically 0 is a good value. However, if you find that there are a lot of low amplitude spikes and they may be causing the model to go astray, you may want to consider making this non-zero. Making it positive will remove low-amplitude spikes if the spike amplitudes are positive. Making it negative will remove low-amplitude spikes if the spike amplitudes are negative.

• batch_size: Int, default 4096. Batch size for optimization. Reducing this too low can cause unstable convergence (we have observed this with batch size 1024 and below). Adjusting this parameter is unlikely to improve results.

• training_steps: Int, default 10,000. Number of optimization steps to take. Reducing this improves runtime, but be careful to keep it greater than motion_noise_steps. Adjusting this parameter is unlikely to improve results.

• initial_motion_noise: Float, default 0.1. Magnitude of noise to add to the motion function output at the start of training. This is annealed to 0 in the first motion_noise_steps of training steps. Adding this noise avoids getting caught in local minima early in training. Adjusting this parameter is unlikely to improve results.

• motion_noise_steps: Int, default 2,000. Number of steps at the beginning of training to anneal the motion noise to 0. Adjusting this parameter is unlikely to improve results unless you reduce training_steps, in which case this should be reduced as well.

• optimizer: Torch optimizer, default torch.optim.Adam. Adjusting this parameter is unlikely to improve results.

• learning_rate: Float, default 0.0005. Adjusting this parameter is unlikely to improve results.

• epsilon: Float, default 0.001. Prevents divide-by-zero instabilities. Adjusting this parameter is unlikely to improve results.

• plot_figures: Bool, default True. Whether to plot and save figures summarizing the model results.

The MEDiCINe model is not sensitive to most of these hyperparameters. We have never needed to tune hyperparameters for any of dozens of our NHP neurophysiology datasets. The only parameters we can imagine may be necessary to tune are motion_bound, time_kernel_width, and amplitude_threshold_quantile.

Troubleshooting Results

After running MEDiCINe, check the figures it produces (figures will be written to the output directory, printed to the console as the model runs). The most useful figure to look at is corrected_motion_raster.png. If you see unsatisfactory results in this figure, here are some potential problems and resolutions:

1. Overfitting. If you have very few neurons or low firing rates, you may find that the motion estimation overfits and looks excessively wiggly. In this case, you may want to try setting num_depth_bins = 1, which will enforce uniform (rigit) motion and reduce overfitting. You may also want to increase the motion smoothing kernel size time_kernel_width.
2. Underfitting. If your data has high-frequency motion and it looks like the motion is not capturing this, you may want to reduce time_kernel_width. If your motion has non-linear dependencies on depth, you may want to increase num_depth_bins.
3. Insufficient motion amplitude. If it looks like you have high-amplitude motion that MEDiCINe is not capturing that, try increasing motion_bound.
4. Bad spikes. If spike detection is poor, you may have a lot of bad spikes, such as low-amplitude spikes that are specific to particular channels and do not show motion. In this case increase amplitude_threshold_quantile. For example, setting amplitude_threshold_quantile = 0.25 will ignore the lowest-amplitude 25% of spikes. If high-amplitude spikes are the issue, set amplitude_threshold_quantile < 0.

Reproducing Our Results

To reproduce the results in our paper, please see https://github.com/jazlab/medicine_paper. This has all code and instructions for replicating our results.

Contact and Support

Please see CONTRIBUTING.md for information about support. Please email Nick Watters at [e-mail] with questions and feedback.

Reference

If you use MEDiCINe or a derivative of it in your work, please cite it as follows:

@article{watters2024,
author = {Nick Watters and Alessio Buccino and Mehrdad Jazayeri},
title = {MEDiCINe: Motion Estimation by DIstributional Contrastive Inference for NEurophysiology},
url = {https://arxiv.org/},
journal = {arXiv preprint arXiv:},
year = {2024}
}

MEDiCINe Website

The MEDiCINe website is a GitHub Pages website with a Slate theme. The website is generated from this README.md with the settings in _config.yml and the Ruby dependencies in Gemfile.

If you would like to modify the website, first make sure you can test deploying it locally by following the GitHub Pages testing instructions. Then modify this README.md and test deploy to view the changes before committing.

MEDiCINe Package