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Neuropixels course 2024 - quality control

This repository contains all resources and assignments that were used the quality control part of UCL's 2024 Neuropixels Course. These can also be useful to anyone starting out with bombcell. An review of these exercises can be found here. If you run into any issues or have any questions, you can create a github issue here.

We will go over a typical workflow to assess unit quality using bombcell and phy.

To help you navigate:

+ Action items are displayed in green code blocks
- Questions are displayed in red code blocks

Happy quality control-ing!

Setting up

We will use a freely available dataset generated by Nick Steinmetz that spans visual cortex, hippocampus, and some parts of thalamus in a mouse. This dataset was recorded on an early version of Neuropixels probes, and spike-sorted with an early version of Kilosort, but all these principles and methods are applicable accross Neuropixels probe types and Kilosort versions.

Download data

All the necessary data is located here. You will need to download the following files, and put them in one same folder :

  • amplitudes.npy
  • channel_map.npy
  • spike_templates.npy
  • spike_times.npy
  • template_feature_ind.npy
  • templates.npy
  • params.py
  • pc_feature_ind.npy
  • similar_templates.noy
  • whitening_mat.npy
  • whitening_mat_inv.npy
  • channel_positions.npy
  • stimInfo.mat
  • pc_features.pny
  • pc_features_ind.npy
  • Hopkins_20160722_g0_t0.imec.ap.meta
  • rawDataSample.bin

ONLY for this tutorial (this does not apply when using bombcell outside of this tutorial) - make you sure you do not have the following files:

  • spike_clusters.npy
  • - cluster_groups.csv

This is so that you don't see the previous manual curation and so you can look at units in un-biased way :)

Download and install bombcell

Requirements

For now, Bombcell is only available in MATLAB. If you don't have MATLAB, you can get a free 1-month license courtesy of Mathworks. See the slack for more details or email us: julie.mfabre@gmail.com.

If you don't wish to use MATLAB, you can wait for the Python version (coming soon!) and, for this exercise, use the pre-computed metrics and plots found in this repository. We will provide a few Python functions to load and inspect the metrics here :).

Bombcell requires MATLAB>=2019a and the following toolboxes:

  • Signal Processing Toolbox
  • Image Processing Toolbox
  • Statistics and Machine Learning Toolbox
  • Parallel Computing Toolbox

To install:

  • clone the repository and the dependencies. You can do this either via git/GitHub desktop or directly by downloading the .zip file and decompressing it (see the image below)

  • add bombcell's and the dependancies' folders to MATLAB's path. More details on how to do this here.

Dependencies

Download and install phy

Phy is a fast GUI to manually curate your data. Installation instructions can be found here and documentation here

Run bombcell

MATLAB users:

+ 1. Open the [`gettingStarted_NPXcourse.mlx`](https://github.com/bombcell/Neuropixels_course_2024/blob/main/gettingStarted_NPXcourse.mlx) file in MATLAB. 

+ 2. Edit line 1, changing the location to where you have saved the example dataset you downloaded - for instance if you saved your dataset in `Neuropixels_course_2024_dataset` folder in your `Downloads` folder: 

toy_dataset_location = 'C:\Users\Poppy\Downloads\Neuropixels_course_2024_dataset'

+ 3. Run the sections 1-3 (Set paths, Load data & Run quality metrics)

Python users:

see this repository: https://github.com/BombCell/PyBombCell-IO You will be able to look at bombcell's output, some plots and load the metrics in phy.

Inspect and refine results

Outputs

When you have run everything, Bombcell will have saved several files locally, and in particular:

  • a series of cluster_xxxx.tsv that contain each unit's quality metric xxxx. These files are automatically loaded in phy and the unit IDs are in the phy format here (0-indexed).
  • in the qMetrics folder:
    • a parquet file containing quality metrics for each unit and quality metric: templates._bc_qMetrics.parquet
    • a parquet file containing parameters for each quality metric: _bc_parameters._bc_qMetrics.parquet
    • (if param.extractRaw is true - in the exercise we have set it to false for the sake of simplicity) npy files containing mean raw extracted waveforms and their peak channels: templates._bc_rawWaveform.npy and templates._bc_rawWaveformPeakChannels.npy
    • (if param.extractRaw is true - in the exercise we have set it to false for the sake of simplicity) npy files to calculate the raw waveform's signal-to-noise ratio: templates._bc_baselineNoiseAmplitude.npy and templates._bc_baselineNoiseAmplitudeIndex.npy
    • a npy file indicated which spikes were detected as duplicates by bombcell: spikes._bc_duplicateSpikes.npy

+ MATLAB users only - Run [section 4 (Examples - accessing bombcell's metrics)] to understand how the data is saved and how it can be used. 
- What is the number of spikes in the unit with the kilosort/phy ID of 2?
- Can a unit be classified as MUA if it has more peaks than param.maxNPeaks?

Setting thresholds, checking bomcbell performance and refining

Look at bombcell's output plots!

Bombcell will output 3 types of plots that can help you get a very quick idea of how well it is performing and if any of the thresholds need to be tweaked.

  1. Waveform overview

The plot should look similar to the example one below (but yours will be slightly different!). This plot allows you to quickly see whether the algorithm is classifying noise and non-somatic units correctly. MATLAB users: look at the plot outputed by bombcell. Python users, you can view the plot here 

- Do the waveforms look well classified (are noise units, noisy, ect.)?
  1. UpSet plots

These plots show the intersections and relationships between multiple sets of data, displaying both the size and composition of these intersections in a compact and easily interpretable format. MOre information on UpSet plots can be found here. Bombcell generates 3: one for units classified as noise, one for units classified as non-somatic and one for units classified as MUA. Looking at them will give you an idea of how well bombcell is performing. The plots should look similar to the example ones below (but yours will be slightly different!). MATLAB users: look at the plot outputed by bombcell. Python users, you can view the plots here, here, and here.

+ Inspect the plots
- How many units are removed by the # troughs metric?
-     How many of these are also removed by other metrics?
- Are there any metrics that remove too many (i.e. the majority) of units?
- Are there any metrics that remove no units?
  1. Histograms of the distributions for each quality metric

The lines at the bottom indicate how the units are classified based on the metric: red for noise, blue for non-somatic, green for good and orange for MUA. The plot should look similar to the example one below (but yours will be slightly different!). MATLAB users: look at the plot outputed by bombcell. Python users, you can view the plots here

Look at bombcell's GUI

+ MATLAB users only - Run [Section 5: Inspect] to bring up bombcell's GUI. This lets you visualize your units, their quality metrics, how they were classified by bombcell and where each unit lies in the distribution of quality metric values.
+ flip through a few units using your keyboard to navigate:
+         left/right arrow: toggle between units 
+         g : go to next good unit 
+         m : go to next multi-unit 
+         n : go to next noise unit
+         a : go to next non-somatic unit ('a' is for aonxal)
+         up/down arrow: toggle between time chunks in the raw data
+         u: brings up a input dialog to enter the unit you want to go to

Python users: look at the two screenshots of the gui: screenshot1, screenshot2

- Look at unit 19:
-   Does it pass the spatial decay metric? 
-   Should it? 
-   Why does bombcell classify it as noise? 
-   Based on this unit, would you change the minimum spatial decay parameter?
- Look at unit 342:
-   Does it pass the # peaks metric? 
-   Should it? 
-   Why does bombcell classify it as noise? 
-   Look at what the current maximum number of peaks a unit can have to not be classified as noise. Would you change this parameter?

Look at and refine the outputs in phy

Once bombcell is run, its outputs are also automatically loaded in phy. (Python users, download all the .tsv files generated by bombcell here.)

+ Load up the dataset in phy (run `cd <your dataset location here>` and `phy template-gui params.py` in your terminal)
+ Sort units by the 'spatial decay' parameter (see image below)

- Where would you set the minimum spatial decay parameter, based on flipping through a few units? 
- In the good units, are there any you should split or merge?

Tip

  • An great live overview of manual curation can be found here.
  • You can arrange the windows in phy by dragging them around
  • Fine-tune the ACG bin size by typing :cb 0.5
  • All phy shortcuts are here: https://phy.readthedocs.io/en/latest/shortcuts/
  • To reset the GUI, launch phy with this command: `phy template-gui params.py --clear-cache --clear-state