Unsupervised Sparse Coding-based Spiking Neural Network for Real-time Spike Sorting

TL;DR

This paper presents NSS, an unsupervised, sparse coding-based spiking neural network for real-time, low-power spike sorting that outperforms traditional methods on neuromorphic hardware.

Contribution

The study introduces NSS, a novel neuromorphic spike sorter utilizing sparse coding and custom neuron models for efficient, online, unsupervised neural signal classification.

Findings

NSS achieves higher F1-score (77%) than WaveClus3 and PCA+KMeans.

NSS operates with low power consumption (8.6mW) on Loihi 2.

NSS processes in 0.25ms per inference, enabling real-time performance.

Abstract

Spike sorting is a crucial step in decoding multichannel extracellular neural signals, enabling the identification of individual neuronal activity. A key challenge in brain-machine interfaces (BMIs) is achieving real-time, low-power spike sorting at the edge while keeping high neural decoding performance. This study introduces the Neuromorphic Sparse Sorter (NSS), a compact two-layer spiking neural network optimized for efficient spike sorting. NSS leverages the Locally Competitive Algorithm (LCA) for sparse coding to extract relevant features from noisy events with reduced computational demands. NSS learns to sort detected spike waveforms in an online fashion and operates entirely unsupervised. To exploit multi-bit spike coding capabilities of neuromorphic platforms like Intel's Loihi 2, a custom neuron model was implemented, enabling flexible power-performance trade-offs via adjustable spike bit-widths. Evaluations on simulated and real-world tetrode signals with biological drift showed NSS outperformed established pipelines such as WaveClus3 and PCA+KMeans. With 2-bit graded spikes, NSS on Loihi 2 outperformed NSS implemented with leaky integrate-and-fire neuron and achieved an F1-score of 77% (+10% improvement) while consuming 8.6mW (+1.65mW) when tested on a drifting recording, with a computational processing time of 0.25ms (+60 us) per inference.