Measuring instability in chronic human intracortical neural recordings towards stable, long-term brain-computer interfaces

Intracortical brain-computer interfaces (iBCIs) enable people with tetraplegia to gain intuitive cursor control from movement intentions. To translate to practical use, iBCIs should provide reliable performance for extended periods of time. However, performance begins to degrade as the relationship between kinematic intention and recorded neural activity shifts compared to when the decoder was initially trained. In addition to developing decoders to better handle long-term instability, identifying when to recalibrate will also optimize performance. We propose a method to measure instability in neural data without needing to label user intentions. Longitudinal data were analyzed from two BrainGate2 participants with tetraplegia as they used fixed decoders to control a computer cursor spanning 142 days and 28 days, respectively. We demonstrate a measure of instability that correlates with changes in closed-loop cursor performance solely based on the recorded neural activity (Pearson r = 0.93 and 0.72, respectively). This result suggests a strategy to infer online iBCI performance from neural data alone and to determine when recalibration should take place for practical long-term use. ### Competing Interest Statement The content is solely the responsibility of the authors and does not necessarily represent the official views of NIH or the Department of Veterans Affairs or the United States Government. The MGH Translational Research Center has a clinical research support agreement with Neuralink, Synchron, Reach Neuro, and Axoft for which L.R.H. provides consultative input. MGH is a subcontractor on an NIH SBIR with Paradromics. G.H.W. is a consultant for Artis Ventures. J.M.H. is a consultant for Neuralink and Paradromics and is a shareholder in Maplight Therapeutics and Enspire DBS. He is also an inventor on intellectual property licensed by Stanford University to Blackrock Neurotech and Neuralink.