A BRAIN-COMPUTER INTERFACE PARADIGM REVEALS DIFFERENT CONSTRAINTS ON CORTICAL AND STRIATAL ACTIVITY

Motor cortex (M1) and striatum are interconnected regions whose functional contributions to behaviour remain elusive. Some studies suggest that striatal activity primarily reflects cortical inputs, whereas others propose more sophisticated functional contributions. To distinguish between these two possibilities, we asked whether these regions show fundamental differences in the neural activity patterns they can produce. We designed a Brain-Computer Interface (BCI) task in which head-fixed mice running on a treadmill had to increase the firing rate of a few Neuropixels channels from either layer 5 of M1 or dorsolateral striatum (DLS) beyond an adaptive threshold to get a reward. At the same time, we simultaneously recorded the activity of hundreds of neurons from both areas. Mice learnt to voluntarily increase the firing rate of the target BCI channels in both areas without overtly modulating their running speed. Moreover, in most sessions, they exhibited anticipatory licking ~1s before the reward delivery, suggesting intentional control of the BCI. Interestingly, when the BCI channels were in M1, the increase in firing rate was reflected in neurons throughout the area, and occasionally even in DLS. In contrast, when the BCI channels were in DLS, the increase in firing rate was predominantly confined to neurons recorded in neighbouring channels. This result is consistent with previous studies showing that DLS population activity is more than a reflection of the ongoing activity in M1; instead, these two areas have fundamental differences in the flexibility and constraints of their neural population activity that we will examine in future work.