DISSOCIATING MOTOR AND COGNITIVE SIGNALS IN MICE TO LOCALIZE SHORT-MEMORY REPRESENTATIONS

Short-term memory is the ability to retain information over seconds to minutes to guide decisions. Its localization and neural basis remain unclear, as memory-related activity has been observed across many brain regions. To investigate this, we trained mice on an auditory delayed Go/No-Go task in which they had to lick 2 seconds after a rewarded sound (S+) and withhold licking after an unrewarded sound (S-). Using Neuropixels 1.0 probes, we recorded neural activity from multiple brain areas during the task, including subregions of the secondary motor cortex (M2), auditory cortex (AC), and hippocampus (HPC), while simultaneously monitoring body and facial movements with video recordings. Consistent with previous work, trial-averaged activity in most regions showed sustained or ramping responses during the delay period. However, these signals were only weakly predictive of behavioral performance due to large trial-to-trial variability. Video analysis revealed that delay-period neural activity was often correlated with facial movements. Removing the movement-predictable component of neural activity reduced stimulus decoding performance in several regions, suggesting that delay-related activity there primarily reflects motor processes rather than memory, itself partially correlated to memory retention. In contrast, a small subset of recording sites, particularly in the anterolateral motor cortex (ALM), maintained high stimulus decoding even after accounting for movement-related activity, indicating a genuine short-term memory representation. Together, these results suggest that while sensory information is actively maintained to guide behavior, robust short-term memory encoding is restricted to sparse neuronal populations, especially within secondary motor cortex.