Coordinated cross-brain activity during accumulation of sensory evidence and decision commitment

Neural correlates of decision-making, like other cognitive variables, can be found throughout the brain, but what coordinated computations generate these brain-wide signals is poorly understood. To address this, we chronically implanted many Neuropixels probes in rats to simultaneously record from thousands of neurons across up to twenty brain regions during performance of an auditory decision making task. This allowed decoding, on the same set of trials and for each of the simultaneously recorded regions, the time-varying state of the decision as it is being formed. During decision formation, we found strong moment-by-moment co-fluctuations in decision states across regions, even across trials with identical stimuli and choices, with the co-fluctuations lying largely along a single dimension, indicating a shared computation. However, the shared decision signals were strongest, and were detected earliest on single trials, in a subset of interconnected frontal cortical regions and anterior striatum, indicating that they are computed in a small subnetwork and then propagated more broadly. We also decoded from each region the estimated time of decision commitment, which corresponds to when the subject internally "makes up their mind" and stops considering new evidence. We again found strong co-fluctuations in the timing of this estimate across regions that lay along a single dominant dimension. Commitment signals were strongest and detected earliest in primary motor cortex. Finally, the moment of decision commitment marked a critical transition in coordinated decision-related activity across the brain. These results show that decision formation and commitment reflect internally-generated signals that are largely unified across the brain, demonstrating the power of large-scale simultaneous recordings to characterize the internal cognitive computations that structure brain-wide neural activity.