Theresa M. Desrochers

Sequential Control in the Frontal Cortex: Studies in Monkeys and Humans

Performing sequential tasks such as making your breakfast are an integral part of daily life. The majority of previous studies have focused on motor sequences or non-sequential abstract control, rather than these kinds of more abstract sequential tasks. Our work using high-density multi-electrode chronic recordings in monkeys has shown that an integrated cost-benefit signal in the striatum is predicts the acquisition of habitual motor sequences. To move beyond motor sequences and address this gap in our knowledge of more abstract sequential tasks, we asked human participants to repeatedly perform simple four-item sequences of shape and color judgements during fMRI scanning. We found a novel dynamic in the rostrolateral prefrontal cortex (RLPFC), where activation ramped up across the four items in each sequence and reset at the beginning of each new sequence. Transcranial magnetic stimulation (TMS) to RLPFC during the same task selectively produced an increasing pattern of errors as each sequence progressed, mirroring the fMRI activation. Effects in the RLPFC during fMRI and two independent TMS experiments dissociated from two other prefrontal control regions. These results show that RLPFC is necessary for sequential control and resolution of uncertainty during sequence performance. Current work focuses on dissociating some of the processes that underlie sequential task control: task execution, sequential monitoring, and sequence memory. Preliminary results show that ramping in the RLPFC is robust to changes in sequential stimuli and monitoring conditions, suggesting that these dynamics in the frontal cortex may be a common mechanism for tracking sequential information. New studies are focusing on investigating frontal cortical dynamics during sequential control in parallel monkey fMRI and multi-electrode recordings.