Dissociation of the rostral and dorsolateral prefrontal cortex during sequence learning in saccades: a TMS investigation

This experiment sought to find if differences exist between the dorsolateral prefrontal cortex (DLPFC) and the medial rostral prefrontal cortex (MRPFC) for performing stimulus-independent and stimulus-oriented tasks respectively. To find a causal relationship in these areas we employed the use of trans-cranial magnetic stimulation (TMS). Prefrontal areas were stimulated whilst participants performed random or predictable sequence learning tasks at stimulus onset (1st presentation of the sequence only for both Random and Predictable), or during the inter-sequence interval. Overall, we found that during the predictable task a significant decrease in saccade latency, gain and duration was found when compared to the randomized conditions, as expected and observed previously. However, TMS stimulation in DLPFC during the delay in the predictive sequence learning task reduced this predictive ability by delaying the saccadic onset and generating abnormal reductions in saccadic gains during prediction. In contrast, we found that stimulation during a delay in MRPFC reversed the normal effects on peak velocity of the task with the predictive task revealing higher peak velocity than the randomized task. These findings provide causal evidence for independent functions of DLPFC and MRPFC in performing stimulus-independent processing during sequence learning in saccades.