Controlling human striatal cognitive function via the frontal cortex.

Cognitive flexibility is known to depend on the striatum. However, the striatum does not act in isolation to bias cognitive flexibility. In particular, cognitive flexibility also implicates the frontal cortex. Here we tested the hypothesis that the human frontal cortex controls cognitive flexibility by regulating striatal function via topographically specific frontostriatal connections. To this end, we exploited a repetitive transcranial magnetic stimulation (TMS) protocol over frontal cortex that is known to increase dopamine release in the striatum. This intervention was combined with functional magnetic resonance imaging to determine the functional and topographic specificity of its consequences at the whole brain level. Participants were scanned both before and after off-line TMS while performing a cognitive switching task that is known to depend on a specific striatal substructure, the putamen. Frontal stimulation perturbed task-specific functional signals in the putamen, while reducing fronto-striatal functional connectivity. There were no such effects of TMS over the medial parietal cortex. These data strengthen the hypothesis that cognitive flexibility involves topographic frontal control of striatal function