Functional connectivity between the dorsolateral prefrontal cortex and the ipsilateral primary motor cortex

Introduction The prefrontal cortex has a crucial role in higher cognitive functions and various line of evidence point to a tight connectivity network between the dorsolateral prefrontal cortex (DFLPC, BA46) and the ipsilateral primary motor cortex (M1). Objectives The main objective of this study was to determine the precise timing and the spatial specificity of this functional connectivity during the performance of a choice-reaction task. Materials and methods Twin coil, neuronavigated transcranial magnetic stimulation (TMS) was used during the performance of a choice-reaction task. By varying the time of stimulation (ISI 6, 8, 12 ms) after a cue (stimulus-onset asynchronies 75, 100, 125 ms) which signalled either a free selection or specified finger movement, the interactions between BA46 and M1 could be investigated. Furthermore, we tested whether the influence of a BA46 stimulation is specific to muscles involved in the task or not by investigating task involved and not-involved muscles. Results Our results indicate that in unselected muscles during trials with externally specified responses, stimulation of BA46 increases excitability of M1 at a SOA of 75 ms. In freely selected trials, stimulation of BA46 at a SOA of 100 ms facilitates M1 excitability. Our data suggested that the main effects occured at a ISI of 12 ms pointing to an indirect connectivity. In selected muscles this differences disappeared and the M1 output to these muscles was influenced by whether or not the muscle was selected or not. No effects could be observed when BA9 was stimulated. Conclusion The present results suggest that there is anatomically specific functional connectivity between left BA46 and left M1 during free and specified selection of a movement. This is the first study allowing to draw conclusions about the precise timing of this important functional connectivity.