Stimulation of the Frontal Aslant Tract's origin in the caudal superior frontal gyrus alters ongoing spontaneous rhythmic activity independently from the effector. Evidence from tractography-guided Transcranial Magnetic Stimulation.

Abstract

the crown of the human Superior Frontal Gyrus (SFG-crown) is a functionally independent region, nestled between the dorsal premotor and supplementary motor cortices, that supports internally-timed action control. The unique SFG-crowns connectivity fingerprint by the Frontal Aslant Tract (FAT), suggests a caudal-rostral pattern of increasing abstractness of action representations. Coherently, since the mid-portion of the caudal SFG contains a representation of action strategies that involve internal timing, we hypothesized that the caudal portion of the SFG may be involved in action execution of internally-timed actions. To test this, we asked 21 healthy participants to perform a self-paced tapping movement with the right index finger or a self-paced articulation of the syllable /da/ while applying online single-pulse TMS to the posterior, middle and anterior origins of the FAT in the left SFG-crown. Results showed that effective TMS (compared to sham) impacted rhythm production in both tasks, only when applied to the posterior SFG region, by reducing the probability of motor events in the 200 ms following TMS. The present data support the hypothesis, that the posterior SFG-crown, associated with the most posterior origin of the FAT fibers, is involved in the production of internally-timed actions, in an effector-independent modality, suggesting a domain-general role in the execution of internally-timed movements.