Selective modulation of interactions between ventral premotor cortex and primary motor cortex during precision grasping in humans

Abstract

In humans, the rostral part of the ventral premotor cortex (PMv), the homologue of F5 in monkeys, is known to be critically involved in shaping the hand to grasp objects. How does information about hand posture, that is processed in PMv, give rise to appropriate motor commands for transmission to spinal circuits controlling the hand? Whereas PMv is crucial for skilled visuomotor control of the hand, PMv sends relatively few direct corticospinal projections to spinal segments innervating hand muscles and the most likely route for PMv to contribute to the control of hand shape is through cortico-cortical connections with primary motor cortex (M1). If this is the case, we predicted that PMv-M1 interactions should be modulated specifically during precision grasping in humans. To address this issue, we investigated PMv-M1 connections by means of paired-pulse transcranial magnetic stimulation (TMS) and compared whether they were differentially modulated at rest, and during precision versus power grip. To do so, TMS was applied over M1 either in isolation or after a conditioning stimulus delivered, at different delays, over the ipsilateral PMv. For the parameters of TMS tested, we found that, at rest, PMv exerted a net inhibitory influence on M1 whereas, during power grip, this inhibition disappeared and was converted into a net facilitation during precision grip. The finding that, in humans, PMv-M1 interactions are selectively modulated during specific types of grasp provides further evidence that these connections play an important role in control of the hand.

Probing the reaching–grasping network in humans through multivoxel pattern decoding

“…Bilateral involvement of PMv during grasping movements has been also observed in TMS studies (Davare et al. 2006, 2008) revealing that lesioning either the left or the right PMv modifies fingertip positioning, which is a prerequisite to grasp an object properly (Sartori et al. 2011).…”

The dorsal premotor cortex exerts a powerful and specific inhibitory effect on the ipsilateral corticofacial system: a dual-coil transcranial magnetic stimulation study

“…The temporal specificity is consistent with corticocortical connections. In fact, other studies exploring corticocortical connections between areas the distances between which are similar to that between the PMCd and the mouthM1 have found interactions at ISIs around 6 ms. (Baumer et al 2009;Cattaneo and Barchiesi 2011;Davare et al 2008Davare et al , 2009Davare et al , 2010. It should be noted that the physical distance between the dorsal premotor cortex and the mouthM1 is of around 6 cm, entirely compatible with a direct corticocortical connection.…”

“…We provide evidence for a specific short-latency inhibitory effect of the The connectivity between the PMC and the ipsilateral M1 in humans is largely hypothesized by analogy with the non-human primates. Still, direct evidence for it has been obtained by means of the dual-coil paradigm of transcranial magnetic stimulation (TMS) (Baumer et al 2009;Cattaneo and Barchiesi 2011;Civardi et al 2001;Davare et al 2008Davare et al , 2009Davare et al , 2010Koch et al 2006;Mars et al 2009). This protocol involves the use of two magnetic stimulators connected to two distinct coils, both of which are used simultaneously on the participant's scalp.…”

Cortical and subcortical interactions during action reprogramming and their related white matter pathways

“…On the other half of the trials, ppTMS trials, the M1 test pulse was preceded by a "conditioning pulse" over the rIFG. The intensity of the preceding conditioning pulse was set at 110% of the resting motor threshold (RMT, defined as the minimum stimulator output required to elicit a 50-μV MEP in 5 of 10 trials) of the left FDI muscle (right M1), and the IPL was 8 ms (23,24). Several studies have used similar interhemispheric TMS coil configuration and conditioning and test pulse intensities, because the size of the head precludes placing two TMS coils over frontal and M1 areas in the same hemisphere in some participants and an interhemispheric configuration produces similar results, albeit with a slightly higher intensity conditioning pulse, to an intrahemispheric configuration (16,23).…”