Functional connectivity of human premotor and motor cortex explored with repetitive transcranial magnetic stimulation

Sobell Department of Neurophysiology, Institute of Neurology, London WC1N 3BG, United Kingdom.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 02/2002; 22(2):554-61.
Source: PubMed


Connections between the premotor cortex and the primary motor cortex are dense and are important in the visual guidance of arm movements. We have shown previously that it is possible to engage these connections in humans and to measure the net amount of inhibition/facilitation from premotor to motor cortex using single-pulse transcranial magnetic stimulation (TMS). The aim of this study was to test whether premotor activation can affect the excitability of circuits within the primary motor cortex (M1) itself. Repetitive TMS (rTMS), which is known to produce effects that outlast the train at the site of stimulation, was given for 20 min at 1 Hz over premotor, primary motor, and sensory areas of cortex at an intensity of 80% of the active motor threshold for the motor hand area. The excitability of some corticocortical connections in M1 was probed by using paired-pulse testing of intracortical inhibition (ICI) and intracortical facilitation (ICF) with a coil placed over the motor cortex hand area. rTMS over the premotor cortex, but not other areas, changed the time course of the ICI/ICF for up to 1 hr afterward without affecting motor thresholds or motor-evoked potential recruitment. The cortical silent period was also shortened. The implication is that rTMS at a site distant from the motor cortex can change the excitability of circuits intrinsic to the motor cortex.

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Available from: Bas Bloem, Jul 24, 2015
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    • "The premotor sites were then determined by moving 3 cm anterior from the corresponding spots in M1 and then to the nearest spot on the precentral gyrus with the help of the navigation system. Whereas prior TMS studies have localized the hand area in left PMC using the same method as that employed here (Kroeger et al., 2010; Münchau, Bloem, Irlbacher, Trimble, & Rothwell, 2002), there is no precedent for the use of the same localization procedure for the premotor lip area. However, the extension of this procedure to the lip area derives support from several sources. "
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    ABSTRACT: Although it is well established that regions of premotor cortex (PMC) are active during action observation, it remains controversial whether they play a causal role in action understanding. In the experiment reported here, we used off-line continuous theta-burst stimulation (cTBS) to investigate this question. Participants received cTBS over the hand and lip areas of left PMC, in separate sessions, before completing a pantomime-recognition task in which half of the trials contained pantomimed hand actions, and half contained pantomimed mouth actions. The results reveal a double dissociation: Participants were less accurate in recognizing pantomimed hand actions after receiving cTBS over the hand area than over the lip area and less accurate in recognizing pantomimed mouth actions after receiving cTBS over the lip area than over the hand area. This finding constrains theories of action understanding by showing that somatotopically organized regions of PMC contribute causally to action understanding and, thus, that the mechanisms underpinning action understanding and action performance overlap.
    Full-text · Article · Feb 2014 · Psychological Science
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    • "To determine the role of the local M1 circuitry within M1 during digit force planning, we used a paired-pulse TMS approach where a subthreshold TMS stimulus preceded delivery of a suprathreshold TMS pulse. Although SICI and SICF are mediated through separate mechanisms, the modulation of MEP size is due to modulation of neural circuits intrinsic to the site of stimulation, i.e., M1 (Chen 2004; Münchau et al. 2002). The modulation of MEP size with different ISI between paired TMS pulses (i.e., SICI and ICF) delivered in synchrony with the go cue but before grasp initiation was similar for HF vs. LF tasks. "
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    ABSTRACT: Control of digit forces for grasping relies on sensorimotor memory gained from prior experience with the same or similar objects, and online sensory feedback. However, little is known about neural mechanisms underlying digit force planning. We addressed this question by quantifying the temporal evolution of corticospinal excitability (CSE) using single-pulse transcranial magnetic stimulation (TMS) during two reach-to-grasp tasks. These tasks differed in terms of the magnitude of force exerted on the same points on the object to isolate digit force planning from reach and grasp planning. We also addressed the role of intracortical circuitry within primary motor cortex (M1) by quantifying the balance between short intracortical inhibition and facilitation using paired-pulse TMS on the same tasks. Eighteen right-handed subjects were visually cued to plan digit placement at predetermined locations on the object and subsequently to exert either negligible force ("Low Force" task, LF) or 10% of their maximum pinch force ("High Force" task, HF) on the object. We found that the HF-task elicited significantly smaller CSE than the LF-task, but only when the TMS pulse coincided with the signal to initiate the reach. This force planning-related CSE modulation was specific to the muscles involved in the performance of both tasks. Interestingly, digit force planning did not result in modulation of M1 intracortical inhibitory and facilitatory circuitry. Our findings suggest that planning of digit forces reflected by CSE modulation starts well before object contact and appears to be driven by inputs from fronto-parietal areas other than M1.
    Full-text · Article · Feb 2014 · Journal of Neurophysiology
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    • "This study, like previous studies, cannot exclude the possibility that the future non-spherical estimation of deep currents along the anterior wall of the central sulcus might provide evidence for higher current densities in M1. Conversely, spurious co-activation cannot explain the success of previous studies in selective modification of PMC functions by tDCS or TMS [8], [12], [15], [20], [52] nor this study's findings of similar response latencies (for PMC and M1 stimulation) and decreased M1 yet enhanced PMC excitability after cathodal stimulation. Additionally, for direct corticospinal tract activation by stimulation of the subcortical white matter, the MEP response latencies would have been remarkably shorter [59] and amplitudes not affected by cathodal tDCS [60]. "
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    ABSTRACT: Premotor cortical regions (PMC) play an important role in the orchestration of motor function, yet their role in compensatory mechanisms in a disturbed motor system is largely unclear. Previous studies are consistent in describing pronounced anatomical and functional connectivity between the PMC and the primary motor cortex (M1). Lesion studies consistently show compensatory adaptive changes in PMC neural activity following an M1 lesion. Non-invasive brain modification of PMC neural activity has shown compensatory neurophysiological aftereffects in M1. These studies have contributed to our understanding of how M1 responds to changes in PMC neural activity. Yet, the way in which the PMC responds to artificial inhibition of M1 neural activity is unclear. Here we investigate the neurophysiological consequences in the PMC and the behavioral consequences for motor performance of stimulation mediated M1 inhibition by cathodal transcranial direct current stimulation (tDCS).
    Full-text · Article · Feb 2013 · PLoS ONE
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