Physiological connectivity of the left ventral premotor cortex to the ipsilateral primary motor cortex explored by TMS
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Abstract:
Paired transcranial magnetic stimulation (TMS) has been applied as a probe to test functional connectivity within distinct cortical areas of the motor system. Depending on the intensity of a conditioning stimulus applied to different areas of the cortical motor network both facilitation and inhibition may be detected in the primary motor cortex (M1), ipsilaterally or contralaterally to the site of conditioning stimulation. Civardi (2001) and our group (Koch; unpublished data) reported that conditioning stimuli applied to the dorsal premotor cortex (PMd) may induce distinct effects on ipsilateral M1 depending on the intensity of stimulation. Low conditioning intensities provoked inhibition with a maximum at 90% active motor threshold (AMT) which turned into facilitation when higher intensities (120% AMT and 110% RMT, respectively) were applied.Keywords:
Premotor cortex
Facilitation
Stimulus (psychology)
Motor area
The motor cortex includes several areas in the frontal agranular cortex. These areas receive inputs from sensory pathways, motor control structures, other cortical areas, and from "modulatory" pathways. Motor cortical outputs are widely distributed to many other parts of the nervous system and can thereby influence each of the major descending motor control pathways and spinal motor circuitry. The most intensively studied motor areas, the premotor area (PMA), supplementary motor area (SMA), and primary motor cortex (MI), appear to have different roles in movement. PMA is involved in coupling arbitrary cues to motor acts, whereas SMA appears to participate more in internal guidance or planning of movement. While MI has been implicated in control of muscle force or length, more recent data suggest that it encodes higher order parameters, such as movement direction. Two new views of motor cortex are presented. First, it is argued that MI contains functional subdivisions of the face, arm, and leg, and that each subdivision contains a highly overlapping, extensively interconnected and non-topographic internal organization. Second, motor representations can reorganize rapidly as a consequence of experience or peripheral lesions. These changes may arise through modifications in synaptic coupling among motor cortex neurons. These features of motor cortex suggest a role for motor cortex in learning and in performing voluntary movements.
Premotor cortex
Supplementary motor area
Motor area
Motor Control
Motor System
Motor coordination
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Summary: Purpose: Studies of motor cortex excitability provided evidence that focal epilepsies may alter the excitability of cortical areas distant from the epileptogenic zone. In order to explore this hypothesis we studied the functional connectivity between premotor and motor cortex in seven patients with frontal lobe epilepsy and seizure onset zone outside the premotor or motor cortex. Methods: Low‐frequency subthreshold repetitive transcranial magnetic stimulation was applied to the premotor cortex and its impact on motor cortex excitability was measured by the amplitude of motor‐evoked potentials in response to direct suprathreshold stimulation of the motor cortex. Results: Stimulation of the premotor cortex of the non‐epileptogenic hemisphere resulted in a progressive and significant inhibition of the motor cortex as evidenced by a reduction of motor evoked potential amplitude. On the other hand, stimulation of the premotor cortex of the epileptogenic hemisphere failed to inhibit the motor cortex. The reduced inhibition of the motor cortex by remote areas was additionally supported by the significantly shorter cortical silent periods obtained after stimulation of the motor cortex of the epileptogenic hemisphere. Conclusion: These results show that the functional connectivity between premotor and motor cortex or motor cortex interneuronal excitability is impaired in the epileptogenic hemisphere in frontal lobe epilepsy while it is normal in the nonepileptogenic hemisphere.
Frontal lobe
Premotor cortex
Frontal cortex
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Temporal interference (TI) could stimulate deep motor cortex and induce movement without affecting the overlying cortex in previous mouse studies. However, there is still lack of evidence on potential TI effects in human studies. To fill this gap, we collected resting-state functional magnetic resonance imaging data on 40 healthy young participants both before and during TI stimulation on the left primary motor cortex (M1). We also chose a widely used simulation approach (tDCS) as a baseline condition. In the stimulation session, participants were randomly allocated to 2 mA TI or tDCS for 20 minutes. We used a seed-based whole brain correlation analysis method to quantify the strength of functional connectivity among different brain regions. Our results showed that both TI and tDCS significantly boosted functional connection strength between M1 and secondary motor cortex (premotor cortex and supplementary motor cortex). This is the first time to demonstrate substantial stimulation effect of TI in the human brain.
Premotor cortex
Transcranial Direct Current Stimulation
Human brain
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Premotor cortex
Supplementary motor area
Middle temporal gyrus
Temporal cortex
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Premotor cortex
Stimulus (psychology)
Pyramidal tracts
Evoked potential
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The primary motor cortex (M1) is highly influenced by premotor/motor areas both within and across hemispheres. Dual site transcranial magnetic stimulation (dsTMS) has revealed interhemispheric interactions mainly at early latencies. Here, we used dsTMS to systematically investigate long-latency causal interactions between right-hemisphere motor areas and the left M1 (lM1). We stimulated lM1 using a suprathreshold test stimulus (TS) to elicit motor-evoked potentials (MEPs) in the right hand. Either a suprathreshold or a subthreshold conditioning stimulus (CS) was applied over the right M1 (rM1), the right ventral premotor cortex (rPMv), the right dorsal premotor cortex (rPMd) or the supplementary motor area (SMA) prior to the TS at various CS-TS inter-stimulus intervals (ISIs: 40-150 ms). The CS strongly affected lM1 excitability depending on ISI, CS site and intensity. Inhibitory effects were observed independently of CS intensity when conditioning PMv, rM1 and SMA at a 40-ms ISI, with larger effects after PMv conditioning. Inhibition was observed with suprathreshold PMv and rM1 conditioning at a 150-ms ISI, while site-specific, intensity-dependent facilitation was detected at an 80-ms ISI. Thus, long-latency interhemispheric interactions, likely reflecting indirect cortico-cortical/cortico-subcortical pathways, cannot be reduced to nonspecific activation across motor structures. Instead, they reflect intensity-dependent, connection- and time-specific mechanisms.
Premotor cortex
Stimulus (psychology)
Supplementary motor area
Motor area
Facilitation
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Premotor cortex
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Objective: Navigated magnetic brain stimulation (NBS) has become a valuable tool for mapping the motor cortex. Until now, the premotor cortex has not been regarded as a target for NBS mapping.
Premotor cortex
Motor area
Brain mapping
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Paired transcranial magnetic stimulation (TMS) has been applied as a probe to test functional connectivity within distinct cortical areas of the motor system. Depending on the intensity of a conditioning stimulus applied to different areas of the cortical motor network both facilitation and inhibition may be detected in the primary motor cortex (M1), ipsilaterally or contralaterally to the site of conditioning stimulation. Civardi (2001) and our group (Koch; unpublished data) reported that conditioning stimuli applied to the dorsal premotor cortex (PMd) may induce distinct effects on ipsilateral M1 depending on the intensity of stimulation. Low conditioning intensities provoked inhibition with a maximum at 90% active motor threshold (AMT) which turned into facilitation when higher intensities (120% AMT and 110% RMT, respectively) were applied.
Premotor cortex
Facilitation
Stimulus (psychology)
Motor area
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The effectiveness of transcranial direct current stimulation (tDCS) placed over the motor hotspot (thought to represent the primary motor cortex (M1)) to modulate motor network excitability is highly variable. The premotor cortex-particularly the dorsal premotor cortex (PMd)-may be a promising alternative target to reliably modulate motor excitability, as it influences motor control across multiple pathways, one independent of M1 and one with direct connections to M1. This double-blind, placebo-controlled preliminary study aimed to differentially excite motor and premotor regions using high-definition tDCS (HD-tDCS) with concurrent functional magnetic resonance imaging (fMRI). HD-tDCS applied over either the motor hotspot or the premotor cortex demonstrated high inter-individual variability in changes on cortical motor excitability. However, HD-tDCS over the premotor cortex led to a higher number of responders and greater changes in local fMRI-based complexity than HD-tDCS over the motor hotspot. Furthermore, an analysis of individual motor hotspot anatomical locations revealed that, in more than half of the participants, the motor hotspot is not located over anatomical M1 boundaries, despite using a canonical definition of the motor hotspot. This heterogeneity in stimulation site may contribute to the variability of tDCS results. Altogether, these preliminary findings provide new considerations to enhance tDCS reliability.
Premotor cortex
Transcranial Direct Current Stimulation
Supplementary motor area
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