Motor cortical function and the precision grip

Abstract

While task‐dependent changes in motor cortical outputs have been previously reported, the issue of whether such changes are specific for complex hand tasks remains unresolved. The aim of the present study was to determine whether cortical inhibitory tone and cortical output were greater during precision grip and power grip. Motor cortex excitability was undertaken by using the transcranial magnetic stimulation threshold tracking technique in 15 healthy subjects. The motor‐evoked potential (MEP) responses were recorded over the abductor pollicis brevis (APB), with the hand in the following positions: (1) rest, (2) precision grip and (3) power grip. The MEP amplitude (MEP amplitude REST 23.6 ± 3.3%; MEP amplitude PRECISION GRIP 35.2 ± 5.6%; MEP amplitude POWER GRIP 19.6 ± 3.4%, F = 2.4, P < 0.001) and stimulus‐response gradient (SLOPEREST 0.06 ± 0.01; SLOPEPRCISION GRIP 0.15 ± 0.04; SLOPE POWER GRIP 0.07 ± 0.01, P < 0.05) were significantly increased during precision grip. Short interval intracortical inhibition (SICI) was significantly reduced during the precision grip (SICI REST 15.0 ± 2.3%; SICI PRECISION GRIP 9.7 ± 1.5%, SICI POWER GRIP 15.9 ± 2.7%, F = 2.6, P < 0.05). The present study suggests that changes in motor cortex excitability are specific for precision grip, with functional coupling of descending corticospinal pathways controlling thumb and finger movements potentially forming the basis of these cortical changes.

Cortical and reticular contributions to human precision and power grip

“…) and short‐interval intracortical inhibition (Geevasinga et al . ) changed to a different extent during precision and power grip. This is also supported by evidence showing that different sets of cortical circuits can be preferentially engaged when humans perform a precision and a power grip (Federico & Perez, ).…”

“…; Geevasinga et al . ). However, when the size of MEPs obtained during precision and/or power grip are compared with MEPs obtained during index finger abduction, differences have been reported.…”

“…) and the magnitude of short‐interval intracortical inhibition (Geevasinga et al . ) changed to a different extent during precision and power grip, suggesting that differential changes might be taking place at a cortical level. Thus, a critical question is which neuronal elements might contribute to modulate intracortical networks during precision and power grip.…”

“…; Geevasinga et al . ). So far, the neural mechanisms contributing to modulate corticospinal output during these different gripping configurations in humans remain largely unknown.…”

The Task at Hand: Fatigue-Associated Changes in Cortical Excitability During Writing

“…Measures of CSE differ between these grips. For example, FDI MEP amplitude is greater during conventional abduction tasks compared to power, pincer, or grasping tasks [5][6][7], whereas APB MEPs are greater during pincer tasks compared to during power tasks or at rest [8]. More direct measures made in the monkey reveal that corticospinal neurons are more active during a precision grip compared to a power grip, despite increased EMG activity in the latter [9].…”