Motor cortex activation is related to force of squeezing

Abstract

Primate studies have demonstrated that motor cortex neurons show increased activity with increased force of movement. In humans, this relationship has received little study during a power grip such as squeezing, and has previously only been evaluated across a narrow range of forces. Functional MRI was performed in eight healthy subjects who alternated between rest and right hand squeezing at one of three force levels. During scanning, motor performances were recorded using a dynamometer. At each force level, activation volume was measured within left sensorimotor cortex, right sensorimotor cortex, and a midline supplementary motor area. In left sensorimotor cortex, % signal change was also assessed. The range of force generated across the three force levels varied from 4.9 N to 276 N. In left sensorimotor cortex, activation volume increased significantly with greater force. The % signal change also increased with greater force and correlated closely with activation volume. In supplementary motor area, activation volume increased significantly with increasing force, but with greater intersubject variability. In right sensorimotor cortex, a trend for larger activation volumes with greater force did not reach significance. The laterality index, an expression of the relative degree of contralateral vs. ipsilateral sensorimotor cortex activation, did not change across the three force levels. Increased force of squeezing is associated with increased contralateral sensorimotor cortex and supplementary motor area activation. This relationship was found across the full spectrum of forces that the human hand is capable of generating. Use of a valid, reliable method for assessing motor behavior during functional MRI may be important to clinical applications.

Brain correlates of autonomic modulation: Combining heart rate variability with fMRI

“…Activation was also observed in typical motor system regions including the supplementary motor area, bilateral thalamus, and ipsilateral cerebellum. These results were consistent with other neuroimaging studies evaluating brain response to a grip task (Dai et al 2001;Cramer et al 2002).…”

“…This grip device, similar to other MRIcompatible grip devices (Dettmers et al 1996), has been used in past studies in our Center to assess brain response to grip tasks (Cramer et al 2002). The subjects were asked to perform a single maximum voluntary contraction (MVC) in order to set the target force level for the following fMRI scan.…”

Aging effects on the control of grip force magnitude: An fMRI study

“…In addition, the ipsilateral supplementary motor area (SMA) showed a greater number of activated voxels as the force increased. Cramer et al (2002) also noted that there was no change in the laterality of the activation of the primary or supplementary motor areas with increasing grip force. Spraker et al (2007) used a region of interest (ROI) analysis to specifically analyze the role of the basal ganglia during a force modulation task, where participants were asked to perform pinch grips ranging between 5% and 80% MVC.…”

“…These motor areas include the M1, S1 and premotor areas in the contralateral hemisphere and the supplementary motor area, prefrontal cortex and cerebellum bilaterally. Cramer et al (2002) specifically analyzed the effect of grip force on the activation of motor areas within the brain across a range of force values. It was found that both the magnitude of activation and the volume of activated voxels within the contralateral SMC increased as the magnitude of the grip force increased.…”

Force related activations in rhythmic sequence production

“…Activation of sensory motor cortex (SMC) in a finger flexion force production task was observed to be greater in repetitive squeezing than in steady contraction (Thickbroom et al, 1999). In thumb-finger squeezing movements, increases in activation with force have been noted in MI (Cramer et al, 2002), SMA, PMC and cerebellum (Dai et al, 2001).…”