Supplementary motor cortex

Separate but concurrent research efforts by many investigators in basic neurophysiology were making significant advancements in developing an understanding of how cortical and spinal neural systems control motor function. Extensive research on control of movement by hundreds of neuroscientists has revealed correlations between parameters of limb movement and neural activity in many motor centers, including the primary motor cortex, premotor and supplementary motor cortex, cerebellum, and spinal cord. 

Basal ganglia output is directed from GPi and SNr to the thalamus. Movement-related basal ganglia output projects from GPi almost exclusively to the ventrolateral nucleus of the thalamus which, in turn, projects to the primary motor cortex, the cortical supplementary motor area, and other premotor cortical areas. Movement-related output from SNr terminates in the ventral anterior and in... 

DBS appears to work by freeing thalamocortical and brainstem motor systems from abnormal and disruptive basal ganglia influences ([67], p. 202). At a local scale DBS appears to inhibit the soma of nerve cells and to activate the axons [42]. At an intermediate scale, DBS appears to alter the dynamics in the GPi-STN network [10]. At a distant scale, DBS appears to normalize the activity in the supplementary motor area and in the premotor cortex [67]. While many hypotheses have been formulated, the experimental results are difficult to reconcile especially when several physiological scales are considered. We now present a computational model based on a population density approach. 

The rodent motor thalamus consists of two main components the ventromedial nucleus and the ventral anterior/ventral lateral nuclear complex. In the rat, both components are targeted by nigrothalamic fibers and by pallidothalamic fibers arising from both the pallidal divisions, and are conveyed to the medial agranular cortex, equivalent to the primate supplementary motor and premotor areas (Sakai et al., 1998 Kha et al., 2000 Sakai and Bruce, 2004). 

In the rat, the motor striatum comprises the lateral portion of the CPu and receives input from the motor cortex (lateral and medial agranular cortical fields). This region of the striatum is equivalent in primates to the dorsolateral portion of the caudate nucleus and the dorsolateral putamen caudal to the anterior commissure, which receives input from the primary motor, premotor and supplementary motor areas. 

Nambu A, Takada M, Inase M, Tokuno H (1996) Dual somatotopical representations in the primate subthalamic nucleus evidence for ordered but reversed body-map transformations from the primary motor cortex and the supplementary motor area. J Neurosci 76 2671-2683. 

Elsworth JD, Deutch AY, Redmond DE, Sladek JR, Roth RH (1990) MPTP reduces dopamine and norepinephrine concentrations in the supplementary motor area and cingulate cortex of the primate. Neurosci Lett 774 316-322. 

Despite the limitations of fMRI outlined above, fMRI studies have shown similar findings to those of positron emission tomography studies in recovery after stroke (Yozbatiran and Cramer 2006 Rijntjes 2006). Increased ipsilateral primary sensorimotor cortical activity with posterior displacement of the ipsilesional focus of activity, bilateral supplementary motor area activation and premotor cortical activation occurs after stroke with use of the affected hand in comparison with use of the unaffected hand (Weiller et al. 1992 Cramer et al. 1997 Cao et al. 1998 Pineiro et at 2001). Specifically, in patients with capsular or other subcortical stroke, good recovery is related to enhanced recruitment of the lateral premotor cortex of the lesional hemisphere and lateral premotor and, to a lesser extent, primary sensorimotor and parietal cortex of the contralateral hemisphere (Gerloff et al. 2006). 

The supplementary motor area plays an indirect preparatory role in movement generation. Both prefrontal cortex and supplementary motor areas receive inputs from posterior parietal areas, but differ in their subcortical projections. The prefrontal cortex receives afferents from the cerebellum, the supplementary motor area from thalamic nuclei. 

Supplementary motor area Primary motor cortex (UtC + VC)... 

Remy et al. (1994) investigated the cerebral blood flow with positron emission tomography induced in 10 healthy subjects by two different tasks a repeated flexion-extension of all fingers and a repeated flexion-extension of the middle finger. The all-finger movement only activated the primary sensorimotor cortex (SM) and the supplementary motor area (SMA) contralateral to the movement. However the 5MA activation was only observed when the movement was triggered by an auditory cue but not when it was self-paced. 

Richter et al. (1997) measured activity in the human primary motor cortex, the premotor cortex and the supplementary cortex during a delayed cued finger movement task. All three areas were active during movement preparation and movemement execution. Activity in the primary motor cortex was considerable... 

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