Premotor cortex

Barbas, H., and Pandya, D. N. (1987). Architecture and frontal cortical connections of the premotor cortex (area 6) in the rhesus monkey. J. Comp. Neurol. 256, 211-228. 

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. 

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). 

DTI provides a measure (fractional anisotropy) of the coherence and integrity of myelinated pathways. Children with ADHD displayed a reduced fractional anisotropy in the right neostriatum and premotor cortex, and in the left cerebellum and parieto-occipital cortex compared to matched controls (Ashtari et al., 2005). The lower the cerebellar fractional anisotropy, the more severe were the ratings of symptoms of inattention (Ashtari et al., 2005). These findings point to a link between white matter abnormalities and the symptomatology of ADHD. 

Hassler R., Haug P, Nitsch C, Kim J S., and Paik K. (1982) Effect of motor and premotor cortex ablation on concentrations of amino acids, monoamines, and acetylcholine and on the ultrastructure in rat striatum. A confirmation of glutamate as the specific cortico-stnatal transmitter /. Neurochem 38, 1087-1098... 

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... 

Schluter etal (1998) used transcranial magnetic stimulation (TMS) to disrupt the processing in the human premotor cortex while the subjects carried out visual choice reaction tasks and simple reaction tasks. They were able to delay responses in the contralateral hand by stimulating the premotor cortex. They were also able to delay responses with the ipsilateral hand while stimulating over the left premotor cortex, but not while stimulating over the right premotor cortex or either sensorimotor cortex. They concluded that the premotor cortex is important for selecting movements after a visual cue and that the left hemisphere is dominant for the rapid selection of action,... 

W. Gerschlager, H.R. Siebner, and J. C. Rothwell Dexreased corticospinal excitability after subthreshold 1 Hz rTMS over lateral premotor cortex. , Neurology., 57, pp.449-455, 2001. 

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