File:Inter-hemispheric competition model.jpg

English: A schematic representation of the inter-hemispheric competition model, as it has been used to account for motor deficits resulting from stroke. Panel A represents the assumption that in the healthy brain there is balanced mutual inhibition between motor centres that give rise to efferent projections onto motoneurons innervating the homologous muscles of the opposite limb. Panel B represents the assumption that damage to one cerebral hemisphere as a consequence of stroke leads to a reduction of inter-hemispheric inhibition from the damaged to the non-damaged hemisphere. Panel C represents the assumption that there is as a result, elevated excitability of the non-damaged side of the brain that brings about greater (inter-hemispheric) inhibition of the damaged side. It is emphasised that Panels B and C represent physiological states that are not necessarily separable in time. The key (enclosed by the rectangle) shows the symbols used to represent the presumed characteristics of the cortical motor output associated with each state. In an abstract sense, these might be conceived of in terms of spatial and/or temporal “noise”. Although any such characteristics should not be regarded as strictly prescriptive, they may account for the abnormal patterns of muscle activation, including low specificity and high levels of muscle co-contraction, exhibited by stroke survivors (e.g. Dewald et al., 1995). Plausible corresponding effects on general motor function are given in the lower portion of each panel. It should be noted that the inter-hemispheric competition model does not typically encompass the bilateral deficits in motor control (shown here) that are observed frequently following unilateral brain injury (e.g. Desrosiers et al., 1996).