Abstract
We previously reported that rhesus monkeys recover spontaneous use of the more impaired (contralesional) hand following neurosurgical lesions to the arm/hand representations of primary motor cortex (M1) and lateral premotor cortex (LPMC) (F2 lesion) when tested for reduced use (RU) in a fine motor task allowing use of either hand. Recovery occurred without constraint of the less impaired hand and with occasional forced use of the more impaired hand, which was the preferred hand for use in fine motor tasks before the lesion. Here, we compared recovery of five F2 lesion cases in the same RU test to recovery after unilateral lesions of M1, LPMC, S1 and anterior portion of parietal cortex (F2P2 lesion – four cases). Average and highest %use of the contralesional hand in the RU task in F2 cases were twice that in F2P2 cases (p < 0.05). Recovery in the RU task was closely associated with volume and percentage of lesion to caudal (new) M1 (M1c) in both F2 and F2P2 lesion cases. One F2P2 case, with the largest M1c lesion and a large rostral somatosensory cortex (S1r) lesion developed severe contralesional hand non-use despite exhibiting some recovery of fine motor function initially. We conclude that the degree of reduced use of the contralesional hand is primarily related to the volume of M1c injury and that severe non-use requires extensive injury to M1c and S1r. Thus, assessing peri-Rolandic injury extent in stroke patients may have prognostic value for predicting susceptibility to RU and non-use in rehabilitation.
Highlights
Learned non-use (LNU) is a clinical term that refers to a motor deficit after nervous system damage due to learned suppression of limb use, reinforced over time by poor quality movements (Taub, 1980; Wolf et al, 1989)
In the rhesus monkey model, we have previously shown that reduced use (RU) of the contralesional hand occurs for varying lengths of time and to varying degrees following unilateral surgical lesions of frontal lobe motor areas including primary motor cortex (M1), M1 + lateral premotor cortex (LPMC) and M1 + LPMC + supplementary motor cortex (M2 or SMC) (Darling et al, 2010, 2014)
Compared to cases with F2 lesions, notable differences in F2P2 cases which persisted throughout the post-lesion survival/testing period included: (1) dragging of the contralesional hand with finger-tips contacting the cage floor during quadrupedal gait, and (2) attentively looking at the hand after picking up food in motor tests
Summary
Learned non-use (LNU) is a clinical term that refers to a motor deficit after nervous system damage due to learned suppression of limb use, reinforced over time by poor quality movements (Taub, 1980; Wolf et al, 1989). Non-use has been observed in patients with unilateral cerebral palsy (Crocker et al, 1997), traumatic brain injury (Wolf et al, 1989) and stroke-induced hemiplegia (Wolf et al, 1989, 2006; Taub et al, 1993). This non-use is considered learned because it persists either fully, or as reduced use (RU), even when the monkey or human is able to use the impaired hand when forced. We use the term non-use, rather than LNU, throughout this report
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