Behavioral and neurophysiological effects of delayed training following a small ischemic infarct in primary motor cortex of squirrel monkeys

Abstract

A focal injury within the cerebral cortex results in functional reorganization within the spared cortex through time-dependent metabolic and physiological reactions. Physiological changes are also associated with specific post-injury behavioral experiences. Knowing how these factors interact can be beneficial in planning rehabilitative intervention after a stroke. The purpose of this study was to assess the functional impact of delaying the rehabilitative behavioral experience upon movement representations within the primary motor cortex (M1) in an established nonhuman primate, ischemic infarct model. Five adult squirrel monkeys were trained on a motor-skill task prior to and 1 month after an experimental ischemic infarct was induced in M1. Movement representations of the hand were derived within M1 using standard electrophysiological procedures prior to the infarct and again one and two months after the infarct. The results of this study show that even though recovery of motor skills was similar to that of a previous study in squirrel monkeys after early training, unlike early training, delayed training did not result in maintenance of the spared hand representation within the M1 peri-infarct hand area. Instead, delaying training resulted in a large decrease in spared hand representation during the spontaneous recovery period that persisted following the delayed training. In addition, delayed training resulted in an increase of simultaneously evoked movements that are typically independent. These results indicate that post-injury behavioral experience, such as motor skill training, may modulate peri-infarct cortical plasticity in different ways in the acute versus chronic stages following stroke.

Constraint-Induced Movement Therapy Overcomes the Intrinsic Axonal Growth–Inhibitory Signals in Stroke Rats

“…35,36 Delayed stroke rehabilitation may reduce the efficacy of treatment, ultimately limiting functional recovery in patients. 37,38 Upregulation of growth-promoting factors and increased excitability in the peri-infarct cortex and contralateral cortex may be involved in shaping this critical period. 21,22,39 In our study, CIMT was initiated at poststroke day 7 and persisted for 21 days.…”

Transcranial magnetic stimulation in cognitive rehabilitation

“…Therefore, TMS could be used to achieve a strengthening or modification of a network that is specific for a diminished cognitive function. Studies have suggested that the best way to perpetrate this strengthening is to stimulate the area and activate the network supporting the specific function (Barbay et al, 2006). This approach can be achieved by combining exogenously induced plasticity (i.e., brain stimulation) with a specific training-induced plasticity (i.e., cognitive training).…”

Behavioral Findings during Recovery after Experimental Stroke in Monkeys-Assessment with Modified Hand Performance Test-

“…This indicates that the reorganization of the brain is different from that induced by the training started earlier. Moreover, these multi-joint responses in the forearms 9) showed a negative correlation with the behavioral improvement in clinical evaluation 10) .…”

“…Barbay et al indicated that delayed training resulted in an increase of co-contractive movements evoked with microstimulation 9) . This suggests motor skill training in the chronic stages following stroke may modulate peri-infarct cortical plasticity in a different way.…”