Neurobiological Mechanism of CIMT and fMRI Testing
Rehabilitation in adults is believed to result in the experience-induced expansion of motor maps and related improvements in motor performance.30 Therapy-related improvements in hand function are shown to correlate with increases in fMRI activity in adults,31 and 2 distinct mechanisms of increased synaptic efficiency or reorganization involving extension and recruitment of additional cortical areas were proposed to explain these effects.32
The specific effects of CIMT on cortical reorganization following insult have only recently begun to be addressed. Constraint-induced movement therapy is believed to alter the representation of the UE within the primary motor cortex in adults.33 Only one study has investigated the effects of CIMT in younger patients with congenital hemiparesis and demonstrated increases in activation in the lesioned hemisphere following therapy.34 In contrast to those individuals with both hemispheres in place, we showed that the paretic side in our patients was controlled by the remaining, “healthy” hemisphere, suggesting that residual paretic hand motility is the result of either a partially spared ipsiateral corticospinal tract35 or axonal sprouting of the contalateral corticospinal tract.36 Cortical motor representations of paretic and nonparetic hands were overlapping or closely represented in all 3 patients who underwent fMRI testing.
We conclude that functional imaging is a useful tool in this population and may help to detect reorganization in the remaining hemisphere following intervention. It remains to be seen whether CIMT is associated with the increase in the activation extent or intensity. We did not see an increase in activations, although we did observe subtle shifts in the location of activations that still remained within primary sensorimotor and supplementary motor areas. Due to the preliminary nature of this case report and the small number of patients, we did not investigate correlations between brain activations and motor improvements. We suggest that next step of similar studies should involve studying correlations between changes in fMRI activity and behavioral gains.