Rethinking stimulation of the brain in stroke rehabilitation: why higher motor areas might be better alternatives for patients with greater impairments.

Stimulating the brain to drive its adaptive plastic potential is promising to accelerate rehabilitative outcomes in stroke. The ipsilesional primary motor cortex (M1) is invariably facilitated. However, evidence supporting its efficacy is divided, indicating that we may have overgeneralized its potential. Since the M1 and its corticospinal output are frequently damaged in patients with serious lesions and impairments, ipsilesional premotor areas (PMAs) could be useful alternates instead. We base our premise on their higher probability of survival, greater descending projections, and adaptive potential, which is causal for recovery across the seriously impaired. Using a conceptual model, we describe how chronically stimulating PMAs would strongly affect key mechanisms of stroke motor recovery, such as facilitating the plasticity of alternate descending output, restoring interhemispheric balance, and establishing widespread connectivity. Although at this time it is difficult to predict whether PMAs would be "better," it is important to at least investigate whether they are reasonable substitutes for the M1. Even if the stimulation of the M1 may benefit those with maximum recovery potential, while that of PMAs may only help the more disadvantaged, it may still be reasonable to achieve some recovery across the majority rather than stimulate a single locus fated to be inconsistently effective across all.