Inducing motor cortical plasticity rehabilitates visual neglect
‘Neglect’ is a common disabling neurological syndrome that affects the majority of patients after right hemisphere stroke, particularly when damage affects the parietal cortex or white matter parieto-frontal interconnecting pathways. ‘Neglect’ is a multifaceted disorder, but its core defining feature is that patients lose the capacity to voluntarily direct attention to the region of space opposite their lesion, typically, the left half of space, objects or the body. While approximately two-thirds of neglect patients show spontaneous symptom remission over time, the rest suffer life-long disability, with attendant personal and health economic costs. The goal of neurological rehabilitation is to maximize the functioning of surviving brain tissue, and thus drive behavioural recovery. In the context of neglect, a variety of rehabilitative strategies have been shown to induce short-lasting improvements of in-principle scientific interest, but we are still some way from routine interventions that can bring about clinically meaningful gains. We will present data from a program of experiments in healthy volunteers and neglect patients designed to test the hypothesis that non-invasive brain stimulation, combined with behavioural training, would produce long-lasting improvements in chronic visual neglect. Experiments in healthy volunteers enabled us to identify a protocol that enhanced the retention of training effects, in a manner that was functionally, anatomically and neurochemically specific, as well as cognitive state dependent. When we translated this protocol to neglect patients, we found that a single 20-minute intervention produced large improvements that lasted over a timescale of weeks to months. Notably, these effects occurred in patients with chronic, severe, treatment-resistant neglect, who did not respond to the behavioural training on its own. In a single-case double crossover design, the patient exhibited the same positive response on both occasions, and the effects accumulated, suggesting that repeated treatments might lead to gradual recovery. Our findings constitute the first proof-of-principle demonstration that a single-shot, simple behavioural treatment combined with non-invasive brain stimulation may be an effective strategy for rehabilitation of treatment-unresponsive chronic visual neglect. We will discuss future plans to test this hypothesis in a randomized controlled trial setting, and to interrogate the mechanisms mediating this effect.