Abstract
Right brain injury causes visual neglect - lost awareness of left space. During prism adaptation therapy, patients adapt to a rightward optical shift by recalibrating right arm movements leftward. This can improve left neglect, but the benefit of a single session is transient (~1 day). Here we show that tonic disinhibition of left motor cortex during prism adaptation enhances consolidation, stabilizing both sensorimotor and cognitive prism after-effects. In three longitudinal patient case series, just 20 min of combined stimulation/adaptation caused persistent cognitive after-effects (neglect improvement) that lasted throughout follow-up (18-46 days). Moreover, adaptation without stimulation was ineffective. Thus stimulation reversed treatment resistance in chronic visual neglect. These findings challenge consensus that because the left hemisphere in neglect is pathologically over-excited it ought to be suppressed. Excitation of left sensorimotor circuits, during an adaptive cognitive state, can unmask latent plastic potential that durably improves resistant visual attention deficits after brain injury.
Highlights
Stroke is a leading cause of adult disability (Adamson et al, 2004)
The consequent AE was measured as a leftward error when participants pointed without prisms at a central, untrained target
Given that prism adaptation (PA) + M1 anodal transcranial direct current stimulation (a-Transcranial Direct Current Stimulation (tDCS)) induced a sustained leftward shift, both in sensorimotor and spatial cognition prism after-effects, we addressed the possibility of unintended leftward reach impairments in patients
Summary
Stroke is a leading cause of adult disability (Adamson et al, 2004). The majority of right hemisphere stroke survivors suffer acute ‘neglect’ – lost awareness of left space (Figure 1A–C) (Buxbaum et al, 2004; Stone et al, 1993). Chronic neglect predicts poor functional outcome, entailing prolonged hospitalization, reduced independence, and lasting disability (Jehkonen et al, 2006). We present initial proof-of-concept scientific evidence for the efficacy of a novel experimental intervention. This single-session protocol used non-invasive brain stimulation to enhance consolidation of behavioural therapy, resulting in long-lasting improvements in visual neglect
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