Boosting Phonological Fluency Following Leftward Prismatic Adaptation: A New Neuromodulation Protocol for Neurological Deficits?

Abstract

Prism adaptation (PA) has been recently shown to modulate a brain frontal-parieto-temporal network, with an increase of excitation of this network in the hemisphere ipsilateral to the side of prismatic deviation. This effect raises the hypothesis that left prismatic adaptation, modulating the excitability of frontal areas of the left hemisphere could modulate subjects’ performance on linguistic tasks that map on those areas. To test this hypothesis, sixty-one healthy subjects participated in experiments in which leftward, rightward or no-PA were applied before the execution of a phonological fluency task, i.e. a task with the strict left hemispheric lateralization and mapping onto frontal areas. Leftward-PA significantly increased the number of words produced compared with the pre-PA (p = .0017), R-PA (p=.00013) and no-PA (p=.0005) sessions. In contrast, rightward-PA did not significantly modulate phonological fluency compared with the pre-PA (p = .92) and no-PA (p = .99) sessions. The effect of leftward PA on phonological fluency correlated with the magnitude of spatial aftereffect, i.e. the spatial bias towards the side of space opposite to prismatic deviation following prisms removal (r = .51; p = .04). The present findings document for the first time modulation of a language ability following prismatic adaptation. The results could have a huge clinical impact on neurological populations, opening new strategies of intervention for language and executive dysfunctions.