Lexical learning in mild aphasia: gesture benefit depends on patholinguistic profile and lesion pattern.

Gestures accompany speech and enrich human communication. When aphasia interferes with verbal abilities, gestures become even more relevant, compensating for and/or facilitating verbal communication. However, small-scale clinical studies yielded diverging results with regard to a therapeutic gesture benefit for lexical retrieval. Based on recent functional neuroimaging results, delineating a speech-gesture integration network for lexical learning in healthy adults, we hypothesized that the commonly observed variability may stem from differential patholinguistic profiles in turn depending on lesion pattern. Therefore we used a controlled novel word learning paradigm to probe the impact of gestures on lexical learning, in the lesioned language network. Fourteen patients with chronic left hemispheric lesions and mild residual aphasia learned 30 novel words for manipulable objects over four days. Half of the words were trained with gestures while the other half were trained purely verbally. For the gesture condition, rootwords were visually presented (e.g., Klavier, [piano]), followed by videos of the corresponding gestures and the auditory presentation of the novel words (e.g., /krulo/). Participants had to repeat pseudowords and simultaneously reproduce gestures. In the verbal condition no gesture-video was shown and participants only repeated pseudowords orally. Correlational analyses confirmed that gesture benefit depends on the patholinguistic profile: lesser lexico-semantic impairment correlated with better gesture-enhanced learning. Conversely largely preserved segmental-phonological capabilities correlated with better purely verbal learning. Moreover, structural MRI-analysis disclosed differential lesion patterns, most interestingly suggesting that integrity of the left anterior temporal pole predicted gesture benefit. Thus largely preserved semantic capabilities and relative integrity of a semantic integration network are prerequisites for successful use of the multimodal learning strategy, in which gestures may cause a deeper semantic rooting of the novel word-form. The results tap into theoretical accounts of gestures in lexical learning and suggest an explanation for the diverging effect in therapeutical studies advocating gestures in aphasia rehabilitation.