The pervasiveness of word-finding difficulties in aphasia has motivated several theories regarding management of the deficit and its effectiveness. Recently, the hypothesis was advanced that instead of simply accompanying speech gestures participate in language production by increasing the semantic activation of words grounded in sensory-motor features, hence facilitating retrieval of the word form. Based on this assumption, several studies have developed rehabilitation therapies in which the use of gestures reinforces word recovery. Until now, however, no studies have investigated the beneficial effects of gesture observation in word retrieval. Here, we report whether a different modality of accessing action-motor representation interacts with language by promoting long lasting recovery of verb retrieval deficits in aphasic patients. Six aphasic participants with a selective deficit in verb retrieval participated in an intensive rehabilitation training that included three daily sessions over two consecutive weeks. Each session corresponded to a different rehabilitation procedure: (1) "action observation", (2) "action observation and execution", and (3) "action observation and meaningless movement". In the four participants with lexical phonologically based disturbances, significant improvement of verb retrieval was found only with "action observation" and "action observation and execution". No significant differences were present between the two procedures. Moreover, the follow-up testing revealed long-term verb recovery that was still present two months after the two treatments ended. In support of a multimodal representation of action, these findings univocally demonstrate that gestures interact with the speech production system, inducing long-lasting modification at the lexical level in patients with cerebral damage.
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