The deficit for the word-class "verb" in corticobasal degeneration: linguistic expression of the movement disorder?

We describe five patients with corticobasal degeneration who had apraxia with an ideational component and reduced action/verb naming ability. Patients also had difficulty in a series of tasks devised to explore the conceptual representation of actions associated with manipulable objects, such as action recognition, action miming and pantomime recognition; however, their ability to name manipulable objects was comparatively preserved. According to the current interpretation of ideational apraxia [De Renzi, E., & Lucchelli, F. (1988). Ideational apraxia. Brain, 111, 1173-1185] we considered the patients' apraxic disorder as the motor expression of decay of the action representation and we hypothesized that this may also have contributed to the action-naming deficit. The results are discussed within a "multimodal model" of semantic memory in which the concept of action is seen as the product of the integration between sensorial and motor attributes. We suggest that corticobasal degeneration might offer a unique opportunity to validate this model because it is typically characterized by a frontoparietal damage [Gibb, W. R., Luthert, P. J., & Marsden, C. D. (1989). Corticobasal degeneration. Brain, 1, 1171-1192] that prevents integration of sensory and motor information. We conclude that the selective impairment of action/verb should also be studied from the point of view of a movement disorder and not only in terms of a lexical-semantic deficit.