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Mathieu Lesourd (Laboratoire de Neurosciences Cognitives, Marseille)

Do we really need gesture engrams to use objects ? New insights in the field of apraxia of tool use

Apraxia is a movement disorder which can impair various tasks, including imitation of gestures, pantomime of tool use and actual use of objects (e.g., Goldenberg, 2009). A deficit in using tools or in producing pantomime of tool use have traditionally been attributed to the impairment of gesture engrams which are assumed to be stored in the left parietal cortex (Buxbaum, 2001 ; van Elk et al., 2014). Gesture engrams are sensorimotor representations subsuming the use of tools and objects (Boronat et al., 2005 ; Canessa et al., 2008).

However, several points tend to show the limitations of this concept. First, gesture engrams are not stored in the left parietal cortex (Lesourd, Reynaud, Navarro et al., 2017) and the left parietal cortex are more likely to sustain allocentric representations about tool use rather than egocentric ones (Reynaud, Lesourd, Navarro et al., 2016). Second, the activation of gesture engrams is not mandatory in the pantomime of tool use task (Lesourd et al., 2017), which is traditionally used to assess the integrity of gesture engrams.

Finally, we propose an alternative framework, in which other forms of representations (i.e., semantic memory and mechanical knowledge) may replace gesture engrams to explain tool use abilities (Lesourd, Baumard, Jarry et al., 2017 ; Lesourd, Budriesi, Osiurak et al., 2017).