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togog: Subproject P3

Neuropsychology of gestural modes of representation

Researchers: Hedda Lausberg, Henning Holle, Hauke Heekeren, Philipp Kazzer, and Isabell Wartenburger

 

 

Aims:
To research the neurobiological correlates of different gestural modes of representation: the pantomime of tool use (acting), and the demonstration of tool use using a body part as an object (representing, or embodying) as compared to the demonstration of tool use with a tool held in the hand.

In neuroimaging studies, inferences concerning the neural basis of tool use are often based on examinations of pantomimed actions in which subjects do not have a real tool but an imaginary one in their hands. However, contrary to the assumption that pantomime is a valid proxy for real tool use, neuropsychological studies of patients with callosal disconnection and unihemispheric brain damage demonstrate dissociations between demonstrations of tool use with a tool in the hand (Tool Demonstration) and pantomimes of tool use (Tool Pantomime). Specifically, reports of impaired Tool Demonstrations but preserved Tool Pantomimes, as well as kinematic studies, reveal that pantomime is not just a difficult version of tool use but that it represents a different cognitive entity. In contrast to Tool Demonstrations, pantomiming requires the abilities of abstraction and symbolization. Furthermore, the competence to perform a Tool Demonstration tends to be represented bihemispherically, while pantomiming depends on left-hemispheric functions.

Our first experiment examined the difference between Tool Demonstration and Tool Pantomime. Lausberg, Heekeren, Kazzer, and Wartenburger compared cerebral activation patterns during Tool Demonstration and Tool Pantomime using functional MRI. The conjunction analysis of Tool Pantomime relative to Tool Demonstration showed activation in the left superior/middle temporal gyrus, i.e. this area was activated when either hand was used to perform pantomimic gestures. In contrast, Tool Demonstration relative to Tool Pantomime revealed large bihemispherically distributed homologous areas of activations for either hand.

Our results suggest that Tool Pantomime and Tool Demonstration partially differ in their cerebral representation. In line with neuropsychological patient studies, our data show bihemispheric contributions to Tool Demonstration and, therefore, indicate some degree of autonomous competence in each hemisphere for this type of tool-related action. In contrast, the ability to pantomime relies on specialized left-hemispheric functions. Specifically, we suggest that the activation in the left superior/middle temporal gyrus that was found when Tool Pantomime was contrasted with Tool Demonstration is the functional correlate of linking a mental representation of a tool with a movement concept (Lausberg et al., subm.).

In the second experiment, Lausberg and Holle investigated the difference between the two modalities examined in experiment 1 and Body-Part-as-Object gestures (BPO), in which the hand represents the tool (e.g. the index and middle fingers represent scissors). As the previous study found that the production of gestures during Tool Pantomime as compared to those produced during Tool Demonstration elicits greater activation in the left superior and middle temporal areas (STG/MTG), we suggested that this reflects the linking of a mental object representation with a movement concept. Accordingly, BPO gestures should not activate STG/MTG. Instead, there is evidence from split-brain patients suggesting a separate representation of BPO gestures in the right hemisphere. The current study tests the following hypotheses: (1) Tool Pantomime as compared to BPO Pantomime should elicit greater levels of activation in the left STG/MTG. (2) BPO Pantomime as compared to Tool Pantomime should elicit activity in the right hemisphere. Preliminary results indicate that Tool Pantomime exclusivily activates a left-hemispheric network including motor, premotor and supplementary motor areas, as well as posterior portions of the left inferior frontal gyrus. In contrast, Tool Demo and BPO additionally activated the right motor cortex.

Preliminary results indicate that Tool Pantomime exclusivily activates a left-hemispheric network including motor, premotor and supplementary motor areas, as well as posterior portions of the left inferior frontal gyrus. In contrast, Tool Demo and BPO additionally activated the right motor cortex.