“School of Cognitive Sciences”
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| Paper IPM / Cognitive Sciences / 17812 |
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Humans utilize both egocentric (subject-dependent) and allocentric (subject-independent) spatial information for target localization during goal-directed movement behavior. The brain regions and neural mechanism for constructing allocentric frames of reference in primates are still under debate. Egocentric spatial encoding is a wellknown property of brain areas along the dorsal pathway, monkey parietal reach region (PRR) and dorsal premotor cortex (PMd) encode spatial parameters for planning upcoming reach movements in different egocentric coordinate systems. Yet, natural reaches are typically directed towards extended physical objects. Not only their location, but also their spatial structure guides reach planning. We ask if planning activities in PRR and PMd can also encode object-centered (allocentric) reach goal information. Monkeys planned reaches towards different sites on an object. During visual memory, they could memorize an on-the-object position; during reach planning, they had to plan a reach to this position after re-occurrence of the object at a potentially different position and with potentially different size. In both brain areas, we find (1) predominant object-centered encoding during visual memory, which (2) changes to predominant egocentric encoding during reach planning corresponding to changing cognitive demands, and which (3) is invariant to object position and size. Such flexible and cognitively controlled encoding within local brain regions contrasts the idea of task-independent functional segregation between processing pathways and is particularly suitable for variable-demand interaction with dynamic environments.
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