Abstract
It has been proposed that the posterior parietal cortex (PPC) is characterized by an effector-specific organization. However, strikingly similar functional MRI (fMRI) activation patterns have been found in the PPC for hand and foot movements. Because the fMRI signal is related to average neuronal activity, similar activation levels may result either from effector-unspecific neurons or from intermingled subsets of effector-specific neurons within a voxel. We distinguished between these possibilities using fMRI repetition suppression (RS). Participants made delayed, goal-directed eye, hand, and foot movements to visual targets. In each trial, the instructed effector was identical or different to that of the previous trial. RS effects indicated an attenuation of the fMRI signal in repeat trials. The caudal PPC was active during the delay but did not show RS, suggesting that its planning activity was effector independent. Hand and foot-specific RS effects were evident in the anterior superior parietal lobule (SPL), extending to the premotor cortex, with limb overlap in the anterior SPL. Connectivity analysis suggested information flow between the caudal PPC to limb-specific anterior SPL regions and between the limb-unspecific anterior SPL toward limb-specific motor regions. These results underline that both function and effector specificity should be integrated into a concept of PPC action representation not only on a regional but also on a fine-grained, subvoxel level.
Highlights
In the present study, we show that regions in posterior parietal regions process information independent of the currently used effector during goaldirected actions
We have recently reported that the planning of goal-directed hand and foot movements evoked markedly similar POSTERIOR PARIETAL CORTEX (PPC) activation, whereas the activation evoked by the planning of eye movements was different from limb-related activation (Heed et al 2011)
All these studies suggest that effector specificity is not a defining processing feature of the PPC and that, instead, the PPC may be organized according to functional criteria rather than in an effector-specific manner
Summary
We show that regions in posterior parietal regions process information independent of the currently used effector (hand, foot, or eye) during goaldirected actions. There is abundant evidence that the PPC distinguishes the processing for eye and hand movements, especially in the monkey (Andersen and Cui 2009; Chang et al 2008; Premereur et al 2015), this division appears gradual rather than absolute, especially in humans (Caminiti et al 2010; Filimon et al 2009; Gallivan et al 2011; Heed et al 2011; Hinkley et al 2009; Leoné et al 2014; Tosoni et al 2008) These observations have traditionally been interpreted in terms of an effector-specific organization of the PPC. MVPA revealed effectorspecific coding where traditional activation analysis did not
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