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Abstract
The planning of goal-directed arm reaching movements is associated with activity in the dorsal parieto-frontal cortex, within which multiple regions subserve the integration of arm- and target-related sensory signals to encode a motor goal. Surprisingly, many of these regions show sustained activity during reach preparation even when target location is not specified, i.e., when a motor goal cannot be unambiguously formed. The functional role of these non-spatial preparatory signals remains unresolved. Here this process was investigated in humans by comparing reach preparatory activity in the presence or absence of information regarding upcoming target location. In order to isolate the processes specific to reaching and to control for visuospatial attentional factors, the reaching task was contrasted to a finger movement task. Functional MRI and electroencephalography (EEG) were used to characterize the spatio-temporal pattern of reach-related activity in the parieto-frontal cortex. Reach planning with advance knowledge of target location induced robust blood oxygenated level dependent and EEG responses across parietal and premotor regions contralateral to the reaching arm. In contrast, reach preparation without knowledge of target location was associated with a significant BOLD response bilaterally in the parietal cortex. Furthermore, EEG alpha- and beta-band activity was restricted to parietal scalp sites, the magnitude of the latter being correlated with reach reaction times. These results suggest an intermediate stage of sensorimotor transformations in bilateral parietal cortex when target location is not specified.
Highlights
To plan goal-directed arm reaching movements, the brain must transform goal-related sensory information into an appropriate pattern of motor commands
All participants gave informed written consent to the experimental protocol, which was approved by the Human Participants Committee, Office of Research, University of California Santa Barbara, or the ethical committee of the Centre Hospitalier de l’Université de Sherbrooke (CHUS)
Reaction time (RT) was similar across Effectors in the Non-Spatial conditions (346 ms for Arm and 346 ms for Finger), but slightly faster for Finger than Arm in the Spatial conditions (292 ms vs. 307 ms, respectively)
Summary
To plan goal-directed arm reaching movements, the brain must transform goal-related sensory information into an appropriate pattern of motor commands. Studies in non-human primates have highlighted the important role of specific regions of the dorsal parieto-frontal cortex in this process, namely the parietal reach region (PRR) (Snyder et al, 1997; Galletti et al, 1999; Andersen and Buneo, 2002; Gail and Andersen, 2006), which encompasses the medial intraparietal sulcus (MIP) and area V6A, as well as the dorsal premotor cortex (PMd) (Cisek and Kalaska, 2002, 2005; Hoshi and Tanji, 2006). These data suggest that these regions encode the visuospatial location of a target, but integrate it with armrelated signals to form a motor goal (i.e., reach direction between the arm and the target)
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