Abstract
In reaching movements, parietal contributions can be distinguished that are based on representations of external space and body scheme. By functional magnetic resonance imaging, we examined 16 healthy subjects to see whether such segregation similarly exists in the frontal lobes when visuomotor actions are not specified but when free choices are allowed. Free selection was button based (target based) or finger based (self-referenced), with invariant instructions as control. To avoid a visual attention bias, instructions were auditory presented. Statistical parametric mapping revealed that free button selection with the same finger was associated with increased activations in the anterior cingulate cortex (ACC), right posterodorsal prefrontal cortex (PFC) including the rostral extension of the dorsal premotor cortex (pre-PMd), and the anterodorsal PFC. Prefrontal activation related to free finger selection (pressing the same button) was restricted to an anteromedial segment of the posterodorsal PFC/pre-PMd. Bilateral inferior parietal activations were present in both free-choice conditions. Pre-PMd and parietal contributions to free selection support concepts on early-stage action selection in dorsal visuomotor pathways. The rostral-caudal segregation in pre-PMd activations reflected that in anterior direction, frontal processing is gradually less involved in selection of environmental information but increasingly committed to self-referenced selection. ACC particularly contributes to free selection between external goals.
Highlights
Object manipulation implies visuomotor transformations that require an adequate representation of the object’s shape and its position in space
A consistent increase of cerebral activations distributed over the anterior cingulate cortex (ACC) and the dorsolateral prefrontal cortex (PFC) has been found when comparing free-choice selection with unequivocally instructed selection (Frith et al 1991; Hyder et al 1997; Desmond et al 1998; Cunnington et al 2006)
Previously described patterns of parietal-prefrontal connections provide general support for the presence of functional interactions between the distributed activations in the present study (Pandya and Yeterian 1990; Johnson et al 1996; Rozzi et al 2006). These anatomical data support the segregation we found between the representations of free finger and free target selection in the pre-PMd and parietal cortex, in such a way that it fits with the observations that rostral premotor and caudal parietal regions are functionally associated as well as preferentially connected, which holds for caudal premotor and rostral parietal loci (Johnson et al 1996)
Summary
Object manipulation implies visuomotor transformations that require an adequate representation of the object’s shape and its position in space. The neural underpinning of such aspects in higher order motor control is anchored in circuitry distributed over parietal and premotor cortical regions (Binkofski et al 1999; Matelli and Luppino 2001) Within these parietopremotor networks, the left anterior parietal cortex facilitates the integration of target shape and hand posture (Grafton et al 1996; Binkofski et al 1998; Buxbaum et al 2006), whereas the superior parietal cortex, with a right-hemisphere dominance in humans, is involved in navigating the hand to the object (Mountcastle et al 1975; Corbetta et al 1993; Wise et al 1997; Vallar 1998). In this respect, Mueller et al (2007) have recently provided arguments that the ACC is critically involved in free selection
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