Department of Experimental Psychology and Wellcome Trust Centre for Integrative Neuroimaging (WIN)
University of Oxford, UK
Voluntary actions are ones that appear to be initiated by people and other animals in the absence of any external instruction or cue. However, the likelihood that voluntary actions are initiated depends on identifiable features of both the current and the recent environment, recent behaviour, and the consequences that will ensure if the action is made (for example, will it lead to reward or not). These factors mediate their influence on the initiation of voluntary action via a distributed neural circuit spanning cortical regions such as the anterior cingulate and insula cortex and subcortical nuclei including habenula, basal forebrain, ventral tegmental area, substantia nigra, and raphe nucleus. I review a series of recent studies conducted in non-human and human primates using a combination of neuroimaging, temporary inactivation via ultrasound stimulation, and pharmacological manipulation that begin to dissect these different influences on voluntary behaviour and to trace the anatomical pathways through which each operates on voluntary behaviour. The timing of action initiation depends both on reward expectations and on recent behaviour and these influences are governed by changes in activity in the basal forebrain and anterior cingulate cortex, altered by disruption of activity in either of these areas, and by cholinergic manipulations. However, whether or not an action is initiated also depends on the richness/sparseness of opportunities in the environment in general and this is tracked by activity in the raphe nucleus and altered by serotonergic manipulation.
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