Abstract
Recent brain imaging research revealed that internally guided actions involve the frontomedian wall, in particular the preSMA and the rostral cingulate zone (RCZ). However, a systematic decomposition of different components of intentional action is still lacking. We propose a new paradigm to dissociate two components of internally guided behavior: Which action to perform (selection component) and when to perform the action (timing component). Our results suggest a neuro-functional dissociation of intentional action timing and intentional action selection. While the RCZ is more strongly activated for the selection component, a part of the superior medial frontal gyrus is more strongly activated for the timing component. However, in a post hoc conducted signal strength analysis we did also observe an interaction between action timing and action selection, indicating that decisional processes concerning action timing and action selection are not completely dissociated but interdependent. Altogether this study challenges the idea of a unitary system supporting voluntary action and instead suggests the existence of different neuroanatomically dissociable subfunctions.
Highlights
Human actions exist along a continuum with regard to whether they are externally or internally controlled
The rostral cingulate zone (RCZ) is involved in the internal selection of an action, whereas an area of the superior frontal gyrus (SFG) in the left paramedian frontal cortex is involved in the decision ‘when’ to perform an action
DIFFERENTIATING WHAT- AND WHEN-COMPONENT OF INTENTIONAL ACTIONS Our findings suggest the existence of at least partially dissociable neural networks underlying the ‘what-’ and ‘when-component’ of intentional action: the RCZ and paramedian frontal cortex are differentially activated for intentional action selection and action timing, respectively
Summary
Human actions exist along a continuum with regard to whether they are externally or internally controlled. Actions rarely correspond to the extremes of the continuum They can be classified into actions guided foremost by internal factors, for example switching on TV to watch the news, and actions guided rather by environmental stimuli, for example stopping in front of a red traffic light. Herwig et al (2007) suggest that, in the stimulus-based mode, the agent passes on control to the environment in that the system merely acts upon presentation of a particular stimulus in a prespecified way (prepared reflex, see Hommel, 2000). These actions are selected with respect to their sensory antecedents. Regarding the underlying neuroanatomical differences between the two action modes (Goldberg, 1985) emphasized the distinction between a medial and a lateral motor system which are involved in internally and externally guided actions, respectively
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