Inhibitory processes in human voluntary action. (360G-Wellcome-086123_Z_08_Z)

The phenomenon of the conscious intention to act is an elusive but interesting aspect of cognition. Actions can be classified as being either stimulus driven or voluntary (Goldberg, 1985). In this context, stimulus driven actions are those that are done in response to an external stimulus. This external stimulus, through an association however arbitrary, unequivocally specifies the movement to be done. Voluntary actions, on the other hand, do not appear to be elicited by any obvious external stimulus. Instead, they arise as a result of the integration of many different sources of information. (Cunnington et al., 2002, Haggard, 2008). According to one recent model, three main components characterise voluntary action (Brass and Haggard, 2008). These are decisions regarding not only the identity (what) and the timing (when) of the action, plus a final check that allows withholding a prepared action (whether decision). This final ?veto? or Intentional Inhibition (II) would be important not only as a self-control mechanism, but also in situations where the task environment has changed. As actions are planned with some anticipation, it is reasonable to expect an online checking mechanism to be advantageous for flexible and appropriate behaviour. Experimental paradigms designed to address voluntary action are very often subject to criticism. Because experiments should be reproducible and interpretable, they tend to be simple, artificial in nature and of a low ecological value (Libet et al., 1983, Haggard and Eimer, 1999, Lafargue and Duffau, 2008). A genuine ?urge? to perform an action is hard to generate in the laboratory environment. Objective methods for studying intentions and convincing measures of the subjective experience of intention are thus relatively scarce. Increasing interest has arisen in the potential mechanisms for II, but in order to experimentally address II, one needs to achieve four things: - generate the urge to perform a movement, - induce participants to prepare to make the movement - allow them to choose to refrain from doing the movement at the very last moment, and - have an appropriate measure of this inhibition. By definition, there is no behavioural outcome to this kind of paradigm. Despite this methodological problem, some experimental paradigms have yielded robust results. Brass and Haggard (2007) asked participants to prepare a button press and to inhibit the prepared action in some trials. They have shown the selective activation of a brain area, associated with an endogenous cancellation function. An area of the anterior frontomedian cortex (dFMC), rostral to the presupplementary motor area (preSMA), was activated more when subjects had to cancel a prepared action than when they carried on with it. We propose to develop a more naturalistic and physiologically plausible paradigm for intentional inhibition, based on inhibiting the urge to scratch following electrically induced itch. In this proposed paradigm, although the urge to move is driven by a specific itch stimulus, the inhibition of the scratching is self-generated, and related to the urge to scratch. This combination therefore represents a significant improvement to the traditional paradigms of II used thus far.