A neuroanatomical model of passivity phenomena

Any attempt to elucidate the nature and mechanism of passivity phenomena, i.e., experiences that one's conscious actions or thoughts have not been 'willed' by oneself, requires an integrative philosophical-neurobiological approach. The model proposed here adopts some fundamental positions that have long been advocated by philosophers and theoretical psychologists and have now found support from functional neuroanatomy. First, we experience our actions not from the standpoint of the executive but through the perception of its effects. Second, the 'self' is not an agent of behaviour. Third, behaviour is energised and integrated by basic drives (instincts). Fourth, the view that the experience of an acting self is related to drive reduction associated with voluntary actions is perhaps less well developed. The model thus proposes that passivity phenomena are actions that are induced by the perception of salient events but that are not integrated with or conducive to the overall motivational state of the organism. It has been suggested that, following the perception of salient events, competition arises between automatic response tendencies seeking expression. The prefrontal cortex appears to play an important role not only in determining which events are to be perceived but also which of the corresponding response dispositions is to be selected and actualised in overt behaviour. Thus, action selection is the outcome of competition between response tendencies in the context of prefrontal biasing signals that represent drives and strivings for goals. Action selection may be uncoupled from drives and strivings as a result of a lowering of the threshold for action selection-as is suggested to be the case in schizophrenic passivity phenomena-or due to disconnection from prefrontal regions-as may be the case in the alien limb syndrome. (C) 2004 Elsevier Inc. All rights reserved.