Based on recent insight into the thalamocortical system and its role in perception and conscious experience, a unified pathophysiological framework for hallucinations in neurological and psychiatric conditions is proposed, which integrates previously unrelated neurobiological and psychological findings. Gamma-frequency rhythms of discharge activity from thalamic and cortical neurons are facilitated by cholinergic arousal and resonate in networks of thalamocortical circuits, thereby transiently forming assemblies of coherent gamma oscillations under constraints of afferent sensory input and prefrontal attentional mechanisms. If perception is based (...) on synchronisation of intrinsic gamma activity in the thalamocortical system, then sensory input to specific thalamic nuclei may merely play a constraining role. Hallucinations can be regarded as underconstrained perceptions that arise when the impact of sensory input on activation of thalamocortical circuits and synchronisation of thalamocortical gamma activity is reduced. In conditions that are accompanied by hallucinations, factors such as cortical hyperexcitability, cortical attentional mechanisms, hyperarousal, increased noise in specific thalamic nuclei, and random sensory input to specific thalamic nuclei may, to a varying degree, contribute to underconstrained activation of thalamocortical circuits. The reticular thalamic nucleus plays an important role in suppressing random activity of relay cells in specific thalamic nuclei, and its dysfunction may be implicated in the biological vulnerability to hallucinations in schizophrenia. Combined with general activation during cholinergic arousal, this leads to excessive disinhibition in specific thalamic nuclei, which may allow cortical attentional mechanisms to recruit thalamic relay cells into resonant assemblies of gamma oscillations, regardless of their actual sensory input, thereby producing an underconstrained perceptual experience. Key Words: Charles Bonnet syndrome; gamma oscillations; hallucinations; late paraphrenia; Lewy body dementia; perception; schizophrenia; thalamocortical system. (shrink)

Social behaviour is but an expression of instinctive mechanisms whereby the aggressive instinct is of particular importance, having given rise to most of the complexity of social behaviour through processes of phylogenetic and cultural ritualisation. The role of the aggressive instinct is to dynamically maintain the ranking order in a group, and much of social interaction is concerned with this, including monetary exchange. What is certain, is that with the elimination of aggression, … the tackling of a task or problem, (...) the self-respect [in] everything that a man does from morning till evening, from the morning shave to the sublimest artistic or scientific creation, would lose all impetus; everything associated with ambition, ranking order, and countless other equally indispensable behaviour patterns would probably also disappear from human life. — Konrad Lorenz (1963/2002, p. 269) (Published Online April 5 2006). (shrink)

Affect mirroring allows infants to distinguish emotional and intentional states of significant others, which – in the pursuit of their own drive satisfaction, including satisfaction of the affiliative drive – become important contextual stimuli predictive of reward. Learning to perceive and manipulate others' attitudes toward oneself in pursuit of affiliative reward may be an important step in social development that is impaired in autism.

A “multifactorial” model should accommodate a psychological perspective, aiming to relate the phenomenology of complex visual hallucinations not only to neurobiological findings but also an understanding of the patient's psychological problems and situation in life. Greater attention needs to be paid to the role of the “lack of insight” patients may have into their hallucinations and its relationship to cognitive impairment.

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 . 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. (shrink)

Instinct theory parsimoniously clarifies the relationships between emotions, such as fear and anxiety, and perceptions, thoughts, and actions. Its acceptance allows more elegant insights into riddles of obsessions and compulsions. Their relationship to anxiety and dysexecutive function needs to be explained, as does their characteristic egodystonia, while avoiding the pitfalls of cognitivist, empiricist, and teleological thinking. (Published Online February 8 2007).

Co-morbidity of schizophrenia and autism is low because interpersonal concerns of schizophrenic patients presuppose developmental achievements that are absent in autism. Autism may arise if primary anxiety is not overcome at a key developmental stage by affective synchronisation between infant and caregiver. Schizophrenic patients will have learned to regulate primitive anxiety by affectively attuning to narrow social networks but remain highly vulnerable to exclusion from larger groups.

The commentators provide a wealth of additional neurobiological data that ought to be integrated in a comprehensive model. This response article, however, focuses on clarification of conceptual queries, thereby outlining the proposed theory of hallucinations more sharply, discussing its relationship with schizophrenia, and explaining why underconstrained thalamocortical activation may well be a candidate mechanism responsible for acute schizophrenic symptoms other than hallucinations.

The insight that, in terms of behaviour control, the mesodiencephalic system is superordinate to the cortex should have profound implications for behavioural sciences. Nevertheless, the thalamocortical system could still be deemed an “organ of consciousness” if we came to accept that consciousness is not central to purposeful behaviour, in accordance with instinct theory. Philosophically, Merker's concepts of basic consciousness and ego-centre warrant critical discussion. (Published Online May 1 2007).

How can be interchangeable with mirroring, which is an automatic response that, from a first-person perspective, enters awareness only after the act? The correspondence between perception of another's action and execution of one's similar action may be an example of a general perception-motor interface that maps perception onto behaviour or disposition towards action, without the need for simulation.