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)

Over the last decade, legal recognition of same-sex relationships in Canada has accelerated. By and large, same-sex cohabitants are now recognised in the same manner as opposite-sex cohabitants, and same-sex marriage was legalised in 2005. Without diminishing the struggle that lesbians and gay men have endured to secure this somewhat revolutionary legal recognition, this article troubles its narrative of progress. In particular, we investigate the terms on which recent legal struggles have advanced, as well as the ways in which resistance (...) to the legal recognition has been expressed and dealt with. We argue that to the extent that feminist critiques of marriage, familial ideology, and the privatisation of economic responsibility are marginalised, conservative and heteronormative discourses on marriage and family are reinforced. Our case studies include two pivotal moments in the quest for legislative recognition of same-sex relationships: the Hearings of the Canadian House of Commons Standing Committee on Justice and Human Rights on Bill C-23, The Modernization of Benefits and Obligations Act, in 2000 and the hearings on Same-Sex Marriage in 2003. We find that the debates operated within a narrow paradigm that bolstered many existing hierarchies and exacerbated conditions for those who are economically disadvantaged. (shrink)

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.