The featured paper is another by Professor Tim Crow and colleagues on his theory of psychosis which was covered albeit briefly in a paper reviewed here on this blog. This paper entitled ‘Callosal misconnectivity and the sex difference in psychosis’ discusses Crow’s theory in more detail and is in the International Review of Psychiatry. The article is 9 pages long with a clear discussion. There are some areas that require supplementary reading in order to get a better understanding of the theory. The paper sets out to explain the ‘Taylor Paradox’ which essentially states that if schizophrenia is a neurodevelopmental disorder, then why does it manifest earlier in men when it is women’s brains which develop more quickly (including in terms of lateralisation). The answer according to Crow’s theory lies in a torque that exists within the brain as well as the nature of the connections between different association ares in the cortex.
Within the article torque is described as a differential concentration or volume of tissue occuring both across hemispheres (hemispheric torque) and within the same hemisphere across coronal sections. Crow has suggested in a previous paper that the four association areas are of importance here – 2 motor and lying anteriorly and 2 sensory and lying posteriorly. Anteriorly the association areas are responsible for speech generation and thought whilst posteriorly they are responsible for speech perception and meaning. Evidence is discussed showing that the corpus callosum develops more quickly in females with more anterior lateralisation. In males by contrast, the development is slower and lateralisation occurs predominantly posteriorly.
Thus in normal development, females would have greater verbal abilities due to lateralisation in the anterior regions of the brain and men would have greater spatial abilities due to lateralisation in the posterior regions of the brain. Furthermore the 4 different association areas communicate with each other and have a directional preference. At this stage the model is dependent upon the assumption that transmission occurs from a larger to smaller area (Presumably this relates to an increased probability of neuronal firing in a larger population) and it is therefore posited that the direction of flow would be from Left Posterior-Occipital-Temporal Cortex to Right PTOC To Right Dorsolateral Prefrontal Cortex to Left DFPC. Then it is suggested that phenomenon such as thought broadcast, insertion and withdrawal occur as a result of abnormal activation of the Right DLPFC and that hallucinations would occur as a result of abnormalities in communication between the Posterior Association Cortices. There is the further assumption that the directionality of communication between association cortices predisposes towards psychosis and that as a result of differences in myelination during development, males are more vulnerable to psychosis at an earlier age.
There is of course a lot more to it than this and the interested reader is referred to the paper (reference given at the end of the article). Having such a specific biological model for psychosis is very important and it will be interesting to follow developments in this area.
T.J.Crow, P.Paez and S.A.Chance. Callosal misconnectivity and the sex difference in psychosis. International Review of Psychiatry. August 2007. 19(4). 449-457.
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