In this post I wish to distinguish between two different theories of the bodily basis of schizophrenic delusions. Well, between three different theories, if we start by definitively laying to one side the potentially unproblematic yet often overly simplistic aetiological idea that 'schizophrenia is [caused by] a disturbance in the brain'. That won't be my concern here, which is rather to distinguish between two different ideas of the relation between abnormal bodily experience and delusional belief.
The first idea, which is fairly widespread, takes abnormal bodily experience (altered somatosensory and proprioceptive experience and micro-motoric behaviours, cenesthesias and the like) to provide a content for delusional thought. The theories of Brendan Maher and Philippa Garety come to mind here. Delusion, it is said, amounts either (Garety) to the deployment of abnormal reasoning ranging over sensation and perception, or to (Maher) normal reasoning ranging over abnormal sensory input. I hallucinate, for example, and, taking up this abnormal perceptual experience within my troubled or untroubled powers of reason, I arrive at a belief the bizarreness of which is either just a function of the hallucinatory content, or is due in addition to inferential disturbances in the cognitive processes by which I try to make sense of what I take myself to hear or see. Similarly, altered somatosensory rather than perceptual experience may give rise to delusional beliefs which have the altered bodily experience featuring in some way as a content of the belief. We only have to think about cenesthesias and delusions of objects or organisms lodged in the body to understand how this relationship might obtain in the somatosensory domain.
Now it might be tempting to consider this the end of the psychological story for the relation between subjective bodily experience and delusional belief. The second idea I wish to consider, however, takes the first as only a small part, and only the end, of a far more comprehensive account of the relation between our embodiment and our thought. All I shall try to do here is to briefly, and piecemeal, attempt a sketch of this latter possibility.
Schizotaxia. The theory of schizotaxia is owed to the venerable American psychologist Paul Meehl. It posits the idea of an inheritable predisposition to developing schizophrenia, which predisposition has characteristic features of its own, and which may be found not only in the pre-prodromal schizophrenic, but also in their kin. The schizotaxic diathesis includes spatial, vestibular, and kinesthetic disturbances, and results in dysdiadochokinesia, a tendency to cognitive slippage, and other symptoms, and when partially decompensated may lead to distortions of body image, blurred ego boundaries, chaotic and confused sexuality, etc. According to Meehl, perhaps 90% of schizotaxic subjects remain compensated throughout their lives, or at least will not develop schizophrenia. The unfortunate 10%, perhaps (we may speculate) because of overt traumata or perhaps (again, speculation) because of developmental (including psychosexual) disturbances, decompensate into the acute and then chronic schizophrenic state. What causes and characterises the decompensation may be psychodynamically explicable; the nature of the experiences may best be characterised using existential phenomenology; but the underlying schizotaxic disturbance, which should be considered a sine qua non of schizophrenia, remains explicable, causally, solely in biological terms.
Conceptual Metaphor and the Body. The theory of conceptual metaphor and its bodily foundation is owed to the well-known cognitive scientists and linguists George Lakoff and Mark Johnson. It depends on two theoretical posits which strike me as prima facie plausible. The first is the metaphorical nature of much of our discourse. Lakoff and Johnson note the way in which many abstract concepts are structured by, and can be understood through a prior acquaintance with, other conceptual domains. For example, ideas to do with warfare play a large part in the language-games to do with arguments (beating, defending, launching an attacking, dealing a striking or killer blow, etc.). We understand what someone means when they describe verbal exchanges in such militaristic terms because we appreciate the conceptual mapping that is going on here. The second posit is the way in which our understanding of 'the mind' is dependent upon our understanding of 'the body'. We intuitively grasp what people are saying when they talk of feeling up tight, grasping the point of an argument, feeling up or down, high or low, spaced out, disturbed, seeing what is meant, thoughts that escape us, etc. ad infinitum. In fact (although this point is somewhat irrelevant to my argument here) our vocabularies of mental disturbance are themselves run through with such bodily metaphors. (The nice idea has even been put forward - by T S Champlin - that the very idea of mental illness stands to bodily illness as a 'rhyme to the eye' stands to one 'for the ear' - i.e. in a metaphorically mapped sense which cannot be further justifies but relies on our innate dispositions to take the discourse in the way we do (cf Wittgenstein on secondary sense).)
The key idea in Lakoff and Johnson's work on the bodily basis of meaning is that our experience of our bodies informs our understanding of the world and of one another. And the way in which it informs it is not through our thinking about our bodies and what is going on in them. Our bodily experience does not inform our comprehension through by our reflecting on it, but rather directly and causally informs our cognitive dispositions. It does not provide us with reasons for our beliefs, but rather structures our extra-rational and foundational dispositions to take one another and grasp events in the way we do.
The thesis which results from the combination of 1 & 2 should now be obvious. Delusional beliefs in schizophrenia may result from the way the schizophrenic's entire world-relation, the way they pre-reflectively grasp at meaning, the way their dispositions to go on (or not go on) in ways which themselves constitute (or fail to constitute) our practical rationality, have altered. Failures in somatosensory integration lead to failures in thought, not through constituting peculiar objects for such thinking, but through leading to disturbances in what we could call its form. But the notion of 'form' must be handled carefully here; we cannot rely on any simple form/content distinction, and we must avoid any facile dualism along these lines at all cost. The appeal to the form or shape of the thought here (another nice couple of conceptual metaphors, note), signifies solely that we cannot help ourselves here to any notion of the perfectly rational grasp of merely perceptually or interoceptively bizarre content (a la Maher).
As a preliminary sketch, this will have to do. I wish to mention here only on the support such a view could also gather from what today is a widespread phenomenological literature on disturbances of the lived-body in schizophrenia - from writers such as Giovanni Stanghellini, Josef Parnas, and Thomas Fuchs.