John Cutting is among the most interesting minds writing in psychiatry today. He has, with a rare combination of erudition and imagination, forged links between aspects of reality as delineated by philosophy and those that come into being through the workings of the two hemispheres of the brain.
In Principles of Psychopathology, Cutting (1997) introduced the concept of the hemispheres as underwriting two separate versions of the world. This was taken further in subsequent work Psychopathology and Modern Philosophy (1999), and The Living, the Dead, and the Never-Alive (2002). The relationship between different aspects of reality as conceived by philosophy, especially modern philosophy, is explored not only as reflected in the part-worlds delivered by the two hemispheres, but further in the experiences of schizophrenia (left hemisphere) and psychotic depression (right hemisphere). Latterly, Cutting has drawn on the works of Max Scheler, and in doing so identified the hemispheres with a further duality—that of Scheler’s Geist (left hemisphere) and Drang (right hemisphere).
Once one has one dichotomy well-established, that within the human brain, it would be natural to line up any further fault lines in experience with it and see what comes of that. Nonetheless, I have some misgivings about the way schizophrenia and depression are mapped onto the first, robust, dichotomy, that of the hemispheres; and graver ones about Geist and Drang, being overlaid on the other two.
The intuition to assent is understandable, and derives from the appearance of symmetry. I start, however, from the opposite intuition, derived from what we know about the relationship between the hemispheres, which is that there are oppositional pairings here that are likely to prove profoundly asymmetrical. This asymmetrical relationship of the hemispheres in relation to cultural history I have explored at length in The Master and his Emissary (2009). I can allude to it only briefly here.
Neuropsychological research has confirmed that almost all brain ‘functions’ are subserved not by one hemisphere, but by both. However, that is to see only the ‘what,’ not the ‘how.’ Each hemisphere deals with these so-called functions in a consistently different way, leading to two apparently complete, entirely coherent, but phenomenologically distinct, versions of the experiential world. The focus of neuroscientific research is inevitably on what are seen as ever more finely discriminated aspects of a mechanism’s functioning; but an integrative analysis of the findings at the neuropsychological level points to clear differences in the realm of experience, which bear directly on philosophical and cultural divisions, as well as on the world experiences of those with psychiatric disorders.
The Asymmetrical Relationship of Schizophrenia and Depression
There are, in my view, three grounds for caution about too closely mapping schizophrenia and depression onto the hemispheres.
First, and most simply, phenomenological aspects of schizophrenia (a quintessentially affectless condition) can overlap with affective conditions, including depression. This is a matter of common observation in many cases of chronic schizophrenia, and formally recognized in the concept of schizoaffective disorder. This suggests that they are less likely to be at either end of the same (right– left brain) axis than to be on different axes. Cutting’s insight that the world of the schizophrenic is the consequence of an over-reliance on the left hemisphere—constructing a world, the affectless nature of which derives from the relative absence of contribution from a normal right hemisphere, and whose apparent cognitive distortions are a consequence of the unnatural salience of what the left hemisphere brings into being—is unquestionably brilliant, but the symmetrical equation of depression with the unopposed action of the right hemisphere leaves the problem above unaddressed.
Second, the neuropsychological evidence linking schizophrenia and right hemisphere defect states is stronger than that linking depression and left hemisphere defect states. Such evidence certainly exists, but the picture is just less clear cut, with evidence suggesting that both left anterior and right posterior lesions can lead to depression. However, the types of depression experienced in right posterior hypoactivity are different from those experienced in left frontal hypoactivity, in ways that are in keeping with the views of the world that the two hemispheres bring into being: depression resulting from damage to the right hemisphere tends more...