Reduction of primary mental illness to brain disease is not possible in principle (see previous post). Neuroimaging studies that literally 'light up the brain' have misled us into accepting the neuro-turn (see another previous post). But the subject matter of psychiatry is the person as a whole, not the brain. The part-function of the brain is not the same as the person (see yet another previous post). More generally, life cannot be understood in mechanical terms, as Kant said some time ago (see previous post). Even though it's absurd to make an attempt to understand primary mental illness in physical terms, nonetheless it seems to make sense to us that we should be able to provide such understanding and explanation (see another previous post). Psychiatry, therefore, always holds out the expectation that it will eventually find the answers to primary mental illness (see yet another previous post).
As Varela et al (2017) said:
[W]e hold with Merleau-Monty that Western scientific culture requires that we see our bodies both as physical structures and as lived, experiential structures - in short, as both "outer" and inner', biological and phenomenological. ... For Merleau-Monty, as for us, embodiment has this double sense: it encompasses both the body as a lived, experiential structure and the body as the context or milieu of cognitive mechanisms.
The trouble is that subjective experience tends to be seen as a mere epiphenomenon and the focus has become so-called objective scientism.
Psychiatry went through a previous phase of brain mythology in the nineteenth century. The enthusiastic search for anatomical localisation in psychiatry led to fanciful notions, as, for example, with Theodor Meynert (1833–1892) who throught he had delineated various ‘fibre-systems’ in the brain and deduced functions for these ‘pathways’. Meynert’s research may have appeared so successful because it seemed to give a material explanation of the basis of mental illness in the same way as modern neuroscience. Despite his skills in brain dissection, Meynert's theories were not based on empirical findings. Nor have any definite biomarkers been linked to primary mental illness in modern research studies as they are plagued by inconsistencies and confounders (see eg. previous post).
Anatomoclinical understanding, which relates symptoms and signs to their underlying physical pathology, was a major advance for medicine in the nineteenth century and still underlies our modern understanding of disease. Pathology emerged as a distinct discipline with autopsy findings of lesions in organs and tissues being related to clinical examination at the bedside. Histological studies established cellular abnormalities for disease. Applying this anatomoclinical method to psychiatry was not as successful, however, because it was not always easy to relate mental conditions to underlying brain pathology.
Eventually it was established that dementia paralytica was a late consequence of syphilis. Senile dementia was also seen as having a physical cause such as Alzheimer’s disease. Focal abnormalities in the brain were identified and physical causes of learning disability were recognised. However, most psychopathology is functional, in the sense that there are no structural abnormalities in the brain. A distinction was, therefore, made between functional and organic mental illness (see previous post). This consensual understanding was broken by DSM-IV (see previous post) and DSM-5 failed in its attempt to create a scientific basis for psychiatric diagnosis and classification (see eg. previous post), based on genetic markers and brain imaging (see another previous post).
I'm sure the wish to find a biological basis for primary mental illness will never go away completely. But psychiatry must stop ignoring that patients are people. This is not a unique requirement for psychiatry, as all medicine needs to be more patient-centred (see eg. previous post). But it is particularly acute for psychiatry when primary mental illness cannot be reduced to brain disease.