The Mind-Body Problem in Psychiatry

The French philosopher René Descartes is often credited with discovering the mind-body problem; a dogma with long-standing implications on psychiatry. Descartes introduced notions that the mind and body are separate entities, albeit later acknowledging that there may indeed be a link via the brain (specifically, the pineal gland). Resultantly, modern psychiatry largely neglected influences of the peripheral body on mental health, with biological psychiatric research often taking a more brain-centric role. But is this truly the case? Is one’s mental state simply a product of our brain function? The evolving field of ‘psychoneuroimmunology’ (PNI) for example, begs to differ. As the portmanteau might have suggested, PNI is a hybrid research area – intersecting psychiatry, neuroscience, and immunology. Importantly, PNI research has shown time and time again that the peripheral body has distal effects on mental health. Previous blog posts by The Mental Elf have also discussed findings supporting this idea (Corsi-Zuelli, F., 2023; Foley, É., 2023; Parker, N. and Andreassen, O., 2023).

To further our efforts towards ending the enduring influence of Cartesian dualism in psychiatry, this blog discusses a recent study by Tian et al., (2023) published in JAMA Psychiatry. This paper compares brain and peripheral bodily system alterations across psychiatric disorders to healthy (control) individuals. The article addresses a timely question in psychiatry, both from a therapeutic and pathophysiological standpoint – what is the importance of physical comorbidities and physical health in our evaluation of psychiatric disorders/mental health?

The Cartesian notion of the mind and body being separate entities has negatively influenced our view of mental vs physical health. In reality, our mind and body work hand-in-hand to determine our overall health and wellbeing.

Methods

Participants and data source(s)

This study leveraged seven publicly available cross-sectional datasets to integrate brain imaging data (structural and diffusion-weighted magnetic resonance imaging [MRI]) with physical and physiological data. Physical and physiological assessments were sourced from 175, 944 individuals participating in the UK Biobank. Participants were further split into two groups: Controls without a neuropsychiatric diagnosis (N=87,420) and those diagnosed with a neuropsychiatric disorder (N=85,748; schizophrenia, bipolar disorder, depression, generalized anxiety disorder, dementia). People who were comorbid for any of the evaluated psychiatric disorders were excluded.

Imaging-Derived Phenotypes (IDPs)

Brain regions of interest examined included proxies of: Regional gray matter (GM) health (NIDP=76; of T1-weighted MRI origin)e. cortical thickness, and cortical as well as subcortical GM volume. Brain white matter (WM) (NIDP=54; of diffusion-MRI origin)e. tract-specific measures of WM microstructure such as fractional anisotropy and mean diffusivity.

Relevant peripheral physical and physiological measures

73 in total and were selected and grouped into seven bodily systems, i.e. pulmonary, musculoskeletal, kidney, metabolic, hepatic, cardiovascular, and immune systems. All input (brain, blood and urine biomarkers, physiological measures) was quality controlled and harmonized for analytic use.

Analytic approach

The study presents a two-step analytic approach to evaluate brain-body health. The initial step involved ‘normative modelling’ i.e., building reference ranges for the various brain and body variables by using measures derived from controls without a neuropsychiatric diagnosis. The resultant reference ranges were then used to estimate deviation scores – from ‘normal’ range – for individuals diagnosed with a neuropsychiatric disorder. Secondly, an organ health score (OHS) was estimated for each bodily system including the brain, i.e. one for brain GM and one for brain WM, per individual. Seven OHS were ultimately generated for each individual (one for each of the bodily systems/organs examined), with an additional eight organ-specific health scores, i.e. overall body health score, computed based on patients with chronic diseases affecting multiple bodily systems. Lower organ-specific health scores denote poorer ‘health’.

Results

The authors evaluated brain-body health under two streams of stratification: Organ/system – differences in OHS were compared between neuropsychiatric disorders and control group. Diagnosis – the eight OHS were compared within the selected neuropsychiatric disorders. On average, all organ-specific health scores were significantly lower in those with a neuropsychiatric disorder diagnosis compared to age- and sex-matched individuals without a diagnosis. Notably, metabolic, hepatic, immune and renal health were most deviated from normative reference ranges for schizophrenia, bipolar disorder, generalized anxiety disorder, and depression.