The wall between neurology and psychiatry

For more than 2000 years in the West, neurology and psychiatry were thought to be part of a single, unified branch of medicine, which was often designated neuropsychiatry. Charcot, Freud, Jackson, Bleuler, among many others, thought in terms of a unified study of the brain and the mind, irrespective of special clinical and research interests. During the 20th century, however, a schism emerged as each of these fields went its separate way. Neurologists focused on those brain disorders with cognitive and behavioural abnormalities that also presented with somatic signs—stroke, multiple sclerosis, Parkinson's, and so forth—while psychiatrists focused on those disorders of mood and thought associated with no, or minor, physical signs found in the neurological examination of the motor and sensory systems—schizophrenia, depression, anxiety disorders, and so on. For certain disorders, conflicting theories emerged about their aetiology and pathogenesis, at times engendering negative attitudes among workers in one or the other field, including derision and incivility. In academic medical centres, separate departments were formed in neurology and psychiatry that had little interest in collaboration in research, teaching, or patient care.¹ Those specialists who supported a more holistic view of these disciplines were in full retreat by midcentury.²

Clearly, recent advances in neuroscience make it untenable at this time to know precisely where to draw the line between neurological and psychiatric disorders. For example, it is well known that many patients with Parkinson's disease and stroke manifest depression and, in some, dementia. Is there a substantive difference between a toxic psychosis (psychiatry) and a metabolic encephalopathy with delirium (neurology)? We have known of these examples for several years. More recent and dramatic evidence has come largely through functional magnetic resonance imaging and positron emission tomography. Obsessive-compulsive disorder is characterised by recurrent, unwanted, intrusive ideas, images, or impulses that seem silly, weird, nasty, or horrible (obsessions) and by urges to carry out an act (compulsions) that will lessen the discomfort due to the obsessions. Increasing the levels of brain serotonin with selective reuptake inhibitors may control the symptoms and signs of this disorder. Evidence of a genetic basis in some patients, structural abnormalities of the brain on magnetic resonance imaging in others, and abnormal brain function on functional magnetic resonance imaging and positron emission tomography collectively suggest that schizophrenia is a disorder of the brain.³

Nor does all of the neuroscientific evidence linking neurology and psychiatry arise from study of patients. Learning to read by braille can enlarge the brain region responding to fingertip stimulation. Brain imaging research shows that several brain areas are larger in adult musicians than in non-musicians. The primary motor cortex and the cerebellum, which are involved in movement and coordination, are bigger in musicians than in people who don't play musical instruments, as is the corpus callosum. Discontinuing the use of braille or the violin can reverse the functional neuroanatomic connections.⁴

Because of the vast increase in neurobiological knowledge in recent years, and the ever increasing number of disorders (including those referred to above) once thought to be psychopathological yet now known to be neuropathological, some neurologists might cling to the view that their specialty has now emerged alone as the reigning queen of the medical sciences. If they do, we do not agree with them. The concept of mental health as much more than the mere absence of brain disease is, we suggest, indispensable for neurological and psychiatric practice and care. From our angle of vision, the fundamental alliance between mental health and brain illness (devoid of the confounding terms brain health and mental illness⁵) as the basis of care derives in the first instance from Aristotle's distinction between efficient causes and final causes. (An efficient cause, or mechanism, is that by means of which something happens; a final cause, or teleological cause, is that for the sake of which something happens.) Neurologists and psychiatrists must have a suitably broad perspective, for theirs is the domain of purposeful behaviour and intentionality (final causes) that is no less a brain/mind function than sense perception and movement. Clearly, the education of future generations of neurologists and psychiatrists must be grounded in neuroscience, but must equally be focused on those dimensions of professional activity that quintessentially define the work of medical doctors from the neck up.⁶