'Dual brain action': The case studies of Lewis C. Bruce in the 1890s

The idea that contrasting states of consciousness or dual personalities may in some way be related to the two hemispheres of the brain drew considerable attention during the nineteenth century, especially after cerebral dominance became accepted in the 1860s. The notion that the better educated and more verbal personality could be associated with the left hemisphere, whereas a more primitive or beast-like personality could be associated with the right, was the subject of two papers by Scottish psychiatrist Lewis Campbell Bruce in the 1890s. Bruce was guided by three beliefs: (a) that quality research can come out of asylums for the insane; (b) that purely psychological theories of mental disorders have been given entirely too much attention; and (c) that insanity must have a physical basis. After encountering three cases of what he called 'dual brain action', he concluded that, at least in some cases, cortical epilepsy is a likely trigger for the switching back and forth from the more intellectual personality of the left hemisphere to the more instinctive and impulsive personality of the right hemisphere.