Throughout the history of schizophrenia as a psychiatric concept, opinions have differed sharply over its essential nature and its causes, giving rise to a wide range of explanations that have drawn upon ideas from almost all of the social and biological sciences. Only one fact has truly survived the vicissitudes of argument about the condition: that genetic factors contribute to its aetiology. Even that conclusion, first reached in the very early days of schizophrenia research, sank temporarily out of sight during the radical psychiatry challenges of the 1960s. However, the continuing collection of family, twin, adoption and other data over that period put the genetic hypothesis beyond reasonable doubt (McGuffin, 1988).

In 1972 the author proposed that schizophrenia represents an aberration of central nervous processes that underlie cognitive and personality characteristics which can be observed in many healthy people. The present paper brings the evidence for that theory up to date and concludes that over the past 15 years it has received considerable empirical support. The way in which the theory confronts the question of whether or not schizophrenia is a disease is also clarified.

Despite over half a century of intensive research the essential nature of the schizophrenias still remains an enigma. Attempts to account for the disordered behaviour of the schizophrenic have ranged over the full spectrum of the biosocial sciences, explanations being sought both in the biochemistry of the organism and in the interpersonal relationships of the whole individual. Sitting somewhere between these two extremes is the psychophysiological view. As a conceptual and methodological approach to behaviour in general, psychophysiology concerns itself with the problem of integrating neurophysiological and psychological data, attempting to bridge the gap between these two disciplines. Of course, the potential value of describing behaviour at a different level of explanation, either more molecular or more molar, is not denied. However, the peculiar contribution of psychophysiology is its concentration on data gathered at the interface between the brain and behaviour. As such its techniques are chosen so as to allow guesses to be made about the functional systems in the brain that underly behaviour. They naturally include the study of E.E.G. and autonomic response but also extend to the measurement of various phenomena derived from conventional experimental psychology, such as perceptual thresholds and vigilance (Claridge, 1970b). The theoretical concepts of psychophysiology reflect its mongrel background and include such terms as ‘arousal’, a notion originating in academic psychology, but made respectable by neurophysiologists.