The introduction of neuroimaging techniques for the study of brain structure and function has revolutionised the endeavour to elucidate the pathology of psychiatric disorder, the Holy Grail in psychiatry (Krishnan, 1990). Emil Kraepelin discovered the two major mental disorders, dementia praecox and manic-depression, and conceived their aetiology in brain pathology. It was Alois Alzheimer, however, his most successful student, who discovered the neuropathology of Alzheimer's disease. Sigmund Freud, who started his inquiries in brain science, lost faith and shifted to the study of the mind. Brain science and mind ‘science’ rapidly became odd bed fellows and parted company. The breakdown in communication fostered a mistrust in both parties, aborting endeavours of reconciliation. The evidence for the neuropathology of the ‘functional’ psychoses has, however, been inconclusive. It was the advent of brain-imaging techniques that rejuvenated brain sciences and modern neurosciences. The introduction of neuroimaging techniques, such as the electroencephalogram (EEG) in the 1920s and the whole-brain blood-flow techniques (Berger, 1929; Kety & Schmidt, 1948), antedated the discovery of psychotropic drugs. Pneumoencephalography was also applied to study brain structure in schizophrenia (Storey, 1966). The true methodological leap, however, was the introduction of computerised methods to construct three-dimensional images from two-dimensional data, enabling the development of computerised tomography (CT), magnetic resonance imaging (MRI), positron-emission tomography (PET) and single-photon emission computerised tomography (SPECT).

The development of the non-invasive technique of computerised tomography (CT) in the mid-1970s revolutionised the clinician's ability to visualise brain structures in vivo. The main use of the CT scan was to exclude intracranial mass lesions such as cerebral tumours and haematomas. This remains its principal application in neurology and neurosurgery, but in psychiatry additional features such as cerebral infarctions, regional cerebral atrophy, ventricular enlargement and white-matter changes have provoked interest. This review outlines the technique of CT scanning, discusses its use in the differential diagnosis of dementia of the Alzheimer type (DAT), and comments on the relative contributions of cortical atrophy and ventricular enlargement to the clinical picture of DAT.

X-ray computerised tomography (CT) has revolutionised diagnostic radiology, particularly neuroradiology, since its inception (Houndsfield, 1973). It has been used widely in the systematic examination of brain structure in schizophrenia since the first study, 15 years ago, by Johnstone et al (1976). Several good reviews of the findings appeared in the mid-1980s (e.g. Reveley, 1985a; Shelton & Weinberger, 1986). Since then, although the spate of published studies has slowed, the quality of more recent published studies has in general been higher than the earlier ones, and it is time to look at the field again. This review examines the methodological pitfalls in CT research in schizophrenia and then attempts to draw some conclusions in the light of these.

The ability to measure the behaviour of protons when influenced by a magnetic field has been known to scientists since the early work of Purcell et al (1946) and Bloch (1946). The application of this technique to man, with the ability to reconstruct the data to create an image, is however a more recent innovation. Early work in this area was carried out by Damadian (1977) and Lautebur (1979) in New York, Mansfield & Maudsley (1977) in Nottingham, and Mallard et al (1979) in Aberdeen. The general principles of all these systems are similar, although the technical approaches have differed.

Psychiatry's lack of understanding of the pathogenesis of mental disorders has resulted in the attempt, within the antipsychiatry movement, to persuade the world that mental disorder does not exist (Szasz, 1961). Progress towards understanding the underlying biological bases of psychiatric syndromes has been impeded by two factors: (a) a most effective physical barrier – the skull; and (b) dichotomous thinking of structure on the one hand and function on the other.

In this new era of structural and functional neuroimaging technologies, it is the unsurpassed anatomical resolution of magnetic resonance imaging (MRI) (Andreasen, 1989; and Besson, this supplement) that has resulted in a new generation of studies on cerebral morphology in schizophrenia. With the recent development of whole-body magnets of very high (⩾ 1.5T) and uniform field strength, it has become possible to extend the scope of this approach to include measurement of certain fundamental neurochemical processes, via magnetic resonance spectroscopy (MRS: Hubesch et al, 1989; Lock et al, this supplement). The purpose of this article is to introduce and review critically the existing literature on the application of MRI and MRS to schizophrenia, and to give a preliminary account of some of our own recent studies in these areas.

The introduction of single-photon emission computerised tomography (SPECT) has markedly enhanced the study of brain function. The development of SPECT was the culmination of a series of investigations of cerebral blood flow (CBF) pioneered by Kety and Schmidt in the late 1940s combined with the introduction of transmission computerised tomography (CT) in the early 1960s, in which three-dimensional images are derived from two-dimensional data. Positron-emission tomography (PET), in addition to providing information on cerebral blood flow, also allows the evaluation of brain metabolism and neurotransmitter receptor function. However, the technology required for PET is expensive and sophisticated, with little prospect for general clinical application. Fortunately, SPECT is relatively cheap and is widely available for clinical use. We aim to review the principles and basic techniques of SPECT, its present utility and application to clinical practice, and its future potential in the investigation of brain function.

There is evidence to suggest that organic cerebral changes occur in elderly depressed patients. Quantitative studies of elderly depressed patients have demonstrated that they have reduced ‘radio-attenuation’ on computerised tomography (CT) scans and as a group resembled more closely a group of demented patients than normal controls (Jacoby et al, 1983). Many biochemical changes associated with ageing are similar to the pathophysiological abnormalities in depression and in dementia (Alexopoulos et al, 1988). These changes, coupled with the high frequency of depressive syndromes in demented patients, suggest a complex relationship between depression and dementia in old age. Mahendra (1985) has suggested that a variety of brain abnormalities can produce a spectrum of clinical manifestations, ranging from depression with minimal cognitive dysfunction at one end to dementia with minimal depression at the other.

Positron emission tomography (PET) differs fundamentally from computerised tomography (CT) and magnetic resonance imaging (MRI) in that it is a method for measuring function as opposed to structure. It is the most powerful tool available for the measurement of in-vivo brain function. This review describes the basic principles of the technique and its application to the study of brain metabolism in neurological and psychiatric disorder. The development of resting-state metabolic studies by the application of specific activation paradigms, a major current focus of the technique, is discussed.

Computerised averaging methods have made it possible to extract and identify the electrical activity accompanying specific activities of the brain, including certain psychological processes, from the random background signals in electroencephalography (EEG). Event-related potentials (ERPs) and the way these change under various recording conditions are a powerful, non-invasive and relatively simple means of relating psychopathology to underlying physiology, and by comparing ERPs with imaging data it should be possible to compare electrical activity with changes in brain structure and blood flow in different disease states.