The first issue of the international journal
Neuropsychologia, in January 1963, contained an editorial which defined the term 'neuropsychology' as 'a particular area of neurology of common interest to neurologists, psychiatrists, psychologists and neurophysiologists'. It added that 'this interest is focused mainly, though not exclusively, on the cerebral cortex', that 'topics of particular concern are disorders of language, perception and action', and that 'although certain of these disorders can, of course, be studied only in man, we are none the less convinced that information of great value to human pathology is to be obtained from animal experiment, which may be expected to throw valuable light on the basic mechanisms of cerebral organization'. An editorial in the same journal nearly twenty years later commented that 'there is still no better definition available'. The developments which led up to the emergence of an autonomous discipline of neuropsychology have a long and chequered history and provide insights into the perennial issues which still occupy neuropsychologists.
Attempts to localize mental processes to particular bodily structures can be traced back at least to the 5th century
bc, when Hippocrates of Cos identified the brain as the organ of intellect, and the heart as the organ of the senses. Empedocles (about 490–430 bc), concerned with the same central and enduring philosophical problem of the relationship of mind to body, located mental processes in the heart. For the next 2,000 years, the relative merits of what have been called 'the brain hypothesis' and the 'cardiac hypothesis' were debated. The natural successor to Hippocrates was the anatomist
Galen, who, in describing aspects of brain anatomy, argued for the brain hypothesis. There is little doubt that both Hippocrates and Galen drew heavily upon their experiences as physicians. Galen as a surgeon tending gladiators was doubtless well aware of some of the consequences of brain damage. His views contrast with those of
Aristotle, who, having decided that the heart was warm and active, saw it as the source of mental processes, whereas the brain was relegated to the minor role of serving as a mechanism cooling the blood of the heart. Galen believed that the mind was located in the fluid found in the large ventricles of the brain, a view which continued to be canvassed until it was refuted by Vesalius (1511–64).
Descartes, continuing the debate, adopted a quite explicit dualist position, seeing the body and the mind as separate but nevertheless able to interact. By the 18th century, some of the issues that were to represent major viewpoints in what was to become neuropsychology were already being identified — the principal one being whether, and to what extent, particular mental functions could be localized in particular parts of the brain.
The detailed argument for localization of function is usually associated with the phrenological theory of
Gall and with his contemporary J. C. Spurzheim (1776–1832). Both Gall and Spurzheim were anatomists and made important contributions to their discipline by which they were assured a place in the history of science. Regrettably, once they went beyond anatomy and attempted to locate functions in different parts of the brain, they indulged in speculation which led them wildly astray. From their observations of the external structure of the skull, they developed the view that such external features might correlate with important aspects of behaviour. Despite the conceptual ingenuity of their views, they failed to produce evidence which was even reasonably objectively based and could be regarded as convincing support for their main hypothesis. The demolition of their views was brought about by the work of the French anatomist
Pierre Flourens, who ablated parts of the brains of pigeons and studied the changes that occurred post-operatively in their behaviour. He concluded that there was no evidence for localization of function within the cerebrum but that any loss that was observed simply reflected the extent of damage to brain tissue.
The possibility of demonstrating localization of function, however, took a decisive step forward on 21 February 1825, when J. Bouillaud (1796–1881) read a paper to a scientific meeting in France in which he argued from his clinical studies that speech was localized in the frontal lobes, a view already suggested by Gall. Shortly afterwards, in 1836, Marc Dax read a paper in Montpellier, also reporting a series of clinical cases; these he believed demonstrated that speech disorders were linked with lesions of the left hemisphere. It was not, however, until 1865 that Dax's manuscript was published, by his son. Meanwhile, in 1861,
Paul Broca, founder of the Anthropological Society of Paris, heard Bouillaud's son-in-law report the case of a patient who had ceased to speak when pressure was applied to his exposed anterior lobes. Soon afterwards, he saw a patient who had lost his speech and could say only one word, 'Tan', and utter oaths. Results of the post-mortem on this patient indicated left frontal pathology. It is usual to credit Broca with describing this syndrome, which consisted of the inability to speak despite normal understanding of language, and also as the person who elaborated the concept of cerebral dominance of language in the left hemisphere. The other outstanding figure at this time was
Wernicke. To him is attributed the discovery that there is more than one language area in the brain.
The history of thought on
aphasia over the past 150 years and more illustrates the continuing debate about how mental functions are related to brain structure. Thus, one group of workers on aphasia, taking their lead from the early phrenologists, maintained that specific mental functions were subserved by separate areas of the brain. Those who opposed this 'localizationist' view believed that mental capability reflected total intact brain volume. While Broca and Wernicke lie in the localizationist tradition,
Hughlings Jackson and Kurt Goldstein represent the so-called holistic approach to aphasia.
In view of these early observations on the relations between brain and behaviour, it remains something of a puzzle why a separate discipline of neuropsychology did not develop by 1900 rather than by 1949. Perhaps part of the reason was the intervention of the world wars, part was the suspicion of any views that seemed to indicate a retreat to the localizationist views of the phrenologists, and part was the strong presence of the so-called
Gestalt theories in psychology. All of these, it would seem, led to the localizationist approach being abandoned in favour of a more holistic approach.
Henry Head, during the First World War, was dissatisfied with the classical neurologists' attempts to deduce schemes from clinical observations, believing that they were, as he put it, 'compelled to lop and twist their cases to fit the procrustean bed of their hypothetical conceptions'. He attempted to bring some order to the field by devising a standard list of tests to be used in the study of aphasia, an idea developed by Weisenberg and McBride (1935). Earlier (1933), Weisenberg and McBride had made the important discovery that individuals who do not understand spoken language, although their hearing is intact and they can identify non-verbal sounds (e.g. a telephone ringing), may have damage in two different locations. Around the same time, the influence of
Karl Lashley, who published his paper 'In search of the engram' in 1938, is usually seen as significant. Lashley proposed a theory of mass action, contending that the behavioural result of a lesion depends on the amount of brain removed more than on the location of the lesion.
During the second half of the 20th century and, in particular, immediately after the Second World War, there was a reawakening of interest in the brain–behaviour relationship, and, as often happens in science, it was not so much the discovery of new ideas but the rediscovery of old ones. In this case it was the views of some of the classical neurologists, combined with the development of the new behavioural techniques of the experimental psychologists, which were to give the necessary impetus to lead to the development of neuropsychology as such. Recent research (Bruce 1985) suggests that the term 'neuropsychology' was first used in 1913 by Sir William Osler in an address he gave at the opening of the Phipps Clinic at the Johns Hopkins Hospital. In his address entitled 'Specialism in the General Hospital' Osler expressed the hope that 'time may be found for general instruction of the senior class in the elements of neuropsychology'. Bruce speculates that Lashley, who was appointed research professor of neuropsychology at Harvard in 1937, may have heard Osler give his address at the Phipps Clinic, since Lashley was a graduate and postdoctoral student at Johns Hopkins from 1911 to 1917. Subsequently in 1949 the term 'neuropsychology' was given wide publicity when Donald Hebb published
The Organization of Behaviour: A Neuropsychological Theory. Nine years later, Heinrich Klüver, in the preface to his book
Behaviour Mechanisms in Monkeys, suggested that it would be of interest to 'neuropsychologists'. In 1960, Lashley's collected writings were published under the title
The Neuropsychology of Lashley. At no point, however, thus far, was the term 'neuropsychology' used systematically, nor was it carefully defined in the text.
Hans-Lukas Teuber, one of the early pioneers in neuropsychology, argued that the task of neuropsychology is twofold. First, to help the patient with the damaged brain to understand his disease and, secondly, by carefully studying such experiments of nature, to provide essential insights into the physiological basis of normal brain function. Although such study draws information from several disciplines, including anatomy, biophysics, ethology, pharmacology, and physiology, nevertheless its central focus continues to be the development of a science of human behaviour based upon the study of the function of the human brain. Teuber showed elegantly and convincingly how the precise methods traditionally used by experimental psychologists in the study of psychophysics could be applied to problems in neuropsychology. His monograph
Visual Field Defects after Penetrating Missile Wounds of the Brain, published in 1960 and written jointly with Battersby and Bender, illustrates the success of such methods.
Thus by 1963 the time seemed ripe for the launching of
Neuropsychologia. The editorial of the first issue traced its background to regular meetings of a small group of European neurologists and psychologists who had first gathered in Austria in 1951 to discuss disorders of higher mental functions associated with injury or disease of the brain.
Today there are several different approaches to the study of the brain–behaviour relationships, but the method which has figured most prominently is the one that is the natural successor or complement to the work of the early neurologists, namely study of the effects of lesions in specific areas of the brain by carefully observing associated changes in behaviour. It is noteworthy that the results of carefully controlled animal studies have been very important in the development of neuropsychology. In studying patients, one must, for obvious ethical reasons, take what comes and thus accept that the limits of any brain damage are not precisely known. By contrast, in animal studies, the locus and extent of lesions can be precisely defined and pre-and postoperative behaviour carefully studied and measured. In human studies, experimental psychologists have contributed significantly by devising ingenious techniques to be used under controlled conditions and by proposing theoretical concepts to account for the deficits in behaviour observed in brain-damaged patients: for example, the distinction between short-term memory and long-term memory and models of their interrelationships.
Neuropsychologists study our awareness of the world in which we move. What we see, hear, and touch are dependent upon the proper functioning of the intact central nervous system. Likewise, how we respond by taking action is dependent on the intactness of those parts of the nervous system concerned with initiating and sustaining coordinated motor activity. But it is not only sensory and motor processes that may be altered by changes in the nervous system: higher functions such as language, thought, and memory may also be changed. The human brain is well endowed with so-called association cortex, i.e. regions of neocortex not specialized as primary sensory or motor regions. Thus,
memory, for long a topic of interest to philosophers, was a central concern of Lashley, who, after years of animal experimentation, concluded that 'it is not possible to demonstrate the isolated localization of a memory trace anywhere in the nervous system'. Only three years after Lashley reached this conclusion, a neurosurgeon, William Scoville, in 1953 operated on a patient known as H.M. and left him unable to remember virtually anything that occurred after his operation. It appeared that the surgical bilateral removal of the hippocampus and adjacent structures had not touched H.M.'s stored memories but had made it impossible for him to store or retrieve new memories. The detailed study of H.M. changed the emphasis in the study of memory from searching for a location for memories to analysing how memories are stored and retrieved. Today, the roles of the temporal, frontal, and parietal lobes in memory form part of a wider study of the complementary specializations of the left and right hemispheres, to which we now turn. Since studies of cerebral asymmetries have been a major part of research in neuropsychology for several decades, they illustrate well the methods used by neuropsychologists, how their results are presented, and the controversies and uncertainties that remain.Cerebral asymmetries. The discovery by Dax and Broca in the 19th century that damage to the left hemisphere resulted in inability to talk, whereas damage to the right hemisphere did not affect speech production, led to the general acceptance of the view that the left hemisphere plays a special role in language which is not shared by the right hemisphere. Language, however, is not the only special function of the left hemisphere. At the beginning of the 20th century, H. Liepmann demonstrated that the left hemisphere has a special role in controlling complex movements. Nevertheless, the special functions of the right hemisphere remained a comparative mystery until the early 1950s when, following the work of
Zangwill, Hécaen, and Milner, it became clear that it was more involved in the analysis of visual and spatial dimensions of the world than was the left hemisphere.
The potential for some behaviours, it would seem, is virtually wired into the structure of the nervous system. These include not only reflex and instinctive behaviours, but also behaviour as complex as language. In this sense, psychological asymmetry is based upon microanatomical asymmetry. In 1968, Geschwind and Levitsky reported gross anatomical asymmetries following their study of a large series of human brains. They reported that the part called the 'planum temporale' was larger on the left-hand side of 65 per cent of the brains they studied and that it was larger by nearly 1 cm than on the right. Subsequent studies have confirmed Geschwind and Levitsky's findings and have shown, moreover, that these structural differences are in evidence very early in life.
In addition to those studies of neurological patients with lesions on one side or other of the brain, there are studies of those who have had the brain stimulated during surgery and of those receiving temporary anaesthetization of one side of the brain before surgery. Most recently, studies of regional blood flow have added another technique for the study of functional asymmetry. Studies of healthy people have also added significantly to neuropsychological knowledge. One widely used technique is to present sensory information selectively to one or other cerebral hemisphere and to ask for some kind of verbal or non-verbal response. Electrical recordings from the two hemispheres have also been studied. Even so, the method that has proved most powerful in demonstrating lateralization is that called, by Teuber, 'double dissociation'. Having demonstrated that lesions in the left hemisphere of right-handed patients produce difficulties in language, including speech, writing, and reading, and that such difficulties do not follow from lesions in the right hemisphere, we may say that the functions of the two hemispheres are dissociated. By contrast, difficulties which follow right-hemisphere damage are found with spatial tasks, with singing, and with playing musical instruments; such abilities are thus more disrupted by damage to the right than the left hemisphere. It is then said that the two hemispheres are doubly dissociated.
Another approach which has proved important in identifying cerebral asymmetries has been study of the results of an operation carried out on a small number of patients to whom
epilepsy had become a problem unresponsive to other forms of therapy. In some such cases, neurosurgeons resorted to cutting through the major fibres which interconnect the two cerebral hemispheres, known as the neocortical commissures. These include the corpus callosum and the anterior commissure. Their complete sectioning is known as 'total commissurotomy'. After the operation, the two hemispheres behave as if they are virtually independent. Because of the particular way in which sensory inputs are connected to the cerebral hemispheres, we know that information coming from the left visual field or the left hand is directed to the right hemisphere, and vice versa for the right visual field and the right hand. From numerous studies of such so-called 'split-brain' patients, it is now acknowledged that when the left hemisphere has access to information it can initiate speech, and thus talk about the information, whereas the disconnected right hemisphere cannot. The right hemisphere apparently is good at recognizing things but is unable to initiate speech because it cannot get access to the speech mechanisms in the left hemisphere. By presenting stimuli such as pictures or words to the left visual field, and thus the right hemisphere (or the right visual field and left hemisphere) and asking the patients to name or otherwise act upon what is seen, it has been possible to carry out careful studies of the functions of the isolated right and left hemispheres (see
split-brain and the mind).
The technique of selectively presenting information to one or the other hemisphere, whether through the eyes or through the ears, or through the sense of touch, has also been applied to normal people. The results indicate relative differences between the two cerebral hemispheres; but it is difficult to repeat such experiments and get the same results each time.
Another approach to the study of brain function arises at times in the course of major brain surgery when a neurosurgeon may briefly stimulate the exposed surface of the brain electrically in order to ascertain which part of the brain he is treating, and also to establish with as much certainty as possible on which side of the brain speech is lateralized. Using such stimulation and asking the conscious patient to report what he feels or to answer questions, further information is gained about the functions of particular areas of the brain.
There is yet another source of neuropsychological knowledge associated with the study of neurological patients. To discover as precisely as possible in which hemisphere speech and language are lateralized, a neurosurgeon may temporarily inactivate one or the other hemisphere by injecting sodium amylobarbitone selectively into the carotid artery supplying one or other side of the brain. In this way, it is possible to study what one side of the brain is able to do in the temporary absence of help from the other side. The flow of blood to the neocortex increases in areas where the neurons are particularly active; by injecting a solution of a radioactive substance into the blood, it is possible to examine where it accumulates when particular cognitive activities are taking place.
The auditory system (see
hearing) is not completely crossed, as both hemispheres receive projections from both ears. It appears that the connections from each ear have a preferred access to the opposite hemisphere, so that sounds to the right ear are principally handled by the left hemisphere and vice versa. Kimura (1973) showed that when words are presented simultaneously to the two ears through headphones, the material that is entering through the right ear is more easily analysed than that coming in through the left ear. The converse seems to be true with musical material similarly simultaneously presented. Observing this difference, it has been inferred that the left hemisphere specializes in the analysis of language and the right hemisphere in music. A similar technique can be used to study sensation through
touch. For example, two flat stimuli can be represented simultaneously, one to each hand, and the subject is asked to identify the objects that are being palpated. In all such experiments the results show that, in normal subjects, hemispheric asymmetry is relative rather than absolute. In the normal subject, since the two hemispheres are intimately interrelated through the corpus callosum, any information that is put into one hemisphere can rapidly be transferred to the other hemisphere. Thus, the most likely reason for the observed asymmetries is that the direct route into the left hemisphere is much more efficient than the indirect interhemispheric route.
Neuropsychologists recognize that such talk about lateralization of function begs a number of important questions. What, for example, is it that is lateralized? On this issue there are a number of competing theoretical arguments. For example, there are those who take the view that the two hemispheres are organized differently. Thus, Josephine Semmes suggested that the left hemisphere functions as if there is a collection of discrete regions, whereas the right hemisphere functions in a much more holistic and diffuse manner. Others take the view that the two hemispheres have distinct ways of processing information, and they argue that the left hemisphere works in a much more analytical way, as it processes information sequentially and abstracts out the relevant details, whereas the right hemisphere synthesizes what comes in. The possibility of different forms of cerebral organization is well illustrated by the continuing debate about how speech and language are organized in the brains of left-handers. Thus some (e.g. Zangwill 1960), noting the higher incidence of aphasia in unilaterally brain-injured left-handers, have postulated an incomplete functional lateralization of speech in the vast majority of left-handers, resulting in greater sensitivity to brain lesions.
As the young science of neuropsychology has grown up in different parts of the world, so it has developed its own distinctive emphases and techniques. In the USA, the emphasis has been on quantitative and psychometric techniques. In some cases batteries of tests have been applied to large groups of patients in an attempt to analyse quantitatively the patterns of deficits that emerge between the different brain-damaged groups. In the UK, the approach has been more qualitative and less psychometric and has paid more attention to the in-depth study of crucial single cases, from which a great deal can be learned and any one of which may, properly studied, call into question an existing neuropsychological hypothesis. The case of H.M. cited earlier is a prime example of work in this tradition, including the work that has been done in Canada. In the former USSR also, under the leadership of
Luria, qualitative and non-psychometric techniques have had pre-eminence. For Luria, the preferred techniques were simple, often using only pencil and paper, which could be administered at the bedside and not requiring the full panoply of the experimental psychologist's laboratory. Commenting on Luria's contributions to neuropsychology, Teuber described them as 'monumental', noting that they spanned a third of a century and, in addition to being concerned with the major syndrome of man's left cerebral hemisphere, encompassed 'a detailed and brilliant analysis of the syndrome of massive frontal-lobe involvement'. The publication in 1965 of an English translation of his book,
The Higher Cortical Functions in Man, made available to the West a wealth of neuropsychological theory and practice.
Each of these distinctive approaches to neuropsychology has contributed significantly to its development and will continue to do so. From time to time, excessive claims have been made for the young discipline, and simplistic accounts have been given of results. In the case of cerebral asymmetries, wide generalizations have been made, speculation going far beyond the relatively limited data and not always helping the development of the subject.
(Published 1987)See also brain imaging.
— Malcolm A. Jeeves
Bibliography- Bruce, D. (1985). 'On the origin of the term "neuropsychology" '. Neuropsychologia, 23.
- Gazzaniga, M. S. (1970). The Bisected Brain.
- — — and Le Doux, J. E. (1978). The Integrated Mind.
- Geschwind, N. (1972). 'Language and the brain'. Scientific American, 226.
- Hécaen, H., and Lateri-Laura, G. (1977). Évolution des connaissances et des doctrines sur les localisations cérébrales.
- Kimura, D. I. (1973). 'The asymmetry of the human brain'. Scientific American, 228.
- Kolb, B., and Whishaw, I. Q. (1980). Fundamentals of Human Neuropsychology.
- Luria, A. R. (1968). The Mind of a Mnemonist.
- — — (1972). The Man with the Shattered World.
- — — (1973). The Working Brain.
- Milner, B. (1971). 'Interhemispheric differences in the localisation of psychological processes in man'. British Medical Bulletin, 27.
- Osler, W. (1913). 'Specialism in the general hospital'. Bulletin of Johns Hopkins Hospital, 24.
- Pribram, K. H. (1971). Languages of the Brain.
- Sperry, R. W. (1964). 'The great cerebral commissure'. Scientific American, 210.
- Zangwill, O. L. (1960). Cerebral Dominance and its Relation to Psychological Function.
