Issues in Psychobiology

Charles R. Legg

• Publisher: Routledge
• Year: 2016
• ISBN:
  9781317266150
• Edition: 1
• Topic: Psychology
• Subtopic: History & Theory in Psychology
• Index: Psychology

At the time of original publication psychobiology was one of the most rapidly developing areas of psychology. Its growth owed much to recent advances both in techniques for studying the physiological bases of behaviour and in major conceptual advances in the way people thought about the brain. First published in 1989, this textbook introduction to the field looks at the state of psychobiology in the light of these advances. The issues covered include: the factors that have shaped the current state of the field; the value of animal subjects in the study of psychological processes; the problems of studying the brain, including the theoretical assumptions underlying the most widely used methods; the current status of influential theories, like Stellar's 2-center theory of motivation and Papez's theory of emotion; the relationship between psychological theory and physiological data, such as recent accounts of the visual system; the problems presented by 'emergent properties' like consciousness.

1

Introduction

In The Hitch-hiker’s Guide to the Galaxy the author, Douglas Adams, describes a planet inhabited by a race of hyperintelligent pan-dimensional beings who build a hyperintelligent computer to help them come up with the answer to Life, the Universe and Everything. After many millions of years of deliberation this machine finally delivers its verdict: the answer is forty-two. Naturally the heirs to the computer-builders are somewhat disappointed about this. After all, one expects better value for money for one’s computer time. In its defence the computer points out that the problem lies not in its answer but in the question it was asked in the first place. In order to understand the answer they first have to understand what the question really means, and that, they are told, will require an even more powerful computer! All of which is a roundabout way of saying that what matters in this world is asking the right questions, rather than knowing the right answers. It is in this spirit that this book is intended to add to your education in psychobiology. It is a book that focuses on the questions that psychobiologists ask, rather than on the answers that they give to them. It is concerned with telling you as much about what we don’t yet know as about what we do know.

Psychobiology, the study of the biological bases of behaviour, is a broad area covering everything from the evolution of mating systems in the toad to the functions of subregions of the human cerebral cortex. In a book of this length it isn’t possible to cover everything, so let me declare my hand right away: what interests me most is the brain. Specifically, what fascinates me is how the operations of the billions of nerve cells that cohabit inside our skulls to form our brains are capable of giving rise to our actions and our conscious experience. This problem, so easy to state, is undoubtedly the greatest scientific challenge of our time, which probably explains why some of our most able scientists are turning their attention to it. Psychobiology is particularly exciting at the moment because advances in instrumentation are bringing us new ways of studying the brain while areas like artificial intelligence are providing new ways of thinking about how it might work as the ‘organ of behaviour’.

One of the frustrations of learning about psychology and psychobiology is that the practitioners frequently behave in what appear to outsiders as totally illogical ways. This usually takes the form of obsessively pursuing the minutiae of experimental phenomena and theories that leave a subsequent generation cold. Someone reading the latest work on the control of food intake, for example, might be puzzled at the amount of effort that went into understanding the effects of hypothalamic lesions on eating and at the theories that were erected around those experiments. To appreciate why certain questions are currently preoccupying psychobiologists, why they favour the particular answers that are in vogue, and why they seem to have neglected, until recently, many of the issues that non-psychologists would consider central to under- standing the biological bases of behaviour, a short lesson on the history of psychobiology is relevant.

The history of psychobiology

Contemporary psychobiology is a blend of two traditions of research and theory. One starts from the question of mind and behaviour and asks: ‘How is it possible for a physical system, the brain, to produce this?’ In other words, the focus is on psychological issues. The other starts from the brain and asks: ‘What does this organ do?’ In other words, the focus is on neurological issues. For many years these traditions operated independently of each other but recently they have converged to give the field a much more integrated look.

The psychological tradition

Psychobiology literally means the ‘biology of mind’. As such its history can be caricatured as having had three stages. In the first the academic community denied the possibility of a biological basis of mind at all, in the second it denied the existence of mind and in the third, into which we have now entered, we are coming to accept both the existence and physical basis of the mind. These changing attitudes in part reflect changes in attitudes in the world at large but they also stem from the evolution of our concepts of ‘mind’ and its possible physical bases. For example, the increasing secularization of the western world means that there is less pressure to accept dogma, based on prescientific thinking, about the status of the mind. The development of electronic devices like digital computers that can have mind-like properties means that a physical basis of mind is much less improbable to us.

All scientists work through analogies with other systems that they already understand. The problem for would-be physiological psychologists is that until relatively recently there have been no other natural phenomena or man-made devices that we understand better than human behaviour that could act as a model or analogy. Indeed, for most of human history we have tended to do the reverse, to use the analogy of the human mind to explain what happens in the physical world, an approach known as ‘animism’. By the seventeenth century, however, engineers had become sufficiently skilled at making complex mechanical devices, powered by clockwork or water, to be able to make toys that moved in a fairly convincing approximation to the way that people and animals move. Some were constructed so that they would only move when a passing person activated a treadle of some sort so that the toy would suddenly spring into ‘life’. The French mathematician Descartes remarked on the similarity between this sort of toy and the behaviour of animals, arguing that the latter were nothing more than automatons whose reactions were constantly triggered by events in the environment (Jeannerod 1985). Not knowing about electricity, but knowing about hydraulic systems, Descartes suggested that the control of these reactions in animals was mediated by movements of fluids, initiated in the sensory nerves by stimuli, being carried to the ventricular system of the brain where contact was made with the motor nerves. The movement of fluid in the motor nerve then caused the actual movement. Since there is a large number of nerves the number of possible combinations and sequences of stimuli is enormous so it is possible for a system like that, in principle, to produce a very large number of possible reactions. Descartes was reluctant to extend this model to human behaviour. In part this reflected religious scruples since mechanical explanations for our behaviour were incompatible with religious teaching. It also reflected philosophical scruples since it wasn’t obvious how a mechanical device could be conscious and, as Descartes is famous for pointing out, the only thing of which we can be certain is that we are conscious.

Although Descartes was wrong to use a hydraulic analogy, his idea that animals come pre-equipped with a range of motor responses to sensory input, reflexes, proved correct. In the nineteenth and early twentieth centuries reflexes were studied with enthusiasm. This work demonstrated two things. The first is that reflexes are largely mediated by the lower parts of the brain, and the second is that they are less rigid than one might think. Both points can be illustrated by studies on frogs. If the brain is removed from a frog but its spinal cord left intact it will still display reflexes including defensive reactions. One of these involves using the hind leg to scratch an area of skin to which an irritant has been applied. Furthermore, if the animal is prevented from using one leg, it will scratch with the other. Thus a sophisticated reflex is mediated by the spinal cord and the ‘reflex’ appears to be goal-directed.

If sophisticated reflexes can be mediated by the spinal cord, what is the purpose of the brain? William James (1950) argued that it was there to elaborate on reflexes, a position largely adopted by the behaviourist school of the early to middle twentieth century. A Cartesian reflex model holds that behaviour will be constant in a constant environment or, if not constant, it will not change in a predictable way. Thorndike (1913) and Pavlov (1927) showed that that is not so. The behaviour of man and other animals does change lawfully, under the impact of reinforcement contingencies. It therefore seems reasonable to suppose that the function of the brain is to mediate these more flexible links between stimuli and responses.

Stimulus-response (S-R) psychology has largely gone out of fashion now, yet in its day it carried the field, and even now its influence is still felt. For example, when describing experiments psychologists still refer to the subjects’ ‘response’ to the ‘stimulus’ materials. Neurobiologists too work within this framework. For example, workers like Kandel and his colleagues (Hawkins and Kandel 1984), who are interested in the cellular bases of memory, are actively studying ‘associative’ learning tasks like classical conditioning in the belief that this represents a fundamental mammalian learning process. The attraction of S-R psychology, in its most radical form, lies in two things. The first is its simplicity; it reduces the whole of psychology to the study of learning. The second is that it unites psychology and biology since, in the early formulations, ‘responses’ were contractions of muscle groups, stimuli were physical events occurring at sensory receptors, and ‘learning’ was a real event occurring in the brain. This then set the agenda for how we study the brain; we treat it as a large reflex arc and trace the circuit from the stimulus ‘analysers’ to the motor system. This attitude is especially apparent in Pavlov’s writings. Indeed, Pavlov believed that the study of classical conditioning was the only way to study the functions of the cerebral cortex.

S-R psychology didn’t have things all its own way. Even in its heyday it was challenged by the Gestalt school (Koffka 1935), mainly working in Germany, who pointed out that there were real perceptual phenomena that were quite incompatible with the more radical versions of S-R theory. What the psychologists showed was that stimulus elements in groups had properties not present in the individual elements. Moreover, those properties are often distortions of the true appearance of objects. That is to say, lines which are physically straight will appear bent, lines that are the same length will appear different, exposure to one stimulus will alter the appearance of one presented subsequently, and lines and edges that are not physically present will be seen by the subject. The consistency of these distortions and the immediacy with which they occur convinced the Gestalt psychologists that they were dealing with a fundamental property of the brain rather than something that we have learned. Using an analogy fashionable at the time the Gestalt psychologists maintained that these distortions were due to interactions between ‘electric’ fields induced in the visual cortex by the stimuli. As was the case with Descartes’s hydraulic model, the electric field model has not been substantiated by more recent studies of the brain. Nevertheless, the insight that the neural representations of stimulus elements interact with each other in the brain to distort our perception of the world has been validated again and again by sensory physiologists. Clearly the brain is more than a passive relay from stimulus to response.

Gestalt psychology is really only a minor nuisance to S-R psychology. The real problems came from studies by people like Tolman (1932), Crespi (1942), and Lashley (1963), who showed that behavioural change can come about too rapidly for incremental learning to explain it and that what animals learn is not a set of reflexes but the location of desirable objects and events. During the 1930s the most commonly used piece of laboratory apparatus was the maze, often modelled on the one at Hampton Court. Rats were trained to negotiate these mazes to obtain food. It was assumed that the food reinforcement in some way strengthened the response tendencies that led to the food, at the expense of other response tendencies. Tolman showed that rats would learn to negotiate mazes without experiencing reinforcement at the goal-box, although the introduction of reinforcement was necessary to persuade them to display their knowledge. Learning of this sort was termed ‘latent-learning’. Crespi showed some surprising effects when you alter the amount of reinforcement a rat is given to run down an alley way. If you increase the amount of reward the rats run faster than rats that have always received the large reward and if you decrease it the reverse happens; the rats run more slowly than those that have always had the small reward. Furthermore, the change in speed occurs within a couple of trials of changing the magnitude of reward, which is too fast for conventional learning mechanisms. Lashley, for his part, showed that surgical damage to parts of the brains of rats could alter the types of movements they would make to negotiate a maze without disrupting their ability to reach the goal. In some of his experiments the rats were rolling along to get to the food in the goal-box. Experiments like these provide a fairly conclusive demonstration that, even in simple learning tasks, animals are learning about the nature and location of biologically important events like food. Their behaviour is a very flexible result of the interaction between that knowledge and their needs, such as their need for food. They are not forming stimulus-response associations.

During his long and distinguished career Lashley (1950, 1951), in fact, carried out a fairly effective hatchet job on S-R psychology. In addition to demonstrating the ease with which rats substitute one movement for another in reaching their goal he also demonstrated that cutting the nerve fibres that join the visual to the motor cortex does not interfere with associative learning, as Pavlov had predicted it would. He presented a detailed theoretical analysis of skilled movement, showing that the sequencing of actions, the serial order of behaviour, could not be due to feedback stimuli from one movement triggering the next, as S-R theory argued, but had to be due to central programming of the sequence.

Unfortunately, Lashley’s achievements were largely negative. Along with people like Tolman and Crespi he showed the inadequacy of the S-R model without really replacing it with anything of use to the psychobiologist. As a consequence, psychobiologists turned away from these sorts of issues and concentrated on supposedly simpler problems like emotion and motivation.

Even while the behaviourist debate had been raging, people had been studying emotion. Indeed, as William James implied in 1884, emotion is a serious challenge to reflex models of behaviour because it implies experience without action. James’s solution to this problem was simplicity itself. He redefined emotions as sets of bodily reactions which could, in turn, effectively act as stimuli to control further behaviour. In other words, emotions are the product of behaviour. Even if it isn’t true, James’s position was an excellent stimulus for research as it forced people who would adopt an alternative position to consider very carefully how else emotions might come about. Cannon and his co-workers launched a fierce attack on James. More accurately, they launched an attack on the idea that activity in the autonomic nervous system was a sufficient condition for emotional experience. The attack was based on a number of strands of evidence, including the fact that activation of the sympathetic branch of the autonomic nervous system was too diffuse to underpin the range of subtle emotional experiences of which we are capable, and the observation that severing the spinal cord in dogs does not prevent them displaying facial signs of emotion when provoked in an appropriate way. As an alternative, Cannon proposed a centralist theory in which emotion was seen as the result of activating specific mechanisms in the central nervous system. However, his evidence didn’t permit particularly precise localization within the brain. It wasn’t until Papez (1939) published his theory of emotion that the field really moved again.

Papez set the agenda for how emotion would be studied for half a century. This is remarkable, given how little evidence he really had for his theory and how much of the evidence he had was wrong! The basis of his argument is that emotional experience and emotional behaviour involve separate, although interlinked, parts of the brain. As Cannon and his colleagues had already shown, animals lacking cerebral cortex could still display emotional behaviour. Indeed, their emotional behaviour was often exaggerated. Papez therefore located the emotional behaviour mechanisms in the brainstem, especially in the mammillary bodies which, he believed, received sensory information via subcortical relay routes, and cognitive information from the cerebral cortex via the hippocampus and its subcortical projection system, the fornix. Emotional experience, on the other hand, he thought was the result of activating specific areas of the cerebral cortex in much the same way as activating other areas produced visual or auditory experience. On the basis of some remarkably weak clinical evidence he decided that the site of emotional experience was the cingulate gyrus, which lies on the medial surface of the hemispheres. All of the areas that Papez implicated in emotion are part of an anatomically identified system known as the limbic system. Many people, therefore, encoded his conclusion to be that the limbic system was the seat of emotion. As we shall see in a later chapter, the issues raised by Papez have yet to be resolved. There are still those who believe that the limbic system is the source of emotional experience, while others have implicated parts of the circuit in spatial ability (McNaughton and Morris 1987) or memory (Olton 1983).

The major developments in psychobiology to take place in the 1940s and 1950s concerned motivation. Motivation is inextricably linked with most S-R theories, explaining both why learning takes place and why animals engage in behaviour. Thorndike explained learning in terms of the action of reinforcement. Positive reinforcement was seen as being due to the presentation of ‘satisfiers’ but that is, of course, completely circular without being able to predict in advance what will satisfy an animal. This problem was largely solved by explaining reinforcement in terms of drive reduction, since drives could be readily manipulated by depriving animals of food or water and then using these items as reinforcement.

‘Drive’ was also called upon to explain variations in behaviour that could not be explained in terms of learning; but what is drive? Following on from Cannon (1947) most psychologists assumed that drive was simply bodily discomfort brought about by the deprivation state and that drive reduction was due to eliminating this discomfort. Again, this is brilliantly simple and probably wrong. It is wrong because you can eliminate all of the possible sensory mechanisms that might detect the tissue disturbance produced by a particular form of deprivation and motivation still persists. For example, cutting the nerve supply to the genitals does not interfere with sexual motivation in the short term; cutting the nerves to the stomach does not interfere with hunger. This led Morgan (1943) to argue that drive must be due to activating a central nervous system mechanism that represents the drive state, much in the same way as Papez was claiming that activation of the cingulate cortex represented emotion. Morgan did not know where to locate the source of this ‘central motive state’ in the nervous system. It was Stellar (1954) who put the finger on the hypothalamus as the seat of motivation, basing his arguments on a number of lesion studies that had shown quite specific disturbances of motivation after lesions in this region. It is a testimony to Stellar’s insight that, even now, no discussion of the neural bases of motivation is complete without a discussion of the hypothalamus.

The 1950s were a watershed for mainstream psychology. They were the era when psychologists rediscovered mind, or, to be more accurate, mental processes like attention and memory. This was hardly accidental. In part it came about as a reaction to the inordinate complexity of S-R theory but, I believe, it had much more to do with S-R theory’s failure to cope with real psychological problems like the performance of radar operators, and with the availability of machines, computers, with mind-like properties that made it respectable to think in mentalistic terms again. The rediscovery of mind had relatively little impact on the psychobiology of the time. If one looks back at the text-books and review papers written about psychobiology during this period one finds that they were largely preoccupied with topics like motivation and emotion. Some workers, like Hernandez-Peon (Hernandez-Peon, Scherrer, and Velasco 1956), began to explore the neural bases of attention, but their approach was tightly linked to the topic of motivation and emotion through the prevailing arousal theory that was gripping people at the time. It is true that a number of books were written that attempted to draw parallels between brains and computers but these largely served to remind us how different they really are. In fact it was largely people working outside the framework of experimental psychology who kept alive research into the physical bases of mental processes. It is to these people, who worked in the neurological tradition, we turn next.

The neurological tradition

Although our commonsense view of the world now tells us that the brain is the seat of mind and action, the idea is remarkably new. Even up to...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Original Copyright Page
• Dedication
• Table of Contents
• List of figures and tables
• 1 Introduction
• 2 Animal subjects in psychobiology
• 3 Methods in psychobiology
• 4 Perception
• 5 Motivation
• 6 Emotion
• 7 Memory
• 8 Plasticity
• 9 Consciousness
• 10 Concluding remarks
• References
• Index