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Addiction and neural ageing
Addiction and neural ageing

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6 Levels of explanation: the key to understanding addiction and neural ageing

Having read the selected research articles in this course, it might seem that you were plunged into the deep end of complex subject matter. Don't worry … you were! Normally, a student would take a series of courses in psychology or biology, and then go on to study, say, neurobiology or biological psychology which would help them to understand the research papers presented in this course. So how is it that we feel able to miss out such courses and go straight to looking at material in academic journals of psychology, biology and medicine?

The essence of what we are trying to do, both in this course and in its parent Master's level OU course SD805, is to not only enable you to gain an understanding of addiction and neural ageing but also to develop your ability to critically evaluate and relate diverse pieces of data and theory derived from different levels of analysis and explanation. To do this, the most important skills you must have are those of handling scientific arguments, thinking rationally and being able to express your ideas in a clear, coherent and cogent fashion. Such necessary skills are general scientific ones, obtained from any first degree in science or science-based subjects.

From your study of the four articles presented in this course you should have appreciated that we live in a time when it is becoming increasingly apparent that no one branch of science can offer a comprehensive answer, even within relatively narrowly defined areas of interest, like those of addiction or neural ageing. The position we have adopted is that if we are to understand addiction or neural ageing, then inputs from psychologists, medical practitioners and sociologists are required – indeed the more disciplines that can shed light on the nature of addiction and the underlying causes of normal and abnormal neural ageing the more logical and consistent will be our understanding of these topics.

In the OU course SD805 Issues in brain and behaviour we investigate the relationship between different disciplines, such as psychology, physiology, neuroanatomy, pharmacology, biochemistry and genetics, and their roles in addiction and neural ageing. This is because the conviction underlying our approach is that no one discipline can provide the answers to the complex issues involved; all of them have some contribution to make. Take an addict who is in a serious state of withdrawal from an addictive drug. He or she will be craving for a fix. We might interview this person and try to gain some appreciation of his or her mental state. The state of despair and the craving for a particular solution, drug or addictive activity seem clearly to be within the private mental world of the addict. We know about this only because the addict chooses to tell us about it. Of course, the addict might be exaggerating the psychological misery in order to get a prescription for methadone, financial support, or to receive a lighter prison sentence. But if we speak to a number of addicts, we can gain a picture of their mental states. All this would seem to be the domain of responsibility of a particular sort of psychologist – one who takes subjective reports as valid data.

Stop and think for a moment though: this all started because of taking a chemical, heroin, into the body. Heroin has known properties and it interacts with cells of the nervous system. This would seem to be the area of responsibility of the experimentally oriented biologist. The challenge comes in trying to relate the two levels of study: that of the individual and that of the cell.

A similar situation applies to neural ageing. We have the reports of ageing people on how they feel about things. They can describe their experiences, such as a depressed mood, loss of memory and poor cognitive ability. We can also look at the biological and neurochemical underpinnings of these phenomena, for example the accumulation of β-amyloid (Aβ) peptide, and try to relate the two areas of study.

When we consider the relationship between subjective reports of a person's inner states (e.g. feelings), we are taken to the heart of a philosophical debate that seems to have occupied thought for as long as there has been recorded written history. That is to say, what is the relationship between physical events in the body (e.g. changes in the brain that accompany ageing) and mental states (e.g. changes in the mental world of an ageing person)? For example, a question sometimes asked is: Can there be disturbed mental states without disturbed brain states? You will be relieved to know that you are not going to be required to solve this problem – one that has baffled philosophers for at least 2000 years. However, what is certain is that in your study of addiction and neural ageing you will have needed some basic familiarity with the issue and will have needed to know how to spot assumptions that relate to it. For example, we discussed earlier the claim that some addictions might be ‘in the body’ (e.g. alcohol or heroin addiction) whereas others might be ‘in the mind’ (e.g. addiction to shopping or the internet). Such a dichotomy is one that many contemporary behavioural scientists would find unacceptable. They would suggest that there can be no mental state that is disembodied, i.e. without a corresponding brain state.

The topic of the mind and brain takes us straight to the crux of the issue of the relationship between academic disciplines. Let us suppose that we all agree that various different disciplines have their place and that no source of insight should be rejected. We still face the problem of exactly how to relate these disciplines. We commonly speak of different levels of explanation, such as the social, physiological, cellular, molecular and subatomic levels. Some might feel that brain science offers a secure base for understanding complex behavioural and social phenomena and that we must attempt to explain everything in these terms. We would urge caution in taking such a reductionist stance. Reductionism is the philosophical position that we can explain events at one level (e.g. social events) in terms of events at a lower level (e.g. brain events).

The general argument on reductionism goes as follows. If we start with the smallest scale, we have such things as electrons and protons (termed the lowest level). Going up in level of study, and in size of object studied, gives us atoms and molecules. Putting molecules together, we have the cells of living systems, e.g. those of the brain. Putting together the cells, we eventually create whole brains, which play a role in producing the behaviour of an individual. Individuals interact with each other to form social groups. Large numbers of individuals make up whole societies, which are at the highest level of analysis and the largest size of subject matter in the study of the human condition. These different levels relate (albeit imprecisely) to different academic disciplines. The lowest level is the subject matter of physicists and the highest level is that of sociologists. The area of our interest – addiction and neural ageing – lies in some of the middle levels – relating brain cells to whole brains, brains to behaviour and the behaviour of individuals to that of social groups. Reductionism suggests that each level looks to the next lower level to gain insight. For example, sociologists would look to psychology for inspiration. Most (but by no means all) scientists would probably reject full-scale reductionism. They would suggest that there are principles peculiar to their level of analysis that cannot be reduced to a lower level.

The issue of reductionism is a general one that is applicable to most sciences, but behavioural scientists discuss it probably more than those in any other scientific discipline. It is an interesting question as to why this should be, but to discuss it would take us beyond our present brief. It is possible that a variety of reductionism seems attractive in the study of brain and behaviour because we are not too sure of what is the level of mental events. Unlike chemicals or people acting in groups, we cannot see or measure mental events. As evidence, we only have the testimony of the individual reporting them. It is tempting, therefore, to suggest that the explanation of such events can be obtained only by directly investigating brain events.

The approach we adopt is certainly to seek insight by looking to so-called lower levels (e.g. attempting to explain mental events in terms of brain events) but not to look there exclusively for our explanations. In understanding neural ageing, we are as likely to seek insight from a sociologist as from a cell biologist. This belief in a broad approach will be reflected in the articles that are made available in SD805 Issues in brain and behaviour. (Of course, after reading these, you are free to champion the reductionist position if you feel you can justify it!)

So, when is it appropriate to move down to a lower level for insight? For example, a person might be suffering from respiratory collapse as a result of a heroin overdose and this state is corrected by the injection of a chemical that competes with the heroin. We understand rather well what is happening at a level of the cells of the nervous system and their component parts. But suppose someone tells us that they experience a particular craving to take cocaine whenever they look in the mirror and feel worthless. Can we reduce a feeling of worthlessness to the biochemical activities of cells in the nervous system? Probably not. It will probably never be a useful way of trying to understand a complex human emotion, but we still need to take the evidence of such reports seriously. We need each piece of the jigsaw to completely understand the whole picture.

This comes back to the central theme that permeates SD805 Issues in brain and behaviour and indeed this course – that of relating the different levels of explanation to provide coherent descriptions of addiction and neural ageing.