The relationship between these domains has been a topic of debate throughout the history of psychiatry. A few words about stress and depressive illness may be helpful.
A state of increased alertness and arousal (in the physiological sense of increased blood pressure, heart rate, muscle tension, reaction times and mental alertness etc.) is a normal adaptive part of the so-called “fight and flight” mechanism with which evolution has equipped us. However, such hyper-normal states come at a cost of effort and energy, and when maintained for long periods of time usually produce disadvantages and negative consequences.
People suffering from depressive illness have a reduced ability to cope by virtue of the fact that they have a lack of mental energy and generally slowed and impaired mental functioning. Just as anaemia of the blood causes low energy and makes people breathless and tired after even slight exertion, so depression, which can be characterised as mental anaemia, causes lack of mental energy and decreased efficiency of mental processes, thinking, concentration and decision-making. I have always emphasised that I think the decreased mental energy and its consequences are central and essential to understanding the illness. In fact, I would suggest they are often more important than subjective symptoms. Therefore assessing the capacity to function in work, social and leisure activities, and mental efficiency generally, is more important than lists of symptom severity (i.e. most depression rating scales).
A useful model of anxiety is to regard it as representing the gap between functional capacity and the difficulty of the task at hand. Although this does not explain all forms of anxiety, generalised anxiety as part of the illness is usefully illuminated in this way. Therefore, the greater the gap between the difficulty of the task and your capability, the greater the level of anxiety (arousal).
At this point it is worth making a slight digression by pointing out that arousal (excitement) and anxiety share a great deal in common. The bodily changes are similar, the main difference is the subjective interpretation of the state. Consider this, a young man doing his first sky-diving trip might well describe it as the most exciting thing he has ever done. However, the Army recruit being kicked out of the plane by the sergeant-major on his first parachute jump will probably not share that view. Nevertheless, the main difference between the two is one of the attitude of mind. That observation constitutes substantial support for the cognitive reframing approaches that are essentially based on Stoic philosophy (1). It was a couple of thousand years ago the Greek philosopher Epictetus made the statement “It is not things themselves that disturb men, but their judgments about those things” (2). Our ‘jumpers’ above vividly illustrate that. Some important aspects of modern cognitive behaviour therapy relate to the philosophy of Epictetus and the ‘Stoics’.
Back to the discrepancy between the difficulty of the task and confidence. The greater the gap is, the more anxiety is experienced. An analogy I frequently used for patients may be useful here. The ups and downs of life can be likened to the waves on the sea, sometimes things are pretty calm and sometimes quite stormy. However most boats survive most of the time. However if the boat is overloaded and low in the water and has little freeboard, then it becomes more and more susceptible to being washed over by smaller and smaller waves. When I first came here to tropical North Queensland I found it difficult to keep out of my mind a picture that reflected an early experience of watching fishermen leave the local boat ramp. A small aluminium dinghy, with three fat Queenslanders, loaded to the gunwales with cartons of beer and chests of ice etc. One does not need much imagination to know what will happen once they get out of the shelter of the harbour and the wind gets stronger. Anyone involved in the local search and rescue services could tell you.
Obviously the analogy here is that the illness lowers your ability and your confidence and that is like being an overloaded boat with insufficient freeboard, as soon as things get a bit rough you just do not have the buoyancy that you need. In fact, it is a double hit, because not only is your actual functional capacity reduced, but also your estimate of whatever capacity you have (confidence) is reduced.
Confidence can be considered as ‘practice makes perfect’. In other words the more often you do something, and the more often you succeed, the more likely you are to be less anxious and more confident. The illness reduces that ability because it reduces your drive and motivation to attempt things, and also it reduces your perception of a positive outcome when you complete them, no matter how well or how badly you actually performed. It is therefore almost inevitable that your sense of confidence is greatly reduced. Furthermore, because confidence is analogous to the buoyancy of the boat it can thus be seen that, whatever the ups and downs of everyday life may actually be, they will all be relatively magnified, and the degree of challenge or difficulty presented by what were previously unremarkable events then becomes something which is overwhelming, and washes over the side of the boat threatening to sink it. In other words, to use that wonderful old expression, you make ‘mountains out of molehills’.
To recapitulate: the illness has as two of its central and essential features, the reduction of drive and motivation (anergia), and the reduced ability to get positive feedback or pleasure (anhedonia).
That means that not only do you attempt to do less, because you have less energy, but also you have a less positive perception of your achievements. That is to say, your ability to get pleasure, or see the positive aspect of things, is reduced. The less you do, and the less positive you feel about it, the more your confidence decreases, because confidence is ‘practice makes perfect’. The more your confidence decreases the more susceptible you are to the normal ups and downs of everyday life, which therefore make you more stressed and more susceptible to feeling tense and anxious. The double hit, as it were, is that you not only perform less well, but also have a reduced positive appreciation of your actual performance.
Some further explanation about the concept of anhedonia may be useful. Anhedonia, the decreased ability to experience pleasure, is a real physical phenomenon. People with severe illness actually perceive the world as being darker and more foreboding. This is simply a severe and specific example of that general tendency to be less able to perceive pleasant stimuli: this affects sight, sound, taste and all other sensations. People may describe food as tasting like cardboard. In my view it is essential to have an full appreciation of this dimension of the illness in order to diagnose it and to understand it.
Early in my career, I remember one of my wealthy patients in London describing this phenomenon. This fortunate gentleman lunched regularly at the Connaught restaurant, which was then, and I believe is still, magnificent. I recall being taken there for lunch on one occasion, not I hasten to add, by a drug company representative, but by a friend. So when this fellow, in response to questioning about anhedonia, described the magnificent food he had recently been presented with, and told me that it tasted like cardboard, I knew for sure there was something seriously wrong with him, and not with the Connaught!
However the reduction of the ability to get positive feedback from stimuli is only one half of the change. Not only is the ability to feel good about pleasant things reduced, but also the tendency to feel distressing emotions about unpleasant things is magnified. It is like looking at negative things through a magnifying glass but at pleasant things from the wrong end of a pair of binoculars.
Thus, people suffering from the illness describe enhanced feelings of distress and upset in the presence of everyday events that most of us would normally brush off or ignore. A simple and common example of this is attending to the media. The news is dominated by sensational events, many of which, perforce, are negative. That is what sells advertising space in newspapers and on TV. Most people have become moderately thick-skinned about such things, although perhaps, as I discuss below, not as thick-skinned as they might imagine. Nevertheless, those suffering from the illness become over-sensitive to a multiplicity of events in everyday life.
In summary, the illness involves a reduced ability to experience pleasure, but an enhanced ability to experience distress.
You may have noted as you were reading this that early on I stopped using the word ‘depression’ and reverted to using the term ‘the illness’. I have always tried to make it to my habit to do this when talking to people in order to de-emphasize the importance of the feeling of depression as a symptom of the illness of depression. It is of course a badly misnamed illness, not only because everybody thinks they know what you mean by depression, but also because depression is not the central problem with the illness. Many people experience quite severe anergia and anhedonia without describing themselves as being depressed.
It has always puzzled me why so many psychiatrists never seem to understand this. The famous English psychiatrist Max Hamilton, he of the Hamilton rating scale for depression fame, did not understand that.
If you read the last paper he ever wrote, where he reported on his interpretation of the results he had got from administering his own rating scale to great number of patients, he concluded the paper by questioning how it could be that so many patients with severe illness did not feel depressed (3). This struck me so forcibly that I wrote to him to explain the above, and why I thought he could not properly understand depression. Unfortunately he did not find my comments enlightening, because between the acceptance of his paper and its publication, he had died.