significant weight loss when not dieting or weight gain (e.g., a change of more than 5% of body weight in a month), or decrease or increase in appetite nearly every day.
(Interestingly, anorexia or significant weight loss, but not weight gain, is a diagnostic subcriterion for what the DSM-IV calls "melancholic features," a sort of diagnostic hanger-on to Major Depressive Disorder that requires either a loss of pleasure in almost all activities, or a loss of reactivity to usually pleasurable stimuli. People exhibiting melancholic features are less likely to respond to placebo, says the DSM-IV.)
Some depressed people, the DSM-IV tells us, overeat, and some fail to eat enough. For simplicity, and to illustrate an aspect of depressed cognition, I will consider in this essay only the depressed people whose appetite is reduced.
Why do some depressed people not eat? Is there some mysterious "chemical imbalance" that causes both depressed feelings and reduced appetite (except that the same imbalance causes increased appetite sometimes)? Instead of reaching for a possible explanation why someone might not eat, let's consider the opposite question: why do non-depressed people eat?
A model of the eating-related introspection of a non-depressed person might look like this:
- The person feels hungry (or, perhaps more commonly in wealthy countries, the person feels bored).
- The person imagines various options for food.
- The person picks something that triggers pleasurable associations, based on a hope that eating will produce pleasurable sensations (satiety, aesthetic interest).
- The person eats.
People eat to relieve hunger or boredom, in a sense, but the cognitive path followed by a person in order to eat must have some basis in hope - hope that eating will make the person feel better, hope that the action of acquiring food, chewing, and swallowing will be worth it.
A model of the eating related introspection of a depressed person, on the other hand, might look like this (and I'm taking this from introspection, and exaggerating a bit for clarity):
- The person feels hungry or bored.
- The person, being depressed, also feels miserable.
- The person imagines various options for food.
- While the person remembers food relieving hunger, the person, if very depressed, also remembers that food does not relieve misery.
- No imaginary food seems that much better than any other, since all will ultimately lead to misery (by failing to relieve the misery).
- Why bother?
- The person may often fail to eat.
Failure to eat by depressed folks has nothing to do with body image, as in eating disorders. It merely has to do with a lack of hope for getting relief from food - and, ultimately, a lack of recognition of the value of eating (distinct from an intention to starve oneself to death).
Despite some evidence for depressive realism, there is some sense in which we might say that the cognition of severely depressed people may be impaired - especially their decision-making capabilities. We might easily say that a person who can't decide what to eat, and so fails to eat, is indeed cognitively impaired, rather than being especially wise. (I feel rather silly when it happens to me.) In fact, "diminished ability to think or concentrate, or indecisiveness, nearly every day" (emphasis mine) is DSM-IV Criterion A8 for a Major Depressive Episode.
Recent work in cognitive science has explored the role that emotion plays in decision-making. For example, in "The role of emotion in decision-making: Evidence from neurological patients with orbitofrontal damage," Brain & Cognition 55 (2004) 30–40, Antoine Bechara reports that
The studies of decision-making in neurological patients who can no longer process emotional information normally suggest that people make judgments not only by evaluating the consequences and their probability of occurring, but also and even sometimes primarily at a gut or emotional level. Lesions of the ventromedial (which includes the orbitofrontal) sector of the prefrontal cortex interfere with the normal processing of ‘‘somatic’’ or emotional signals, while sparing most basic cognitive functions. Such damage leads to impairments in the decision-making process, which seriously compromise the quality of decisions in daily life.
That decisions, in humans, are based on emotion is an empirical fact, to the extent that there is evidence for it. People with impaired capacity to experience emotion are not perfect rational calculators; their decisions appear very strange, and often poor. But that is a mere description of our meat-based decision-making apparatus. It says nothing as to how the best decisions might be made - or, most importantly, what characteristics distinguish the best decisions. To specify that, we need to know what is valuable - for values must be the ultimate criteria for which decisions are good, and which poor. Why do anything? Here psychology must collide with philosophy.
To the extent that a depressed person does not make a normal decision - including the silly case of failing to eat (for lack of a compelling reason, not for lack of resources) - the depressed person is merely revealing his values. To claim that the depressed person is cognitively impaired in a way that would justify intervention into his decisions is to say that his values are incorrect, or that he is not justified in pursuing his values, and should be required to pursue our values instead. We cannot, I think, ethically intervene (force-feed) when a hunger striker decides that she values, say, women's suffrage over the continued satisfaction of her hunger, even unto death. When a depressed person concludes that nothing is valuable, except perhaps an end to suffering, we are in no better ethical position to intervene - either to force-feed, or to withhold the means for suicide.
Depressed people who overeat are consistent with my model. These people - less severely depressed, perhaps - have not completely given up on food as a source of relief, and may in fact clearly remember receiving positive feelings as a result of food. Therefore, instead of triggering the "eat" response every time one is hungry or bored, the overeating depressed person triggers it in addition every time he feels miserable, leading to increased eating and perhaps weight gain. As I pointed out above, increased appetite is not a feature associated with "melancholic features," which might, in a vague sense perceptible from the DSM-IV report on response to placebo, indicate a more severe type of depression. This is consistent with overeaters being less "hopelessly" depressed than undereaters.