Pure Pedantry

Bern et al. wanted to establish what areas activate during the feeling of dread. Dread is defined as the feeling during the wait for a bad outcome that one knows is going to be inevitable. Why would we have dread? What is the purpose of dread? Well, the decision about whether to delay a bad outcome or get it over with quick is determine, in their view, by a comparison of the utility of the time during the delay to the actually bad event itself based on the duration of that delay. Basically, if you know something bad is going to happen, you decision to delay that bad thing is determined by how good or bad the interim is going to be for a variety of waiting periods versus how bad the thing itself is going to be. If the thing itself is absolutely horrible, but the waiting is not going to be that bad, you choose to delay as long as possible. If on the other hand, the longer you wait the worse the worse the waiting is going to feel, you may choose to get the thing over with quick even if in doing so the thing is even worse. This is probably not making all that much sense, so I will let them tell you about the experimental design.

To test our hypothesis that dread follows a time course of activity in the pain matrix consistent with utility theory, we used a delay-conditioning paradigm with different levels of shock and delay. Participants (n = 32) were presented with a series of 96 passive trials inside the scanner (12). Each trial began with the presentation of a cue that indicated both the voltage level and the amount of time one would have to wait for the outcome (Fig. 1). Shocks were delivered to the dorsum of the left foot on a 100% reinforcement schedule (12). After the passive delay-conditioning procedure, but while still in the scanner, the utility of voltage and delay was estimated through a series of forced-choice options. In this phase, participants were presented with pairs of voltage and delay--e.g., "90% in 3 seconds" or "60% in 27 seconds" -- and they had to choose which of the two offerings they would prefer to receive. The choices were real, not hypothetical, and participants received their preferred shock at the chosen voltage level and time. Choosing the shorter delay could not speed up the experiment, as each trial lasted the length of the longer of the two choices (when the shorter duration was chosen, the extra time was added to the intertrial interval after the shock).

This paradigm is good because it makes the participant choose between a worse pain right now and a less pain later on. There are two possible results for the participants. The participants could all decide to get it over with or, a some economic theories would argue, delay the pain as long as possible if the result would be less pain later on.

Standard economic theory posits that preferences for outcomes that occur at different times can be represented by an expected utility of the future outcomes discounted by the amount of time one must wait for them (1). These theories typically apply discounting under the assumption that people care less about outcomes that are more remote in the future than those that are more imminent, which leads to the prediction that people should want to expedite desired experiences and delay undesirable experiences for as long as possible. A wide range of findings, however, shows that people often exhibit the opposite pattern: They prefer to delay gratifications and to speed up the occurrence of unpleasant outcomes. If people do, indeed, discount the future, then why do they so often exhibit patterns of preference that are the opposite of the predictions of time discounting? The answer, we suggest, lies in the fact that the act of waiting may itself bring subjective benefits or costs, such as the joyous anticipation of waiting for a birthday present or the misery of waiting for a dentist's appointment. In the case of bad outcomes, the problem can be reduced to the utility of dread (2).

In contrast to standard discounted utility theory, another type of decision-making model posits that waiting enters the utility function separately from the outcome (3, 4). Here, an individual's preference for waiting at any point in time reflects the relative weight of two considerations: the effect of time discounting on the present value of the outcome itself, and the effect of changes in timing on the length of the period of anticipation. The latter effect can explain why people sometimes delay pleasant outcomes and expedite unpleasant ones.

What did the experimenters find?

When the voltages between the choices were identical, participants generally chose the shorter delay (mean = 78.9% of these types of choices, range = 0 to 100%). Out of the 32 participants, 27 chose the shorter delay more than 50% of the time, indicating that the majority of individuals dreaded waiting for a shock. Some individuals dreaded so much that they were often willing to take the next higher voltage level to avoid waiting the longest delay, even though doing so would not cause the next trial to appear any sooner. Consistent with microeconomic theory, we take these revealed preferences as a measure of expected utility and then ask what neurobiological aspect of the passive experience correlates with this expected utility.

The experimenters find that dread -- or the disutility of waiting -- has a price that most of the participants go out of their way to avoid. But the experimenters delve further. They want to know the areas of the brain that are activated when this perception takes place, and thus those areas that play a role in avoiding pain delay. Here they find something very interesting. The areas that neuroscientists typically associate with fear and anxiety -- areas like the amygdala -- are not the ones activated during dread. Instead the activation during dread happens in the precise areas that are activated during the pain itself.

The manifestation of dread in the more posterior elements of the pain matrix informs our understanding of what dread is and how it impacts decision-making. The pain matrix can be divided broadly into somatosensory, attentive, movement, and emotional divisions. Although dread is usually thought of as an emotion based on fear and anxiety (14), our localization of dread to the posterior elements of the matrix suggests that dread has a substantial attentive component. Both the mild and extreme dreaders displayed time courses of activity in SI, SII, the caudal ACC, and the posterior insula that were consistent with the utility-based theory of dread. The more anterior, "emotional" components (e.g., the anterior insula, the rostral ACC, and the amygdala) did not have such time courses.

This is a very compelling paper. It shows that there is a neurological correllation with behavior and that this correllation is explained by a simple utility function -- the utility function that we would expect from economic theory. See how they all collide:

We used Loewenstein's model for the utility of anticipation to test the hypothesis that the distinguishing characteristic between mild and extreme dreaders lies in the prospective response to future outcomes (3). In this model, the present value of a delayed act of consumption is divided into two components: the utility from consumption and the utility from anticipation (dread). Assuming instantaneous consumption at the time (T) of shock delivery, the present value at time (t) of a future act of consumption is the utility of consumption U discounted by an exponential function with rate r = Ue-r(T - t) (1). In addition to the discounted consumption utility, anticipation--i.e., dread--confers utility in and of itself. For the sake of simplicity, we assumed that the instantaneous intensity of dread was constant and that the present value was this constant, {alpha}, multiplied by the time remaining until the shock. Thus, combining the terms for dread and discounted consumption, the present value U(V,t) = U(V) x [{alpha}(T - t) + e-r(T - t)], where U(V) is the utility of the shock (a function of voltage V) occurring at time T; {alpha} is the dread factor, and r is the discount rate. According to this theory, differences in the utility of dread should be measurable as differences in the dread factor {alpha}. A dread factor that is significantly positive would manifest as an early increase in the time course of activity (as opposed to a slow increase as the shock approached in time).

All of the contralateral (right hemisphere) ROIs and the caudal ACC displayed time courses with dread factors significantly different from zero, but this was an effect observed primarily in the extreme dreaders and not the mild dreaders (compare with the early, sustained, increases in Fig. 4). Both SI and SII showed marked elevations in activity after the presentation of the cue--an elevation which continued to rise in advance of the shock. But the initial elevation in SI, SII, and right posterior insula, which was measured by the dread factor, was significantly greater in the extreme dreaders (12).

This notion that economic utility may have a neural substrate is fascinating to me -- as I have mentioned earlier -- because it gives us the option of putting economic theories to the test. Here we find out that rational choice theory passes.