Decision-making and addiction (part II): myopia for the future or hypersensitivity to reward?

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Abstract

On a decision-making instrument known as the “gambling task” (GT), a subgroup of substance dependent individuals (SDI) opted for choices that yield high immediate gains in spite of higher future losses. This resembles the behavior of patients with ventromedial (VM) prefrontal cortex lesions. In this study, we addressed the possibility that hypersensitivity to reward may account for the “myopia” for the future in this subgroup of SDI. We used a variant version of the GT, in which the good decks yielded high immediate punishment but higher delayed reward. The bad decks yielded low immediate punishment and lower delayed reward. We measured the skin conductance response (SCR) of subjects after receiving reward (reward SCR) and during their pondering from which deck to choose (anticipatory SCR). A subgroup of SDI who was not impaired on the original GT performed normally on the variant GT. The subgroup of SDI who was impaired on the original GT showed two levels of performance on the variant GT. One subgroup (36% of the sample) performed poorly on the variant GT, and showed similar behavioral and physiological impairments to VM patients. The other subgroup of SDI (64% of the sample) performed normally on the variant task, but had abnormally large physiological responses to reward, i.e. large SCR after receiving reward (reward SCR) and large SCR in anticipation of outcomes that yield large reward. Thus, the combined cognitive and physiological approach of assessing decision-making characterizes three sub-populations of SDI. One sub-population is without impairments that can be detected by any measure of the GT paradigm. Another sub-population is similar to VM patients in that they are insensitive to the future, both positive and negative. A third sub-population is hypersensitive to reward, so that the presence or the prospect of receiving, reward dominates their behavior.

Introduction

The primary aim of this study was to test the hypothesis that hypersensitivity to reward might account for the “myopia” for the future of at least a subgroup of SDI.

Using a decision-making instrument known as the “gambling task” (GT), as a tool for measuring decision-making, most substance dependent individuals (SDI) behaved in such a way that they opted for choices that yielded high immediate gains in spite of higher future losses [7], [30], [42]. The poor decision-making seen in SDI using the GT persisted even in the face of a progressive increase in delayed punishment [7]. This behavior resembles that of patients with bilateral lesions of the ventromedial (VM) prefrontal cortex [7]. It also reflects the behavior of SDI in real-life in that they prefer choices that bring immediate benefit (i.e. drug reward), at the risk of negative future consequences (e.g. loss of jobs, home, family and friends). The failure of progressive delayed punishment to deter SDI from seeking immediate reward is consistent with their “myopia” for the future in real-life, which persists in the face of rising negative consequences.

We tested the hypersensitivity to reward hypothesis using an approach we applied to the study of VM patients [8]. We used a variant version of the GT with decks E′, F′, G′, and H′, where we reversed the order of reward and punishment, i.e. the punishment became immediate and the reward became delayed. In the variant task (E′F′G′H′), we set the advantageous decks (E′ and G′) to be those with high immediate punishment, but higher future reward. The disadvantageous decks (F′ and H′) were those with low immediate punishment, but lower future reward. We also measured the skin conductance responses (SCR) triggered by subjects during their performance of the variant GT, before making a choice (anticipatory SCR) and after receiving reward (reward SCR). In the variant GT task (immediate punishment/delayed reward), the schedules of reward and punishment were set in such a way that the future reward would increase progressively as subjects select more cards from the advantageous decks E′ and G′. The future reward would decrease progressively as subjects select more cards from the disadvantageous decks F′ and H′ [8].

We reasoned that hypersensitivity to reward would be associated with generation of abnormally high reward SCR. Furthermore, when the “thought” of a potential reward comes to mind during the deliberation of a decision, SDI would trigger abnormally high anticipatory SCR. Thus, from the combined behavioral and SCR measures, we made the following predictions.

Hypersensitivity to reward in SDI would be consistent with a profile of behavioral and SCR measures that include impairment on the original GT, no impairment on the variant GT, coupled with abnormally high reward SCR, as well as anticipatory SCR when expecting a large gain. The rationale for a normal performance of SDI on the variant GT is based on observations revealing that normal control subjects are initially reluctant to sample the good decks, especially deck E′, because of the higher cost associated with the decks before receiving reward. Hypersensitivity to reward, especially when combined with hyposensitivity to punishment, can help overcome this reluctance and promote faster sampling of the good deck, an earlier encounter of large reward, and a further reinforcement to sample the same deck again.

On the other hand, insensitivity to the future, positive or negative, would be consistent with a profile of behavioral and SCR measures that include impairment on the original GT as well as the variant GT, coupled with normal reward SCR, but defective anticipatory SCR. In other words, insensitivity to the future would be consistent with a pattern of results similar to VM patients [8]. Studies have shown that abnormal mechanisms of processing drug reward in SDI generalize to other rewards, including monetary reward [10]. Thus, we predicted that our test of the hypersensitivity to reward hypothesis would apply not only to drugs, but also to reward in general, such as the monetary reward used in the GT paradigm.

Section snippets

Subjects

The subjects who participated in this study were the same subjects who participated in study Part I using the original GT [4].

Psychological and neuropsychological tests

We used the structured clinical interview for DSM-IV (SCID-IV) to assign axis I diagnoses (including alcohol and other drug abuse and/or dependence) as described in study Part 1 [4].

We also used the Hare psychopathy checklist-revised (PCL-R) to probe psychopathy and antisocial personality, the Beck depression inventory (BDI) and Beck anxiety inventory (BAI) [4].

We

Results

All statistical analyses of the data presented below were conducted using the software STATISTICA 4.1 for the MacIntosh of Statsoft, Inc. There were no significant differences between the demographics from impaired and non-impaired groups shown in Table 1. Differences in drug histories shown in Table 2 were not significant. The psychological and neuropsychological measures from the “non-impaired” and “impaired” groups of normal controls, SDI, or VM patients are presented in Table 3. With the

Discussion

The assessment of decision-making using combined behavioral and physiological approaches enabled us to differentiate among three distinct sub-populations of SDI. In a relatively small sub-population of SDI, the behavioral choices, reward SCR, punishment SCR, and anticipatory SCR (for both positive and negative outcomes) always revealed results indistinguishable from normal controls. Another relatively small sub-population of SDI (impaired on task A′B′C′D′ and E′F′G′H′) was indistinguishable

Acknowledgements

This study was supported by NIDA DA11779-02. Jon Spradling wrote the software for the computerized gambling task.

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