Reprint of: DAT genotype modulates striatal processing and long-term memory for items associated with reward and punishment

Reward association impairs recognition of incidentally encoded negative information: Electrophysiological evidence

Previous studies investigating the effect of reward on emotional episodic memory have produced inconsistent results. In this study, through two experiments using event-related potentials (ERPs), we investigated the effect of reward association on the encoding and retrieval of incidentally encoded emotional information, and examined whether this effect changes over time. Participants in the two experiments were asked to discriminate the emotional valence of color images under reward or no-reward condition and incidentally encode them. Immediate (in Experiment 1) or 24-hour delayed (in Experiment 2) recognition after encoding was tested. In Experiments 1 and 2, reward (relative to no-reward) significantly improved the recognition of positive and neutral items, but significantly reduced the recognition of negative items. During encoding, the significant ERP reward effects (significantly more positive ERP amplitude for rewarded items than for non-rewarded ones) for positive and neutral images were widely distributed from 200 to 1500 ms after image onset, while those for negative stimuli occurred mainly from 200 to 500 ms. During retrieval, the significant ERP reward effects for positive and neutral items occurred in the two experiments, but the reversed ERP reward effects for negative items were found only in Experiment 1. The results of the present study suggest that reward association affects the encoding and retrieval of emotional images by enhancing memory processing efficiency of positive and neutral items, while impairing recognition of negative items, thus yielding a robust and sustained modulation over frontal/frontocentral or centroparietal/parietal areas where mechanisms of reward and emotion processing operate in conjunction.

Developmental trajectories to reduced activation of positive valence systems: A review of biological and environmental contributions

Reduced activation of positive valence systems (PVS), including blunted neural and physiological responses to pleasant stimuli and rewards, has been shown to prospectively predict the development of psychopathology. Yet, little is known about how reduced PVS activation emerges across development or what implications it has for prevention. We review genetic, temperament, parenting, and naturalistic and laboratory stress research on neural measures of PVS and outline developmentally-informed models of trajectories of PVS activation. PVS function is partly heritable and appears to reflect individual differences in early-emerging temperament traits. Although lab-induced stressors blunt PVS activation, effects of parenting and naturalistic stress on PVS are mixed and depend on the type of stressor, developmental timing, and interactions amongst risk factors. We propose that there may be multiple, dynamic developmental trajectories to reduced PVS activation in which combinations of genes, temperament, and exposure to severe, prolonged, or uncontrollable stress may exert direct and interactive effects on PVS function. Critically, these risk factors may alter PVS developmental trajectories and/or PVS sensitivity to proximal stressors. Distinct factors may converge such that PVS activation proceeds along a typical, accelerated, chronically low, or stress-reactive trajectory. Finally, we present directions for future research with translational implications.

Punishment-related memory-guided attention: Neural dynamics of perceptual modulation

Remembering the outcomes of past experiences allows us to generate future expectations and shape selection in the long-term. A growing number of studies has shown that learned positive reward values impact spatial memory-based attentional biases on perception. However, whether memory-driven attentional biases extend to punishment-related values has received comparatively less attention. Here, we manipulated whether recent spatial contextual memories became associated with successful avoidance of punishment (potential monetary loss). Behavioral and electrophysiological measures were collected from 27 participants during a subsequent memory-based attention task, in which we tested for the effect of punishment avoidance associations. Punishment avoidance significantly amplified effects of spatial contextual memories on visual search processes within natural scenes. Compared to non-associated scenes, contextual memories paired with punishment avoidance lead to faster responses to targets presented at remembered locations. Event-related potentials elicited by target stimuli revealed that acquired motivational value of specific spatial locations, by virtue of their association with past avoidance of punishment, dynamically affected neural signatures of early visual processing (indexed by larger P1 and earlier N1 potentials) and target selection (as indicated by reduced N2pc potentials). The present results extend our understanding of how memory, attention, and punishment-related mechanisms interact to optimize perceptual decision in real world environments.

Previously rewarding environments enhance incidental memory formation

Declarative memory performance is superior for items that were encoded in temporal proximity to reward delivery or expectancy. How reward-predicting contexts affect subsequent declarative memory formation in those contexts are, however, unknown. Using an ecological experimental setup in the form of a naturalistic driving simulator task, we examined the effect that previously rewarded environments may have on incidental memory formation. After driving in two distinct environments, one of which associated with monetary reward, participants drove again in the environments, which were embedded with unique images on billboards. A recognition test 24 h later demonstrated that incidental memory was superior for items presented in the reward-associated environment. These findings suggest that environmental cues imbued with incentive salience promote memory processes even in the absence of reward.

Mutual Influence of Reward Anticipation and Emotion on Brain Activity during Memory Retrieval

Previous studies on the joint effect of reward motivation and emotion on memory retrieval have obtained inconsistent results. Furthermore, whether and how any such joint effect might vary over time remains unclear too. Accordingly, using the event-related potential (ERP) measurement of high temporal resolution, our study investigates the cognitive and brain mechanisms of monetary reward and emotion affecting the retrieval processes of episodic memory. Twenty undergraduate and graduate students participated in the research, and our study’s behavioral results indicated that reward (relative to no reward) and negative emotion (relative to positive and neutral emotion) significantly improved recognition performance. The ERP results showed that there were significant interactions between monetary reward and emotion on memory retrieval, and the reward effects of positive, neutral, and negative memory occurred at varied intervals in mean amplitude. The reward effect of positive memory appeared relatively early, at 260–330 ms after the stimulus onset in the frontal-frontocentral area, at 260–500 ms in the centroparietal-parietal area and at 500–700 ms in the frontocentral area. However, the reward effects of neutral and negative memory occurred relatively later, and that of negative memory appeared at 500–700 ms in the frontocentral and centroparietal area and that of neutral memory was at 500–700 ms in the frontocentral and centroparietal-parietal area. Meanwhile, significant FN400 old/new effects were observed in the negative and rewarded positive items, and the old/new effects of negative items appeared earlier at FN400 than positive items. Also, significant late positive component (LPC) old/new effects were found in the positive, negative, and rewarded neutral items. These results suggest that, monetary reward and negative emotion significantly improved recognition performance, and there was a mutual influence between reward and emotion on brain activity during memory retrieval.

Memory Performance for Everyday Motivational and Neutral Objects Is Dissociable from Attention

Episodic memory is typically better for items coupled with monetary reward or punishment during encoding. It is yet unclear whether memory is also enhanced for everyday objects with appetitive or aversive values learned through a lifetime of experience, and to what extent episodic memory enhancement for motivational and neutral items is attributable to attention. In a first experiment, we investigated attention to everyday motivational objects using eye-tracking during free-viewing and subsequently tested episodic memory using a remember/know procedure. Attention was directed more to aversive stimuli, as evidenced by longer viewing durations, whereas recollection was higher for both appetitive and aversive objects. In the second experiment, we manipulated the visual contrast of neutral objects through changes of contrast to further dissociate attention and memory encoding. While objects presented with high visual contrast were looked at longer, recollection was best for objects presented in unmodified, medium contrast. Generalized logistic mixed models on recollection performance showed that attention as measured by eye movements did not enhance subsequent memory, while motivational value (Experiment 1) and visual contrast (Experiment 2) had quadratic effects in opposite directions. Our findings suggest that an enhancement of incidental memory encoding for appetitive items can occur without an increase in attention and, vice versa, that enhanced attention towards salient neutral objects is not necessarily associated with memory improvement. Together, our results provide evidence for a double dissociation of attention and memory effects under certain conditions.

Behavioral and Neural Manifestations of Reward Memory in Carriers of Low-Expressing versus High-Expressing Genetic Variants of the Dopamine D2 Receptor

Dopamine is critically important in the neural manifestation of motivated behavior, and alterations in the human dopaminergic system have been implicated in the etiology of motivation-related psychiatric disorders, most prominently addiction. Patients with chronic addiction exhibit reduced dopamine D2 receptor (DRD2) availability in the striatum, and the DRD2 TaqIA (rs1800497) and C957T (rs6277) genetic polymorphisms have previously been linked to individual differences in striatal dopamine metabolism and clinical risk for alcohol and nicotine dependence. Here, we investigated the hypothesis that the variants of these polymorphisms would show increased reward-related memory formation, which has previously been shown to jointly engage the mesolimbic dopaminergic system and the hippocampus, as a potential intermediate phenotype for addiction memory. To this end, we performed functional magnetic resonance imaging (fMRI) in 62 young, healthy individuals genotyped for DRD2 TaqIA and C957T variants. Participants performed an incentive delay task, followed by a recognition memory task 24 h later. We observed effects of both genotypes on the overall recognition performance with carriers of low-expressing variants, namely TaqIA A1 carriers and C957T C homozygotes, showing better performance than the other genotype groups. In addition to the better memory performance, C957T C homozygotes also exhibited a response bias for cues predicting monetary reward. At the neural level, the C957T polymorphism was associated with a genotype-related modulation of right hippocampal and striatal fMRI responses predictive of subsequent recognition confidence for reward-predicting items. Our results indicate that genetic variations associated with DRD2 expression affect explicit memory, specifically for rewarded stimuli. We suggest that the relatively better memory for rewarded stimuli in carriers of low-expressing DRD2 variants may reflect an intermediate phenotype of addiction memory.

Methylphenidate effects on brain activity as a function of SLC6A3 genotype and striatal dopamine transporter availability

We pharmacologically challenged catecholamine reuptake, using methylphenidate, to investigate its effects on brain activity during a motor response inhibition task as a function of the 3'-UTR variable number of tandem repeats (VNTR) polymorphism of the dopamine transporter (DAT) gene (SLC6A3) and the availability of DATs in the striatum. We measured the cerebral hemodynamic response of 50 healthy males during a Go/No-Go task, a measure of cognitive control, under the influence of 40 mg methylphenidate and placebo using 3T functional magnetic resonance imaging. Subjects were grouped into 9-repeat (9R) carriers and 10/10 homozygotes on the basis of the SLC6A3 VNTR. During successful no-go trials compared with oddball trials, methylphenidate induced an increase of blood oxygen level-dependent (BOLD) signal for carriers of the SLC6A3 9R allele but a decrease in 10/10 homozygotes in a thalamocortical network. The same pattern was observed in caudate and inferior frontal gyrus when successful no-go trials were compared with successful go trials. We additionally investigated in a subset of 35 participants whether baseline striatal DAT availability, ascertained with (123)I-FP-CIT single photon emission computed tomography, predicted the amount of methylphenidate-induced change in hemodynamic response or behavior. Striatal DAT availability was nominally greater in 9R carriers compared with 10/10 homozygotes (d=0.40), in line with meta-analyses, but did not predict BOLD or behavioral changes following MPH administration. We conclude that the effects of acute MPH administration on brain activation are dependent on DAT genotype, with 9R carriers showing enhanced BOLD following administration of a prodopaminergic compound.