On the molecular genetics of flexibility: The case of task-switching, inhibitory control and genetic variants

Effects of DRD2/ANKK1 and COMT Val158Met polymorphisms on stabilization against and adaptation to unexpected events

Genetic variations affecting dopaminergic neuromodulation such as the DRD2/ANKK1 and the COMT Val158Met polymorphisms contribute to goal-directed behavior that requires a balance between stabilization and updating of current states and behaviors. Dopamine is also thought to be relevant for encoding of surprise signals to sensory input and adaptive learning. A link between goal-directed behavior and learning from surprise is therefore plausible. In the present fMRI study, we investigated whether DRD2 and COMT polymorphisms are related to behavioral responses and neural signals in the caudate nucleus and dlPFC during updating or stabilizing internal models of predictable digit sequences. To-be-detected switches between sequences and to-be-ignored digit omissions within a sequence varied by information-theoretic quantities of surprise and entropy. We found that A1 noncarriers and Val-carriers showed a lower response threshold along with increased caudate and dlPFC activation to surprising switches compared with A1-carriers and Met-homozygotes, whose dlPFC activity increased with decreasing switch surprise. In contrast, there were overall smaller differences in behavioral and neural modulation by drift surprise. Our results suggest that the impact of dopamine-relevant polymorphisms in the flexibility-stability trade-off may result in part from the role of dopamine in encoding the weight afforded to events requiring updating or stabilization.

Cognitive Neural Mechanism of Backward Inhibition and Deinhibition: A Review

Task switching is one of the typical paradigms to study cognitive control. When switching back to a recently inhibited task (e.g., “A” in an ABA sequence), the performance is often worse compared to a task without N-2 task repetitions (e.g., CBA). This difference is called the backward inhibitory effect (BI effect), which reflects the process of overcoming residual inhibition from a recently performed task (i.e., deinhibition). The neural mechanism of backward inhibition and deinhibition has received a lot of attention in the past decade. Multiple brain regions, including the frontal lobe, parietal, basal ganglia, and cerebellum, are activated during deinhibition. The event-related potentials (ERP) studies have shown that deinhibition process is reflected in the P1/N1 and P3 components, which might be related to early attention control, context updating, and response selection, respectively. Future research can use a variety of new paradigms to separate the neural mechanisms of BI and deinhibition.

A neural model of vulnerability and resilience to stress-related disorders linked to differential susceptibility

Expert opinion remains divided concerning the impact of putative risk factors on vulnerability to depression and other stress-related disorders. A large body of literature has investigated gene by environment interactions, particularly between the serotonin transporter polymorphism (5-HTTLPR) and negative environments, on the risk for depression. However, fewer studies have simultaneously investigated the outcomes in both negative and positive environments, which could explain some of the inconclusive findings. This is embodied by the concept of differential susceptibility, i.e., the idea that certain common gene polymorphisms, prenatal factors, and traits make some individuals not only disproportionately more susceptible and responsive to negative, vulnerability-promoting environments, but also more sensitive and responsive to positive, resilience-enhancing environmental conditions. Although this concept from the field of developmental psychology is well accepted and supported by behavioral findings, it is striking that its implementation in neuropsychiatric research is limited and that underlying neural mechanisms are virtually unknown. Based on neuroimaging studies that examined how factors mediating differential susceptibility affect brain function, we posit that environmental sensitivity manifests in increased salience network activity, increased salience and default mode network connectivity, and increased salience and central executive network connectivity. These changes in network function may bring about automatic exogenous attention for positive and negative stimuli and flexible attentional set-shifting. We conclude with a call to action; unraveling the neural mechanisms through which differential susceptibility factors mediate vulnerability and resilience may lead us to personalized preventive interventions.

Dopamine, Cognitive Flexibility, and IQ: Epistatic Catechol-O-MethylTransferase:DRD2 Gene-Gene Interactions Modulate Mental Rigidity

Cognitive flexibility has been hypothesized to be neurochemically rooted in dopamine neurotransmission. Nonetheless, underpowered sample sizes and contradictory meta-analytic findings have obscured the role of dopamine genes in cognitive flexibility and neglected potential gene-gene interactions. In this largest neurocognitive-genetic study to date (n = 1400), single nucleotide polymorphisms associated with elevated prefrontal dopamine levels (catechol-O-methyltransferase; rs4680) and diminished striatal dopamine (C957T; rs6277) were both implicated in Wisconsin Card Sorting Test performance. Crucially, however, these genetic effects were only evident in low-IQ participants, suggesting high intelligence compensates for, and eliminates, the effect of dispositional dopamine functioning on flexibility. This interaction between cognitive systems may explain and resolve previous empirical inconsistencies in highly educated participant samples. Moreover, compensatory gene-gene interactions were discovered between catechol-O-methyltransferase and DRD2, such that genotypes conferring either elevated prefrontal dopamine or diminished striatal dopamine-via heightened striatally concentrated D2 dopamine receptor availability-are sufficient for cognitive flexibility, but neither is necessary. The study has therefore revealed a form of epistatic redundancy or substitutability among dopamine systems in shaping adaptable thought and action, thus defining boundary conditions for dopaminergic effects on flexible behavior. These results inform theories of clinical disorders and psychopharmacological interventions and uncover complex fronto-striatal synergies in human flexible cognition.

Interactive effects of DRD2 rs6277 polymorphism, environment and sex on impulsivity in a population-representative study

Previous research has shown that dopaminergic dysregulation and early life stress interact to impact on aspects of impulse control. This study aimed to explore the potentially interactive effects of the rs6277 polymorphism of the dopamine D2 receptor gene (DRD2), stressful or supportive environment and sex on behavioural and self-reported measures of impulsivity, as well as alcohol use - a condition characterised by a deficit in impulse control. The sample consisted of the younger cohort (n = 583) of the longitudinal Estonian Children Personality, Behaviour and Health Study. The results showed that the CC homozygotes (suggested to have decreased striatal D2 receptor availability) who had experienced stressful life events (SLE) or maltreatment in the family prior to age 15 showed higher self-reported maladaptive impulsivity at age 15. The genotype-SLE interaction and further association with sex was also evident in the frequency of alcohol use at age 15. Lack of warmth in the family contributed to significantly higher levels of thoughtlessness and more frequent alcohol use in CC carriers at age 25, whereas family support was associated with lower thoughtlessness scores in CC males, which may suggest a protective effect of supportive family environment in this group. Together the findings suggest that DRD2 rs6277 polymorphism, in interaction with environmental factors experienced in childhood and youth may affect facets of impulsivity. Future work should aim to further clarify the sex and age-specific effects of stressful and supportive environment on the development of neuronal systems that are compromised in disorders characterised by deficits in impulse control.

Further investigating effects of task repetition proportion on n - 2 repetition costs: Task shielding as a potential modulating factor?

Previous research has shown that n - 2 repetition costs are reduced when the experimental procedure allows for task repetitions. The present study aimed to further elucidate possible mechanisms underlying this effect. To this end, three experiments were conducted in which the possibility of task repetitions was tied to individual tasks. In Experiment I, the specific repetition proportions varied between participants. The reduction of n - 2 repetition costs was stronger when the relative amount of task repetitions associated with a particular task was high, suggesting that inhibition is reduced when the presence of repetitions tied to a specific task can easily be detected. In Experiment II, task preparation time varied between blocks to investigate whether cue-based preparation underlies this reduction of n - 2 repetition costs. While the duration of the preparation interval had no effect in this respect, additional combined analyses of both experiments revealed an influence of stimulus congruency: n - 2 repetition costs were highest when repetitions were precluded and the task stimulus was incongruent, whereas no effect of stimulus congruence on n - 2 repetition costs was observed with tasks that possibly repeated. This data pattern was replicated in Experiment III. This result is interpreted in terms of task shielding which is reduced for tasks without repetitions, making these tasks more vulnerable to crosstalk from competing tasks when they are still in an inhibited state.

MAO-A Phenotype Effects Response Sensitivity and the Parietal Old/New Effect during Recognition Memory

A critical problem for developing personalized treatment plans for cognitive disruptions is the lack of understanding how individual differences influence cognition. Recognition memory is one cognitive ability that varies from person to person and that variation may be related to different genetic phenotypes. One gene that may impact recognition memory is the monoamine oxidase A gene (MAO-A), which influences the transcription rate of MAO-A. Examination of how MAO-A phenotypes impact behavioral and event-related potentials (ERPs) correlates of recognition memory may help explain individual differences in recognition memory performance. Therefore, the current study uses electroencephalography (EEG) in combination with genetic phenotyping of the MAO-A gene to determine how well-characterized ERP components of recognition memory, the early frontal old/new effect, left parietal old/new effect, late frontal old/new effect, and the late posterior negativity (LPN) are impacted by MAO-A phenotype during item and source memory. Our results show that individuals with the MAO-A phenotype leading to increased transcription have lower response sensitivity during both item and source memory. Additionally, during item memory the left parietal old/new effect is not present due to increased ERP amplitude for correct rejections. The results suggest that MAO-A phenotype changes EEG correlates of recognition memory and influences how well individuals differentiate between old and new items.

Dopamine D2 gene expression interacts with environmental enrichment to impact lifespan and behavior

Aging produces cellular, molecular, and behavioral changes affecting many areas of the brain. The dopamine (DA) system is known to be vulnerable to the effects of aging, which regulate behavioral functions such as locomotor activity, body weight, and reward and cognition. In particular, age-related DA D₂ receptor (D2R) changes have been of particular interest given its relationship with addiction and other rewarding behavioral properties. Male and female wild-type (Drd₂ +/+), heterozygous (Drd₂ +/−) and knockout (Drd₂ −/−) mice were reared post-weaning in either an enriched environment (EE) or a deprived environment (DE). Over the course of their lifespan, body weight and locomotor activity was assessed. While an EE was generally found to be correlated with longer lifespan, these increases were only found in mice with normal or decreased expression of the D₂ gene. Drd₂ +/+ EE mice lived nearly 16% longer than their DE counterparts. Drd₂ +/+ and Drd₂ +/− EE mice lived 22% and 21% longer than Drd₂ −/− EE mice, respectively. Moreover, both body weight and locomotor activity were moderated by environmental factors. In addition, EE mice show greater behavioral variability between genotypes compared to DE mice with respect to body weight and locomotor activity.

Sleep Deprivation Diminishes Attentional Control Effectiveness and Impairs Flexible Adaptation to Changing Conditions

Insufficient sleep is a global public health problem resulting in catastrophic accidents, increased mortality, and hundreds of billions of dollars in lost productivity. Yet the effect of sleep deprivation (SD) on decision making and performance is often underestimated by fatigued individuals and is only beginning to be understood by scientists. The deleterious impact of SD is frequently attributed to lapses in vigilant attention, but this account fails to explain many SD-related problems, such as loss of situational awareness and perseveration. Using a laboratory study protocol, we show that SD individuals can maintain information in the focus of attention and anticipate likely correct responses, but their use of such a top-down attentional strategy is less effective at preventing errors caused by competing responses. Moreover, when the task environment requires flexibility, performance under SD suffers dramatically. The impairment in flexible shifting of attentional control we observed is distinct from lapses in vigilant attention, as corroborated by the specificity of the influence of a genetic biomarker, the dopaminergic polymorphism DRD2 C957T. Reduced effectiveness of top-down attentional control under SD, especially when conditions require flexibility, helps to explain maladaptive performance that is not readily explained by lapses in vigilant attention.

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.

Meditation and Metacontrol

In addition to longer-term engagement in meditation, the past years have seen an increasing interest in the impact of single bouts of meditation on cognition. In this hypothesis and theory article, we adopt the distinction between focused-attention meditation (FAM) and open-monitoring meditation (OMM) and argue that these different types of meditation have different, to some degree, opposite impact on cognitive processes. We discuss evidence suggesting that single bouts of FAM and OMM are sufficient to bias cognitive control styles towards more versus less top-down control, respectively. We conclude that all meditation techniques are not equal and that successful meditation-based intervention requires the theoretically guided selection of the best-suited technique.

The social transmission of metacontrol policies: Mechanisms underlying the interpersonal transfer of persistence and flexibility

Humans often face binary cognitive-control dilemmas, with the choice between persistence and flexibility being a crucial one. Tackling these dilemmas requires metacontrol, i.e., the control of the current cognitive-control policy. As predicted from functional, psychometric, neuroscientific, and modeling approaches, interindividual variability in metacontrol biases towards persistence or flexibility could be demonstrated in metacontrol-sensitive tasks. These biases covary systematically with genetic predispositions regarding mesofrontal and nigrostriatal dopaminergic functioning and the individualistic or collectivistic nature of the cultural background. However, there is also evidence for mood- and meditation-induced intraindividual variability (with negative mood and focused-attention meditation being associated with a bias towards persistence, and positive mood and open-monitoring meditation being associated with a bias towards flexibility), suggesting that genetic and cultural factors do not determine metacontrol settings entirely. We suggest a theoretical framework that explains how genetic predisposition and cultural learning can lead to the implementation of metacontrol defaults, which however can be shifted towards persistence or flexibility by situational factors.

The neurophysiological basis of reward effects on backward inhibition processes

The ability to flexibly switch between tasks is an important faculty in daily life. One process that has been suggested to be an important aspect of flexible task switching is the inhibition of a recently performed task. This is called backward inhibition. Several studies suggest that task switching performance can be enhanced by rewards. However, it is less clear in how far backward inhibition mechanisms are also affected by rewards, especially when it comes to the neuronal mechanisms underlying reward-related modulations of backward inhibition. We therefore investigated this using a system neurophysiological approach combining EEG recordings with source localization techniques. We demonstrate that rewards reduce the strength of backward inhibition processes. The neurophysiological data shows that these reward-related effects emerge from response and/or conflict monitoring processes within medial frontal cortical structures. Upstream processes of perceptual gating and attentional selection, as well as downstream processes of context updating and stimulus-response mapping are not modulated by reward, even though they also play a role in backward inhibition effects.

Neurophysiology of rule switching in the corticostriatal circuit

The ability to adjust behavioral responses to cues in a changing environment is crucial for survival. Activity in the medial Prefrontal Cortex (mPFC) is thought to both represent rules to guide behavior as well as detect and resolve conflicts between rules in changing contingencies. While lesion and pharmacological studies have supported a crucial role for mPFC in this type of set-shifting, an understanding of how mPFC represents current rules or detects and resolves conflict between different rules is still unclear. Meanwhile, medial dorsal striatum (mDS) receives major projections from mPFC and neural activity of mDS is closely linked to action selection, making the mDS a potential major player for enacting rule-guided action policies. However, exactly what is signaled by mPFC and how this impacts neural signals in mDS is not well known. In this review, we will summarize what is known about neural signals of rules and set shifting in both prefrontal cortex and dorsal striatum, as well as provide questions and directions for future experiments.

Rule encoding in dorsal striatum impacts action selection

Cognitive flexibility is a hallmark of prefrontal cortical (PFC) function yet little is known about downstream area involvement. The medial dorsal striatum (mDS) receives major projections from the PFC and is uniquely situated to perform the integration of responses with rule information. In this study, we use a novel rule shifting task in rats that mirrors non-human primate and human studies in its temporal precision and counterbalanced responses. We record activity from single neurons in the mDS while rats switch between different rules for reward. Additionally, we pharmacologically inactivate mDS by infusion of a baclofen/muscimol cocktail. Inactivation of mDS impaired the ability to shift to a new rule and increased the number of regressive errors. While recording in mDS, we identified neurons modulated by direction whose activity reflected the conflict between competing rule information. We show that a subset of these neurons was also rule selective, and that the conflict between competing rule cues was resolved as behavioural performance improved. Other neurons were modulated by rule, but not direction. These neurons became selective before behavioural performance accurately reflected the current rule. These data provide an additional locus for investigating the mechanisms underlying behavioural flexibility. Converging lines of evidence from multiple human psychiatric disorders have implicated dorsal striatum as an important and understudied neural substrate of flexible cognition. Our data confirm the importance of mDS, and suggest a mechanism by which mDS mediates abstract cognition functions.

Acute physical exercise improves shifting in adolescents at school: evidence for a dopaminergic contribution

The executive function of shifting between mental sets demands cognitive flexibility. Based on evidence that physical exercise fostered cognition, we tested whether acute physical exercise can improve shifting in an unselected sample of adolescents. Genetic polymorphisms were analyzed to gain more insight into possibly contributing neurophysiological processes. We examined 297 students aged between 13 and 17 years in their schools. Physical exercise was manipulated by an intense incremental exercise condition using bicycle ergometers and a control condition which involved watching an infotainment cartoon while sitting calm. The order of conditions was counterbalanced between participants. Shifting was assessed by a switching task after both conditions. Acute intense physical exercise significantly improved shifting as indicated by reduced switch costs. Exercise-induced performance gains in switch costs were predicted by a single nucleotide polymorphism (SNP) targeting the Dopamine Transporter (DAT1/SLCA6A3) gene suggesting that the brain dopamine system contributed to the effect. The results demonstrate the potential of acute physical exercise to improve cognitive flexibility in adolescents. The field conditions of the present approach suggest applications in schools.

Dopamine DRD2/ANKK1 Taq1A and DAT1 VNTR polymorphisms are associated with a cognitive flexibility profile in pathological gamblers

Like drug addiction, pathological gambling (PG) has been associated with impairments in executive functions and alterations in dopaminergic functioning; however, the role of dopamine (DA) in the executive profile of PG remains unclear. The aim of this study was to identify whether the DRD2/ANKK1 Taq1A-rs1800497 and the DAT1-40 bp VNTR polymorphisms are associated with cognitive flexibility (measured by Wisconsin Card Sorting Test (WCST) and Trail Making Test (TMT)) and inhibition response (measured by Stroop Color and Word Test (SCWT)), in a clinical sample of 69 PG patients. Our results showed an association between DA functioning and cognitive flexibility performance. The Taq1A A1+ (A1A2/A1A1) genotype was associated with poorer TMT performance (p<0.05), while DAT1 9-repeat homozygotes displayed better WCST performance (p<0.05) than either 10-repeat homozygotes or heterozygotes. We did not find any association between the DRD2 or DAT1 polymorphisms and the inhibition response. These results suggested that pathological gamblers with genetic predispositions toward lower availability of DA and D2 receptor density are at a higher risk of cognitive flexibility difficulties. Future studies should aim to shed more light on the genetic mechanisms underlying the executive profile in PG.

Relationship between frontostriatal morphology and executive function deficits in bipolar I disorder following a first manic episode: data from the Systematic Treatment Optimization Program for Early Mania (STOP-EM)

OBJECTIVES

Executive function impairments are a core feature of bipolar I disorder (BD-I), not only present during acute episodes but also persisting following remission of mood symptoms. Despite advances in knowledge regarding the neural basis of executive functions in healthy subjects, research into morphological abnormalities underlying the deficits in BD-I is lacking.

METHODS

Patients with BD-I within three months of sustained remission from their first manic episode (n = 41) underwent neuropsychological testing and a 3T magnetic resonance imaging scan and were compared to healthy subjects matched for age, sex, and premorbid IQ (n = 30). Group dorsolateral prefrontal cortex (DLPFC; Brodmann areas 9 and 46) and caudate volumes were examined and analyzed for relationships with the average score from three computerized tests of executive function: Spatial Working Memory, Stockings of Cambridge, and Intradimensional/Extradimensional Shift.

RESULTS

Right caudate volumes were enlarged in patients (z = 3.57, p < 0.05 corrected). No differences in DLPFC volumes were found. Patients showed large deficits in executive function relative to healthy subjects (d = -0.92, p < 0.001). While in healthy subjects, a larger right (r = +0.39, p < 0.05) and left (r = +0.44, p < 0.05) caudate was associated with better executive function score, in patients, larger right (r = -0.36, p < 0.05) and left (r = -0.34, p < 0.05) volumes correlated with poorer performance.

CONCLUSIONS

Although the etiology of gray matter changes is unknown, volume increases in the right caudate may be an important factor underlying executive function impairments during remission in patients with BD-I.

The neural and genetic basis of executive function: attention, cognitive flexibility, and response inhibition

Executive function is a collection of cognitive processes essential for higher order mental function. Processes involved in executive function include, but are not limited to, working memory, attention, cognitive flexibility, and impulse control. These complex behaviors are largely mediated by prefrontal cortical function but are modulated by dopaminergic, noradrenergic, serotonergic, and cholinergic input. The ability of these neurotransmitter systems to modulate executive function allows for adaptation in cognitive behavior in response to changes in the environment. Because of the important role these neurotransmitter systems play in regulating executive function, changes in these systems can also have a grave impact on executive function. In addition, polymorphisms in genes associated with these neurotransmitters are associated with phenotypic differences in executive function. Understanding how these naturally occurring polymorphisms contribute to different executive function phenotypes will advance basic knowledge of cognition and potentially further understanding and treatment of mental illness that involve changes in executive function. In this review, we will examine the influence of dopamine, norepinephrine, serotonin, and acetylcholine on the following measures of executive function: attention, cognitive flexibility, and impulse control. We will also review the effects of polymorphisms in genes associated with these neurotransmitter systems on these measures of executive function.

Dopamine genes (DRD2/ANKK1-TaqA1 and DRD4-7R) and executive function: their interaction with obesity

Obesity is a multifactorial disease caused by the interaction between genotype and environment, and it is considered to be a type of addictive alteration. The A1 allele of the DRD2/ANKK1-TaqIA gene has been associated with addictive disorders, with obesity and with the performance in executive functions. The 7 repeat allele of the DRD4 gene has likewise been associated with the performance in executive functions, as well as with addictive behaviors and impulsivity. Participants were included in the obesity group (N = 42) if their body mass index (BMI) was equal to or above 30, and in the lean group (N = 42) if their BMI was below 25. The DRD2/ANKK1-TaqIA and DRD4 VNTR polymorphisms were obtained. All subjects underwent neuropsychological assessment. Eating behavior traits were evaluated. The 'DRD2/ANKK1-TaqIA A1-allele status' had a significant effect on almost all the executive variables, but no significant 'DRD4 7R-allele status' effects were observed for any of the executive variables analyzed. There was a significant 'group' x 'DRD2/ANKK1-TaqIA A1-allele status' interaction effect on LN and 'group' x 'DRD4 7R-allele status' interaction effect on TMT B-A score. Being obese and a carrier of the A1 allele of DRD2/ANKK1-TaqIA or the 7R allele of DRD4 VNTR polymorphisms could confer a weakness as regards the performance of executive functions.