Showing posts with label motivation/reward. Show all posts
Showing posts with label motivation/reward. Show all posts

Friday, February 17, 2023

The touch sensitive nerve cells that make mice (and probably us) horny.

From Elias et al. (open source) in the journal Cell:  


• Activation of Mrgprb4-lineage touch neurons induces lordosis-like posture
• Activation of Mrgprb4-lineage touch neurons is rewarding
• Mrgprb4-lineage touch neurons are required for female sexual receptivity
• Mrgprb4-lineage touch neurons engage dopaminergic neurons during social behavior
Pleasurable touch is paramount during social behavior, including sexual encounters. However, the identity and precise role of sensory neurons that transduce sexual touch remain unknown. A population of sensory neurons labeled by developmental expression of the G protein-coupled receptor Mrgprb4 detects mechanical stimulation in mice. Here, we study the social relevance of Mrgprb4-lineage neurons and reveal that these neurons are required for sexual receptivity and sufficient to induce dopamine release in the brain. Even in social isolation, optogenetic stimulation of Mrgprb4-lineage neurons through the back skin is sufficient to induce a conditioned place preference and a striking dorsiflexion resembling the lordotic copulatory posture. In the absence of Mrgprb4-lineage neurons, female mice no longer find male mounts rewarding: sexual receptivity is supplanted by aggression and a coincident decline in dopamine release in the nucleus accumbens. Together, these findings establish that Mrgprb4-lineage neurons initiate a skin-to-brain circuit encoding the rewarding quality of social touch.

Monday, February 13, 2023

An fMRI marker of drug and food craving

Koban et al. identify an fMRI-based neural signature of craving that is common to both food and drugs, predicts self-reported craving, distinguishes drug users from non-users, and tracks the efficacy of a cognitive therapy technique to reduce craving:
Craving is a core feature of substance use disorders. It is a strong predictor of substance use and relapse and is linked to overeating, gambling, and other maladaptive behaviors. Craving is measured via self-report, which is limited by introspective access and sociocultural contexts. Neurobiological markers of craving are both needed and lacking, and it remains unclear whether craving for drugs and food involve similar mechanisms. Across three functional magnetic resonance imaging studies (n = 99), we used machine learning to identify a cross-validated neuromarker that predicts self-reported intensity of cue-induced drug and food craving (P < 0.0002). This pattern, which we term the Neurobiological Craving Signature (NCS), includes ventromedial prefrontal and cingulate cortices, ventral striatum, temporal/parietal association areas, mediodorsal thalamus and cerebellum. Importantly, NCS responses to drug versus food cues discriminate drug users versus non-users with 82% accuracy. The NCS is also modulated by a self-regulation strategy. Transfer between separate neuromarkers for drug and food craving suggests shared neurobiological mechanisms. Future studies can assess the discriminant and convergent validity of the NCS and test whether it responds to clinical interventions and predicts long-term clinical outcomes.

Wednesday, June 15, 2022

The brain signature of choosing to accept pain in exchange for future reward

From Coll et al.


We often willingly experience pain to reach a goal. However, potential pain can also prevent reckless action. How do we consider future pain when deciding on the best course of action? To date, the precise neural mechanisms underlying the valuation of future pain remain unknown. Using functional MRI, we derive a whole-brain signature of the value of future pain capable of predicting participants’ choices to accept pain in exchange for a reward. We show that this signature is characterized by a distributed pattern of activity with clear contributions from structures encoding reward and salience, notably the ventral and dorsal striatum. These findings highlight how the brain assigns value to future pain when choosing the best course of action.
Pain is a primary driver of action. We often must voluntarily accept pain to gain rewards. Conversely, we may sometimes forego potential rewards to avoid associated pain. In this study, we investigated how the brain represents the decision value of future pain. Participants (n = 57) performed an economic decision task, choosing to accept or reject offers combining various amounts of pain and money presented visually. Functional MRI (fMRI) was used to measure brain activity throughout the decision-making process. Using multivariate pattern analyses, we identified a distributed neural representation predicting the intensity of the potential future pain in each decision and participants’ decisions to accept or avoid pain. This neural representation of the decision value of future pain included negative weights located in areas related to the valuation of rewards and positive weights in regions associated with saliency, negative affect, executive control, and goal-directed action. We further compared this representation to future monetary rewards, physical pain, and aversive pictures and found that the representation of future pain overlaps with that of aversive pictures but is distinct from experienced pain. Altogether, the findings of this study provide insights on the valuation processes of future pain and have broad potential implications for our understanding of disorders characterized by difficulties in balancing potential threats and rewards.

Monday, January 17, 2022

Different circuits in the brain for reward seeking and novelty seeking.

Work by Ogasawara et al. is noted by Peter Stern.
Novelty seeking is a key feature of intelligent behavior and adaptive cognition. However, we know little about the circuits that regulate our attraction to novel objects for novelty’s sake. Ogasawara et al. discovered that a brain nucleus called the zona incerta was causally related to novelty seeking. A region in the anterior medial temporal lobe projected to the zona incerta and sent motivational signals required to control novelty seeking through the zona incerta circuit. A novelty-seeking task, in which monkeys were motivated by the receipt of novel objects, showed that this behavior was not regulated by the dopamine reward-seeking circuitry. This work provides evidence for a clear dissociation in the brain circuitry between reward seeking and novelty seeking.

Monday, April 12, 2021

Why does passion matter more in individualistic cultures?

Tsai does an interesting commentary  (open source) on work noted in MindBlog's recent post on an article by Li et al.  Some clips:

Our research finds that, because achieving independence requires increased arousal and action, cultures that foster these goals value high-arousal positive states like passion, excitement, and enthusiasm. In contrast, because achieving interdependence requires decreased arousal and action, cultures that foster these goals value low-arousal positive states like calm, peacefulness, and balance.
These ideals matter because people use them to judge their own feelings, and, perhaps even more importantly, to judge the feelings of others. For instance, because European Americans value excitement more than Hong Kong Chinese, they rate “excited” faces (with broad toothy smiles) as much friendlier and warmer than “calm” faces (with closed smiles), compared to Hong Kong Chinese. And, because European Americans perceive excited (vs. calm) faces as friendlier and warmer, they share more money with excited vs. calm partners in economic games (e.g., the Dictator Game), compared to East Asians.
Experiencing and expressing cultural ideals can have life-altering consequences in the real world. When deciding whom to lend to on a web-based microlending platform (, people from countries with an excitement ideal loaned more to borrowers who had “excited” smiles in their profile photos and less to borrowers who had “calm” smiles. In a business setting, when selecting an intern, European Americans viewed the “ideal applicant” as being more excited (vs. calm), and chose more excited (vs. calm) applicants than Hong Kong Chinese did. Even in health settings, European Americans chose excitement-focused physicians who promoted dynamic lifestyles (vs. calm-focused physicians who promoted relaxing lifestyles) more than Hong Kong Chinese did. Interestingly, European Americans also recalled and adhered to the recommendations of the excitement- versus calm-focused physician more than East Asian Americans did. These findings suggest that people may also be more receptive to the advice and feedback of people who express their cultural ideal. the context of a European American focus on passion, calm East Asian Americans are often inaccurately judged to be “cold” and “stoic” . This may explain why, compared to European Americans, East Asian Americans are less likely to be promoted to top leadership positions, a problem often described as “the Bamboo Ceiling”. But this might be avoided if teachers, employers, and other decision makers in individualistic cultures understood that in many cultures — as illustrated by the findings of Li et al. — passion matters less. Instead of passion, people are finding, following, and fueling calm, balance, and the other affective states that their cultures value more.

Friday, May 01, 2020

How do cognition-enhancing drugs work?

Westbrook et al. do experiments with drugs influencing dopamine levels that suggest that cognition-enhancing drugs may act at the motivational level rather than directly boosting cognition per se.
Stimulants such as methylphenidate are increasingly used for cognitive enhancement but precise mechanisms are unknown. We found that methylphenidate boosts willingness to expend cognitive effort by altering the benefit-to-cost ratio of cognitive work. Willingness to expend effort was greater for participants with higher striatal dopamine synthesis capacity, whereas methylphenidate and sulpiride, a selective D2 receptor antagonist, increased cognitive motivation more for participants with lower synthesis capacity. A sequential sampling model informed by momentary gaze revealed that decisions to expend effort are related to amplification of benefit-versus-cost information attended early in the decision process, whereas the effect of benefits is strengthened with higher synthesis capacity and by methylphenidate. These findings demonstrate that methylphenidate boosts the perceived benefits versus costs of cognitive effort by modulating striatal dopamine signaling.

Wednesday, January 01, 2020

Increased emotional reactivity in men with high hair testosterone concentrations.

As I was scanning the table of contents of the latest issue of the journal "Social Cognitive and Affective Neuroscience" the article whose abstract I pass on below jumped out at me. (This is because I feel more emotional and sexual when my androgen levels reach their highest point in a monthly cycle, with lower points in the cycle correlating with lower motivation and anhedonia.) From Klein et al.:
Testosterone has been linked to alterations in the activity of emotion neurocircuitry including amygdala, orbitofrontal cortex (OFC) and insula and diminished functional amygdala/prefrontal coupling. Such associations have only ever been studied using acute measures of testosterone, thus little is known about respective relationships with long-term testosterone secretion. Here, we examine associations between hair testosterone concentration (HTC), an index of long-term cumulative testosterone levels and neural reactivity during an emotional passive viewing task using functional magnetic resonance imaging (fMRI). Forty-six men viewed negative, positive and neutral pictures in the MRI. HTCs were assessed from 2 cm hair segments. The emotional paradigm elicited neural activation in the amygdala, insula and OFC. HTCs were associated with increased reactivity to negative pictures in the insula and increased reactivity to positive pictures in the OFC. We show an association of long-term testosterone levels with increased emotional reactivity in the brain. These results suggest a heightened emotional vigilance in individuals with high trait testosterone levels.

Thursday, February 23, 2017

Scientific curiosity counters politically motivated reasoning.

Jasny points to work by Kahan et al. (open source) showing that science curiosity (of the sort shown by MindBlog readers!) promotes open-minded engagement with information that is contrary to individuals’ political predispositions. Jasny's summary:
Knowledge does not always change biases, and people tend to absorb information that fits their prejudices. However, rather than studying scientific knowledge, Kahan et al. studied scientific curiosity—the tendency to look for and consume scientific information for pleasure. Two sets of subjects, including several thousand people, were given questions about their interests and activities. Reactions to documentaries and to news stories that contained surprising or unsurprising material were also tracked. The more scientifically curious people were (regardless of their politics), the less likely they were to show signs of politically motivated reasoning. People with higher curiosity ratings were more willing to look at surprising information that conflicted with their political tendencies than people with lower ratings.

Wednesday, December 14, 2016

Why does time fly when you’re having fun? Dopamine neurons…

Soares et al. find by observing timing behavior in mice that dopaminergic neurons control temporal judgments on a time scale of seconds.
Our sense of time is far from constant. For instance, time flies when we are having fun, and it slows to a trickle when we are bored. Midbrain dopamine neurons have been implicated in variable time estimation. However, a direct link between signals carried by dopamine neurons and temporal judgments is lacking. We measured and manipulated the activity of dopamine neurons as mice judged the duration of time intervals. We found that pharmacogenetic suppression of dopamine neurons decreased behavioral sensitivity to time and that dopamine neurons encoded information about trial-to-trial variability in time estimates. Last, we found that transient activation or inhibition of dopamine neurons was sufficient to slow down or speed up time estimation, respectively. Dopamine neuron activity thus reflects and can directly control the judgment of time.

Wednesday, November 23, 2016

The teenage brain and the pleasure of “likes”

Rabin points to work by Sherman et al. showing that positive feedback given to a teenager's post on social media ('likes') stimulates the same reward center in the brain activated by thoughts of sex, money or ice cream...
We investigated a unique way in which adolescent peer influence occurs on social media. We developed a novel functional MRI (fMRI) paradigm to simulate Instagram, a popular social photo-sharing tool, and measured adolescents' behavioral and neural responses to likes, a quantifiable form of social endorsement and potential source of peer influence. Adolescents underwent fMRI while viewing photos ostensibly submitted to Instagram. They were more likely to like photos depicted with many likes than photos with few likes; this finding showed the influence of virtual peer endorsement and held for both neutral photos and photos of risky behaviors (e.g., drinking, smoking). Viewing photos with many (compared with few) likes was associated with greater activity in neural regions implicated in reward processing, social cognition, imitation, and attention. Furthermore, when adolescents viewed risky photos (as opposed to neutral photos), activation in the cognitive-control network decreased. These findings highlight possible mechanisms underlying peer influence during adolescence.

Monday, November 21, 2016

Sex differences in brain regulation of aggression

Interesting work from Terranova et al., done with hamsters, and almost certainly applicable to us humans. Here is their summary of the significance of the study, and the abstract with more technical stuff:

There are profound sex differences in the expression of social behavior and in the incidence of many psychiatric disorders, and yet little is known about how the brain mechanisms underlying these phenomena differ in females and males. Here, we report that serotonin (5-HT) and arginine–vasopressin (AVP) act in opposite ways within the hypothalamus to regulate dominance and aggression in females and males. Dominance and aggression are promoted by 5-HT in females and by AVP in males. Because dominance and aggressiveness have been linked to the resistance to stress-related psychiatric disorders, these disorders may be more effectively treated with 5-HT–targeted drugs in females and AVP-targeted drugs in males.
There are profound sex differences in the incidence of many psychiatric disorders. Although these disorders are frequently linked to social stress and to deficits in social engagement, little is known about sex differences in the neural mechanisms that underlie these phenomena. Phenotypes characterized by dominance, competitive aggression, and active coping strategies appear to be more resilient to psychiatric disorders such as posttraumatic stress disorder (PTSD) compared with those characterized by subordinate status and the lack of aggressiveness. Here, we report that serotonin (5-HT) and arginine–vasopressin (AVP) act in opposite ways in the hypothalamus to regulate dominance and aggression in females and males. Hypothalamic injection of a 5-HT1a agonist stimulated aggression in female hamsters and inhibited aggression in males, whereas injection of AVP inhibited aggression in females and stimulated aggression in males. Striking sex differences were also identified in the neural mechanisms regulating dominance. Acquisition of dominance was associated with activation of 5-HT neurons within the dorsal raphe in females and activation of hypothalamic AVP neurons in males. These data strongly indicate that there are fundamental sex differences in the neural regulation of dominance and aggression. Further, because systemically administered fluoxetine increased aggression in females and substantially reduced aggression in males, there may be substantial gender differences in the clinical efficacy of commonly prescribed 5-HT–active drugs such as selective 5-HT reuptake inhibitors. These data suggest that the treatment of psychiatric disorders such as PTSD may be more effective with the use of 5-HT–targeted drugs in females and AVP-targeted drugs in males.

Tuesday, October 25, 2016

Issues or Identity? Cognitive foundations of voter choice.

This open source article in Trends in Cognitive Sciences by Jenki and Huette is worth a look. I pass on the summary and one figure.
Voter choice is one of the most important problems in political science. The most common models assume that voting is a rational choice based on policy positions (e.g., key issues) and nonpolicy information (e.g., social identity, personality). Though such models explain macroscopic features of elections, they also reveal important anomalies that have been resistant to explanation. We argue for a new approach that builds upon recent research in cognitive science and neuroscience; specifically, we contend that policy positions and social identities do not combine in merely an additive manner, but compete to determine voter preferences. This model not only explains several key anomalies in voter choice, but also suggests new directions for research in both political science and cognitive science.

Key Figure: Voter Choice Reflects a Competition between Policy and Identity
Building on recent work in neuroscience and cognitive science, we argue that voter choice can be modeled as a competition between policy and identity. Significant evidence now supports the idea that a domain-general neural system (including the ventromedial prefrontal cortex, shown at top left) tracks the values of economic outcomes (left column). Such values can enter into rational choice models, in economics as well as political science, as variables that are weighted according to their importance (i.e., decision weights, W). Yet, many decisions also involve tracking social information like how one's actions reinforce social categories relative to one's identity (e.g., community involvement, veteran status), a process for which social cognitive regions (e.g., the temporal-parietal junction, TPJ, shown at upper right) play a key role (right column). We develop a simple model in which policy variables and identity variables compete to determine voter choice. Policy variables provide utility according to the importance of the underlying issue; for example, a given voter might prioritize affordable healthcare and a strong national defense. Identity variables provide utility through the act of voting itself, such as by strengthening one's ties to a social group (e.g., pride in one's state) or by signaling one's civic responsibility (e.g., ‘I voted’). Whether policy or identity exerts a dominant influence on choice is determined by a single trade-off parameter (δ).

Wednesday, July 06, 2016

Why we become more cautious with age.

Rutledge et al. find that the decrease in risk-taking that occurs on aging may be related to dopamine-modulated changes in Pavlovian approach behavior, and not a reduction in the subjective value of incremental rewards as traditional models from economics and psychology would have claimed.

•Aging reduced risk taking for potential gains but not potential losses
•Computational models revealed that a Pavlovian influence of reward decreased with age
•Age-related dopamine decline can explain the decrease in Pavlovian biaseswhy we
The extent to which aging affects decision-making is controversial. Given the critical financial decisions that older adults face (e.g., managing retirement funds), changes in risk preferences are of particular importance. Although some studies have found that older individuals are more risk averse than younger ones, there are also conflicting results, and a recent meta-analysis found no evidence for a consistent change in risk taking across the lifespan. There has as yet been little examination of one potential substrate for age-related changes in decision-making, namely age-related decline in dopamine, a neuromodulator associated with risk-taking behavior. Here, we characterized choice preferences in a smartphone-based experiment (n = 25,189) in which participants chose between safe and risky options. The number of risky options chosen in trials with potential gains but not potential losses decreased gradually over the lifespan, a finding with potentially important economic consequences for an aging population. Using a novel approach-avoidance computational model, we found that a Pavlovian attraction to potential reward declined with age. This Pavlovian bias has been linked to dopamine, suggesting that age-related decline in this neuromodulator could lead to the observed decrease in risk taking.
(You might also check out this article on how monkeys, like humans, become less sociable with age.)

Thursday, June 30, 2016

Cognitive fatigue increases impulsivity.

Sort of makes sense..Blain et al. show that if you use your lateral prefrontal cortex (LPFC) for control process required for an extended intense workday, its function in resisting the temptation of immediate rewards is diminished, you're more likely to eat that late afternoon sugar roll. Their abstract:
The ability to exert self-control is key to social insertion and professional success. An influential literature in psychology has developed the theory that self-control relies on a limited common resource, so that fatigue effects might carry over from one task to the next. However, the biological nature of the putative limited resource and the existence of carry-over effects have been matters of considerable controversy. Here, we targeted the activity of the lateral prefrontal cortex (LPFC) as a common substrate for cognitive control, and we prolonged the time scale of fatigue induction by an order of magnitude. Participants performed executive control tasks known to recruit the LPFC (working memory and task-switching) over more than 6 h (an approximate workday). Fatigue effects were probed regularly by measuring impulsivity in intertemporal choices, i.e., the propensity to favor immediate rewards, which has been found to increase under LPFC inhibition. Behavioral data showed that choice impulsivity increased in a group of participants who performed hard versions of executive tasks but not in control groups who performed easy versions or enjoyed some leisure time. Functional MRI data acquired at the start, middle, and end of the day confirmed that enhancement of choice impulsivity was related to a specific decrease in the activity of an LPFC region (in the left middle frontal gyrus) that was recruited by both executive and choice tasks. Our findings demonstrate a concept of focused neural fatigue that might be naturally induced in real-life situations and have important repercussions on economic decisions.

Friday, April 15, 2016

Brain correlates of how the risk taking of others influences our own risk taking

From Suzuki et al., another upstairs/downstairs story. Risk is represented in the caudate nucleus (downstairs), the risk activity of others is represented in the dorsolateral prefrontal cortex (upstairs). The strength of the connections between these areas determines how susceptible our behavior is to influence by others.
Our attitude toward risk plays a crucial role in influencing our everyday decision-making. Despite its importance, little is known about how human risk-preference can be modulated by observing risky behavior in other agents at either the behavioral or the neural level. Using fMRI combined with computational modeling of behavioral data, we show that human risk-preference can be systematically altered by the act of observing and learning from others’ risk-related decisions. The contagion is driven specifically by brain regions involved in the assessment of risk: the behavioral shift is implemented via a neural representation of risk in the caudate nucleus, whereas the representations of other decision-related variables such as expected value are not affected. Furthermore, we uncover neural computations underlying learning about others’ risk-preferences and describe how these signals interact with the neural representation of risk in the caudate. Updating of the belief about others’ preferences is associated with neural activity in the dorsolateral prefrontal cortex (dlPFC). Functional coupling between the dlPFC and the caudate correlates with the degree of susceptibility to the contagion effect, suggesting that a frontal–subcortical loop, the so-called dorsolateral prefrontal–striatal circuit, underlies the modulation of risk-preference. Taken together, these findings provide a mechanistic account for how observation of others’ risky behavior can modulate an individual’s own risk-preference.

Tuesday, March 15, 2016

Our brains remember the good stuff.

Anderson et al. show how our brains are attracted to items that have pleased us in the past, even if they are no longer relevant. People in a study were asked to look at a computer screen filled with colored objects and find the red and green ones, They received a small amount of money for each red or green object found. On the next day, the subjects were asked to find certain shapes on the screen, the color being irrelevant. Even so, when a red object appeared it captured attention, and PET brain imaging showed dopamine release in the ventral striatum, which plays a role in reward learning. Here is their technical abstract:

•We examined the neural correlates of value-based attention using PET
•Previously reward-associated stimuli involuntary captured attention as distractors
•Such attentional capture was predicted by dopamine release in the dorsal striatum
•Our findings elucidate the neurochemical basis of value-based distraction

Reward learning gives rise to strong attentional biases. Stimuli previously associated with reward automatically capture visual attention regardless of intention. Dopamine signaling within the ventral striatum plays an important role in reward learning, representing the expected reward initiated by a cue. How dopamine and the striatum may be involved in maintaining behaviors that have been shaped by reward learning, even after reward expectancies have changed, is less well understood. Nonspecific measures of brain activity have implicated the striatum in value-based attention. However, the neurochemical mechanisms underlying the attentional priority of learned reward cues remain unexplored. Here, we investigated the contribution of dopamine to value-based attention using positron emission tomography (PET) with [11C]raclopride. We show that, in the explicit absence of reward, the magnitude of attentional capture by previously reward-associated but currently task-irrelevant distractors is correlated across individuals with changes in available D2/D3 dopamine receptors (presumably due to intrasynaptic dopamine) linked to distractor processing within the right caudate and posterior putamen. Our findings provide direct evidence linking dopamine signaling within the striatum to the involuntary orienting of attention, and specifically to the attention-grabbing quality of learned reward cues. These findings also shed light on the neurochemical basis of individual susceptibility to value-driven attentional capture, which is known to play a role in addiction. More broadly, the present study highlights the value and feasibility of using PET to relate changes in the release of a neurotransmitter to learning-dependent changes in healthy adults.

Wednesday, October 07, 2015

Methionine, an amino acid, enhances recovery from cocaine addiction.

Wright et al. use a mouse model to show that the common amino acid methionine - which can serve as a methyl group donor for the DNA methylation that regulates neural functions associated with learning, memory, and synaptic plasticity - can reduce addictive like behaviors such as drug seeking, and block a cocaine-induced marker of neuronal activation after reinstatement in the nucleus accumbens and the medial prefrontal cortex, two brain regions responsible for drug seeking and relapse. Here is the technical abstract:
Epigenetic mechanisms, such as histone modifications, regulate responsiveness to drugs of abuse, such as cocaine, but relatively little is known about the regulation of addictive-like behaviors by DNA methylation. To investigate the influence of DNA methylation on the locomotor-activating effects of cocaine and on drug-seeking behavior, rats receiving methyl supplementation via chronic L-methionine (MET) underwent either a sensitization regimen of intermittent cocaine injections or intravenous self-administration of cocaine, followed by cue-induced and drug-primed reinstatement. MET blocked sensitization to the locomotor-activating effects of cocaine and attenuated drug-primed reinstatement, with no effect on cue-induced reinstatement or sucrose self-administration and reinstatement. Furthermore, upregulation of DNA methyltransferase 3a and 3b and global DNA hypomethylation were observed in the nucleus accumbens core (NAc), but not in the medial prefrontal cortex (mPFC), of cocaine-pretreated rats. Glutamatergic projections from the mPFC to the NAc are critically involved in the regulation of cocaine-primed reinstatement, and activation of both brain regions is seen in human addicts when reexposed to the drug. When compared with vehicle-pretreated rats, the immediate early gene c-Fos (a marker of neuronal activation) was upregulated in the NAc and mPFC of cocaine-pretreated rats after cocaine-primed reinstatement, and chronic MET treatment blocked its induction in both regions. Cocaine-induced c-Fos expression in the NAc was associated with reduced methylation at CpG dinucleotides in the c-Fos gene promoter, effects reversed by MET treatment. Overall, these data suggest that drug-seeking behaviors are, in part, attributable to a DNA methylation-dependent process, likely occurring at specific gene loci (e.g., c-Fos) in the reward pathway.

Monday, August 03, 2015

Brain correlates of the impatience of adolescents.

Teens and young adults show greater impulsivity than children and adults, reflected by increases in emergency room visits, accidents from drug or alcohol use, and increased mortality risk. van den Bos et al. relate this to developmental changes in the structural and functional connectivity of different frontostriatal tracts. Participants made choices between smaller, sooner (SS)  and larger, later (LL) monetary rewards in a delay-discounting task. Accepting a delay for a larger, later reward correlated with prefrontal inhibition of areas in the striatum:
Adolescence is a developmental period associated with an increase in impulsivity. Impulsivity is a multidimensional construct, and in this study we focus on one of the underlying components: impatience. Impatience can result from (i) disregard of future outcomes and/or (ii) oversensitivity to immediate rewards, but it is not known which of these evaluative processes underlie developmental changes. To distinguish between these two causes, we investigated developmental changes in the structural and functional connectivity of different frontostriatal tracts. We report that adolescents were more impatient on an intertemporal choice task and reported less future orientation, but not more present hedonism, than young adults. Developmental increases in structural connectivity strength in the right dorsolateral prefrontal tract were related to increased negative functional coupling with the striatum and an age-related decrease in discount rates. Our results suggest that mainly increased control, and the integration of future-oriented thought, drives the reduction in impatience across adolescence.
This clip from one of the figures shows the relevant brain areas:

By the way, on the subject of adolescents, I'll point to another piece of work by Baker et. al. on developmental changes in brain network hub connectivity in late adolescence

Tuesday, July 28, 2015

Dopamine and subjective well-being

Dolan and collaborators note influences of dopamine on emotion and decision making that are distinct from its known role in learning.:
The neuromodulator dopamine has a well established role in reporting appetitive prediction errors that are widely considered in terms of learning. However, across a wide variety of contexts, both phasic and tonic aspects of dopamine are likely to exert more immediate effects that have been less well characterized. Of particular interest is dopamine's influence on economic risk taking and on subjective well-being, a quantity known to be substantially affected by prediction errors resulting from the outcomes of risky choices. By boosting dopamine levels using levodopa (L-DOPA) as human subjects made economic decisions and repeatedly reported their momentary happiness, we show here an effect on both choices and happiness. Boosting dopamine levels increased the number of risky options chosen in trials involving potential gains but not trials involving potential losses. This effect could be better captured as increased Pavlovian approach in an approach–avoidance decision model than as a change in risk preferences within an established prospect theory model. Boosting dopamine also increased happiness resulting from some rewards. Our findings thus identify specific novel influences of dopamine on decision making and emotion that are distinct from its established role in learning.