Posts tagged reward system
Articles and news from the latest research reports.
Brain Activity Provides Evidence for Internal “Calorie Counter”
As you glance over a menu or peruse the shelves in a supermarket, you may be thinking about how each food will taste and whether it’s nutritious, or you may be trying to decide what you’re in the mood for. A new neuroimaging study suggests that while you’re thinking all these things, an internal calorie counter of sorts is also evaluating each food based on its caloric density.
The findings are published in Psychological Science, a journal of the Association for Psychological Science.
“Earlier studies found that children and adults tend to choose high-calorie food,” says study author Alain Dagher, neurologist at the Montreal Neurological Institute and Hospital. “The easy availability and low cost of high-calorie food has been blamed for the rise in obesity. Their consumption is largely governed by the anticipated effects of these foods, which are likely learned through experience.”
“Our study sought to determine how people’s awareness of caloric content influenced the brain areas known to be implicated in evaluating food options,” says Dagher. “We found that brain activity tracked the true caloric content of foods.”
For the study, 29 healthy participants were asked to examine pictures of 50 familiar foods. The participants rated how much they liked each food (on a scale from 1 to 20) and were asked to estimate the calorie content of each food. Surprisingly, they were poor at accurately judging the number of calories in the various foods, and yet, the amount participants were willing to bid on the food in a simulated auction matched up with the foods that actually had higher caloric content.
Results of functional brain scans acquired while participants looked at the food images showed that activity in the ventromedial prefrontal cortex, an area known to encode the value of stimuli and predict immediate consumption, was also correlated with the foods’ true caloric content.
Participants’ explicit ratings of how much they liked a food, on the other hand, were associated with activity in the insula, an area of the brain that has been linked to processing the sensory properties of food.
According to Dagher, understanding the reasons for people’s food choices could help to control the factors that lead to obesity, a condition that is linked to many health problems, including high blood pressure, heart disease, and Type 2 diabetes.
Nicotine withdrawal reduces response to rewards across species
Cigarette smoking is a leading cause of preventable death worldwide and is associated with approximately 440,000 deaths in the United States each year, according to the U.S. Centers for Disease Control and Prevention, but nearly 20 percent of the U.S. population continues to smoke cigarettes. While more than half of U.S. smokers try to quit every year, less than 10 percent are able to remain smoke-free, and relapse commonly occurs within 48 hours of smoking cessation. Learning about withdrawal and difficulty of quitting can lead to more effective treatments to help smokers quit.
In a first of its kind study on nicotine addiction, scientists measured a behavior that can be similarly quantified across species like humans and rats, the responses to rewards during nicotine withdrawal. Findings from this study were published online on Sept. 10, 2014 in JAMA Psychiatry.
Response to reward is the brain’s ability to derive and recognize pleasure from natural things such as food, money and sex. The reduced ability to respond to rewards is a behavioral process associated with depression in humans. In prior studies of nicotine withdrawal, investigators used very different behavioral measurements across humans and rats, limiting our understanding of this important brain reward system.
Using a translational behavioral approach, Michele Pergadia, Ph.D., associate professor of clinical biomedical science in the Charles E. Schmidt College of Medicine at Florida Atlantic University, who completed the human study while at Washington University School of Medicine, Andre Der-Avakian, Ph.D., who completed the rat study at the University of California San Diego (UCSD), and colleagues, including senior collaborators Athina Markou, Ph.D. at UCSD and Diego Pizzagalli, Ph.D. at Harvard Medical School, found that nicotine withdrawal similarly reduced reward responsiveness in human smokers - particularly those with a history of depression - as well as in nicotine-treated rats.
Pergadia, one of the lead authors, notes that replication of experimental results across species is a major step forward, because it allows for greater generalizability and a more reliable means for identifying behavioral and neurobiological mechanisms that explain the complicated behavior of nicotine withdrawal in humans addicted to tobacco.
"The fact that the effect was similar across species using this translational task not only provides us with a ready framework to proceed with additional research to better understand the mechanisms underlying withdrawal of nicotine, and potentially new treatment development, but it also makes us feel more confident that we are actually studying the same behavior in humans and rats as the studies move forward," said Pergadia.
Pergadia and colleagues plan to pursue future studies that will include a systematic study of depression vulnerability as it relates to reward sensitivity, the course of withdrawal-related reward deficits, including effects on relapse to smoking, and identification of processes in the brain that lead to these behaviors.
Pergadia emphasizes that the ultimate goal of this line of research is to improve treatments that manage nicotine withdrawal-related symptoms and thereby increase success during efforts to quit.
"Many smokers are struggling to quit, and there is a real need to develop new strategies to aid them in this process. Therapies targeting this reward dysfunction during withdrawal may prove to be useful," said Pergadia.
Eating is addictive
People can become addicted to eating for its own sake but not to consuming specific foods such as those high in sugar or fat, research suggests.
An international team of scientists has found no strong evidence for people being addicted to the chemical substances in certain foods.
The brain does not respond to nutrients in the same way as it does to addictive drugs such as heroin or cocaine, the researchers say.
Instead, people can develop a psychological compulsion to eat, driven by the positive feelings that the brain associates with eating.
"This is a behavioural disorder and could be categorised alongside conditions such as gambling addiction", say scientists at Edinburgh.
They add that the focus on tackling the problem of obesity should be moved from food itself towards the individual’s relationship with eating.
The study, which examined the scientific evidence for food addiction as a substance-based addiction, is published in Neuroscience & Biobehavioral Reviews.
The researchers also say that the current classification of mental disorders, which does not permit a formal diagnosis of eating addiction, could be redrawn.
However, more research would be needed to define a diagnosis, the scientists add.
They add that the focus on tackling the problem of obesity should be moved from food itself towards the individual’s relationship with eating.
(Source: ed.ac.uk)
Training Your Brain to Prefer Healthy Foods
It may be possible to train the brain to prefer healthy low-calorie foods over unhealthy higher-calorie foods, according to new research by scientists at the Jean Mayer USDA Human Nutrition Research Center on Aging (USDA HNRCA) at Tufts University and at Massachusetts General Hospital. Published online today in the journal Nutrition & Diabetes, a brain scan study in adult men and women suggests that it is possible to reverse the addictive power of unhealthy food while also increasing preference for healthy foods.
“We don’t start out in life loving French fries and hating, for example, whole wheat pasta,” said senior and co-corresponding author Susan B. Roberts, Ph.D., director of the Energy Metabolism Laboratory at the USDA HNRCA, who is also a professor at the Friedman School of Nutrition Science and Policy at Tufts University and an adjunct professor of psychiatry at Tufts University School of Medicine. “This conditioning happens over time in response to eating – repeatedly! - what is out there in the toxic food environment.”
Scientists have suspected that, once unhealthy food addiction circuits are established, they may be hard or impossible to reverse, subjecting people who have gained weight to a lifetime of unhealthy food cravings and temptation. To find out whether the brain can be re-trained to support healthy food choices, Roberts and colleagues studied the reward system in thirteen overweight and obese men and women, eight of whom were participants in a new weight loss program designed by Tufts University researchers and five who were in a control group and were not enrolled in the program.
Both groups underwent magnetic resonance imaging (MRI) brain scans at the beginning and end of a six-month period. Among those who participated in the weight loss program, the brain scans revealed changes in areas of the brain reward center associated with learning and addiction. After six months, this area had increased sensitivity to healthy, lower-calorie foods, indicating an increased reward and enjoyment of healthier food cues. The area also showed decreased sensitivity to the unhealthy higher-calorie foods.
“The weight loss program is specifically designed to change how people react to different foods, and our study shows those who participated in it had an increased desire for healthier foods along with a decreased preference for unhealthy foods, the combined effects of which are probably critical for sustainable weight control,” said co-author Sai Krupa Das, Ph.D., a scientist in the Energy Metabolism Laboratory at the USDA HNRCA and an assistant professor at the Friedman School. “To the best of our knowledge this is the first demonstration of this important switch.” The authors hypothesize that several features of the weight loss program were important, including behavior change education and high-fiber, low glycemic menu plans.
“Although other studies have shown that surgical procedures like gastric bypass surgery can decrease how much people enjoy food generally, this is not very satisfactory because it takes away food enjoyment generally rather than making healthier foods more appealing,” said first author and co-corresponding author Thilo Deckersbach, Ph.D., a psychologist at Massachusetts General Hospital. “We show here that it is possible to shift preferences from unhealthy food to healthy food without surgery, and that MRI is an important technique for exploring the brain’s role in food cues.”
“There is much more research to be done here, involving many more participants, long-term follow-up and investigating more areas of the brain,” Roberts added. “But we are very encouraged that, the weight loss program appears to change what foods are tempting to people.”
(Image caption: Whole brain functional connectivity between the nucleus accumbens (NAc) and other brain areas in response to cannabis cues (vs. neutral cues) in all participants)
Dependence Alters the Brain’s Response to Pot Paraphernalia
New research from The University of Texas at Dallas demonstrates that drug paraphernalia triggers the reward areas of the brain differently in dependent and non-dependent marijuana users.
The study, published July 1 in Drug and Alcohol Dependence, demonstrated that different areas of the brain activated when dependent and non-dependent users were exposed to drug-related cues.
The 2012 National Survey on Drug Use and Health shows marijuana is the most widely used illicit drug in the United States. According to a 2013 survey from the Pew Research Center, 48 percent of Americans ages 18 and older have tried marijuana. The National Institute on Drug Abuse says that 9 percent of daily users will become dependent on marijuana.
“We know that people have a hard time staying abstinent because seeing cues for the drug use triggers this intense desire to seek out the drugs,” said Dr. Francesca Filbey, lead author of the study and professor at the Center for BrainHealth in the School of Behavioral and Brain Sciences. “That’s a clinically validated phenomenon and behavioral studies have also shown this to be the case. What we didn’t know was what was driving those effects in the brain.”
To find this effect, Filbey and colleagues conducted brain-imaging scans, called functional magnetic resonance imaging (fMRI), on 71 participants who regularly used marijuana. Just more than half of those were classified as dependent users. While being scanned, the participants were given either a used marijuana pipe or a pencil of approximately the same size that they could see and feel.
A comparison of the images revealed that the nucleus accumbens, the reward region in the brain, was activated in all users in response to the pipe. However, the strengths of the connections with other areas differed between dependent and non-dependent users.
“We found that the reward network is actually being driven by other areas unrelated to reward, like the areas in memory and attention or emotion,” Filbey said.
Non-dependent users showed greater activations in the orbital frontal cortex and hippocampus, suggesting that memory and attention were connected to the activation of the reward network. Dependent users had greater activations in the amygdala and anterior cingulate gyrus, suggesting a more emotional connection.
Additionally, the areas of the brain activated resemble areas activated for other addictions, such as nicotine or cocaine, lending greater support to the addictiveness of marijuana.
These findings suggest that marijuana abuse intervention needs to cater more specifically to a user’s level of addiction.
"Clinicians treating people with problems with marijuana dependence should consider the different processes that trigger the reward response when determining possible pharmacological or behavioral interventions,” Filbey said.
The Biology of Addiction Risk Looks Like Addiction
Research suggests that people at increased risk for developing addiction share many of the same neurobiological signatures of people who have already developed addiction. This similarity is to be expected, as individuals with family members who have struggled with addiction are over-represented in the population of addicted people.
However, a generation of animal research supports the hypothesis that the addiction process changes the brain in ways that converge with the distinctive neurobiology of the heritable risk for addiction. In other words, the more one uses addictive substances, the more one’s brain acquires the profile of someone who has inherited a risk for addiction.
One such change is a reduction in striatal dopamine release. Dopamine is a key brain chemical messenger involved in reward-related behaviors. Disturbances in dopamine signaling appear to contribute to reward processing that biases people to seek drug-like rewards and to develop drug-taking habits.
In the current issue of Biological Psychiatry, researchers at McGill University report that individuals at high risk for addiction show the same reduced dopamine response often observed in addicted individuals, identifying a new link between addiction risk and addiction in humans.
Dr. Marco Leyton and his colleagues recruited young adults, aged 18 to 25, who were classified into three groups: 1) a high-risk group of occasional stimulant users with an extensive family history of substance abuse; 2) a comparison group of occasional stimulant users with no family history; and 3) a second comparison group of individuals with no history of stimulant use and no known risk factors for addiction. Volunteers underwent a positron emission tomography (PET) scan involving the administration of amphetamine, which enabled the researchers to measure their dopamine response.
The authors found that the high-risk group of non-dependent young adults with extensive family histories of addiction displayed markedly reduced dopamine responses in comparison with both stimulant-naïve subjects and non-dependent users with no family history.
“This interesting new parallel between addiction risk and addiction may help to focus our attention on reward-related processes that contribute to the development of addiction, perhaps informing prevention strategies,” said Dr. John Krystal, Editor of Biological Psychiatry.
Leyton, a Professor at McGill University, said, “Young adults at risk of addictions have a strikingly disturbed brain dopamine reward system response when they are administered amphetamine. Past drug use seemed to aggravate the dopamine response also but this was not a sufficient explanation. Instead, the disturbance may be a heritable biological marker that could identify those at highest risk.”
This finding suggests that there are common brain mechanisms that promote the use of addictive substances in vulnerable people and in people who have long-standing habitual substance use.
Better understanding this biology may help to advance our understanding of how people develop addiction problems, as well as providing hints related to biological mechanisms that might be targeted for prevention and treatment.
(Source: elsevier.com)
Neural reward response may demonstrate why quitting smoking is harder for some
For some cigarette smokers, strategies to aid quitting work well, while for many others no method seems to work. Researchers have now identified an aspect of brain activity that helps to predict the effectiveness of a reward-based strategy as motivation to quit smoking.
The researchers observed the brains of nicotine-deprived smokers with functional magnetic resonance imaging (fMRI) and found that those who exhibited the weakest response to rewards were also the least willing to refrain from smoking, even when offered money to do so.
"We believe that our findings may help to explain why some smokers find it so difficult to quit smoking," said Stephen J. Wilson, assistant professor of psychology, Penn State. "Namely, potential sources of reinforcement for giving up smoking — for example, the prospect of saving money or improving health — may hold less value for some individuals and, accordingly, have less impact on their behavior."
The researchers recruited 44 smokers to examine striatal response to monetary reward in those expecting to smoke and in those who were not, and the subsequent willingness of the smokers to forego a cigarette in an effort to earn more money.
"The striatum is part of the so-called reward system in the brain," said Wilson. "It is the area of the brain that is important for motivation and goal-directed behavior — functions highly relevant to addiction."
The participants, who were between the ages of 18 and 45, all reported that they smoked at least 10 cigarettes per day for the past 12 months. They were instructed to abstain from smoking and from using any products containing nicotine for 12 hours prior to arriving for the experiment.
Each participant spent time in an fMRI scanner while playing a card-guessing game with the potential to win money. The participants were informed that they would have to wait approximately two hours, until the experiment was over, to smoke a cigarette. Partway through the card-guessing task, half of the participants were informed that there had been a mistake, and they would be allowed to smoke during a 50-minute break that would occur in another 16 minutes.
However, when the time came for the cigarette break, the participant was told that for every 5 minutes he or she did not smoke, he or she would receive $1 — with the potential to earn up to $10.
Wilson and his colleagues reported in a recent issue of Cognitive, Affective and Behavioral Neuroscience that they found that smokers who could not resist the temptation to smoke also showed weaker responses in the ventral striatum when offered monetary rewards while in the fMRI.
"Our results suggest that it may be possible to identify individuals prospectively by measuring how their brains respond to rewards, an observation that has significant conceptual and clinical implications," said Wilson. "For example, particularly ‘at-risk’ smokers could potentially be identified prior to a quit attempt and be provided with special interventions designed to increase their chances for success."
Researchers Decode How the Brain Miswires, Possibly Causing ADHD
Neuroscientists at Mayo Clinic in Florida and at Aarhus University in Denmark have shed light on why neurons in the brain’s reward system can be miswired, potentially contributing to disorders such as attention deficit hyperactivity disorder (ADHD).
They say findings from their study, published online today in Neuron, may increase the understanding of underlying causes of ADHD, potentially facilitating the development of more individualized treatment strategies.
The scientists looked at dopaminergic neurons, which regulate pleasure, motivation, reward, and cognition, and have been implicated in development of ADHD.
They uncovered a receptor system that is critical, during embryonic development, for correct wiring of the dopaminergic brain area. But they also discovered that after brain maturation, a cut in the same receptor, SorCS2, produces a two-chain receptor that induces cell death following damage to the peripheral nervous system.
The researchers report that the SorCS2 receptor functions as a molecular switch between apparently opposing effects in proBDNF. ProBDNF is a neuronal growth factor that helps select cells that are most beneficial to the nervous system, while eliminating those that are less favorable in order to create a finely tuned neuronal network.
They found that some cells in mice deficient in SorCS2 are unresponsive to proBDNF and have dysfunctional contacts between dopaminergic neurons.
“This miswiring of dopaminergic neurons in mice results in hyperactivity and attention deficits,” says the study’s senior investigator, Anders Nykjaer, M.D., Ph.D., a neuroscientist at Mayo Clinic in Florida and at Aarhus University in Denmark.
“A number of studies have reported that ADHD patients commonly exhibit miswiring in this brain area, accompanied by altered dopaminergic function. We may now have an explanation as to why ADHD risk genes have been linked to regulation of neuronal growth,” he says.
“SorCS2 is produced as a single-chain protein — one long row of amino acids — but it can be cut into two chains to perform a different function. While the single-chain receptor is essential to tell the neuron that it is time to stop growing, the two-chain form tells cells that support neurons in the developing peripheral nervous system to die when they should,” says Dr. Nykjaer.
Unfortunately, if damage occurs to a nerve in the peripheral nervous system, these cells that wrap around and nourish the neurons will die, preventing efficient regeneration, he says. “Our finding suggests that it may be possible to develop drug therapy to prevent this deadly cut of SorCS2 and treat acute nerve injury,” Dr. Nykjaer says.
(Source: newswise.com)
Does porn affect the brain? Scientists urge more study
Researchers found less grey matter in the brains of men who watched large amounts of sexually explicit material, according to a new study.
The research, which appeared Wednesday in the journal JAMA Psychiatry, could not determine if porn actually caused the brain to shrink however, and the authors called for additional study on the topic.
"Future studies should investigate the effects of pornography longitudinally or expose naive participants to pornography and investigate the causal effects over time," said researchers at the Max Planck Institute for Human Development in Berlin, Germany.
‘Free choice’ in primates can be altered through brain stimulation
When electrical pulses are applied to the ventral tegmental area of their brain, macaques presented with two images change their preference from one image to the other. The study by researchers Wim Vanduffel and John Arsenault (KU Leuven and Massachusetts General Hospital) is the first to confirm a causal link between activity in the ventral tegmental area and choice behaviour in primates.
The ventral tegmental area is located in the midbrain and helps regulate learning and reinforcement in the brain’s reward system. It produces dopamine, a neurotransmitter that plays an important role in positive feelings, such as receiving a reward. “In this way, this small area of the brain provides learning signals,” explains Professor Vanduffel. “If a reward is larger or smaller than expected, behavior is reinforced or discouraged accordingly.”
Causal link
This effect can be artificially induced: “In one experiment, we allowed macaques to choose multiple times between two images – a star or a ball, for example. This told us which of the two visual stimuli they tended to naturally prefer. In a second experiment, we stimulated the ventral tegmental area with mild electrical currents whenever they chose the initially nonpreferred image. This quickly changed their preference. We were also able to manipulate their altered preference back to the original favorite.”
The study, which will be published online in the journal Current Biology on 16 June, is the first to confirm a causal link between activity in the ventral tegmental area and choice behaviour in primates. “In scans we found that electrically stimulating this tiny brain area activated the brain’s entire reward system, just as it does spontaneously when a reward is received. This has important implications for research into disorders relating to the brain’s reward network, such as addiction or learning disabilities.”
Could this method be used in the future to manipulate our choices? “Theoretically, yes. But the ventral tegmental area is very deep in the brain. At this point, stimulating it can only be done invasively, by surgically placing electrodes – just as is currently done for deep brain stimulation to treat Parkinson’s or depression. Once non-invasive methods – light or ultrasound, for example – can be applied with a sufficiently high level of precision, they could potentially be used for correcting defects in the reward system, such as addiction and learning disabilities.”