Creatures of habit: disorders of compulsivity share common pattern and brain structure

In a study published in the journal Molecular Psychiatry and primarily funded by the Wellcome Trust, researchers show that people who are affected by disorders of compulsivity have lower grey matter volumes (in other words, fewer nerve cells) in the brain regions involved in keeping track of goals and rewards.

In our daily lives, we make decisions based either on habit or aimed at achieving a specific goal. For example, when driving home from work, we tend to follow habitual choices – our ‘autopilot’ mode – as we know the route well; however, if we move to a nearby street, we will initially follow a ‘goal-directed’ choice to find our way home – unless we slip into autopilot and revert to driving back to our old home. However, we cannot always control the decision-making process and make repeat choices even when we know they are bad for us – in many cases this will be relatively benign, such as being tempted by a cake whilst slimming, but extreme cases it can lead to disorders of compulsivity.

In order to understand what happens when our decision-making processes malfunction, a team of researchers led by the Department of Psychiatry at the University of Cambridge compared almost 150 individuals with disorders including methamphetamine dependence, obesity with binge eating and obsessive compulsive disorder, comparing them with healthy volunteers of the same age and gender.

Study participants first took part in a computerised task to test their ability to make choices aimed a receiving a reward over and above making compulsive choices. In a second study, the researchers compared brain scans taken using magnetic resonance imaging (MRI) in healthy individuals and a subset of obese individuals with or without binge eating disorder (a subtype of obesity in which the person binge eats large amounts of food rapidly).

The researchers demonstrated that all of the disorders were connected by a shift away from goal-directed behaviours towards automatic habitual choices. The MRI scans showed that obese subjects with binge eating disorder have lower grey matter volumes – a measure of the number of neurons – in the orbitofrontal cortex and striatum of the brain compared to those who do not binge eat; these brain regions are involved in keeping track of goals and rewards. Even in healthy volunteers, lower grey matter volumes were associated with a shift towards more habitual choices.

Dr Valerie Voon, principal investigator of the study, says: “Seemingly diverse choices – drug taking, eating quickly despite weight gain, and compulsive cleaning or checking – have an underlying common thread: rather that a person making a choice based on what they think will happen, their choice is automatic or habitual.

“Compulsive disorders can have a profoundly disabling effect of individuals. Now that we know what is going wrong with their decision making, we can look at developing treatments, for example using psychotherapy focused on forward planning or interventions such as medication which target the shift towards habitual choices.”

Fruit flies ‘think’ before they act

Oxford University neuroscientists have shown that fruit flies take longer to make more difficult decisions.

In experiments asking fruit flies to distinguish between ever closer concentrations of an odour, the researchers found that the flies don’t act instinctively or impulsively. Instead they appear to accumulate information before committing to a choice.

Gathering information before making a decision has been considered a sign of higher intelligence, like that shown by primates and humans.

'Freedom of action from automatic impulses is considered a hallmark of cognition or intelligence,' says Professor Gero Miesenböck, in whose laboratory the new research was performed. 'What our findings show is that fruit flies have a surprising mental capacity that has previously been unrecognised.'

The researchers also showed that the gene FoxP, active in a small set of around 200 neurons, is involved in the decision-making process in the fruit fly brain.

The team reports its findings in the journal Science. The group was funded by the Wellcome Trust, the Gatsby Charitable Foundation, the US National Institutes of Health and the Oxford Martin School.

The researchers observed Drosophila fruit flies make a choice between two concentrations of an odour presented to them from opposite ends of a narrow chamber, having been trained to avoid one concentration.

When the odour concentrations were very different and easy to tell apart, the flies made quick decisions and almost always moved to the correct end of the chamber.

When the odour concentrations were very close and difficult to distinguish, the flies took much longer to make a decision, and they made more mistakes.

The researchers found that mathematical models developed to describe the mechanisms of decision making in humans and primates also matched the behaviour of the fruit flies.

The scientists discovered that fruit flies with mutations in a gene called FoxP took longer than normal flies to make decisions when odours were difficult to distinguish – they became indecisive.

The researchers tracked down the activity of the FoxP gene to a small cluster of around 200 neurons out of the 200,000 neurons in the brain of a fruit fly. This implicates these neurons in the evidence-accumulation process the flies use before committing to a decision.

Dr Shamik DasGupta, the lead author of the study, explains: ‘Before a decision is made, brain circuits collect information like a bucket collects water. Once the accumulated information has risen to a certain level, the decision is triggered. When FoxP is defective, either the flow of information into the bucket is reduced to a trickle, or the bucket has sprung a leak.’

Fruit flies have one FoxP gene, while humans have four related FoxP genes. Human FoxP1 and FoxP2 have previously been associated with language and cognitive development. The genes have also been linked to the ability to learn fine movement sequences, such as playing the piano.

'We don't know why this gene pops up in such diverse mental processes as language, decision-making and motor learning,' says Professor Miesenböck. However, he speculates: 'One feature common to all of these processes is that they unfold over time. FoxP may be important for wiring the capacity to produce and process temporal sequences in the brain.'

Professor Miesenböck adds: ‘FoxP is not a “language gene”, a “decision-making gene”, even a “temporal-processing” or “intelligence” gene. Any such description would in all likelihood be wrong. What FoxP does give us is a tool to understand the brain circuits involved in these processes. It has already led us to a site in the brain that is important in decision-making.’

Primates and patience — the evolutionary roots of self control

A chimpanzee will wait more than two minutes to eat six grapes, but a black lemur would rather eat two grapes now than wait any longer than 15 seconds for a bigger serving.

It’s an echo of the dilemma human beings face with a long line at a posh restaurant. How long are they willing to wait for the five-star meal? Or do they head to a greasy spoon to eat sooner?

A paper published today in the scientific journal Proceedings of the Royal Society B explores the evolutionary reasons why some primate species wait for a bigger reward, while others are more likely to grab what they can get immediately.

"Natural selection has shaped levels of patience to deal with the types of problems that animals face in the wild," said author Jeffrey R. Stevens, a comparative psychologist at the University of Nebraska-Lincoln and the study’s lead author. "Those problems are species-specific, so levels of patience are also species-specific."

Studying 13 primate species, from massive gorillas to tiny marmosets, Stevens compared species’ characteristics with their capacity for “intertemporal choice.” That’s a scientific term for what some might call patience, self-control or delayed gratification.

He found the species with bigger body mass, bigger brains, longer lifespans and larger home ranges also tend to wait longer for a bigger reward.

Chimpanzees, which typically weigh about 85 pounds, live nearly 60 years and range about 35 square miles, waited for a reward for about two minutes, the longest of any of the primate species studied. Cotton-top tamarins, which weigh less than a pound and live about 23 years, waited about eight seconds before opting for a smaller, immediate reward.

The findings are based partially on experiments Stevens performed during the past ten years with lemurs, marmosets, tamarins, chimpanzees and bonobos at Harvard’s Department of Psychology and at the Berlin and Leipzig zoos in Germany. In those experiments, individual animals chose between a tray containing two grapes that they could eat immediately and a tray containing six grapes they could eat after waiting. The wait times were gradually increased until the animal reached an “indifference point” when it opted for the smaller, immediate reward instead of waiting.

Stevens combined those results with those of scientists who performed similar experiments with other primates. He scoured primate-research literature to gather data on the biological characteristics of each species.

In addition to characteristics related to body mass, Stevens analyzed but found no correlation with two other hypotheses for patience: cognitive ability and social complexity.

"In humans, the ability to wait for delayed rewards correlates with higher performance in cognitive measures such as IQ, academic success, standardized test scores and working memory capacity," he wrote. "The cognitive ability hypothesis predicts that species with higher levels of cognition should wait longer than those with lower levels."

But Stevens found no correlation between patience levels and an animal’s relative brain size compared to its body size, the measure he used to quantify cognitive ability.

Researchers also have argued that animals in complex social groups have reduced impulsivity and more patience to adapt to the social hierarchies of dominance and submission. But Stevens did not find correlations between species’ social group sizes and their patience levels.

Stevens said he believes metabolic rates may be the driving factor connecting patience with body mass and related physical characteristics. Smaller animals tend to have higher metabolic rates.

"You need fuel and you need it at a certain rate," he said. "The faster you need it, the shorter time you will wait."

Metabolic rates also may factor in human beings’ willingness to wait. Stevens said human decisions about food, their environment, their health care and even their finances all relate to future payoffs. The mental processes behind those decisions have not yet been well identified.

"To me, this offers us interesting avenues to start thinking about what factors might influence human patience," he said. "What does natural selection tell us about decision making? That applies to humans as well as to other animals."

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How the Brain Decides When to Work and When to Rest: Dissociation of Implicit-Reactive from Explicit-Predictive Computational Processes

A pervasive case of cost-benefit problem is how to allocate effort over time, i.e. deciding when to work and when to rest. An economic decision perspective would suggest that duration of effort is determined beforehand, depending on expected costs and benefits. However, the literature on exercise performance emphasizes that decisions are made on the fly, depending on physiological variables. Here, we propose and validate a general model of effort allocation that integrates these two views. In this model, a single variable, termed cost evidence, accumulates during effort and dissipates during rest, triggering effort cessation and resumption when reaching bounds. We assumed that such a basic mechanism could explain implicit adaptation, whereas the latent parameters (slopes and bounds) could be amenable to explicit anticipation. A series of behavioral experiments manipulating effort duration and difficulty was conducted in a total of 121 healthy humans to dissociate implicit-reactive from explicit-predictive computations. Results show 1) that effort and rest durations are adapted on the fly to variations in cost-evidence level, 2) that the cost-evidence fluctuations driving the behavior do not match explicit ratings of exhaustion, and 3) that actual difficulty impacts effort duration whereas expected difficulty impacts rest duration. Taken together, our findings suggest that cost evidence is implicitly monitored online, with an accumulation rate proportional to actual task difficulty. In contrast, cost-evidence bounds and dissipation rate might be adjusted in anticipation, depending on explicit task difficulty.

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The Influence of Spatiotemporal Structure of Noisy Stimuli in Decision Making

Decision making is a process of utmost importance in our daily lives, the study of which has been receiving notable attention for decades. Nevertheless, the neural mechanisms underlying decision making are still not fully understood. Computational modeling has revealed itself as a valuable asset to address some of the fundamental questions. Biophysically plausible models, in particular, are useful in bridging the different levels of description that experimental studies provide, from the neural spiking activity recorded at the cellular level to the performance reported at the behavioral level. In this article, we have reviewed some of the recent progress made in the understanding of the neural mechanisms that underlie decision making. We have performed a critical evaluation of the available results and address, from a computational perspective, aspects of both experimentation and modeling that so far have eluded comprehension. To guide the discussion, we have selected a central theme which revolves around the following question: how does the spatiotemporal structure of sensory stimuli affect the perceptual decision-making process? This question is a timely one as several issues that still remain unresolved stem from this central theme. These include: (i) the role of spatiotemporal input fluctuations in perceptual decision making, (ii) how to extend the current results and models derived from two-alternative choice studies to scenarios with multiple competing evidences, and (iii) to establish whether different types of spatiotemporal input fluctuations affect decision-making outcomes in distinctive ways. And although we have restricted our discussion mostly to visual decisions, our main conclusions are arguably generalizable; hence, their possible extension to other sensory modalities is one of the points in our discussion.

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Brain scans link concern for justice with reason, not emotion

People who care about justice are swayed more by reason than emotion, according to new brain scan research from the Department of Psychology and Center for Cognitive and Social Neuroscience.

Psychologists have found that some individuals react more strongly than others to situations that invoke a sense of justice—for example, seeing a person being treated unfairly or mercifully. The new study used brain scans to analyze the thought processes of people with high “justice sensitivity.”

“We were interested to examine how individual differences about justice and fairness are represented in the brain to better understand the contribution of emotion and cognition in moral judgment,” explained lead author Jean Decety, the Irving B. Harris Professor of Psychology and Psychiatry.    

Using a functional magnetic resonance imaging (fMRI) brain-scanning device, the team studied what happened in the participants’ brains as they judged videos depicting behavior that was morally good or bad. For example, they saw a person put money in a beggar’s cup or kick the beggar’s cup away. The participants were asked to rate on a scale how much they would blame or praise the actor seen in the video. People in the study also completed questionnaires that assessed cognitive and emotional empathy, as well as their justice sensitivity.

As expected, study participants who scored high on the justice sensitivity questionnaire assigned significantly more blame when they were evaluating scenes of harm, Decety said. They also registered more praise for scenes showing a person helping another individual.

But the brain imaging also yielded surprises. During the behavior-evaluation exercise, people with high justice sensitivity showed more activity than average participants in parts of the brain associated with higher-order cognition. Brain areas commonly linked with emotional processing were not affected.

The conclusion was clear, Decety said: “Individuals who are sensitive to justice and fairness do not seem to be emotionally driven. Rather, they are cognitively driven.” 

According to Decety, one implication is that the search for justice and the moral missions of human rights organizations and others do not come primarily from sentimental motivations, as they are often portrayed. Instead, that drive may have more to do with sophisticated analysis and mental calculation.

Decety adds that evaluating good actions elicited relatively high activity in the region of the brain involved in decision-making, motivation and rewards. This finding suggests that perhaps individuals make judgments about behavior based on how they process the reward value of good actions as compared to bad actions.

“Our results provide some of the first evidence for the role of justice sensitivity in enhancing neural processing of moral information in specific components of the brain network involved in moral judgment,” Decety said.

Understanding Binge Eating and Obesity

Researchers at the University of Cambridge have developed a novel method for evaluating the treatment of obesity-related food behavior. In an effort to further scientific understanding of the underlying problem, they have published the first peer-reviewed video of their technique in JoVE, the Journal of Visualized Experiments.

In the video, the authors demonstrate their means of objectively studying the drivers and mechanisms of overconsumption in humans. To do this, they assesses their subject’s willingness to work or pay for food, and they simultaneously track the corresponding brain activity using an MRI scanner.

“We present alternative ways of exploring attitudes to food by using indirect, objective measures—such as measuring the amount of energy exerted to obtain or view different foods, as well as determining brain responses during the anticipation and consumption of desirable foods,” said the lab’s principal investigator, Dr. Paul Fletcher. He and his colleagues use participant hand-grip intensity (referred to as “grip force” in the video) to calculate the motivation for a given food reward.

According to Dr. Fletcher, typical approaches for evaluating anti-obesity type drugs rely on more subjective methods—like having test subjects self-report their ratings of hunger and cravings.  

“When a person is asked how much they subjectively desire a food, they may feel pressured to give a ‘correct’ rather than a true answer,” said Dr. Fletcher, “[Our] grip force task may, under certain circumstances, present a more accurate reflection of what they really want.”

Dr. Fletcher and his colleagues brought the technique to JoVE after using it in their earlier publication, “Food images engage subliminal motivation to seek food,” published in 2011. They decided to publish a video capturing the protocol “Because it offered the opportunity to demonstrate the methods more fully,” he said.

In the video, Dr. Fletcher expands on the purpose of publishing the method with JoVE. “Individuals new to the technique may struggle because there aren’t many examples of grip-force tasks published in the literature, and there are no full and clear descriptions of how to design and set up the tasks,” he said.

With rising concerns surrounding obesity, researchers can use the technique presented in the JoVE video to determine the efficacy of a potential emerging market in anti-obesity medicine.