Recent Research Findings

Learning adjusts to the environment but sub-optimally

Value-based decision making often involves integration of reward outcomes over time, but this becomes considerably more challenging if reward assignments on alternative options are probabilistic and non-stationary. Despite the existence of various models for optimally integrating reward under uncertainty, the underlying neural mechanisms are still unknown. Here we propose that reward-dependent metaplasticity (RDMP) can provide a plausible mechanism for both integration of reward under uncertainty and estimation of uncertainty itself. We show that a model based on RDMP can robustly perform the probabilistic reversal learning task via dynamic adjustment of learning based on reward feedback, while changes in its activity signal unexpected uncertainty. The model predicts time-dependent and choice-specific learning rates that strongly depend on reward history. Key predictions from this model were confirmed with behavioral data from non-human primates. Overall, our results suggest that metaplasticity can provide a neural substrate for adaptive learning and choice under uncertainty.

Study: Teens' View of Fairness Shifts as Brain Develops

September 20, 2017 by Office of Public Affairs

Research links cortical thinning over time to the ability to consider others’ intentions.

When it comes to the concept of fairness, teenagers’ ability to consider the intentions of others appears to be linked to structural changes in the brain, according to a study led by Assistant Professor of Psychological and Brain Sciences Luke Chang.

The research found that cortical thinning of specific areas of the brain from youth into young adulthood corresponded to the transition from an emphasis on equality in all transitions to a more complex consideration of the intentions of others in exchanges. This developmental change in the social brain continued through late adolescence, the researchers said.

How to Tell if Someone is Really Listening to You

A recent study conducted by the Dartmouth Social Intelligence Laboratory led by principal investigator Associate Professor Thalia Wheatley was featured in an article in the Daily Mail (UK).  As the article describes, "using eye-tracking technology, researchers have found collective pupillary synchrony between speakers and listeners were greatest during emotional peaks of a narrative - and decreased as the story became less engaging."  Read more at the DailyMail.com.

Why ‘Don’t Even Start’ Doesn’t Work With Teenagers

Researcher David Bucci flips the neural switches to replicate an “adolescent brain.”

January 10, 2017 by Bill Platt
Originally published in the Dartmouth News.

As parents of a teenager can tell you, adolescents don’t always think about risks before they act, whether it is venturing onto thin ice on a dare or spending the weekend watching an entire Star Wars marathon before starting a project that’s due Monday.

For many years psychologists and researchers have observed this behavior and linked it to data showing that the part of the brain that regulates impulsivity—the prefrontal cortex—is not yet fully developed in adolescents, while the deeper reward-seeking part of the brain, called the nucleus accumbens, develops more rapidly, leaving teens with less control over impulses.

Now Dartmouth researchers have identified and altered the precise neural circuits that control reward-seeking impulses and risk-assessment controls, effectively flipping the switches to create an “adolescent brain” in adult rats.

Alda’s ‘Brains on Trial’ Tapped Dartmouth’s Expertise

Bill Platt

Neuroscience plays a starring role in a two-part series Brains on Trial With Alan Alda, airing on PBS Wednesday, September 11, and Wednesday, September 18, from 10 to 11 p.m., a project that Dartmouth Professor Thalia Wheatley, an expert in brain science and social intelligence, worked on as a consultant.

Brains on Trial centers on the trial of a fictional crime: a robbery staged in a convenience store. A teenager stands accused of the attempted murder of the store clerk’s wife, who was shot during the crime. While the crime is fictional, the trial is conducted before a real federal judge and argued by real practicing attorneys.

Familiar Faces (ScienceNews)

In a story about “super recognizers”—people who have an exceptional ability to remember faces—ScienceNews turns for comment to Dartmouth’s Bradley Duchaine.

Duchaine, an associate professor of psychological and brain sciences, and colleagues in England are studying super recognizers to understand how some people are able to recognize nearly everyone they’ve ever seen, the magazine writes. Knowledge gained from such studies may aid in police work and other fields that rely on identifying people by how they look, notes the magazine.

“By identifying strategies used by super recognizers, we may find ways to train others who have problems with face recognition, or help people who are in the normal range but have professional demands in which superior face recognition would be beneficial,” Duchaine tells ScienceNews.

Read the full story, published 8/23/13 by ScienceNews.

Scientists Identify an Off Switch for Bad Habits

What if the brain had a light switch that could be flipped to turn off a bad habit?

Research by Assistant Professor Kyle Smith, who joined the faculty of Dartmouth’s Department of Psychological and Brain Sciences last month, has found just that in lab rats. Smith and others have identified brain cells involved in habit formation and inhibition. Researchers introduced DNA for photosensitive molecules into the brain’s cortex to make specific neurons respond to light from a fiber optic implant. Then, by flashing a light on these key cells, researchers managed to abruptly halt habits and inhibit the formation of new habitual behaviors. 

Smith and his colleagues trained rats to run a maze for a reward. They then overtrained the animals so they ran the pattern even after the behavior brought negative results—in this case, food that tasted bad. So the rats continued the habit, in a sense, against their better judgment. It is not unlike a person continuing to bite his fingernails even though he wants to stop, Smith says.

Rare Disorder Leaves Woman Lost in Familiar Places

In a story about a rare disorder that makes it difficult for people to recognize even familiar places, NBC’s The Today Show interviews Dartmouth’s Jeffrey Taube, who studies the navigational processes used by rats.

Taube, a professor of psychological and brain sciences, says “the rat’s—and probably people’s—brain cells fire like a compass. There is a neuron that fires any time the rat heads north and another that fires when the rat heads south-southeast.”

When everything is working properly, he says, the brain constructs a map that allows us to find our way through familiar surroundings without needing directions.

“There’s a system that’s important for perceiving where you are, another for keeping track of where you are heading and another for keeping track of the distance you’ve moved,” he tells The Today Show. “Any one of these without the others won’t do you any good.”

Read the full story, published 5/13/13 by The Today Show.

Neuroscientist Says Humans Are Wired for Free Will

Dartmouth’s Peter Tse ’84, an associate professor of psychological and brain sciences, says he has identified a neurological basis for free will in the human brain, challenging a majority opinion that has dominated neuroscience for the last 40 years.

Measurements of human brain signals on the level of neurons and synapses have long shown that acts of will are preceded by a buildup of neural activity in the brain. These signals can begin up to seconds before a person is consciously aware of the exercise of volition, according to the weight of data, Tse explains.

Until now, neuroscientists have argued that because this buildup of signals comes before a person acts, or is even conscious of having decided to act, free will cannot exist, because it would require that a thought causes itself to exist before it exists.

“How can something cause its own physical basis? It is this ‘you can’t pick yourself up by your own bootstraps’ idea that has been the main argument against the possibility of free will,” Tse says.

How Music and Movement Communicate Emotion

Joe Blumberg

Music and movement reflect the rhythm of life, stirring human emotions in societies around the world. Even infants display signs of the interconnectedness of music and movement as they bounce up and down to musical rhythms. Music and movement might be characterized as two sides of the same coin—the coin being emotion.

Gaining an understanding of the connections between these behavioral expressions is a quest Dartmouth researchers have undertaken. The research team in Cambodia included (from left) Thalia Wheatley, Stanford graduate student Trent Walker (Khmer translator), Yam Pan (the commune village chief and translator from Khmer to Kreung—the tribal language), and Dartmouth graduate students Beau Sievers and Carolyn Parkinson. (Photo courtesy of Thalia Wheatley)