Posts Tagged ‘behavior’


Greater activation of neurons on one side of the superior colliculus versus the other signals the detection of a relevant event. Credit: James Herman, Ph.D., National Eye Institute

by Aswini Kanneganti

Perceptual choice behavior, taking action based on the information received from the senses is often described by mathematical models. Although the associated neural activity was interpreted in 2007, translating the simulated evidence to the complex biological process has been challenging. Additionally, identifying the exact code and the behavioral changes to subtle changes in the neural code had proven to be difficult to test.

Researchers at the National Eye Institute (NEI) have investigated the neurons in the superior colliculus (SC) as they have activity related to target probability and comprise an activity map of the visual field. Previous work published by the same team showed that SC neuronal activity correlates with behavior in a covert color-change detection task. So, the scientists hypothesized that SC neuronal activity would be ideal to test decision outcome when a relevant or irrelevant perturbation occurs. The findings were published today in the journal Nature Neuroscience. NEI is part of the National Institutes of Health.

In their new study, Krauzlis, Herman, and colleagues used an “accumulator threshold model” to study how neuronal activity in the superior colliculus relates to behavior. This model assumes that the information builds up over time until it hits a certain threshold, after that a person or animal makes a decision. Because individual neurons can slowly build up information in this way, Herman and Krauzlis elected to use neuronal signals (instead of the experimental stimulus) as the input for their behavior-prediction model. Two non-human primates were tested for their behavioral responses and neuronal firing patterns in response to a covert color-change detection task. The monkeys were trained to release the joystick in response to subtle saturation changes at a relevant (cued) location and ignore changes at an irrelevant (uncued) foil location.

The findings support the notion that neurons in the SC are critical players in allowing us to detect visual objects and events. This structure doesn’t help us recognize what the specific object or event is; instead, it’s the part of the brain that decides something is there at all. By comparing brain activity recorded from the right and left superior colliculi at the same time, the researchers were able to predict whether an animal saw an event. The study provides evidence that, if the difference in neuronal activity between the two sides reached a specific threshold (e.g., neurons in the right superior colliculus fired more strongly than the left), the monkey would release the lever, confirming visualization of the event. To further confirm this finding, the researchers perturbed the neural activity on one side by either inhibiting on increasing the neural tone, and the behavioral responses were altered.

“While we’ve known for a long time that the superior colliculus is involved in perception, we really wanted to know exactly how this part of the brain controls the perceptual choice, and find a way to describe that mechanism with a mathematical model,” said James Herman, Ph.D., lead author of the study.

“The superior colliculus plays a foundational role in our ability to process and detect events,” said Richard Krauzlis, Ph.D., principal investigator in the Laboratory of Sensorimotor Research at NEI and senior author of the study. “This new work not only shows that a specific population of neurons directly cause behavior but also that a commonly used mathematical model can predict behavior based on these neurons.”

One reason for using the color change stimulus, Krauzlis said, was that the superior colliculus doesn’t itself process this information. Instead, other parts of the brain process the changing color and transmit that information to the superior colliculus for a decision to be made. In essence, this simple differential threshold of neuronal activity in the superior colliculus triggers the animal to report the presence of something in the visual field.

“It’s surprising to discover that despite the sophisticated visual machinery that we have in the cerebral cortex, these evolutionarily older structures are still critical for the visual perception that we’re used to,” said Herman.

“For this sort of task, where you’re not asked to say exactly what was the thing, but you’re just saying, did it happen, then this activity in the superior colliculus seems to be both necessary and sufficient,” said Krauzlis.

While the model accurately predicted behavior based on activity in the superior colliculus, the pattern of activation of neurons in the superior colliculus and the signal threshold itself was unique to each monkey, meaning that each monkey had its behavioral signal code.

For more information on how this neural code is decoded, watch the video by Marlene Behrmann, Professor at Carnegie Mellon University.

https://www.labroots.com/trending/neuroscience/13378/behavior-predicting-neural-code-identified

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A new study from the University of Chicago found that people who report feeling lonely also say they sit or stand physically farther away from close friends and family. Their “personal space” for intimate partners is larger than those who report less loneliness, even when adjusted for marital status and other factors such as gender, anxiety and depression.

In two experiments, published Sept. 6 in PLOS ONE, the researchers surveyed nearly 600 U.S.-based men and women on how far they preferred to sit or stand near different groups of people, including friends and family, romantic partners and acquaintances. On average, loneliness doubles the odds of someone staying farther away from those in their closest circle of intimacy. (It had no effect on how far they preferred to stand from acquaintances or strangers).

“To our knowledge, this is the first direct evidence for a link between interpersonal distance preferences and loneliness,” said Elliot Layden, a UChicago graduate student and first author on the paper. “This finding may be important to consider in the context of loneliness interventions—such as client-therapist interactions and community programs seeking to combat loneliness.”

The effect persists even when scientists adjusted for how much social interaction the person experiences; for example, those who felt lonely despite high levels of social interaction still kept their distances.

“You can feel alone even in a crowd or in a marriage—loneliness is really a discrepancy between what you want and what you have,” said Stephanie Cacioppo, director of the Brain Dynamics Laboratory, assistant professor of psychiatry and behavioral neuroscience, and senior author on the paper.

The authors say this fits with the evolutionary model of loneliness, pioneered by Stephanie Cacioppo and her late husband, John Cacioppo, the Tiffany and Margaret Blake Distinguished Service Professor of Psychology at the University of Chicago and a co-author on the paper, who passed away earlier this year. The Cacioppos’ transformative work in this field connected feelings of loneliness to physical health outcomes, including sleep disturbances, inflammation and earlier death.

The evolutionary model suggests that even though loneliness might be expected to prompt people to move closer to others, it also increases an individual’s short-term self-preservation instincts, triggering an instinct to stay farther away. Previous Cacioppo studies using neuroimaging techniques have found evidence that lonelier individuals also exhibit heightened vigilance for social threats—such as social rejection or interpersonal hostility.

“This ‘survival mode’ means that even though a lonely person wants more social interaction, they may still unconsciously keep their distance,” Stephanie Cacioppo said. “The hope is that by bringing this to conscious attention, we can reduce the incidence of divorce as a byproduct of loneliness and increase meaningful connections among people.”

Cacioppo and her team are working to incorporate the finding into a program to reduce loneliness with the National Institutes of Health, she said. In further studies, she wants to explore gender differences in personal space; men are consistently found to prefer larger personal spaces than women.

https://medicalxpress.com/news/2018-09-lonely-people.html


Pinpoint stimulation of a cluster of nerve cells in the brains of mice encouraged timid responses to a perceived threat, whereas stimulation of an adjacent cluster induced boldness and courage.

Researchers at the Stanford University School of Medicine have identified two adjacent clusters of nerve cells in the brains of mice whose activity level upon sighting a visual threat spells the difference between a timid response and a bold or even fierce one.

Located smack-dab in the middle of the brain, these clusters, or nuclei, each send signals to a different area of the brain, igniting opposite behaviors in the face of a visual threat. By selectively altering the activation levels of the two nuclei, the investigators could dispose the mice to freeze or duck into a hiding space, or to aggressively stand their ground, when approached by a simulated predator.

People’s brains probably possess equivalent circuitry, said Andrew Huberman, PhD, associate professor of neurobiology and of ophthalmology. So, finding ways to noninvasively shift the balance between the signaling strengths of the two nuclei in advance of, or in the midst of, situations that people perceive as threatening may help people with excessive anxiety, phobias or post-traumatic stress disorder lead more normal lives.

“This opens the door to future work on how to shift us from paralysis and fear to being able to confront challenges in ways that make our lives better,” said Huberman, the senior author of a paper describing the experimental results. It was published online May 2 in Nature. Graduate student Lindsey Salay is the lead author.

Perilous life of a mouse
There are plenty of real threats in a mouse’s world, and the rodents have evolved to deal with those threats as best they can. For example, they’re innately afraid of aerial predators, such as a hawk or owl swooping down on them. When a mouse in an open field perceives a raptor overhead, it must make a split-second decision to either freeze, making it harder for the predator to detect; duck into a shelter, if one is available; or to run for its life.

To learn how brain activity changes in the face of such a visual threat, Salay simulated a looming predator’s approach using a scenario devised some years ago by neurobiologist Melis Yilmaz Balban, PhD, now a postdoctoral scholar in Huberman’s lab. It involves a chamber about the size of a 20-gallon fish tank, with a video screen covering most of its ceiling. This overhead screen can display an expanding black disc simulating a bird-of-prey’s aerial approach.

Looking for brain regions that were more active in mice exposed to this “looming predator” than in unexposed mice, Salay pinpointed a structure called the ventral midline thalamus, or vMT.

Salay mapped the inputs and outputs of the vMT and found that it receives sensory signals and inputs from regions of the brain that register internal brain states, such as arousal levels. But in contrast to the broad inputs the vMT receives, its output destination points were remarkably selective. The scientists traced these outputs to two main destinations: the basolateral amygdala and the medial prefrontal cortex. Previous work has tied the amygdala to the processing of threat detection and fear, and the medial prefrontal cortex is associated with high-level executive functions and anxiety.

Further inquiry revealed that the nerve tract leading to the basolateral amygdala emanates from a nerve-cell cluster in the vMT called the xiphoid nucleus. The tract that leads to the medial prefrontal cortex, the investigators learned, comes from a cluster called the nucleus reuniens, which snugly envelopes the xiphoid nucleus.

Next, the investigators selectively modified specific sets of nerve cells in mice’s brains so they could stimulate or inhibit signaling in these two nerve tracts. Exclusively stimulating xiphoid activity markedly increased mice’s propensity to freeze in place in the presence of a perceived aerial predator. Exclusively boosting activity in the tract running from the nucleus reuniens to the medial prefrontal cortex in mice exposed to the looming-predator stimulus radically increased a response seldom seen under similar conditions in the wild or in previous open-field experiments: The mice stood their ground, right out in the open, and rattled their tails, an action ordinarily associated with aggression in the species.

Thumping tails

This “courageous” behavior was unmistakable, and loud, Huberman said. “You could hear their tails thumping against the side of the chamber. It’s the mouse equivalent of slapping and beating your chest and saying, ‘OK, let’s fight!’” The mice in which the nucleus reuniens was stimulated also ran around more in the chamber’s open area, as opposed to simply running toward hiding places. But it wasn’t because nucleus reuniens stimulation put ants in their pants; in the absence of a simulated looming predator, the same mice just chilled out.

In another experiment, the researchers showed that stimulating mice’s nucleus reuniens for 30 seconds before displaying the “looming predator” induced the same increase in tail rattling and running around in the unprotected part of the chamber as did vMT stimulation executed concurrently with the display. This suggests, Huberman said, that stimulating nerve cells leading from the nucleus reunions to the prefrontal cortex induces a shift in the brain’s internal state, predisposing mice to act more boldly.

Another experiment pinpointed the likely nature of that internal-state shift: arousal of the autonomic nervous system, which kick-starts the fight, flight or freeze response. Stimulating either the vMT as a whole or just the nucleus reuniens increased the mice’s pupil diameter — a good proxy of autonomic arousal.

On repeated exposures to the looming-predator mockup, the mice became habituated. Their spontaneous vMT firing diminished, as did their behavioral responses. This correlates with lowered autonomic arousal levels.

Human brains harbor a structure equivalent to the vMT, Huberman said. He speculated that in people with phobias, constant anxiety or PTSD, malfunctioning circuitry or traumatic episodes may prevent vMT signaling from dropping off with repeated exposure to a stress-inducing situation. In other experiments, his group is now exploring the efficacy of techniques, such as deep breathing and relaxation of visual fixation, in adjusting the arousal states of people suffering from these problems. The thinking is that reducing vMT signaling in such individuals, or altering the balance of signaling strength from their human equivalents of the xiphoid nucleus and nucleus reuniens may increase their flexibility in coping with stress.

Reference:
Salay, L. D., Ishiko, N., & Huberman, A. D. (2018). A midline thalamic circuit determines reactions to visual threat. Nature. doi:10.1038/s41586-018-0078-2

http://med.stanford.edu/news/all-news/2018/05/scientists-find-fear-courage-switches-in-brain.html

By Beckie Strum

Science says it’s OK to pay your children to eat their fruits and vegetables.

The strategy not only works in the short term, but can create healthful eating habits in children in the long run if the little bribe is carried out consistently for several weeks, according to a study published earlier this year in the Journal of Health Economics.

“As a parent, imagine that there’s something to do that might be worth my effort, and I get the long-term benefit,” says Joseph Price, associate professor of economics at Brigham Young University. He co-wrote the paper with George Loewenstein, professor of economics and psychology at Carnegie Mellon University, and Kevin Volpp, professor of medicine at the University of Pennsylvania.

For a year and a half, the researchers carried out a study of 8,000 children in first through sixth grade at 40 elementary schools to test whether short-run incentives could create better, and lasting, eating habits in children.

At lunchtime, students who ate at least one serving of fruit or vegetable, such as an apple, fresh peaches, pineapple, side salad or a banana, received a 25-cent token that could be redeemed at the school’s store, carnival or book fair.

The researchers saw an immediate spike in consumption, Dr. Price says. “These small incentives produced a dramatic increase in fruit and vegetable consumption during the incentive period,” the researchers wrote. “This change in behavior was sustained.”

Two months after the incentives ended, many more students than before the program started were still eating a fruit or vegetable at lunch. For schools that provided the 25-cent incentive for three weeks, 21% more children were eating at least one serving of fruit or vegetable at lunch than before.

The effect was even greater for schools that implemented the program for five weeks, which led to a 44% increase in consumption two months out.

Positive peer pressure played a role in getting the children to adopt and then stick to the program. A health economist from Cornell University has even suggested that one way to establish the social norm even quicker was by making sure the “cool kids” were the early adopters of the behavior, Dr. Price says.

The researchers also believe that the more often students ate fruits and vegetables, the more they learned to like them. Dr. Price draws an example from his personal life, saying he offered his son an incentive to practice hitting a baseball. The more his son practiced, the better he got and the more he liked playing, Dr. Price says.

Parents or schools could also try nonmonetary rewards, such as extended recess or gym class, Dr. Price says.

http://www.wsj.com/articles/heres-why-you-should-pay-your-children-to-eat-their-vegetables-1476670380