Posts Tagged ‘free will’


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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New research suggests it’s possible to detect when our brain is making a decision and nudge it to make the healthier choice.

In recording moment-to-moment deliberations by macaque monkeys over which option is likely to yield the most fruit juice, scientists have captured the dynamics of decision-making down to millisecond changes in neurons in the brain’s orbitofrontal cortex.

“If we can measure a decision in real time, we can potentially also manipulate it,” says senior author Jonathan Wallis, a neuroscientist and professor of psychology at the University of California, Berkeley. “For example, a device could be created that detects when an addict is about to choose a drug and instead bias their brain activity towards a healthier choice.”

Located behind the eyes, the orbitofrontal cortex plays a key role in decision-making and, when damaged, can lead to poor choices and impulsivity.

While previous studies have linked activity in the orbitofrontal cortex to making final decisions, this is the first to track the neural changes that occur during deliberations between different options.

“We can now see a decision unfold in real time and make predictions about choices,” Wallis says.

Measuring the signals from electrodes implanted in the monkeys’ brains, researchers tracked the primates’ neural activity as they weighed the pros and cons of images that delivered different amounts of juice.

A computational algorithm tracked the monkeys’ orbitofrontal activity as they looked from one image to another, determining which picture would yield the greater reward. The shifting brain patterns enabled researchers to predict which image the monkey would settle on.

For the experiment, they presented a monkey with a series of four different images of abstract shapes, each of which delivered to the monkey a different amount of juice. They used a pattern-recognition algorithm known as linear discriminant analysis to identify, from the pattern of neural activity, which picture the monkey was looking at.

Next, they presented the monkey with two of those same images, and watched the neural patterns switch back and forth to the point where the researchers could predict which image the monkey would choose based on the length of time that the monkey stared at the picture.

The more the monkey needed to think about the options, particularly when there was not much difference between the amounts of juice offered, the more the neural patterns would switch back and forth.

“Now that we can see when the brain is considering a particular choice, we could potentially use that signal to electrically stimulate the neural circuits involved in the decision and change the final choice,” Wallis says.

Erin Rich, a researcher at the Helen Wills Neuroscience Institute, is lead author of the study published in the journal Nature Neuroscience. The National Institute on Drug Abuse and the National Institute of Mental Health funded the work.

Could a device tell your brain to make healthy choices?