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Clarifying the Fundamental Mechanisms of the Brain Information Processing for Decision-making

2014.06.20

Unit Name:
Brain Information Processing of Decision Making
Unit representative:
Professor Munetaka Shidara, Faculty of Medicine

Unit members:
6 (6 faculty members, 0 postdoctoral fellows, none from other organizations)

Key words:
Reward values, decision-making, information-processing of the brain, primate models, single neuron analysis, theoretical neuroscience

 

The brain processes information to appropriately recognize a given situation and perform optimal behavior. Considering items with a positive value for living organisms as rewards, such as food indispensable for life or happiness, how is the brain conducting processing of reward expectation and value judgments? This research unit comprehensively examines the information-processing of the brain by combining neurophysiology with behavioral science, psychology, molecular biology, medicine, and pharmacology, as well as economics covering computational biology, mathematics, and the evolutionary game theory. It also aims to clarify the fundamental mechanisms of the brain (Figure 1).

Figure 1: Professor Shidara Standing by Devices for Experimental Data Analysis; he is a multi-talented person who enjoys mountain-climbing, tennis, shakuhachi (bamboo flute) master, and piano.

Figure 1: Professor Shidara Standing by Devices for Experimental Data Analysis; he is a multi-talented person who enjoys mountain-climbing, tennis, shakuhachi (bamboo flute) master, and piano.

Neurons with Reward Expectation

We focus on neuronal mechanisms of reward expectation. For example, in an animal experiment, we trained a monkey to perform a task, with juice as a reward. The typical task consisted of 4 trials, and it was necessary for the monkey to appropriately complete all trials to be rewarded (Figure 2). The rate of correct responses and reaction time improved with task progress toward the 4th rewarded trial. In line with this, the neurons in the basal ganglia, which started responding from just before reward delivery during the task, were identified as the cells associated with short-term reward expectation, and it was confirmed that their activity was paralleled with behavioral changes. On the other hand, the response of neurons in the medial frontal cortex showed gradually increasing response with task progress (Figure 3); these neurons were identified as those associated with long-term reward expectancy.

Figure 2: An Experiment to Identify Neurons Associated with Reward Expectation

Figure 2: An Experiment to Identify Neurons Associated with Reward Expectation

Figure 3: Activity of Neurons Associated with Long-term Reward Expectancy

Figure 3: Activity of Neurons Associated with Long-term Reward Expectancy

Clarification and Application of the Information-processing Mechanism of the Brain through Analysis of Neuron Function

In another experiment on reward value judgments, a monkey was allowed to select one of two options: 1 drop of juice for 1 appropriate answer; or 3 drops of juice for 3 appropriate responses. Although they are arithmetically equal, 1 drop of juice in reward for 1 appropriate answer, the monkey chose the former option at a rate of 70%, considering a decrease in the reward value with time and workload (discounting of delayed rewards). In contrast, when the options were: 1 drop of juice for 1 appropriate answer; or 4 drops of juice for 3 appropriate responses, the monkey chose the latter at a little higher rate (Figure 4). By changing options of reward size and time/workload, we can clarify the mechanism of value judgments, and we are now analyzing value-coding neurons in orbitofrontal cortex.
Through these studies, we aim to clarify the information-processing mechanism of the brain, and use the results for the development of treatment methods for brain diseases and life-supporting robots.

Figure 4: An Example of an Experiment to Identify Neurons Associated with Reward Value Judgments

Figure 4: An Example of an Experiment to Identify Neurons Associated with Reward Value Judgments

Social contributions and achievements
● Contributing to clarification of the information-processing mechanism of the brain for decision-making and value judgments as one of the most important issues in neuroscience today
● Combining neuroscience, computational theories, behavioral psychology, and game theories as an interdisciplinary research model
● Contributing to the field of marketing by applying findings on the information-processing mechanism of the brain for reward value judgments to purchase patterns
● Developing effective education methods based on neuroscience and the mechanism of reward value judgments. We also hope to contribute to the development of treatment and re-education methods for mental disorders due to impairment of the brain reward system, such as drug abuse, attention deficit disorder, mania, depression, and personality disorder.

(Interviewed on July 22, 2013)


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