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Getting the picture - Decisions are made in the forebrain

Researchers at the Bernstein Center Berlin, Charité - Universitätsmedizin Berlin and Freie Universität Berlin have for the first time clearly demonstrated that the forebrain is causally involved in human decision-making. In the journal Current Biology* they report that subjects were less accurate and took significantly longer to make decisions when a certain region of the forebrain was inhibited by so-called transcranial magnetic stimulation (TMS). Using a computer model, the scientists can also explain how the decision-making process was affected by the intervention.

Without us even noticing our brain is constantly making decisions. Does the picture show a man or a woman? Even when the image is blurred, our brain usually interprets the information correctly. Scientists around Felix Blankenburg, research assistant at Bernstein Center Berlin and Charité, and Hauke Heekeren at the Freie Universität Berlin investigate how this works. For quite some time, experts have suspected that a certain forebrain region - the dorsolateral prefrontal cortex - is involved in decisions. Using TMS, the researchers switched this area off for a short period of time. Then, they asked their twelve subjects to decide as fast as possible whether a noisy stimulus on a screen contains a car or a face. The result: when the brain region was inhibited, people hesitated longer and chose the wrong alternative more often. The image quality did not influence the effect.

Thus, the researchers showed for the first time that the human dorsolateral prefrontal cortex has a causal influence on decision making. "With this study, we were able to close the gap between the state of knowledge acquired in animals and in humans in this respect. We are now a step closer to understanding the brain regions involved in decision making," says Blankenburg. "However, this doesn't mean that we know how the different areas interact yet."

A computer model supported the scientists' reasoning. It allows separating factors such as visual processing of sensory stimuli from decision-making. The model also captures how decisions are made under different conditions, such as in poor-quality images. "The combination of theoretical models with TMS can help ascribe causal and functional role to brain areas involved in various cognitive processes. This model gives us new opportunities to estimate parameters from our behavioral data that play a role in decision-making," explains Marios Philiastides, first author of the study.

The drift-diffusion model suggests that the process of decision-making is not linear. Its behaviour is comparable with a stock price. Random effects result in a fluctuation of the course. A broker establishes an upper and lower limit for selling the stock. The more positive or negative information is known about the company, the stronger the price moves in one direction. The process of collecting information for a decision-making is comparable to the fluctuating stock price, while the decision itself can be compared with a break of boundaries.

The model explains both why we have different response times and why sometimes we decide wrong. Nowadays, the model is used in many aspects, including the investigation of attention and memory. The findings could also be used to develop new therapies for diseases such as depression or obsessive-compulsive disorder, in which decision making is impaired.

*Original publication: Philiastides et al., Causal Role of Dorsolateral Prefrontal Cortex in Human Perceptual Decision Making, Current Biology (2011), doi:10.1016/j.cub.2011.04.034 <http://www.cell.com/current-biology/abstract/S0960-9822%2811%2900476-3>

For further Information please contact: Dr. Felix Blankenburg Department of Neurology, Charité and Bernstein Center for Computational Neuroscience Philippstr. 13, 10115 Berlin Tel: +49 (0) 30 2093 6775 E-Mail: felix.blankenburg@charite.de

idw :: 27.05.2011

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