Researchers at the University of Amsterdam (UvA) have developed a new method that can be used to study how fear is acquired, stored, unlearned and even eliminated.
Researchers at the University of Amsterdam (UvA) have developed a new method that can be used to study how fear is acquired, stored, unlearned and even eliminated. The study also shows how the acquisition of fear may overshadow existing associations in the brain. Psychology department researchers Renée Visser, Dr Steven Scholte and Prof. Merel Kindt have published their findings in the latest edition of The Journal of Neuroscience.
The brain forms networks of associations based on past experiences. Thanks to this mechanism, people can interpret the world around them without having to learn how to handle each new situation individually. An example is timely recognition and avoidance of danger: you may see a dog as a pet, but if you are bitten by that dog your first association upon seeing any dog changes to that of a dangerous animal. Your initial association thus retreats to the background.
In the study, test subjects were placed in an MRI scanner and repeatedly shown several pictures, with two of houses and two of faces. By administering a small electrical shock immediately after showing one of the two houses and one of the two faces, the two existing categories (houses/faces) were joined by two new ones, of a threat vs. no threat of a shock. Pictures that were followed by an electrical shock, and which therefore became predictors of pain or danger, evoked a more marked pattern of brain activity than pictures not followed by a shock. This was expressed in higher correlations between two successive presentations of the picture, suggesting that it was processed differently than the pictures that did not predict danger.
Another notable finding was that pictures which originally had nothing in common (houses and faces) began to show increasing neural similarity when they became predictors of danger, but not if they did not predict danger. In other words, a new, ‘dominant’ category had been created, which was stronger than the original categories of houses and faces.
The precise mechanism by which the brain deals with existing associations when learning new ones was still a relative mystery. The researchers therefore decided to investigate the neural basis of fear associations using a new fMRI method. The new method differs from traditional approaches to analysing fMRI data in two important ways. Firstly, it looks at the chiefly spatial pattern of brain activity instead of at average activity in a particular area. Each stimulus that is administered generates a distinctive pattern of activity, thus providing a unique neuralrepresentation of the stimulus at that moment. Secondly, it examines the patterns of multiple stimuli individually rather than all together. By correlating the patterns of two stimuli offered in immediate succession, researchers can measure how the representation of a stimulus changes over time and thereby see how the brain learns fear.
The research is being funded by the Netherlands Organisation for Scientific Research (NWO) and is part of the Vici grant project led by Prof. Merel Kindt.
Renée M. Visser, H. Steven Scholte, Merel Kindt: Associative Learning Increases Trial-by-Trial Similarity of BOLD-MRI Patterns. The Journal of Neuroscience (augustus 2011).