Scientists Find the Origin of Fear Memory in the Brain

Rebecca Lewis January 29, 2013

The concept of fear has been a subject of scientific research for a very long time. Although we don’t want to experience it, fear is an emotion critical for survival and decision-making. Past studies that investigated the nature of fear suggest that it evolves from the amygdala – a structure in the brain involved in emotion and reward-based behaviour. The current study explores more of this theory.

Neuroscientists from the Cold Spring Harbour Laboratory (CSHL) in New York, USA, conducted a study to examine how fear responses are created, controlled and memorised. To do this, they trained a group of mice to respond to a source of fear from a Pavlovian manner to an auditory cue. Whenever the mice hear or sense the thing they learned to be afraid of, they ‘freeze’, which is a common fear response in both animals and humans.

The team, headed by Bo Li, assistant professor at the CSHL, noticed that whenever the mice ‘freeze’ in fear, the neurons in the central amygdala called lateral division light up. The researchers theorised that for the fear memory to be encoded, the neuronal signals in the said area must be activated.

To further study the neurons involved, the team used a variety of methods, such as optogenetics – a method which involves implanting a very thin fibre-optic cable directly into the area that contains photosensitive neurons. Through this procedure, the researchers were able to accurately pinpoint the cells and activate them, which in turn, enabled them to monitor the brain activities in mice as they respond to fear.

Central Amygdala – the Brain’s Source of Fear

The team found that fear memories are induced by the experience-related changes in the release of the neurotransmitters in excitatory synapses connecting the inhibitory neurons or the neurons that tend to suppress the activity of other neurons. Such changes are known as ‘synaptic plasticity’.

They discovered the somatostatin positive neurons – hormones that affect the release of the neurotransmitters in the central amygdala. The researchers also found that the formation of fear memories was impaired whenever they block the activation of the Somatostatin neurons.

Additional findings show that the somatostatin neurons were also responsible for the recall of fear memories.

Overall, their work demonstrates that the central amygdala is a major component in the fear formation, control and recall. In future studies, the team hopes to explore how the processed discovered in their research could be altered to improve the condition of patients suffering from disorders that involved abnormal fear response, including post traumatic stress disorder or PTSD.

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Source of this article:

Experience-dependent modification of a central amygdala fear circuit