Oct 22 2008
To make us braver
Fear circuits can be tweaked to make us braver.
By Roger Highfield, Science Editor
Drugs to curb the irrational terrors experienced by the survivors of a disaster could emerge from studies that reveal the brain’s “fear circuits” in unprecedented detail.
The work raises hopes of new treatments for post-traumatic stress disorder, by using drugs to flick these switches to control our sense of fear.
However, the advances reported by two teams in the journal Nature also raise the prospect that a drug that tinkers with the brain’s fear circuitry could also be abused so that, for example, governments could create fearless soldiers.
In one study, Prof Andreas Lüthi and colleagues at the Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland, suggest that feelings of fear for stimuli previously linked to unpleasant consequences are triggered by rapid switching in the balance of activity between two brain circuits.
The team found that two distinct populations of neurons (brain cells) in a part of the brain called the amygdala, two almond shaped structures deep in both hemispheres of the brain, are involved in different aspects of fear memory - one in the elimination of established fear responses, and the other in the ability to refresh those memories.
In normal situations, activation of these two types of cells is sparked by information that we receive from our surroundings and, by tipping the balance, it should be possible to stop cues linked with a trauma from triggering panic, so that the survivor of a tube bombing could board an underground train again without feeling a sense of deep foreboding.
As for when fear-quelling drugs could emerge, Prof Lüthi, remarked: “Guessing these kind of things is not realistic - results of basic research tend to be notoriously unpredictable.”
In a related Nature study, Prof Denis Paré and colleagues at Rutgers State University, Newark, New Jeresey, uncovered another mechanism underlying our ability to “unlearn” fearful memories.
They found that a different population of neurons within another part of the amygdala, called intercalated amygdala neurons, also helps us to become ‘not scared’ of previously scary stimuli.
By destroying these neurons in rats they observed a decrease in the extinction of learnt fear memories, so that the rats remained afraid. Equally, by stimulating them with drugs it should be possible to erase a specific fear.
Prof Lüthi explained the two findings are linked: “We discovered two neuronal networks in the basal nucleus of the amygdala that are important for triggering changes in fear behaviour (either the elimination or rather suppression of established fear memories, and then the ability to refresh them under the appropriate circumstances (context). These two networks are only required to initiate these changes, not to maintain these changes over time. Here comes the second paper by Denis Paré, who elegantly shows that special types of interneurons within the amygdala, the so-called intercalated cells, are necessary for maintaining a state of low fear. One possible interpretation could be that the neurons described in the Paré paper are downstream of and might get activated by one of the two networks we describe.”
Fear is part of a primitive defence system that helped animals cope with danger. This skill of perceiving fear was honed by evolution: ancestors who were able to respond quickly probably had a greater chance of survival, helping to spread this trait to future generations.
www.telegraph.co.uk
