Most interesting, LeDoux discovered a previously unsuspected route from the senses, in this case the auditory system, direct to the amygdala. "This was important," he explains, "because for at least 100 years many psychologists believed that for us to register a sight or a sound as frightening we had to be aware of it consciously. What this shows is that you can be frightened of something without knowing what it is."The value of this back door route is speed. A message from one of the senses, say the sound of a twig snapping, can reach the amygdala in half the time it takes for the impulse to travel to the thinking judging part of the brain and then down to the amygdala. In the wild those few milliseconds could make the difference between life and death. But it's a route that can also lead us astray."That gut feeling you get that something is wrong may not be revealing an inner truth," says LeDoux, "but a demonstration of the way we are all slaves to past emotional learning." Another idea is that this fast, low road to the amygdala becomes the favoured one in certain disorders like post-traumatic shock syndrome when a single sight or sound can unleash a wave of terror. The slower high road via the cortex allows a more reasonable response.
It is insights into psychiatric problems like those that has prompted giving to the cause of further research into the subject.Even more intriguing is a finding that may lead to improved treatment for phobias. LeDoux's rats all learned a fear response by getting an electric shock that was linked with a sound. Normally rats, and humans in similar situations, gradually lose their fear of the sound on its own when it stops being followed by a shock. But one groups of rats never lost their fear.Many of the rats had bits of their brain removed before being put in the cage with the sound and the shock. "Those who had damage to a part of the prefrontal cortex," says LeDoux, "never lost their fear response, no matter how many times they heard the sound on its own." It seems possible that people with an irrational fear they just cannot get rid of may also have a malfunction of their medial prefrontal cortex, the part of the brain involved with planning and judgement.This improved mapping of the pathways of fear hold out the possibility of more effectively targeted drugs. But, combined with an awful lot of patience, they were enough.The end result was a far clearer picture of where fear is handled in the brain and some surprises.
The hub of the system is the amygdala - two tangles of neurones, shaped like an almond and about the size of a chick pea, near the centre of the brain. "We found that it has connections to planning centres, action centres and the hormone system," says LeDoux. "It's the centre of a wheel of fear."Rats with the amygdala removed will saunter nonchalantly past a cat, when normally they would freeze, their heart rate would soar and their fur would stand on end. I suspect that each of the basic emotions has its own system and pathways." So LeDoux set out to map the anatomy of fear, a phenomenon common to all vertebrate species.The world of brain research has become so high-tech, with brain scanners showing neurones lighting up in brilliant colours, that the tools he used have a distinctly old-fashioned feel to them.
