The Neurology of a Phobia

The latest research by Joseph Ledoux has shown what happens in the brain when a phobic stimulus is detected.

The following information is an over simplified example of the neurological response to a phobic stimulus.

There are two path ways in the brain one is know as the fast and dirty path way and the other is the slow and clean.

Pathway 1: Visual Input – Thalamus – Visual cortex – Hippocampus – Amygdala

Pathway 2: Visual input – Thalamus – hypothalamus – amygdale

Pathway 1 takes about 12 milliseconds it is known as the fast and dirty pathway because of its speed but it also gives off some false alarms.

Pathway 2 takes 30-40 milliseconds is known as the slow and accurate pathway which takes long but is more accurate.

There is a trade off between speed and accuracy.

What is better a fast system that give false alarms and wastes energy or a slow system that could cause you to be harmed?

In Chapter 6 LeDoux pinpoints the amygdala as the portion of the brain responsible for emotional fear responses.

The sensory signals go from the hypothalamus to the amygdala in 12 milliseconds and from the hypothalamus to the cortex in 30-40 milliseconds. As a result, the amygdala is creating emotional responses before the cortex has even received the signal to be processed.

The hypothalamus has limited pattern recognition capabilities compared to the cortex and performs a quick and dirty pattern recognition and response.

The cortex applies its refined cognitive processes to the same signal and provides the amygdala with signals for a more reasoned approach to the same sensory input.

“The shorter pathway is fast but imprecise,” LeDoux explains. “If a bomb goes off, you might not quickly be able to evaluate any of the perceptual qualities of the sound, but the intensity is enough to trigger the amygdala. If you knew a lot about bombs, then through the cortex pathway you could evaluate the danger, but it will take longer.”

When are fears considered phobias?

Fear is a natural human response to danger. It helps to protect us by activating the “fight-or-flight” response of the sympathetic nervous system. When faced with danger, our sympathetic nervous system which is activated by the amygdala produces a cocktail of chemicals for example adrenaline and cortisol as well as others. These chemicals prepare us to fight or flee the physical threat.

The fight-or-flight response the following physiological responses in the body.

Physiological responses:

Acceleration of heart and lung action
Inhibition of stomach and intestinal action
General effect on the sphincters of the body
Constriction of blood vessels in many parts of the body
Liberation of nutrients for muscular action
Dilation of blood vessels for muscles
Inhibition of Lacrimal gland (responsible for tear production) and salivation
Dilation of pupil
Relaxation of bladder
Inhibition of erection
Auditory Exclusion (loss of hearing)
Tunnel Vision (loss of peripheral vision)