The Brain

The human brain is very highly developed. Many people would argue that its size and complexity are the vital features that make us human. It is also quite complex, so a diagram is shown below:

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In the image above:
A) View of the middle surface of right side of the 'higher' brain showing several major structures.
B) Enlarged view of the brain structures that form the 'limbic system' - note the prominent size and position of the amygdala.

The brain stem (which lies below the brain regions shown in Figure A) is the oldest part of the brain, and messages pass to and from it without the need for conscious thought. This area is lower in the head and is also called the 'lower brain', because it consists of parts similar to those found in some very primitive creatures.

The cortex makes up part of the 'higher brain'. It is a highly folded sheet of nerve cells about 3mm thick covering the outer part of the brain, and is the region of the brain that is most noticeably expanded in humans. The limbic system, which includes the amygdala, lies between the cortex and the brain stem - the major parts of the limbic system are shown in Figure B.

The Amygdala
The amygdala is an almond-shaped structure contained within the limbic structures of the brain, and is located at the base of the temporal lobe (see B in the image above). To the non-expert, this means that it is about level with the top of the ears and about half way towards the centre of the head. Recent research, using sophisticated equipment which maps the parts of the human brain that are active during particular tasks, has revealed that the amygdala is a very important neural centre involved with the expression of emotions - particularly fear. Unfortunately, some individuals who have a damaged amygdala have trouble feeling fear - they also lack the ability to recognise fear from the facial expressions of other people.

It turns out that the amygdala plays a critical role in the chain of events where a person (or animal) is able to recognise a threat from stored information of previous experiences - that is, from memory. The retrieval of this emotional information allows people to act quickly - without necessarily thinking. It also turns out that conscious thought can influence emotions - for example, the straight face of a poker player with a lousy hand!

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