Body Story

Crash: Amnesia

Just 1.5 kilograms of tissue inside your head contains you. Essentially human and individually unique, your brain thinks, feels, remembers and hopes. It learns from its mistakes and it invents new strategies for your survival. As the supreme co-ordinator of your body's complex workings, it knows things you don't realise you know. It runs your life, and if it dies, you die.

• Complex connections
Small wonder then that your brain is a system of mind-boggling complexity. The basic brain cell, the neuron, is a nerve cell with cable-like and thread-like outgrowths connecting it to other neurons. There are a staggering 100 billion neurons in the brain, and a typical neuron makes between 1,000 and 10,000 connections to other neurons. The brain's activity is carried out through message-bearing electrical impulses, which travel along complex routes through the brain's web of connections.

So much activity requires energy, and the brain has an insatiable appetite for sugar and oxygen. It consumes 20% of all the oxygen available to your body, and it requires 120 grams of glucose a day. It can only store two grams of glucose itself, so when you're asleep and glucose isn't being provided by food intake, it removes glucose from storage in the muscles and liver to feed itself, and if you fast (for example, by dieting), it will find glucose by breaking down your muscle proteins.

Both sugar and oxygen are carried to the brain by the blood. The brain receives 15%-20% of the blood flowing from your heart.

The vital and complex nature of this organ means that if it is damaged, the consequences are at once extremely grave and very difficult to treat. Although scientists have mapped out certain areas of the brain, their map is by no means comprehensive. Nor do they fully understand the connections between different parts of the brain.

• Types of memory
Amnesia (memory loss) is usually one of the first problems people experience after a head injury, and it is one of the last of the cognitive functions — that is, functions to do with knowing and being aware — to return. Studies suggest that around 70% of people who have sustained a traumatic brain injury, such as that suffered by David in the car accident, complain of memory problems for up to a year after the trauma has occurred.

Exactly how the brain stores memories is not understood. What we do know is that the brain stores different types of information in different places. Researchers have divided up our memories into three types:

Immediate memory, which takes a mental snapshot of raw stimuli corresponding to sounds, sights, smells or tastes. Unless this snapshot is transferred to the short-term memory, it is lost.
Short-term memory, where sensory information is organised and co-ordinated.
Long-term memory, which forms a permanent database of memories. In order for short-term memories to be filed, permanent changes to brain cells have to take place.

When the brain suffers an injury, not all memories are treated equally. Long-term memory is rarely affected, but short-term memories, which have not yet been permanently imprinted on our consciousness, are often lost.

The most common form of post-traumatic memory loss is anterograde amnesia. With this condition, a patient's memory of events before the accident are clear, but they find it difficult to hold short-term memories following the accident. For example, a doctor treating such a patient may be greeted as a new acquaintance at each consultation. This type of amnesia is rarely permanent.

Retrograde amnesia, which refers to the loss of memories before the accident, often for several months before the trauma occurred, is more serious.

Global transitory amnesia is short-lived and involves anterograde amnesia followed by retrograde amnesia.

• Can memories be rescued?
Unlike amnesia due to emotional trauma, amnesia that results from a brain injury cannot be rectified with hypnosis or counselling. In the case of anterograde amnesia, patients must be retrained to process their memories. Noting dates, personal information, and things to do in notebooks can help, as can associating words or events with pictures.

With retrograde amnesia, some patients find that, at first, they cannot recall events that occurred months or years prior to the onset of their memory loss, but that over time the forgotten period shrinks to weeks, days or even hours. Some patients may respond, as David did, to photographs, songs, or stories of their forgotten past. Others are less fortunate – their memories are lost, irretrievably, in the complex web of the brain's connections.

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