Some people lose their memory after some accident or on hearing some tragic news. Such people forget their past and even fail to recognize their close friends and relatives. So much so they even forget their names. In psychology, this disease is called ‘Amnesia.’

Causes of amnesia

Many factors cause Amnesia. Head injury, mental shock, extreme tiredness, ill- effects of medicines, surgery of the brain, psychological processes, old age, and aftereffects of drinking are some of the reasons which reduce or destroy memory. Whatever may be the reasons causing Amnesia, its effect on the brain is almost the same in each case.
In our brain, memories get stored as a “memory trace.” What makes up this trace is not known. According to one theory, each experience sets up an oscillating pattern or wave pattern of excitation in a cell group. Each learning experience generates its way of excitation. A given neuron may participate in thousands of separate memories, but its removal will not appreciably diminish any of them.

Types of Memory

Memory is considered a three-part system:
Sensory Information Store(SIS), Short-Term Memory (STM), and long-term memory.

Sensory Information Store

The SIS forms an instant, but very temporary, storage of every piece of information. Information can last for only about three-tenths of a second in the SIS. If it has not been selected and transferred to short-term memory within this time, it fades away.

Short-Term Memory

Short-term memory carries information a person needs for a few seconds but can afford to forget later. Two characteristics of short term memory prevent its use as a permanent information store. First, concentration is required to maintain a particular piece of information in it. Second, it can store only six or seven items, such as a ten-digit telephone number.
For any information to be permanently stored, it must be passed from short term to long-term memory by rehearsal mechanism.

Long-term memory

The long-term memory has virtually unlimited capacity. It allows a person to remember events that have happened years before. Permanent memory occurs through structural changes in the nerve cells, caused by electrical activity patterns in these cells.
When somebody suffers from Amnesia, he forgets events, either preceding it or following it. It can last for weeks, months, or years. Some people have lost memory for life. After the restoration of memory, one remembers all the forgotten things but forgets every event during that period when one had lost memory. 
However, one thing is sure that despite the restoration of memory, some aftereffects do remain, thereby weakening the memory; in cases involving loss of memory, immediate assistance of psychiatrists to be required. Usually, old age weakens memory, but sometimes peptic ulcers, high blood pressure, asthma, etc . also affect memory leading to Amnesia.



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