You must have seen numerous movies in which a person loses his/her memory after an accident or on hearing tragic news. Such people forget their past and even fail to recognize their close friends and relatives. So much so, they even forget their own names. These incidents happen in real life, too, and in psychology, this condition is called amnesia.
Loss of Memory is a Psychological condition
Amnesia can be caused by a number of factors, like a severe head injury, mental shock, extreme tiredness, and ill effects of medicines, surgery of brain, psychological processes, and old age and may even be due to drinking alcohol. Whatever may be the cause of amnesia, their effect on the brain is mostly the same in each case.
Memory is said to be stored in the brain as a memory trace. What this trace is made of is still unknown. According to one theory, each experience sets up an oscillating pattern or wave of electrical excitation in groups of cells.
Each learning experience generates its own pattern of excitation. It is amazing that though a given neuron may participate in thousands of separate memories, yet its removal will not noticeably reduce any of them.
Memory is considered a three-part system- sensory information store SIS, short term memory STM and long term memory LTM. The SIS forms an instant, but very temporary storage of every piece of information that comes in. 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 is used for carrying information for a few seconds only. Two characteristics of short term memory prevent its use as permanent information store. First, concentration is required to maintain a particular piece of information in it. Second, it is able to store only seven or eight items such as an eight-digit telephone number.
For any information to be permanently stored, it has to be passed form short term to long term memory by the mechanism of rehearsal. The long term memory has unlimited capacity. It allows a person to remember events that happened years before. Permanent memory takes place through structural changes in nerve cells caused by pattern of electrical activity in these cells.
When somebody suffers form amnesia, he forgets event either preceding it or following it. It can last for weeks, months or even years. There are people who have lost their memory for the rest of their lives. When memory is restored, one remembers all the forgotten things but forgets every event, which took place during the period of amnesia.
One thing is however certain in spit of restoration of memory; some after effects do remain, thereby weakening the memory.