The term 'anterograde amnesia' means the short term memory loss disorder. The person is unable to program new information and store them in the brain as new memory. He remembers everything about the incidents that happened before the trauma, which caused the condition but cannot register anything fresh. He fails to remember incidents that happened after that.
Anterograde amnesitic people suffer from widely varying degrees of forgetfulness. It is natural for all of us to forget some information from time to time. If we did not, our brain would get exhausted of trying to remember every little thing. However, in case of anterograde amnesia, the patient keeps forgetting information so frequently that it may interfere with his daily routine activities. Imagine walking out of your house for a routine walk around the block, then within minutes not remembering why you came out, where you were going, or even where your house was! Definitely, anterograde amnesia is devastating to both the patient and the relatives associated with him.
Such a person may not even remember what day is today, what he did yesterday, whether he had taken breakfast, whom he met just half an hour ago and so on. However, the person's personality, judgement and aptitude may remain intact. He can perform day to day activities. He may not be able to retain his job, not because of his incapability of doing it rather simply, his inability to remember anything other than what is in his current attention.
Even with severe forms of amnesis, people can still be taught to learn new things. There are basically two types of long term human memory namely, declarative memory and procedural memory.
Declarative memory is memory for the storage of factual information, such as where were you born, names of cities, types of food, etc. This type of memory is stored in the temporal lobe of the brain, so a defect in the same can lead to this disease. Procedural memory is the memory of sequence of events, process or routine. It involves remembering how to brush your teeth, tie a shoe lace, ride a cycle, etc.
In other words, declarative memory is the 'knowing that' memory and procedural memory is 'knowing how' memory. In most cases of anterograde amnesia, the declarative memory is lost while the procedural memory is retained.
The main conditions for the occurrence of anterograde amnesia are described below:
1) Diabolic drugs
The use of certain drugs of benzodiazepine group is associated with possible amnesic side-effects and may cause anterograde amnesia. Such drugs are usually prescribed to treat anxiety and insomnia (sleeplessness). Examples include diazepam, midazolam, flunitrazipam, temazepam, triazolam, lorazepam and nimetazepam.
2) Brain damage
Many areas of the brain are involved in memory formation and recall. So, memory disorders can be caused by several different kinds of damage to the brain. There are mainly three areas in the human brain which when damaged can cause anterograde amnesia. One is the thalamus and its surrounding area, located in the midline of the brain just above the brain stem. Another is the hippocampus which lies deep in the front part of the brain, and some associated structures present in the inner side of the temporal lobes. A third area is in the basal forebrain region at the lower part of the frontal lobe.
Traumatic brain injury in any of these areas can occur due to several causes. Some of the commonest causes include traumatic head injury such as following a road traffic accident or a brain tumor that puts pressure on or damages the important memory areas of the brain.
In hydrocephalus, there is abnormal accumulation of cerebrospinal fluid in the cavities of the brain. This can put excessive pressure in the memory areas. Viral infections such as encephalitis caused by herpes simplex virus can damage these areas. If a person is epileptic with the affected temporal lobe, he can develop anterograde amnesia following unprovoked seizures for a long time.
3) Alcohol intoxication
Severe alcohol abuse over years is believed to damage the neuronal connections in the brain and cause this type of memory loss; the phenomenon is called as blackout. A rapid rise in blood alcohol concentration can compromise the blood flow to a specific area of the brain, cut off oxygen supply and cause anterograde amnesia. Compromise of the oxygen flow to the brain may also occur during a cardiac arrest, carbon monoxide poisoning, near drowning and near-suffocation. Patients with Alzheimer's disease also show some symptoms of short term memory loss.
Unfortunately, there is no surefire cure for this anterograde amnesia. What helps is cognitive rehabilitation therapy, psychotherapy that teaches such subjects the best way in which they can cope with the demands of daily living. Results of rehabilitation depend on how severe the memory deficit is. Family support is must in getting a patient out of this disease.
In addition, new prescription drugs are now available to treat some of the symptoms of Alzheimer's disease. They may be helpful in treating other form of anterograde amnesia as well. If a person has tumor in the brain, its surgical removal may help to some extent.
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Written by Debasis Sahu and Shikha Sharma