Different types of amnesia cause different types of memory loss. Amnesia can be caused by trauma or by damage to the brain. Anterograde amnesia affects a person's ability to form new memories. Retrograde amnesia - - the most common type - - affects past memories; the extent of memory loss and how far back it goes depends on the severity of the amnesia. Newer memories are destroyed before older ones because the paths to them are weaker. In other words, these newer memories haven't been recalled enough times for the neural pathways to strengthen. This is called Ribot's law. The memories that are lost are called episodic memories, or memories of events.
There are other kinds of memories called procedural memories. These memories relate to performance and motor skills and also may be called implicit memories. When a person has amnesia, he retains his procedural memories, personality, identity and intelligence. This is why people with amnesia can remember how to ride a bike or play a musical instrument and perform daily functions. These memories are stored in the cerebellum, and are not affected by brain damage to the cortex, where episodic memories or long-term memories are stored.
Neurological amnesia happens when a person damages the cortex and hippocampus of his or her brain. These are the areas where the nerve pathways to stored memories are created, and when these pathways are cut off there is no way to retrieve memories. New memories also cannot be made because there is no way to form long-term memories. Amnesia can be caused by injury, infection, reduced blood flow to the brain, trauma and even stress. The extent of memory loss depends on the area of the brain damaged.
Nothing can help people restore memories lost from amnesia. Treatment mostly concentrates on coping techniques. Treating inability to form new memories, as in anterograde amnesia, is focused on learning to make new habits that can be integrated into daily life and recalled on a daily basis. Recording data and new information can also be helpful, like keeping a calendar of events. Familiar patterns need to be established to help amnesia patients lead independent lives.
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