Localisation of Memory Chapter 28

Memory

My Dog Boo- Purchased Saturday 26th February 1984 I was nine years old. I can remember the address of the breeder and how much we paid for her and also how she burnt her nose on the radiator as soon as she came home!! I can remember all sorts of other details like what the breeder looked like.

Different Types of Memory These are associated with different parts of the brain. There is some overlap. Declarative Memories (facts and episodes) are needed and drawn upon when performing mental recall operations such as identifying a familiar object or recalling past experience. Procedural Memories (skills and habits) are needed and drawn upon in order to perform mental skills such as remembering how to read and motor skills such as swimming and cycling

Declarative Memories (‘remembering that…’) Successful declarative memories are associated with areas of the temporal lobes at the sides of the cerebrum and parts of the limbic system The limbic system surrounds the hypothalamus. It possesses a structure called the hippocampus which projects into the temporal lobe

Procedural Memories (‘remembering how to….’) Procedural memories (skills and habits) are needed and drawn upon in order to perform mental skills such as remembering how to read, how to play chess etc., and motor skills such as swimming, cycling and knitting. The cerebellum is involved these types of memories where muscular co-ordination is involved.

Amnesia Amnesia is the partial or complete loss of memory. It takes several forms and can result from an injury, disease or stroke which affects the brain; or from surgery or electric shocks applied to the brain. Symptoms of amnesia include being unable to remember childhood events, problems recalling names, faces and words and having difficulty remembering day-to day events

Evidence for Localisation of Memory- A Case History The limbic system was removed from the brain of a patient to relieve life-threatening epilepsy. This patient was unable to recall new factual information for any longer than a few minutes. He could still recall old declarative memories stored before the operation. He could also retained procedural skills such as tying his laces and reading a book although he was happy to read the same book everyday because he failed to retain any of the information that he had read.. He was able to retain procedural memories like how to play a new sport.

Conclusions for Localisation of Memory This case study shows that the limbic system is needed for the formation and transfer of new declarative memories but are not the storage sites. The declarative memories are stored in the temporal lobes. This patient still had his temporal lobes so was able to recall old declarative memories but not deposit any new ones there hence he couldn’t store any of the facts he was reading from the book. Procedural memories involve the cerebellum and so as this part of the brain was not affected, the patient was able to form and store new procedural memories like learning to play a new sport after the operation and retrieve old procedural memories like tying laces

Personal Versus General Memories Some people suffering amnesia forget the details of their personal history but remember general facts such as the meaning of the words of the language they speak. This is because the personal and general declarative memories occupy different areas of the brain. It is thought that personal D.M are stored in the right temporal lobe and General D.M are stored in the left temporal lobe.

Memory Circuits It is thought that each memory is held by a group of neurones and is arranged in a particular way to form a memory circuit. In order to retrieve the memory, a nerve impulse is passed through the memory circuit reactivating it. This can be likened to operating an electrical appliance by passing electricity through its circuit. It is thought that neurotransmitters are needed to allow flow of impulses through the memory circuits and the more often an impulse passes through a circuit, the more likely it is that the memory will become long lasting

Alzheimer’s Disease This condition is characterised by the presence of numerous abnormal tangles of brain neurones, the death of many brain cells and the irreversible loss of parts of the memory. Loss of acetylcholine- producing cells in the limbic system is thought to be a factor in this condition. Experiments on monkeys have shown that when drugs are given to block acetylcholine, memory is impaired. If drugs are given to enhance acetylcholine production then memory is good.

Alzheimer’s and NMDA Receptors There is evidence to link Alzheimer’s with a breakdown in NMDA receptors. The flow chart shows nerve transmission in the hippocampus region of the brain’s limbic system( the region needed for developing a new memory) The neurones in the limbic system of a normal healthy human are found to be rich in NMDA receptors