The term memory does not refer to a single entity. It refers to a number of interactive systems in the brain. This is illustrated by different types of memory complaints. When a person says “my memory is awful”, they can mean a range of different things. Sometimes people mean “I went to the market and forgot what I have come for”. Similarly another person complains “I picked up the telephone and was told a number, but I forgot the number”. These familiar memory failures reflect lapses in our very short-term (working) memory system. This system largely depends on the frontal lobes of the brain. This area that malfunctions in patients with depression and in Parkingan’s disease can also be injured following head injury and decline in efficiency with advancing age.
The knowledge about other types of memory system has been derived from patients with “accidents of nature”. Experts study these patients because it is not ethical to lesion the human brain. Animal studies are also not appropriate as most of the aspects of memory which interest us can only be understood from studying human subjects because of the unique self-reflective aspects of human memory. Of course researchers study patients with memory problems to learn about the disease that affect human memory, particularly Alzheimer’s disease.
Apart from the familiar memory failures in very short-term (working) memory system, most people complain of a different types of memory problem. For instance, a person may say–“I discussed many things with a friend of mine last week, but I don’t remember what I talked about. I also don’t remember who I talked to”. This type of memory for events which are specific to time and place is referred to as episodic memory.
The ability to lay down new episodic memory and to build a coherent autobiography is essential for our awareness of self. It has been shown that the system depends on a pair of ancient structures deep in the temporal lobes of the brain known as the hippocampus. The hippocampus receives input from all other areas of the brain, but particularly from those concerned with sensory information: It receives visual, tactile, auditory, olfactory, and gustatory inputs. It is ideally placed to act as the central telephone exchange connecting togetherness of sensory information.
The role of hippocampus in episodic memory was discovered when surgeons in Canada removed the medial temporal lobe (containing hippocampus) to treat patients with severe epilepsy. The removal produced good results. Subsequently surgeons removed bilateral lobes to treat patients with more severe epilepsy. This resulted in the loss of episodic memory. One of the patients is still alive. He is called H. M. He has been intensively studied following surgical intervention. He is perhaps the most famous patient in neuropsychology. H. M. had surgery in late 1950’s and since he has no new episodic memory. He does not remember that his family members have died. When asked about his age, he reports that he is still at his at 20’s.He has a pattern of memory loss technically known as anterograde amnesia. Although he is unable to lay down new episodic memory, his old memories are available to him.
During 1950’s, it was possible to identify the linkage between a specific brain structure and memory loss through the removal of brain structure. Now-a-days the application of Magnetic Resonance Imaging (MRI) provides scientific evidence in this context.
In recent years, there has been another ‘accident of nature’. A musician, Clive, suffered from encephalitis. His memory loss is more profound than H. M. He consistently thinks that he has “just woken up”. He can’t remember anything for more than a few second. His wife leaves room and comes in. He thinks that he has not seen her for years. But unlike H. M., Clive has also been robbed of the memories of his early life. He is unable to remember any specific episodes from his life. MRI scanning in Clive shows that in addition to damage in his hippocampus, he has more extensive involvement of the other parts of temporal and frontal lobes.
The key point in contrasting the two patients, H. M. and Clive, is that separate structures are involved in the laying down of the new memories and the storage of old memories. Damaged to the hippocampus is linked with loss of new memories.
Patients like H. M. and Clive are rare. But patients with Alzheimer disease is very common. The pathology of Alzheimer disease begins in and around hippocampus. These patients show progressive loss of episodic memory. Now it possible to use some simple tests of associative memory (such as linking faces and names) to predict the onset of the disease.
The third types of memory failure involves semantic memory. When a person cannot remember the name of an object (say a hammer), the type of memory loss is called loss of semantic memory. One of the most significant development in understanding the loss of semantic memory has occurred in the 1980’s. Experts come across a rare disorder known as “semantic dementia”. In semantic dimentia, there is progressive erosion of the database. Patients are unable to name objects and understand meaning of words and objects. These deficits are more apparent in language, but can also be demonstrated on visual tests.
More recently, it has been shown that the right temporal lobe seems to play a particular role in the storage of knowledge about people while left side of the temporary lobe is involved in the loss of knowledge for nonliving things. Thus, semantic memory for living and man made things seem to be segregated.
The knowledge about other types of memory system has been derived from patients with “accidents of nature”. Experts study these patients because it is not ethical to lesion the human brain. Animal studies are also not appropriate as most of the aspects of memory which interest us can only be understood from studying human subjects because of the unique self-reflective aspects of human memory. Of course researchers study patients with memory problems to learn about the disease that affect human memory, particularly Alzheimer’s disease.
Apart from the familiar memory failures in very short-term (working) memory system, most people complain of a different types of memory problem. For instance, a person may say–“I discussed many things with a friend of mine last week, but I don’t remember what I talked about. I also don’t remember who I talked to”. This type of memory for events which are specific to time and place is referred to as episodic memory.
The ability to lay down new episodic memory and to build a coherent autobiography is essential for our awareness of self. It has been shown that the system depends on a pair of ancient structures deep in the temporal lobes of the brain known as the hippocampus. The hippocampus receives input from all other areas of the brain, but particularly from those concerned with sensory information: It receives visual, tactile, auditory, olfactory, and gustatory inputs. It is ideally placed to act as the central telephone exchange connecting togetherness of sensory information.
The role of hippocampus in episodic memory was discovered when surgeons in Canada removed the medial temporal lobe (containing hippocampus) to treat patients with severe epilepsy. The removal produced good results. Subsequently surgeons removed bilateral lobes to treat patients with more severe epilepsy. This resulted in the loss of episodic memory. One of the patients is still alive. He is called H. M. He has been intensively studied following surgical intervention. He is perhaps the most famous patient in neuropsychology. H. M. had surgery in late 1950’s and since he has no new episodic memory. He does not remember that his family members have died. When asked about his age, he reports that he is still at his at 20’s.He has a pattern of memory loss technically known as anterograde amnesia. Although he is unable to lay down new episodic memory, his old memories are available to him.
During 1950’s, it was possible to identify the linkage between a specific brain structure and memory loss through the removal of brain structure. Now-a-days the application of Magnetic Resonance Imaging (MRI) provides scientific evidence in this context.
In recent years, there has been another ‘accident of nature’. A musician, Clive, suffered from encephalitis. His memory loss is more profound than H. M. He consistently thinks that he has “just woken up”. He can’t remember anything for more than a few second. His wife leaves room and comes in. He thinks that he has not seen her for years. But unlike H. M., Clive has also been robbed of the memories of his early life. He is unable to remember any specific episodes from his life. MRI scanning in Clive shows that in addition to damage in his hippocampus, he has more extensive involvement of the other parts of temporal and frontal lobes.
The key point in contrasting the two patients, H. M. and Clive, is that separate structures are involved in the laying down of the new memories and the storage of old memories. Damaged to the hippocampus is linked with loss of new memories.
Patients like H. M. and Clive are rare. But patients with Alzheimer disease is very common. The pathology of Alzheimer disease begins in and around hippocampus. These patients show progressive loss of episodic memory. Now it possible to use some simple tests of associative memory (such as linking faces and names) to predict the onset of the disease.
The third types of memory failure involves semantic memory. When a person cannot remember the name of an object (say a hammer), the type of memory loss is called loss of semantic memory. One of the most significant development in understanding the loss of semantic memory has occurred in the 1980’s. Experts come across a rare disorder known as “semantic dementia”. In semantic dimentia, there is progressive erosion of the database. Patients are unable to name objects and understand meaning of words and objects. These deficits are more apparent in language, but can also be demonstrated on visual tests.
More recently, it has been shown that the right temporal lobe seems to play a particular role in the storage of knowledge about people while left side of the temporary lobe is involved in the loss of knowledge for nonliving things. Thus, semantic memory for living and man made things seem to be segregated.