This chapter focused on the areas of the brain that are involved in the formation and retrieval of different types of memories.

The following diagram shows the process through which an experience obtained through the senses is formed into a long-term memory. This diagram can be found on page 537.




This does not imply that all long term memories are the same, or, can be retrieved in the same manner. There are different types of long-term memories and different brain regions involved in eliciting each type of memory.

Long term memory is divided into two main groups: declarative memory and procedural memory. Declarative memory is facts and information acquired through learning. This type of learning is further divided into two more subgroups: episodic and semantic memory. An episodic memory is a specific, autobiographical memory that pertains to a person's history. An example of this would be remembering where your last class was. A semantic memory is a general memory. An example of this type of memory would be knowing the Pythagorean Thereom.

The second main type of long term memory is procedural memory. Procedural memories are those which are shown by performance rather than by conscious recollection. This type of memory is further divided into three subgroups: skill learning, priming, and conditioning. Skill learning occurs when a subject performs a difficult task on repeated trials in one or more sessions. Priming occurs when there is a change in processing a stimulus due to prior exposure to that stimulus of to one that is closely related. In classical conditioning, a previously neutral stimulus is paired with a stimulus that evokes a response. Eventually, through a series of trials, the previously neutral stimulus comes to elicit the same response as the other stimulus. In operant conditioning, an association is formed between the animal's behavior and it's consequences.

The following table provides a summary of the types of long-term memory and also lists the different areas of the brain that are involved with each type of memory. (This table can be found on p. 544)



The role of specific areas of the brain in the formation and retrieval of memories listed in the above table were discovered through the study of patients with brain trauma and experiments conducted with the use of animals. 

One patient, H.M., was completely unable to form new memories after his surgery which removed much of his anterior lobe, including most of the amygdala and the hippocampus on both sides. Even though H.M.'s declarative memory was damaged, his procedural memory remained intact as shown through his progressively increasing performance on the mirror-tracing task. Psychologists Brenda Spiegler and Mortimer Mishkin developed the delayed non-matching-to-sample task test to test declarative memory in monkeys. Various parts of the monkey's medial temporal lobes were lesioned in order to test their behavior. This showed that "some impairment was produced by lesions that included the hippocampus proper, the dentate gyrus, and the subiculum; increased impairment was caused by lesions that included not only these regions but also the adjacent entorhinal cortex and the parahippocampal cortex; finally, the greatest impairment was caused by lesions that also included the anterior entorhinal and perirhinal cortices" (p. 534). These findings, combined with the findings found with human subjects show that "damage restricted only to the hippocampus produce memory impairments similar to but not as severe as the more extensive damage in H.M. [This] concluded that the hippocampus is the final stage of convergence within the medial temporal lobe, combining operations of the adjacent, more specialized regions of the cortex" (p.534).

Patient N.A. is a case that proves that other parts of the brain are involved in the formation of declarative memories other than the medial temporal lobe. N.A. is amnesic, especially with verbal material and can give little information about events since his accident. He has, however, practically normal recall for events that occured prior to his accident. MRIs done of N.A.'s brain shows "damage to the left dorsal thalamus, bilateral damage to the mammillary nuclei, and probable damage to the mammillothalamic tract" (p.526). A defining characteristic between cases such as H.M. and N.A. is confabulation, or showing disorientation to time and place. This is a characteristic of Korsakoff's syndrome, a disease caused by lack of thiamine in which memory loss is a main feature. People with this disease have shrunken, diseased mammillary bodies, as well as some damage in the dorsomedial thalamus. This type of damage is similar to that found in N.A..

The final patient, K.C., sustained brain injuries to the left frontal-parietal and the right parietal-occipital cortex, in addition to shrinkage of the hippocampus and parahippocampal cortex. K.C. can, with difficulty, acquire new semantic knowledge, but cannot acquire new episodic knowledge. It is believed that the cortical damage is the cause of K.C.'s impairment for two reasons: 1. Other patients with hippocampal damage do not experience loss of episodic memory and 2. Studies have indicated increased blood flow in anterior regions of the cortex during recall of episodic memory.


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