learning
how experience changes the brain.
memory
how these changes (experiences) are stored and subsequently reactivated.
Bilateral medial temporal lobectomy
the removal of the medial portions of both temporal lobes, including most of the hippocampus, amygdala, and adjacent cortex.
lobectomy
is an operation in which a lobe, or a major part of one, is removed from the brain.
Lobotomy
an operation in which a lobe, or a major part of one, is separated from the rest of the brain by a large cut but is not removed.
Retrograde (backward-acing amnesia)
deficits of the ability to remember things before the brain damaging event.
Anterograde (forward-acting) amnesia
deficits of the ability to remember things after the brain damaging event.
short term memory
storage of new information for brief periods of time while a person attends to it.
long term memory
storage of new information once the person stops attending to it.
global amnesia
amnesia for information presented in all sensory modalities.
incomplete picture test
a nonsensorimotor test of memory that employs five sets of fragmented drawings. Each set contains drawing of the same 20 objects, but the sets differ in their degree of sketchiness
Three contributions from H.M.’s case proved influential:
- Showed that the medial temporal lobes play an especially important role in memory. Challenged the then prevalent view that memory functions are diffusely and equivalently distributed throughout the brain. his case renewed the effort to relate individual brain structures to specific mnemonic (memory-related) processes. Particularly spawned an effort aimed at clarifying the mnemonic functions of the hippocampus and other medial temporal lobe structures.
- The discovery that bilateral medial temporal lobectomy abolished H.M.’s ability to form certain kinds of long-term memories without disrupting his performance on tests of shirt-term memory or his remote memory (memory from experiences in the distant past) supported the theory that there are different modes of storage for short-term, long-term, and remote memory. H.M.’s specific problem seemed to be a difficulty in memory consolidation (the translation of short-term memories into long-term memories).
- First case to reveal that an amnesic patient might claim no recollection of a previous experience, while demonstrating memory for it by improve performance. Lead to the discovery of two distinct categories of long-term memories: explicit and implicit memories.
explicit memories
known as declarative memories; conscious long-term memories.
implicit memories
long-term memories without conscious awareness.
Many people with amnesia lose their ability to form
explicit memories while maintain their ability to form implicit memories.
medial temporal lobe amnesia
neuropsychological patients with a profile of menemonic deficits similar to those of H.M., with preserved intellectual functioning and with evidence of medial temporal lobe damage.
repetition priming tests
tests that assess implicit memory.
Explicit long-term memories come in two varieties:
semantic and episodic
semantic memories
explicit memories for general facts or information.
episodic memories
explicit memories for the particular events of one’s life. People with medial temporal lobe amnesia have particular difficulty with these memories.
- It is difficult to spot episodic memory deficits because neuropsychologists usually have no way of knowing the true events of a patient’s life and in part because the patients become very effective at providing semantic answers to episodic questions.
Global cerebral ischemia
experienced an interruption of blood supply to their entire brains; often suffer from medial temporal lobe amnesia.
R.B.’s case
brain damage that was restricted largely to the pyramidal cell layer of just one part of the hippocampus – the CA1 subfield. Suggests that hippocampal damage by itself can product medial temporal lobe amnesia.
Transient global amnesia
defined by its sudden onset in the absence of any obvious cause in otherwise normal adults. Provides the strongest evidence that selective hippocampal damage can cause medial temporal lobe amnesia. Severe anterograde amnesia and moderate retrograde amnesia for explicit episodic memories, however, the amnesia in this case is transient, typically lasting only between 4 to 6 hours.
diffusion weight brain imaging technique
identified the cause of transient global amnesia; identified abnormalities to the CA1 subfield in the hippocampus. The time course of these abnormalities – they are not usually apparent for several hours after the beginning of the attack and have usually cleared up 10 days layer – are suggestive of stroke-induced damage.
