section 11.4 Flashcards
concussion
a temporary disturbance of consciousness produced by a non-penetrating head injury. Most common causes of amnesia.
Posttraumatic amnesia (PTA)
amnesia following a nonpenetrating blow to the head. Testing usually reveals that the patient has permanent retrograde amnesia for the events that led up to the blow and permanent anterograde amnesia for many of the events that occurred during the subsequent period of confusion.
Islands of memory
surviving memories for isolated events that occurred during periods for which other memories have been wiped out.
Gradients for retrograde amnesia after concussion seem to provide evidence for
memory consolidation. Concussions disrupt recent memories and that suggests that the storage of older memories has been strengthened (consolidated).
Hebb’s theory of memory consolidation
argued that memories of experiences are stored in the short term by neural activity reverberating (circulating) in closed circuits. These reverberating patterns of neural activity are susceptible to disruption, but eventually they induce structural changes in the involved synapses, which provide stable long-term storage.
Electroconvulsive shock (ECS)
an intense, brief, diffuse, seizure-inducing current that is administered to the brain through large electrodes attached to the scalp. By disrupting neural activity, ECS would erase from storage only those memories that had not yet been converted to structural synaptic changes; the length of the period of retrograde amnesia produced by an ECS would thus provide an estimate of the amount of time needed for memory consolidation.
Hebb’s theory implies that
memory consolidation is relatively brief, a few seconds or minutes, about as long as specific patterns of reverberatory neural activity could conceivably maintain a memory. However, many studies found evidence for much longer gradients.
Squire, Slater, and Chace
study that found a long gradient of ECS-produced retrograde amnesia.
Each time a memory is activated, it is
updated and linked to additional memories. These additional links increase the memory’s resistance to disruption by cerebral trauma, such as concussion or ECS.
Standard consolidation theory
Scovile and Milner; concluded that the hippocampus and related structures play a role in consolidation. Suggested that memories are temporarily stored in the hippocampus until they can be transferred to a more stable cortical storage system.
It seems unlikely that the hippocampus plays a special role in
consolidation. It appears that when a conscious experience occurs, it is rapidly and sparsely encoded in a distributed fashion throughout the hippocampus and other involved structures.
Nadel and Moscovitch
retained memories become progressively more resistant to disruption by hippocampal damage because each time a similar experience occurs or the original memory is recalled, a new engram (a change in the brain that stores a memory) is established and linked to the original engram, making the memory easier to recall and the original engram more difficult to disrupt.
Each time a memory is retrieved from long-term storage, it is temporarily held in
labile (changeable or unstable) short-term memory, where is it once again susceptible to posttraumatic amnesia until it is reconsolidated.
Nader, Schafe, and LeDoux
infused the protein-synthesis inhibitor aniomyein into the amygdalae of rats shortly after the rats had been required to recall a fear conditioning trial. This infusion produced a retrograde amnesia for the fear conditioning, even though the original conditioning trial had occurred days before.
