LEARNING, MEMORY & AMNESIA

Bilateral Medial Temporal Lobectomy - the removal of the medial portions of the temporal lobes, which includes parts of the hippocampus and amygdala.

Global amnesia - amnesia for information presented through all of the senses. Retrograde amnesia - affects the memory from before a surgery.

Anterograde amnesia affects the memory after a surgery.

H.M. - suffered mild retrograde amnesia, lost the ability to form long-term memories, global amnesia.

Medial temporal lobe amnesia - patients with evidence of damage to the medial frontal lobe with similar memory deficits to H.M. who also preserve their intellectual functioning.

Implicit memories - unconscious.

Explicit memories - conscious.

Semantic memories – explicit memories of general information and facts.

Episodic memories – explicit memories of particular events from one’s life people. suffering from medial temporal lobe amnesia in general have a much bigger issue with episodic memories.

There was a setback in R.B.’s cardiac bypass surgery, and as a result, R.B. suffered brain damage, most to a part of the hippocampus (CA1), the ischemic brain damage left him amnestic.

Global cerebral ischemia – interruption of blood supply to the brain, often those suffering from it also suffer from medial temporal lobe amnesia.

Transient global amnesia – sudden onset in the absence of any obvious cause in an otherwise normal adult, usually lasts between 4 and 6 hours; severe anterograde amnesia and mild retrograde amnesia for explicit episodic memories are present; it is connected to abnormalities in a part of the hippocampus (CA1).

Alzheimer’s Disease - acetylcholine depletion.

Involves many areas including the medial temporal lobes and the prefrontal cortex, which play major roles in memory.

Alzheimer’s Symptoms:

• Initially, mild loss of memory

• Eventually incapacitates patient

• Pathological changes

• Reduced acetylcholine

• Degeneration of basal forebrain

• Predementia Alzheimer’s - Alzheimer’s patients who have yet to develop dementia

• Both anterograde and retrograde amnesia

• Short-term and implicit memory deficits

Memory Consolidation refers to translation of short-term memories into long-term memories.

Older memories stored in a more permanent form.

Hebb argued that memories of experiences are stored in the short term by neural activity reverberating (circulating) in closed circuits.

New evidence - it could take years for consolidation to occur. Lasting memories become more and more resistant to disruption throughout a person’s life. Each time a memory is activated, it is updated and linked to additional memories . These additional links increase the memory’s resistance to disruption

Dual-trace theory suggests hippocampus holds memory until it is stored elsewhere. Scoville and Milner suggested that.

Current view is hippocampus stores memory every time it is recalled.

Nadel and Moscovitch - retained memories become progressively more resistant to disruption by hippocampal damage.

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.

Many hippocampal neurons - place cells (respond only when a subject is in specific locations).

Rodent spatial memory tests:

• Morris water maze

• Radial arm maze

Hippocampal place cells - fire when rat is in a specific location. Specific cell for each “place”.

Entorhinal grid cells - each have an extensive array of evenly spaced place fields, producing a pattern reminiscent of graph paper.

Grid cells represent evenly spaced place fields.

Head-direction cells are tuned to the direction of head orientation.

Border cells - fire when the subject is near the borders of its immediate environment.