amnesia Flashcards
what area of the brain is episodic memory associated with?
hippocampus
what area of the brain is semantic memory associated with?
cortex
what part of the brain is conditioning (implicit memory) associated with?
cerebellum
what part of the brain is skills (implicit memory) associated with?
striatum
what is classic amnesic syndrome?
loss of declarative memory (non-declarative memory is spared)
moss targeted loss is episodic not semantic
what is retrograde amnesia?
trauma results in loss of pre-injury memory- rare to occur in isolation
what is anterograde amnesia?
trauma results in inability to encode new information but can remember old memories
patient HM (1926-2008) symptoms
could not find his way home to a new address
does not recognise anyone he met post-surgery
has no idea what day or year it is
anterograde amnesia but also slight retrograde (3 years pre-surgery)
features of the classic amnesic syndrome
severity is determined by the extent of damage in the medial temporal lobe and other brain regions
memories from long ago seem to be spared
normal perception
general intellectural functions intact
new learning is possible when considering skills
skill learning in classic amnesic syndrome (non-declarative)
mirror writing task (motor learning)
subject cannot see hand but are being asked to copy an image only using information provided by a mirror
start slowly as they learn to interpret the mirror but with practice, performance improves
anoxia and classic amnesic syndrome
anoxia can be caused by premature birth, heart attacks, smoke/carbon monoxide inhalation
anoxia is the result of oxygen deprevation in the brain and significantly affects pyramidal cells in CA fields of the hippocampus
alcohol and classic amnesic syndrome
10-24% of all cases of dementia due to cell loss and degeneration in the diencephalon- korsakoff’s syndrome (wernicke’s encephalopathy)
acute thiamine deficiency death in up to 20% of cases
in 85% of survivors=korsakoff’s which is associted with memory loss (details in anterorgrade and retrograde)
up to 25% of those with KS require LT institutionalisation
loss of neurons, axons damage and punctuate haemorrhages in the thalamus
particular issues in the mammillary bodies
herpes encephalitis and classic amnesic syndrome
rare but severe viral infection, in the main caused by HSV-1
survivors suffer with severe brain damage with consequent memory loss
cell loss in the medial temporal lobes and in the frontal lobes
selective brain damage through trauma and classic amnesic syndrome
patients NA and BJ- damage to the diencephalon and mamillary bodies
example of herpes encephalitis patient
clive wearing
patient NA
amnesic since 1960 ages 22 years sustained benetrating brain injury with miniature fencing foil
amnesia for verbal material no other detectable cognitive deficits
lesion in left thalamus and mamillothalamic tract
patient BJ
amnesic following a penetrating brain injury caused y a snooker cue which entered through his left nostril
amnesia primarilty affects verbal material
lesion in hypothalamus in region of mamillary bodies
modelling amnesia in animals
a series of influential experiments from 1970s attempted to identify critical neural regions for explicit memory
experiments used ablation techniques to assess whether removal of areas of the medial temporal lobe affected memory
studies first conducted in macaque brain
main of the studies used the dalyed matching or non-matching sample tasks
matching/non-matching sample tasks
monkey is orginally presented with a sample object, when he displaces it he finds food underneath
after a variable delay the monkey is presented with the original object and another
over a series of trials with different object pairs, the monkey learns that food is present under objects that differ from teh sample
how do we assess matching tasks in rodents?
y-mazes
medial temporal lobe
comprised of hippocampus and the entorhinal cortex and perirhinal cortex (parahippocampal gyrus)
recieve multi-modal information e.g from visual cortex
effects on visual recognition of combined and separated ablations of the entorhinal and perirhinal cortex in rhesus monkeys
selectively target the hippocampus and parahippocampal regions
entorhinal cortex=no significant errors in delayed non matching sample task
significant errors in perirhinal cortex
therefore hippocampal lesions have little effect on this type of recognition memory
