L3 - Memory Loss, Amnesia and the Hippocampus Flashcards
What is an engram?
A memory trace - a hypothetical, permanent change in the brain as a result of a memory.
How does patient HM provide evidence for a localised memory engram?
Surgeons removed patient HM’s hippocampus, and its associated, surrounding structures to treat their epilepsy. Although the epilepsy was treated, patient HM’s ability to form new memories, and remember old ones, were significantly impaired - anterograde and retrograde amnesia respectively.
Demonstrates that there could be some localised structures that are pivotal in the formation of new memories and recall of old ones.
What cognitive functions were intact in patient HM?
- IQ (118)
- Digit span
- Spatial working memory
- Procedural memory
What was impaired in patient HM?
Declarative memory - episodic and semantic memory impairments.
What was the reason for Clive Wearing’s memory deficits?
Virus in the brain which affected the hippocampus - herpes simplex infection at 46.
What were Clive Wearing’s memory deficits?
Lost his episodic memory
What is retrograde amnesia?
Loss of access to events that happened in the past, prior to a trauma
What is anterograde amnesia?
A deficit encoding, storing or retrieving new events occurring after a trauma.
What was Ribot’s law?
For retrograde amnesia, memory impairments are more pronounced for events occurring briefly before the traumatic event.
What is post-traumatic amnesia (PTA)?
The loss of ability to form new memories, typically following some form of concussive head injury. Gradually improves over time.
What is Transient Global Amnesia (TGA)?
A sudden impairment in forming and retrieving new memories in normal, otherwise healthy individuals. Tends to resolve rapidly.
Define etiology
Cause, or set of causes, of a disease or condition.
What are the 4 most common causes/etiologies of anterograde amnesia?
- Bilateral damage to the temporal lobes and hippocampus
- Alcoholic Korsakoff syndrome
- Prolonged anoxia
- Herpes
What is the key deficit in anterograde amnesia?
Episodic learning - this is regardless of the domain of information (visual or verbal) and the type of test (recall or recognition).
What are the preserved abilities in those with anterograde amnesia?
- intellect and language
- non-declarative memory (priming, procedural memory, etc)
- digit span
- recency effect in free recall tasks
- Brown-Peterson short term forgetting task
Describe the Brown-Peterson short term forgetting task.
A 3-word, or 3-letter phrase is read out, and followed by a 3-digit number which participants have to count down from, for example in 2s.
Ex: farm, mouse, car. 124 –> 122, 120, 118, etc.
Then a cue appears which instructs participants to recall the 3 earlier words.
This is one trial, so this procedure repeats
many times.
Why do neurotypical participants have difficulties remembering items on the Brown-Peterson task?
Proactive interference. As trials progress, the accumulation of more and more 3-word combinations in short term memory interferes with learning of novel 3 word combinations, decreasing recall ability.
Why might people with anterograde amnesia have an intact ability to perform the Brown-Peterson task?
Short term memory is unaffected, but when items enter long term memory, recall becomes difficult. Therefore, 3-word phrases do not build up in memory, causing less interference for learning of current 3-word phrases.
What was initially suggested to be the reason for amnesia?
Cognitive deficits in the ability to process information at a deep enough level. However, the lack of deep enough processing was later found to result from frontal deficits, and when these were accounted for, memory impairments remained.
What other reasons were later suggested as the cause of amnesia?
- quicker forgetting; perhaps long term memory traces decay more rapidly in amnesiacs. This was proven wrong, however - when the initial rate of learning was equated, the rate of forgetting was equivalent between subtypes of amnesiacs Koppelman (1985).
- retrieval interference; perhaps there is a build up of cues, triggering the activation of many interfering memories, blocking the retrieval of the correct memory. This was also proven wrong, it was found that explicit instructions did not benefit amnesiacs in accessing the relevant item (explicit cue should link to the relevant memory and induce recall of the correct memory trace.
What is the contextual processing theory of amnesia?
The hippocampus requires what and where (contextual) information about an object or event. It’s deficits in the hippocampal integration of this information which causes an impairment in forming episodic memories
What is the animal evidence for the contextual processing theory of amnesia?
Animals with hippocampal regions are poor at using environmental context in spatial learning tasks (Winocur & Mills, 1970).
What is the human evidence for the contextual processing theory of amnesia?
Amnesiacs were worse at stating which day they saw particular stimuli on, compared to controls. However, amnesiacs were more likely to report seeing the stimulus more recently than another if they saw it twice, and only saw the other stimulus once. This was interpreted as a reliance on familiarity in the absence of contextual information, by amnesiacs (Huppert & Piercey, 1978).
They confuse recency with familiarity.
What is the modal model of amnesia (Baddeley, 1998)?
Assumes:
- an episodic memory is consolidated when ‘mnemonic glue’ binds items together with their contexts.
- recall and recognition involve he same underlying processes (we now know this is flawed).
- semantic memory is a consequence of episodic information over time.
