In this article introduces memory disorders; specifically anterograde amnesia. Using one of the most famous case studies of amnesia; the case of HM Henry Gustav Molaison (1926-2008).
POST-TRAUMATIC AMNESIA (PTA)
- Most common form of amnesia
- Cause: severe head trauma
- Leads to brain lesions, twisting and tearing of microstructures, bony skull protrusions may scar (especially in temporal lobe)
- Symptoms: initial unconciousness followed by period of confusion, inability to keep track of on-going activities or where they are
- Duration: few minutes/hours
- Recovery: Gradual return to normal although period around trauma may remain lost
Extreme head trauma may lead to long-term amnesia; the inability to recall old or encode new memories.
- Anterograde amnesia: inability to create new memories
- Retrograde amnesia: inability to recall memories prior to trauma
CASE STUDY: HM
Henry Gustav Molaison(1926-2008)
- Severe epilepsy from 10 yrs
- 1953 Experimental removal of medial temporal lobe (MTL)
- Hippocampus, amygdala and parts of lateral temporal areas
- Severe anterograde amnesia
- Some retrograde amnesia
- Preserved working memory
- Preserved motor-skill learning
- Deficit in transfer from WM to LTM
- Language essentially frozen in the 1950s
- H.M. was widely studied because the precise surgical removal of most of his hippocampus allowed its function to be tested without other confounding impairments.
- Brain Trauma is typically non-specific e.g. Hypoxia (lack of oxygen) can kill neurons throughout the brain.
- H.M. was studied by thousands of psychologists/neuroscientists.
- But, every day of testing was like the first.
- Never recovered
ANTEROGRADE: NEW/OLD MEMORIES
- Working memory (WM) is intact
- Hippocampus (HC) is not critical for WM
- Difficulty learning new information
- HC is critical for the formation of new memories
- Good memory up to brain injury
- Recall of established LTM does not require HC
- Personality, intelligence, judgment IQ unaffected
- Not located in HC
- Located in frontal lobes (as shown by other cases)
Hippocampus “Gateway” to Permanence
- Brain legion evidence suggests that the hippocampus is important in the process of “consolidation”
- “Binding” episodes (input from sensory areas)
- Transfering WM to LTM
- Strengthening memories by
- Learning new pathways
- reusing existing pathways (through retrieval)
Amnesic evidence: Conditioning
- Neuropsychiatrist shook hands every morning with his amnesic patients.
- Patients had no explicit recollection of him.
- One day, hides a pin (US) in his hand patient recalls in shock (UR)
- Unconditioned stimulus – unconditioned response
- Next day, patient refuses to shake hands (CS) but cannot say why!
- Conditioned stimulus – anticipation of shock (CR)
Conditioning does not require explicit memory or the brain regions (HC) necessary for explicit memory.
Amnesic evidence: Procedural Memory
- H.M’s Existing procedural memories (i.e. Motor and perceptual skills ) intact
- Can form new procedural memories!
Corkin (1968): Mirror-tracing task
- Can learn skill and retain for up to 1 year.
- Even though he has no episodic memory of doing it before!
Amnesic evidence: Priming
Repetition Priming = easier perception due to repetition, e.g. Words recognised faster if presented previously even in the absence of explicit memory!
Graf & Schacter (1985):
- Study: word list (table, garden, umbrella)
- Free recall (= poor as no explicit memory)
- Cued recall: complete word stem with word from study list
- word stem completion: complete word stem with first word that comes to mind
= Faster on both due to Priming.
Read next: ‘How do we store memories?‘