PSYCH 202 Memory

HM - The Person Who was Henry Gustav Molaison (HM) and why is he important in neuroscience

• Most famous amnesiac patient in neuropsychology

• Demonstrated that memory consists of multiple, dissociable systems

• Showed that medial temporal lobes (hippocampus) are critical for forming certain types of memory

• His case revolutionised memory research

HM - The Person What was HM’s medical history before surgery

• Age 9: Bicycle accident with brief loss of consciousness.

• Age 10: Minor seizures began.

• Age 16: Grand mal seizures developed.

• By age 27: Severe epilepsy uncontrolled by medication.

• Unable to work due to seizure severity.

HM - The Person Why did HM undergo bilateral temporal lobectomy

• EEG showed seizures originated from both medial temporal lobes

• Unilateral surgery has previously helped other epilepsy patients

• Surgeons removed tissue from both medical temporal lobes to reduce seizures

HM - The Person What brain structures were removed during HM’s surgery

• large portions of both hippocampi

• most of the entorhinal cortex

• much of the amygdala

• other surrounding medial temporal structures

• posterior hippocampus remained partially intact

HM - The Person Bilateral Temporal Labectomy successes

• seizures became less frequent and less severe

• intelligence remained largely intact

• emotional stability remained intact

HM - The Person Bilateral Temporal Labectomy unexpected consequences

• Profound global amnesia

• Unable to form most new long-term memories

HM - The Person Which major memory problem did HM develop after surgery

Severe anterograde amnesia

• coudn’t form new long-term explicit memories

• could remember information only while actively rehearsing it

Dissociability of Memory Systems How did H.M. demonstrate that short-term memory and long-term memory are separate systems?

• Normal digit scan (5-6 items)

• could maintain information indefinitely through rehearsal

• Information disappeared immediately if distracted

• could not transfer information into LTM

Dissociability of Memory Systems H.M. digit scan implications

STM and LTM are dissociable systems because his STM was unaffected while LTM was impaired

Dissociability of Memory Systems What was intact in HM’s memory system

• Working Memory

• sensory register

Dissociability of Memory Systems What was impaired in HM’s memory system

• LTM encoding

info never successfully entered permanent storage

Dissociability of Memory Systems What key principle did HM establish

Damage to the MTL can severely impair LTM formation while leaving STM relatively intact

Types of STM/Working Memory

Explicit memory (declarative)

• facts

• events

Types of LTM

Implicit (Non-declarative)

• skills and habits

• priming

• simple classical conditioning

• nonassociative learning

Explicit vs Implicit Memory What is explicit (declarative) memory

Memory involving

• conscious awareness

• recall or recognition

• facts and events

Explicit vs Implicit Memory What is implicit (non-declarative) memory

Memory expressed through performance rather than conscious recollection

• e.g. riding a bike

Explicit vs Implicit Memory How did HM demonstrate intact implicit memory

Mirror Drawing Task

• Improved steadily with practice

• Retained improvements across days

• Learned at the same rate as healthy controls

Yet he insisted he had never done the task before

Explicit vs Implicit Memory What did the mirror drawing experiment demonstrate

Learning can occur without conscious memory

• Implicit memory was intact despite profound explicit memory loss

Explicit vs Implicit Memory What brain structures are important for explicit memory

hippocampus and medial temporal lobe

What is procedural memory

a type of long-term, implicit memory that guides the execution of skills and physical actions

Explicit vs Implicit Memory What brain structures are important for procedural memory

basal ganglia

Explicit vs Implicit Memory What brain structures are important for motor skill learning

Basal ganglia corcuits

Semantic vs Episodic Memory What is semantic memory

Memory for

• facts

• concepts

• general world knowledge

Semantic vs Episodic Memory What is episodic memory

memory for personally experienced events, inclusing

• time

• place

• thoughts

• feelings

• sensory details

Semantic vs Episodic Memory What does semantic memory play during episodic recollection

According to Irish & Piguet (2013):

• Semantic memory provides schemas and meaning.

• Helps fill gaps during memory retrieval.

• Supports reconstruction of episodic memories.

Semantic vs Episodic Memory According to Addis (2020), why is memory not like a video recording?

Memory is not stored as a complete, high-fidelity recording.

Instead:

• Different elements of experience are stored across different brain regions.

• Memory is distributed throughout the brain.

Semantic vs Episodic Memory How does remembering occur according to Addis (2020)

Remembering involves

• reactivating distributed memory elements

• recombining those elements

• simulalating the remembered event

Memory is reconstructed rather than replayed.

Semantic vs Episodic Memory What role does the hippocampus play in memory retrieval

• pulls memory elements together

• binds sensory, emotional, conceptual, and semantic info

• enables conscious recollection

• allows a person to relive the event

Semantic vs Episodic Memory Why are episodic memories prone to distortion

• memories are reconstructed, not replayed

• elements are stored seperately

• Recombination can introduce errors

Semantic vs Episodic Memory What is the key feature of episodic memory according to Tulving

Mental time travel and autonoetic consciousness

• the ability to mentally relive past experiences

Semantic vs Episodic Memory How was HM’s sensory semantic memory affected

• older semantic knowledge mostly preserved

• could not acquire much new semantic knowledge

Semantic vs Episodic Memory How was HM’s episodic memory affected

Profoundly impaired.

Could not:

• Form new autobiographical memories

• Remember meeting people after surgery

• Recall recent life events

Semantic vs Episodic Memory What is anterograde amnesia

Inability to form new memories after brain injury or illness

• HM’s most severe impairment

Semantic vs Episodic Memory What is retrograde amnesia

Loss of memories acquired before injury

Semantic vs Episodic Memory What evidence suggested HM has extensive retrograde amnesia

Autobiographical Interview

• could recall only one specific autobiographical memory

• produced mostly vague, script-like descriptions

• lacked detailed episodic recollections

Semantic vs Episodic Memory What is double dissociation between episodic and semantic memory

Semantic vs Episodic Memory What causes semantic dementia

Damage to the anterior temporal cortex

Semantic vs Episodic Memory What does semantic dementia produce

• loss of factual knowledge

• naming deficits

• difficulty describing objects and people

Semantic vs Episodic Memory What are major causes of severe memory loss

• Stroke

• Traumatic brain injury

• Brain tumour

• Cerebral hypoxia

• Herpes simplex encephalitis

• Korsakoff's syndrome (Vitamin B1 deficiency)

• Alzheimer's disease

Mental Time-Travel and Future Thinking Why is episodic memory described as a mental time-travel system?

Because it allows conscious movement through subjective time:

• Re-experiencing the past.

• Simulating the future.

Mental Time-Travel and Future Thinking According to Suddendorf, what may be the evolutionary advantage of episodic memory?

The ability to accurately predict and prepare for the future.

Future simulation may be more important than remembering the past.

Mental Time-Travel and Future Thinking What finding supports the link between remembering and imagining?

Remembering the past and imagining the future activate a common core neural network

Mental Time-Travel and Future Thinking What is the Constructive Episodic Simulation Hypothesis?

(Schacter & Addis)

The same system:

• reconstructs past experiences

• simulates future experiences

Memory and imagination rely on shared mechanisms.

Mental Time-Travel and Future Thinking What evidence suggests H.M. had difficulty imagining the future?

When asked “what do you believe you would do tomorrow”, his responses lacked specific future events

Mental Time-Travel and Future Thinking What evidence links MTL damage to impaired future thinking

Patients with MTL amnesia

• cannot imagine future detailed events Race et al. (2011)

• cannot imagine fictional scenes (Hassabis et al 2007)

Mental Time-Travel and Future Thinking What was unique about Case K.C.?

• severe episodic amnesia

• could not recall persona events

• could not imagine his future

strong evidence episodic memory supports future simulation

Memory and Sense of Self How is Alzheimer's disease commonly portrayed in society?

A gradual loss of self

Memory and Sense of Self What alternative perspective exists regarding selfhood in dementia?

People may lose memories but retain a strong sense of self

Memory and Sense of Self What are the three major components of self?

• Self-knowledge: Traits, beliefs, preferences

• Narratives: Personal life stories

• Core self: Subjective experience of being you

Memory and Sense of Self What is self-continuity

“I am the same person over time despite change”

Memory and Sense of Self What is the I-Self

• core essense

• subjective self

• often unchanged in AD

Memory and Sense of Self What is the Me-self

• content of identity

• personal facts and roles

• most likely to change

Memory and Sense of Self What did Self-Continuity Interview studies find in Alzheimer's disease?

Most individuals with AD believed they were still the same person they had been in early adulthood.

Memory and Sense of Self What did the IDEAL cohort study find about self-continuity?

Sample:

• 1465 people with mild-moderate dementia.

Results:

• 79% agreed they were still the same person.

• 21% reported discontinuity.

Memory and Sense of SelfWhat was associated with loss of self-continuity in dementia?

Those reporting discontinuity had:

• Lower psychological wellbeing.

• Poorer quality of life.

• Lower "living well" ratings.

What is the major conclusion regarding memory and self?

eople with Alzheimer's disease can retain a strong sense of core self despite severe autobiographical memory loss.

This suggests memory contributes to identity, but is not the sole basis of selfhood.