PSYC327: Long-Term Memory

The Hippocampus

involved in memory; tucked deep inside the temporal lobes on the left and right

Medial Temporal Memory System (MTS)

hippocampus + Surrounding Cortex + Subcortical Structures

Other Structures Involved in Memory

The Parahippocampal, perirhinal and entorhinal cortices

- they "wrap around" the hippocampus

Two Subcortical Structures for Memory

fornix & mammillary body

- Damage to either of these structures result in severe and profound long-term memory losses

Damage to MTS

Medial Temporal Amnesia

Medial Temporal Amnesia

memory disorder primarily caused by damage to the medial temporal lobe structures, especially the hippocampus, which leads to difficulties forming new memories (anterograde amnesia) and recalling old ones (retrograde amnesia).

- Onset is cumulative

Patient HM & Medial Temporal Amnesia

after removal of the medial portions of the temporal lobes (including the hippocampus), H.M. became profoundly amnesic

- Tissue where the hippocampus lies was completely removed

- Amnesia due to the MTS & Hippocampus

Causes of Medial Temporal Amnesia

- Surgery (HM)

- Infection (e.g., herpes simplex encephalitis: Clive Wearing)

- Hypoxia (e.g., carbon monoxide poisoning)

- Alzheimer's (most common cause)

- Korsakoff's (damage to mammillary bodies from a deficit in b vitamin)

Medial Temporal Amnesia: Two Components

1. Loss of memories for at least 1 yr before illness (retrograde amnesia)

2. Cannot remember new facts/events (anterograde amnesia)

Retrograde Component: Features

- memory disorder characterized by the inability to recall events, information, or experiences that occurred before the onset of the amnesia.

- impaired period at least 1 yr

- pattern may be more continuous (shows a temporal gradient)

- Memory for semantic facts learned before illness may be large sparedAnterograde Component: Features

Measuring Retrograde Amnesia: H.M.

- Corkin and colleagues gave H.M. a series of cue words (e.g. holiday, friend), and asked him to recall a personal experience connected with each one.

- On this test, all of H.M.'s spontaneous recollections were from events occurring prior to his 16th birthday - even though he did not undergo surgery until age 27

- demonstrates some memory from before illness remained

Retrograde Component: Tests

- Giving a series of cues words

- Autobiographical Memory Interview

Limitation of Giving a Series of Cued Words

cannot control the period

- Patient may prefer a different period and discusses that instead

Autobiographical Memory Interview

- Askes questions/cued recall of experiences from three time periods: Childhood, Early adult life and Recent events

- Probe the pp to provide as many details about the event as possible

- Analyse whether they were able to come up with an event and extra points on if they had internal details of the eve

Anterograde Component: Features

- Much more profound and severely impaired

- Knowledge and personal history can be "frozen in time"

- Patients have a short "window" of recall before memory is lost

- Both episodic and semantic memory are affected BUT a tiny bit of semantic learning can occur, even in the most severe cases.

Anterograde Components: Tests

- Free recall

- Recongition

- Paired Associate Learning

Free Recall

ask pp to report back what words were presented a few minutes prior

Recognition

Giving a series of items (e.g., faces) -> 5-15 min break -> give more items -> ask whether they saw it prior e.g.,

Paired Associate Learning

two words presented as a pair -> give them one word and ask them to recall the word paired with it

- Most difficult and highly sensitive

Function of MTS

MTS - specifically hippocampus - appears critical for learning associations that occurred on a single occasion

Consolidation Theory (Alvarez & Squire, 1995)

All aspects of an experience cause changes in the relevant cortical areas. The MTS (/Hippocampus) c takes one of changes during an experience and forms new connections between itself and these cortical areas. This leads to activation of one component spreading throughout the network and it allows you to experience an entire experience from one trigger

Process of Consolidation

1. You need the Hippocampus to retrieve the memory (period before damage where hippocampus is still healthy). Memory is laid down accurately

2. But, repeated recollection (via reminiscing, talking to others, photos etc.) strengthens direct cortico-cortical connections

3. Eventually, can recall entire experience without hippocampus

Retrograde Amnesia & Consolidation Theory: Reason for Temporal Gradient

Process takes time, meaning events 1-3 years prior to onset of illness is unable to be remembered (hasn't had time for recent memories to recollect them and remember them enough to develop these connections)

Strengths of Consolidation Theory & Retrograde Amnesia

- Makes sense of the temporal gradient

- Explains why people with amnesia can't encode new memories (Need hippocampus for initial step to occur; without it, the other stages cannot occur)

Limitations of Consolidation Theory & Retrograde Amnesia

Is the memory really the same after we have repeatedly recalled it? ...or does it change in some important way?

- memories are sparce

- 90%ish is not recollected on or reminisced

- Our memory is always changing and contorting as a result of recollection

Multiple Trace Theory (Nadel & Moscovitch)

Each time you recall a memory, you create a new memory (trace) of the recollection of the event itself and repeated recall doesn't just strengthen the cortical connections and instead make new traces/changes the nature of the memory

Evidence Supporting Multiple Trace Theory

- Found that healthy people are bad at remembering details from earlier memories compared to recent memories

- Found that people with temporal amnesia had the same inability to remember childhood memories but their level of detail is still low for recent memories

Strengths of Multiple Trace Theory

- How semantic memories develop

- why remote memories are so fragmented

- Why we sometimes misremember thing

Hippocampus

linking/binding elements together that occurred during a single event to make up a single memory

- Measuring this is paired associate task

Other structures that work with the hippocampus

- Parahippocampal Gyrus =

- Entorhinal Cortex

- Perirhinal Cortex = remembering elements and items

The Perirhinal Cortex

remembering elements and items

The Parahippocampal Cortex

coding the background scenes and settings/context

The Parahippocampal Cortex: Neuropsychology Evidence

Case of GR: had damage to Parahippocampal cortex but not hippocampus and was unable to navigate new environments

Demonstrates that navigating in unfamiliar environments is a central role of the Parahippocampal cortex

Eichenbaum: Binding in Context (BIC) Model

semantic dementia

Memory for facts more impaired than events

The earlier the memory was learned, the more likely it is to be affected

Semantic Dementia: Brain Damage

Lateral Temporal Lobes

Semantic Dementia: Assessing Knowledge Loss

- Picture Naming

- Drawing from Memory

- Picture-to-Picture Matching Tasks

The Hub-and-Spoke Model

A model of semantic knowledge that proposes that areas of the brain that are associated with different functions are connected to the anterior temporal lobe, which integrates information from these areas.

Language + auditory + visual + olfactory + motor praxis + somatosensory = extract our core common to the experience and tip of temporal lobe creates an abstract storage for it