Lecture 24: Memory Systems

What are the types of memory?

declarative and non-declarative

What is declarative memory?

things you can tell someone

Where is declarative memory located?

medial temporal lobe; diencephalon

What are the two subcategories of declarative memory?

• events (episodic memory)

• facts (semantic memory)

What are the timescales of memory?

• long-term

• short-term

• working memory

What is the timescale of short-term memory?

seconds-to-minutes

What happens when you consolidate short-term memory?

you form long-term memories

What is the timescale of long-term memory?

days-to-years

What is amnesia?

abnormal forgetting; loss of long-term, declarative memories that should have been retained, and/or inability to store new memories

What are the types of amnesia?

• retrograde

• anterograde

• transient global

What is retrograde amnesia?

forgetting things that had occurred prior to the time of trauma

What is anterograde amnesia?

inability to form new memories following the time of trauma

What is transient global amnesia?

brief episode (hours-few days) usually involving both anterograde and retrograde symptoms

What is episodic memory (autobiographical memory)?

memory for distinct events

What are examples of episodic memory?

• what you had for breakfast

• conversation you had last week

What kind of memory do patients mean when they say ‘short-term memory?’

episodic memory

How do you test episodic memory?

• by giving people new episodic memories

  • word list learning task (primacy and recency effects)

  • story recall (more ecological)

    • different people may respond to different aspects of the story based on own personal history

  • confound testing

    • can hide objects in the room

What are examples of primacy in the Rey auditory verbal learning task?

• drum

• curtain

• bell

• coffee

What are examples of recency in the Rey auditory verbal learning task?

• turkey

• color

• horse

• river

What happened to Patient H.M.?

underwent surgery to bilaterally remove large portions of the medial temporal lobes including most of hippocampus and amygdala

What was an unexpected side effect that Patient H.M. had?

• had severe anterograde amnesia and partial retrograde amnesia

  • he could not commit any new event to declarative memory - poor episodic memory

  • needed full time care to carry out daily activities

  • could not remember anyone he had met after the surgery

What did Patient H.M.’s surgery have little effect on?

• perception

• intelligence

• personality

• short-term memory

What was still intact in Patient H.M.?

procedural memories and procedural learning

What did H.M. learn in tests carried out by Dr. Milner?

to improve his ‘mirror drawing’ skills over several days, but had no recollection of the task or of having ever practiced it before

What brain region is critical for episodic memory, and what are its main structures?

he medial temporal lobe. It includes the hippocampus, entorhinal cortex, perirhinal cortex, and parahippocampal cortex.

What are diseases affecting the hippocampus?

• AD

• Herpes Simplex Encephalitis

• Global cerebral hypoperfusion

What is DNMS?

delayed non-match to sample task

What is done in the DNMS?

• compare presented objects with a previously presented object after a delay, select the ‘novel’ non-matching object to obtain a reward

• a form of episodic memory

What is important for memories longer than about 10-30 seconds?

medial temporal lobe

What are the effects of medial temporal lobe lesions on DNMS?

• large bilateral lesions of medial temporal lobe results in an inability to remember the first stimulus beyond 10-30 seconds

• task involved ‘recognition memory’ - subject must recognize the object as one that has been seen recently

• anterograde amnesia

What is the Morris water maze?

• rate must learn to find the location of a submerged platform

• visual cues are placed around the pool

• requires intact hippocampus

What happens with the hippocampal place cells in the Morris water maze?

• fire when animal is in a specific location

• place cells rotate with external visual cues

What is activated in human PET imaging study during spatial navigation of a virtual town?

hippocampus

What brain area is larger in more experienced London cab drivers?

posterior hippocampus

What is the hypothesis of Hebbian Cell Assemblies?

external events are represented by reciprocally interconnected groups of cortical neurons

What is the cell assembly concept?

• formed via Hebb rule: cells that fire together, wire together

• memories are distributed among all the linked cells in the assembly

• memory completion: partial activation of the assembly can trigger activation of the entire assembly

What structures play an important role in memory consolidation?

hippocampus and related medial temporal lobe structures

What are the steps of episodic memory consolidation?

• initially, the medial temporal lobe (MTL) links together various attributes of an event originating in diverse cortical areas

• during consolidation, the links are moved from MTL to the original cortical areas

• before consolidation is complete, the hippocampus and related structures are required to access and retrieve the stored memories

What brain structure does working memory involve?

prefrontal cortex (PFC)

What does the central executive of the PFC do?

holds entire plan, including language and visual component

What does the language scratch pad of the PFC do?

uses Broca’s area as ‘inner voice’ that repeats information

What does the visual scratch pad of the PFC do?

maintains an image of what needs to be done by activating areas near visual cortex

What does the phonological loop of the PFC do?

‘inner ear’ where the sounds of the words are kept in ming

How do you test working memory?

• digit span tasks

• trails ‘B’ test

What is the digit span test?

most people can do about 7 forward and 5 backwards

What is the Trails ‘B’ test?

• serial sevens (count backwards from 100 by sevens)

• months of the year backwards

• spelling the word ‘WORLD’ backwards

What happens when working memory fails?

all new learning is impaired

In working memory, what broad networks are involved?

• PFC

• parietal cortex

Describe the three phases of the delayed response task.

• a target flashes briefly while the monkey fixates.

• Delay: the target disappears and the monkey must remember its location.

• Response: the monkey moves its eyes to the remembered location.

Does working memory require protein synthesis?

No. It’s maintained by ongoing (possibly oscillatory) neural activity, so it doesn’t produce structural changes in the brain.

When is working memory impaired?

during metabolic encephalopathy (delirium)

Why does metabolic encephalopathy occurs?

due to drugs or metabolic changes (infection)

What is delirium?

it is not only working memory loss, but also comes with confusion, agitation, and arousal changes

What is a main diagnostic test that you can do to test for metabolic encephalopathy?

EEG

What are treatments for memory disorder?

• memory aids

• physical/cognitive exercise

• sleep

• cholinesterase inhibitors

• memantine (NMDA antagonist)

What are examples of memory aids?

• elaboration principle

  • we remember things better when we connect them to things that we already know

• Organization principle

  • we remember things in groups

  • look for ‘anchor points’ in memory

• Prosthetics - dry erase boards, texting information

What is true of sleep when it comes to memory?

many patients have undiagnosed sleep disorders

What do cholinesterase inhibitors do?

increasing ACh enhances encoding phase