CNR W7 - Learning and Memory

most common neurodegenerative disease

alzheimer’s

Memory + Learning

Memory =

• encoding, storage and retrieval of learned information

• Forgetting of transiently (short time) useful information is important

Learning =

• new information is acquired + integrated by the nervous system

• Learning is observable by changes in behaviour

Declarative (explicit) memory

• Episodic (event based) memory (‘I remember’)

• Semantic (fast based) memory

• These memories are consciously available + are usually easy to verbalise or declare

Nondeclarative (implicit) memory

• Involve skills + associations

BUT

• Not available to consciousness

• Not easy to verbalise

• ‘Knowing how’

Working memory

• Works in the range of seconds to minutes

• Short-term memory buffer = allows for manipulation of stored information

• Working memory = has to be actively maintained

• Is fragile + easily disrupted

• Has a limited capacity

Long term memory

• LTM can store larger quantities of information (potentially unlimited duration)

• Does not have to be actively maintained

• Very stable - once memories are made long-term = hard to disrupt

• E.g. working memory digit span of 7/8 numbers - but can remember phone number from childhood

Categories of human memory

Association can improve memory

• Our capacity for remembering arbitrary info is poor (e.g. 7-9 number string) - practice can improve

• Over months a student developed the ability to remember 80 element digit strings

  • Did this by associating subsets of the numbers to dates / times at track meetings (he was a runner)

• Professional ‘mnemonists’ use the same technique of associating meaningless data with meaningful + memorisable elements (e.g. using a tune)

• ability to remember is related to how much the info means to you

fun fact: world record for Pi is 67 thousand decimal places

motivation will increase association

• Asked if stimuli included food or not

• If they were hungry = identified food items more accurately

Conditioned learning

• Another form of associative learning

• Conditioned learning is a form of non-declarative learning

• a response becomes more frequent / predictable in a given environment as a result of reinforcement (stimulus or reward for desired response)

Classical conditioning vs Operant conditioning

Classical conditioning	Operant conditioning
Modifying existing (unconditioned) reflex by associating its normal (unconditioned) stimulus with a new unrelated (conditioned) stimulus	Altering the probability of behaviour by associating it with reward (or punishment) Unlike classical - the behaviour being conditioned doesn’t have to be a natural response to the US

Pavlov’s dogs

• unconditioned stimulus (food) elicits an unconditional response (salivating)

• with repeated association of a neutral stimulus (bell) with the unconditional stimulus (food), the neutral stimulus becomes a conditioned stimulus that elicits the unconditioned response

operant conditioning

• Behaviour is altered (by increasing or decreasing its probability of occurring) by associating the behaviour with a reward or punishment

• Unlike classical conditioning the behaviour that is being altered is not reflexive

• Forms the training regimes for pets and animals

HM

• Henry Molaison (1926 - 2008)

• Suffered from grand mal seizures following a bike accident

  • Unconscious

  • Tongue biting

  • Incontinent

• experimental surgery (1953) for epilepsy

• Bilateral surgery to remove the source of the seizures

  • Medial temporal lobe including:

  • Amygdala

  • Uncus

  • Hippocampal gyrus

  • ⅔ anterior hippocampus

Destruction of hippocampus causes anterograde amnesia

• No longer form episodic memories - e.g. HM had no idea he underwent surgery

• Memories of events before the surgery remained intact

• Perceptual ability, reasoning, abstract thinking all remained normal

• The part of the brain that encodes new memories + part that stores + retrieves memories are different

• He could never recognise Brenda Milner (studies him for 50 years)

other cases

• RB - Hippocampus damage following ischemia surgery = normal IQ + amnesia

• KC - motorbike accident = HC damage = amnesiac

Morris water maze

• Crucial part of episodic memory = place

• The mouse has to find a platform under water surface

• With practice, the place is remembered and mouse swims directly to the platform

• But in mice with hippocampal lesions = unable to remember + each trial is like the first

place cells

• hippocampus contains place cells

• place cell = neuron withing HC that becomes active in certain place / environment

fun fact:

• London taxi drivers have been shown to have larger hippocampi than age matched controls

• The volume of the hippocampi is correlation with the amount of time spent as a taxi driver

declarative vs non-declarative

• Mirror drawing task - HM couldn’t remember it but improved on the task

• Shows that he can learn non-declarative = diff types = this not in HC

• HM could learn Gollin figures with practice + still claimed to never seen the figures before

Memory flowchart (image)

Diseases that affect memory

Dementia	Amnesia
= syndrome in which there is deterioration in memory, thinking, behaviour and the ability to perform everyday activities Alzheimer's disease Dementia with Lewy Bodies Frontotemporal Dementia HIV Dementia Mild Cognitive Impairment Normal Pressure Hydrocephalus Vascular Dementia	= syndrome that involves substantial difficulty learning and retaining new information Korsakoff's Syndrome Transient Global Amnesia

Alzheimer’s

• Hippocampus is affected early

• Memory loss is often one of the first symptoms reported

• Hippocampal volume i=lost rapidly

• Loss of hippocampal volume is associated with decreasing memory deficits

Fronto-temporal dementia

• most common form in under 60s

• memory less is NOT often one of the first symptoms

• in both variants memory loss occurs later, when it involved the hippocampus

Behavioural variant FTD	Primary progressive aphasia
characterized by prominent changes in personality and behaviour associated with more frontal degeneration	degeneration that affects language skills, speaking, writing and comprehension Temporal lobe degeneration

Korsikoff’s

• chronic alcoholism

• thiamine isn’t absorbed

• thiamine deficiency causes damage to several parts or the brain including the mamillary bodies

• chronic amnesia – though implicit learning is relatively preserved

Temporal lobe epilepsy - acute

• Most common form of epilepsy (60%)

• Focal seizures in the temporal lobe (1-2mins) can spread to rest of the brain

• Acute effect on memory - sufferers often do not remember the seizure of the events leading up to the seizure

Temporal lobe epilepsy - chronic

• Loss of cells in HC can lead to long-term memory deficits

• These mechanisms of cell loss are not clear though they are related to the seizures

Cannabis

• The HC has cannabinoid receptors that are stimulated by the psychoactive ingredient of cannabis THC

• = the known effect of cannabis on memory

• This has been demonstrated in animal models such as the Morris water maze