Memory And Forgetting Flashcards
What types of memory are there (+associated brain regions)?
Short-term memory
- prefrontal cortex
Working memory
- prefrontal cortex, parietal lobe, temporal lobe, hippocampus
Long-term memory
- declarative memory (explicit memory): hippocampus, neocortex, amygdala
- non-declarative memory (implicit memory): basal ganglia and cerebellum
Hippocampus
= situated in mesial temporal lobe within the inferior horn of the lateral ventricle
- seahorse-like appearance
- three parts:
-> head = mesolateral axis
-> body = anteroposterior axis
-> tail = mesiolateral axis
Long-term potentiation (LTP)
pyramidal neurons in rodent hippocampus:
- high frequency stimulation of synapse makes the post-synaptic neuron more responsive to future stimulations at this synapse
- effect can last hours to years
- specificity:
-> no general increase in responsiveness of the post-synaptic neuron (= synapses that are inactive during the high-frequency depolarisation are not reinforced) - will arise both when the pre-synaptic and the post-synaptic neuron are depolarised in synchrony (= within approx. 100ms)
–> Cells that fire together, wire together
Activation of NMDA receptors
NMDA receptors = ligand-gated cation channels activated by glutamate
- at resting potential (post-synaptic cell not depolarised): no NMDA receptor activity
- during post-synaptic depolarisation: depolarisation activates NMDAR –> Ca2+ influx
- Ca2+ activates proteins that contribute to expression of AMPA receptors on surface –> locally amplifying glutamate effects or activating ‘silent synpases’ (=previously not expressing AMPA receptor)
How to study memory: Behavioural experiments
1) memory tests
- recall tasks to measure woking and short term memory
2) eye witness memory studies
- to examine how people recall events, often focusing on how memories can change over time or be influenced by suggestion
How to study memory: Neuroimaging
1) fMRI
- measures brain activity by detecting changes in blood flow to see which areas of the brain are activated when people form or recall memories
2) PET
- measure glucose metabolism in the brain to see which regions are more active during memory tasks
3) EEG
- measure electrical activity in the brain
How to study memory: lesions
- examine people or animals with brain damage to see which parts of the brain are involved in memory
- for example: damage to the hippocampus is associated with problems in forming new memories (patient HM)
How to study memory: TMS
- temporarily disrupt or enhance activity in specific areas of the brain to see how disrupting these areas affects memory performance
How to study memory: pharmacological studies
- using drugs to investigate memory processes (drugs that modulate acetlycholine, glutamate, dopamine systems)
–> how different neurotransmitters or receptors affect memory formation
How reliable are our memories?
memory is reconstructive
- based on a combination of the original experience and external information
- each time we retrieve a memory, it can be altered and re-stored with new details
false memory
- false memories can be created –> people can vividly recall events that never happened, especially when they are given misleading information or are asked leading questions
Loftus’s research: suggestive questions leading to people remembering details that were never part of the original event
What affects memory?
- emotion and stress
- attention
- age-related memory decline
- neurodegenerative diseases (AD, dementia)
- cognitive bias (stereotypes, ideologies)
- sleep
- drugs
Influence of LTP and LTD
- LTP and LTD cannot happen at the same time (mutually exclusive)
- dopamine is used as a neuromodulator in both
- LTD provides necessary balance for fine-tuning neural signals
- LTP alone would result in all synapses becoming maximally strong
LTD versus forgetting
LTD ≠forgetting
LTD
- single synaptic mechanism
- induced within minutes
- can sometimes result in forgetting
Forgetting
- multiple mechanisms
- occurs in minutes to years
Forgetting: Passive forgetting
Passive forgetting:
- natural decay of memories over time
- loss of retrieval cues/context
Forgetting: Two mechanisms
Two mechanisms:
- memory inhibition: direct suppression of memories
- process inhibition: general suppression of memories
