Memory Flashcards
what are the definitions of learning, memory, recall and ‘the engram’?
learning = acquisition of info/skills
memory = storage of learned info
recall = reacquisition of stored info
the engram = physical embodiment of a memory
what are the 2 independent memory systems?
- procedural - implicit
2. declarative - explicit
what is procedural memory?
- skills and associations that are largely unavailable to the conscious mind
- e.g. acquired skills which after you practice you can naturally do e.g. riding a bike
what is declarative memory?
- available to conscious mind
- can be encoded in symbols and language
- e.g. speaking/communicating knowledge
what is explicit memory?
- memory that can be consciously recalled
- e.g. recalling riding a new bike
what is implicit memory?
- memory that cannot be consciously recalled
- e.g. learning to ride a bike
what are the 3 types of implicit memory?
- Procedural memory
- classical conditioning e.g. Pavlov’s dogs
- Priming - when one stimulus influences the response to subsequent stimuli
what are the 3 types of memory duration?
- immediate memory = few seconds
- short-term memory = seconds/minutes
- working memory - long-term memory = days/months/years
how is the temporal lobe involved in memory?
- electrical stimulation of the temporal lobe causes hallucinations and recollection of past events
- important in generating long-term memory
what are epileptic seizures?
when neurons in local, specific areas of the brain fire APs uncontrollably, causing complex sensations and memories
what happens when a patient’s temporal lobe is removed? (lobectomy)
- intelligence, personality and long-term memory in tact
- epileptic seizures stopped
- extreme anterograde amnesia - couldn’t acquire new memories
what are the important brain structures involved in memory?
- Prefrontal cortex: working memory
- Hippocampus: declarative memory
- converts short to long term memory - amygdala: implicit memory
- multiple, processed sensory inputs i.e. emotional memory and learnt fear - cerebellum: procedural memory
- sensorimotor
how is the hippocampus involved in memory?
- 3 layered cortex with inputs from the entorhinal cortex
- outputs to many regions
- enlarged in people with good spatial memory
- hippocampal lesions cause memory loss
what are the mechanisms of memory?
long-term storage is distributed across brain regions
reverberating circuits: memory part of a specific population of neurons in the brain
the Hebbian synapse concept: gain of synapses increases/decreases during memory formation
- synaptic plasticity
what is the Hebbian synapse concept?
- synaptic strength changes cause an increase in amplitude of EPSP
- facilitation/depression: short-term changes in synaptic strength due to Ca2+ availability or vesicle depletion
- long-term facilitation/depression is sustained
what is Long-Term Potentiation (LTP)?
an increase in synaptic strength that lasts over days/weeks:
- in hippocampus
- synaptic plasticity was studied between CA3 presynaptic and CA1 postsynaptic neurons
what is post-tetanic LTP?
- high frequency burst of depolarisations on CA3 causes increase in EPSP amplitude
- if a different neuron has the same high frequency depolarisation applied, the EPSP stays the same
- shows that changes in the synapse are at local level and specific to certain cells (CA3 and CA1)
- even if other neurons synapse to CA1, their EPSPs will remain the same
what is paired LTP?
- stimulus and depolarisation of CA3 and CA1 at the same time causes change in strength of synpase
- causes increase in amplitude of EPSP
- classical conditioning
what is Long-Term Depression (LTD)?
a decrease in synaptic strength that lasts over days/weeks:
- in hippocampus
- if presynaptic neurons are stimulated at low frequency, amplitude of EPSP decreases
what are the characteristics of the Aplysia californica snail?
- lacks many neurons so can correlate specific neurons with specific behaviours
- larger neurons than mammalian neurons so easy to study
- has gill-withdrawal reflex: stimulation of areas close to gill (siphon) causes gill to move inwards
what is the short-term habituation and sensitisation of the snail?
- repeated gentle stimuli to siphon causes reduced gill-withdrawal as snail releases no danger = habituation
- random tail pinch causes re-established withdrawal reflex which is short term (60 mins)
what is the long-term sensitisation of the snail?
- repeated pairing of siphon touch and tail pinch causes long-term withdrawal reflex
what are the characteristics of LTP, LTD and aplysia?
- require receptor activation by glutamate or serotonin
- alters synaptic responsivity
- mediated by second messengers
- require protein phosphorylation in early stages and protein synthesis in late stages
- involve pre and post synaptic changes
how does LTP occur?
- a postsynaptic event involving Ca2+
- trafficking of AMPA receptors to the postsynaptic membrane
