what are the two forms of memory processes?
Implicit (unconscious recall) and Explicit (conscious recall)
what does implicit memory include and what regions in the brain are responsible for it?
motor and perceptual skills
amygdala, cerebellum, reflex pathways
what does explicit memory include and what regions in the brain are responsible for it?
Facts and events
hippocampus, medial temporal lobe
what features does implicit and explicit memory have in common? (3)
- there are stages in both types of memory (short and long term)
- repetition converts short to long term memory
- long term differs from short term as it requires new protein synthesis
name an animal study that looks at implicit memory and name another that looks at explicit memory
implicit-
aplysia: learned fear (memory of sensitisation)- gill withdrawal response using reflex pathways
explicit-
mouse: place learning (spatial memory)- barnes maze using medial temporal lobe and hippocampus
what kind of inhibitors can block long term memory?
protein synthesis inhibitors
in what experimental way can you compare short term and long term memory?
by inserting a protein synthesis inhibitor to the animal or abdominal ganglion. this blocks long term process without interfering with short term process.
describe what happens in short-term sensitisation (6)
- stimulation of the tail activates serotonergic cells which release serotonin
- this binds to serotonin receptors on the presynaptic sensory neurons
- these engage AC which converts ATP to cAMP
- when the level of cAMP rises, the regulatory PKA subunit binds cAMP, undergoes a conformational change, frees the catalytic subunit
- the catalytic subunit can now phosphorylate ion channels on the membrane (K+ and Ca2+)
- increased Ca2+ enters the presynapse and more vesicles can now bind and enhance neurotransmitter release
This is the mechanism of short term memory for synaptic facilitation
describe what happens during repeated stimulation (aplysia tail shock experiment) (4)
- repeated stimulation of serotonergic neurons releases more serotonin
- this increases the level of cAMP more and therefore activates PKA more persistently
- PKA catalytic subunit phosphorylates ion channels but additionally travels into the nucleus where it activates CREB-1.
- CREB-1 binds to CRE on DNA and activates genes which lead to the growth of new synaptic connections.
This growth is the maintained form of memory storage
what two proteins are required for formation of synaptic connections?
- neurexin in presynaptic terminal
- neuroligin in postsynaptic terminal
what side of the synapse do the effects of implicit memory formation occur on and what side in explicit?
implicit- pre-synapse
explicit- post-synapse
describe the mechanism for short term synaptic plasticity in early LTP in the hippocampus (schaffer collateral -> CA1) (4)
- schaffer collateral releases glutamate
- NMDA and AMPA receptors on the CA1 neuron become active (NMDA become active only after a train of stimuli)
- influx of calcium results in activation of CAMKIIa
- CAMKIIa inserts additional AMPA receptors into the membrane
describe the mechanism for long term synaptic plasticity in late LTP in the hippocampus (schaffer collateral -> CA1) (5)
- repeated stimulation of schaffer collateral induces dopamine (modulatory neurotransmitter) release
- dopamine activates dopamine receptor
- dopamine receptor activates AC which increases production of cAMP
- cAMP activates catalytic PKA
- catalytic PKA activates CREB-1 which binds to CRE and produces new synaptic connections
what happens when you block PKA in mice?
early LTP is normal but late LTP is significantly compromised
describe the circuitry in the hippocampus (4)
- Dentate Gyrus has both perforant path and mossy fibre path
- mossy fibre path forms glutamatergic connections with CA3
- CA3 neurons connect with schaffer collateral which forms synapses with CA1 neurons
- CA1 neurons form excitatory connection with subiculum neurons
what is LTP and LTD?
persistent upregulation (LTP) or downregulation (LTD) of synaptic strength
what are 4 protocols used to induce LTP?
- Tetanic stimulation (100Hz for 1s)- robust but unphysiological
- Theta burst (short burst @ 5Hz)- more physiological
- Primed burst- v similar to theta stimulation
- Realistic stimulation protocols- can feed recorded brain activities into computer simulation
describe the differences between AMPA receptors and NMDA receptors activation
AMPA- these channels are activated solely by glutamate. they are non-selective so allow Na+ in and K+ out
NMDA- these are activated by glutamate AND membrane depolarisation. the Mg2+ block in the channel is briefly removed by the depolarisation at which point Na+ and Ca2+ flow into the cell and K+ flows out of the cell
which ion is responsible for driving the synaptic plasticity changes?
calcium
what receptor is responsible for the basal transmission levels typically seen?
AMPA receptors
