Class 5 - Memory 1 Flashcards
What was intact with HM
- Short-term memory
- Childhood memories
- Ability to learn new tasks and skills
- Above-normal IQ (117)
What was impaired with HM
- No new memories for facts and events (declarative memory)
- Cannot learn information about surroundings
- Cannot remember names or faces of people who he met after his operation
- Loss of memory from 2 years prior to surgery
Flow Chart of memory
Memory is
the presistance of learning
Delarative memory
explicit memory
Events
Episodic Memory
Facts
Semantic Memory
Non declarative memory
implicit memory
Aplysia
A simple nervous system
Amnesia
loss of memory and/or loss of the ability to learn
Storage in LTM requires
consolidation
Testing the gill withdrawal reflex
repeated touching reduces vesicles available
Reaped touchings less and less withdrawl
Hebbian assemblies
“cells that fire together wire together”
- Stimulus activates a cell assembly (reciprocally connected and distributed set of cells)
- Persistence of activation leads to strengthening of assembly’s connections
Activity-dependent change in synaptic networks can
support many different kinds of memory
Excitatory connections between different regions of the hippocampus demonstrate
Hebbian learning
Long-term potentiation (LTP)
Long-lasting increase in synaptic activation
• Happens with repeated patterns of activation close in time
LTP is mediated by
- NMDA and AMPA receptor activity at the post synaptic neuron
- Both are ionotropic glutamate receptors
- Mostly post-synaptic changes (increase in # of receptors)
Antrograde
Everythign afer moment of trama
retrograde
before moment of trama
A strong EPSP at one site can help potentiate nearby synapses that also release glutamate, leading to the
strengthening of that other synapse
(electric depolrization can travel to close by neurons)
Long-term depression (LTD)
Long-lasting decrease in synaptic activation
LTD is important for
plasticity, such as in clearing out old memory traces
unlearning an accosation (PTSD) - when learned assocation is no longer adaptive
LTD is a reuslt of
Mainly result of decreased postsynaptic receptor density and some presynaptic decreases in NT release
- AMPA recptors being removed
Non assocative learning
habituation, sensatization
Classical conditioning
happen closely in time they get assocated together - expect something to happen with inital sitmulus
Shift from reacting to antisapating
is where condition and uncondtion stimulus is stored
cerabellum
Subsequent activation by part of a stimulus will activate the
entire representation via the reciprocal connections
“Memory Trace”
Consequences of hebbian assemblies
- A ‘memory trace’ can be widely distributed
- The same neurons involved in sensory processing also participate in memory
- Partial destruction of the assembly may not cause loss of all memory
- Activity-dependent change in synaptic networks can thus support many different kinds of memory
NMDA receptor and LTP
Three properties associated with LTP (and learning):
Cooperativity: more than one input active at once
Associativity: weak inputs boosted when paired with a stronger imput
Specificity: occurs at specific synapse
NMDA sites
glutamate site but also Mg block, sits in recptor
post synaptic neuron depolarized, Mg is pushed out of chanel
results in opening of chanel
Ca can enter via NMDA recptor into post synaptic cell
4 steps of NMDA recptor and LTP
Postsynaptic neuron is depolarized via non-NMDA receptors
Depolarization of postsynaptic neuron pushes out Mg2+ from NMDA receptor
Opening of NMDA receptor allows entry of Ca2+ into postsynaptic cell
This can include insertion of AMPA receptors into the membrane (either ones already readymade or via protein synthesis
LTP does not envolve which of the folowing
Signaling of Mg2+ within the post synaptic neuron
- it is the Ca2+ that does the post synaptic neuron signaling
anterograde amnesia
inability to learn new things
Retrograde amnesia
loss of memory for events before trama
temporally limited
when retrograde amnesia exteens bacl only a few minutes or hours
Temporal gradent or Ribot’s Law id
the effect that retrograde amnesia tends to be the greatest for most recent events
Hebb’s Law
cells that fire together wire together
Hebbian Learning
mechanism of learning is the strengthing of sysaptic connections that results when a weak input and a strong input act on a cell at the same time
Neurons in the hippocampus must be ___, meaning that they have the ability to ____ synaptic interactions
plastic
change
three major excitatory neuronal pathways of the hippocampus that extend from ____ to ___
from the subiculum to the CA1 cells
- the perforant pathway
- the mossay fibers
- the schaffer collaterals
The perforant pathway
neurons from the entorhinal cortex travel by the subiculum along this pathway and synapse with granule cells that have distincive looking unmylenated axons known as mossy fibers
The mossy fibers
granule cells that have distincive looking unmylenated axons known as mossy fibers which connect the dentate gyrus to the dendritic spines of the hippocamal CA3 paramidal cells
Schaffer collaterals
CA3 paramidal cells connect to the CA1 paramidal cells by axon collaterals known as Schaffer collaterals
Stimulating the axons of the perforant pathway results in
long term increase in the magnitude of excitatory post synaptic potentals leading to greater synaptic strength
known as LTP
When pulses are presented slowly (as low frequency pulses) the ___ effect is seen
opposite or LTD
Three properties of LTP in CA1 synapses
- Cooperativity
- Associativity
- Specificity
Blocking LTP prevents
normal spatial memory (blocking NMDA recpetors prevents LTP)
NMDA recptors may be needed for ___ but not __
for learning a spatial strategy but not to encode a new map
