Synaptic Plasticity in Learning and Memory Flashcards
Types of memory
- … - declarative memory - facts, events
- … - nondeclarative memory - classical conditioning e.g. procedural memory: skills,habits, skeletal musculature, emotional responses (Amygdala)
- Explicit - declarative memory - facts, events
- Implicit - nondeclarative memory - classical conditioning e.g. procedural memory: skills,habits, skeletal musculature, emotional responses (Amygdala)
- Explicit - … memory - facts, events
- Implicit - … memory - classical conditioning e.g. procedural memory: skills,habits, skeletal musculature, emotional responses (Amygdala)
- Explicit - declarative memory - facts, events
- Implicit - nondeclarative memory - classical conditioning e.g. procedural memory: skills,habits, skeletal musculature, emotional responses (Amygdala)
How do we learn?
- Learning: the response of the brain to … events and involves … changes in … connectivity which will in turn alter …
- Learning: the response of the brain to environmental events and involves adaptive changes in synaptic connectivity which will in turn alter behaviour
Wiring/Synaptic Connections
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Donald Hebb Theory - 1949
- Group of cells connected with each other - cell assembly
- Neurons that … together … together
- Group of cells connected with each other - cell assembly
- Neurons that fire together wire together
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Rules of synaptic modification
- 1) Neurons that … together … together
- 2) Neurons that fire out of … lose their …
- Strengthening and weakening synaptic connections in the brain provide a means by which learning occurs and memories can be formed
- 1) Neurons that fire together wire together
- 2) Neurons that fire out of sync lose their link
- Strengthening and weakening synaptic connections in the brain provide a means by which learning occurs and memories can be formed
Rules of synaptic modification
- 1) Neurons that fire together wire together
- 2) Neurons that fire out of sync lose their link
- … and … synaptic connections in the brain provide a means by which … occurs and … can be formed
- 1) Neurons that fire together wire together
- 2) Neurons that fire out of sync lose their link
- Strengthening and weakening synaptic connections in the brain provide a means by which learning occurs and memories can be formed
Take a hippocampal neuron with inputs from:
- Cell A - sensory input for sight of rose
- Cell B - sensory input for smell of rose
- Cell C - sensory input for smell of onion
- Individually stimulation of the hippocampal neuron by any of these cells may be insufficient to create an EPSP great enough to fire an action potential
- When A and b are activated … - on seeing and smelling the rose the coincident EPSPs may summate sufficiently to cause an action potential in the hippocampal neuron
- If this association is made … - the simultaneous firing of cells A and B onto the hippocampal neuron - those synapses will be … (over the synapse from cell C which does not fire coincidently)
- The … of the synapses of Cell A and B will be sufficient that they will individually be able to elicit action potentials in the hippocampal neuron - the sight of a rose will become … with the smell of a rose rather than the smell of an onion
- Cell A - sensory input for sight of rose
- Cell B - sensory input for smell of rose
- Cell C - sensory input for smell of onion
- Individually stimulation of the hippocampal neuron by any of these cells may be insufficient to create an EPSP great enough to fire an action potential
- When A and b are activated together - on seeing and smelling the rose the coincident EPSPs may summate sufficiently to cause an action potential in the hippocampal neuron
- If this association is made repeatedly - the simultaneous firing of cells A and B onto the hippocampal neuron - those synapses will be strengthened (over the synapse from cell C which does not fire coincidently)
- The strengthening of the synapses of Cell A and B will be sufficient that they will individually be able to elicit action potentials in the hippocampal neuron - the sight of a rose will become associated with the smell of a rose rather than the smell of an onion
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Long term potentiation (LTP)
What is it?
- Mechanism underlying synaptic strengthening
- Hippocampus - shape and anatomy means pathways can be easily distinguished and recorded from electrophysiologically
- LTP has now been studied in most other brain areas too
Long term potentiation (LTP)
- Mechanism underlying … …
- … - shape and anatomy means pathways can be easily distinguished and recorded from electrophysiologically
- LTP has now been studied in most other brain areas too
- Mechanism underlying synaptic strengthening
- Hippocampus - shape and anatomy means pathways can be easily distinguished and recorded from electrophysiologically
- LTP has now been studied in most other brain areas too
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LTP - mechanism underlying synaptic strengthening
- … - shape and anatomy means pathways can be easily distinguished and recorded from electrophysiologically - LTP has now been studied in most other brain areas too
Record from cells within the … gyrus: subsequent perforant pathway stimulation results in
- High frequency electrical stimulation (HFS) of the perforant pathway (input)
- One HFS - LTP lasts …
- Multiple HFS - LTP lasts …/…
LTP - mechanism underlying synaptic strengthening
- Hippocampus - shape and anatomy means pathways can be easily distinguished and recorded from electrophysiologically - LTP has now been studied in most other brain areas too
Record from cells within the dentate gyrus: subsequent perforant pathway stimulation results in
- High frequency electrical stimulation (HFS) of the perforant pathway (input)
- One HFS - LTP lasts hours
- Multiple HFS - LTP lasts days/months
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LTP
- … - summation of inputs reaches a stimulus threshold that leads to the induction of LTP e.g. repetitive stimulation (HFS)
- … - simultaneous stimulation of a strong and weak pathway will induce LTP at both pathways. (Spatial summation) coincidence detection “cells that fire together wire together”
- … - LTP at one synapse is not propagated to adjacent synapses (input specific)
- Temporal - summation of inputs reaches a stimulus threshold that leads to the induction of LTP e.g. repetitive stimulation (HFS)
- Associative - simultaneous stimulation of a strong and weak pathway will induce LTP at both pathways. (Spatial summation) coincidence detection “cells that fire together wire together”
- Specific - LTP at one synapse is not propagated to adjacent synapses (input specific)
LTP
- Temporal - summation of inputs reaches a stimulus threshold that leads to the induction of LTP e.g. … stimulation (HFS)
- Associative - simultaneous stimulation of a strong and weak pathway will induce LTP at both pathways. (… summation) coincidence detection “cells that fire together wire together”
- Specific - LTP at one synapse is not … to adjacent synapses (input specific)
- Temporal - summation of inputs reaches a stimulus threshold that leads to the induction of LTP e.g. repetitive stimulation (HFS)
- Associative - simultaneous stimulation of a strong and weak pathway will induce LTP at both pathways. (Spatial summation) coincidence detection “cells that fire together wire together”
- Specific - LTP at one synapse is not propagated to adjacent synapses (input specific)
What’s happening at the synapse? - learning and memory (LTP)
- Glutamate release onto inactive cell (membrane at … …)
- … receptor activated to create EPSP
- NMDA receptor blocked by Mg2+ ion
- Depolarization from … activation not sufficient to expel Mg2+
- Glutamate release onto an active cell (membrane …)
- … receptor activated
- Mg2+ block on NMDA receptor relieved
- Na+ through … and NMDA channels
- Ca2+ through NMDA channel
- Glutamate release onto inactive cell (membrane at resting potential)
- AMPA receptor activated to create EPSP
- NMDA receptor blocked by Mg2+ ion
- Depolarization from AMPA activation not sufficient to expel Mg2+
- Glutamate release onto an active cell (membrane depolarized)
- AMPA receptor activated
- Mg2+ block on NMDA receptor relieved
- Na+ through AMPA and NMDA channels
- Ca2+ through NMDA channel
What’s happening at the synapse? - learning and memory (LTP)
- … release onto inactive cell (membrane at resting potential)
- AMPA receptor activated to create EPSP
- … receptor blocked by Mg2+ ion
- Depolarization from AMPA activation not sufficient to expel Mg2+
- … release onto an active cell (membrane depolarized)
- AMPA receptor activated
- Mg2+ block on … receptor relieved
- Na+ through AMPA and … channels
- Ca2+ through … channel
- Glutamate release onto inactive cell (membrane at resting potential)
- AMPA receptor activated to create EPSP
- NMDA receptor blocked by Mg2+ ion
- Depolarization from AMPA activation not sufficient to expel Mg2+
- Glutamate release onto an active cell (membrane depolarized)
- AMPA receptor activated
- Mg2+ block on NMDA receptor relieved
- Na+ through AMPA and NMDA channels
- Ca2+ through NMDA channel
What’s happening at the synapse? - LTP Contd.
- Ca2+ entry through the … receptor leads to activation of:
- Protein kinase …
- Calcium …-dependent protein kinase II (CAMKII)
- Phosphorylase existing AMPA receptors, increasing their effectiveness
- Stimulates the insertion of new … receptors into the membrane
- Ca2+ entry through the NMDA receptor leads to activation of:
- Protein kinase C
- Calcium calmodulin-dependent protein kinase II (CAMKII)
- Phosphorylase existing AMPA receptors, increasing their effectiveness
- Stimulates the insertion of new AMPA receptors into the membrane
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- Before high frequency stimulation - few … receptors, small EPSPs
- After - More … receptors working more effectively, larger EPSPs leading to …
- Before high frequency stimulation - few AMPA receptors, small EPSPs
- After - More AMPA receptors working more effectively, larger EPSPs leading to LTP
CAMKII - molecular switch - sustained activity after repolarization
- Ca2+ entry though the NMDA receptor leads to activation of calcium calmodulin-dependent protein kinase II (CaMKII)
- CaMKII has autocatalytic activity - becomes …
- When … is constitutively active - no longer requires Ca2+
- Maintains …, insertion of AMPA receptors etc. after the depolarizing stimulus has …
- Molecular switch which maintains increased … of neuron for minutes to hours
- Ca2+ entry though the NMDA receptor leads to activation of calcium calmodulin-dependent protein kinase II (CaMKII)
- CaMKII has autocatalytic activity - becomes phosphorylated
- When phosphorylated is constitutively active - no longer requires Ca2+
- Maintains phosphorylation, insertion of AMPA receptors etc. after the depolarizing stimulus has receded
- Molecular switch which maintains increased excitability of neuron for minutes to hours
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Presynaptic events in LTP
- Long term potentiation also involves presynaptic events
- Postsynaptic neuron can feed back to presynaptic neuron by retrograde NT - … …
- Ca2+ through the NMDA channel activates … synthase
- … diffuses from site of production and activates guanylyl cyclase in the presynaptic terminal
- Guanylyl cyclase produces the second messenger cGMP
- Signal transduction cascade leads to increased … release from the synaptic button
- Long term potentiation also involves presynaptic events
- Postsynaptic neuron can feed back to presynaptic neuron by retrograde NT - Nitric oxide
- Ca2+ through the NMDA channel activates NO synthase
- NO diffuses from site of production and activates guanylyl cyclase in the presynaptic terminal
- Guanylyl cyclase produces the second messenger cGMP
- Signal transduction cascade leads to increased glutamate release from the synaptic button
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Presynaptic events in LTP
- Long term potentiation also involves presynaptic events
- Postsynaptic neuron can feed back to presynaptic neuron by retrograde NT - Nitric oxide
- Ca2+ through the … channel activates NO synthase
- NO diffuses from site of production and activates guanylyl cyclase in the presynaptic terminal
- Guanylyl cyclase produces the … … cGMP
- Signal transduction cascade leads to … glutamate release from the synaptic button
- Long term potentiation also involves presynaptic events
- Postsynaptic neuron can feed back to presynaptic neuron by retrograde NT - Nitric oxide
- Ca2+ through the NMDA channel activates NO synthase
- NO diffuses from site of production and activates guanylyl cyclase in the presynaptic terminal
- Guanylyl cyclase produces the second messenger cGMP
- Signal transduction cascade leads to increased glutamate release from the synaptic button
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Late phase LTP
- Protein … required for long-lasting LTP (Days, months)
- Protein … inhibitors prevent the … of long term memories and LTP
- Stages of memory formation
- Acquisition (training)
- Consolidation
- Recall (testing)
- Protein … inhibitor injected just post-acquisition (training) inhibits recall - necessary for …
- Protein synthesis required for long-lasting LTP (Days, months)
- Protein synthesis inhibitors prevent the consolidation of long term memories and LTP
- Stages of memory formation
- Acquisition (training)
- Consolidation
- Recall (testing)
- Protein synthesis inhibitor injected just post-acquisition (training) inhibits recall - necessary for consolidation
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Late phase LTP
- Protein synthesis required for long-lasting LTP (Days, months)
- Protein synthesis inhibitors prevent the consolidation of long term memories and LTP
- Stages of memory formation
- … (training)
- …
- … (testing)
- Protein synthesis inhibitor injected just post-… (training) inhibits … - necessary for …
- Protein synthesis required for long-lasting LTP (Days, months)
- Protein synthesis inhibitors prevent the consolidation of long term memories and LTP
- Stages of memory formation
- Acquisition (training)
- Consolidation
- Recall (testing)
- Protein synthesis inhibitor injected just post-acquisition (training) inhibits recall - necessary for consolidation
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Early vs Late phase LTP (short vs long term events)
- Early phase LTP lasts a … to an … and can be explained by the actions of Ca2+ through the … receptor and subsequent enhancement of … receptor efficiency, presynaptic events etc.
- Late phase LTP lasts hours, days or months - requires new protein … and can involve morphological changes and the establishment of new …
- Ca2+ activated signal transduction cascades:
- Activate new protein synthesis from dendritically localized mRNAs
- Filter back to the cell body to stimulate new gene transcription (CREB-mediated), protein synthesis and recruitment of new proteins to the synapse
- Early phase LTP lasts a minute to an hour and can be explained by the actions of Ca2+ through the NMDA receptor and subsequent enhancement of AMPA receptor efficiency, presynaptic events etc.
- Late phase LTP lasts hours, days or months - requires new protein syntheses and can involve morphological changes and the establishment of new synapses
- Ca2+ activated signal transduction cascades:
- Activate new protein synthesis from dendritically localized mRNAs
- Filter back to the cell body to stimulate new gene transcription (CREB-mediated), protein synthesis and recruitment of new proteins to the synapse
Early vs Late phase LTP (short vs long term events)
- Early phase LTP lasts a minute to an hour and can be explained by the actions of Ca2+ through the NMDA receptor and subsequent enhancement of AMPA receptor efficiency, presynaptic events etc.
- Late phase LTP lasts …, … or … - requires new protein … and can involve morphological changes and the establishment of new synapses
- Ca2+ activated signal transduction cascades:
- Activate new protein … from dendritically localized mRNAs
- Filter back to the cell body to stimulate new gene transcription (CREB-mediated), protein … and recruitment of new proteins to the synapse
- Early phase LTP lasts a minute to an hour and can be explained by the actions of Ca2+ through the NMDA receptor and subsequent enhancement of AMPA receptor efficiency, presynaptic events etc.
- Late phase LTP lasts hours, days or months - requires new protein syntheses and can involve morphological changes and the establishment of new synapses
- Ca2+ activated signal transduction cascades:
- Activate new protein synthesis from dendritically localized mRNAs
- Filter back to the cell body to stimulate new gene transcription (CREB-mediated), protein synthesis and recruitment of new proteins to the synapse
Always an opposite - Long term depression (LTD)
- Long term potentiation is created in slice preparations by … frequency stimulation (…: 100x 100Hz)
- … frequency stimulation (…: 100X 1 Hz) actually causes the opposite and rather than getting an increase in EPSP amplitude on further stimulation you get a decrease
- Same players involved:
- … dependent process
- … receptors are de-phosphorylated and removed from the membrane
- Prolonged low level rises in Ca2+ activate phosphatases rather than kinases
- Long term potentiation is created in slice preparations by high frequency stimulation (HFS: 100x 100Hz)
- Low frequency stimulation (LFS: 100X 1 Hz) actually causes the opposite and rather than getting an increase in EPSP amplitude on further stimulation you get a decrease
- Same players involved:
- NMDA dependent process
- AMPA receptors are de-phosphorylated and removed from the membrane
- Prolonged low level rises in Ca2+ activate phosphatases rather than kinases
Always an opposite - Long term depression (LTD)
- Long term … is created in slice preparations by high frequency stimulation (HFS: 100x 100Hz)
- Low frequency stimulation (LFS: 100X 1 Hz) actually causes the opposite and rather than getting an increase in EPSP amplitude on further stimulation you get a decrease
- Same players involved:
- … dependent process
- AMPA receptors are de-phosphorylated and removed from the membrane
- Prolonged … level rises in Ca2+ activate … rather than kinases
- Long term potentiation is created in slice preparations by high frequency stimulation (HFS: 100x 100Hz)
- Low frequency stimulation (LFS: 100X 1 Hz) actually causes the opposite and rather than getting an increase in EPSP amplitude on further stimulation you get a decrease
- Same players involved:
- NMDA dependent process
- AMPA receptors are de-phosphorylated and removed from the membrane
- Prolonged low level rises in Ca2+ activate phosphatases rather than kinases
LFS - leads to long term …
LFS - leads to long term depression
LTP and LTD reflect bidirectional regulation of:
- P…
- Number of postsynaptic … receptors
- Phosphorylation
- Number of postsynaptic AMPA receptors
Do all these changes in synaptic activity really lead to learning?
- … receptor activity in the hippocampus essential for both … and spatial learning
- AP5 - … receptor antagonist
- Blocks hippocampal …
- Blocks learning in the Morris Water Maze
- NMDA receptor activity in the hippocampus essential for both LTP and spatial learning
- AP5 - NMDA receptor antagonist
- Blocks hippocampal LTP
- Blocks learning in the Morris Water Maze
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Studies on animals - relevance to humans? - learning and memory
- LTP recorded in human brain? yes or no
- LTP in human brain? yes or no
- HFS - produced LTP
- LFS - produced LTD
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Drug effects on learning and memory - ALCOHOL
- … receptor antagonist (as well as other sites)
- Blackouts and … caused by drinking
- Directly blocking normal … processes???
- Alcohol disrupts hippocampal theta rhythms and disrupts short term memory
- Chronic alcoholism and associated nutritional deficiency can result to Korsakoff syndrome or psychosis: loss of recent memory, and tendency to fabricate accounts of recent events (confabulation)
- NMDA receptor antagonist (as well as other sites)
- Blackouts and amnesia caused by drinking
- Directly blocking normal LTP processes???
- Alcohol disrupts hippocampal theta rhythms and disrupts short term memory
- Chronic alcoholism and associated nutritional deficiency can result to Korsakoff syndrome or psychosis: loss of recent memory, and tendency to fabricate accounts of recent events (confabulation)
Drug effects on learning and memory - ALCOHOL
- NMDA receptor antagonist (as well as other sites)
- Blackouts and amnesia caused by drinking
- Directly blocking normal LTP processes???
- Alcohol disrupts … theta rhythms and disrupts … term memory
- Chronic alcoholism and associated nutritional deficiency can result to … syndrome or psychosis: loss of recent memory, and tendency to fabricate accounts of recent events (…)
- NMDA receptor antagonist (as well as other sites)
- Blackouts and amnesia caused by drinking
- Directly blocking normal LTP processes???
- Alcohol disrupts hippocampal theta rhythms and disrupts short term memory
- Chronic alcoholism and associated nutritional deficiency can result to Korsakoff syndrome or psychosis: loss of recent memory, and tendency to fabricate accounts of recent events (confabulation)
Chronic alcoholism and associated nutritional deficiency can result to … syndrome or psychosis: loss of recent memory, and tendency to fabricate accounts of recent events (C…)
Chronic alcoholism and associated nutritional deficiency can result to Korsakoff syndrome or psychosis: loss of recent memory, and tendency to fabricate accounts of recent events (confabulation)
Drug effects on learning and memory - BENZODIAZEPINES
- … agonist of GABA…. receptors:
- Binding increases the receptor affinity for GABA
- … frequency of channel opening
- Anxiolytic and hypnotic drugs
- Side effect to anxiolytic and sedative properties - … amnesia
- Indirect agonist of GABAalpha receptors:
- Binding increases the receptor affinity for GABA
- Increase frequency of channel opening
- Anxiolytic and hypnotic drugs
- Side effect to anxiolytic and sedative properties - anterograde amnesia
Drug effects on learning and memory - BENZODIAZEPINES
- Indirect … of GABAalpha receptors:
- Binding … the receptor affinity for GABA
- Increase frequency of channel …
- Anxiolytic and hypnotic drugs
- Side effect to anxiolytic and sedative properties - anterograde …
- Indirect agonist of GABAalpha receptors:
- Binding increases the receptor affinity for GABA
- Increase frequency of channel opening
- Anxiolytic and hypnotic drugs
- Side effect to anxiolytic and sedative properties - anterograde amnesia
Drug effects on learning and memory - CHOLINERGICS/ANTICHOLINERGICS
- Acetylcholine …:
- Basal forebrain bundle: medial septum to hippocampus, basal nucleus to cortex
- Septum to hippocampus projection regulates … waves
- Scopolamine (muscarinic receptor …) suppresses theta waves and impairs spatial learning
- Acetylcholine projections:
- Basal forebrain bundle: medial septum to hippocampus, basal nucleus to cortex
- Septum to hippocampus projection regulates theta waves
- Scopolamine (muscarinic receptor antagonist) suppresses theta waves and impairs spatial learning
Drug effects on learning and memory - CHOLINERGICS/ANTICHOLINERGICS
- Acetylcholine projections:
- Basal forebrain bundle: … septum to hippocampus, basal … to cortex
- Septum to hippocampus projection regulates theta waves
- Scopolamine (muscarinic receptor antagonist) … theta waves and … spatial learning
- Acetylcholine projections:
- Basal forebrain bundle: medial septum to hippocampus, basal nucleus to cortex
- Septum to hippocampus projection regulates theta waves
- Scopolamine (muscarinic receptor antagonist) suppresses theta waves and impairs spatial learning
Drug effects on learning and memory - Alzheimer’s disease
- Alzheimer’s disease - … inhibitors (E.g. physostigmine) boost cholinergic function and improve memory …
- Alzheimer’s disease - Acetylcholinesterase inhibitors (E.g. physostigmine) boost cholinergic function and improve memory impairments
Drug effects on learning and memory - Healthy brain?
- In alzheimers - Acetylcholinesterase … (E.g. physostigmine) boost cholinergic function and improve memory impairments
- In a healthy brain:
- Controversial as to whether they improve memory, may increase …
- Most cognitive enhancing effects of both acetylcholinesterase and other cholinergic drugs e.g. nicotine, seen in in impaired subjects, i.e. Alzheimer’s patients, or in restoring performance of animals with lesions.
- In alzheimers - Acetylcholinesterase inhibitors (E.g. physostigmine) boost cholinergic function and improve memory impairments
- In a healthy brain:
- Controversial as to whether they improve memory, may increase attention
- Most cognitive enhancing effects of both acetylcholinesterase and other cholinergic drugs e.g. nicotine, seen in in impaired subjects, i.e. Alzheimer’s patients, or in restoring performance of animals with lesions.
Other learning processes which use LTP or similar mechanism:
- Activity dependent … (Development)
- … learning - e.g. riding a bike - cerebellar
- Activity dependent synaptogenesis (Development)
- Motor learning - e.g. riding a bike - cerebellar