TASK 3: CONSOLIDATION, PLASTICITY
AND LM
CHAPTER 2 BOOK
THE SYNAPSE: WHERE NEURONS CONNECT
• Neurons throughout the NS are continually communicating with one another in vast networks
• Communicate but are not physically connected: separated by a synapse – across which neurons
pass chemicals
o Most formed between axon of presynaptic and dendrite of postsynaptic neurons
o Some between axon and cell body, axon and another axon or between dendrites
• Given neuron produces and releases only one kind of neurotransmitter, but it may be able to receive
and interpret messages from many neurons
• Some neurotransmitters are excitatory – activating receptors that tend to increase the likelihood of
the postsynaptic neuron firing (Glutamate)
• Some are inhibitory – decrease the likelihood of the postsynaptic neuron firing (GABA)
NEUROMODULATORS: ADJUSTING THE MESSAGE
Neuromodulators are neurotransmitters released by neurons in areas in the brainstem
• Neurons in the brainstem send axons widely throughout the brain and when these neurons fire they
release neuromodulators
• They can affect activity in entire brain areas and alter/modulate how neurons exchange messages,
even if they themselves are not part of messages
• Many diseases involve global decline in neuromodulators:
o Acetylcholine function is to temporarily alter the number of receptors needing to be active
before a postsynaptic neuron can fire. Thus, whether the message heard is a whisper or a
shout.
o Alzheimer’s – decline in acetylcholine
o Parkinson’s – decline in dopamine
,SYNAPTIC PLASTICITY
Synaptic plasticity is the ability of synapses to change as a result of experience
• Neurons can change physically, as a result of learning à these changes affect how neurons
communicate and how brain systems function
Ramón y Cajal (1852-1934) – theorized that learning involves strengthening or weakening connections
between individual neurons
• Golgi Stain Technique – small piece of brain tissue is treated with solution of silver chromate
and small % of neurons in tissue sample take up this stain
o Findings:
1. Neurons communicate through specialized junctions (synapses)
2. Learning involves changes in synapses, strengthening / weakening ability of
messages to cross from one neuron to another
HOW DOES THE BRAIN KNOW WHICH CONNECTIONS TO WEAKEN/STRENGTHEN?
• Hebb (1949) – “when an axon of cell A is near enough to excite cell B and repeatedly or persistently
takes part in firing it, some growth process or metabolic change takes place such that A’s efficiency,
as one of the cells firing B, is increased”
o if two neurons that meet at a synapse often fire at nearly the same time, then the synapses
between them should be strengthened, ‘wiring’ the two neurons together
• Neurons that fire together wire together – increases probability that whenever neuron A is active, it
causes neuron B to become active too
• Neurons can change synaptic connections automatically, as a function of their mutual activity
HEBBIAN LEARNING
• The principle that learning involves strengthening connections between neurons – Hebbian learning
• Repeated exposure to a stimulus can strengthen connections within a distinctive subset of
cortical neurons, and this subset can then provide an increasingly reliable basis for identifying the
stimulus that is activating them. Changing the connections between cortical neurons creates a
pattern that makes a repeated stimulus more likely to be recognized and distinguished from other
stimuli
• Hebbian learning can also explain how repeated experiences can enhance the ability to recognize
familiar stimuli
• Only some of the subset of neurons that represents the familiar stimulus are activated at first, but
the connections already established through repeated experiences will produce outputs that
complete the familiar pattern
, Simple model of Hebbian learning
a. Stimulus input activates a subset of the neurons
b. Connections between coactive neurons are strengthened
c. After connections between coactive neurons are established, an incomplete version of a
familiar stimulus may activate just some of the neurons in the subset that represents the
stimulus. Activation flows along the strengthened connections and ultimately retrieves the
complete stimulus, resulting in B
According to Hebb, learning-related changes in synaptic connections between neurons are an automatic
result of the neuron’s mutual activity
LONG TERM POTENTATION
LTP is an effect in which synaptic transmission becomes more effective as a result of recent activity
• Lomo (1966) – demonstrated that neurons could actually change their activity as a function of
experience and that these changes could last for hours / days
o Stimulated the axons of the presynaptic neurons that provided input for the hippocampus
and recorded the electrical activity in postsynaptic neurons in the hippocampus
simultaneously
o Findings: high frequency stimulation caused a lasting change in responding, so that
hippocampal neurons would over respond to subsequent weak stimulation
§ Potentiated your response to a weak stimulus that normally would not have evoked
such a reaction
o Strong stimulation can potentiate a neuron, making it more likely to respond to subsequent
stimulus
§ Synaptic transmission becomes more effective as a result of recent activity: LTP
o Electrical stimulation of presynaptic neuron is not required to produce this – as long as both
pre and post are active at the same time, LTP can occur
o Associative LTP – if to neurons are conjointly active, synapse between them is potentiated.
Specific synapses can change from conjoint activation – Hebb was right
AND LM
CHAPTER 2 BOOK
THE SYNAPSE: WHERE NEURONS CONNECT
• Neurons throughout the NS are continually communicating with one another in vast networks
• Communicate but are not physically connected: separated by a synapse – across which neurons
pass chemicals
o Most formed between axon of presynaptic and dendrite of postsynaptic neurons
o Some between axon and cell body, axon and another axon or between dendrites
• Given neuron produces and releases only one kind of neurotransmitter, but it may be able to receive
and interpret messages from many neurons
• Some neurotransmitters are excitatory – activating receptors that tend to increase the likelihood of
the postsynaptic neuron firing (Glutamate)
• Some are inhibitory – decrease the likelihood of the postsynaptic neuron firing (GABA)
NEUROMODULATORS: ADJUSTING THE MESSAGE
Neuromodulators are neurotransmitters released by neurons in areas in the brainstem
• Neurons in the brainstem send axons widely throughout the brain and when these neurons fire they
release neuromodulators
• They can affect activity in entire brain areas and alter/modulate how neurons exchange messages,
even if they themselves are not part of messages
• Many diseases involve global decline in neuromodulators:
o Acetylcholine function is to temporarily alter the number of receptors needing to be active
before a postsynaptic neuron can fire. Thus, whether the message heard is a whisper or a
shout.
o Alzheimer’s – decline in acetylcholine
o Parkinson’s – decline in dopamine
,SYNAPTIC PLASTICITY
Synaptic plasticity is the ability of synapses to change as a result of experience
• Neurons can change physically, as a result of learning à these changes affect how neurons
communicate and how brain systems function
Ramón y Cajal (1852-1934) – theorized that learning involves strengthening or weakening connections
between individual neurons
• Golgi Stain Technique – small piece of brain tissue is treated with solution of silver chromate
and small % of neurons in tissue sample take up this stain
o Findings:
1. Neurons communicate through specialized junctions (synapses)
2. Learning involves changes in synapses, strengthening / weakening ability of
messages to cross from one neuron to another
HOW DOES THE BRAIN KNOW WHICH CONNECTIONS TO WEAKEN/STRENGTHEN?
• Hebb (1949) – “when an axon of cell A is near enough to excite cell B and repeatedly or persistently
takes part in firing it, some growth process or metabolic change takes place such that A’s efficiency,
as one of the cells firing B, is increased”
o if two neurons that meet at a synapse often fire at nearly the same time, then the synapses
between them should be strengthened, ‘wiring’ the two neurons together
• Neurons that fire together wire together – increases probability that whenever neuron A is active, it
causes neuron B to become active too
• Neurons can change synaptic connections automatically, as a function of their mutual activity
HEBBIAN LEARNING
• The principle that learning involves strengthening connections between neurons – Hebbian learning
• Repeated exposure to a stimulus can strengthen connections within a distinctive subset of
cortical neurons, and this subset can then provide an increasingly reliable basis for identifying the
stimulus that is activating them. Changing the connections between cortical neurons creates a
pattern that makes a repeated stimulus more likely to be recognized and distinguished from other
stimuli
• Hebbian learning can also explain how repeated experiences can enhance the ability to recognize
familiar stimuli
• Only some of the subset of neurons that represents the familiar stimulus are activated at first, but
the connections already established through repeated experiences will produce outputs that
complete the familiar pattern
, Simple model of Hebbian learning
a. Stimulus input activates a subset of the neurons
b. Connections between coactive neurons are strengthened
c. After connections between coactive neurons are established, an incomplete version of a
familiar stimulus may activate just some of the neurons in the subset that represents the
stimulus. Activation flows along the strengthened connections and ultimately retrieves the
complete stimulus, resulting in B
According to Hebb, learning-related changes in synaptic connections between neurons are an automatic
result of the neuron’s mutual activity
LONG TERM POTENTATION
LTP is an effect in which synaptic transmission becomes more effective as a result of recent activity
• Lomo (1966) – demonstrated that neurons could actually change their activity as a function of
experience and that these changes could last for hours / days
o Stimulated the axons of the presynaptic neurons that provided input for the hippocampus
and recorded the electrical activity in postsynaptic neurons in the hippocampus
simultaneously
o Findings: high frequency stimulation caused a lasting change in responding, so that
hippocampal neurons would over respond to subsequent weak stimulation
§ Potentiated your response to a weak stimulus that normally would not have evoked
such a reaction
o Strong stimulation can potentiate a neuron, making it more likely to respond to subsequent
stimulus
§ Synaptic transmission becomes more effective as a result of recent activity: LTP
o Electrical stimulation of presynaptic neuron is not required to produce this – as long as both
pre and post are active at the same time, LTP can occur
o Associative LTP – if to neurons are conjointly active, synapse between them is potentiated.
Specific synapses can change from conjoint activation – Hebb was right
