Download Synapse formation

Unit 4 Psychology
Learning:
Neural Pathways, Synapse Formation
& the Role of Neurotransmitters
Synapse Formation in Learning
• A neural pathway (also referred
to as neural tract) is a bundle of
myelin-covered neurons (white
matter) which provide a
connection between one part of
the nervous system and another.
• Synapse formation during
learning involves:
– Creation of new neural pathways
– Strengthening of existing neural
pathways
Neural synapse
http://www.youtube.com/watch?v=
HXx9qlJetSU
Synaptogenesis
•
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The forming of new synapses or
moulding of existing synapses
Particularly evident during early
childhood
– Also occurs in parts of the adult brain
Synapse: Zone / junction between two
neurons
– Comprises: axon terminal of
presynaptic neuron, the synaptic gap,
and the dendrite of the postsynaptic
neuron.
During Learning:
– axon terminals of the presynaptic
neuron release a neurotransmitter
called glutamate into the synaptic
gap between the presynaptic neuron
and the dendrites of a neighbouring
postsynaptic neuron
Neuron Changes during Learning
Filigree Appendages
• As the process of learning
new information or a new
skill occurs, the neurons
form new connections with
each other.
• These new ‘sprouts’ grow
from the axon terminal of a
presynaptic neuron towards
the dendrites of
neighbouring postsynaptic
neurons
Learning means:
• Strengthening of the neural
pathway between neurons.
• Newly learnt information to be
transferred from one neuron
to the next is more efficient
• The more that a particular
neural pathway is activated
during learning, the more
likely it is to be strengthened
and the less likely the learning
will be forgotten.
Neural Basis of Learning:
Hebbian theory
• Learning results in the creation of cell
assembles or neural networks
• ‘neurons that fire together wire together’
• When a neurotransmitter is repeatedly sent
across the synapse this can effect the strength
of these connections
• Neurons that do not fire together weaken
their connections
Neural Basis of Learning :
Kandel’s Research
• Research on the cellular basis of learning and memory
formation in the Aplysia (sea hare) found that learning
resulted in strengthened synapses between the sensory
neurons (activated by the touch of the glass rod) and motor
neurons (response of flexing gill muscle).
• The greater the number of learning trials, the more readily
activated the presynaptic and postsynaptic neurons
became.
• A small number of learning trials produced changes which
lasted from 10 minutes to a few hours.
• A greater number of trials produced changes which lasted
for several days (Bailey & Kandel 1995; Martinez & Derrick
1996).
Long-term Potentiation (LTP)
• Long-term potentiation (LTP) is a process that
has been produced only in laboratory settings,
where presynaptic neurons that are
electrically stimulated will increase the
tendency of a group of neighbouring
postsynaptic neurons to fire.
• That is… that neurons which have been
stimulated will have a greater ‘potential’ to
fire when they are stimulated again.
The Role of Glutamate in Learning
• When learning takes place, neurons excite one another
through the release of neurotransmitters. In this process,
glutamate is released by the presynaptic neurons.
• Glutamate is the main excitatory neurotransmitter in the
brain for learning.
• When glutamate is released by the presynaptic neuron, it
acts on two types of glutamate receptors in the
postsynaptic neuron: AMPA & NMPA
– the AMPA receptor which activates the postsynaptic neuron.
– the NMDA receptor produces long-lasting modifications to the
synapse.
Dopamine Effects on Neurons
• Repeated Glutamate release
stimulates the release of
Dopamine
• Dopamine activates genes in
postsynaptic neurons to produce
additional dendritic spines.
– Outgrowths from the dendrites in
the synaptic gap.
• This in turn makes the
postsynaptic neuron more
sensitive to future firing by other
neighbouring presynaptic
neurons.
• Process takes about 30 minutes
The Effects of Dopamine on Learning
• Dopamine is a neurotransmitter that is associated with
pleasurable feelings.
• When a learner shows a behaviour that is followed by a
pleasant consequence or reward, the behaviour is likely to
be repeated.
• Humans will repeat behaviours that cause the release of
dopamine and therefore the connection between the
neuron increases.
• With repeated activations of the neurons in the amygdala
(through repeated pairings of the behaviour and the
reward) the neurons are more readily able to release
dopamine and adjacent neurons become more easily
activated by dopamine.
• It is little wonder that dopamine is also linked with
addiction.
Long Term Potentiation
Review - Learning, Memory and the
Anatomy Behind it all
Next Time in Psych
• Plasticity of the Brain