Chapter 25 Neuroscience Notes
Procedural memory involves learning a motor response (procedure) in reaction to a sensory
input. It includes:
1. Non-Associative Learning: there are two types of responses
Habituation: learning to ignore a stimulus that lacks meaning. So repeated
presentation of the same stimulus produces a progressively smaller response
Sensitization: learning to intensify your response to stimuli, even ones that
previously evoked little or no reaction
2. Associative Learning: this involves forming associations between events
Classical conditioning (involves stimulus): remember Ivan Pavlov’s dogs; this
involves the unconditional stimulus (meat) and conditional stimulus (tone).
Conditioning occurs when a conditioned response (CR) is learnt via close
association of CS and US. The CS has to be presented slightly before or
simultaneously with the US to work.
Instrumental conditioning (involves behaviour): an individual learns to associate
a response, a motor act, with a meaningful stimulus, typically a reward such as
food. Think of a lever pressing rat in this case. So in summary, instrumental
conditioning involves the subject learning a particular behaviour is associated
with a particular consequence
Why are invertebrate models of learning used?
Small nervous systems: few thousand to less than 10 million times than humans
Non-associative learning in Aplypsia
If a jet of water is squirted onto its siphon, the gill will retract. This is called the gill-
withdrawal reflex. Overtime, the Aplypsia will habituate to this
Habituation of Aplysia
The motor neuron that receives input from the siphon sensory neuron is called
L7, and this neuron innervates muscles that cause the gill-withdrawal reflex
Where does the habituation occur? Habituation occurs @ the presynaptic side
of the sensory-motor synapse. So the sensory neuron side. Look @ figure 25.6
After habituation, there are less quanta containing neurotransmitter released.
This occurs because the presynaptic sensory neuron becomes less effective to
Calcium entry, resulting in less trigger release of NT.
Sensitization of Aplysia
Applying brief electric shock causes sensitization in Aplysia
How does increased sensitization occur? A third neuron, L29, is activated by the
shock, and makes a synapse on the axon terminal of the sensory neuron L29 releases serotonin, which sensitizes the sensory axon terminal so that it lets
in more Calcium in order to release more quanta packets
The sensory receptor on the sensory axon terminal is a G-protein-coupled
receptor. It causes the release of an intracellular second messenger, cyclic AMP
(cAMP) produced by adenylyl cyclase, which then activates protein kinase A
(remember kinases phosphorylate proteins).
Protein kinase A then phosphorylates a potassium channel resulting in it’s
closure. This leads to a prolonging of presynaptic action potential, meaning
more quanta are released resulting in sensitization
Look @ figure 25.9 page 768
Associative learning in Aplypsia is summarized well in lecture notes
Long Term Potentiation (LTP): long lasting enhancement of stimulated synapses. After
potentiation, a previous stimuli could now evoke a larger response
Anatomy of the hippocampus: it contains the dentate gyrus and Ammon’s horn