Lecture 28: Learning and Memory and Basic Mechanisms (Invertebrate System)

What are the types of procedural learning?

• nonassociative learning

• associative learning

What are the types of nonassociative learning?

• habituation

• sensitization

What is habituation?

learning to ignore stimulus that lacks meaning

What is sensitization?

learning to intensify response to stimuli

What are the types of associative learning?

• classical conditioning

• instrumental conditioning

What are examples of instrumental conditioning?

• the delayed-response task

• lever pressing task

Who introduced instrumental conditioning?

Thorndike

True or False: Thorndike and Skinner both found that the most effective way to teach a person or animal a new behavior is with positive reinforcement.

true

What are the experimental advantages in using invertebrates?

• small nervous systems

• large neurons

• identifiable circuits

• simple genetics

Describe what Eric R. Kandel is doing.

• his studies on the molecular basis of learning and memory using the sea slug, Aplysia

• Aplysia is capable of learning to modify its reflex, and this learning involves making memories

What are the types of learning and memory in Aplysia?

• habituation (nonassociative learning)

• sensitization of the gill withdrawal reflex (nonassociative)

• gill withdrawal reflex (associative learning with tail shock)

What is the habituation of the gill-withdrawal reflex?

repeated electrical stimulation of a sensory neuron leads to a progressively smaller EPSP in the postsynaptic motor neuron

Where is the presynaptic modification at for the habituation of gill-withdrawal reflex?

L7

What is the sensitization of the gill-withdrawal reflex?

• a very gentle water jet to the siphon initially produces no response

• a brief electric shock to the head sensitizes the animal to produce a much stronger response

What type of axoaxonic synapse is the sensitization of the gill-withdrawal reflex?

L29

What happens when sensitizing stimuli is applied to the Aplysia?

interneurons (L29) release modulatory neurotransmitter 5HT to sensory (SN) neuronal axon

Which two processes are occurring at the L29-SN-L7 synapse?

• synaptic facilitation

• intrinsic plasticity

Which factors promote synaptic facilitation?

• residual Ca2+ at the presynaptic terminal

• partial saturation of Ca2+ buffer

Describe synaptic facilitation.

• a presynaptic action potential triggers a small EPSP in a postsynaptic neuron

• when the same presynaptic fiber fires action potentials in quick succession, the individual EPSPs add together as long as the probability of neurotransmitter release

What is intrinsic plasticity?

a learning- and memory-related change in a neuron’s intrinsic excitability, shown here by changes in spontaneous activity or spike number

Hermissenda: learning type, cell, and change?

• classical conditioning

• photoreceptors

• paired light + aversive rotation → increased firing to light

Aplysia: learning type, neuron, and change?

• sensitization

• neuron B51

• siphon tap + tail shock → increased spike number/siphon-withdrawal response

Rabbit: learning type, neurons, and change?

• classical conditioning

• CA1 and CA3 neurons

• tone + airpuff → eyeblink CR and increased spike number

Describe the molecular mechanism in short-term facilitation.

• 5-HT released by L29 in response to head shock leads to G-protein coupled activation of adenylyl cyclase and PLC in sensory axon terminal

• decreased K+ conductance in sensory axon terminal

• more Ca2+ ions admitted into the terminal and more transmitter release to the motor neuron

Describe the molecular mechanism in long-term sensitization.

• sensitization leads to cAMP-dependent initiation of CREB1

• MAPK-dependent phosphorylation and inhibition of CREB2, which acts as a repressor of transcription

Describe associative learning in Aplysia.

• CS +/SN1 but not CS -/SN2 activity syncs with MN; the US directly activates MN and IN which releases 5HT to SN axons

• after the paired activity in A, the synapse from SN1 to MN is selectively enhanced and showed CR

What are the invertebrate models of learning?

• learning and memory can result from modifications of synaptic transmission

• synaptic modifications can be triggered by conversion of neural activity into intracellular second messengers

• memories can result from alterations in existing synaptic proteins