Non-Associative Learning PDF

Habituation Habituation: weakening of a stimulus response as a result of repeated presentations of neutral stimulus Reductionist Approach: If elementary forms of learning are common to all animals with an evolved nervous system, there must be conserved features in the mechanisms of learning at the...

Habituation Habituation: weakening of a stimulus response as a result of repeated presentations of neutral stimulus Reductionist Approach: If elementary forms of learning are common to all animals with an evolved nervous system, there must be conserved features in the mechanisms of learning at the cell and molecular level that can be studied effectively even in simple invertebrate animals Aplysia = model organism for studying learning and memory - Largest nerve cells in any known animal - Small number of neurons (~20,000) - Extremely stable neuroanatomy (similar neuronal layout) - Simple behaviour to study: the gill-withdrawal reflex ❖ If repeated water jet stimulus, then the gill will withdrawal less and less (less contraction) ❖ the APs in sensory neuron do not change before vs after habituation - Stimulation of the sensory neuron had small change in AP ❖ Stimulating the motor neuron do not change before vs after habituation ❖ EPSPs were reduced throughout habituation SUMMARY - No change in activity in the sensory neuron - EPSPs are reduced during habituation ❖ Reduction in influx of Ca2+ in response to an action potential ❖ Reduction in synaptic vesicles available for neurotransmitter release at terminals ❖ Less neurotransmitter in the synapse ❖ Less depolarization of the post-synaptic neuron Sensitization Sensitization: enhanced stimulus response following single or multiple exposures to a noxious stimulus the gill-withdrawal reflex - shock on the tail (sensory neuron) creating an AP to the interneuron (shocked once) - EPSPs are increased S neuron get shock > AP > Interneuron releases 5-HT taken by 5-HTR on S neuron In S neuron: Adenylyl cyclase > cAMP > PKA > PO4 the K+ channels = conformational change (smaller) > let fewer K+ ions out cell = longer AP ❖ = More Ca2+ into the cell (voltage gated) so cell stays open longer Ca2+ enters vesicles > gets into synaptic cleft > taken by GluR in M neuron **PKA also triggers CREB (crucial for transcription) = more mRNA production = production of more proteins + production of more synapse *** CREB also triggers production of ubiquitin hydrolase = leaves PKA active = more NT release SUMMARY - role of interneurons - release of serotonin by interneurons, via second messengers: ❖ G-protein activation, dissociation and binding to adenylyl cyclase ❖ Production of cAMP (from ATP), which binds and liberates to PKA to phosphorylate ion channels ❖ Reduced efflux of K+ - Increased influx of Ca2+ - increase in neurotransmitter release at synapse - greater depolarization of post-synaptic neuron - Heterosynaptic process Long-Term Habituation 4 days of training, habituation was present for up to 3 weeks Long-Term Sensitization 4 days of training = sensitized for up up to 4 days 4 days of training (4 times a day) = sensitized for up to 7 days Short-term effects are due to local changes at the synapse Long-term effects require protein synthesis: structural changes take place through second messengers which leads to DNA transcription and translation of a set of proteins involved in axonal growth