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Lecture 4

Tuesday, Sept 18/2012 - Lecture 4 Notes

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PSYC 2330
Francesco Leri

PSYC 2330 Lecture 4 Tuesday, September 18, 2012 Experiments performed in the Aplysia have demonstrated that habituation is caused by: a) Increase in withdrawal reflexive reactions b) Reduction of interest in the task c) Reduction of pool of synaptic vesicles d) Expression of synaptic extracellular potassium e) Increase in intracellular sodium I guess C (Correct!) Habituation & Sensitization • non-associative – means that the organism is not making an association between two events • Habituation is a decrease in the strength of a response after repeated presentation of a stimulus that elicits the response ◦ Examples ▪ When you go outside it may initially be cold but you get used to it ▪ When you change the lighting it is initially harder to see but you get used to it ◦ Habituation is a form of learning because your response is changing • Sensitization refers to the increment in response ocurring upon repeated presentation of a stimulus that reliably elicit the response ◦ Examples ▪ Essential oils can sensitize the skin ▪ Noises that become increasingly annoying the more you hear them ◦ Sensitization is also a form of learning because your response is changing ◦ Sensitization can also occur when the organism is more sensitive to other emotional reactions because of a heightened emotional state. • In habituation, the response goes down, and in sensitization the response goes up • Habituation is generally easier to understand and that we all experience on a regular basis • Sensitization and habituation are some of the most basic forms of learning for an organism • Sensitization and habituation occur biologically at all times • Aplysia is a slug with a very simple nervous system ◦ their neurons are so few and so big that they can be seen under a regular microscope ◦ Aplysia displays habituation and sensitization Neuron and Synaplse • Neurons are the cells that do most of the work transmitting information from one area to another • Neuronal processing represents human thought • How neurons are inerconnected represent the associations between stimuli • Connection between the button and the synapse is not physical in that there is space between them. This tiny space is called the synaptic cleft. • The action potential travels to the presynaptic terminal and releases neurotransmitters into the synaptic cleft • Most drugs that alter cognitive functions achieve their effects by changing regular synaptic functioning Neurotransmitters and Calcium (Ca+) • The action potential opens calcium channels • calcium is an ion • Calcium enters the neuron and allows the vesicles to bind to the wall of the presynaptic terminal and release neurotransmitters • Calcium is critical for neurotransmitter release • Calcium channels are regulated by a number of factors inside and outside the neuron • It is possible to change how long neurotransmitters are released into the postsynaptic cleft Habituation of the Gill-Withdrawal Reflex: • Habituation is caused by a decrease in the release of neurotransmitters from the sensory neuron due to a reduction of pool of synaptic vesicles and inactivation of calcium channels by calcium itself • TheAplysia has a thin gill that is withdrawn when there is a risk to it • The syphon is a portion of the body that is particularly sensitive to touch • When you touch the syphon area, the sensory neuron is activated, which then activates the gill which causes it to withdraw • The sensory neuron demonstrates the same activation pattern with every poke/touch • The motor neuron, however, decreases the amount of neurotransmitter released • There are less vesicles available to be released as habituation continues • Calcium channels are essentially blocked, which blocks the ability of the neuron to release increased levels of neurotransmitter • The calcium channels change shape and when the action potential arrives the calcium channel can no longer be activated • Habituation is usually reversible – if you wait long enough, the system will generally reset. The time it takes to reset depends on how long you were habituated • Sensitization is not always reversible because its mechanisms are much more complex • Learning means that behaviour is changing as the result of experience Sensitization of the Gill-Withdrawal Reflex • Involves facilitory interneurons (serotonin) • One shock: ◦ More Ca+ ◦ More vesicles in the sensory neuron lasting minutes • Five shocks ◦ Growth of new synapses in the sensory neuron can last days
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