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Chapter 4

Lecture 5 (Chapter 4 - Feb 4) - PSYCH 2TT3

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Brett Beston

PSYCH 2TT3 2013 Lecture 5 – February 4 Learning  Evolution implies a change in gene frequency, so we must also think at the level of genes Models of Learning  The ability to acquire a neuronal representation of new information  An individual may use that information to determine subsequent behaviour  Donald Hebb – first to describe learning on a synaptic scale  What is learning at the neuronal level?  A stimulus from a neuron produces a typical responds from the neuron to which it connects  Action potential – input comes in, triggers a response from another cell  Cells that fire together wire together o If the stimulus reliably produces a response, the strength of the physiological response increases o If the stimulus doesn’t reliably produce a response, the strength of the physiological response decreases  Learning at the neuronal level o Change in conductivity in the brain o A stimulus from a neuron produces a typical response from the neuron to which it connects  Non-Associative Learning o Sensitization – increased response to stimuli following the presentation of a prominent stimulus (eg/ loud sound, strong smell) o Habituation – decreased response to a stimulus following the repeated presentation of that stimulus (eg/ loud sound, strong smell)  Gradual decrease in instinctive response  Become less aware over time  Habituation and Sensitization in Humans o Bright light (habituation) o Clothes (habituation) o Alarm clock (habituation) o Your name (sensitization) o Habituation – anxiety about finals in first vs. fourth year, your response to your parents nagging o Sensitization – repeating scaring will produce fear response to any stimulus  Erik Kandel – won Nobel prize for study of memory and learning o Aplysia (sea slug) – can vary in size o Wanted to show that the strength of a connection can change through learning  Learned basic defensive reflexes  Capable of reacting to an ocean of predators (crabs, lobsters)  Able to modify basic reflexes when exposed to certain predators numerous times  Aplysia and its role in understanding the neural basis of learning o Give Aplysia shocks o Giving it shocks to see its gill siphon withdrawal reflexes  Siphon – sensory neurons o Reflex shows if learning has occurred o Reflex is 4x as long if learning has occurred  Earned there is danger in the environment o Longer the withdrawal reflex, the more relevant it is o If animal is habituated – more likely to ignore it o Aplysia studied due to gigantic neurons – 40000 neurons in 9 ganglia  Large size allows figuring out pathway between neurons to be easy  Gigantic Neurons o Studies due to their gigantic neurons o 40,000 neurons in 9 ganglia o Due to large size, easy to figure out pathway between neurons o Picture – freshly dissected ganglia of sea slugs  Nerve endings are 1.1 mm wide  larger than any other species  Aplysia and its role in understanding the neural basis of learning o Large neurons allow you to (more) easily record/monitor activity o Simple connectivity between connections o Can demonstrate simple forms of learning (non-associative learning in particular) 1 PSYCH 2TT3 2013  Habituation in Aplysia o Touch siphon with relatively harmless stimuli (pencil) – leads to a change in gill withdrawal reflex o First time will have a response – with each consecutive trial the magnitude of response decreases o In a typical experiment (patch clamp, in vitro done in culture dish) – stimulate presynaptic neuron and view stimulation (exactly the same in each trial – weak stimulus) o Record output of post-synaptic neuron – measure current; response over time decreases – by trial 20, get minimum amount of current  Sensitization in Aplysia o Use shock instead of pencil – should see response increasing o In each subsequent trial the magnitude of response increases  Hypothetical data of Aplysia GSWR after shock o Have to think about simple reflexes o Stimulus that elicits response Associative Learning – Pavlov’s Drooling Dogs  Ivan Pavlov o Not a psychologist – studied digestion; discovered “psychic secretions” Classical Conditioning  When dog sees food  responds with salivation  Non-associative Conditioning o Unconditional Stimulus (US)  Unconditional Response (UR) o Relationship exists – every time stimulus is presented, response will follow  Neutral stimuli (nothing to do with reflexive response) can elicit a response  Conditional stimulus – neutral stimulus that initially produces no response but over time it does when it is repeatedly presented alongside of the unconditional stimulus o Animal learns  When food is brought out; ring a bell  dog salivates o Eventually can ring bell and dog will salivate, without presentation of food  Associative Learning o Following pairings with an unconditional stimulus, a neutral stimulus can come to control a new response  Conditioned Stimulus (CS) o After a number of pairings, the CS produces a new response – Conditioned Response (CR) 2 PSYCH 2TT3 2013 o Eg/ Salivation to the sound of a bell is the new learned response  Response generated must be relevant to current context  Relevant for dog to salivate for food – relevant to salivate at sound of bell because it foreshadows food coming  Eg/ In Class – Popping Balloons o US – popping sound o UR – startled response o CS – countdown o CR – bracing yourself for pop o Being startled is no longer relevant after subsequent trials  classical conditioning or habituation  Learned association between countdown and popping of balloon  Consistent – happens in reliable manner in virtually all animals – can be modeled; amount of learning can occur in an animal, how fast learning occurs  Relevant  Allows understanding the basis of complex behaviour (eg/ drug addiction) Understanding the basis of physiological responses  Learning Drug Tolerance o Overtime, the effect of the drug decreases as a result of learned compensatory response  First experience with alcohol – takes very little to become intoxicated o Not a result of habituation, but result of learned habituation o Graph – Trial vs. Level of Intoxication  Behavioural indication of tolerance in rats o Rats given morphine – measure changes in response to a dose of heroin over time o Measured time it takes for rat to sense heat  Put rat on hot plate - lick paws if heat is sensed o Compare normal (Saline) rat to rat with heroin o Over a period of 5 sessions – paw lick in morphine group begins to decrease over time Physiological indication of tolerance in rats  Looking at how core body temperature changes in response to consumption of alcohol - Look at physiological response  Consuming alcohol decreases core body temperature  Graph – (Right) Hypothermic effect of alcohol changes over time  In first trial hypothermic effect is great – in subsequent trials, effects aren’t as great or last as long  Graph – Tolerance to Alcohol-Induced Hypothermia
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