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PSYB64H3 (201)
Chapter 12

Chapter 12

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Janelle Leboutillier

Chapter 12Learning and Memory LEARNING Behaviour of organisms can be divided into 3 categories 1 Reflexesinvoluntary responses to stimuliproduced by prewired neural connections or reflex arcs They have the advantage of producing rapid and reliable responses but their inflexibility is a disadvantage with environmental changes 2 Instinctsautomatic but with complex behavioursmost include mating or parenting behaviourslightly modified by experience but are mostly a fixed pattern of action 3 Learningrelatively permanent change in behaviour or capacity for behaviour due to experience provides organisms with the most flexible means for responding to the environmentmuch of humans adaptability stems from our ability to learnlearning extends only to behaviour that changes from experience and not from short emotional bursts or maturation and growth Types of LearningLearning occurs in two ways Associative learning when an organism forms a connection between 2 features of its environmentclassical conditioningNon associative learning processes of habituation sensitization involves changes in the magnitude of responses to stimuli rather than the formation of connections between specific elements or eventsHabituation and Sensitization Habituationoccurs when an organism reduces its response to unchanging harmless stimuliSensitizationoccurs when repeated exposure to a strong stimuli increases response to other environmental stimuli exaggerated movement after an earthquake to movement and shitthis allows us to react more quickly to sources of potential harmClassical Conditioning organism learns that a stimuli predicts the occurrence of another event conditionedlearningunconditionedinnate or unlearnedUsing Invertebrates to Study Learning Invertebrates large celled simple bodies allow their nervous system to be easily observed most research has relied on Aplysia Californica On the dorsal surfaceyou can locate the gill which the animal uses to breathe The gill can be covered by a structure known as the mantle shelf At one end of the mantle shelf is the siphon a tube through which the animal releases waste and seawater Touching the animals siphon produces a protective response known as the gill withdrawal reflex in which the gill is retracted the gill withdrawal reflex eventually habituates Habituation in Aplysia simple invertebrates have neural nets as opposed to brainswithin these neural nets ganglia or collections of cell bodies serve as major processing centers The siphon is served by 24 touch receptors whose cell bodies are located in the animals abdominal ganglion In the Aplysia abdominal ganglion the touch receptors form synapses with a number of excitatory and inhibitory interneurons as well as with the six motor neurons serving the gill Kandel and his colleagues considered several hypotheses that might account for habituation within this simple network with repeated stimulation the sensory neurons serving the siphon might become less responsivethis possibility was discarded after recordings form the sensory neurons demonstrated steady ongoing activity in response to touch even after the gill withdrawal reflex had become very weakAnother possibility was a reduction in the gill muscles ability to react in response to input from the motor neurons 0 this was also ruled out when electrical stimulation of the motor neurons reliably produced muscle contraction even after habituation had occurredThe final alternativerepeated touching of the siphon produces changes at synapses between he sensory neurons of the siphon and motor neurons that serve the gill muscleskandel successfully demonstrated that repeated touching of the siphon reduced the size of the excitatory post synaptic potentials in both the interneurons and motor neurons a smaller input to the motor neurons results in diminished activity between he motor neurons and gill muscles with in turn produced a weak withdrawal reflex Kandel furthered demonstrated that the reduced activity at the synapse between the sensory and motor neurons in habituation was a direct result of the release of less neurotransmitterThe repeated stimulation depletes the amount of available neurotransmitter in the presynaptic sensory neuron producing a short term habituation lasting from minutes to several hours Habituationeven in Aplysiacan last up to three weeks depletion of available neurotransmitter is unlikely to be the cause of this longer lasting habituationinsteadlongterm habituation probably depends on post synaptic processes involving the NMDA glutamate receptorwhich has special qualities that allow it to participate in the structural changes that accompany learningChemicals that block glutamate receptors effectively prevent the development of long term habituation Sensitization in Aplysia Habituation in Aplysia occurs in a single pathway connecting sensory input from the siphon to neurons controlling the movement of the gillIn sensitization howevera stimulus gains the ability to influence more than one neural pathwayafter sensitization by administration of an electric shock to the head or tail touching the siphon results in an enhanced gillwithdrawal responseDiagram is on 344 Shocking the animals tail stimulates sensory neurons which form excitatory synapses with a group of interneuronsthese interneurons then form synapses with the sensory neurons serving the siphon
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