PSY260, Week 4-5, Classical Conditioning

• Hippocampus


  Important for spatial navigation and memory
• Place cells


  • Whose receptive field seems to be a particular location or place that is familiar
  • In a rat, a place cell fires in arm 2 of the maze; rotating the landmarks shows the place cell defines "arm 2" based on these landmarks
• Place cell


  Only responds to a specific place
• Grid cell


  Creates a backdrop of a map
• Unconditioned Response (UR)


  Preparatory response (e.g. salivation)
• Conditioned Stimulus (CS)


  Computer sound
• Conditioned Response (CR)


  Reaching for altoids

  
• Classical Conditioning


  1. Begins with an innate (unlearned) reflex

  2. Unconditioned stimulus (US) [food]

  3. Unconditioned response (UR) [salivation]

  4. A neutral stimulus (CS) is then repeatedly presented before the reflex is triggered, producing a new reflex

  5. Conditioned stimulus (CS) [bell]

  6. Conditioned response (CR) [salivation]
• Classical conditioning


  • Helps an organism prepare for the future (the bell triggers behaviours to prepare for the food)
  • Represents an association between the CS and the US (bell is associated with food)
• Quail Sex Conditioning


  • Exposure to female (US) innately produces arousal (UR) in male quail
  • CS is a tone or light, initially neutral
  • After pairing the CS with the US, the CS comes to produce approach (CR)
• Fear Conditioning: Fruit Flies

  • Add odor to compartment where shock happens
  • Flies, given a choice, start to avoid that compartment
  • Exposure to shock (US) innately produces escape/ avoidance behaviour
  • CS is an odour, initially neutral
  • After CS is paired with US, CS comes to produce avoidance (CR)
• Aversive conditioning


  New CS → CR reflex helps avoid noxious US
• Eyeblink Conditioning


  • Puff of air to eye (US) innately produces eyeblink (UR)
  • CS is a tone or light, comes to produce a gradual eye closure (CR)
  • Works on rabbits and humans, but takes many trials
  • The CR is not exactly the same as the UR: it takes place before the US and can be different in speed, form, etc.
• In most cases, classical conditioning builds gradually over many trials
• Conditioned Compensatory Response


  A CR that is the opposite of the UR, helping to balance/correct for the US-UR reflex
• Extinction


  1. Breaking the association between the CS and US can extinguish the new CS → CR reflex

  2. Present the CS alone repeatedly

  3. Initially, CS evokes strong CRs

  4. With repetition, however, CS becomes less effective, similar to beginning of training
• Extinction does not erase the CS-US connection, just inhibits it
• Renewal


  Return of responding to a previously extinguished CS, when that CS is tested in a context that is different from the extinction context
• Delay Conditioning


  CS comes on and the US is presented right at the end of the CS
• Trace Conditioning


  CS comes on then ends, followed by a trace interval and then the US is presented
• Trace conditioning only works well if the trace interval isn't super long
• Blocking


  Prior experience with the light + US association blocks learning of the tone + US association
• Latent Inhibition


  Pre-exposure to CS repeatedly inhibits learning when CS is later paired with US
• Associative Bias/ Biological Preparedness

  Some associations are innately easier to make
• Stimulus-Stimulus (S-S)


  • Classical conditioning is the CS-CR formation in prediction of US
  • However representation of US can modify CR
  • Classical conditioning is not just an S-R association
• CS Modulation Theory


  • Stimuli have a salience that determines attention
  • Repeated exposure with no consequences decreases salience (attention), a form of habituation
  • In latent inhibition, pre-exposure to the CS decreases attention for that stimulus, making it harder to learn about in the training phase
• Error-Prediction learning


  Learning through trial and error to reduce discrepancy (error) between what is predicted and what actually occurs
• Rescorla-Wagner model


  • Based on learning from errors
  • Does not predict latent inhibition

  
• Mammalian Conditioning of Motor Reflexes

  • CS input pathway: Sensory input processed in various brain regions, Sensory nuclei of the pontine nuclei, Mossy fibers split to cerebellar cortex and interpositus nucleus
  • US input pathway: Inferior olive of midbrain to climbing fibers that split to interpositus nucleus and Purkinje neurons in the cerebellar cortex
  • CR output: Purkinje cells of cerebellar cortex, which collects both CS and US input, Inhibits output neurons of the interpositus nucleus
• CS-US association may be stored in Purkinje cells of the cerebellar cortex and cerebellar interpositus nucleus (eyeblink CR pathway)
• In many well-trained animals, the Purkinje cells switch off in response to the CS, shutting off the Purkinje inhibition to the interpositus enables the CS to generate CRs
• Electrical stimulation of pontine + inferior olive or CS + US can create CS-US association without "experience"
• Inhibitory feedback pathway projects from the interpositus nucleus of the inferior olive, in a well-trained animal, production of CR will inhibit the inferior olive from sending US information to Purkinje cells
• The Hippocampus in CS Modulation


  • Removal of the hippocampus does not alter basic classical conditioning paradigms, but does eliminate latent inhibition and disrupt other paradigms that depend on changes in the processing of the CS
  • US modulation (Rescorla-Wagner) occurs in the cerebellum, CS modulation (Mackintosh) occurs in the hippocampus and medial temporal lobe