Non-Associative Learning and Perceptual Learning

Overview

• Types of non-associative learning:
  • Habituation
  • Sensitization
  • Perceptual learning (including priming and discrimination tasks)

Early Studies on Learning and the Brain

• Pavlov: Removal of dog’s cortex halted habituation
• Katz: Habituation observed even below a spinal cord cut
• Roaches: Show habituation without having a cortex
• Studies reveal complexity of neuron interactions in learning

Studying Simple Nervous Systems

• Aplysia (sea snail) as a model organism
  • Central nervous system with ~20,000 neurons
  • Large neurons make study easier
  • Frequently used to study habituation and sensitization

Mechanisms of Habituation and Sensitization in Aplysia

• Habituation Process:

  • Touching siphon activates sensory neurons
  • Sensory neurons release glutamate onto motor neurons
  • Motor neurons activate gill muscle to retract
  • Repeated activation leads to less glutamate release
  • Decrease in motor neuron response and quicker gill release
  • Long-term habituation: fewer glutamate receptors due to reduced glutamate

• Sensitization Process:

  • Gentle touch of siphon produces gill withdrawal
  • Mild aversive shock to the tail leads to longer gill withdrawal upon next touch
  • Involves interneurons that release serotonin, increasing acetylcholine release
  • Long-term sensitization: increase in acetylcholine receptors

Summary of Habituation and Sensitization

• Opposing changes in synapse function
  • Habituation: synapse depression and receptor pruning
  • Sensitization: synapse facilitation and addition of receptors
• Learning involves direct changes in synapse function and modulation by interneurons
• Repeated training leads to long-lasting structural changes

Perceptual Learning

• Definition: Repeated exposure to a stimulus improves recognition and processing
• Brain Processing:
  • Somatosensory cortex (S1) processes touch
  • Each neuron has a distinct receptive field organized topographically

Example: Auditory Cortex

• Neurons respond to specific pitch frequencies
• Training sharpens neural response to specific pitches
• Increased ability to distinguish between pitches after training

Cortical Plasticity and Perceptual Learning

• Experience shapes cortical networks, tunes receptive fields, and prunes synapses
• Example: Touch sensitivity and training with toothpicks
  • Training improves discriminatory ability
  • Increased activation in relevant sensory cortex areas
  • Temporary changes unless practiced over a longer period

Formation of Mental Maps

• Incidental learning involving place cells in the hippocampus
• Neurons respond to specific locations in space
• Controlled by local visual cues

Clinical Perspectives

• Stroke and Neural Plasticity:

  • Paralyzed limbs worsen over time due to lack of use
  • Constraint-induced movement therapy (CIMT) forces use, improving function

• Man-Machine Interfaces:

  • Examples: Cochlear implants
  • Microphone translates sound into electrical signals sent to auditory neurons
  • Brain eventually interprets these signals as intelligible sounds through neural plasticity

• Training and experience critical for effective learning and adaptation