bio

• Brain plasticity


  The nervous system's potential for physical and chemical change that enhances (or decreases) its adaptability
• Brain plasticity is a concept that had been overlooked for a long time
• Brain

  • Does not work like a machine with parts
  • Learning is the focus of this module
• Levels of brain plasticity

  • Macro: changes in behaviour
  • Micro: changes in DNA activation, in protein synthesis, in neural connection
• Learning


  A relatively permanent change in behavior that results from experience
• Memory


  • The ability to recall or recognize previous experience
  • Behavioral change caused by an experience
• Types of learning

  • Non-associative learning
  • Associative learning
• Habituation


  Learning behavior in which a response to a stimulus weakens with repeated stimulus presentations
• Sensitization


  Learning behavior in which the response to a stimulus strengthens with repeated presentations of that stimulus
• Habituation


  1. Calcium channels habituate

  2. Reduced sensitivity of Ca2+ channels and decreased release of neurotransmitter

  3. Excitatory postsynaptic potentials in the motor neuron become smaller
• Habituation

  • Specific to the stimulus presented
  • Spontaneous recovery when stimulation ends
• Sensitization


  1. Potassium channels sensitize

  2. K+ ions cannot repolarize the membrane quickly, so action potential lasts longer than normal

  3. Prolongs the inflow of Ca2+ and more transmitter is released
• Sensitization


  • More harmful (painful) stimulation, more sensitization
  • Stronger stimulus, more sensitization
• Associative learning

  Learning process in which a new response becomes associated with a particular stimulus
• Classical conditioning


  1. Pairing CS with US

  2. CS evokes CR
• Classical conditioning

  • Speed of conditioning depends on nature and strength of CS and US, previous experience, and motivational state
  • Conditioning sensitive to causal relevance of CS and reinforcer
• Stimulus substitution theory


  Conditioning does not involve acquisition of new behavior, but tendency to respond in old ways to new stimuli
• Lashley failed to find the engram (the physical trace of a memory)
• Lashley's principles

  • Equipotentiality - all parts of the cortex contribute equally to complex functioning behaviours
  • Mass action - the cortex works as a whole, not as solitary isolated units
• Thompson identified the lateral interpositus nucleus (LIP) as essential for eye-blink conditioning
• Severity of memory disturbance


  Related to size of injury rather than location
• Declarative memory

  Memory for facts and events that can be consciously recalled
• Episodic memory

  Memory for personal experiences and their context
• Hippocampus

  • Critical for declarative memory, especially episodic memory
  • Important for spatial memory
  • Important for contextual memory
• Delayed matching-to-sample tasks

  • Subject sees an object and must later choose the object that matches
• Delayed non-matching-to-sample tasks

  • Subject sees an object and must later choose the object that is different than the sample
• Hippocampal lesions produce specific deficit in the ability of rats to navigate mazes using place cues
• Taxi drivers have a larger than average posterior hippocampus, and the longer they had been taxi drivers, the larger their posterior hippocampus
• Contextual learning


  Memory includes much detail initially, but becomes less detailed and less dependent on the hippocampus over time
• Procedural memory


  Memory for skills and procedures, more dependent on the basal ganglia
• Other brain areas involved in learning and memory

  • Amygdala - fear learning
  • Parietal lobe - piecing information together
  • Anterior and inferior region of the temporal lobe - semantic memory
  • Prefrontal cortex - learning about rewards and punishments
• There is little need to distinguish classical vs operant conditioning, or learning vs memory, from a biological perspective
• Case studies and animal models are crucial for studying brain and memory, but subjects are unable to directly report their memories
• The location of memory storage is still an open question