Learning and Memory

Multiple Timescales of Memory

  • Stimulus leads to perception via sensory organs.
  • Sensory Memory: Lasts milliseconds to 1 second.
  • Short-Term Memory/Working Memory: Lasts less than 1 minute.
  • Long-Term Memory: Lasts days, months, or years. Includes encoding, consolidation, and forgetting.

Types of Long-Term Memory

  • Long-term memory is divided into:
    • Explicit (Declarative) Memory: Requires conscious recall.
      • Episodic: Memory of experienced events.
      • Semantic: Memory of knowledge and concepts.
    • Implicit (Non-Declarative) Memory: Does not require conscious recall.
      • Procedural: Memory of skills and actions.
      • Associative/Emotional Conditioning: Learned associations.

Henry Molaison (H.M.)

  • H.M. is considered "the most important patient in the history of neuroscience."
  • He suffered from incapacitating seizures.
  • He received an experimental treatment: a medial temporal lobectomy.
  • Surgery: Removed the hippocampus on both sides of the brain.

H.M.'s Deficits

  • Spatial Disorientation: H.M. could no longer recognize hospital staff or find his way to the bathroom and Couldn’t remember family’s new address, had to be helped to find his way home.
  • Lack of Improvement: He did the same jigsaw puzzles every day with no sign of improvement.

Amnesia

  • Anterograde Amnesia: Inability to form new memories after the lesion.
  • Retrograde Amnesia: Impaired memory for events before the lesion.

Brenda Milner

  • Developed a system of memory tests for neurological patients.
  • She studied H.M.

H.M.'s Preserved Abilities

  • Remote Memory: Could remember events from before his surgery.
  • Short-Term Memory: Could still remember items over very short intervals.
  • Intelligence: IQ of 112 (100 is average).
  • Skill Learning: Could still learn some tasks.

Mirror-Tracing Task

  • H.M. was given a mirror-tracing task to test motor skill.
  • His performance progressively improved over successive days, demonstrating a type of long-term memory.

Morris Water Maze

  • Experimental animal (mouse or rat) must swim to a hidden platform.
  • Environmental cues in room provide information that permits animals to orient themselves in space.

Place Cells in Hippocampus

  • Place Cells: Neurons in the hippocampus that fire when an animal is in a specific location.

Place Cells Causal Role in Navigation

  • Intervention experiment Reading & writing neural activity with holographic Ca-imaging & optogenetics.

Hippocampus and Navigation in Humans

  • The right hippocampus is activated during navigation through a virtual reality environment.

Patient N.A.

  • Brain was punctured by a small fencing foil in his nose.
  • Suffered damage to mammillary bodies, thalamus.

Korsakoff Syndrome

  • Memory impairment suffered by long-time alcoholics.
  • Caused by a deficiency of Vitamin B.
  • Involves damage to mammillary bodies.

Semantic Memory Deficits

  • Can name objects but not living things, or vice versa.
  • This patient’s deficit is specific to words, not pictures.

Semantic Memory Patient ROX

  • 'The man is a sack of potatoes' (target: carrying);
  • 'The woman is a cup of tea' (target: drinking);
  • 'The child was laddering' (target: climbing);
  • 'The daughter is chairing' (target: sitting).

Semantic Memory Deficits and Dementia

  • Associated with “frontotemporal dementia”.
  • Common in Alzheimer's and other forms of dementia.

Perceptual Learning (Procedural)

  • Process of learning improved skills of perception through practice.
  • Simple sensory discriminations in all sensory modalities (visual, auditory, tactile, olfactory, and taste).
  • Real-world expertise – Reading – Seeing relations among chess pieces – Finding a tumor in an X-ray.

Perceptual Learning Through Video Games

  • Examples: Identifying game elements, reading text quickly, etc.

Motor Learning (Procedural)

  • Learning new motor skills. Henry was given this mirror-tracing task to test motor skill.
  • Increased activation in motor cortex, thalamus, basal ganglia, and cerebellum after learning a motor skill.

Motor Learning and Brain Structure

  • Violinists have a bigger finger representation in motor cortex.
  • Motor learning causes increased synapse formation in motor cortex.

Associative Conditioning - Ivan Pavlov

  • Set out to study salivation response in dogs.
  • Found that stimuli that predicted food would come to evoke the salivation response.

Classical Conditioning

  • Unconditioned stimulus: stimulus that evokes an innate response.
  • Unconditioned response: an innate response to a salient stimulus.
  • Conditioned stimulus: an initially neutral stimulus which precedes an unconditioned stimulus, and predicts its occurrence.
  • Conditioned response: a response evoked by a conditioned stimulus.

Fear Conditioning

  • Amygdala is necessary for fear conditioning.

Instrumental (Operant) Conditioning

  • Learning to associate an action with an outcome (“if I do this, I will get something good”).
  • An animal will learn to work for water/food.
  • Animals will also learn to work for stimulation of some brain regions.

Natural Rewards and Dopamine

  • Natural Rewards Elevate Dopamine Levels.

Effects of Drugs on Dopamine Release

  • Drugs: Amphetamine, Cocaine, Nicotine, Morphine.

Dopamine and Reward

  • Dopamine neurons increase (or decrease) their spiking rate for a prediction error “Wow, that was better (or worse) than I expected!”.
  • Lateral habenula (LHb) makes the prediction?
  • Dopamine=actualreward–expectedrewardDopamine = actual reward – expected reward

Optogenetic Activation of Dopamine Neurons

  • Drives operant learning.
  • Artificially activating dopamine neurons when the mouse pokes its nose in a certain hole “Wow, that was better than I expected!”.

Optogenetic Inhibition of Dopamine Neurons

  • Reduces operant learning Artificially inhibiting dopamine neurons when the mouse receives a food reward “Wow, that was worse than I expected!”.

Types of Learning

  • Declarative learning: learning facts and information of which we can be aware (what we normally think of as memory)
    • Episodic memory – autobiographical memories
    • Semantic memory – generalized memory of facts
  • Nondeclarative learning: memory about perceptual and motor procedures
    • Procedural learning
    • Perceptual learning: learning to recognize objects and events in the world by their sight, sound, taste, etc.; categorization
    • Motor (skill) learning: learning how to control the body in order to respond appropriately
    • Associative learning:
      • Classical conditioning – Associating a stimulus with an outcome
      • Instrumental (operant) conditioning -- Associating an action with an outcome