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?
• $Dopamine = actual reward – expected reward$

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