Learning and Memory - Comprehensive Notes

Learning & Memory I

Overview

• Cerebral Cortex: Involved in higher-order cognitive functions.
• Prefrontal Cortex: Crucial for planning, decision-making, and working memory.
• Striatum & Globus Pallidus: Part of the basal ganglia, involved in motor control and habit formation.
• Amygdala: Processes emotions, especially fear and aggression.
• Parahippocampal Region: Surrounds the hippocampus and is involved in memory encoding and retrieval.
• Hippocampus: Critical for forming new long-term memories and spatial navigation.
• Cerebellum: Important for motor learning and coordination.

Outline

• Information processing model of memory.
• Four types of learning and associated neural processes.
• Relating learning to memory.

Learning and Memory

• Learning:
  • Acquiring new information.
  • The process by which our nervous system changes as a result of experience.
• Memory:
  • How changes from learning are expressed (recalled) and maintained over time.
  • Short and long-term changes in the nervous system that follow learning.
• Interconnection:
  • Learning is impossible without memory.
  • Memory is impossible without learning.
• Memory Storage:
  • Memories are not stored as discrete elements but as changes in circuits related to how we perform, think, plan, and behave.
• Plasticity:
  • Learning, memory, and their effects on behavior are only possible through plasticity.
• Contribution to Identity:
  • Learning and memory contribute to who we are.

Information Processing Model of Memory

• Encoding (Learning): Acquisition of new information.
• Consolidation (Memory): Conversion of short-term to long-term memory.
• Storage (Memory): Maintaining information over time.
• Retrieval (Memory): Accessing and expressing stored information.
• Acquisition: Initial learning phase.
• Expression: Demonstration of what has been learned.

Relating Learning to Memory

• Not all information from short-term memory makes it to long-term memory.
• Long-term memories can be retrieved throughout a lifetime and strengthened with increased retrieval.
• Consolidation of Memories:
  • Conversion of short-term to long-term memory.
  • Changing the memory from a labile/vulnerable state to a stronger, more permanent state. Sec - min hours - years

Types of Long-Term Memory

• Human Memory
  • Sensory memory (< 1 sec)
  • Short-term memory/working memory (< 1 min)
  • Long-term memory (life-time)
    • Declarative Memory: (facts, events)
      • Episodic memory (events, experiences)
      • Semantic memory (facts, concepts)
    • Nondeclarative Memory: (skills, tasks)

Four Types of Learning

• Perceptual Learning
• Motor Learning
• Stimulus-Response Learning
  • Classical Conditioning
  • Operant Conditioning
• Relational Learning

Perceptual Learning

• Learning about sensory information.
• Accompanied by changes in sensory circuits that detect the particular stimulus.
• The primary function is to identify and categorize objects and situations.
• Examples:
  • Learning to distinguish between stimuli.
  • Learning to recognize stimuli that have been perceived before (identify stimuli as familiar or unfamiliar).

Motor Learning

• Learning a sequence of motor behaviors over repeated trials.
• Skill learning / Procedural learning.
• Accompanied by changes in motor circuits that control a particular behavior.
• Motor learning cannot occur without sensory stimuli from the environment.

Stimulus-Response Learning

• Learning to perform a particular behavior when a particular stimulus is present.
• This form of learning establishes connections between circuits involved in perception and movement.
• Can take the form of an automatic response (defensive reflex) or a more complicated sequence of movement.
• Two Categories:
  • Classical Conditioning
  • Operant Conditioning

Classical Conditioning

• Form of S-R Learning: Learning to perform a particular behavior when a particular stimulus is present.
• AKA Pavlovian Conditioning.
• Involves an association between two stimuli.
• A stimulus that previously had little effect on behavior becomes able to evoke a reflexive, species-typical behavior.
• Accompanied by synaptic changes: strengthening and weakening of synaptic connections.
• Can increase avoidance or approach behaviors.

Classical Conditioning: Avoidance

• US (Unconditioned Stimulus): puff of air
• UR (Unconditioned Response): blink
• CS (Conditioned Stimulus): tone
• CR (Conditioned Response): blink

Neural Model of Classical Conditioning

• Pairing of US (puff of air) with CS (tone) leads to the CS (tone) eliciting the UR (blink).
• When the tone is presented just before the puff of air to the eye, the auditory synapse is strengthened.
• EPSP After Learning > EPSP Before Learning

Brain Structures Involved in Classical Conditioning

• Cerebellum: Important for eyeblink conditioning.
• Amygdala: Important for fear conditioning.

Classical Conditioning: Approach

• US: food

• UR: salivation

• CS: whistle

• CR: salivation

• DA neurons are important for pavlovian conditioning because they signal reward information

• Schultz et al (1997) Science

  • Sensitive to timing of reward delivery
  • follows the shift in behavioral responses

Operant Conditioning

• Operant conditioning involves an association between a stimulus and a response (such as a tone and lever-pressing behavior).
• AKA Instrumental Conditioning.
• Form of learning in which a reinforcing or punishing outcome follows a specific behavior in a specific situation.
• The reinforcer increases the likelihood of the behavior occurring again in the future, while the punisher decreases it.
• Specific consequences are associated with a voluntary behavior

Thorndike's Law of Effect

• Reinforcement: Aims to increase behavior.
  • Positive: add appetitive stimulus following correct behavior (e.g., parent gives child candy for good behavior).
  • Negative: remove noxious stimulus following correct behavior (e.g., parent foregoes child’s boring chore for good behavior).
    • Escape - remove noxious stimulus
• Punishment: Aims to decrease behavior.
  • Positive: add noxious stimulus following behavior (e.g., parent spanks child for bad behavior).
  • Negative: remove appetitive stimulus following behavior (e.g., parent takes away child’s toy for bad behavior).
    • Active Avoidance - behaviour avoids noxious stimulus

Neural Model of Operant Conditioning

• More complex than Classical Conditioning.
• Synapses between sensory neurons and motor output are strengthened.
• Hungry rats increase lever presses because they learn presses result in food.
• Via complex circuitry, the reward can help strengthen the synapse between the cue and press response.
• Cue: sight of light or lever, Reward: food, Lever press: Stimulus Response

Relational Learning

• Establishment and retrieval of memories of events, episodes, and places.
• More complex than first three and often relates to memory you can think and talk about (declarative memory).
• Learning the relationships among many individual stimuli.
• Relative locations of objects.
• Learned and retaining sequences of events that we perform or witness.
• Perception of spatial location: spatial learning.
• It also involves learning relationships among other memories
• Photograph reminds you of a person’s name and the movements you need to make to pronounce it
• Arriving at a building calls to mind the directions to a specific office

Relating Learning to Memory

• Acquisition Expression:
  • Perceptual Learning à Perceptual Memory
  • Motor Learning à Motor Memory
  • Stimulus-Response Learning à S-R Memory
  • Relational learning à Relational Memory
• Not all information from short-term memory makes it to long-term memory.
• Long-term memories can be retrieved throughout a lifetime and strengthened with increased retrieval.
• Consolidation of memories: conversion of short-term to long-term; changing the memory from a labile/vulnerable state to a stronger, more permanent state.
• Reconsolidation of memories: modification of long-term memories. Sec - min hours - years

Amnesia

• Incapacity to remember
• Retrograde Amnesia
  • Inability to remember events prior to injury (i.e., some sort of damage to your brain)
  • Can’t remember the past
• Anterograde Amnesia
  • Inability to remember events after injury
  • Incapacity to form new memories

Learning & Memory II

Overview

• Rhinal Cortex, Amygdala, Hippocampus

Outline

• The Case of HM: HPC & Consolidation
• Neural basis of 4 types of learning & associated memories
• Distributed memory storage

The Case of HM

• HM is the most famous patient in the history of neuroscience research.
• He has made a valuable contribution to research on the neurobiology of memory. He was extensively tested for over 50 years.
• Demonstrated that the medial temporal lobe is critical for consolidating episodic memories
• Bilateral Medial Temporal Lobectomy:
  • Removal of the medial temporal lobe (MTL) bilaterally to alleviate serious epilepsy (1953).
    • Hippocampus
    • Amygdala
    • Rhinal Cortical Areas
  • Epilepsy improved
  • Had devastating amnesic effects
  • He was last patient to receive this treatment
• Intellect was above average
• Normal perceptual and motor abilities
• Well-adjusted individual
• Mild retrograde amnesia (~ 2 years prior to surgery)
• Profound anterograde amnesia for episodic memories
• Never learned the names of people he met since the operation
• Never learned to navigate his new neighborhood
• HM has relatively intact short-term memory
  • Remember a list of 6-7 digits
  • Tap a sequence of 5 blocks
• HM has normal sensory-motor learning skills
  • Eye-blink conditioning
  • Mirror-tracing task
  • Rotary-Pursuit Test
• Milner (1965): “… Forgetting occurred the instant the patient’s focus of attention shifted.”

Long-Term Memory

• Declarative (explicit): things you know that you can tell others
  • Episodic: breakfast this morning
  • Semantic: the name of the 30th president
• Non-declarative (implicit): things you know that you can show by doing
  • Skill/Procedural Learning: skiing, riding a bike
  • Priming: more likely to use a word you heard recently
  • Conditioning: salivating when I see a nice steak!

Why do we need 2 parallel memory systems?

• Although subjects with MTL amnesia can form procedural (implicit) memories, they can not transfer that memory to a new or different context (situation)
• The conscious (explicit) system may have evolved to confer flexibility, that is, ability to use implicit learning in different ways or contexts.

What has HM Taught US?

• Evidence that there are different kinds of memory
• Certain brain regions are more important for some kinds of memory, but not others
• Evidence for two parallel memory systems
• Consolidating episodic memories (conversion from short-term to long-term) depends on the medial temporal lobe (especially the Hippocampus)

Post-traumatic Amnesia: Evidence for Memory Consolidation

• Concussion or Coma (closed head trauma)
• Usually results in amnesia for events occurring just after regaining consciousness
• Failure to convert short-term memories to long-term memories
• Permanent retrograde amnesia for events just prior to the injury
• Older memories are spared!
• Suggests that these memories have been protected by some mechanism and are stronger than newly formed memories

Hippocampus and Consolidation

• HM:
  • Some retrograde amnesia and severe anterograde episodic amnesia
• Suggests that hippocampus and related cortical areas are important for consolidating episodic memories for long-term storage in other cortical areas
• Over time, memories are stored in distributed networks of cortical and subcortical areas and become less and less connected to the hippocampus
• Engram – the change in the brain that represents a memory
• Where is the memory stored? The search for engrams has implicated many areas of the brain

Where are Memories Stored?

• In general, memories are stored in areas that contribute to the acquisition of the memories
  • Inferotemporal cortex: object recognition
  • Hippocampus: spatial location
  • Amygdala: learned fear
  • Cerebellum: implicit sensory-motor tasks (eye blink response) skilled motor performance
  • Prefrontal cortex: working memory
  • Striatum (basal ganglia): habit formation

Neural Changes

A simplified view of neural changes that support Perceptual, Stimulus-Response, and Motor Learning

Strengthened connections between neurons that analyze sensory information and those that produce responses

Brain Areas Involved in Visual Memories?

Given that memories are stored in areas that contribute to the acquisition of the memories, Which brain areas are likely involved in visual memories?

Perceptual Memory: Neural Evidence

• Changes in circuits of neurons that detect the presence of a particular stimulus
  • Neural evidence of perceptual learning: Response properties of sensory neurons change as individual learns to perceive differences
  • Typically occurs in sensory association cortices
  • Yang & Maunsell (2004)- recordings show single neurons in extrastriate cortex become more sensitive to small differences (firing selectivity changes) as animals learn to detect differences in visual patterns.
• Following consolidation, cues can re-activate sensory association circuits that underwent changes
  • Ex: Visual association cortex that responds to movement (MT; dorsal stream) is activated by pictures that imply motion
  • Kourtzi, Z., & Kanwisher, N. (2000).

Brain areas are likely involved in motor memories?

Given that memories are stored in areas that contribute to the acquisition of the memories

Motor Memory: Neural Evidence

• Changes in circuits of neurons that initiate or execute movement
  • The cerebellum, thalamus, basal ganglia, and motor cortex are involved in motor learning across many different tasks.
  • Neural evidence of motor learning: routing of signals through those areas changes as individuals improve a movement, skill, or procedure.
  • Note: as motor actions become more habitual, there is increased signaling through the basal ganglia Typically involves a period of fast learning when the motor movements to be learned show rapid improvement during initial trials followed by slower improvements (consolidation after each attempt)
• Motor Memory: every time a movement is attempted, the circuits are activated and refined (consolidation and reconsolidation of memory)

Stimulus & Response Memory: Neural Evidence

• Strengthened connections between neurons that analyze sensory information and those that produce responses
  • Cue: sight of lever, Reward: food, Lever press: Stimulus Response
  • Note: DA is important for classical and operant conditioning

Relational Learning

• Establishment and retrieval of memories of events, episodes, and places
• Learning the relationships among many individual stimuli
• Relative locations of objects
• Learned and retaining sequences of events that we perform or witness
• Perception of spatial location—spatial learning

Hippocampus (HPC)

• Receives info from sensory and motor cortices as well as subcortical regions (basal ganglia and amygdala)
• It process that information and links elements together in ways that permit us to consolidate learning and remember relationships among elements
• Functions:
  • Consolidation of episodic memory
  • spatial memory, navigation, and timing
• Hippocampus (HPC) and Spatial Memory

Morris Water Maze

Normal vs Lesion

• Normal rat learning the location of the hidden platform (Relational Learning)
• Hippocampal lesions impair rats’ ability to learn and remember the location of the platform
• Control rat remembers task
• Hippocampal lesion rat does not learn task
• This can also test non-relational, stimulus-response learning.

Spatial Memories

• Remember: Over time, memories are stored in distributed networks of cortical areas and become less and less connected to the hippocampus Update: this is true for spatial memories
  • 1 day after leaning
    • HPC deactivation prevents consolidation
    • Cortex deactivation has no effect
  • 30 days after leaning
    • HPC deactivation has no effect
    • Cortex deactivation disrupts performance

Hippocampus and Spatial Memory in Many Species

• Birds that store seeds have larger hippocampi than non-food caching birds
• In humans, there is hippocampal activation during performance of virtual navigation tasks
• London taxi cab drivers have larger hippocampi than normal subjects

Hippocampus and Surrounding Structures in Spatial Memory and Navigation

• Hippocampus seems to be critical for spatial memory, but how/why is this?
• Place Cells!
  • Cells that fire when the subject occupies a particular location in the environment
• Spatially modulated neurons are also found outside of the hippocampus
• Head direction cells: Firing is tuned to the direction the animal is facing
• Border cells: Firing is tuned to the perimeter or border of the environment
• Grid cells: Firing is tuned to the vertices of hexagonal grids
• Specific tuning/ pattern differs among individual cells ( different direction, grid sizes, and places)
• Entorhinal cortex: head direction cells, border cells, and grid cells
• Hippocampus: place cells
• Main takeaway: a network of spatially-modulated neurons works together to support spatial navigation, a form of relational memory

Storing Memories

• Where are Memories Stored?
  • In general, memories are stored in areas that contribute to the acquisition of the memories
    • Inferotemporal cortex: object recognition
    • Hippocampus: spatial location
    • Amygdala: learned fear
    • Cerebellum: implicit sensory-motor tasks (eye blink response) skilled motor performance
    • Prefrontal cortex: working memory
    • Striatum (basal ganglia): habit formation