Explicit Implicit Memory (1)

Brain & Behaviour

  • Explicit & Implicit Memory

    • Presented by: Dr. Rebecca Knight (r.knight4@herts.ac.uk)

    • Course Code: 2H270

Learning Outcomes

  • To introduce neuronal and synaptic processes underlying learning and memory.

  • To consider contributions of brain structures: temporal lobe and basal ganglia in explicit and implicit memory and learning processes.

Learning at the Synapse

Neuronal Changes in Learning

  • Learning results in structural changes in synapses.

  • Hebb's Rule (1949): Co-activation of connected cells strengthens their connections.

    • Quote: “When an axon of cell A is near enough to excite a cell B... some growth or metabolic change takes place...

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Short-Term and Long-Term Memory

  • Short-Term Memory:

    • Short-term memory is maintained by neural activity in closed-loop CNS circuits according to Hebb.

  • Long-Term Memory:

    • Extended reverberating activity leads to structural synaptic changes, facilitating deeper transmission and influencing motor output and behavior.

Long-Term Potentiation (LTP)

Overview

  • First described in the hippocampus by Bliss et al. in the 1970s.

  • Characteristics of LTP:

    • Long-lasting enhancement of synaptic transmission.

    • Involves priming of NMDA glutamate receptors, key to learning and memory.

    • Opposite effect is Long-Term Depression (LTD).

Mechanisms of LTP

  • Role of Receptors:

    • Glutamate activates AMPA receptors, causing brief depolarization (EPSP).

    • NMDA receptors initially blocked by magnesium but can open after EPSPs sum.

    • Calcium's Role: Once unblocked, calcium enters, activating processes crucial for memory formation.

    • Increased glutamate receptors lead to increased synaptic sensitivity.

Mechanistic Insights

  • Early LTP leads to more AMPA/NMDA receptors at the postsynaptic membrane.

  • Late-phase LTP signals nuclear changes (e.g., BDNF release) supporting synaptogenesis (neuroplasticity).

Classical Conditioning

Process of Classical Conditioning

  1. Unconditioned Stimulus (US) → Unconditioned Reflex (UR)

    • Example: Food → Salivation.

  2. Pairing: Unconditioned (US) with Conditioned Stimulus (CS)

    • Example: Food + Bell → Bell becomes conditioned.

  3. Conditioned Stimulus (CS) → Conditioned Reflex (CR)

    • Example: Bell → Salivation (not identical to UR).

Examples of Conditioning

  • Example 1:

    • US: Puff of air → UR: Eye blink.

    • Pairing: Puff of air + Tone → Tone becomes a CS.

    • CR: Tone → Eye blink.

Case Study: HM (Henry Molaison)

  • Major surgery in 1953 leading to severe amnesia; could not form new memories (anterograde amnesia).

  • Retained childhood memories (retrograde amnesia partial).

  • Studies revealed crucial insights into types of memory.

Ribot’s Law

  • Memory's migration from hippocampus to neocortex; initial consolidation maintained by the hippocampus.

Types of Memory

  • Explicit Memory: (Declarative)

    • Types:

      • Episodic (events), Semantic (facts).

  • Implicit Memory: (Non-declarative)

    • Examples: Procedural (skills), Priming.

Role of Medial Temporal Lobe (MTL) in Explicit Memory

  • Case Study Findings:

    • Significant damage to MTL impacts long-term event memory and fact retention.

    • Immediate memory, procedural memory remain intact.

Testing Recognition Memory

  • Delayed non-matching to sample task (DNMTS):

    • Used in monkeys to assess recognition memory.

    • No deficit at short intervals, but performance impaired with delays (temporal damage).

Perirhinal Cortex

  • Significant role in recognition memory; neuron response decreases with repeated stimulus.

  • Association with déjà vu experiences.

Hippocampus & Spatial Memory

Experimental Evidence

  • Morris Water Maze:

    • Rats form cognitive maps; performance impaired with hippocampal lesions.

    • Place cells represent spatial locations within the hippocampus.

Human Studies

  • Iaria et al (2003):

    • Activation patterns in hippocampus reflect strategy types for spatial navigation.

Implicit Memory: The Striatum

Role of the Striatum

  • The striatum forms stimulus-response associations within action selection.

    • Unique contribution to implicit/procedural memory.

Evidence of Learning Mechanisms

  • Double Dissociation:

    • Implicit (S-R) learning tied to striatum; explicit learning tied to hippocampus.

  • Habit Formation:

    • Transition from goal-directed to habitual responses after repeated training.

    • Evidence seen through devaluation procedures in experimental contexts.

Summary of Implicit Memory Findings

  • Striatum's role in implicit memory includes regulating actions associated with past rewards.

    • Affects ongoing behavior even when expected outcomes diminish.

Exam Preparation

Topics Covered

  • Explicit Memory: Role of MTL (hippocampus and surrounding structures).

  • Implicit Memory: Understanding S-R learning in the striatum.

Questions Practice

  • Describe the roles of MTL areas in explicit memory, utilizing evidence.