Long-Term Memory: Types and Examples

• Topic is Long-Term Memory (Part 1)

What is Memory?

• Memory includes various processes, types, systems, and tasks
• Method for studying memory involves lesions and double dissociation
• Short-term and long-term memory are two types
• Memory can be implicit or explicit

Implicit Long-Term Memory

• Implicit memory includes non-associative learning, conditioning, skill learning, and priming

Explicit Long-Term Memory

• Explicit memory includes semantic and episodic memory, as well as consolidation and reconsolidation

Examples of Memory

• Examples include the taste of breakfast, what was eaten for breakfast, usual breakfast items, typical breakfast foods, the concept of breakfast, how to eat breakfast, and even a coffee stain

Long-Term Memory (LTM)

• Key problem: Acquiring information from experience, maintaining it, and using it to guide behavior and plan future actions
• Importance: Progress depends on retaining experiences; those who forget the past are doomed to repeat it
• Challenge: Determining what to remember from all experiences and how to retrieve it

Learning vs. Memory

• Learning is closely related to memory
• Memory involves processes like encoding, storage, and retrieval
• Types of memory include semantic, episodic, and procedural
• Memory systems: hippocampus, cortex, amygdala
• Memory tasks: free recall, stem completion, and motor sequence learning
• Physical changes occur in the nervous system with memory
• Memory is pervasive throughout the nervous system

LTM Processes

• Encoding: Initial creation of memory traces in the brain from incoming information
• Consolidation: Continued organization and stabilization of memory traces over time
• Storage: Retention of memory traces over time
• Retrieval: Accessing/using stored information from memory traces
• Reconsolidation: Possible reorganization and restabilization of memory traces after retrieval

LTM Types & Systems

• Memory is divided into long-term, sensory, short-term and working memory.
• Long-term memory includes declarative (explicit) and nondeclarative (implicit) memory
• Declarative memory encompasses events (episodic) and facts (semantic)
  • Episodic memory involves specific personal experiences
  • Semantic memory includes world knowledge
  • Brain regions include the medial temporal lobe, middle diencephalon, and neocortex.
• Nondeclarative memory includes procedural memory, perceptual representation system, classical conditioning, and nonassociative learning
  • Procedural memory involves skills (motor and cognitive)
    • Regions: Basal ganglia and skeletal muscle
  • Perceptual representation system involves perceptual priming
    • Regions: Perceptual and association neocortex
  • Classical conditioning involves conditioned responses between stimuli
    • Regions: Cerebellum and Reflex pathways
  • Nonassociative learning encompass habituation and sensitization,
    • Regions: Reflex pathways

Short-Term and Long-Term Memory

• Memory is categorized into short-term and long-term memory

Dissociating Short-Term and Long-Term Memory

• Goal is to determine if STM and LTM are separate systems using dissociation logic
• Dissociation: Performance differs across two tasks.
• Single Dissociation: If one function is impaired and another is spared
  • A single dissociation does not necessarily demonstrate separable systems, distinct brain regions, or cognitive processes
• Double Dissociation: If two patterns are flipped
  • Two patterns that are flipped and can be independently impaired is strong evidence that they rely on different brain mechanisms

Short-Term Memory (STM) Task

• Memory span is tested by hearing three words and immediately recalling them in the same order. "Time base offer" is an example

Long-Term Memory (LTM) Task

• Involves list learning, such as hearing ten words and immediately recalling them in any order, then repeating until all ten are recalled

Patient K.F

• Patient with damage to the left temporoparietal cortex
• Displays single dissociation

Danger: Single Dissociation Conclusion

• It's tempting to conclude that a short-term memory task depends on the temporoparietal junction, but long-term memory task doesn't
• Therefore, short-term and long-term memory are separate systems that depend on different brain regions and distinct cognitive processes-

Problem: Alternative Explanations for STM/LTM Dissociation

• Two alternative explanations exist: partial damage argument and compensation argument.

Partial Damage Argument

• Maybe there’s only one system for both STM and LTM.
• The STM task is harder than the LTM task.
• When partially damaged, the STM task suffers more than the LTM task.

Compensation Argument

• Maybe there is only one system for both short-term and long-term memory.
• STM task is harder than the LTM task.
• When this system is completely damaged, the brain can compensate for the LTM task but not the STM task

Patient H.M.

• Patient with damage to bilateral medial temporal lobes

Double Dissociation

• Double dissociation involves two different areas of damage resulting in two opposing single dissociations
• This pattern cannot be explained by task difficulty and strongly suggests that short-term and long-term memory are separable systems

Short-term Memory

• Timescale: seconds
• Capacity: extremely limited
• Neural basis: sustained activation of neurons

Long-term Memory

• Timescale: minutes, hours, days, years
• Capacity: massive
• Neural basis: number and strength of synapses

Implicit & Explicit Memory

• Memory can be classified into implicit and explicit forms

Dissociating Implicit & Explicit LTM

• Implicit memory task: Perceptual identification with a study and test phase
  • Study phase: 24 words are presented for 2 seconds each
  • Test phase: 24 old (studied) and 24 new words are flashed briefly to identify the word (priming effect)
• Explicit memory task: Word recognition with a study and test phase
  • Study phase: 24 words are presented for 2 seconds each
  • Test phase: 24 old (studied) and 24 new words are presented until response; participants respond "yes” or “no” if words are from study phase

Single Dissociation of Implicit & Explicit LTM

• Patient M.S. shows damage to the right occipital lobe
• Patient M.S. shows shows word recognition (explicit memory)
• Patient shows no priming effect (impairment in implicit memory)

Amnesia Patients

• Amnesia patients exhibit Korsakoff's syndrome & epilepsy.
• Amnesia patients display a larger than normal priming effect
• Amnesia patients display Impaired word recognition (impairment in explicit memory)

Double Dissociation of Implicit & Explicit LTM

• Involves two different areas of damage that results in two opposing single dissociations
• Cognitive and brain systems involved in perceptual identification (implicit memory) are distinct from those involved in word recognition (explicit memory)

Implicit Long-Term Memory

• Non-declarative
• Independent of conscious awareness
• Includes procedural memory, conditioning, nonassociative learning, or priming
• Timescale: minutes, hours, days, years
• Capacity: massive (e.g., ~1,000s of skilled motor sequences)
• Neural basis: number & strength of synapses

Explicit Long-Term Memory

• Declarative
• Available to conscious awareness
• Can be semantic or episodic
• Timescale: minutes, hours, days, years
• Capacity: massive (e.g., ~20,000 word families in adult vocabulary)
• Neural basis: number & strength of synapses

Implicit Memory: Non-Associative Memory

• Involves a change in the strength of a response to a single stimulus due to repeated exposure

Non-Associative Memory

• A stimulus does not change, but your response to it changes over time

Habituation

• Reduced response to a repeated stimulus
  • Eg, stop noticing the ticking of a clock

Sensitization

• Increased response to a repeated stimulus
  • Eg, rubbing your arm hurts more the longer you do it

Non-Associative Learning

• Involves sensory-motor reflex pathways

Non-Associative Memory

• First evidence of neural basis of non-associative memory came from studies in sea slug Aplysia
• Studied by Eric Kandel - 2000 Nobel Prize in Physiology or Medicine

Non-Associative Memory: Habituation

• Habituation: A decrease in response to a repeated stimulus
• Touching the siphon causes withdrawal of the gill
• Repeated siphon stimulation leads to less withdrawal
• Habituation leads to Pre-synaptic depression
  • Same action potential
  • Reduced neurotransmitter release
  • Smaller EPSP

Non-Associative Memory: Sensitization

• Sensitization: An increased response to a repeated stimulus
• Touching siphon causes withdrawal of gill
• Shocking tail then touching siphon leads to more withdrawal
• Sensitization leads to Pre-synaptic facilitation
  • Same action potential
  • Increased neurotransmitter release
  • Larger EPSP

Habituation & Sensitization: “Short-Term”

• Last for minutes
• Changes in amount of neurotransmitter released
• "Short-term” habituation/sensitization ≠ short-term memory

Habituation & Sensitization: “Long-Term”

• Last for hours, days, weeks
• Changes in number of synapses

Implicit Memory: Conditioning

• Memory type involves conditioning

Classical Conditioning

• Pavlov noticed that a dog learned to salivate in response to a bell that predicted food
• Unconditioned stimulus (US) = food and Unconditional response (UR) = salivation
• Neutral stimulus (NS) = bell (before pairing) leads to Conditioned stimulus (CS) = bell and Conditioned response (CR) = salivation
• Initially US (food) leads to UR (salivation). After pairing, CS (bell) leads to CR (salivation)

Fear Conditioning

• US = shock and UR = freezing and CS = tone which results in CR = freezing

Neural Circuit in Fear Conditioning

• CS and US converge in the lateral nucleus of the amygdala

Fear Conditioning: EPSP

• EPSP to tone increases in lateral nucleus of amygdala after repeated pairing with shock

Memory: Skill Learning

• Category of implicit memory

Skill Learning

• Motor adaptation
• Cerebellar loops
• Motor sequence learning
• Cortico-basal ganglia-thalamocortical loops

Skill Learning: Motor Adaptation

• Task: Throwing darts with prism glasses
  • Eye-hand coordination
  • Prism glasses shift visual field to side
  • Control participants adapt to distortion
  • Patients with cerebellar lesions fail to adapt

Motor Coordination & Cerebellum

• Cerebellum uses forward model to predict results of motor commands
• Uses differences between actual results and predicted results for online error correction, motor learning, and feedback control

Skill Learning: Motor Sequence Learning

• Serial reaction time (SRT) task: Each light turns on in a certain order; the job is to hit the appropriate buttons in that order
  • Repetition improve completion and does not require conscious processing
  • Depends on basal ganglia thalamo cortical loops

Skill Learning: Motor Sequence Learning

• Depends on basal ganglia & reinforcement learning by selecting actions expected to lead to maximum reward
  • Prediction error = actual reward – predicted reward is used to update expectations
  • Dopamine signal from substantia nigra pars compacta (SNc) represents prediction error
• Larger dopamine response means better than expected, smaller response means worse than expected

Basal Ganglia & Reinforcement Learning

• Unexpected rewards generate dopamine signals from the substantia nigra pars compacta (SNc)
• This excites the direct pathway (via D1 receptors) and inhibits the indirect pathway (via D2 receptors)
• This allows modification of behavior based on reward