Long-Term Memory: Implicit and Explicit

• Assigned chapter 9 reading and lab 6 due March 21 cover long-term memory.
• Memory involves processes, types, systems, and tasks.
• Lesions and double dissociation are methods used in memory study.
• Memory includes short-term and long-term forms.
• Memory can be implicit or explicit.

Implicit Memory

• A type of long-term memory
• Includes non-associative, conditioning, skill learning, and priming.

Explicit Memory

• A type of long-term memory
• Consists of semantic, episodic, consolidation, and reconsolidation aspects.
• Remembering breakfast illustrates different memory components, such as taste, what was eaten, breakfast habits, types of food, the definition of breakfast, how to eat it, and unrelated details.
• Problem:
  • Acquiring information, maintaining it, and using it to guide behavior and plans.
• Importance:
  • Progress depends on retaining information.
  • Those unable to remember the past are doomed to repeat it, according to George Santayana.
• Challenge:
  • Determining what to remember and how to retrieve it.
• Learning is approximately equal to memory.
• Memory involves encoding, storage, and retrieval processes, and has semantic, episodic, and procedural types.
• The hippocampus, cortex, and amygdala are the systems involved.
• Free recall, stem completion, and motor sequence learning are tasks.
• Memory requires physical change in the nervous system and is found to be pervasive throughout.
• Encoding is the initial creation of memory traces from incoming information.
• Consolidation involves the organization and stabilization of memory traces.
• Storage is the retention of memory traces.
• Retrieval is accessing stored information.
• Reconsolidation is the possible reorganization and restabilization of memory traces after retrieval.

Long-Term Memory Types and Systems

• Long-term memory dives into declarative(explicit) and nondeclarative(implicit) forms,
• Sensory, short-term and working memories are also subsets.
• Declarative memory includes episodic memory for events and semantic memory for facts.
• Nondeclarative memory includes procedural memory, perceptual representation, classical conditioning, and non-associative learning.
• Dissociation logic distinguishes between STM and LTM by assessing how performance varies across tasks.
• Single dissociation occurs when one function is impaired while another is spared.
  • Single dissociation does not definitively prove separate systems.
• Double Dissociation:
  • This occurs with two patterns that are flipped, which could indicate reliance on different brain mechanisms if both systems can be impaired independently.
• Short-term memory task:
  • Includes memory span via hearing and immediately recalling three words in order.
• Long-term memory task:
  • Includes list learning via hearing and immediately recalling ten words in any order, repeating until all are recalled.
• Patient K.F.:
  • Experienced damage to the left temporoparietal cortex.
  • Demonstrates single dissociation.
• Danger:
  • It is tempting to conclude that short-term and long-term memory are separable systems after single dissociation, however, this may not always be true.
• Partial damage argument:
  • posits that there is one system for both STM and LTM
  • STM is more vulnerable when the system is damaged.
• Compensation argument:
  • Suggests one system exists for both STM and LTM, but the brain compensates for LTM tasks when the system is damaged.
• Patient H.M. had damage to bilateral medial temporal lobes.

Double Dissociation

• Seen across two different bran areas can show opposing single dissociations.
• Double dissociation cannot be explained by task difficulty.
• Short-term and long-term memory are separate systems.
• Short-term memory operates on the scale of seconds with limited capacity.
• The neural basis:
  • Sustained activation of neurons.
• Long-term memory spans minutes, hours, days, and years and has a massive capacity.
• The neural basis:
  • Number and strength of synapses.
• Implicit memory task:
  • Uses perceptual identification in the study phase which involves presentation of 24 words for 2 seconds each.
  • In the test phase, identification of flashed old and new words is done very briefly to measure priming effect,
• Explicit memory task:
  • Requires word recognition, presenting 24 words for 2 seconds each in the study phase, and testing with a mix of old and new words until a response is achieved.
  • Participants respond "yes" or "no" if the words were in the study phase.
• Patient M.S. has damage to the right occipital lobe.
  • Shows typical word recognition (explicit memory).
  • Does not show priming effect (impairment in implicit memory).
• Amnesia patients with Korsakoff’s syndrome & epilepsy show larger than normal priming effects, but have impaired word recognition.
• Cognitive and brain systems for perceptual identification (implicit memory) differ from those for word recognition (explicit memory).
• Implicit long-term memory is non-declarative and independent of conscious awareness.
• It includes procedural memory, conditioning, non-associative learning, and priming
• It operates on the scale of minutes, hours, days, and years.
  • Massive capacity and relies on the number and strength of synapses.
• Explicit long-term memory is declarative and available to conscious awareness.
• Explicit memory:
  • Can be semantic or episodic.
  • Operates on the scale of minutes, hours, days, and years.
  • Massive capacity (e.g. ability to hold20,000 word families in adult vocabulary).
  • It's neural basis is number & strength of synapses.
• Non-associative learning:
  • Involves changes in response to a stimulus over time, with the stimulus itself remaining constant.
• Habituation:
  • A reduced response to a repeated stimulus, like no longer hearing a clock ticking.
• Sensitization:
  • Increased response to a repeated stimulus, like rubbing your arm until it hurts.
• Non-associative learning involves sensory-motor reflex pathways.
• First evidence of neural basis of non-associative memory found after studies in sea slug Aplysia.
• Habituation involves pre-synaptic depression, seen via same action potential, reduced neurotransmitter release and smaller EPSP.
• Sensitization involves pre-synaptic facilitation, same action potential, increased neurotransmitter release and larger EPSP.
• "Short-term" changes during Habituation & Sensitization last for minutes.
  • Shown change in the amount of neurotransmitter released.
• "Long-term" changes during Habituation & Sensitization last for hours, days, weeks.
  • Demonstrated change in the number of synapses.
• Conditioning falls under implicit memory.
• In classical conditioning Pavlov noticed there dog learned to salivate in response to a bell that predicted food
• Classical Conditioning:
  • Unconditioned Stimulus (US) = food.
  • Unconditional Response (UR) = salivation.
  • Neutral Stimulus (NS) = bell (before pairing).
  • Conditioned Stimulus (CS) = bell
  • Conditioned Response (CR) = salivation.
• An initially US (food) leads to UR (salivation).
• After pairing, the CS (bell) leads to CR (salivation).

Fear Conditioning

• US = shock
• UR = freezing
• CS = tone
• CR = freezing
• CS and US converge in the lateral nucleus of amygdala.
• EPSP to tone increases in lateral nucleus of amygdala after repeated pairing with shock.
• Motor skill learning:
  • Motor adaptation and motor sequence learning, involving cerebellar loops and cortico-basal ganglia-thalamocortical loops
• The task for motor adaptation is throwing darts with prism glasses.
• Motor coordination relies on:
  • Forward model to predict results of motor commands.
  • Differences between actual results and predicted results for online error correction, motor learning, and feedback control.
• Serial reaction time (SRT) task:
  • The task involves hitting the appropriate buttons when each light turns on in a certain order.
  • R designates random order.
  • S designates repeating sequence.
  • Repetition causes you to get better as it does not require conscious awareness.
  • This process is dependent on basal ganglia thalamo cortical loops.
• Depends on basal ganglia & reinforcement learning by selecting action expected to lead to maximum reward, performing action, and using prediction error to update expectations.
• a Dopamine signal from substantia nigra pars compacta (SNc) represents prediction error.
• A larger response is better than expected, where as a smaller response is worse than expected.
• Unexpected rewards generate dopamine signals from the substantia nigra pars compacta (SNc), which excites the direct pathway (via D1 receptors) and inhibits the indirect pathway (via D2 receptors), modifying behavior based on reward