Memory and Learning Mechanisms

Memory Mechanisms

Components of learning and memory
- Acquisition: Exposure to stimuli or information.
- Retention: Time period in which information is retained.
- Retrieval: Recovery of stored information used to guide behavior.
Retrieval
- Recovery of stored information used to guide behavior.
Memory Engagement
- Acquisition: Engage working memory through conscious attention.
- Retention: Engage working and reference memory; a transition between the two.
- Reference memory is more long-term.
- Retrieval: Reference memory.
Retrieval Failure: In healthy organisms, memory failure is more likely due to retrieval failure than loss of information.
Retrieval Cues: Reminders that produce the retrieval of memory.

Retrieval of Memory

Stimuli during acquisition can serve as retrieval cues.
Borovsky and Rovee-Collier, 1990
- Subjects: 6-month-old infants.
- Training: Playpen liners (retrieval cues)
  - Patterned (striped or checkered).
  - Distinct wallpaper around the playpen.
  - Predicted contingency was active.
  - Operant Response
    - Response - Leg Kick
    - Outcome - Mobile movement
- Test: 1 day post-training
  - Performance is best with the SAME liner (retrieval cue).
  - Lasted up to 14 days.
Young children have a capacity for learning and memory very early.
Types of learning and memory differ.

Forgetting

Forgetting: Memory failure resulting in a lack of response in accordance with past experiences of learning.
Negative Forgetting: Has a negative impact on performance. Example: Explaining the reinforcer devaluation procedure.
Positive Forgetting: Positively impacts performance, increases response variety. Allows increased response variability. Example: Learning a new password or changes in job requirements.
Sources of Forgetting
- Proactive Interference: Previously learned information disrupts new memories. Example: Learning omission training after already knowing about positive/negative reinforcement.
- Retroactive Interference: New memories disrupt previously learned information. Example: Meeting new people and disrupting memory of those met earlier.

Forgetting: Retrograde Amnesia

Retrograde Amnesia: Graded memory loss of information close to the event that induced the loss.
- Example: Seizure, blackout, and concussion.
Zhou and Riccio, 1995
- Rats in a single shock avoidance trial.
  - Light/Dark Room
  - Rats prefer the dark side, receive a shock contextualized to the dark area.
- Mild concussions at various Training-concussion Intervals.
- Avoidance measured by latency to visit the shock side.
- Results: Reduced avoidance when training-concussion intervals were short.
Consolidation: Consolidating information so that it’s in our memory.
Time period is important to allow the organism to consolidate that information.
How does a concussion disrupt memory?
- Is consolidation of information to long-term memory affected?
- Is retrieval of information from long-term memory affected?
Sensory information → Perception → Sensory Memory → Attention → Working Memory → Rehearsal → Long-term memory.
Working memory → long term memory: consolidation
Long term → working: retrieval

Rehearsal and Retention

Post-concussion, a retrieval cue can reverse amnesia.
Zhou and Riccio, 1995
- G1: Concussion
  - Avoidance trial, concussion (1 min later).
- G2: Reminder
  - Shock avoidance trial, concussion (1 min later), + Shock (reminder) in novel environment.
  - Opportunity to remember that training again.
  - Already consolidating, putting it in long-term, and using this information WITH HELP
- Findings
  - The concussion group is amnesic.
  - G2 rats with a reminder show avoidance.
  - Retrieval is facilitated!
By starting with prospective memory coding, over time, the memory load will decrease.
Start with retrospective memory then flip to prospective memory

Neurobiology of Memory

Learning and memory must have a neural substrate: THE BRAIN!
Where is memory located?
Engram: Physical representation of learning and memory (Lashley, 1929).
- Cuts in the cortex before/after maze
- No single cut, big or small impaired learning – could always solve it
- Only amount removed predicted impairment – removal of large parts of the rat brain
- Lashley concluded the search for the engram is a “hopeless endeavor.”
- Where did Lashley go wrong?
  - Maze-running isn’t as simple as he thought it was
  - Remove information, animals can still sort of solve a maze, just not as well
  - Other features of the maze can be utilized to solve the maze – different senses can be utilized
    - Olfactory
Acquisition of knowledge engages several brain circuits.
Complex memories are retained in multiple area.
- Severing a place where part of the memory residing but other areas pay be retained to help them solve it
Memories are retrieved from many brain areas.
Not as efficient as before but task can be done sufficiently with the amount of information you can retain

Acquisition

The strengthening or weakening of neural connections as a result of experience with the environment.
- Attention
- When cells fire together (associate), they wire together.
  - Central principle of neurobiology
How does neural stimulation affect the activity of downstream targets?
Bliss and Lomo, 1973
- Stimulated hippocampus input
  - Moderate [electrical stimulation]
  - Strong
  - Weak
- Recorded downstream activity
- Hypothesized that each kind of stimulation would produce a different response
- Results of stimulation
  - Moderate – Moderate activity
    - No change in synaptic strength
  - Strong – long-term potentiation (LTP)
    - Enhanced synaptic strength – LEARNING
    - Stimulate again – Response would be stronger and maintained – reorganization of that pathway with that specific stimulus
    - Percieving information and changing how the synapses are organized so that they work more effectively
    - Acquisition of information
  - Weak – long-term depression (LTD)
    - Reduced synaptic strength – LEARNING
      - Disrupt
External stimulation can produce changes in synaptic strength is bidirectional and creates structural changes in our brain
- Strong stimulation – Stronger relationships between cells
- Weak stimulation – break associations between cells
These changes last days to weeks
Memory has a structural component and LTP and LTD proves that
LTP increases the efficiency of memory paths
- Increase # of dendritic spines
- Increase the size of the dendritic spine head
- Increase excitatory receptor density on dendritic spine head
We can make the dendritic spines more stable and receptive to input
Structural differences that occur due to external stimuli

Retention

The permanent physical change in neural circuitry coding for the information
- Rehersal and Consolidation
Once rehearsal conditions are met, information is consolidated and retained in PERMANENT memory stores
Rat in the maze – navigating the maze and stimulating sensory pathways, the animal is attending to it’s environment – places information into long-term storage
- The requirement is experience with specific stimuli and our environment

Retrieval

The recollection of memories to working memory
Wilder Penfield (1891 - 1976)
- Medical temporal lobe stimulation induced specific memories
MRI confirms that consolidated memory is stored in and retrieved from cortex
Rehearsal Circuit
- Hippocampus
- Basal Forebrain
- Thalamus
- Amygdala
Stepping on the Coat – Visual Stream
Perception
Conscious – Cortex (trace)
- Conscious but fleeting (trace of a memory)
  - We ended to attend and rehearse it to retain the information
Acquisition
Rehearsal Circuit
Consolidation to Association Cortex (permanent)
Stepping on the Coat
Retrival (cues)
Bring it back into conscious memory
Retention and consolidation are dependent upon the rehearsal of the information
Disorders of Memory
- Can affect the rehearsal circuit, association cortex, and cortex (trace)