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
Long-term vs. short term memory
STM: extremely limited capacity, lasts seconds, based on sustained activation of neurons
LTM: massive capacity, lasts minutes, hours, days, years, based on number & strength of synapses
Single dissociation
- performance difference across two tasks of one case compared to controls
- A single dissociation does not necessarily demonstrate separable systems, different brain regions, or distinct cognitive processes
Double dissociation
- two opposing single dissociations put together
- provides strong evidence for separable systems that depend on different brain regions and distinct cognitive processes
Types of LTM
Implicit memory and explicit memory
Implicit long-term memory
- Non-declarative
- Independent of conscious
awareness - Procedural, conditioning,
nonassociative, 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 - 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
Non-associative memory
- A type of implicit memory
- A change in responce to an unchanging stimulus
- Habituation
● Reduced response to an unchanging stimulus - Sensitization
● Increased response to an unchanging stimulus - Primarily involves sensory-motor reflex pathways
Changes from habituation & sensitization
- Short-term changes: lasts minutes, changes in. amount of neurotransmitter released
- Long-term changes: lasts for hours, days and weeks, changes in number of synapses
Types of implict memory
- Procedural (motor and cognitive skills)
- Perceptual priming
- Classical conditioning
- Non associative learning
Stimuli and responses in classical conditioning
An initially neutral conditioned stimulus (CS) comes to elicit a conditioned
response (CR) due to pairing
with an appetitive or aversive unconditioned stimulus (US) which reflexively elicits an unconditioned response (UR)
Procedural memory (reinforcement learning)
- In the basal ganglia
- Unexpected rewards generate dopamine signals from the substantia nigra pars compacta (SNc)
- This excites the direct
pathway (via D 1 receptors)
and inhibits the indirect
pathway (via D 2 receptors) - This allows modification of
behavior based on reward
Priming
- Change in stimulus processing due to prior exposure to the same or related stimulus without conscious awareness
- Depends on region of cortex processing relevant representations
- Perceptual priming: Sensory cortices (occipital lobe)
- Conceptual/semantic priming: Unimodal & multimodal association cortices (anterior temporal, prefrontal cortex)
Semantic memory
- A type of explicit memory
- Memory for concrete word meanings activates areas of
cortex involved in relevant processing
Sensory/functional theory
- Organization of semantic
representations is based on
relevant sensory and motor
features - E.g.: Action words activate
region of primary motor
cortex for specific body part
Domain-specific theory
- Organization of semantic representations is based on semantic categories
- E.g.: Fruits & vegetables, living things, nonliving things
How are new semantic memories formed?
- They often start as episodic memories
Example: - At first…
● What is the capital of British Columbia?
● “I learned yesterday in school that it is Victoria.” - Years later…
● What is the capital of British Columbia?
● “Victoria.”
● How do you know that?
● “I have no idea!”
Encoding of episodic memory
- Hippocampus and related structures form indices (pointers) to bind cortical representations
Retrieval of episodic memory
- Hippocampus and related structures use indices (pointers) to re-instantiate cortical representations
- Retrieval of episodic memories is reconstruction
- A best guess based on: Memory trace, genes, past experience, internal state, and environmental context
Role of medial temporal lobes in episodic memory
Cognitive map theory
- Memory for spatial relationships in environment
- Place cells
● Fire when an animal is in a
particular location
Relational memory theory
- Memory for associations in general
- Odor association task
Long-term potentiation
- Increase in synaptic strength
- Exhibits necessary properties for Hebbian learning
- Found in hippocampus (and other brain regions)
Early vs. Late LTP
Early:
- Increased presynaptic
release of neurotransmitter
- Increased number of
postsynaptic receptors
Late:
- Increased number of dendritic spines and synapses
Long-term depression (LTD)
- When presynaptic action potential does not lead to
postsynaptic action potential, connection is weakened - Reduction in neurotransmitter released, number of
receptors, and number of synapses
DRM paradigm
- Presented list of semantically related words
- Recall/recognition memory test
- Related lures reported almost as often as words actually on the list!
- High confidence in accuracy
- Participants often report specifically remembering presentation of lures
