Kap. 7 - Memory Systems

What is the distinction between explicit memory and implicit memory?

Explicit memory

• Declarative memory

• “Ability to consciously remember and report facts, events, and associations”

  • Either:

    • Episodic

    • Semantic

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Implicit memory

• Non-declaraitve memory

• “Skills and habits that are learned but that are usually not consciously accessible”

• Revealed though performance (rather than recollection)

Give some examples of episodic memory versus semantic memory

Both are types of explicit memory!
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Episodic memory

• Allows people to recall past experiences, single events in specific places at specific times

  • What, where, when:

    • Spatiotemporal context

      • Memory is tied to specific place and time

    • Autonoetic consciousness

      • Aware of ourselves “moving through time” as we recall the memory

• The sensory world is continuous, yet the brain naturally segments it into distinct, bounded units (event boundaries):

  • Event boundaries are derived directly from prediction errors:

    • When the brain's internal predictive model experiences a mismatch, a boundary is established - these prediction errors happen at multiple cognitive levels/hierarchies:

      • Perceptual Shifts:

        • Changes in raw sensory surroundings

        • (e.g., seeing trees, then suddenly seeing buildings)

      • Spatial Shifts:

        • Changes in physical environment

        • (e.g., moving out of a park onto a city street)

      • Goal Shifts:

        • Changes in internal priorities

        • (e.g., trying to locate a water fountain, then shifting to watching for oncoming traffic)

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• Recognition:

  • Recollection vs familiarity

    • Tested with “Remember/know procedure”

    • Recollection

      • Conscious experience of remembering details

      • Retrieval of qualitative information

      • Hippocampus is important!

    • Familiarity

      • (Weak or strong) sense/feeling of having seen something or someone before - without retrieval of contextualized details

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Semantic memory

• Facts and knowledge that can be stated or recounted - learned though accumulation of information over time across repeated occasions

  • Either:

    • Procedural

    • Priming

    • Statistical

    • Contextual

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Amnesia

• Amnesic patients show greater impairments in episodic memory than in semantic memory - also in learning new information after lesion

What is procedural learning?

• Give an example.

• “The aquisition of skills and habits”

• Motor sequence learning

  • A task for studying procedural learning in the lab

  • Asking participants to quickly respond to a target that can appear in one of four different locations

• Amnesia - H.M.

  • Capable of normal motor sequence learning - activate motor areas of the brain (even though not able to remember that he has learned it)

  • E.g. - can improve in mirror tracing tasks

    • Proves separation between explicit and implicit memory!

Which major brain structure is critically linked to procedural memory (motor skills learning)?

Procedural memory and motor skill learning are critically linked to the basal ganglia:

• Clinical Evidence (Huntington's Disease):

  • Patients with Huntington's disease suffer from severe atrophy of the basal ganglia and cerebral nerve tissue, resulting in noticeably enlarged ventricles

  • Consequently, these patients "often" show severely impaired procedural memory

  • Double Dissociation Context:

    • Contrast to Medial Temporal Lobe (MTL) amnesics like H.M.!

      • H.M. had a destroyed MTL but intact basal ganglia

        • (allowing normal mirror-drawing adaptation)

      • Huntington's patients present the reverse pattern

        • I.e. so, the basal ganglia handle implicit procedural learning independently of the MTL declarative system

What is priming?

• Distinguish between different types of priming

Priming

• “How a perception, response, or thought is enhanced by prior exposure to an identical or related stimulus, action, or idea”

• A form of implicit/non-declarative memory

• Amnesia:

  • Show normal priming - even if don’t recognize the repeated pictures as familiar/don’t remember having been tested before

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Repetition priming

• Priming that occurs because of direct repetition

  • Faster at recognizing and responding to repeated items than to new items

• Studied in naming task

  • Participants name a stimulus as quickly and accurately as possible

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Associative priming

• Priming that occur from related items (usually related in everyday life)

  • E.g. if presented with “nurse” before being asked to name a word starting with “d” - people are more likely to say “doctor”

• Studied naming task or lexical decision task

  • Latter: quickly judge whether a string of letters forms a word or not

    • e.g. “candy” or “curfy”

      • Make lexical decision more quickly if “candy” is preceded by “sweet” rather than “prickly”

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Perceptual priming

• Priming where “perception is improved by repeated exposure to perceptual features”

  • Perceptual features are shared, but no semantic ones:

    • E.g. seeing “cat” improves subsequent recognition of the word “cot”

  • fMRI shows: relies on perceptual brain areas

    • When same stimuli is repeated, fMRI shows less activity - indicating:

      • Processing now requires less effort (and therefore time)! - aka “Repetition suppression”

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Conceptual priming

• Priming where recognition is improved by semantic relations (shared meaning/categorization)

• Reveals how the meanings of stimuli are processed

  • E.g. seeing word “cat” improves subsequent recognition of the word “dog”

Define Classical Conditioning and outline the timeline of the four core components (US, UR, CS, CR) using Pavlov's classic experiment

Definition:

• An unconscious or automatic learning process in which behavioral responses are modified by forming predictive associations between distinct stimuli

• A type of implicit memory because it forms automatic, unconscious associations between stimuli that trigger reflexive responses without deliberate recall

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Unconditioned Stimulus (US):

• A stimulus that naturally and automatically triggers a specific response before any learning takes place (e.g., FOOD)

Unconditioned Response (UR):

• The unlearned, reflexive reaction naturally produced by the US (e.g., SALIVATION to food).

Conditioned Stimulus (CS):

• An initially neutral stimulus that, after repeated pairings with the US, comes to trigger a learned response (e.g., BELL).

Conditioned Response (CR):

• The learned behavioral response produced exclusively by the CS after conditioning has occurred (e.g., SALIVATION to the bell alone)

Explain the experimental setup of the Fear Conditioning paradigm (Bechara et al., 1995), the physiological measure used, and what amygdala damage reveals about this system

The Paradigm:

• Participants view squares of four different colors:

  • A neutral color (Blue Square = CS) is repeatedly paired with an aversive event (Electric Shock = US)

  

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The Measurement:

• Autonomic changes are tracked using Skin Conductance Response (SCR)

Normal Controls vs. Amygdala Damage:

• Normal Controls:

  • Develop a strong conditioned response (spike in SCR) when seeing the blue square alone, anticipating the shock

• Amygdala Damage:

  • They show a normal unconditioned reaction to the shock itself, but completely fail to develop an SCR response to the conditioned stimulus (blue square)

Conclusion:

• Proves that the amygdala is the critical neural substrate responsible for encoding implicit emotional associations and fear conditioning

Describe an example of statistical learning and contextual cueing

Statistical learning

• The brain calculates probabilities based on statistical regularities - temporal focus

• “Encodes statistical regularities, which help us function in the world by making it more predictable”

  • Encoding regularities makes our complex sensory world predictable, allowing us to function efficiently without needing conscious calculation

  • Statistical regularities

    • Meaningful patterns in the sights and sounds we experience daily

    • Stable and predictable features of an environment, object, or task

    • E.g. Supermarket layouts - are usually similar

    • E.g. structure in language - a statistical regularity

      • Help us in learning languages!

      • E.g. sequential probabilities: “pri-tee-bay-bee”

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Contextual cueing

• An effect of statistical learning - specifically for visual/spatial features

• “Learning where to attend and what to expect based on statistical regularities“

• “Enables faster search of targets whose location or identity is predictable from surrounding context”

  • Brain “extracts” repeating spatial regularities in visual scenes to speed up and guide visual search

  • E.g. - faster search time for targets in repeated displays versus targets in novel displays

    • An implicit mechanism!

      • Observers aren’t aware that contexts were repeated and predictive of target locations

How do you test for the serial position curve, and what explains the primacy effect and the recency effect?

Serial position curve

• A U-shaped curve for memory performance according to serial position

• Evidence for distinction between STM and LTM

  • Primacy effect - LTM

    • Rehearsal time

  • Recency effect - STM

    • Close to the time of recall with minimal distraction

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Primacy effect

• Higher memory performance for the items at the beginning of the list

• Testing primacy and STM:

  • Interference added to end of the list (counting backwards)

    • Result: Poorly performance on the latter items in the list

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Recency effect

• Higher memory for the items toward the end of the list

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What is reactivation in memory?

The act of remembering is to reactivate distributed records within the modality-specific or category-specific brain regions that were engaged during initial encoding

• LTM - Stored in neocortex

  • Neocortex: Outer layers of neurons forming the bulk of the human brain - same place where initial perception and processing of an experience happens

    • Entire cortex as a storage device for memories!

  • Processing of experiences leave a distributed code:

    • Experiences are multisensory and are initially processed in multiple cortical regions - where the code (record) will then be distributed

  • Episodic details in memories - also encoded i modality-specific areas

    • The brain mechanisms from the initial perception and cognitive experience are reactivated - they show patterns of activity similar to what occured during the initial encoding

Describe the roles of the hippocampal system and the neocortex in forming a complementary memory system

The hippocampal memory system:

• Medial temporal lobe:

  • Hippocampus

  • Entorhinal cortex

  • Parahipocampal cortex

  • Perirhinal cortex

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Hippocampal system and neocortex work together to form new memories and make them accessible for later retrieval

• Hippocampal system - active during initial encoding

  • Damage to hippocampal structures —> Anterograde amnesia

  • First: Associates items and their contexts across different brain areas - leaving a distributed code

    • e.g. contexts: time, space, characters etc.

  • Second: Binds all the features together so that they are all associated and can activate each other when any of the pieces are activated

    • i.e. so that activation of one feature is a cue for activation for the other pieces

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• Hippocampal system - active during retrieval (i.e. reactivation)

  • Reactivating the pieces of information from around the cortex!

  • Hippocampal system - mainly active during memory retrieval of relatively new memories

    • Over time the connections in cortical regions are gradually strengthened to a point where cortical memory can be accessed without hippocampal involvement

      • H.M - hippocampal lesion —> anterograde amnesia:

        • Able to retrieve older memories - formed prior to the removal of hippocampus

          • i.e. - over time, memories become encoded strongly in neocortical regions such that the hippocampal system is no longer necessary to retrieve information

        • Not able to encode new information into LTM

      • Lesions in some non-hippocampal, cortical regions —> Retrograd amnesia (i.e. contrast to H.M)

        • Consistent with idea that older memories are stored outside the hippocampus and medial temporal lobe regions

    • Recollection vs. familiarity:

      • MTL damage (hippocampus + other):

        • Impairment in both

      • Only hippocampus damage:

        • Only impairment in recollection

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• Hippocampal system + neocortex = complementary memory system:

  • Hippocampal system:

    • Allows for quick learning of new items

      • Why not quick learning for all memories?:

        • If information could be rewritten so easily, this could be chaotic for existing memories

  • Neocortex:

    • Stores LTM!

    • Learns and changes slowly

      • Allowing stability in memory storage - maintaining their integrity and knowledge

Explain how the clinical profiles of patients H.M., Clive Wearing, and K.F. demonstrate a double dissociation between short-term memory (STM) and long-term memory (LTM)

A double dissociation proves that STM and LTM rely on independent cognitive systems and distinct neural structures:

• H.M. + Clive Wearing

  • (Preserved STM / Impaired LTM):

    • Both retained functional short-term/working memory buffers!

      • H.M. could hold a number (e.g., 584) for 15 minutes via intense mnemonic rehearsal

        • Clive Wearing could carry on conversations

    • H.M.

      • The bilateral surgery removed the anterior hippocampus, amygdala, entorhinal cortex (EC), and perirhinal cortex (PR) within the Medial Temporal Lobe (MTL)

    • However, once attention shifted, the information vanished completely; they were entirely unable to form new long-term explicit memories (severe anterograde amnesia)

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• Patient K.F.

  • (Impaired STM / Preserved LTM):

    • Suffered a traumatic brain injury (bike accident) that severely impaired STM

      • (reduced digit span, completely abolished the recency effect)

    • However, K.F.’s long-term memory remained perfectly intact,

      • meaning they could successfully encode and retrieve new long-term information despite a broken short-term buffer

Explain how the clinical profiles of H.M., K.F., and Patient K.C. (Kent Cochrane) systematically demonstrate double dissociations across short-term, episodic, and semantic memory systems

STM vs. LTM Dissociation (H.M. vs. K.F.):

• H.M. had a functional short-term buffer but severely impaired long-term consolidation

• K.F. displayed the exact opposite: an impaired short-term buffer (reduced digit span) but perfectly preserved long-term encoding.

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Episodic vs. Semantic Dissociation (Patient K.C.):

• Following a lesion affecting his medial temporal lobe and hippocampi bilaterally, K.C. suffered dense anterograde amnesia and asymmetrical retrograde amnesia.

• The Dissociation:

  • K.C. could not remember any personally experienced events from his past (impaired retrograde episodic memory),

    • but his memory for facts, school subjects (math, history, geography), and generic world knowledge acquired before the accident remained intact (preserved semantic memory)

• Conclusion:

  • This proves that the hippocampus has a highly specific role in processing episodic memory, but is not strictly necessary for the retention of established semantic knowledge

Define memory consolidation and distinguish between the timelines, mechanisms, and anatomical levels of synaptic and systems consolidation

Memory Consolidation:

• The cognitive process by which recently created, fragile memories (sensitive to interference and forgetting) are transformed into a stable, permanent state

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Synaptic Consolidation (Fast):

• Timeline:

  • Occurs quickly, within minutes (stabilizing around 60–90 minutes)

• Mechanism:

  • Driven by structural changes at the level of individual synapses, directly linked to Long-Term Potentiation (LTP)

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Systems Consolidation (Slow):

• Timeline:

  • Occurs gradually over days, weeks, months, or years

• Mechanism:

  • Driven by the large-scale reorganization of neural circuits across the brain

How does the hippocampus bind features during initial encoding, and how do the Standard Model and Multiple Trace Theory disagree on its role during remote retrieval?

Initial Encoding:

• The hippocampus acts as a central hub that binds together distributed, feature-specific cortical modules (e.g., sights, sounds, text) into a single unified experience

The Debate on Remote Retrieval (After Consolidation):

• Standard Model (Squire & Alvarez, 1995):

  • Direct connections between cortical modules strengthen over time

  • Eventually, the memory becomes independent, and the hippocampus is no longer needed to retrieve it.

• Multiple Trace Theory (Nadel & Moscovitch, 1997):

  • While semantic details may become independent, the hippocampus is always required to retrieve true, detailed episodic memories, regardless of how old they are

Explain the Competitive Trace Theory (Yassa & Reagh, 2013), detailing what happens to a memory's features and neural storage as it ages

The Mechanism:

• As memories grow older, repeated retrievals create partially overlapping traces that compete with one another

Decontextualization:

• This competition forces the memory to lose its highly detailed, localized episodic context (hippocampus-dependent) and transform into generalized semantic content (neocortex-dependent)

The Outcome:

• Remote retrieval enhances conceptual/semantic knowledge at the expense of exact episodic details

  • This can lead to either an accurate but plain fact ("I've been to a U2 concert") or an inaccurate, falsely reconstructed memory context ("I remember going with high school friends...")

How does the subsequent memory paradigm work?

What does the paradigm tell us about how the brain encodes and retrieves memories?

• How can Hebb’s Rule help explain interference/distraction effects in consolidation?

Subsequent memory paradigm

• “A common way to study why we successfully encode some things and not others”

• fMRI or EEG data collected while participants view series of items - and later tested for their memory for the same items:

  • e.g. words or pictures

  • Comparing the data for encoding and retrieval:

    • Reveals how the brain activates differently for items that are remembered vs. forgotten

      • Brain regions in remembered items:

        • Many regions are more active: suggesting their importance for encoding + attention instructions

          • E.g. regions:

            • PFC, PC, HPC-system and specific cortical regions depending on the stimuli type

          • E.g. attention instructions:

            • Attending to face vs. scene in an overlapping picture

              • Only showing memory for the stimuli attended to + significant activity in brain regions correlated with the type of stimuli

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Consolidation, Hebb’s Rule and Interference

• Consolidation:

  • The act of stabilizing memories

  • Makes memories durable and resistant to corruption

• Hebb’s rule:

  • LTP:

    • Experience strengthens connections between specific neurons, and is the basis for memory

      • i.e. Communication across the synapse strengthens future communication between the presynaptic and postsynaptic neurons

    • A slow process

      • Helps explain interference and distraction effects

        • (e.g. concussions or drugs)

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Retrieving memories

• Memory retrieval

  • “Reactivation of the brain regions involved during initial encoding”

• Retrieval of a memory with sensory information:

  • Involves reactivation ot the same sensory regions that were active during initial perception and encoding of items

    • e.g. visual cortex if asked to imagine a previously seen picture - or auditory regions for sound items

• fMRI to distinguish whether someone is recalling a scene, a face or an object

  • e.g. decode whether people thought they recognized a face - and how familiar/strong the sense of recognition was

    • (whether the memory was accurate/real couldn’t be decoded)

• Understanding brain mechanisms in retrieval help explain why memory is impaired by damage, aging and environmental factors (e.g. stress)

  • Depression/combat-stress and hippocampus

    • The longer the period of stress, the smaller the hippocampus (a correlation)

What is the function of spatial memory?

Spatial memory

• Helps us navigate around the environment - like a GPS

  • Fundamental to mobile organisms

• Heavily studied in animals

  • From ants to humans!

Describe cognitive map theory

Cognitive map theory

• The theory that: Hippocampus constructs a map of the environment - providing the basis for spatial memory/navigation (a form of implicit memory)

  • Also useful for episodic memory!

    • Events coded to spatial and temporal context

Explain what place cells and grid cells are, and what role they play in spatial navigation and memory

Place cells

• Fire when an animal is in a particular location within an environment

  • As revealed by recordings of individual neurons in hippocampus

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Grid cells

• Track an individual’s position as the individual moves around in space

  • As revealed by recordings in the entorhinal cortex (neighboring area to hippocampus)

• Different grid cells fire depending on where the individual is located along the two-dimensional grid in space

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Place- and grid cell’s roles in spatial navigation in memory

• Track location within the environment

  • i.e. Like the blue dot indicating current position with GPS

• Also active when imagining being in/moving though a location

• Hippocampus size and London taxi drivers

  • Supports the idea that hippocampus is important for spatial memory and navigation

Give examples distinguishing an allocentric spatial framework from an egocentric spatial framework.

Allocentric spatial framework

• One object’s location defined relative to the location of another object/landmark

• E.g.:

  • When giving directions referencing fixed locations

    • “head north on College Street, then turn west on Wall Street“

• More useful for explaining location of a place to others irrespective of their current location

• Hippocampus codes space in an allocentric manner!

  • E.g. a rat roaming freely in a space

    • Hippocampus represents the rat’s location in a constant way - regardless of the direction it’s facing

  • Lesion in hippocampus (or parietal lobe) —> bad at remembering and navigating

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Egocentric spatial framework

• The environment’s layout defined relative to the viewer

• E.g.:

  • When giving directions from the perspective of someone following a path:

    • “turn left at the first intersection, then…“

• More useful for the actual navigator

• Other brain regions than hippocampus (e.g. parietal cortex) support egocentric processing

  • E.g. a rat in a space

    • Other regions - “head-direction cells” - encode the direction of the rat’s head

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Spatial memory is viewpoint-dependent

• i.e. Best when viewer maintains a consistent viewing angle to the spatial array

• Can be tested by trying to remember an array of objects on a circular table that gets rotated

  • The more rotated, the mor poorly at confirming whether the layout is the same or not

  • Shows: spatial memory is viewpoint-dependent + reliant on egocentric framework