PSY2061 Lecture 10: Learning, Memory and Amnesia Notes

Memory

What is Memory?

• Memory involves more than just recalling events; it also includes skills, habits, and the influence of previous experiences.

• It is essential for environmental adaptation and survival, forming the basis of perception, thought, and behavior.

• Defined as "The cognitive process of acquiring, storing, and retrieving information essential for environmental adaptation and survival."

Memory Hierarchy

• Memory is categorized into sensory memory, short-term memory, and long-term memory.

• Long-term memory is further divided into declarative (explicit) and nondeclarative (implicit) memory.

  • Declarative memory includes episodic memory (events) and semantic memory (facts).

  • Nondeclarative memory includes procedural memory (skills), perceptual representation system, classical conditioning, and nonassociative learning.

Short-Term Memory

• Closely related to attention and working memory.

• Responsible for temporarily storing information in conscious awareness, ready for utilization.

• Maintained by rehearsal (repeating the information).

• Examples: directions, tracking conversations.

• Once actioned, information may be dismissed/lost or committed to long-term memory.

Neurobiology

• Sensory information is represented by spatiotemporal patterns of neural activity.

• Short-term memory sustains neural activity in the absence of current stimulation (not stored), particularly in the prefrontal cortex.

Demonstration

• Word list recall test demonstrates short-term verbal memory capacity.

• Short-term memory has limited capacity and is time-limited.

• Information needs long-term storage to be retained and to allow intake of new information.

Case Study - KF

• 28-year-old man with damage to the left peri-sylvian fissure.

• Could only recall 1-2 words, but had normal everyday memory and could learn word pairs.

• Demonstrates that short- and long-term memory are somewhat distinct.

Long-Term Memory

Stages

• Encoding: Receiving and processing information, converting sensory input into a storable form, and organizing information in relation to similar information.

• Storage: Maintaining information over time.

• Retrieval: Accessing the memory stores and taking out relevant information.

Neurobiology

• Learning occurs when the brain stores a pattern of neural activity that can be reactivated later.

• Hebbian theory: "Neurons that fire together wire together" via long-term potentiation.

  • When two joining cells fire simultaneously, the connection between them strengthens.

Long-Term Potentiation

• Complex process where the connection between two neurons becomes stronger following the firing of an action potential.

• Synaptic plasticity can change the amount of neurotransmitter released and the number of postsynaptic receptors available, altering current flow into the postsynaptic neuron.

Reactivation

• Memory is when a previously stored neural pattern is reactivated in the absence of full sensory stimulation.

• Leverages strong connections to reactivate a full neural representation of the stimulus.

Demonstration

• Recalling words from a list can be aided by cues like categories (animals, clothing, fruits).

• Remembering one word can help remember another, illustrating neural reactivation.

• Recognition provides a partial representation of the initial stimulus, cuing the brain.

Types of Long-Term Memory

• Implicit memory

  • Information stored and processed unconsciously and unintentionally.

  • Resistant to common brain impairment.

• Explicit memory

  • Information stored and recalled consciously.

  • Vulnerable to common brain impairment.

Implicit Memory

Classical Conditioning

• Unconscious association of an involuntary response and a stimulus (e.g., Pavlov’s dogs).

• Involves the hippocampus (learning & memory) and cerebellum (unconscious behavior).

Operant Conditioning

• Unconscious association of a voluntary behavior and a consequence (e.g., Skinner’s rats).

• Involves the amygdala (emotion) and orbitofrontal prefrontal lobe (reward centers).

Motor Learning

• Practice-induced changes in motor performance (e.g., learning to play an instrument).

• Importance of neuroplasticity in the frontal lobe (M1, PMA, SMA), cerebellum, and basal ganglia.

Priming

• Exposure to one stimulus influences the response to a subsequent stimulus.

• Decreases the threshold for reactivation of a particular pattern of neural activity.

Explicit / Declarative Memory

Semantic Memory

• Recall of knowledge and facts (general knowledge).

• Examples: knowing cows are brown with horns and eat carrots.

Episodic Memory

• Recall of events and experiences.

• Example: remembering feeding a brown cow on a farm last week.

• Both rely on similar neurobiological systems and processes.

Semantic Memory Details

• Knowledge base accumulated over a lifetime, including world knowledge, object details, vocabulary, meanings, and rules.

• Lacks experiential / autobiographical content.

• Patient K.C. retained the ability to form and use knowledge without episodic recall of where the information was acquired.

Semantic Dementia/ svPPA

• Variant of frontotemporal dementia (FTD).

• Characterized by progressive neurodegeneration of lateral temporal structures.

• Presents as progressive language impairment, including impaired comprehension and confrontation naming.

• Underpinned by loss of semantic knowledge but intact memory for experiences/events.

• Highlights the importance of lateral temporal structures in storing semantics.

Episodic Memory Details

• Memory for the “what, when, and where”.

• Includes the ability to ‘relive’ the episode (autonoetic consciousness).

• Complex process involving diffuse brain regions, including:

  • Medial temporal lobe structures

  • Hippocampal complex

  • Parahippocampal areas

  • Diencephalon

  • Anterior and posterior cortex

• Left hemisphere more implicated in verbal memory, right hemisphere in visual memory (but bilateral activation in both).

Episodic Memory - Neurobiology

• During encoding, presentation of a stimulus event activates cortical regions captured by the hippocampus.

• Following encoding, the pattern of cortical activity is stored as a memory representation in the hippocampus.

• Later, a retrieval cue leads to partial reinstatement of the original pattern of cortical activity, feeding forward to the hippocampus.

• Overlap between the activity elicited by the retrieval cue and the stored pattern of activity causes the hippocampal representation to be reactivated, leading to full reinstatement of the original pattern of cortical activity.

Hippocampus

• With assistance from the prefrontal cortex, ‘binds’ and stores a memory trace across cortex.

• Higher level of activity in the hippocampus (and left frontal regions) during encoding predicts later success.

• Subsequently, cues reactivate this trace via the hippocampus.

• Correct recognition vs. incorrect recognition is associated with increased activity in bilateral medial temporal lobes.

• Important in both storage and retrieval.

• Patients with hippocampal/medial temporal dysfunction often have trouble storing information.

Frontal Lobes

• Important for strategic processing and decision making.

• Roles in sequencing events in order, providing source context, and applying strategies to encode information in an organized manner.

• Roles in encoding (predominantly left hemisphere) and retrieval (predominantly right hemisphere).

• Access (correct recall vs. correct recognition) is associated with the left inferior frontal cortex.

• Patients with frontal damage often show impairment in encoding and retrieval.

Amnesia

What is Amnesia?

• Broad term describing impairment of episodic memory.

• Includes many kinds of memory disorders.

• Most common categories:

  • Anterograde amnesia: Inability to form new memories, but can remember what came before the injury/illness.

  • Retrograde amnesia: Inability to recall past memories, but can learn and recall new information.
    *Note: must be over and above normal degree of ‘forgetfulness’

• Mnemonic: “retro” means “in the past”

What Amnesia Isn’t

• Amnesia is NOT mere forgetfulness.

• Example: Forgetting a name during a conversation is not amnesia if substantial episodic details can be recalled and the information is remembered later.

• This is a transient loss of access to a particular piece of information.

What Amnesia Is

• Inability to recall specific events or training sessions, even with cuing and prompting.

• Demonstrates a lack of autonoetic awareness of time.

Putting it all Together - HM

• Epileptic seizures treated with bilateral medial temporal lobectomy resulted in:

  • Retrograde amnesia for episodic/semantic information formed in the 3 years prior.

  • Anterograde amnesia, preventing the formation of new long-term memories.

  • Preservation of implicit memory (i.e., could learn new skills) even when he did not remember doing the task previously

  • Intact short-term memory

• Demonstrated the role of medial temporal structures, including the hippocampus, in long-term storage.

Amnestic Disorders

A range of clinical disorders can cause amnesia, including:

• Infection

• Stroke

• Traumatic brain injury

• Surgical resection

• Epilepsy

• Dissociative disorders/trauma responses

• Alzheimer’s disease

• Korsakoff’s syndrome

Alzheimer’s Disease (AD)

• Progressive disease characterized by the accumulation of extracellular amyloid plaques and intracellular neurofibrillary tangles (tau).

• Leads to atrophy of brain tissue.

• Most common cause of dementia.

  • Alzheimer’s disease is the underlying pathology; Alzheimer’s dementia is the clinical phenotype.

• Most common in older age (>65), but can rarely be seen in early onset forms (often genetic linkage).

• Current opinion is that AD is not an inevitability of age.

Pathological Progression

• Early hippocampal involvement = memory impairment often first

• Broadening of temporal atrophy = language involvement

• Generalization of atrophy = visuospatial impairment, executive dysfunction

Memory Impairment Phenotype

• Anterograde amnesia – difficulties learning new episodic information

• Characteristic feature = rapid forgetting: once information is stored, decays at faster than normal rate

• Retrograde amnesia later in disease course – temporal gradient where older memories better preserved

• Implicit memory generally preserved, semantic memory affected later

Wernicke’s Encephalopathy

• Alcohol misuse leads to malnutrition and thiamine deficiency.

• Causes an acute neuropsychiatric syndrome called Wernicke’s Encephalopathy.

  • Encephalopathy = generic term to describe a disturbance of brain function.

• Classical clinical symptom triad:

  • Ataxia – loss of full control of bodily movements

  • Eye movement disorders – e.g., nystagmus, ophthalmoplegia

  • Delirium – temporary mental state disorder characterized by confusion and disorientation

Korsakoff’s Syndrome

• Severe, progressive disorder that can emerge if Wernicke’s encephalopathy is not adequately treated.

• Whereas WE is generally temporary, Korsakoff’s is associated with sometimes irreversible brain damage.

• Preferential atrophy of the medial thalamus and connections to the hippocampus and cerebellum.

Clinical Progression

• Early stages: anterograde amnesia for episodic memories.

  • Difficulties learning new information.

  • Distinguished from AD due to the absence of rapid forgetting – trouble learning information, but once stored, normal rate of forgetting.

• As the disease progresses, retrograde amnesia extends further back towards childhood.

• Difficulties with source monitoring are common.