Learning, Memory, and Plasticity (class 9)

Memory

The ability to store and retrieve information, or the specific information stored in the brain.

Amnesia

A severe memory impairment- could cause you to forget a huge chunk of your life, or you cannot form new memories

Learning

The process of acquiring new information

Clive Wearing

• He suffered from viral encephalitis in his 40s

• The virus particularly affected the medial temporal lobe bilaterally/hippocampus

• As a result, has ended up being best known for having the most severe case of amnesia

• Developed both retrograde and anterograde amnesia but still had memories of his wife and could play music

• His memory for events lasts between seven and thirty seconds. He spends every day 'waking up' every 20 seconds

H.M. (Henri Molaison)

• Suffered from temporal epilepsy since childhood

• Had to undergo a temporal lobe lobectomy at 27 to cure the seizures

• Resection of bilateral medial temporal lobes, including the Hippocampus, Amygdala, and Anterior parahippocampal gyrus

• Developed mild retrograde amnesia (struggled to remember some events a few years before surgery) and severe anterograde amnesia (lost the ability to form new memories)

• Could still remember his childhood and who he was

Dr. Brenda Milner

The psychologist who famously studied H.M. at the Montreal Neurological Institute performed tests on him, such as the intact digit span, which showed that he still had intact short-term memory.

He got better at the mirror drawing task with practice over days, yet had no memory of performing it before, so procedural memory is not sustained by the medial temporal lobes

Digit Span

A test run by Dr. Milner that involves repeating a list of numbers to assess short-term memory. H.M. showed intact digit span

Mirror Drawing Task

A task used by Dr. Milner to test procedural memory, requiring tracing a star while looking only at its reflection. H.M. could learn this task over time despite having no memory of doing it before

Key learning from H.M.'s case

Demonstrated that memory is a distinct cognitive process and that there are different types of memory, with the medial temporal lobes being important for long-term/declarative memory formation and NOT procedural

Patient N.A.

• Had a miniature plastic sword stuck in nostril

• Damaged the Dorsomedial thalamus & Mammillary bodies

• Developed anterograde amnesia (can’t form new memories) & Impairments in forming long-term declarative memories

• So memory system extends beyond the medial temporal lobe

Korsakoff's Syndrome

A condition resulting from a vitamin thiamine deficiency often due to severe alcoholism, leading to the degeneration of the mammillary bodies and the dorsomedial thalamus while preserving temporal lobe structures. Symptoms include severe anterograde and retrograde amnesia, object recognition problems, confabulation, and apathy

Patient K.C.

• Suffered a motorcycle accident at 30

• Damaged the left frontoparietal cortex and right parieto-occipital cortex, as well as shrinkage in the bilateral hippocampus and nearby cortex

• Led to anterograde declarative amnesia and a loss of autobiographical memory, but preserved semantic knowledge

Hippocampus

A seahorse shape region in the brain, particularly affected and removed bilaterally in Clive Wearing and in H.M, important for forming lasting new memories and memory consolidation, especially for spatial location

Anterograde Amnesia

The condition where one is unable to form new memories after brain trauma. Instantiation of deficit- when the brain trauma occurs, forward-acting

Retrograde Amnesia

The condition where one is unable to remember the past before an injury, causing one to forget chunks of your life that happened to you before that accident, but can form new memories

Medial Temporal Lobe

The brain region most particularly affected bilaterally in Clive Wearing and where resection of bilateral medial temporal lobes occurred in H.M.; considered important for memory

Perirhinal/Rhinal Cortex

A brain region that plays an important role in object recognition

Striatum

A brain region involved in habit formation

Prefrontal Cortex

A brain region involved in the temporal order of events and working memory, with different parts potentially mediating different types of working memory

Basal Forebrain

A brain region involved in acetylcholine release and facilitating plasticity at the neuronal level, potentially implicated in Alzheimer's disease

Morris Water Maze

A test where rodents learn to find a submerged platform in a pool using external visual landmarks, assessing spatial learning and memory. indicating the hippocampus's key role in memory for spatial location

Delayed Nonmatching-to-Sample Test

A task used in the 1970s with monkeys who had bilateral medial temporal lobectomies, revealing long-term memory deficits in explicit memory, similar to H.M.'s. Performance was normal when memory only needed to be held for a few seconds (within STM duration)

Tower of Hanoi

A puzzle where the objective is to move the entire stack to another rod, obeying the following simple rules:

• Only one disk can be moved at a time.

• Each move consists of taking the upper disk from one of the stacks and placing it on top of another stack or on an empty rod.

• No larger disk may be placed on top of a smaller disk

Explicit Memory

Knowledge-based memory, also referred to as Declarative memory. The formation of long-term declarative memory is most likely sustained by medial temporal lobes.

• Two types are Episodic (autobiographical memory) and Semantic (memory of facts)

Implicit Memories

• Procedural memories: how to do things, motor actions, balance, etc.

• Priming: facilitation or inhibition of a process after repeated exposure to a stimulus

• Conditioning: developing positive/negative associations with 2 stimulus

Procedural Memory

Memory for how to do things, motor actions, balance, etc., also referred to as implicit memory. It is most likely not sustained by medial temporal lobes.

Short-Term Memory (STM)

Memory that usually lasts about 30 seconds or throughout rehearsal. H.M. had it intact, demonstrated by his intact digit span and ability to sustain conversation. It appears to be more of an attention function, and is largely controlled by prefrontal regions

Long-Term Memory (LTM)

Memory that lasts days, weeks, months, or years. Medial temporal lobes most likely sustain the formation of this declarative memory, while long-term memory itself is spread across multiple systems in the brain

Episodic Memory

Autobiographical memory, a type of explicit memory that involves conscious recollection of previous experiences (together with their context in terms of time, place, associated emotions). It may be impaired in medial temporal lobe amnesia while semantic memory functions normally

Semantic Memory

Memory of facts, words, etc., representing general world knowledge that we accumulate, and is also a type of explicit memory. It may function normally in medial temporal lobe amnesia

Consolidation

The process that transforms new memories from a “fragile” state to more permanent state. The hippocampus is known to play a role in this.

It can be synaptic consolidation, involving the reorganization of synaptic structures like LTP, or systems consolidation, involving the gradual reorganization of neural circuits

Systems Consolidation

The gradual reorganization of neural circuits that occurs during memory consolidation. The standard model of consolidation suggests that connections between the cortex and hippocampus are initially strong for recent memories but weaken as connections within the cortex strengthen for remote memories

Gradients of Retrograde Amnesia

The phenomenon where concussions disrupt consolidation of recent memories more than older ones

Slow-Wave Sleep

A stage of sleep during which research shows consolidation increases. The more sleep we get, the better we will remember things from that day. As we age, our slow-wave sleep becomes increasingly interrupted.

Retrieval

The process by which stored information is retrieved. Each time a memory is retrieved from LTM, it is temporarily held in STM and is susceptible to post-traumatic amnesia until it is reconsolidated

Long-Term Potentiation (LTP)

A synaptic mechanism of learning and memory where synapses are effectively made stronger by repeated stimulation. It is consistent with Hebb’s theory that changes in synaptic efficiency are the basis of LTM

Neural Plasticity

The ability of the nervous system to change in response to experience or the environment. Reorganization of synapses is how it changes, allowing new connections to be created

Amygdala

A brain structure involved in memory linked to strong negative emotions. Memory linked to amygdala activity can lead to reliving fear upon retrieval

Cerebellum

A brain structure involved in sensorimotor skills and classical conditioning

Basal Ganglia

A brain structure mostly involved in learning skills, particularly sensorimotor, perceptual, and cognitive skills

Priming

Facilitation or inhibition of a process after repeated exposure to a stimulus. It does not involve declarative memory and was intact in H.M.

Perceptual Priming

A type of priming involving the shape of words, associated with activity in the bilateral occipitotemporal cortex

Conceptual Priming

A type of priming involving the meaning of words, associated with activity in the left frontal cortex

Encoding

The process of transferring sensory information to short-term memory

Classical Conditioning

Developing positive/negative associations with a stimulus based on that stimulus being paired with positive/negative outcomes, considered a form of associative learning. Cerebellum activity is involved in the association between two stimuli

Confabulation

A symptom seen in Korsakoff’s Syndrome where the individual creates new stories to fill the gaps due to anterograde amnesia

Place Cells

Many hippocampal cells that respond when a subject is in a particular place and to other cues

Reconsolidation

Each time a memory is retrieved from LTM, it is temporarily held in STM and needs to be stabilized again. This process can be disrupted by protein synthesis inhibitors

Alzheimer's disease

A form of dementia characterized by loss of recent memories, progressive cognitive decline, and disorientation. Affected/caused by:

• Amyloid plaques: Build-up of beta-amyloid protein

• Affect: Cortex, Hippocampus, and Limbic system

• Neurofibrillary tangles: Knots of neurofilaments = cognitive impairments

Cognitive Cushion

The idea that keeping the brain active can help prevent memory decline, potentially relevant to aging and conditions like Alzheimer's disease

Anisomycin

A protein synthesis inhibitor used in rat experiments to prevent the consolidation or reconsolidation of conditioned fear when applied to the amygdalae

Reactivation

The process of retrieving a memory from long-term storage, making it temporarily susceptible to disruption before reconsolidation

Memory and Aging

Memory is normally not affected by age. Mild cognitive impairment (MCI): little things; annoying things, enough to go consult a doctor but not enough to not live alone (putting keys in fridge, forgetting)

Hippocampal shrinkage: usually precursor to Alzheimer’s disease