Learning, Memory & Amnesia (Week 11)
Definition (#f7aeae)
Important (#edcae9)
Extra (#fffe9d)
Fundamental Types of Learning:
Classical Conditioning:
Ivan Pavlov
Involves linking two stimuli to alter the reaction to one.
Stimuli: Conditioned stimulus & Unconditioned stimulus.
Conditioned Stimulus (CS): A neutral stimulus that, after repetition, elicits a response.
Unconditioned Stimulus (UCS): A stimulus that automatically elicits a response.
Instrumental (Operant) Conditioning: Learning based on consequences.
Reinforcement: Rewards that increase the likelihood of a response.
Punishment: Consequences that decrease the likelihood of a response.
Lashley’s Engram (Memory Trace):
Engram: Physical trace of a learned experience.
Early Research: Investigated the "engram," the physical trace of a learned experience.
Hypothesis: Cutting the connection between brain regions should erase the new learning. (disproven)
Lashley’s Principles:
Equipotentiality: Every part of the cortex contributes equally to complex behaviors.
Mass Action: The entire cortex works together; more cortex results in better performance.
Modern Research for engram (Thompson):
Proposed classical conditioning engram is in the cerebellum, specifically the lateral interpositus nucleus (LIP), not the cortex.
Key findings:
Lateral interpositus nucleus (LIP) is crucial for learning.
Responses in LIP increase as learning occurs.
Findings: Concluded from experiments that learning happens in the LIP.
Identified specific cells and neurotransmitters involved in changes in the LIP.
PET Scans on Young Adults:
Revealed the cerebellum is crucial for classical conditioning.
Only when the delay between the conditioned stimulus (CS) and unconditioned stimulus (UCS) is short.
Categories of Memory:
Short-term Memory (STM): Memory of recent events with limited capacity that fades quickly without rehearsal.
Long-term Memory (LTM): Memory of past events with unlimited capacity that persists over time and can be stimulated with cues.
Memory Process: Information first enters short-term memory. Brain consolidates some information into long-term memory. Findings:
Distinction between short and long-term memory is less clear.
Not all rehearsed short-term memories become long-term.
Emotionally Significant Memories:
Epinephrine and cortisol boost the consolidation of recent experiences.
Emotional experiences → Locus coeruleus → Norepinephrine → Cortex & dopamine → Hippocampus
Working Memory: A temporary storage system for actively manipulating information, primarily stored in the prefrontal cortex.
Delayed response task: Common working memory test. Involves responding to recently seen or heard information.
Findings:
Prefrontal cortex stores this information.
Damage to this area affects performance and impairment can be very specific.
Prefrontal Cortex Activity:
Declining activity in the elderly is linked to decreasing memory.
Increased activity suggests compensation for other brain regions.
Brain Structures and Memory Disorders
Hippocampus:
Crucial for forming new long-term and episodic memories, as well as spatial and contextual navigation.
Various areas are active during memory formation and recall.
Damage = amnesia.
Amnesia: Memory loss. Types:
Anterograde: Inability to form new long-term memories.
Retrograde: Loss of older memories from before brain damage.
Explicit (Declarative) Memory: Conscious recall of information or facts.
Procedural Memory: A type of implicit memory involving motor skills and habits.
Implicit Memory: Influence of past experiences on behavior without conscious awareness.
Memory loss: Difficulty imagining future events due to the inability to use past experiences.
Brain damage:
2 types:
Korsakoff’s Syndrome:
Memory loss caused by thiamine (Vitamin B1) deficiency, often due to chronic alcoholism; patients may confabulate.
Leads to memory loss, especially for recent events.
Effect: Impairs the ability to metabolize glucose. Leads to neuron loss or shrinkage.
Symptoms:
Confabulation: Making guesses or stories to fill memory gaps.
Apathy: Lack of motivation or interest.
Confusion: Disorientation in time or place.
Memory loss: Difficulty forming new memories and recalling recent events.
Alzheimer’s Disease:
Progressive memory decline linked to the build-up of Amyloid Beta (forming plaques) and Tau (forming tangles) proteins.
Caused by degeneration of brain cells.
Begins with difficulty remembering new information and impacts daily functioning.
Amyloid Beta Protein: Causes widespread damage to the cerebral cortex, hippocampus.
Tau Protein: An abnormal form affects the support system inside neurons.
Plaques: Formed from damaged axons and dendrites.
Tangles: Formed from degeneration within neurons.
Treatment: Enhances acetylcholine activity to boost arousal.
Brain and Memory: Most parts of the brain contribute to memory.
Amygdala: Related to learning from fear.
Parietal Lobe: Involved in integrating information.
Anterior Temporal Complex: Damage leads to loss of semantic memory.
Prefrontal Cortex: Involved in learned behaviors and decision-making.
Theories on functions of the hippocampus:
Hippocampus Function Research:
Essential for declarative memory (episodic memory).
Research with Rats: Damage affects performance on two types of tasks.
Delayed Matching-to-Sample Tasks:
Rat sees an object. Later, it must choose the matching object.
Delayed Non-Matching-to-Sample Tasks:
Rat sees an object. Later, it must choose a different object from the sample.
Hippocampus & Spatial Memory:
Hippocampus Damage: Affects spatial tasks; ability to remember locations and navigate spaces.
Radial Mazes: Navigate a maze with eight or more paths. Reward at the end of each path.
Morris Water Maze: Swim through murky water. Find a platform just under the surface.
Hippocampus & Contextual Memory:
Hippocampus Hypothesis: Important for memory context, the “where,” “when,” and “how” of an experience.
Hippocampus role: Acts as a coordinator, reconstructing context.
Episodic memory:
Recent memories: include detailed context..
Older memories: have less detail.
Biological Mechanisms of Learning:
Storing information in the nervous system:
Brain Activity and Memory:
Brain activity creates physical changes.
Not all changes are specific memories.
Memory Storage: Understanding how the brain stores memories is challenging.
Scientific Progress: Research progress is complex and often involves obstacles, like navigating a maze with dead ends.
Hebbian Synapse: A synapse that becomes more effective when the presynaptic and postsynaptic neurons are active together. Important for associative learning.
Habituation in Aplysia:
Decrease in response to a repeated stimulus that is harmless.
The sensory neuron fails to activate the motor neuron as strongly as before
Sensitization in Aplysia:
Increased response to a mild stimulus after exposure to a stronger stimulus.
Serotonin blocks potassium channels in presynaptic neurons → neurons release neurotransmitters longer → stronger response.
Long-Term Potentiation (LTP): Process involving glutamate receptors (AMPA and NMDA) where repeated excitation leads to long-lasting increases in signal transmission between neurons.
When one or more axons repeatedly stimulate a dendrite, making the synapse stronger and more responsive for a while.
Principles:
Specificity: Only highly active synapses get stronger.
Cooperativity: Two or more axons stimulating together create stronger LTP than one axon alone.
Associativity: Pairing a weak input with a strong input boosts later responses to the weak input.
Compensatory process: Synapses strengthen through learning (LTP), less-used synapses weaken to balance the system.
Mechanism: Depolarization removes magnesium blocking NMDA receptors, allowing calcium to enter the neuron and strengthen the synapse.
The LTP Process in Hippocampal Neurons:
Repeated Glutamate Excitation: Activates AMPA receptors. Causes membrane depolarization.
Magnesium Displacement: Depolarization removes magnesium blocking NMDA receptors.
NMDA Receptor Activation: Glutamate excites NMDA receptors. Opens a channel for calcium ions to enter the neuron.
LTP:
Effects:
Increased activity in the presynaptic neuron.
Increased responsiveness in the postsynaptic neuron.
Significance:
Understanding LTP is a step towards understanding learning.
Could lead to memory-improving drugs.
Learning Enhancement:
Caffeine and Ritalin: Boost learning by increasing arousal.
Herbal Effects: Effects are uncertain for Ginkgo biloba, Bacopa monnieri.
Improving memory:
Altering Gene Expression:
Scientists can change genes in mice to try to improve memory.
Effects: Some memory types slightly improve. But other types of memory can get worse, showing a trade-off.
Behavioral Methods:
Best way to improve memory is through practice and learning strategies. Supported by studies in both animals and humans.
Repetition, spaced learning, mnemonic techniques, and active engagement.