Learning and memory

Definition:
- Memory is the representation of the world in our brain.
- Learning is the creation or modification of this representation by experience.
- Significance: Learning and memory are inseparable and enable adaptation to the environment, allowing appropriate responses based on previous experiences.
Are all behaviors learned?
- Some behaviors, like finding food or avoiding danger, have a genetic basis encoded in DNA.

Human memory is not merely a recorder but a representation of past experiences.
- Individual interpretations of witnessed events may vary significantly.
Stages and Forms of Memory:
- Sensory Memory: Initial stage where sensory information is briefly retained.
- Short-term Memory: Temporarily holds information needed for tasks but does not store it long-term.
- Long-term Memory: Can be divided into:
- Declarative Memory (Explicit): Memories that can be consciously described.
- Non-declarative Memory (Implicit): Unconscious knowledge like skills, habits, and conditioned responses.
Working Memory: A form of short-term memory focusing on mental operations (e.g., doing arithmetic in your head).
- Requires constant refreshing and is prone to being overwritten.

Definition:
- LTP is an activity-dependent enhancement of synaptic transmission lasting from hours to months.
Mechanism:
- Activation of both AMPA and NMDA receptors leads to increased numbers of AMPA receptors on the postsynaptic membrane.
- Believed to underlie learning and memory processes.
Properties of LTP:
- Input Specificity: Only active synapses get potentiated.
- Associativity: Weakly active synapses can be potentiated when paired with strongly active ones.

Semantic Memory: General knowledge without recollection of when or where learned.
Episodic Memory: Specific events from the past, which may be distinct from semantic memory especially in conditions like Alzheimer's disease.

Amnesia:
- Retrograde Amnesia: Loss of memories prior to trauma, but older memories may remain intact.
- Anterograde Amnesia: Ability to recall events prior to trauma but inability to form new memories afterward.
Reality of Amnesia: Typically presents as a combination of both types.

Example: The difficulty in recalling events surrounding an incident, like Diana's death, highlights the nature of memory.
A remarkable achievement by Alex Mullen, who memorized a shuffled deck of cards in 19.4 seconds in 2016, illustrates the extremes of short-term memory without formation of long-term memory.

Definition: Involves exposure to a single stimulus leading to behavior modification.
- Types include:
- Habituation: Diminished response to repeated stimuli (e.g., reduced gill withdrawal in Aplysia).
- Sensitization: Increased response after a strong stimulus.
- Notable Figure: Eric Kandel, Nobel Prize winner in 2000 for work on learning mechanisms.

Definition: Involves a relationship between two or more stimuli.
Types:
- Classical Conditioning: Associating an emotional or physiological response (e.g., fear responses).
- Operant Conditioning: Learning via consequences (reinforcement/punishment).
- Example: Rat in an operant chamber learns pressing a lever results in food reward.
Commonalities: Timing and predictability are critical in both types of associative learning.

Mechanism:
- Involves strengthening of synaptic connections due to simultaneous firing of neurons.
- Discovered mainly in the hippocampus, demonstrating essential properties such as input specificity and associativity.

Background: Patient H.M. underwent bilateral removal of medial temporal lobe to treat epilepsy, resulting in severe anterograde amnesia.
Consequences: Retained long-term memories prior to surgery but could not create new declarative memories post-surgery.

Comprising perirhinal, entorhinal, and parahippocampal cortices, the hippocampal complex is crucial for explicit memory formation.

Place and Grid Cells:
- Neurons in the hippocampus (place cells) and entorhinal cortex (grid cells) create spatial maps to aid navigation and place recognition.

Concept: “Neurons that fire together, wire together,” which explains neuroplasticity in memory formation.

Neural assemblies represent memories and can be activated by stimuli for recall.
Memory consolidation leads to dormant states of neuronal ensembles until retrieval.
Reconsolidation introduces the ability to update memories after recall.

Suggests memory storage capacity is linked to patterns of synaptic connections across neurons to represent various memories effectively.

Neurogenesis in the dentate gyrus aids memory formation by supplying new neurons to existing circuits.

Memory is distributed across different brain regions, maintaining structural specificity (e.g., visual memory in visual cortices).

Multiple brain regions contribute to different types of memory, indicating that brain injury can affect various memory types distinctly and significantly.