Neur2201 Module 4

Synaptic Plasticity

Synaptic Plasticity

The ability of synapses to strengthen or weaken over time, impacting neural communication and memory formation.

Neuronal Integration

The process by which neurons combine information from various sources to generate an output signal.

Synaptic Strength

The intensity of communication between neurons, influenced by factors like neurotransmitter release probability and receptor expression levels.

Associative Learning

The process where new information is acquired by linking stimuli or events together, often mediated by changes in synaptic strength.

Ionotropic Receptors

Receptors that allow ions to pass through when activated, leading to rapid synaptic transmission.

Metabotropic Receptors

Receptors that trigger signaling cascades upon activation, influencing slower synaptic processes.

Long-Term Potentiation (LTP)

A persistent increase in synaptic strength, often associated with learning and memory formation.

Calcium Signaling

The regulation of cellular processes, including synaptic plasticity, through the controlled release of calcium ions.

Protein Synthesis

The production of new proteins crucial for maintaining long-lasting changes in synaptic connections and memory formation.

Intrinsic Excitability

The inherent ability of a neuron to generate action potentials, influenced by ion channel expression and neuronal properties.

Neurogenesis Mechanism

The hippocampus continuously makes new neurons.

Complex Memories

Memories that are more intricate and involve processes like episodic memories, which are poorly understood.

Associative Learning Tasks

Simple learning tasks that are believed to share biological processes with more complex memories.

Neural Network Models

Models used in artificial intelligence that process signals by transmitting them through a network of nodes similar to neurons.

Memory Consolidation

The process by which newly acquired memories are transformed into stable, long-lasting forms, involving protein synthesis and gene transcription regulation.

Sensory Memory

A memory buffer that briefly retains sensory information after the original stimulus has ended, divided into sensory-specific subsystems like iconic and echoic memory.

Short-Term Memory (STM)

Memory that holds a small amount of information in an active state for a brief period, limited in duration and capacity.

Long-Term Memory (LTM)

Memory that allows information to be stored for extended periods, involving changes in protein synthesis and gene regulation.

Hippocampus

Brain structure crucial for forming episodic memories and spatial navigation, supporting the creation of cognitive maps and integrated representations of spatiotemporal contexts.

Amygdala

Collection of subcortical nuclei essential for learning associations with a motivational component or danger, involved in fear conditioning and decision-making processes.

Malleability of memory

Memory is susceptible to changes, including errors, and can be distorted by misleading information, leading to the creation of false memories.

Confabulation

Unintentional memory errors that involve fabricated, distorted, or misinterpreted information, which can occur in various neuropsychiatric conditions.

Memory updating

The process of integrating new information into existing knowledge, critical for adapting behaviors, where outdated information is downgraded, and newer information is promoted.

Extinction learning

A fundamental form of associative/behavioral updating where a cue or action no longer leads to an outcome, resulting in behavior changes.

Recovery after extinction effects

Behaviors that were extinguished can spontaneously reappear over time, in non-extinction contexts, or when re-exposed to the unconditioned stimulus.

Acetylcholine in memory interlacing

Acetylcholine plays a role in interlacing new and existing memories to reduce interference between them, crucial for flexible behavior.

Clinical relevance of CBT

Cognitive Behavioral Therapy focuses on updating memories through cognitive reappraisals and behavioral procedures, essential for effective psychotherapies.

Extinction and the "erasure" of unwanted memories

Extinction learning is crucial for treating anxiety disorders, and targeting memory reconsolidation can weaken fear responses.

Promoting memory updating

New approaches aim to enhance memory modification and generalizability across time and contexts, potentially improving treatment outcomes.

What does probability of releasing transmitter rely on?

• The number of docked vesicles

• Concentration of Calcium at exocytosis site

Features of AMPA receptors

Fast kinetics, NOT voltage dependent, permeable to sodium and potassium, # of receptor varies as they scale with synapse surface area

Features of NMDA receptors

Slower kinetics, Blocked to Magnesium (requires depolarisation), Permeable to sodium, potassium AND calcium, NMDA receptor expression is relatively constant

Which receptor mediates synaptic transmission?

Under normal conditions its AMPA receptors, as at resting membrane potential NMDA receptors are blocked by magnesium

Why is synaptic integration needed?

CNS synapses are generally weak, where a single vesicle is released and EPSP is a few tenths of a millivolt. Thus, many synaptic inputs needed to depolarise cell and generate AP.

Timing is critical for integration because…

It requires temporal overlap of synaptic potential AKA coincident activation

Inputs into the Amygdala

• Unimodal sensory inputs from cortex and thalamus

• Convergence of CS and US

• Also connected to Hippocampus and Prefrontal Cortex

Outputs from the amygdala

• Hypothalamus and brain stem

• Hippocampus and PF Cortex

Larger spine heads contain more?

AMPA receptors, creating a bigger EPSP

Cellular Mechanisms of LTP Step 1

Stimulation of NMDA-type glutamate receptors

Cellular Mechanisms of LTP Step 2

Increased Post-Synaptic Calcium

Cellular Mechanisms of LTP Step 3

Activation of CAMKII

Cellular Mechanisms of LTP Step 4

Gene transcription and protein synthesis

Cellular Mechanisms of LTP Step 5

Enhanced AMPA-type glutamate receptor functions

Synapses in the hippocampus and amygdala contain ?

AMPA and NMDA receptors

Calcium functions

• Regulates every cellular process e.g. neurogenesis

• Maintains Kinase / Phosphatase balance

• Calcium is tightly regulated in cells

Where are synaptic contacts made between excitatory neurons?

The spines ; signalling molecules activates by calcium restricted to activated spine (input specificity)

What needs to be maintained to maintain LTP?

• Protein synthesis

• Gene transcription (only necessary for induction, not expression)

• PKM-Zeta (continuous phosphorylation of receptors/signalling molecules)