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General Neuron Anatomy and Circuits - Coggle Diagram
General Neuron Anatomy and Circuits
The Amygdala and Emotional Memory
The amygdala is a small but powerful structure located deep within the temporal lobes of the brain
Plays a key role in the processing of emotional events and assisting with forming emotional memories
Emotional memories are a type of memory that is formed in response to a strong emotional event
E.g. a car accident, wedding, birth, mugging
Greater understanding of amygdala attributed to patient S.M. who had damage to area due to rare genetic condition
Scientists conducted studies on her to explore amygdala's role in storage and retrieval of emotionally charged events
Found she was unable to recall personal events that were emotionally charged
e.g. mugging or traumatic accident
Research has shown that the amygdala is activated during emotionally charged experiences
This activation allows the amygdala to help the memory of the emotional event become consolidated into long-term memory storage
It "tags" the event and says "this is important"
It adds emotional significance to it
Further allows the emotional event to be stored quicker or more readily than memories not associated with an emotional event
Memory consolidation is like saving a file on your computer. When you learn something new, your brain takes time to process and store it securely so that you can access it later, just like saving a document so you don't lose it.
The hippocampus is involved in long-term memory storage
Without emotional significance, the sensory information about a bear encounter is still processed by the brain
In this case, the hippocampus (responsible for memory formation), receives the information but many not prioritize it as emotionally significant or deem it as something that should be stored in long-term
The amygdala evaluates the situation as emotionally significant and becomes activated.
When activated, encountering a bear makes it an emotionally charged or significant event
In this case the amygdala perceives the event as emotionally significant because it "sees: event as one that might be fearful or dangerous
This means that it needs to tell the hippocampus this should be an event to be remembered, it needs to "speak" to the hippocampus
Brain regions "speak to each other
Via neurons and synapses
When brain regions are connected and involved in a particular behaviour or function this forms a/is a network or "circuit"
Networks/circuits can be found within/between brain regions
Recall: generally speaking cell bodies of neuron (pre-synaptic) exist in one area - axon goes to another area and synapses with next neuron (post-synaptic)
The Amygdala and Emotional Event Processing
When we are referring to the amygdala "speaking" to the hippocampus to say "hey this is an emotionally significant event"
Neuron originating in the amygdala (i.e. where their cell bodies are) project to and communicate (or synapse with) neurons in the hippocampus
Axons from the cell bodies in the amygdala will project to and synapse with hippocampal neurons
Think about neural circuits as being like teams of neurons working together to perform specific functions in the brain
Just like players in a sports team, different neurons have specific roles and collaborate to achieve a common goal
The hippocampus responds by strengthening the connections between neurons in the area
The hippocampus itself is actually separated into different subregions
Subregions include the dentate gyrus DG, CA1 and CA3
Subregions defined by nuclei
They are their own circuit of neurons/local circuit
Neurons in DG, CA3 and CA1 regions of the hippocampus work together to process and store memories
Long term memory storage involves strengthening of connections between neurons/subregions in the hippocampus
Imagine some of these neurons just hanging out and even though they are connected they don't really form a function together
When we are learning or consolidating something this can allow for these neurons to become more connected/they become a part of their own functional circuit
i.e. function = consolidate memory
Their connections become strengthened/changed.
Simplified e.g. to grasp concept of strengthening connections between neurons
When we are trying to learn or consolidate something we might repeat it over and over to activate neurons in our brain and consolidate it
Just like repeatedly walking on a path in a garden can make it clearer and easier to navigate over time, repeating information can make the connections between neurons stronger and more efficient
Process known as Long-Term Potentiation
Whatever the case, in order for connections between neurons to become stronger what can happen is some really cool events
Neurons within circuit will form more synapses with each other
More synapses = more connected
Postsynaptic neuron will increase receptors on its dendrites to be more responsive to the presynaptic neuron
More able to respond to neurotransmitters released by presynaptic neurons making it more likely to fire
To strengthen connection of neurons in the hippocampus the amygdala connection will lead to the release of two factors: Dopamine (DA) and brain-derived neurotrophic factor (BDNF)
BDNF = protein that is involved in the growth and survival of neurons in the brain
trophic = nutrition and growth
To strengthen connection between neurons BDNF
Promotes the growth of new synapses (connections) between neurons
strengthens existing synapses, making them more efficient (e.g. increases receptors on post-synaptic neuron)
The neuroanatomy of the hippocampus and how neurons (and other cell types) grow
Neurons grow or are differentiated from a particular cell type (i.e. neural stem cell; NSC)
NSC --> Neural Progenitor cell --> Immature Neuron --> Neuron
Neural stem cell (NSC): undifferentiated cells capable of self-renewal and differentiation into various cell types in the nervous system
They serve as a source of new neurons, astrocytes or oligodendrocytes
NSCs give rise to Neural Progenitor cells (NPCs) or Glial Progenitor cells (GPCs)
Neural Progenitor Cells (NPCs): more specialized cells committed to becoming neurons
These progenitor cells undergo further division and differentiation and eventually become immature neurons
Immature neurons: when the neurons start developing their characteristic features, including dendrites and an axon to eventually become mature neurons
Essentially as the immature neuron continues its development, growing its axons and dendrites, it will form synapses with other neurons, and acquire functional properties (i.e. be able to fire, release neurotransmitters, etc.)
will become part of a circuit
The process of generating new neural cells in the brain (including neurons) is what we call neurogenesis
For neurons, neurogenesis involves the birth, development, and integration of these newly formed neurons into existing neural circuits
The process of neurogenesis is huge in neurodevelopment and generally stops in most brain regions by birth or early infancy
However in some regions neurogenesis still occurs in adults (e.g. hippocampus - particularly the DG)
Thought to be involved in memory consolidation to long term memory
In the case of memory consolidation for memory to be stored long term it is thought that new neurons in the DG may join the memory circuit to contribute to the memory formation
This helps that circuit for that memory to become stronger
In the context of the amygdala "speaking" to the hippocampus this leads to increased neurogenesis in the DG possibly contributing to the memory of the emotional event to be consolidated and stored.
The Amygdala and Emotional memory CONT
It is important to note that the amygdala and hippocampus have a bi-directional relationship
When an emotional memory is retrieved/recalled for e.g. the hippocampus and amygdala work together
during recall the PFC helps to control and regulate the individual's emotional response
There is more circuitry at play
Recall: the PFC - sends inhibitory input onto lower brain regions
Down-grades activity in the amygdala
During emotional/fearful events amygdala is responsible for activating our fear response
E.g. when a threatening stimulus is detected (like a bear or snake) amygdala will trigger the fear response
Involves activation of stress response systems: HPA (cortisol) and SAM (fight or flight)