creating & erasing fear memories, emotional valence in the amygdala

fear conditioning

pairing tones and shocks to induce learning is dependent on the amygdala

emotional conditioning

is dependent on the amygdala; damage to the amygdala prevented tone-shock conditioning but left declarative memory intact

declarative learning

is dependent on the hippocampus; hippocampus damage prevented declarative memory but left tone-shock conditioning intact

damage to both areas

damage to both amygdala and hippocampus prevented declarative memory and tone-shock conditioning

immediate early genes (IEGs)

genes that also become active for a few hours during learning

different IEGs

Arc, Homer1a (H1a), C-fos, Zif/Egr. etc

Arc activation time

transcribe around 4-8 minutes after activation

Homer1a (H1a) activation time

transcribed 25-35+ minutes after activation

green flourescence

genetic modification in mice that makes neurons appear green when the IEG is turned on so we can visualize which neurons were active during learning

red fluorescence

used to identify/tag cells active during consolidation and retrieval

yellow

a combination of green and red, which means the cell was involved in all phases of memory

activity-dependent genes to detect a memory

a subset of BLA neurons were activated during learning had IEGs that were activated due to the neuron’s activity

neurons activated during learning were labeled with red and neurons active during retrieval were labeled with green. neurons mediating learning and retrieval appeared yellow

neural ensembles

sets of cells active at the same time during a given task

CREB

a protein that makes a cell more likely to fire an action potential than controls/more likely to be active in general

memories can be artificially forced into neurons

researchers can force cells to have heightened levels of CREB, which will make them preferentially become active during fear conditioning; we know that fear conditioning was acquired when the conditioned animals freeze in response to a tone

memories can be erased from neurons

modified version of CREB which can be injected into the animal with the molecular key that fits into a type of lock that CREB has on it. When the key meets the lock, it causes cell death which erases the animal’s fear memory by killing these neurons

the CREB-modified animal no longer freezes to the tone that was previously paired with the footshock

the amygdala is not all fear

the basolateral amygdala projects to the central amygdala which processes fear and the nucleus accumbens which processes reward

neurobiology of reward

the nucleus accumbens is part of the mesolimbic dopamine reward pathway and is active in response to many rewards like food, social activities, exercise, and addictive drugs

central amygdala (CeM)

BLA sends direct axons to the central amygdala which mediates fear; animals will show avoidance or run away from an environment, which is a measure of fear

nucleus accumbens (NAc)

BLA sends direct axons to the nucleus accumbens which processes rewards; animals will nose poke a lot, which si a measure of reward since they “want” more

high sensation seekers

increased activation of reward and reinforcement brain systems, decreased actvation of emotional circuitry, and less sensitive to intense imagery

low sensation seekers

greater activation of emotional circuitry, less activation of reward systems

charles whitman

tumor that compressed his amygdala; he shot and killed many people, but wasn’t the “normal suspect” for a crime like this, he had a high IQ and good jobs, etc