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Memory Consolidation/Modulation - Coggle Diagram
Memory Consolidation/Modulation
Consolidation
Neural Bases of Memory
Even though there are a lot of cells in the brain, researchers focus on neurons because they believe they are the basis of memory.
model
: When you encounter an event and start processing information, different neurons become active. Working together, they form an ensemble > connected.
Activating those neurons gives you the memory (more activated = better memory).
Neuronal Ensembles (Frankland, Josselyn & Kohler (2019))
What did they do?
two experiments checking the activation of regions in the hippocampus (neuronal ensembles)
EXPERIMENT 1:
Checking CA1 area of the hippocampus.
Rat placed in novel context, after a few minutes the animal gets a shock (environment-predicts-shock memory being formed).
All active neurons are tagged.
All tagged neurons are injected with ArchT (a light-activated substance. used to turn off that neuron when light is shined into the brain (inhibitory)).
EXPERIMENT 2:
Same training procedure, looking at dentate gyrus (still in the hippocampus).
Active cells tagged with ChR2 (light-activated, excitatory).
Placed in novel context.
Artificial activation of neuronal ensemble.
What did they find?
Rats feel the fear with good memory (activated neuronal ensembles), and don’t with bad memory (inhibited neuronal ensembles).
Interpretation:
suggests that the hippocampus is important for memories of space and context
Memory Consolidation
After an event, you form a memory, and after some time it “solidifies”.
Due to the time it takes for the structural and functional changes in the brain (protein production, pruning what isn’t necessary, etc).
Temporal gradient of memory consolidation
While a memory is being consolidated, you can disrupt it.
Each time you recall a memory you may strengthen it.
Passive avoidance procedure:
Rats tend to spend time in the dark area of the box. Shocking the rats in the dark side to make them passively avoid it. The stronger the memory, the stronger the avoidance.
Retrograde Amnesia Experiment (Riccio et al 1968 (?))
What did they do?
6 groups, 2 control (immersion and retention)
Passive avoidance training procedure
IMMERSION GROUP: Placed in room temp water for a while, and then into ice water
RETENTION GROUP: passive avoidance training procedure, no water.
What did they find?
immersion group walked straight into the dark area without any fear the next day
Interpretation
:
suggests that retrograde amnesia can be induced by environmental conditions that cause excess stress?
Gisquet-Verrier & Riccio (2018)
what did they do?
passive avoidance procedure
given an amnestic treatment 0, 3, 10, or 20 minutes after training.
test phase.
what did they find?
amnestic treatment at 20 minutes had little effect > had the highest response latency.
interpretation:
the memory in the 20 minute rats had already been consolidated, and so it was less vulnerable to change compared to the rats given less time before their treatment.
Epinephrine/Adrenaline for Improving Memory
Epinephrine increases during stress.
Epinephrine can’t cross the blood-brain barrier, but has effects on other parts of the body.
Increases glucose, increases the activity of neurons.
lick suppression procedure:
shocked when licking water.
Lick Suppression (Gold & VanBuskirk (1975 (?))
what did they do?
Drink water get shocked. Weak shock to see if they can enhance memory, and may increase shock later.
Injected with epinephrine either 0, 10, 30 and 120 mins after.
Some injected with saline for controls.
what did they find?
epinephrine at the start increases latency, epinephrine injection after a longer time decreased lick suppression (on par with controls)
interpretation:
suggests that levels of epinephrine may be a signal to the body to recall a memory, but that the effect is limited by time delays.
Glucose for Human Memory
Effects of Glucose on Human Memory (Manning et al (1998))
what did they do?
Glucose or saccharine, read a story, come back a week later, test memory.
Few weeks later they had the opposite and read another story, come back later and are tested for recall.
what did they find?
Recalled almost twice the items in the story relative to their saccharine scores
Inverted u-shape function
Interpretation:
glucose improves memory to a certain extent; u-shape function suggests that too much glucose has lesser effects.
glucose is not a long lasting effect > time delays result in similar effects of control substances.
Noradrenaline on Memory Consolidation
Gazarini et al (2023)
what did they do?
EXPERIMENT 1
adult rats get trained on a context fear task (1 context). in the space for 30 seconds before a shock.
then injected with yohimbine or vehicle immediately after training.
test 1 day later.
what did they find?
yohimbine rats spent ~30% more time freezing than vehicle controls.
EXPERIMENT 2
what did they do?
follow-up where they delayed injection for 6 hours
what did they find?
vehicle and yohimbine rats spent the same amount of time freezing
interpretation:
yohimbine increases noradrenaline levels in several brain regions, and therefore enhances memory consolidation, but it has a time-limited effect.
Modulation
Hormonal Modulation of Memory Consolidation
Gold et al (1976))
what did they do?
Rats trained on lick suppression procedure; injected with ACTH afterwards (produced by the pituitary gland and affects adrenal glands)
4 groups of trained rats injected immediately after training
Good memory is defined by long latency > taking a long time to lick after lick suppresion training
what did they find?
inverted u-shaped function. up to 0.3IU enhances memory when injected immediately, anything more impairs memory beyond control condition. after a 2hr delay any injection of ACTH is on par with control.
interpretation
ACTH affects memory both ways > there is a sweet spot between enhancing memory and amnesia.
Cavalcante et al (2017)
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what did they do?
testing hormonal modulation of social memories.
put a rat in a box with two cylinders and gave them time to get habituated with the space.
cylinders had holes to touch noses or smell what's inside them
24 hr later they had a sample phase and an infusion of a drug (veh, iso, tim)
timolol = beta-adrenergic antagonist
retention test further 24 hr later
new animal put in one of the cylinders.
if good retention, most time will be spent at new cylinder (showing a good memory of what's been in the other during previous exploration).
what did they find?
timolol rats spent close to an equal amount of time with the new and familiar rat
interpretation:
timolol (beta-adrenergic antagonist > memory modulation system) impairs social memory.
further experiment was done to prove that the drugs only affect memory and not behaviour.
Stress Modulation of Memory in Humans
Does Stress/Arousal Affect Memory in Humans? (Cahill et al (1996))
what did they do?
EXPERIMENT 1
human adults showed emotionally arousing clips (E) or emotionally-neutral (N) clips; within-subjects design > 8 participants (important to note for correlations).
Took a PET scan (brain imaging based on glucose utilisation > not very anatomically precise) while watching both clips
Free recall test 3 weeks later
Looking at the amygdala > very important for emotional learning in rats, humans and monkeys
what did they find?
more emotional films recalled than neutral
EXPERIMENT 2
film clips in previous experiment differed in a number of features in addition to how “emotional” they were (noise, action, colour, etc)
To fix this they exposed participants to very similar material > story with slides about a mother and her son.
Showing pictures and clips of the mother and her son and what they’re doing
There was an accident in the clips
Half the participants were told it was a real accident they witnessed, the other half were told that it was fake for a movie set.
Half the participants took a placebo beforehand, the other half took propranolol (beta blocker)
Beta-blockers block beta adrenaline receptors
all tested a week later
what did they find?
Those given a placebo had a better memory of the emotional part of the story, but those given propranolol didn’t
interpretation:
stress/arousal increases memory performance in humans through extra activity in the amygdala (?)
McReynolds et al (2021)
Y-maze
what did they do?
Pre-exposure: determining which arm of the why the rats like more
training phase: using food to teach the rats to go to the other arm.
implanted cannulas in the basolateral amygdala to give either a vehicle or clenbuterol (beta-adrenergic agonist)
what did they find?
rats given clenbuterol spend more time in the trained (paired) arm of the maze. vehicle rats spent an equal time in each.
interpretation:
amygdala is important for emotional memories, including liking > like the food arm more > agonist strengthens that memory and alters the time spent in each arm.