Learning and Memory

Yerkes-Dodson law

mid level of stress best for memory

U shape curve

effect of arousal varies w/ task complexity

complex task performance quality is a U curve

simple task performance drops off later

why does high impact running improve learning and memory?

High epinephrine

administered epinephrine and memory performance

U shape curve

doesn’t work if administered before or 60 mins after training, but effective immediately after

glucose administration and memory performance

Increases memory

Epinephrine can’t access CNS, but epinephrine effects are mediated w/ glucose

Also sees U shape curve

how are glucose effects mediated?

Acetylcholine

-cognitive enhancers affect either glucose or Ach

-glucose increases hippocampal Ach

memory problems and Ach

alzheimer’s and AIDS associated w/ less Ach producing neurons

insulin on memory

Memory and cognition are impaired in diabetics

-destruction of B cells impairs spatial memory in rats

Insulin receptor knockout mice have impaired memory

Alzheimer’s patients have reduced insulin receptors in brain

Streptozocin and passive avoidance tasks

Streptozocin (STZ) toxic to pancreatic beta cells

When STZ given to mice, they forget that dark room = shock

peripheral receptors importance

stimulation of ascending pathways to amygdala by epinephrine w/ B-adrenergic receptors along vagus nerve

important for emotional memories!

amygdala and memories sexually dimorphic

men use right hemisphere amygdala for arousing memories

women use left hemisphere amygdala for arousing memories

sAA importance

sAA = salivary a-amylase is a biomarker of adrenergic activity

sAA increases with emotional memory but not neutral memory

how to test for B-adrenergic receptors signaling in amygdala being used for emotional memories?

Human study w/ propranolol (B-adrenergic receptor antagonist)

Propranolol in human studies

Causes impaired memory of emotionally arousing stories but not non-arousing stories

Glucocorticoid and memories

Biphasic: acute improves memories but chronic is amnestic

Dose dependent in rats and humans

GC antagonists block memory while agonists improve memory

Glucorticoid agonist in rats

facilitates stress evoked learning but only if rat has intact basolateral amygdala

What is needed for glucocorticoid receptors to facilitate learning

need to be in basolateral amygdala

experiment for GC agonist effect on learning in rats

passive avoidance latency- training rats to avoid dark room w/ the shock

Testing spatial memory in rat

Morris Water Maze

Morris water maze experiment

Rats w/ hippocampus lesioned will swim aimlessly to platform and not learn

Impairment of retrieval by stress

nonstressed rat swam more efficiently

stressed rat swum all randomly

chickadee cortisol

having limited and unpredictable food increases corticosterone levels in mountain chickadees

long term cortisol elevation in avians

long term moderate elevation of corticosterone facilitates avian food-catching behavior and enhances spatial memory

dominance related differences in spatial memory of chickadees

spatial memory performance differences between dominants and subordinates are correlated w/ differences in hippocampal cell birth

depression in humans

total hippocampal volume = less time depressed

high cortisol may lead to depression

-cushing syndrome is excess cortisol, reduced hippocampal volumes and memory impairment