15: instrumental

115 blair

what is a satiety signal

it suppresses hunger when we are full and energy needs are met

what are 4 major satiety signals and where do they come from

insulin: from pancreas to convert glucose to energy

leptin: from fat cells when they are large (body has a lot of fat)

PYY_3-36 & GLP-1 (glucagon-like protein 1): from intestines to signal gut is full

what are the gut-derived hormones

leptin, GLP-1, Ghrelin

what is ghrelin

hormone produced by stomach when empty (hunger signal)

what are brain signals that promote hunger

orexigenic signals (hunger = orexia)

what are brain signals that suppress hunger

anorexigenic signals (anorexia = satiety)

what role does ventromedial hypothalamus (VMH) have on appetite

it is anorexigenic: suppresses hunger

when it is lesioned rats have enhanced appetite and maintain homeostasis at higher weight

what role does lateral hypothalamus (LH) have on appetite

it is orexigenic: promote hunger

LH lesions cause rats to have suppressed appetite & maintain homeostasis at lower weight

what does the arcuate nucleus do

projects to LH and VMH, contains: appetite supressing POMC/CART neurons & appetite-enhancing AgRP/NPY neurons

what hormones affect POMC/CART neurons and what does it do when activated

excited by leptin, insulin, & GLP-1

when activated, releases a-melanocyte-stimulating hormone (a-MSH) to inhibit LH

what hormones affect AgRP/NPY neurons and what does it do when activated

excited by ghrelin, inhibited by insulin, leptin, GLP-1, & PYY

releases NPY to inhibit appetite-suppressing neurons in paraventricular nucleus (PVN)

releases AgRP to block effects of a-MSH in LH

what happens when mice can’t produce leptin

it becomes obese because fat cells can not communicate to turn off hunger

can leptin help obese people lose weight

no, they don’t suffer from leptin deficiency, they suffer from leptin insensitivity so they typically have higher than normal levels of leptin (likely since they have more fat)

what are GLP-1 agonists

ozempic, wegovy, saxenda

revolution in weight loss

what is anorexia nervosa and can it be treated

pathological loss of appetite (anorexia) that originates in nervous system (nervosa)

not treatable with appetite stimulating drugs (psychological!)

what is operant (instrumental) conditioning

learning to choose or act rather than expect (pavlovian)

subject learns to perform non-innate operant response to obtain reinforcing outcome

a discriminative stimulus can signal when the outcome is available to be earned

what are the types of operant reinforcement

positive: reward reinforcer

negative: aversive stimulus is stopped

punishment: delivery of aversive stimulus

extinction: withholding expected delivery of reward

what is the mesolimbocortical pathway & why is it important

originates from dopamine neuron cell bodies in VTA which sends axons to cortex, hippocampus, nucleus accumbens

important for motivation & reward

what happened when rats mesolimbocortical pathway was lesioned

after being trained to press lever for cocaine, they stopped pressing lever even though they would get cocaine, so VTA is necessary for rewarding feeling

what is the hedonic/reward theory of midbrain dopamine function

dopamine acts as a positive reinforcer for instrumental behaviors

dopamine = liking

what happened when rats mesolimbocortical pathway was lesioned and there was a condition of easy work & hard work

lesion did not significantly reduce response rates for easy work, but did for hard work

what is incentive salience theory of midbrain dopamine function

dopamine release triggers a feeling of wanting, which drives motivation/incentive to work for an outcome

dopamine = wanting

what is the motivation to exert effort

when it is expected to have a good return on investment, so VTA dopamine neurons may be activated by an incentive

when a monkey was taught that a CS (visual stimulus) would deliver a US (juice) what happened to dopamine (DA) neurons in VTA

baseline: DA responds to only US

late training: DA responds to CS but not US

extinction: DA responds to CS and inhibited when the expected US stops

what is the prediction error theory of midbrain dopamine function

dopamine release occurs when the outcome is better than expected

dopamine = surprise

δ prediction error = R_earned − R_expected