Urgent 2
studystudent
lambert_chapter_8PPT.pptxChapter 8
Maintenance and Motivation
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Outline
The brain’s reward circuitry
Hunger regulation
Thirst regulation
Motivating the brain to work
Grooming
Barbering (Extreme Grooming)
Reward circuitry
Time budgets help us understand what people spend their time doing/find rewarding
How might you experimentally determine the reward center of the brain?
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Reward circuitry
(a) Rats press a bar to receive electrical stimulation to the mesolimbic dopaminergic pathway. (b) If rats increase bar press responses to obtain stimulation to a specific brain area; this indicates that the stimulation is rewarding.
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Reward circuitry
We can also measure behavioral responses to particular stimuli
Similarities observed between rodents and humans suggest that facial responses to sweet and bitter tastes have been conserved across mammalian species.
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Reward circuitry
Critical regions
mesolimbic dopaminergic pathway
septal nuclei
snucleus accumbens
Reward circuitry
Various brain areas and neurochemicals guide us to desired outcomes based on how much we enjoy the activity (liking), wish to engage in the activity (wanting), or have come to associate specific stimuli with subsequent desired activities (learning).
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Reward circuitry
Liking vs. wanting vs. learning
Various brain areas and neurochemicals guide us to desired outcomes based on how much we enjoy the activity (liking), wish to engage in the activity (wanting), or have come to associate specific stimuli with subsequent desired activities (learning).
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Reward circuitry
The environment can shape how our brain processes stimuli
How could we apply this research?
In this study, the rat’s habitat influenced the proportion of the nucleus accumbens shell assigned to positive and negative emotional responses.
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Hunger Regulation
We eat to live, so the brain is good at motivating us to eat
How it accomplishes this feat is based in part on our environment
Brain size and stomach size relate to habitat/food availability
Hunger Regulation
Orangutans, who eat only raw foods, require a large stomach for storage. (b) Eating cooked foods enables humans to have smaller stomachs, since we obtain necessary levels of nutrients in smaller volumes of food
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Hunger Regulation: Neurobiology
Hyperphagia
Lesions to VMH
Lesions to LH
Sensory-specific satiety
Key players: insulin, leptin, ghrelin
Hunger Regulation: Neurobiology
Mice expressing a recessive gene associated with leptin deficiency have more body fat than mice that do not express the recessive gene.
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Hunger Regulation: Neurobiology
How can we determine which brain regions are involved in regulating hunger?
As indicated by the presence of darkly stained Fos-positive cells, there is less activation in the arcuate nucleus of (a) rats that are fed to satiety and administered saline than in that of (b) rats that are food deprived with a saline infusion. (c) However, if the hungry animals receive an insulin infusion, less Fos activity is observed.
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Hunger Regulation: Neurobiology
Leptin and ghrelin interact with the arcuate nucleus to affect hunger and energy regulation.
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Hunger Regulation: Neurobiology
Can we be addicted to particular kinds of food?
Why is ‘junk food’ so good?
Is it adaptive to like junk food?
Hunger Regulation: Neurobiology
Sugar “withdrawal” in rats
Rats that had experienced greater access to sugar consumed much more sugar after a period of sugar deprivation than did control rats.
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Hunger Regulation: Neurobiology
Extended access to food (buffet style) can raise reward thresholds
Hunger Regulation: Neurobiology
Having people around also influences eating
Can you think of why?
Are there possible confounds?
(a) Eating with friends may be enjoyable, (b) but it leads us to consume more calories.
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Hunger regulation: Eating disorders
Anorexia nervosa
Bulimia nervosa
Hunger regulation: Eating disorders
Anorexia nervosa
Bulimia nervosa
Still a lot of research to be done
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Hunger regulation: Eating disorders
Serotonergic receptors and anorexia. Research suggests that the proportion of 5-hydroxyindoleacetic acid 1A and 2A receptors in (a) healthy patients is distorted in (b) patients diagnosed with anorexia
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Hunger regulation: Eating disorders
The insula plays a role in determining whether food is perceived as positive or negative.
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Hunger regulation
Some nutrients that we need for healthy brain function are acquired by our diet
A lot of speculation about the benefits of supplementing these nutrients
More research still to be done
Hunger regulation
Impact of high-fat maternal diet on offspring
Three groups of rats
HFD: High-fat pups raised by high-fat diet mothers
HFD-BD: High-fat pups raised by balanced-diet mothers
BD: Balanced-diet pups raised by balanced-diet mothers
Any predictions?
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Hunger regulation
(a) The pups of rats placed on a high-fat diet during pregnancy developed more orexin-producing neurons than did o spring from mothers kept on a balanced diet during pregnancy, even if these offspring consumed a balanced diet after birth. (b) As indicated by the arrows, more orexin cells were double stained for bromodeoxyuridine in the brain tissue of offspring from the mothers with the high-fat diet than from offspring of mothers with the balanced diet.
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Thirst regulation
Osmoregulatory thirst
Hypovolemic thirst
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Thirst regulation: Osmoregulartory
Osmoreceptors
Anterior third ventricle
When a hypertonic solution was infused into the hypothalamic area of goats, they started drinking water from the bucket.
very sensitive osmoreceptors have been identified in two areas of the anterior third ventricle
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Thirst regulation: Osmoregulartory
Human PET
Anterior and posterior cingulate activity
Insula also involved
When human subjects were thirsty, more activity along the cingulate cortex was observed than after the subjects relieved their thirst by drinking water.
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Thirst regulation: Hypovolemic
Baroreceptors
Role of vasopressin
Angiotensin II
Motivation to work
Many projects require sustained work
Nonhumans have this problem too
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Motivation to work: Anatomy
brain areas implicated in directing and sustaining work efforts
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Motivation to work
Ratio strain
Why does caffeine help us work?
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Motivation to work
Role of dopamine
Rats are more likely to exert more effort for highly desirable food when their dopaminergic system is intact and functioning normally.
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Motivation to work: Plasticity
We learn the relationship between effort and outcome
Learned helplessness
Learned persistence
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Grooming as a motivator
Many mammals spend lots of time grooming
Rats as much as 50% of their day
Grooming as a motivator: Neurobiology
Striatum lesions reduces grooming in rats
Parkinson’s patients and patients with depression also show reduced grooming
Grooming in rat models of depression is restored via antidepressants
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Barbering
Extreme grooming, usually of a cage mate
No clear adaptive value (unseen in the wild)
Theories
Establish dominance
Cope with stress
Compensatory action response (increase stimulation in an otherwise boring environment)
Barbering
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Barbering
Relationship to humans?
Barbering patterns in mice resemble the bald patches resulting from hair picking in humans diagnosed with a condition known as trichotillomania
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