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The Primordial Emotions:
The Dawning of Consciousness
Denton 2006
Christina Weng
October 17, 2008
The Physiology of the
Primordial Emotion of Thirst
Questions to Keep in Mind
1)
2)
3)
4)
How is thirst generated?
Where is the change in physical state that generates thirst
detected?
Where does the thirst system fit on the evolutionary development
timeline?
How is immediate gratification of thirst possible?
The Mechanisms Producing Thirst
Cellular Dehydration
caused by
Change in osmotic pressure
Rise in extracellular [Na]
detected by
Sensors in the hypothalamus
impulses to
Other areas of the brain
Consciousness of thirst
Evolution of thirst
Aquatic Animals
Conserve Water
Reptiles/birds
eggs
freshwater
Mammals
urine
limit to water intake
seawater
consciousness
The Dry Mouth Theory
Claude Bernard: continuous wetting of the mouth does not satisfy thirst
In animals: some salivation continues even when water is withheld—wetting of
mouth is not sufficient to satisfy thirst
Claude Bernard’s Experiment
In humans: less salivation  dry mouth sensation exacerbates signals from
hypothalamic sensors.
Rapid Gratification of Thirst
Loss of thirst occurs long before the water is absorbed from the gut and
the chemical imbalance (origin of thirst sensation) is corrected.
In experiments, animals drink just enough to repair the water and/or
sodium deficit.
HOW?
Taste of water Esophageal metering Filling of stomach
Satisfaction
The Neuroimaging of Thirst by
Positron Emission Tomography
PET/Radioactive Water Technology
Detects local change in cerebral blood flow
Regional cerebral blood flow
Activation
Deactivation
Neural activity
Anatomy
The Experiment
9 males: 24-36 years
1) Baseline scans
2) Rapid venal infusion of 3% NaCl (vs. 0.9% in normal blood)
3) Sensation of thirst appears (+25 min)  Image
4) Thirst sensation maximum (+40 min)  Image
5) Mouth rinse  Image
6) Drink  Image
Effect of Salt Solution on Blood Plasma and
Thirst
Primary Sensation of Thirst
(+25/+30 Minutes)
Evolutionary Ancient Areas
Parahippocampus
(limbic system)
Cingulate gyri
(limbic emotional system)
Insula
(visceral sensory area)
Cerebellum
Activation: yellow to red
Deactivation: green to blue
Maximum Thirst
(+ 40 min)
Activation of Papez Circuit: linked to emotional behavior
Maximum activation in left parahippocampus, major deactivation in
parahippocampus; bypass Papez circuit
Activation of parietal region: “dry mouth” sensation
Activation of thalamus: sensory inflow from “dry mouth,” transmission of
sensation
Wetting the Mouth
Knee of corpus callosum: remains highly activated
Strong activation of frontal lobe: taste
Drinking Water to Satiation
ACTIVATION IN KNEE OF CORPUS CALLOSUM DISAPPEARS!
Other Observations
Cerebellum: more significant role than expected
Posterior cingulate area: reflected correlation with thirst score
Cingulate regions: cortical response to rise in salt concentration,
concious sensation of thirst
Receives most impact from more primitive regions of brain
Robinson and Mishkin Experiment
Electrical stimulation of the anterior cingulate area in monkeys
Water drinking behavior
The Cerebellum
Contains 70% of neurons in the brain
Traditionally associated with motor control and learned
tasks
Possible connection with the hypothalamus and thalamus
(http://www.mult-sclerosis.org/cerebellum.html)
fMRI Imaging of Thirst
Agrees with
PET scan
results
Strong activation in
third ventricle:
Site of receptors
that detect changes
in salt concentration.
Activation of lamina terminalis vs. AC
Future Directions
1)
2)
3)
Activity of the anterior cingulate with respect to rapid increase of
sodium concentration in the plasma.
Involvement of the cerebellum in response to rising sodium
concentration
Role of the cerebellum in the emergence of consciousness of
thirst