Download - The Primordial Emotions: The Dawning of Consciousness Denton 2006 Christina Weng October 17, 2008
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) How is thirst generated?
2) Where is the change in physical state that generates thirst detected?
3) Where does the thirst system fit on the evolutionary development timeline?
4) How is immediate gratification of thirst possible?
The Mechanisms Producing ThirstCellular Dehydration
Change in osmotic pressure Rise in extracellular [Na]
Sensors in the hypothalamus
Other areas of the brain
Consciousness of thirst
caused by
detected by
impulses to
Aquatic Animals Conserve Water
Reptiles/birds Mammals
eggs urine limit to water intake freshwater seawater
consciousness
Evolution of thirst
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 Neural activity
Activation
Deactivation
Anatomy
The Experiment
9 males: 24-36 years
1) Baseline scans2) Rapid venal infusion of 3% NaCl (vs. 0.9% in normal blood)3) Sensation of thirst appears (+25 min) Image4) Thirst sensation maximum (+40 min) Image5) Mouth rinse Image6) 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 ObservationsCerebellum: 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) Activity of the anterior cingulate with respect to rapid increase of sodium concentration in the plasma.
2) Involvement of the cerebellum in response to rising sodium concentration
3) Role of the cerebellum in the emergence of consciousness of thirst