Which signals push thirst up or down?

Switch signals on and off. Gold signals excite thirst and green ones inhibit it; the bar shows only how many push each way, not their real strengths.

less thirstmore thirst

1 excitatory and 0 inhibitory signals active. Thirst is not one signal: several can add or cancel.

Signals from Stricker and Sved (2000), who list four excitatory signals and three that appear to inhibit thirst, among seven that appear to influence water intake in rats (the seventh, decreased plasma osmolality, is left out because it cannot occur together with the first). Counting signals is an illustrative simplification. Computed locally, not stored.

Drinking versus the blood

Move the clock after 24 hours without water. Compare how much of the total intake has been drunk with how much of the body's fluid deficit is still uncorrected.

DrunkDeficit2.5 min: 65% drunkby 20 min: deficits removed

At 3.0 min: about 66% of intake drunk, about 85% of the deficit still to correct.

The 65% within 2.5 minutes and the removal of systemic deficits within 20 minutes are from Rolls et al. (1980); the straight-line paths between those points are illustrative. Computed locally, not stored.

The same sip, a different feeling

Set how dehydrated the drinker is and see whether an identical sip of water is rated pleasant or unpleasant.

unpleasantpleasant

Drinking now is pleasant: the body needs the water.

Illustrates alliesthesia (Cabanac, 1971) and the finding that drinking when thirsty is pleasant whereas drinking after satiation is unpleasant (Saker et al., 2014). The scale and crossover point are illustrative. Computed locally, not stored.