Nematodes have a negative-valence neuron that triggers turning when temperatures increase, but only if the temperature is already above a certain threshold; it is a Too hot! neuron. Nematodes also have a Too cold! neuron; it triggers turning when temperatures decrease, but only when temperatures are already below a certain threshold. Together, these two negative-valence neurons enable nematodes to quickly steer away from heat when they’re too hot and away from cold when they’re too cold. Deep in the human brain is an ancient structure called the hypothalamus that houses temperature-sensitive
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