Human temperature regulation when given the opportunity to behave

Area of Science:

• Human thermoregulation
• Behavioral physiology
• Environmental adaptation

Background:

• Human thermoregulatory behavior is crucial for maintaining core body temperature homeostasis.
• The precise triggers for initiating behavioral thermoregulation, particularly the roles of skin versus core temperature, remain incompletely understood.
• Autonomic responses such as sweating and shivering are known to accompany thermoregulatory behavior.

Purpose of the Study:

• To investigate whether human thermoregulatory behavior is initiated by changes in skin temperature preceding core temperature alterations.
• To determine if behavioral thermoregulation occurs with indiscernible differences in sweating or shivering.
• To examine the relationship between environmental temperature, skin temperature, core temperature, and thermal discomfort during behavioral thermoregulation.

Main Methods:

• Nine healthy males were allowed to voluntarily move between a cold (~8 °C) and a hot (~46 °C) environment.
• Measurements included skin, rectal, and esophageal temperatures, cutaneous vasomotor tone, metabolism, evaporation, and thermal discomfort.
• Data were collected upon the decision to move between environments (cold to hot [C→H] and hot to cold [H→C]).

Main Results:

• Skin temperature differed significantly upon behavioral decisions (C→H: 28.4 ± 0.9 °C vs. H→C: 35.0 ± 0.6 °C), while rectal temperatures were similar.
• Metabolic heat production was higher during C→H transitions (101 ± 20 W/m²) compared to H→C (79 ± 10 W/m²).
• Evaporative heat loss showed no statistical difference between conditions, and whole-body thermal discomfort was similar, though inter-segmental differences existed.

Conclusions:

• Skin temperature, rather than core temperature, appears to be a primary signal initiating human behavioral thermoregulation.
• Behavioral thermoregulation is not entirely independent of autonomic responses, as evidenced by metabolic heat production variations.
• These findings highlight the complex interplay between peripheral and central signals in regulating body temperature through behavior.