| Abstract No.: | C-G3181 |
| Country: | Canada |
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| Title: | NEURAL CORRELATES OF THERMAL COMFORT AND DISCOMFORT IN HUMANS: FUNCTIONAL MAGNETIC RESONANCE IMAGING |
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| Authors/Affiliations: | 1 Peter Shizgal*; 1 Kent Conover; 1 Brian Dunn; 2 Gilles Plourde; 1 David Munro; 1 Robert Kilgour;
1 Concordia University, Montreal, QC, Canada; 2 MNI / McGill University, Montreal, QC, Canada.
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| Content: | Hedonic responses harness behavior to correct deviations from physiological set points. Stimuli that reduce such deviations are pleasant whereas those that exacerbate deviations are aversive. Thus, warming of the skin feels good under hypothermia and bad under hyperthermia. Although the hedonic responses to warming or cooling have opposite signs under hypothermia versus hyperthermia, the signs of sensory responses are the same. Regardless of whether one is hyperthermic or hypothermic, one knows whether one’s skin is being warmed or cooled. The present study is based on the contrasting dependence of hedonic and sensory responses on deviations from the thermoregulatory set point.
Hedonic dysfunction can be profoundly maladaptive. Indeed, the overshadowing of long-term objectives by immediate, affectively powerful influences is a hallmark of behavioural pathologies, such as drug abuse. Thus, insights into the neural underpinnings of hedonic processing can shed light both on normal behaviours crucial to survival and on pathological tendencies.
Objective: to apply functional brain-mapping methods to identify hemodynamic correlates of hedonic responses to thermal stimuli and to distinguish these from correlates of concurrent sensory responses.
Materials and Methods:
Subjects were healthy young men and women who exercise regularly. A water-perfused suit was used, both to deviate core temperature and to deliver thermal stimulation to the skin. The subjects developed mild hyperthermia (1°C) by pedaling an exercise bicycle while wearing insulating clothing as hot water circulated through the suit. Mild hypothermia (1°C) was induced by exposure to cool air, with the insulating clothing removed, while cold water circulated through the dampened suit. Following each deviation of core temperature, the subjects entered a 3T functional magnetic resonance imaging scanner, where they rated suit temperature and thermal comfort during alternating nine-second epochs. The temperature of the circulating water was changed from hot to cold every 2.25 minutes, and blood oxygen level dependent (BOLD) signals were sampled throughout the brain every 2.25 seconds. Core and skin temperature were monitored once per second.
Results:
Subjects were exposed to opposite sequences of alternating hot and cold stimulation during hyperthermia and hypothermia (hot first under hyperthermia and cold first during hypothermia). Therefore, the same sequence of hedonic responses should obtain during hyperthermia and hypothermia, and congruence of BOLD responses recorded under these opposite conditions of deviated core temperature was taken as the signature of a hedonic response. Such congruence was observed in regions of the orbitofrontal cortex and the amygdala. In individual subjects, high correlations were also seen between hedonic ratings and BOLD signal in these regions.
Conclusions:
The orbitofrontal cortex has been proposed as a convergence zone for hedonic signals from different modalities. Our results suggest that hedonic signals of thermal origin are among them. The amygdala has also been implicated in hedonic responses, primarily those of negative sign. Our results are consistent with the idea that the amygdala contributes to thermally driven hedonic responses. Future work will distinguish BOLD correlates of the anticipation and experience of thermally induced hedonic states.
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