Recent research suggests that yawning is an adaptive behavior that functions to promote brain thermoregulation among homeotherms. To explore the relationship between brain temperature and yawning we implanted thermocoupled probes in the frontal cortex of rats to measure brain temperature before, during and after yawning. Temperature recordings indicate that yawns and stretches occurred during increases in brain temperature, with brain temperatures being restored to baseline following the execution of each of these behaviors. The circulatory changes that accompany yawning and stretching may explain some of the thermal similarities surrounding these events. These results suggest that yawning and stretching may serve to maintain brain thermal homeostasis.

The ultimate function of yawning continues to be debated. Here, we examine physiological measurements taken before, during, and after yawns in humans, in an attempt to identify key proximate mechanisms associated with this behavior. In two separate studies we measured changes in heart rate, lung volume, eye closure, skin conductance, ear pulse, respiratory sinus arrhythmia, and respiratory rate. Data were depicted from 75 s before and after yawns, and analyzed at baseline, during, and immediately following yawns. Increases in heart rate, lung volume, and eye muscle tension were observed during or immediately following yawning. Patterns of physiological changes during yawning were then compared to data from non-yawning deep inhalations. In one study, respiration period increased following the execution of a yawn. Much of the variance in physiology surrounding yawning was specific to the yawning event. This was not the case for deep inhalation. We consider our findings in light of various hypotheses about the function of yawning and conclude that they are most consistent with the brain cooling hypothesis.

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Previous research demonstrates that listeners perceive women's voices as more attractive when recorded at high compared to low fertility phases of the menstrual cycle. This effect has been repeated with multiple voice recording samples, but one stimuli set has shown particularly robust replications. First collected by Pipitone and Gallup (2008), women were recorded counting from 1-10 on approximately the same day and time once a week for 4 weeks. Repeatedly, studies using these recordings have shown that naturally cycling women recorded at high fertility are rated as more attractive compared to voices of the same women at low fertility. Additionally, these stimuli have been shown to elicit autonomic nervous system arousal and precipitate a rise in testosterone levels among listeners. Although previous studies have examined the acoustic properties of voices across the menstrual cycle, they reach little consensus. The current study evaluates Pipitone and Gallup's voice stimuli from an acoustic perspective, analyzing specific vocal characteristics of both naturally cycling women and women taking hormonal contraceptives. Results show that among naturally cycling women, variation in vocal amplitude (shimmer) was significantly lower in high fertility recordings compared to the women's voices at low fertility. Harmonics-to-noise ratio and variation in voice pitch (jitter) also fluctuated systematically across voices sampled at different times during the menstrual cycle, though these effects were not statistically significant. It is possible that these acoustic changes could account for some of the replicated perceptual, hormonal, and physiological changes documented in prior literature using these voice stimuli.