Effects of yawning and related activities on skin conductance and heart rate.

Accompanying physiological changes may clarify the functions of yawning, an act that is ubiquitous in the animal kingdom. The skin conductance, muscle tension, and heart rate of 30 young adult humans were recorded before, during, and after their yawns. These measures were also taken in 20 control subjects who merely opened their mouths or took deep breaths. Yawning, mouth opening and deep breathing each increased arousal initially, as measured by skin conductance. Some cumulative effects of successive yawns were found.