Recently Chang
et al. [1] describe how pathological
yawning was extinguished following tracheostomy
in a patient with locked-in syndrome. In
response, Prasad
described a connection between the amelioration
of symptoms and selective brain cooling via the
upper respiratory tract [2]. He suggests
that the cerebral cooling stimulated by the
nasal air passage might be strong enough to
inhibit mechanisms that would normally trigger
yawning. We are in agreement with these points;
however, we think it is important to set the
archival record straight by summarizing the
current literature on yawning, brain cooling,
and abnormal thermoregulation.
Prasad suggests that research is needed to
connect yawning with nasal breathing, but he
neglects to mention a recent study, which showed
that nasal breathing eradicated contagious
yawning in humans [3]. Also, Prasad
brings to light evidence of selective brain
cooling via nasal breathing in sheep, but it is
important to note that Mariak et al. and more
recently, Harris et al. have both found a direct
reduction in human brain temperature following
nasal air flow [4,5]. Therefore, these
are not novel interpretations. In addition,
Chang et al. report the blocking of basilar
arteries prior to treatment, and Zenker and
Kubik report the importance of brain artery
function for cerebral cooling in humans
[6].
Excessive yawning has been identified as a
symptom of abnormal thermoregulation
[7]. For example, multiple sclerosis,
epilepsy, and migraine headaches are all related
to temperature regulation/ dysfunction, and each
have been linked to yawning. Likewise, drugs
that increase brain temperature often produce
excessive yawning, whilst drugs that produce
hypothermia inhibit yawning [7]. We
emphasize that excessive yawning is not
necessarily associated with inadequate sleep, as
evidenced by Chang et al., and may in fact be
indicative of abnormal thermoregulation.
References
1. Chang CC,
Chang ST, Chang HY, Tsai KC. Amelioration of
pathological yawning after tracheostomy in a
patient with locked-in syndrome. Eur J Neurol
2008; 15: e66&endash;e67.
2. Prasad H.
Amelioration of pathological yawning after
tracheostomy in a patient with locked-in
syndrome: a thermoregulatory approach. Eur J
Neurol 2008; 15: e114.
3. Gallup
AC, Gallup GG Jr. Yawning as a brain cooling
mechanism: nasal breathing and forehead cooling
diminish the incidence of contagious yawning.
Evol Psychol 2007; 5: 92&endash;101.
4. Mariak Z, White MD, Lewko J, Lyson T,
Piekarski P. Direct cooling of the human brain
by heat loss through the upper respiratory
tract. J Appl Physiol 1999; 87:1609&endash;
1613.
5. Harris BA, Andrews PJD, Murray GD.
Enhanced upper respiratory tract airflow and
head fanning reduce brain temperature in
brain-injured, mechanically ventilated patients:
a randomized, crossover, factorial trial. Br J
Anaesth 2007; 98: 93&endash;99.
6. Zenker W, Kubik S. Brain cooling in
humans &endash; anatomical considerations. Anat
Embryol (Berl) 1996; 193: 1&endash;13.
7. Gallup
AC, Gallup GG Jr. Yawning and
thermoregulation. Physiol Behav 2008;
95:10-16(e120)
