Perhaps we are living through boring times
but a growing interest in the processes and
phylogenetic pressures underlying yawning is
emerging [1,2]. In particular,
contagious yawning appears to offer a fruitful
avenue of investigation to the growing fields of
developmental, affective and social
neuroscience.
Contagious yawning is observed in humans and
other primates [3,4] and here we suggest
a possible candidate for a physiological
mechanism common to primates and a potential
method for investigating this hypothesis. The
candidate mechanism is the mirror neuron system.
Mirror neurons were first discovered in primates
by Rizzolatti and colleagues in the 1990s
[5] and have since been demonstrated in
humans using various psychophysiological
techniques: e.g. fMRI [6], PET
[7], intracranial recording (see
[8]), EEG/ MEG [9] and TMS
[10].
Mirror neurons fire not only when carrying
out an action but also during the observation of
that action carried out by another.
Consequently, they have been posited as a means
for the emergence of action understanding,
imitation and even theory of mind and empathy
[11]. Given the correspondence between
these attributes and the deficits seen in
autism, mirror neurons have also been implicated
in this disorder [12]. Interestingly, a
recent study by Senju and colleagues reported an
absence of contagious yawning in children with
autism spectrum disorder (ASD)
[13].
One potentially useful way of examining this
hypothesis is with the use of EEG to measure
changes in mu activation during the observation
of yawns. Mu oscillations are typically seen in
the alpha and low beta bandwidths of the EEG
(8-12 Hz and 13-20 Hz) over sensorimotor areas.
Previous work has shown that mu-suppression is a
useful index of mirror neuron activation
[14] and is sensitive for example, to
differences between control subjects and those
with ASD [15].
It will be interesting to see whether
changes in mu activation accompany observation
of yawn stimuli and whether they vary according
to individual differences in autistic
traits/levels of empathy. Indeed, this is a
not-too-boring enterprise we are currently
involved in.
[4]
Paukner A, Anderson JR. Video-induced
yawning in stumptail macaques (Macaca
arctoides). Biol Lett 2006;2(1):36-8.
[5] Gallese V, Fadiga L, Fogassi L,
Rizzolatti G. Action recognition in the premotor
cortex. Brain 1996;119:593-609.
[6] Iacoboni M, Woods RP, Brass M,
Bekkering H, Mazziotta JC, Rizzolatti G.
Cortical mechanisms of imitation. Science
1999;286:2526-8.
[7] Grafton ST, Arbib MA, Fadiga L,
Rizzolatti G. Localization of grasp
representations in humans by PET: 2.
Observation
compared with imagination. Exp Brain Res
1996;112:103-11.
[8] Iacoboni M. Mesial frontal
cortex and super mirror neurons. Behav Brain Sci
2008;31:30.
[9] Nishitani N, Hari R. Temporal
dynamics of cortical representation for action.
Proc Natl Acad Sci USA 2000;97:913-8.
[10] Fadiga L, Fogassi L, Pavesi G,
Rizzolati G. Motor facilitation during action
observation: a magnetic stimulation study. J
Neurophysiol 1995;73:2608-11.
[11] Rizzolati G. The mirror neuron
system and imitation. In:Harley S, Charter N,
editors. Perspective on imitation: from
neuroscience to social science. Mechanisms
of imitation and imitationin animals, vol. 1.
London: MIT Press/ Bradford Books.
[12] Ramachandran VS, Oberman LM.
Broken mirrors: a theory of autism. Sci Am
2006;295(5):38-45.
