1. Introduction Contagious
yawning, the onset of a yawn triggered by seeing
or hearing someone yawn, or even reading, or
thinking about another person yawn is a
well-documented phenomenon. Contagious yawning
is independent
of generalized emotional contagion, occurs
in 40Ð60% of adult human research subjects
[18,21], and has also
been reported in chimpanzees.
It has been hypothesized that contagious
yawning may be related to empathy. Specifically,
contagious yawning
is thought to be a primitive expression of
cognitive processes involved in self-awareness
and theory of mind, the ability to empathize
with and infer what others want, know, or intend
to do. Seeing or hearing another person yawn may
act as a
releasing stimulus that activates
neurological substrates that initiate yawning.
Thus, it may be that contagious yawning
occurs by activating a system that is also
involved in modeling other aspects of
interpersonal mentality at conscious
levels. Two recent studies have provided
support for this hypothesis. Platek et al.
[18] demonstrated that susceptibility to
contagious yawning increases among people that
can identify their own face faster and do better
on theory of
mind tasks. Further, Platek
et al. demonstrated that susceptibility to
contagious yawning is negatively correlated with
expression of schizotypal personality traits,
which have been shown to impair self-processing
and theory of mind.
Anderson et
al. has also provided support for the
empathic modeling hypothesis of contagious
yawning by demonstrating
contagious yawning in chimpanzees. The
importance of this study is that chimpanzees,
unlike most other primates,
also show rudimentary forms of empathy and
selfawareness. In line with these data, the
empathic modeling
hypothesis predicts that species who do not
recognize themselves in mirrors and do not show
evidence of mental state attribution ought to
fail to show evidence for contagious
yawning.
An alternative hypothesis of contagious
yawning is that it may be related to an innate
imitation system driven by the
so-called
mirror neuron system. That is, contagiou
yawning is presumed to be an automatic mirroring
mechanism related to synchronizing one's own
behaviors with others. One way of investigating
these hypotheses is to explore the neural
correlates of contagious yawning.
However, the neural substrates recruited
during contagious yawning are unknown. In the
present study, we used functional magnetic
resonance imaging (fMRI) to investigate the
brain substrates involved in contagious yawning
when compared to laughing, which is also
reported to be contagious, and a neutral
expressive condition. We hypothesized that
neural substrates known to be involved in
self-processing and mental state attribution
would be recruited when viewing yawn videos.
Specifically, we predicted significant
activation in right prefrontal substrates
[19,20] and midline cortical
structures
2. Materials and methods
2.3. Design
The study was designed to measure blood
oxygenation level dependent (BOLD) responses to
viewing and responding to videos of people
yawning and laughing. A boxcar (block) design
was used, in which participants were shown three
7-s video clips in a 24-s block (1 s
inter-stimulus interval). There were three video
conditions: neutral, laugh, and yawn. Each block
consisted of only one type of video. There were
6 neutral/null blocks and 5 yawn and laugh
blocks. Participants were asked to look at
the images and respond yawn or laugh using a
button press using an MRI compatible response
pad (Resonance Technologies, Inc.). Stimuli were
delivered through stereoscopic goggles
designed for use within the fMRI environment
(Resonance Technologies) and Neurobehavioral
Systems Presentation software
(www.neurobs.com).
2.4. fMRI image processing and
analysis
3. Results
No significant activation was observed when
contrasting laugh with the null stimulus, nor
was there any significant activation when
contrasting laugh minus yawn. Table 1 and Fig. 1
depict the significant activations associated
with the
yawn minus laugh contrast. This contrast
revealed significant (FDR-corrected P b 0.01)
activation in bilateral posterior cingulate (BA
31) and precuneus (BA 23), and bilateral
thalamus and parahippocampal gyrus (BA 30),
which supports the hypothesis that viewing yawns
may evoke self-referent information. Activation
in the posterior cingulate/precuneus region has
been associated with selfreferent processing and
retrieval of autobiographical memories.
Activation in the thalamus and parahippocampal
gyrus may be related to general sensory aspects
of face perception.
4. Discussion
In contrast with laughter contagion, our
findings suggest that there are unique neural
substrates involved in contagious
yawning. This phenomenon has been of
interest to researchers for decades but until
now no one had identified the neurobiological
substrates involved in the process.
Our findings also support the empathic
modeling hypothesis by showing significant
activation in bilateral precuneus and posterior
cingulate. These regions have been implicated in
identifying self-referent information. Thus, it
is possible that contagious yawning is a
primitive form of empathic modeling that is
subserved by substrates that are precursors to a
more sophisticated and distributed system
involved in conscious self-processing (e.g.,
theory of mind, self-face recognition). The
posterior cingulate/precuneus region has been
implicated in identifying words that describe
oneself, retrieval of autobiographical
events/memories, engaging in self-generated
actions and self-monitoring, and discriminating
between theory of mind stories and "physical"
stories.
Furthermore, several studies have also
implicated medial/midline cortical structures in
self-processing. For example, Vogely et al.
demonstrated that medial prefrontal regions are
associated with taking one's own (first person)
perspective and another person's (third person)
perspective when solving an avatar task. Gusnard
et al. demonstrated that activation in medial
prefrontal and anterior cingulate regions
vascillates depending upon attentional demands
of self-referent or externally cued conditions.
We did not find significant activation in other
regions that have been associated with
self-processing, such as the right prefrontal
cortex. This lack of involvement is consistent
with the empathic modeling hypothesis, which
suggests that contagious yawning is a primitive,
unconscious form of empathic modeling and hence
would not be expected to activate regions
associated with conscious recognition of
self-processing.
Additionally, the yawn minus laugh contrast
revealed significant bilateral thalamic and
parahippocampal gyrus (BA 30) activation. These
activations are likely related to the visual and
facial sensory processing of the stimuli. In a
recent study of familiar face recognition,
Blonder et al. report that presentation of both
human and dog faces activated so-called "face
areas" (e.g., fusiform gyrus, inferior occipital
gyrus), but the parahippocampal gyrus was
uniquely activated by human faces. We observed
similar activations when contrasting yawn with
the null condition (neutral face video) when we
did not apply P value [FDR]
correction
Our findings support our hypothesis that
viewing yawns activate regions implicated in
self-processing, but not the hypothesis that
viewing yawns activate areas associated with the
mirror neuron system. In fact, we found no
evidence of activation in areas that would
suggest contagious yawning is related to the
mirror neuron system (e.g., left inferior
frontal gyrus, frontalÐparietal network,
etc.). Platek
et al. reported that the susceptibility to
contagious yawning was reduced in subjects with
increased levels of schizotypal personality
traits and suggested that schizophrenic-spectrum
traits negatively impact susceptibility to
contagiously yawn. Patients with schizophrenia
and schizotypal personality disorder show
metabolic decreases and structural asymmetries
in the posterior cingulate region [12],
which may contribute to a failure to show
contagious yawning. Also, given that
chimpanzees, but not monkeys, show the capacity
for mirror self-recognition, theory of mind and
contagious yawning, it would be interesting to
study the behavioral and neural correlates of
contagious yawning in other species as
well.
In conclusion, our findings point to
a relationship between watching videos of people
yawn and posterior midline cortical regions,
which supports the hypothesis that contagious
yawning may be a primitive form of
selfprocessing, subserved by similar neural
substrates.
-Schurmann
M, Hari R et al Yearning to yawn: the neural
basis of contagious yawning NeuroImage 2005; 24;
4; 1260-1264
-Gallup
A, Gallup G. Yawning as a brain cooling
mechanism: nasal breathing and forehead cooling
diminish the incidence of contagious yawning.
Evolutionary Psychology www.epjournal.net
&endash; 2007. 5(1): 92-101
