Yawning, besides being a spontaneous
behavior, can also be evoked by observing others
yawn. However, contagious yawning does not
always occur, depending possibly on several
factors, such as one's propensity to
spontaneously yawn and a heightened level of
sleepiness. The aim of this study is to
investigate in young adults whether contagious
yawning frequency varies throughout the day, and
if it is related to the daily time course of
spontaneous yawning frequency and level of
sleepiness. For the study, 22 subjects were
instructed to log hourly, throughout
wakefulness, the number of spontaneous yawns and
sleepiness level. Subjects were required to
continue this procedure for 3 consecutive days,
after which they underwent five experimental
sessions occurring at regular intervals
throughout the same day. During each
experimental session, subjects observed others
yawn (stimulus condition) and smile (control
condition). Our findings show that the
contagious effect of yawning is always present
throughout the daytime. Both contagious and
spontaneous yawning peaked in the early morning
and in the late evening, according to the
sleepiness time course. However, the frequency
of spontaneous yawns was remarkably lower than
the frequency of contagious yawns around 19:00.
This difference suggests that different
mechanisms control spontaneous and contagious
yawning.
-Abe K
et al. Occurrences of Yawn and Swallow are
Temporally Related. Dysphagia 2014
-Giganti
F, Hayes MJ Cioni G, Salzarulo P Yawning
frequency and distribution in preterm and near
term infants assessed throughout 24-h recordings
Infant Behav & Development
2007;30(4):641-647
-Giganti
F, Ziello ME Contagious and spontaneous
yawning in autistic and typically developing
children CPL 2009
-Giganti
F, Zilli I. The daily time course of
contagious and spontaneous yawning among humans.
J Ethol 2011;29(2):215-216
-Giganti F,
Toselli M, Ramat S. Developmental trends in
a social behaviour: contagious yawning in the
elderly. Giornale di Psicologia dello Sviluppo.
2012;101:111-117
-Zilli
I, Giganti F, Uga V. Yawning and subjective
sleepiness in the ederly. J Sleep Res
2008;17:3003-308
Introduction
Yawning is an involuntary and stereotyped
behavior observed in many animal species,
including humans (Baenninger 1997; Walusinski
and Deputte 2004). Its antiquity and wide
phylogenetic distribution are welldocumented
(Baenninger 1997; Walusinski and Deputte 2004),
and a variety of hypotheses on its function have
been derived from behavioral observations
(Guggisberg et al. 2010). In birds, fish,
amphibians, and reptiles (Ficca and Salzarulo
2002), yawning may be involved in homeostatic
processes, whereas in mammals and primates
(Ficca and Salzarulo 2002), yawning may be
linked to the environment (increased vigilance
level, danger, hunting prey), or even to
communicative actions (sign of aggressiveness,
hierarchical dominance, frustration, sexual
excitement, or a means of synchronizing
activities within the group).
In humans, spontaneous yawning signals
sleepiness (Provine et al. 1987; Zilli et al.
2008) or boredom (Provine and Hamernik 1986). It
has also been suggested that yawning could be
arousing (Baenninger et al. 1996). However, a
recent review (Guggisberg et al. 2010)
emphasized the hypothesis of a social function
to yawning: yawning may work as a nonverbal
signal that communicates one's own physiological
/psychological state to other members of a
social group.
Spontaneous yawning changes throughout life.
At very early ages, between 31 and 40 weeks of
postconceptional age, the number of spontaneous
yawns is about 25 over a 24 h period (Giganti et
al. 2007). In young adults ages 17-35 years,
yawns per day average 8.7 (Baenninger et al.
1996), and there are fewer yawns among elderly
over 75 years of age (Zilli et al. 2008). In
preterm and near-term infants, yawning is
uniformly distributed over a 24 h period
(Giganti et al. 2007). At later ages, both in
young
(Baenninger et al. 1996) and old subjects
(Zilli et al. 2008), the number of yawns
increases in the early morning, after awakening,
and in the evening, before sleep onset and when
the sleepiness level is high (Provine et al.
1987; Baenninger et al. 1996; Zilli et al.
2008).
In human subjects (Provine 1986), in
chimpanzees (Anderson et al. 2004; Campbell et
al. 2009), in gelada baboons (Palagi et al.
2009), and probably in macaques (Paukner and
Anderson 2006), yawning-besides being a
spontaneous behavior-can also be evoked by a
yawn produced by another of their own species.
Contagious yawning is not a reflex response
since it does not follow a short and predictable
latency period. Instead, it is evoked within 5
min of the time in which subjects observe
another' s yawn (Provine 1986) or within 30 min
of the time in which they think about an other's
yawn (Provine 2005). Recently, some studies have
documented a relationship between contagious
yawning and the capacity for empathy (Platek et
al. 2003; Schurmann et al. 2005). In fact, the
contagious effect of yawning is impaired in
individuals suffering from empathy disorders
such as autism (Senju et al. 2007; Giganti and
Esposito Ziello 2009).
In contrast to the spontaneous yawning that
occurs very early in the human life (de Vries et
al. 1982; Walusinski et al. 2005; Giganti et al.
2002, 2007), contagious yawning is first
observed at 4 or 5 years of age (Anderson and
Meno 2003). The time lag between the emergence
of spontaneous yawning and contagious yawning
leads us to believe that different mechanisms
control these two acts.
In addition, some authors (Anderson and Meno
2003) have proposed that the occurrence of
contagious yawning as a response to a
psychological stimulus (a yawn produced by
another person) might reflect both self
awareness and social awareness in children.
According to this theory, contagious yawning is
a type of behavior that is triggered primarily
by unknown factors that are most likely linked
to developmental acquisition, for example,
sensitivity to other people's behavior. This
could explain why contagious yawning is not
present in children under 5 years and why there
is a lack of contagious yawning in subjects with
impaired empathy and impaired social skills
(Senju et al. 2007; Giganti and Esposito Ziello
2009). However, in adults contagious yawning
does not always occur, and possibly depends on
several factors. We asked the question: "Are
there factors that facilitate this type of
response in adults?" In order to answer this
question, we observed subjects' propensity to
catch others' yawning and assessed if this
propensity varied throughout the day. In
addition, we evaluated if the response to yawns
produced by another person (considered a
psychological stimuli) is related to the time
course of spontaneous yawning and sleepiness.
Specifically, the contagious effect of yawning
will be considered in relation to the daily time
course of spontaneous yawning and
sleepiness.
Discussion
Since both the preceding wakefulness
duration and the time of day (circadian rhythm)
regulate sleep (Borbely 1982) and sleepiness
(Akerstedt and Folkard 1995), and possibly
influence yawning frequency (Giganti et al.
2010), we attempted to take into account both
factors. For that reason, we excluded extreme
sleep times and durations (see criteria for
subject selection) and the temporal
distributions of variables were calculated using
clock time (instead of hours preceding bedtime
and following awakening). As expected, the time
course of spontaneous yawning and sleepiness
varies across the daytime. Specifically, the
number of yawns is high between 8:00 and 10:00,
in the morning hours after awakening, and
increases between 21:00 and 23:00, in the
evening hours before sleep onset, paralleling
the time course of sleepiness. These findings
are consistent with what has been documented by
previous research in different populations
(Provine et al. 1987; Baenninger et al. 1996;
Zilli et al. 2007, 2008) and support the strong
relationship among yawning, sleep-wake
transitions, and sleepiness (Giganti et al.
2010).
Our subjects were "infected" by observing
others yawn in each experimental session,
demonstrating that the contagiousness of yawning
is a strong phenomenon that takes place at
different times of the day. Furthermore,
contagious yawning is moderately related to
sleepiness; however this association is weaker
than that observed between spontaneous yawning
and sleepiness, suggesting that other factors,
for instance the propensity to yawn
spontaneously, may influence contagious yawning
to a greater extent.
In order to evaluate to what extent the
contagious yawning production may be influenced
by diurnal variations of spontaneous yawning, we
compared their time courses. Our results showed
that the frequency of both contagious and
spontaneous yawning peaks in the early morning
and in the late evening. However, the two
temporal distributions diverge during early
evening (at 19:30):
the frequency of spontaneous yawning is
significantly lower than that of contagious
yawning. The very low frequency of spontaneous
yawning at this time of day is in agreement with
previous studies (Baenninger et al. 1996; Zilli
et al. 2007, 2008) and it is, interestingly,
consistent with the difficulty of sleeping
during this period ("forbidden zone" for sleep;
Lavie 1986). Moreover, the remarkable difference
between the frequencies of spontaneous and
contagious yawning during early evening suggests
that the probability of yawning while observing
others yawn is not entirely influenced by
diurnal variations of spontaneous yawning. The
time course of contagious yawning is probably
entrained by the spontaneous yawning time
course, but the overlap between the two time
courses is not complete and so this discrepancy
suggests that different mechanisms control
spontaneous and contagious yawning. Studies on
developmental trends in spontaneous (de Vries et
al. 1982; Walusinski et al. 2005; Giganti et al.
2002, 2007) and contagious (Piaget 1951;
Anderson and Meno 2003) yawning, specifically
the asynchrony between the age at which they are
first observed, support this hypothesis.
Our study provides evidence of the
difference between spontaneous and contagious
yawning (Anderson and Meno 2003; Provine 2005)
and suggests that different factors could
influence them. While spontaneous yawning may be
more strictly related to physiological factors
such as changes of vigilance level throughout
the day and sleep / wake transitions, contagious
yawning may also be largely influenced by social
factors (such as the cultural context, the
degree of familiarity between individuals, and
their emotional bond). This is consistent with
the hypothesis that emphasizes the communicative
function of yawning. As recently reported by
Guggisberg et al. (2010, p. 1272), yawning may
be "a non-verbal form of communication that
synchronizes the behavior of a group." Further
studies that investigate the temporal
distribution of contagious yawning under
constant environmental conditions might further
shed light on the autonomy of the production of
contagious yawning with respect to the
propensity to spontaneously yawn.
In conclusion, our findings show that
contagious yawning varies with time of day; it
is more frequent in the early morning, decreases
around noon, and increases again in the evening.
Thus, the time of day should be taken into
account in future studies of the contagiousness
of yawning.
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