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studies have found that corrugator EMG is related to
unpleasant emotional experience and zygomatic EMG is related
to pleasant emotional experience (i.e., Greenwald, et al.,
1989) .
Ipsilateral corrugator and bilateral zygomatic EMG did
not differentiate the shock from control trials. There are
at least two possible factors that may have contributed to
the lack of the expected finding: the age of the subject
and the gender.
A recent study examining the relationship between age
in the general population on surface EMG of pericranial
muscles provides partial support for the decrease in EMG
with age. Jensen and Fuglsang-Fredriksen (1994) revealed
that EMG activity was significantly decreased in older
individuals during maximal voluntary contraction. These
authors suggest that the decrease in amplitude is related to
decrease in number of muscle fibers along with an increase
in age-related type II atrophy. However, in this study
when subjects were exposed to pain (blood being drawn) and
a cold-pressor test the increase in muscle activity was not
affected by age. This study differs from the present in
that different facial muscles were measured and that they
were measured under voluntary contraction and exposure to
pain. Moreover, the subjects in this study were divided
into four age groups. The oldest group ranged from 55-64
years of age. In the present study, the average age is in