Effect of gender and hand laterality on pain processing in human neonates.
BACKGROUND
Previous studies in adults have reported that handedness and gender can affect pain perception. However, it is currently unclear when these differences emerge in human development. Therefore, we examined prefrontal responses to pain stimulation among newborns during their first acute pain experience after birth.


METHODS
Forty newborns at 4-6 days postnatal age were observed during clinically required blood sampling while prefrontal activation was measured with near infrared spectroscopy. Blood sampling in this study was the first experience of a procedure involving skin breaking for these infants. We divided subjects into a right-hand stimulation group (n=21) and a left-hand stimulation group (n=19), depending on whether blood was sampled from the right or the left hand. A three-way analysis of variance (ANOVA) was conducted to examine the effects of several variables on the magnitude of the oxy-Hb value in response to pain stimulus, including stimulus side (right hand or left hand), gender (male or female), recording side (right prefrontal area or left prefrontal area) and interactions between these variables.


RESULTS
The data revealed a significant effect of stimulus side (F (1, 72)=9.892, P=0.002), showing that the right-hand stimulation induced a greater prefrontal activation than the left-hand stimulation. No significant gender difference or interactions were found.


CONCLUSIONS
Our findings suggest that hand laterality affects pain perception even in neonates. However, gender differences in pain perception did not appear to occur during the neonatal period. Further investigations using brain-imaging techniques are required to identify laterality- or gender-related differences in pain processing in humans.
Department of Nursing Administration/Advanced Clinical Nursing, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan. ozawamio-tky@umin.ac.jp
Mio
M
Ozawa
Katsuya
K
Kanda
Michio
M
Hirata
Isao
I
Kusakawa
Chieko
C
Suzuki
D000704:Analysis of Variance; D005260:Female; D007839:Functional Laterality; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D015997:Neonatal Screening; D010146:Pain / Q000503:physiopathology*; D012737:Sex Factors