P27-S Sex differences and cortical excitability in healthy adolescents

Abstract

Background Sex is known to influence brain development. However, sex differences in cortical excitability and their relationship to motor functions is unclear. Aim We examined the sex related differences in the degree of handedness, left and right motor cortex excitability and manual dexterity. Methods 28 healthy adolescents (age 16–19 years,19 girls) were studied. The degree of right-handedness was determined by the Waterloo Handedness Questionnaire. Motor threshold (MT) of the abductor pollicis brevis was measured on both hemispheres. Box and block test (BBT) was used for manual dexterity. Independent samples t-test was used in statistical analysis. Results There were no differences between sexes in handedness (mean score 27 for girls, 24 for boys) or manual dexterity (78 in girls, 74 in boys for right hand; 75 in girls, 72 in boys for left hand). MT of the right hemisphere was significantly higher in boys (46%) compared with girls (39%) (p = 0.012). The MT of the left hemisphere was also higher in boys (44%) compared with girls (39%) but this did not reach significance (p = 0.077). Discussion Although the handedness or the manual dexterity did not differ between the sexes, the cortical excitability was lower (as indicated by higher MT) in the right (non-dominant) hemisphere in boys. There is a well-established developmental decrease in MT from childhood to adolescence, and the higher MT in the right hemisphere may indicate that cortical development of the boys lags behind the girls. These preliminary results need more power to confirm the findings of sex differences.