Date of Award
Doctor of Philosophy
In the present series of experiments, the possibility that ovarian hormones act differentially on the left and right hemispheres of the adult human brain was investigated through the assessment of several behavioral asymmetries. Lateralized behaviors or performance patterns are believed to arise through underlying functional or neurochemical asymmetries in the brain. Therefore, an asymmetric effect of ovarian hormones on the underlying brain areas may be revealed as an alteration in the laterality of these behavioral patterns.;The first study involved the administration of a battery of visual and auditory perceptual asymmetry tests to a group of young women. Test sessions took place during the menstrual and midluteal phases of the menstrual cycle, associated, respectively, with low and high levels of estradiol and progesterone. On two visual tests there was a significant decrease in accuracy for stimuli presented to the left visual field/right hemisphere at the midluteal phase relative to the menstrual phase. A comparable change was not apparent for right visual field/left hemisphere stimuli. This finding was attributed to reduced efficiency of specific right hemisphere processing areas at higher levels of ovarian hormones.;In the second experiment, a novel paradigm for assessing whole-body turning preferences was developed and tested on a large group of males and females. On average, subjects displayed a rightward turning bias which was significantly stronger in women than in men. The consistency of the bias between two test sessions was greater for males and for females taking oral contraceptives than for naturally-cycling females. This observation raised the possibility that hormonal fluctuations influenced the turning bias of the naturally-cycling women. This possibility was examined systematically in the third study, in which turning bias was evaluated during the menstrual and midluteal phases of the menstrual cycle. Turning bias was shown to be significantly reduced at the midluteal phase, at least among right-turning subjects.;These studies lend tentative support to the hypothesis that ovarian hormones act asymmetrically on brain function. The hormone effects appear to be regionally specific and may be relevant to findings of sex differences in cognitive and motor abilities.
Mead, Larissa Araxe, "Differential Effects Of Ovarian Hormones On The Left And Right Cerebral Hemispheres: Evidence From Perceptual And Motor Asymmetries" (1996). Digitized Theses. 2621.