Academic journal article Pre- and Peri-natal Psychology Journal

Prenatal Stress and Handedness among Offspring

Academic journal article Pre- and Peri-natal Psychology Journal

Prenatal Stress and Handedness among Offspring

Article excerpt

ABSTRACT: Stressful experiences recalled by 270 mothers beginning a year prior to pregnancy through to the end of pregnancy were compared for right, left, and mixed handed offspring of both sexes. For the male offspring, mothers of left handers recalled significantly more severe stress throughout pregnancy than mothers of either right or mixed handers. For the female offspring, no significant differences were found. Results were interpreted as consistent with the view that stress hormones secreted by the mother during pregnancy can significantly affect the hemispheric functioning of the neocortex of offspring.

Stress hormones-such as adrenaline, Cortisol, corticosterone-produced and secreted by mother mammals during pregnancy have been shown to reach the fetus(es) via the placenta (Zarrow, Philpott, & Denenberg, 1970). It has been well established that stress hormones interfere temporarily with the synthesis and release of sex hormones, particularly testosterone (Davidson, Smith, & Levine, 1978; Harding, 1981; Ward & Weisz, 1984; Anderson, Rhees, & Fleming, 1985; Delahant & Mellsop, 1987).

Several lines of evidence indicate that prenatal exposure to sex hormones, especially testosterone, are involved in organizing the hemispheres of the neocortex (Dawson, 1977; Geschwind, 1984; Diamond, 1988). In particular, exposing the brain to high levels of testosterone (and/or its metabolite, estradiol) during fetal development seems to shift the normal tendency for the left hemisphere to dominate in higher thought and fine motor control at least partially to the right hemisphere (Levy & Levy, 1978; Diamond, 1984). This would help to explain why, in humans, males have been often observed to be somewhat more left or mixed handed than females (e.g., Annett, 1970; Oldfield, 1971; Teng, et al., 1976; Le Roux, 1979; Lewkowicz & Turkewitz, 1982).

The above lines of evidence lead one to suspect that maternal stress during pregnancy (prenatal stress) might alter handedness (and possibly other aspects of sidedness) of offspring. In support of this hypothesis, a recent study of rats showed that male offspring of mothers subjected to stress during pregnancy were unusually prone to lead with the left, instead of their right, paw (Fleming, Anderson, Rhees, Kinghorn, & Bakaitis, 1986). Two other studies of rats have found that prenatal stress alters the rate of dopamine turnover in various regions of the right hemisphere Of offspring in ways that are likely to reduce the normal degree of left cerebral dominance (Friede & Weinstock, 1987, 1988).

The present study was undertaken to determine if stress experienced by human mothers during pregnancy would be related to the handedness of their offspring in adulthood.

METHOD

As part of a larger study primarily designed to discover whether or not prenatal stress was associated with variations in sexual orientation, 270 mothers and their offspring were recruited to complete anonymous questionnaires which could be matched according to a common code number appearing on both the mother's and offspring's forms (Ellis, Ames, Peckham, & Burke, 1988). Because the primary aim was to identify prenatal factors related to sexual orientation of offspring, homosexual and bisexual offspring were purposely over-sampled, constituting approximately 30% of the male offspring and 10% of the female offspring (Ellis, Burke, & Ames, 1987).

Mothers ranged in age from 36 to 77 years, with a mean of 51.5 (SD = 8.6). Offspring ranged in age from 19 to 50, with a mean of 25.5 (SD = 6.5). Nearly all of the mother/offspring pairs (98%) were Caucasian, and 56% of the offspring listed north-midwestern states as the place of birth, with the remainder scattered throughout the rest of the United States.

Mothers responded to a 6-page questionnaire, three pages of which were devoted to inquiries about emotional stress during all three trimesters of pregnancy as well as during the year preceding pregnancy. …

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