Saccadic characteristics of monozygotic and dizygotic twins before and after alcohol administration

To evaluate the degree of heritability in the latency, accuracy, and peak velocity of reflexive saccades in young adult monozygotic (MZ) and dizygotic (DZ) twins before and after the administration of a single dose of ethanol. Saccades were recorded using a scleral search coil before and after alcohol consumption, and data were analyzed offline. Estimates of heritability based in intraclass correlations (ICCs) and using a maximum likelihood estimates of genetic variance were calculated for the saccadic measures made before and after alcohol, as well as for the changes in latency, accuracy, and velocity. Intraclass correlations for MZ twins (rMZ) were highly significant; those for DZ twins (rDZ) were not significantly different from zero. This disparity between rMZ and rDZ suggests either multiple gene interactions or in utero environmental differences in the MZ twins. Alcohol significantly prolonged latency, reduced accuracy, and lowered peak velocity. Although the changes after alcohol were not significant, heritability values increased in all three measures after alcohol administration. Latency, accuracy, and peak velocity appear to be controlled by multiple genes or to depend on prenatal environmental factors. Even a single low dose of alcohol appeared to enhance heritability measures. Differences seen between ICCs for latency, accuracy, and velocity after alcohol administration suggest that developmental control of the neural mechanisms underlying each measure may vary.