Hemispheric lateralization

Females and males differ in several features of their spindle oscillations, as well as in the hemispheric lateralization of their neurocognitive processes. In addition, the hemispheric lateralization of cognitive functions was shown to vary in an age-dependent manner. In spite of the above knowledge, data on the hemispheric lateralization of these oscillatory phenomena are scarce and no sex differences or age effects in the hemispheric lateralization of sleep spindles were reported. Here, we aim to fill this gap by the description of the hemispheric lateralization of sleep spindles in healthy human subjects. Data sets from three research groups were unified (N = 251, age range: 4−69 years, 122 females) in this retrospective multicenter study. The amplitude, density, and duration of slow (frontally dominant) and fast (centroparietally dominant) spindles were analyzed using the individual adjustment method. Hemispheric lateraliza-tion was quantified by the (L − R)/mean (L, R) index. Orbitofronto-temporo-occipital and parietal fast sleep spindle measures are left lateralized, while prefrontal spindle amplitude is characterized by right hemispheric dominance. Left lateralization of fast spindle density and duration in the temporal and orbitofrontal regions, respectively, increases as a function of age in males, but not in females. In turn, females are characterized by higher left hemispheric dominance in occipitally measured fast spindle durations as compared with males. Sleep spindles are asymmetrically distributed over the two hemispheres. This phenomenon is sexually dimorphic and region-specific perhaps indexing sex differences in neurocognitive architectures.

Introduction: Based on the previous studies, we know that the hemispheric lateralization
defects, increase the probability of psychological disorders. We also know that dominant limb is
controlled by dominant hemisphere and limb preference is used as an indicator for hemisphere
dominance. In this study we attempted to explore the hemispheric dominance by the use of three
limbs (hand, foot and eye).
Methods: We performed this survey on two samples, psychiatric patients compared with normal
population. For this purpose, knowing that the organ dominance is stabilized in adolescence, and
age has no effect on the people above 15, we used 48 high school girls and 65 boys as the final
samples of normal population. The patient group included 57 male and 26 female who were
chronic psychiatric patients.
Results: The result shows that left-eye dominance is more in patients than the normal
group(p=0.000) but the handedness and footedness differences are not significance. In psychotic,
bipolar and depressive disorders, eye dominance had significant difference (P= 0.018). But this
is not true about hand and foot dominance.
Discussion: Our findings proved that generally in psychiatric patients, left-eye dominance is
more common, left-eye dominance is also more in psychotic and depressive disorders. It is less
common in bipolar disorders. Key words: hemispheric lateralization, limb dominance, mental
disorders.