Examination of Attention Level in Nurses Working Night Shifts in terms of the Relationship between Electrodermal Activity and Sex Hormones.

INTRODUCTION: Electrodermal activity (EDA) is an electrical activity of eccrine sweat gland stimulated by the sympathetic nervous system. Skin conductance level (SCL) is measured with EDA. SCL and sweat gland activity increase in emotional situations, such as high activation, attention or stress. In this study, we investigated whether working in shifts affects attention level of nurses with EDA and explored the relationship between EDA and sex hormones. METHOD: The study was carried out on nurses working night shifts (16.00-08.00 h) (n=22) and nurses working without a shift (08.00-16.00 h) (n=20). Firstly, The Epworth Sleepiness Scale which evaluates a person's daytime sleepiness was applied to the subjects. For EDA measurement, Ag/AgCl electrodes were put on two fingers of their dominant hand. SCL was measured via MP30 system and GSR connection. The blood samples were analyzed for cortisol and ACTH hormone levels to investigate the changes in sleep and circadian rhythm. RESULT: It was found that there was no statistically significant difference in skin conductance levels between the groups. Moreover, in the comparison of hormone values between the groups, the cortisol levels in night shift nurses were higher than in those working without a shift. CONCLUSION: Night shift had no significant effect on the attention levels in the nurses. This situation is thought to be related to the fact that the nurses responsible for the night service raise their attention level to the highest point. The reason for higher level of cortisol in nurses working shifts may reflect that cortisol has no effect on the breadth of attention but reflects a high level of stress.

Dynamics of manual skill: a computerized analysis of single peg movements and stochastic resonance hypothesis of cerebral laterality.

Hand skill was analyzed using a computerized peg moving task. The durations of single hand movements (PMTs) were accurately measured in right-hand (RH) and left-hand (LH) writers. One trial consisted of 10 movements of the right hand and 10 movements of the left hand. Each participant performed five trials. Women showed significantly higher percentage than men in right-handedness; men showed higher percentage than women in left-handedness. This sex difference completely disappeared after taking the same height range in participants. The mean RH- and LH-PMTs decreased in 5 successive trials, even within a single trial during 10 successive hand movements, indicating a learning effect of repeated hand movements. The LH- minus RH-PMTs exhibited fluctuations within a single trial between positive (faster right hand) and negative (faster left hand) values. LH-RH PMTs were significantly greater than zero, in favor of right hand, in RH-writers, but not significantly different from zero in LH-writers, exhibiting a true fluctuating asymmetry. Participants with no familial sinistrality (FS-) were preponderantly right-handed (ca. 90%), those with left-handed mother and right-handed father (FS+1) showed stochastic distribution of hand preference (50:50). Participants with right-handed mother and left-hander father (FS+2) were not different from FS- individuals. LH-RH PMT was significantly greater than zero in FS- participants, almost equal to zero in FS+1 participants, and greater than zero in FS+2 participants exhibiting greater asymmetry than that in FS- participants. These results suggest a genetic inheritance of direction and degree of handedness, being a a X-linked trait originating from mother's genotype. It was suggested that fluctuating asymmetries may reflect interactions between stochastic resonance phenomena within right and left brains. This property of brain may genetically transmitted from mother's X chromosome; a net effect of stochastic interactions between hemispheres may result in right- or left-handedness, a predominantly unidirectional coupling creating right-handedness, in favor of left brain, and a stochastic bi-directional coupling between hemispheres would be a main trait of left-handers. This new "stochastic resonance hypothesis of cerebral laterality" concerns with stochastic fluctuations in hand-skill asymmetry and inter-hemispheric coupling through corpus callosum, and seems to be important for new developments in handedness research.

Sexual dimorphism in relations of blood growth-hormone levels to body and brain weights in newborn rats.

The growth promoting effects of growth hormone (GH) are well-known. However, the studies in this respect did not consider the sexual dimorphism. The adverse--growth limiting--GH effects were also reported in human newborns (see Tan, 1992, 1995; Tan et al., 1998). A similar study was replicated in the newborn rat pups in the present work. The serum GH level, body weight, body height, right- and left-brain weights were measured just after birth in rat pups. The relations of the serum GH levels to the bodily measurements were found to be sexually dimorphic. Namely, there were no significant correlations between the serum GH levels and the body size (weight and height) in males, whereas there were inverse relations between these parameters in females. The GH level negatively linearly related to the right-, left-, and right- minus left-brain weights in females, whereas only the right-brain weight positively linearly correlated with the serum GH level, the right- minus left-brain weight being also positively linearly correlated with the serum GH level in males. The results suggested that the sexual dimorphism should be taken into consideration in studies concerning the global GH effects. The relation of the serum GH level to the right-left brain asymmetry, also sexually dimorphic, suggests a role of GH in cerebral lateralization.

Hand preference in Turkish population.

The distribution of hand preference (self report) was studied in siblings and their parents originating from all parts of Turkey (N = 22,461). In total sample and siblings, there were significantly more right-handed women than men, and significantly more left-handed men than women--no significant sex difference for parents' handedness. The relative number for the right-handed parents significantly exceeded that for the right-handed siblings; the relative number for the left-handed siblings significantly exceeded that for the left-handed parents. It was concluded that there may be a sex difference in hand preference, but being only about 1% more left-handed men, and only about 1% more right-handed women; the right-handedness in new generation (siblings) is less than that in old generation (parents), due to freeing from cultural pressures against the left-hand use in everyday activities.

Population-level right-paw preference in rats assessed by a new computerized food-reaching test.

We re-studied the distribution of paw preference in rats using a new computerized food-reaching test, which recorded the times and time intervals between the single right- and left-paw entries. Using the traditional food-reaching test, we found that of 144 rats, 72.7% were right-handed, 19.7% left-handed, and 7.6% mixed-handed. This population-level J-shaped right-hand preference did not fit a binomial chance distribution (25:25:50). Of right -handers, 99.5% first used their right paw and 0.5% left paw; of left-handers, 98.6% first used their left paw and 1.4% right paw. Of mixed-handers, 59% first used the right paw and 41% left paw for food reaching. The time interval between putting the rat into the test cage and the first right-paw entry was significantly shorter than the first left-paw entry in total sample. Males were faster than females (shorter time intervals between right- or left-paw entries). The distribution of the time intervals between right- or left-paw entries was inverse J-shaped, which exhibited a normal distribution after taking the logarithms of the time intervals. There was no significant difference between time intervals for the left-paw entries; time intervals for the right-paw entries were significantly shorter in males than females, accentuating the role of the left brain for sex differences in motor control. The results suggested that humans are not unique in population-level right-hand preference; our new method would be suitable for new developments in handedness research.

Differential contributions of right and left brains to paw skill in right- and left-pawed female rats.

Paw preference and paw frequency was studied in female rats. Paw preference was assessed using a modified version of food reaching task in quadrupedal position. Of 68 rats, 56 (82.4%) were right-handed, 7 (10.3%) were left-handed, and 5 (7.4%) were mixed-handed. There were significantly more right-handers than left-handers. The distribution of right minus left (L) paw reach (R + L = 50) was not U-shaped, it was J-shaped like in humans. Estrus cycle was a significant factor influencing the right-paw entry scores: most of left-handers were in estrus and proestrus, most of left -handers were in estrus, and most of mixed-handers were in postestrus. In right- and non-right- handers, the frequency of right-paw usage (right-hand skill) increased linearly with testing days, but the frequency of left-hand usage (left-hand skill) did not show significant changes with the successive testing days. Controlling for body weight and estrus only accentuated these results. It was concluded that distribution of hand preference in rats is J-shaped and there is a right-sided population bias in handedness in rats like in humans. The results suggested that motor learning in paw skill is mainly involved the left brain in right- and mixed-handed rats, not the right brain: only the left brain has the inbuilt capacity for motor learning in female rats. Such an asymmetric cognitive control in an animal model may have a major impact in many aspects of biology in respect to normal functioning, superior talents, and disease (see Geschwind, 1985).