Hormonal phases affect hemispheric asymmetry in spatial attention

Fluctuating sex hormone levels during the menstrual cycle have been shown to affect functional cerebral asymmetries (FCAs) in cognitive domains, contributing to sex-related differences in functional cerebral organization. This study aims to observe changes induced by anodal tDCS in left parietal cortex on performance in a computer based visual line bisection task and event related potentials across menstrual cycle in fertile compared to menopause women. Twenty-three healthy volunteers (ten fertile women and thirteen menopausal women) were investigated. Subjects were submitted to a computer based line-bisection task (position 1: central; 2 low distance on right; 3 high distance on right; 4 low distance on left; 5 high distance on left): baseline (B), sham (S), tDCS (T), which were randomized in three consecutive months. EEG was recorded by 38 scalp electrodes according to the enlarged 10-20 system. Anodal tDCS was performed on the P3 derivation (cathode on left supra orbital site) (20 min 2 mA intensity). The group of fertile women was investigated during follicular, secretive and menstrual phases. Subjects were instructed to press the computer bar soon after the presentation of the subjective judged central position. The positive component in the time interval between 200-400 msec was evaluated by means of Brain Vision Analyzer 2.0, after a visual inspection and rejection of artifact. In basal condition the GLM test showed a significant increase of P300 amplitude (Phase p=0,002; Condition p=0,00; Phase *Conditions p=0,026) related to the 5 (high distance) target on the left hemisphere in the menstrual phase, compared to the secretive and follicular phases (fig.1). After the left parietal TDCS, the P3 amplitude was similar across the different phases and in relation to the different targets, in all the considered EEG derivations related to 5 line position across the different phases (Figure 2). Post hoc analysis (Bonferroni Test) for Left Latence and Amplitude indicated a significant effect in follicular condition (p =0,00), in secretive condition (p=0,00) and in menstrual condition (p=0,00). In menopause group, analyses for Condition showed in all lateralization channel significant values in A and in L (p<0,05). Post hoc analyses indicated a particular effect for T vs B (p<0,05) in all derivations, in direction of lower latencies and higher amplitudes in T conditions. Analyses for Position showed in all lateralization channels significant values in amplitudes and in L (p<0,05) except in L position. Post hoc analyses indicated a lower latency and higher amplitude in 5 position (p<0,05). We can conclude that hormonal phase can influence spatial perception and it could be in direction of a predominant activation of Left Asymmetry. Furthermore these results are not affected by stimulation like tDCS.