Gender-related differences in non-linear phase synchronizations between subthalamic rhythms in Parkinson's disease

The human brain substantially differs between males and females. A recent study demonstrated the existence of significant gender-related differences in the electrical activity (local field potentials, LFPs) recorded from the human subthalamic area in Parkinson's disease. However, these results do not clarify whether these differences are reflected also in the neural network architecture and in the information processing at the basal ganglia level. In this work, we sought for possible gender-related differences in non-linear phase synchronizations between LFP rhythms by means of bispectral analysis. Bispectral analysis of LFP disclosed significant gender-related differences in the non-linear phase synchronizations between rhythms. Our results showed that, besides the already known differences in spectral power of rhythms expressed in the STN area in PD, also the non-linear phase synchronizations between those rhythms differ across genders. In particular, in the absence of levodopa stimulation, males had higher synchronization within the low-frequency band, whereas the pattern of synchronizations between and within the other rhythms was similar. After dopaminergic therapy had restored more physiological dopamine levels, the non-linear phase coupling phenomena were similar between the two genders. Gender-related differences in the phenomenology of PD as well as in LFPs cannot be explained only in terms of modulation of rhythm amplitude. In conclusion, sexual-dimorphism in the central nervous system involves the human STN, not only in terms of amplitude of the oscillatory, but also in terms of non-linear phase synchronizations among rhythms.