Behavioral and electroencephalographic correlates of the effect of the menstrual cycle on motor imagery practice
Menstrual cycle, motor imagery, action observation, Manual Laterality Recognition Test, motor control, EEG, Mu, Alpha, Beta, ERP, P100, Event-related Negativity, reaction time, accuracy.
Female sex steroids (FSS) have a wide influence on brain functions and pathologies. They can specifically affect the motor system, modulating the excitability of the motor cortex, as well as performance in tasks of dexterity and coordination. There is a lack of studies that investigate its effects on motor cognitive processing. Changes in the amplitude of the electroencephalography (EEG) alpha and beta frequency bands over the frontal, central (mu rhythm) and parietal regions during kinesthetic motor imaging (IM) and action observation (AO) are important measures to investigate the modulation of cortical areas involved in motor planning. Another tool used to investigate cognitive motor processing is the Manual Laterality Recognition Test (TRLM). It is able to modulate the P100 and P300 components of the Event-Related Evoked Potential (ERP) in the EEG and has behavioral measures that allow inferences about cognitive processes related to the spatial manipulation of parts of the body (in this specific case, the hands). This process is known as implicit motor imagery. In this study, we investigated whether
the cortical activity obtained through the EEG and the behavioral measures related to the aforementioned tasks (IM, AO, TRLM) are modulated according to the phases of the menstrual cycle. Thirty-two women of reproductive age participated in this study, which was carried out in a familiarization session and 3 experimental sessions. The FSS comprise estrogen and progesterone and their levels were quantified using the ELISA technique by chemiluminescence in the menstrual (low levels of both), follicular (high levels of estrogen) and luteal (high levels of progesterone) phases. Blood collections for hormonal dosage and experiments with the IM, AO and TRLM protocols were performed in the three phases of the volunteers' menstrual cycle. EEG measurements (for obtaining alpha and beta power, P100-ERP and P300-ERP), reaction time and accuracy were collected during the practice of the tasks. In the statistical analysis, the Friedman test was used to compare the measurements between the phases of the menstrual cycle. Behavioral and electrophysiological measures were also correlated with hormone levels (estradiol and progesterone) through Spearman's correlation and the P value considered was <0.05. The results showed that the desynchronization related to the beta event (beta-ERD) on the bilateral frontal region during the practice of MI was significantly greater in the follicular phase when compared to the menstrual and luteal phases, suggesting the effect of estrogens on the disinhibition of the control areas of motor cognitive processing. Beta-ERD in the medial parietal region and Alpha-ERD in the central medial region were significantly lower in the luteal phase when compared to the follicular and menstrual phases, areas that are related to the vividness of motor imagery. No difference between the phases of the menstrual cycle was observed on alpha-ERD and beta-ERD on the sensorimotor region or on any cortical region studied during the practice of AO, but a positive correlation was found between the amplitude of these frequency bands and estradiol levels in the follicular phase, suggesting the effect of estradiol on the activation of mirror neurons. The behavioral analysis in TRLM indicated better performance during the follicular and luteal phases when compared to the menstrual phase. According to what is observed in the literature, the spatial manipulation of objects is impaired by the ESF. According to the results presented, when the objects to be moved are hands, the FHS favor the task, suggesting its effect on the motor cognitive component present in the task. In the EEG analysis of the TRLM, it was possible to observe a difference between the medial and lateral orientations of the hands in the follicular phase, suggesting greater engagement in the intrinsic motor imagery in this phase of the menstrual cycle.