Abstract
Resting-state neural oscillations are used as biomarkers for functional diseases such as dementia, epilepsy, and stroke. However, accurate interpretation of clinical outcomes requires the identification and minimisation of potential confounding factors. While several studies have indicated that the menstrual cycle also alters brain activity, most of these studies were based on visual inspection rather than objective quantitative measures. In the present study, we aimed to clarify the effect of the menstrual cycle on spontaneous neural oscillations based on quantitative magnetoencephalography (MEG) parameters. Resting-state MEG activity was recorded from 25 healthy women with normal menstrual cycles. For each woman, resting-state brain activity was acquired twice using MEG: once during their menstrual period (MP) and once outside of this period (OP). Our results indicated that the median frequency and peak alpha frequency of the power spectrum were low, whereas Shannon spectral entropy was high, during the MP. Theta intensity within the right temporal cortex and right limbic system was significantly lower during the MP than during the OP. High gamma intensity in the left parietal cortex was also significantly lower during the MP than during the OP. Similar differences were also observed in the parietal and occipital regions between the proliferative (the late part of the follicular phase) and secretory phases (luteal phase). Our findings suggest that the menstrual cycle should be considered to ensure accurate interpretation of functional neuroimaging in clinical practice.
Highlights
Advancements in neuroimaging techniques have led to their widespread adoption in the clinical examination of functional brain diseases (Brammer, 2009; Khanna et al, 2015; Hoshi and Shigihara, 2020; Tanoue et al, 2021)
The menstrual cycle is produced by a network between the hypothalamus, pituitary gland, and ovaries, which interact via sex hormones such as gonadotropinreleasing hormone (GnRH), follicle-stimulating hormone (FSH), luteinising hormone (LH), oestradiol, and progesterone (Creutzfeldt et al, 1976; Franz, 1988; Hawkins and Matzuk, 2008; Brötzner et al, 2014; see Figure 1)
Our analysis revealed four major findings: (i) median frequency (MF) and individual alpha frequency (IAF) were lower during menstrual period (MP) than during OP, mainly on the right side of the MEG dewar; (ii) Shannon entropy (SE) was higher during MP than during OP; (iii) theta oscillatory intensity was lower in the right temporal cortex and limbic system during MP than during OP; and (iv) theta oscillatory intensity in the parietal and occipital regions differed between the proliferative and secretory phases
Summary
Advancements in neuroimaging techniques have led to their widespread adoption in the clinical examination of functional brain diseases (Brammer, 2009; Khanna et al, 2015; Hoshi and Shigihara, 2020; Tanoue et al, 2021). Functional changes appear as a slowing down or attenuation of spontaneous neural oscillations during the menstrual cycle, and are accompanied by molecular-related changes in sex hormone levels such as oestradiol and progesterone (Creutzfeldt et al, 1976; Becker et al, 1982; Bazanova et al, 2014; Brötzner et al, 2014) These two alterations have recently attracted attention because they are often observed in patients with cognitive dysfunction, including those with dementia (Ferna and Hornero, 2006; Poza et al, 2007; López et al, 2014; Shigihara et al, 2020a). Given that neural signal processing methods have dramatically improved over the last two decades, further studies are required to explore the influence of the menstrual cycle on neural patterns
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