Comparisons of PAC strength between two conditions or with a control baseline, similarly to EEG coherence, are often interpreted as falling along an axis of hypo-connectivity to hyper-connectivity (Gonzalez et al., 2016; Hu et al., 2010; Leocani and Comi, 1999). For example, reduced PAC strength has been associated with diminished emotional face discrimination by those with autism spectrum disorder (Khan et al., 2013), lower cognitive functioning scores in patients with mild cognitive impairment (Musaeus et al., 2020), and poor sleep quality in individuals with Insomnia disorder (Guo et al., 2023), while excessive PAC magnitude has been associated with pathological symptoms in obsessive compulsive disorder (Bahramisharif et al., 2016; Treu et al., 2021; Yakubov et al., 2022), and in Parkinson's disease (de Hemptinne et al., 2013; López-Azcárate et al., 2010; van Wijk et al., 2016; Yin et al., 2022). As research into cross frequency coupling in the brain has expanded over the past two decades, this initial interpretation has given way to more sophisticated models where changes in PAC strength have different effects depending on the neural circuits where they appear and in the context of within-frequency and cross-frequency manifestations of neural synchrony (Gong et al., 2022; Stujenske et al., 2014).
