Tese de mestrado integrado, Engenharia Biomédica e Biofísica (Sinais e Imagens Médicas) Universidade de Lisboa, Faculdade de Ciências, 2021Meditation research has been a topic of increasing interest over the past decades. However, scientific research in this area is experiencing several drawbacks, such as the troublesome definition of meditation, adequate study designs and variable outcomes. In the present study, the physiological changes occurring during meditation practice were evaluated by means of a headband capable of acquiring electroencephalography (Fp1 and Fp2 locations) and photoplethysmography signals simultaneously, using a mobile application. A total of 19 participants were divided in two groups: meditators (10 participants, aged between 34–58 years, with a total experience of 1587.9 ¥ 2814.8 h) and non-meditators (9 participants, aged between 21–61 years). The meditation practices considered in this study were divided into three main categories: focused attention (4 participants), open monitoring (4 participants) and compassion (2 participants). The differences between meditators and non-meditators (control group), meditation practices and the effects of a daily practice as opposed to a regular meditation practice were evaluated. In order to do so, three periods of acquisition were considered, such as baseline, meditation and postmeditation. The main differences between groups for the electroencephalography analysis were found during each period for the relative alpha power band, for the right and left hemispheres and combination of both hemispheres of the prefrontal brain. Additionally, the meditation period in comparison to baseline mainly revealed decreases in the absolute theta, alpha and beta power, as well as a decrease in relative beta power. The control group showed decreases in the same measures but mainly on the right hemisphere. The relative delta power and theta/beta ratio showed an increase between baseline and meditation periods, which may indicate a shift in brain function for greater detachment combined with greater levels of attention for the meditator group. There were no significant differences between the meditation practices nor in the frequency of practice for the electroencephalography analysis. The photoplethysmography analysis revealed lower RR-intervals during each period as well as lower breathing rate during baseline period for the meditator group. The average and maximum heart rate were significantly higher for meditator group. Additionally, the control group showed lower standard deviation of the heart rateand low frequency power during baseline and post-meditation periods in comparison to the meditators.The meditation period mainly revealed increases in the frequency domain measures, for both groups. The focused attention meditation practices revealed greater sympathetic activation in comparison to the open monitoring practices. In summary, meditation practice revealed significant differences between the meditator and control groups, both in brain activity and in cardiac activity, which may imply that its practice over time results in altered traits. Additionally, this study showed that meditation practice alters the physiological signals of electroencephalography and photoplethysmography according to task, i.e. relaxation or meditation, which allows to identify its state effects
