Publication Type:Book Chapter
Source:Posture, Balance and the Brain, International Workshop Proceedings, p.45-54 (2015)
Keywords:EEG spectra, LORETA, sensory conflict, Standing balance, t-VNS
Transcutaneous vagal stimulation (t-VNS) is a prospective method as a cheap and noninvasive alternative of surgical cervical vagal stimulation widely used for treatment of refractory epilepsy, depression etc. Data on its application in healthy people are scarce. A lot of problems concerning the acting mechanisms and cortical representation are unsolved. We did acute t-VNS and studied the standing balance steadiness, EEG absolute power maps and sources distribution. We found improvement of the steadiness of standing with eyes open (EO), but no changes in the eyes closed (EC) series.
In EO Delta and Theta power in the right frontal area increased and Beta and Gamma bands of EEG absolute power in the left and right parieto-occipital areas also increased, which sustained for 20 min after t-VNS. The distribution of maxima of EEG sources revealed by LORETA showed shifts to the right and occipital direction after t-VNS, while 20 min later the maxima were symmetrically located, but the occipital shift was preserved. Pre-treatment sources during EO were in multisensory fields: the inferior parietal lobule, superior temporal gyrus and precuneus, after t-VNS they were in the inferior parietal lobule, middle temporal gyrus, right posterior cingulate, precuneus, cuneus and right lingual gyrus. After 20 min the maxima of EEG sources were in the inferior parietal lobule, superior and middle temporal gyrus and left insula.
In EC following t-VNS Delta power first decreased in the right frontal and occipital areas and in the central parietal area, 20 min later it was greater than in pre-treatment series in these areas. The results showed an increase of EEG absolute power in the Beta and Gamma ranges mainly in the occipital area and less expressed in the postero-parietal one. The increase was more expressed for Gamma than Beta band similarly to the EO series. However, this increase in Beta and Gamma EEG power in EC was mainly located in the left side of the cortex. After t-VNS we observed shifts of electrical sources locations to the occipital and top parts of the brain. Unlike, during the EO series we observed shift to the lower frequencies in the absolute power cortical maps. After 20 min a tendency to return to the pre-treatment coordinates occurred, the power, increased immediately after t-VNS, dropped much lower than its initial value. The locations of maxima of electrical sources during EC before t-VNS were in the middle and inferior frontal gyrus, right inferior parietal lobule, cingulate and precuneus. Immediately after t-VNS these locations were in the superior temporal gyrus, middle temporal gyrus, precuneus, cuneus and left inferior parietal lobule. After 20 min the locations of the maxima of electrical sources were in the anterior cingulate cortex, medial frontal gyrus, precuneus, cuneus and lingual gyrus.
Our results show that cortical processing of the t-VNS information and its effect on standing balance are quite different during standing with EO compared to standing with EC and that suggests differences due to the pairing of t-VNS with different sensory environment. This hypothesis can explain much of controversies connected with vagal stimulation in animals, healthy people and patients.