Multiple frequency functional connectivity in the hand somatosensory network: An EEG study

ObjectiveTo investigate the dynamics of communication within the primary somatosensory neuronal network.MethodsMultichannel EEG responses evoked by median nerve stimulation were recorded from six healthy participants. We investigated the directional connectivity of the evoked responses by assessing the Partial Directed Coherence (PDC) among five neuronal nodes (brainstem, thalamus and three in the primary sensorimotor cortex), which had been identified by using the Functional Source Separation (FSS) algorithm. We analyzed directional connectivity separately in the low (1–200 Hz, LF) and high (450–750 Hz, HF) frequency ranges.ResultsLF forward connectivity showed peaks at 16, 20, 30 and 50 ms post-stimulus. An estimate of the strength of connectivity was modulated by feedback involving cortical and subcortical nodes. In HF, forward connectivity showed peaks at 20, 30 and 50 ms, with no apparent feedback-related strength changes.ConclusionsIn this first non-invasive study in humans, we documented directional connectivity across subcortical and cortical somatosensory pathway, discriminating transmission properties within LF and HF ranges.SignificanceThe combined use of FSS and PDC in a simple protocol such as median nerve stimulation sheds light on how high and low frequency components of the somatosensory evoked response are functionally interrelated in sustaining somatosensory perception in healthy individuals. Thus, these components may potentially be explored as biomarkers of pathological conditions.

► This is the first EEG study that investigates functional connectivity between subcortical and cortical structures in the somatosensory pathway. ► Assessment of functional connectivity under median nerve stimulation reveals a time lag of high-frequency oscillations with respect to low-frequency ones. ► Inter-node low-frequency connectivity is modulated by cortico-subcortical feedback.