The cortical and sub-cortical network of sensory evoked response in healthy subjects

The aim of this study was to find the cortical and sub-cortical network responsible for the sensory evoked coherence in healthy subjects during electrical stimulation of right median nerve at wrist. The multitaper method was used to estimate the power and coherence spectrum followed by the source analysis method dynamic imaging of coherent sources (DICS) to find the highest coherent source for the basic frequency 3Hz and the complete cortical and sub-cortical network responsible for the sensory evoked coherence in healthy subjects. The highest coherent source for the basic frequency was in the posterior parietal cortex for all the subjects. The cortical and sub-cortical network comprised of the primary sensory motor cortex (SI), secondary sensory motor cortex (SII), frontal cortex and medial pulvinar nucleus in the thalamus. The cortical and sub-cortical network responsible for the sensory evoked coherence was found successfully with a 64-channel EEG system. The sensory evoked coherence is involved with a thalamo-cortical network in healthy subjects.

I. Introduction

In non-human primates there have been several studies on anatomical and microelectrode recordings stating that the somatosensory evoked inputs functions with a generalized network of cortical areas. These cortical areas are interconnected either through cortico-cortical connections or thalamo-cortical connections [1]–[3]. But in humans there have been limited number of studies were the complete network responsible for the sensory evoked potentials have been analyzed using dipole source analysis [4], [5]. The involvement of thalamus, brain stem and other cortical areas has been addressed in an MEG study using functional source separation [6]. The functional magnetic resonance imaging (FMRI) also revealed the same cortical areas in response to right median nerve stimulation [7], [8]. In certain studies the sensory evoked coherence were estimated for sensory stimulation and found coherence at the stimulated frequency and there harmonics [9], [10]. In this study, we used a 64-channel EEG system, coherence and a spatial filter technique [11], [12] in healthy subjects to find the complete network of sources responsible for the right median nerve stimulation, in particular, to determine whether the thalamus source could be identified as indicated from non-human primate studies and FMRI studies on humans.