Abstract
Previous evidence suggests different cortical areas naturally oscillate at distinct frequencies, reflecting tuning properties of each region. The concurrent use of transcranial magnetic stimulation (TMS) and electroencephalography (EEG) has been used to perturb cortical regions, resulting in an observed post-stimulation response that is maximal at the natural frequency (Rosanova et al., 2009; Ferrarelli et al., 2012). These frequencies were reported to progress from high-to-low in a rostro-caudal gradient across the cortex, such that a consistently evoked dominant α-band oscillations (8–12 Hz) occurred in the occipital cortex (BA 19), β-band oscillations (13– 20 Hz) in the parietal cortex (BA 7), and fast β/γ-band oscillations (21–50 Hz) in the frontal cortex (BA 6). Thus far, literature investigating natural frequencies in cortical circuits with TMS-EEG have only been demonstrated in the left hemisphere. Here, we attempted to replicate these previous findings in the right hemisphere by employing TMS-EEG to directly perturb approximately homologous cortical areas in human subjects during a passive state (N=12) and during an active task (N=12) in both sexes. Contrary to previous reports, we found limited evidence of differences in fundamental frequency between stimulation sites; while frequency-specific responses differed between sites, the same features displayed in previous studies were not replicated, such as the rostro-caudal gradient. Instead, each site possessed its own complex pattern of global and local changes in response to stimulation, with the pattern differing per subject. These findings suggest that cortical regions exhibit complex frequency-specific profiles that cannot be described by a hierarchical progression alone.