In humans, significant progress has been made to link spatial changes in electroencephalographic (EEG) spectral density, connectivity strength and phase-amplitude modulation to neurological, physiological and psychological correlates. In contrast, standard rodent EEG techniques employ only few electrodes which results in poor spatial resolution. Recently a technique was developed to overcome this limitation in mice. This technique was based on a polyimide-based micro-electrode (PBM) array applied on the mouse skull maintaining a significant number of electrodes with consistent contact, electrode impedance and mechanical stability. The present study built on this technique by extending it to rats. Therefore, a similar PBM array, but then adapted to rats, was designed and fabricated. In addition, this array was connected to a wireless EEG headstage allowing the recording in untethered, freely moving rats. The advantage of a high-density array relies on the assumption that the signal recorded from the different electrodes is generated from distinct sources, i.e. not volume-conducted. Therefore, the utility and validity of the array was evaluated by determining the level of synchrony between channels due to true synchrony or volume conduction during basal vigilance states and following a subanesthetic dose of ketamine. Although the PBM array allowed recording with high signal quality, under both drug and drug-free conditions, high synchronization existed due to volume conduction between the electrodes even in the higher spectral frequency range. Discrimination existed only between frontally and centrally/distally grouped electrode pairs. Therefore, caution should be used in interpreting spatial data obtained from high density PBM arrays in rodents.
- high density EEG
- Copyright © 2015, Journal of Neurophysiology