High frequency synchrony in the cerebellar cortex during goal directed movements.

The cerebellum is involved in sensory-motor integration and cognitive functions. The origin and function of the field potential oscillations in the cerebellum, especially in the high frequencies, have not been explored sufficiently. The primary objective of this study was to investigate the spatio-temporal characteristics of high frequency field potentials (150-350 Hz) in the cerebellar cortex in a behavioral context. To this end, we recorded from the paramedian lobule in rats using micro electro-corticogram (µ-ECoG) electrode arrays while the animal performed a lever press task using the forelimb. The phase synchrony analysis shows that the high frequency oscillations recorded at multiple points across the paramedian cortex episodically synchronize immediately before and desynchronize during the lever press. The electrode contacts were grouped according to their temporal course of phase synchrony around the time of lever press. Contact groups presented patches with slightly stronger synchrony values in the medio-lateral direction, and did not appear to form parasagittal zones. The size and location of these patches on the cortical surface are in agreement with the sensory evoked granular layer patches originally reported by Welker's lab (Shambes et al., 1978). Spatiotemporal synchrony of high frequency field potentials has not been reported at such large-scales previously in the cerebellar cortex.

Differential effects of ketamine/xylazine anesthesia on the cerebral and cerebellar cortical activities in the rat.

Cerebellum is a highly organized structure with a crystalline morphology that has always intrigued neuroscientists. Much of the cerebellar research has been conducted in anesthetized animals, particularly using ketamine/xylazine combination in rats. It is not clear how and to what extent the cerebellar cortical circuitry is affected by this anesthesia. In this study, we recorded spontaneous and evoked potentials from the cerebellar surface with chronically implanted, flexible-substrate, multielectrode arrays in rats and compared them to the signals simultaneously recorded from the motor cortex with similar electrodes. The power spectra and the intercontact coherence plots of the spontaneous activity in the awake-quiet animals extended up to 800 Hz in the cerebellum and only up to 200 Hz in the motor cortex. Ketamine/xylazine anesthesia suppressed most of the activity in the cerebellar cortex, which was in clear contrast to the motor cortex. In the awake cerebellum, large coherence values were observed between contact pairs as far apart as ∼2 mm. Otherwise, there was not a discernable relation between the coherence and the intercontact distance. These results suggest that the surface electrodes can provide much more detailed information about the state of neural circuits when they are used on the cerebellar cortex compared with the cerebral areas. This may be due to the proximity of the molecular layer cells to the pial surface in the cerebellum.

Effect of anesthesia on spontaneous activity and evoked potentials of the cerebellar cortex.

Cerebellum is a highly organized structure with a crystalline morphology that has always intrigued neuroscientists. Much of the cerebellar research has been conducted in anesthetized animals, particularly using ketamine and xylazine combination. It is not clear how the cerebellar cortical circuitry is affected by anesthesia. In this study, we have recorded spontaneous and evoked potentials from the cerebellar surface with chronically implanted, flexible-substrate, multi-electrode arrays. The frequency contents of the spontaneous activity suggest that ketamine/xylazine anesthesia suppresses most of the components except those below 30 Hz. This preliminary study also showed that multi channels of cerebellar cortical activity can be recorded using flexible multi-electrode arrays in behaving animals, which is very challenging task with single microelectrodes.

Signal characteristics of cerebellar activity recorded with 2D micro-electrode arrays.

Recordings were performed on the rat paramedian lobule of the cerebellum with a surface micro-electrode array during hand licking and quiet states. The Fast Fourier Transform (FFT) and average coherence both showed a change in the frequency distributions between active and quiet conditions. The signals were segregated into different frequency bands and the signal compositions were analyzed. In each of the bands an increase in neural activity was seen at the onset of activity. Frequency coherence analysis was performed between electrodes at two different separations for active and quiet conditions. The coherence analysis showed that there was an increase in coherence for shorter distances and during activity.