RAPID COMMUNICATION Oscillatory Activity in the Cerebellar Hemispheres of Unrestrained Rats

M E T H O D S Sevento 8-Hz oscillatory activity was seen during behavioral states in which the animal was immobile; any movement the animal Five female albino Sprague-Dawley rats, aged 4–10 mo, were made coincided with termination of the oscillations. However, implanted with microwire electrode arrays, either in left Crus IIa nearly one-third of oscillatory episodes appeared to cease spontane(n Å 3) or in both right and left Crus IIa (n Å 2). During implantaously, in the absence of any observable sensory input or movement. tion animals were anesthetized with xylazine/ketamine-hydrochloOscillations were synchronized both within and between cerebellar ride delivered intramuscularly (70 mg/kg ketamine, 3.5 mg/kg hemispheres, demonstrating precise temporal coordination among xylazine, 0.7 mg/kg acepromazine) and pentobarbital sodium demultiple, bilateral levels of the somatosensory system. We interpret livered intraperitoneally (20 mg/kg). During the surgery five or these data in the context of similar oscillations observed in other six stainless steel screws were placed over neocortical areas and brain structures and suggest that the oscillations are an underlying covered with dental acrylic to form a stable base. Next, Crus IIa dynamic property of the entire somatosensory network. was exposed and the grid of wire electrodes (either 18-mm-diam platinum-iridium or 50-mm-diam stainless steel) was fixed with acrylic above the exposure. The electrodes were lowered and fixed I N T R O D U C T I O N in position, and the receptive field at each recording site was deterIn the awake rat, 7to 12-Hz synchronous activity has mined. During implantation surgery, we confirmed that the rebeen seen at multiple levels of the sensory trigeminal system, sponses were physiologically characteristic of the Crus IIa GCL. The reference electrode was a stainless steel (76-mm diam) wire including the spinal trigeminal nucleus (SpV), ventrobasal laid flat over the entire length of Crus IIa. All animal procedures thalamus (VB), and primary somatosensory (S1) cortex were approved by Caltech’s Animal Use Committee. (Buzsáki 1991; Kandel and Buzsáki 1993, 1997; Nicolelis Field potentials and multiunit activity were recorded from the et al. 1995; Semba et al. 1980, 1984). In addition, it is well most superficial GCL of Crus IIa as in previous experiments established that 7to 12-Hz spindle oscillations occur in (Bower and Kassel 1990). Maximum amplitude responses were many neocortical areas during the early stages of drowsiness found between 400 and 700 mm below the pial surface. A highand sleep (Contreras et al. 1997; Hammond et al. 1979; input-impedance preamplifier (Microprobe, CFP-1020) mounted Kandel and Buzsáki 1993, 1997; Steriade and Deschenes directly on the animal’s head carried neural signals to a custom1984; Steriade and Llinás 1988). In this study, we examined built amplifying system with a minimum of mechanical and electrioscillations in tactile regions of the granule cell layer (GCL) cal artifact. Signals were amplified and filtered in analog between 1 Hz and 5 kHz and collected at a ¢10-kHz sampling rate. Neural of the lateral cerebellar hemispheres (Crus IIa) in unredata were synchronized with behavioral data in real time with the strained rats. This cerebellar folium receives projections use of a custom-built video mixer (Rasnow et al. 1997). During from S1 via the pontine nuclei (Bower and Woolston 1983; subsequent computer analysis, data were digitally filtered either Brodal 1983; Mihailoff et al. 1981) as well as direct tactile between 1 and 300 Hz (field potential activity) or between 300 input from the trigeminal sensory nuclei (Huerta et al. 1983; and 3,000 Hz (multiunit burst activity) . To detect and quantify Watson and Switzer 1978; Woolston et al. 1981, 1982). Our periods of oscillation, continuous neural recordings were divided results demonstrate clear 7to 8-Hz field potential oscillainto 1-s trials and processed through a standard fast Fourier transtions in the GCL of Crus IIa, synchronized both within and form (FFT; Matlab v5.0.