J Neurophysiol (April 1, 2003). 10.1152/jn.00728.2002
Submitted on Submitted 26 August 2002; accepted in final form 4 December 2002

Evoked Oscillations in the Thalamo-Cortical Auditory System Are Present in Anesthetized but not in Unanesthetized Rats

Laboratoire de Neurobiologie de l'Apprentissage de la Mémoire et de la Communication (NAMC), Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8620, Université Paris-Sud, Orsay, France

Cotillon-Williams, Nathalie and Jean-Marc Edeline. Evoked Oscillations in the Thalamo-Cortical Auditory System Are Present in Anesthetized but not in Unanesthetized Rats. J. Neurophysiol. 89: 1968-1984, 2003. Over the last decade, a large number of studies have characterized stimulus-evoked oscillations in the visual cortex of anesthetized and unanesthetized animals. Comparatively, only a few studies have been performed in auditory cortex. This study compared the tone-evoked oscillations detected from the same recording sites in the thalamo-cortical auditory system of unanesthetized and anesthetized rats. Simultaneous multiunit recordings were collected in auditory cortex, auditory thalamus, and the auditory sector of the reticular nucleus of restrained rats, which spontaneously shifted from waking (W) to slow-wave sleep (SWS) and paradoxical sleep (PS). Subsequently, the same recording sites were tested under pentobarbital anesthesia, then under high doses of diazepam, and finally under urethan anesthesia. Under these drugs, oscillations were detected in 54% of the recordings: one-half of them were stimulus-locked oscillations and were directly observed on peri-stimulus time histograms (PSTHs); one-half of them were non-stimulus-locked oscillations and were detected on autocorrelograms. Spontaneous oscillations were present for 17% of the recordings. During SWS, only non-stimulus-locked oscillations were observed for a small percentage of recordings (12%). This percentage did not differ significantly from the one of spontaneous oscillations obtained during SWS (8%). No oscillations were found in W and PS. Both under anesthesia and in SWS, the frequency range of the oscillations was 5-15 Hz, and there was no frequency difference between evoked and spontaneous oscillations. Although surprising, the absence of oscillations in awake animals may allow each neuron to process acoustic information independently of its neighbors and may in fact benefit auditory perception.