Behavioural Brain Research 116 (2000) 55 – 59 Research report Effect of slow-wave sleep deprivation on topographical distribution of spindles Luigi De Gennaro *, Michele Ferrara, Mario Bertini Dipartimento di Psicologia, Sezione di Neuroscienze, Uniersita ` degli Studi di Roma ‘La Sapienza’ Via dei Marsi, 78, 00185 Roma, Italy Received 27 January 2000; received in revised form 26 May 2000; accepted 26 May 2000 Abstract Spindle activity, visually scored in the 12 – 15 Hz range over antero-posterior midline derivations, has been assessed in ten normal subjects during a baseline and a recovery sleep after 2 nights of selective slow-wave sleep (SWS) deprivation. The recovery sleep, characterized by a significant increase of stage 4 and SWS as compared to the baseline, revealed that sleep spindles are reduced in the first NREM sleep cycle. The size of this reduction in spindle density progressively decreased in the course of the night, paralleling the depletion of SWS rebound. Topographical distribution of spindle activity showed a global linear increase over consecutive NREM-REM sleep cycles, regarding to the whole antero-posterior midline EEG derivations except the occipital one. It is concluded that the SWS rebound after 2 nights of selective SWS deprivation is associated with a reduction of spindles during stage 2. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Sleep spindles; Slow wave sleep (SWS) deprivation; SWS rebound; Topographical distribution; Intra-night variations; Sleep cycles www.elsevier.com/locate/bbr 1. Introduction Recent neurophysiological findings have enhanced the interest in changes of sleep spindles: variations of the membrane potentials in the thalamocortical net- work oscillate in the frequency range of spindles at an intermediate level of hyperpolarization and in the fre- quency range of delta at an higher level of hyperpolar- ization [19]. It has been hypothesized that a close relationship between changes at neuronal level in the thalamocortical network and at the level of macro- scopic EEG, with a reciprocal relationship between sleep spindles and slow waves [20,5]: the increasing hyperpolarization of thalamocortical neurons when sleep begins [11] should generate first the spindle activ- ity during stage 2 and, later, the prevalence of delta rhythm during slow-wave sleep (SWS). Quantification of EEG in the frequency range of delta and sigma by means of fast Fourier transform (FFT) shows the existence of an inverse relationship between sigma and delta activity [1,6,21]. Furthermore, power density in the frequency range of sleep spindles has been demonstrated to be higher during stage 2 than SWS [3,5,14]. The procedure of sleep deprivation allows a direct assessment of this inverse relationship since it is well known that delta EEG activity increases after total sleep deprivation [3,5] and partial sleep deprivation [2,4,7]. Contrasting results have been provided by the only two studies that analyzed the relationship between delta and spindle activity after total sleep deprivation: in humans, power spectra analysis and transient pat- terns detection algorithms revealed that spindle activity was reduced in the recovery night after 40 h of wakeful- ness, while delta activity was enhanced [5]; in the cat, total sleep deprivation enhanced slow-wave activity (SWA) but did not reduce spindle activity in the corti- cal EEG, while EEGs derived from thalamic structures showed an inverse relationship between these two activ- * Corresponding author. Tel.: +39-06-49917647; fax: +39-06- 4451667. E-mail addresses: degennaro@uniroma1.it (L. De Gennaro), fer- raram@uniroma1.it (M. Ferrara), bertini@uniroma1.it (M. Bertini). 0166-4328/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII:S0166-4328(00)00247-3