Preterm infants prefer to be awake at night Fiorenza Giganti a , Igino Fagioli a , Gianluca Ficca b , Giovanni Cioni c , Piero Salzarulo a, * a Department of Psychology, University of Florence, Via San Niccolo ` 93, 50125 Firenze, Italy b Department of Psychology, II University of Naples, Via Vivaldi 43, 81100 Caserta, Italy c Division of Child Neurology and Psychiatry, University of Pisa and Stella Maris Foundation, Pisa, Italy Received 20 June 2001; received in revised form 23 July 2001; accepted 25 July 2001 Abstract Wakefulness distribution during a 24-h period was studied in ten low-risk preterm and near term infants through video-recording. The highest amount of wakefulness was found in the night-time period between 02:00 and 05:00 h. This result is different from what was observed in infants during the first year of life, and similar to what was found in the foetus. q 2001 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Preterm; Wakefulness; Motility; Biological rhythms Lavie [8] showed that in the adult a ‘forbidden zone’ for sleep, i.e. a time when the subject is more likely awake (whatever his previous sleep-wake history), exists in the evening. Recently, we found that, in their first year of life, full- term infants show the greatest amount of wakefulness at the same hours of the adult [4]; thus, we proposed that the ‘forbidden zone’ for sleep might start to emerge quite early during development. As for previous ages, a preliminary study [3] showed in preterm infants a higher amount of wakefulness at night- time than at day-time. Here we look closer at the 24-h waking distribution of preterm and near-term babies, by using the same time inter- vals adopted for full-term born infants in their first year of life [4], in order to assess the existence of a favoured time of wakefulness at such an early epoch of development. Ten low-risk infants (five males, five females) were selected among those admitted to the neonatal ward of the University of Pisa, according to previously published criteria [3], suitable to exclude any clinical complication. Mean gestational age was 36 weeks (range 33–39). Post- menstrual age at recording ranged from 34 to 40 weeks; postnatal age from 3 days to 4 weeks. All infants were observed and video-recorded in the incu- bator, located in a quiet room of the neonatal ward; older infants, already in a cot, were put back into the incubator at neutral temperature for the recording, which began after about 30 min of adaptation. A S-VHS video-camera, posi- tioned approximately 1 m above the incubator, at an angle of 458, and a video-recorder (Panasonic SG-DP200) were used. Infant’s behaviour and all interventions (medications, feed- ings etc) carried out by the neonatal ward staff were recorded at normal speed. Nutrition was provided either by oro-gastric tube or by bottle. Feedings were scheduled at every 3–4 hours in all cases. All observations began in the morning between 09.00 and 10.00 h and lasted about 24 h (mean 21.6, range 19.8–24.1). Light intensity was maintained at full light during the day (range of light intensity measured in lux (lumen/m 2 ); 1000– 2200), and was reduced during the night (range 30–1000 lux). During off-line analysis of the videos, minute-by-minute codes were given to infant activity, using a coding system based on the observation of neonatal motility and its rela- tionship to behavioural states reported by Stefanski et al. [12] and Hadders-Algra et al. [5]. Four motility patterns were distinguished [3]. In particular, the pattern character- istic of wakefulness has been defined as follows: presence of gross generalised body movements, often forceful, varying in speed and amplitude, with prolonged startles, marked stretching and writhing. The pattern characteristics of crying were: presence of generalised body movements, usually vigorous, forceful and abrupt; high frequency tremor some- times superimposed upon movements; frequent and regular contractions of the diaphragm also possible [5,12]. No coding was given in case of technical problems Neuroscience Letters 312 (2001) 55–57 0304-3940/01/$ - see front matter q 2001 Elsevier Science Ireland Ltd. All rights reserved. PII: S0304-3940(01)02192-9 www.elsevier.com/locate/neulet * Corresponding author. Tel.: 139-55-2491604; fax: 139-055- 2345326. E-mail address: salzarulo@psico.unifi.it (P. Salzarulo).