ORIGINAL ARTICLE Sleep characterization of a one-month-old freely moving stumptail macaque (Macaca arctoides): a pilot study M.A. Cruz-Aguilar 1 , I. Ramı´rez-Salado 3 , R.V. Arenas-Rosas 2 , A.M. Santilla ´ n-Doherty 2 & J.I. Mun ˜ oz-Delgado 2 1 Laboratorio de Suen ˜ o, Direccio ´ n de Investigaciones en Neurociencias, Instituto Nacional de Psiquiatrı ´a Ramo ´ n de la Fuente Mun ˜ı ´z, Calz. Me ´ xico-Xochimilco No. 101, Col. Sn Lorenzo Huipulco, Delegacio ´ n Tlalpan 14370, Me ´ xico, D.F. Me ´ xico 2 Linea de Crono-ecologı ´a y Etologı ´a Humana, Direccio ´ n de Investigaciones en Neurociencias, Instituto Nacional de Psiquiatrı ´a Ramo ´n de la Fuente Mun ˜ı ´z, Calz. Me ´ xico-Xochimilco No. 101, Col. Sn Lorenzo Huipulco, Delegacio ´ n Tlalpan 14370, Me ´ xico, D.F. Me ´ xico 3 Departamento de Cronobiologı ´a, Direccio ´ n de Investigaciones en Neurociencias, Instituto Nacional de Psiquiatrı ´a Ramo ´ n de la Fuente Mun ˜ı ´z, Calz. Me ´ xico-Xochimilco No. 101, Col. Sn Lorenzo Huipulco, Delegacio ´ n Tlalpan 14370, Me ´ xico, D.F. Me ´ xico Introduction Non-human primates have a close phylogenetic rela- tionship with humans [1]. Because of this relation, pri- mates have been considered an exceptional mammal model in the scientific study of basic biological pro- cesses such as sleep; superior to rat and cat models [2, 3]. Furthermore, physiological resemblances between human and monkey sleep patterns have been demon- strated. Similarities in electroencephalographic (EEG) sleep activity between adult humans and non-human primates have been described, pointing out the possi- bility that EEG methods of evaluation among these species might be comparable. In a study carried out in an adult Macaca mulatta [4], sleep was classified in non-REM (NREM) and REM sleep states. The NREM sleep was subdivided in four stages: stage 1 is characterized by a slow EEG, lower frequency waves (theta waves) with greater amplitude than in the Wake (W), slow ocular move- ments and decrement of muscular tone. During stage 2 of NREM sleep, theta wave activity continues, but is interspersed with sleep spindles, which are character- ized by frequencies of 12–14 cycles per second (cps), increasing amplitude and a minimal duration of 5 s. It is also known that, during the stage 2 of sleep, K com- plexes; consisting of well defined waves which have a negative sharp component followed by a positive one with a minimal duration of 0.5 s, can be observed. They are clearly generated in the vertex zone and they may or may not be integrated to a sleep spindle. Stages 3 and 4, collectively known as Delta sleep, are defined by lower and larger frequency and amplitude of the EEG, slower ocular movements and a progres- sive drop of muscular tone. REM sleep is defined by low voltage cortical desynchronization of EEG, rapid Keywords Brain development – Macaca arctoides – monkey – sleep – sleep micro-architecture Correspondence Manuel Alejandro Cruz-Aguilar, Instituto Nacional de Psiquiatrı ´a, Laboratorio de Suen ˜ o, Calz. Me ´ xico-Xochimilco No. 101, Col. Sn Lorenzo Huipulco 14370, Me ´ xico. Tel.: (+5255) 5655-2811; fax: (+5255) 5655-9980; e-mail: macrag@gmail.com Accepted March 24, 2009. Abstract Electroencephalographic (EEG) activity during both human and adult primates’ sleep has been proven to be similar and consequently, it could be assessed under similar parameters. However, there is no information regarding this EEG activity in the early stages of development in non- human primates. Therefore, the aim of this study was to describe EEG sleep patterns in a 1-month-old Macaca arctoides with a non-invasive and free-movement method. Sleep stages were initially scored using the criteria of quiet sleep and active sleep. This procedure allowed us to observe gra- phoelements to distinguish sleep phases as described in adult macaques. Afterwards, the final score was recorded following the Slow Wave Sleep and Rapid Eye Movement Sleep criteria. The present results suggest that sleep features of this monkey are similar to those of a 2-month-old human neonate. J Med Primatol doi:10.1111/j.1600-0684.2009.00358.x J Med Primatol (2009) 1–6 ª 2009 John Wiley & Sons A/S 1