Ultradian rhythms in the mobility and behavior of rhesus monkeys

The presence of ultradian rhythms in the mobility and behavior of rhesus monkeys was explored in eleven animals equipped with mobility FM transmitters and placed alone or in pairs in laboratory cage situated in a sound proof, temperature controlled room, with food and water ad libitum. After an habituation period of 3 to 7 days, telemetric recordings of the mobility of the animals showed ultradian rhythms with a periodicity of 70 min during the daily 12-h light period. During the corresponding 12-h dark period, there were two dominant cycles of 103-144 min and 48 min respectively. Restriction of food and water to 1h/day did not change the duration of these cycles, and the presence of random noise also had little effect. Spontaneous behavior occurred in regular sequences within each cycle. Social relationships were found to affect rhythmicity of behavior, since pairs of monkeys synchronized their cycles. The lever press response recorded during auto-shaping showed the same rhythmicity found in mobility, demonstrating the influence of ultradian rhythms on learned behavior.