Neuronal correlates of sleep, wakefulness and arousal in a diurnal insect

Abstract

The discovery that various states of sleep, rest, wakefulness and arousal in man can be correlated with specific forms of the electroencephalogram¹ has led to intensive studies of these states, mostly in mammals^2–5. Today it is generally accepted that circadian sleep-wakefulness cycles occur in mammals and birds^2,3,6. Behavioural observations on sleep in moths have also been published⁷; many other invertebrates demonstrate rest/activity cycles⁸. Circadian sensitivity fluctuations in both central⁹ and peripheral^10–15 components of the visual system of various nocturnal arthropod species have been demonstrated. We now report that long-term, extracellular, single-unit recordings from optomotor interneurones in the optic lobes of forager honey bees reveal an oscillation in their sensitivity to moving visual stimuli^16,17. The oscillation displays properties typical of a circadian rhythm^6,18. The sensitivity of the neurones is higher during the subjective day than during the subjective night. The locomotor activity of individual, fixed walking forager bees shows a similar circadian oscillation and is also higher during the subjective day. Visual and mechanical stimuli can act directly on the interneurones and restore their sensitivity during times of reduced neuronal responsiveness. A comparison with results available for mammals makes it likely that the neuronal phenomena presented here are correlates of the bee's circadian sleep-wakefulness rhythm.