Local sleep: a spatial learning task enhances sleep in the right hemisphere of domestic chicks (Gallus gallus)

Abstract

During sleep, domestic chicks (Gallus gallus) show brief and transient periods during which one eye is open while the other remains shut. Electrophysiological recordings showed that the hemisphere contralateral to the open eye exhibited an EEG with fast waves typical of wakefulness, whereas the hemisphere contralateral to the closed eye exhibited an electroencephalogram (EEG) typical of slow-wave sleep. We investigated the time spent in sleep and in monocular-unihemispheric sleep (Mo-Un sleep) following the learning of a spatial discrimination task. A group of experimental chicks from days 8 to 11 post-hatching were trained singly to select one container among four, having a hole on the top (making food available) and positioned in a corner of a rectangular arena. Chicks of the control group did not learn the task because all four containers had a hole on the top and therefore chicks could randomly select any one of them. Experimental and control chicks underwent the same number of trials. Experimental chicks had more total time spent sleeping than control chicks. Experimental chicks spent more time in left Mo-Un sleep, which would be connected with a dominance of the right hemisphere during learning trials. Control chicks showed no eye closure bias at days 8 and 9; however, a slight bias for more right eye closure at days 10 and 11 was observed, suggesting that there was an absence of hemispheric dominance during the first 2 days of control trials and a dominance of the right hemisphere during the last 2 days of control trials. Overall, chicks that learned the spatial task slept significantly more than chicks that were exposed to the experimental paradigm but did not learn the task. This suggests that the Mo-Un sleep pattern showed by experimental chicks is a type of local sleep associated with a process of functional recovery and/or with consolidation of memory in the right hemisphere, which would be mainly engaged during training trials.

Local sleep homeostasis in the avian brain: convergence of sleep function in mammals and birds?

“…Moreover, this suggests that eye state alone may not be a good indicator of local sleep homeostasis, at least in pigeons under these conditions [50].…”

Monocular learning of a spatial task enhances sleep in the right hemisphere of domestic chicks (Gallus gallus)

“…Control chicks that did not learn the task showed no eye-closure bias at the Wrst 2 days of training and a slight bias for more right eye closure at the latter two. It was assumed that there was an absence of hemispheric dominance in former days and an activation of the left hemisphere in latter ones (Nelini et al 2010). In Nelini et al (2010) study, experimental chicks were trained binocularly, and therefore a right hemisphere dominance during trials was safely inferred from previous behavioural studies (Rashid and Andrew 1989;Rogers and Anson 1979;Vallortigara et al 1996).…”

“…It was assumed that there was an absence of hemispheric dominance in former days and an activation of the left hemisphere in latter ones (Nelini et al 2010). In Nelini et al (2010) study, experimental chicks were trained binocularly, and therefore a right hemisphere dominance during trials was safely inferred from previous behavioural studies (Rashid and Andrew 1989;Rogers and Anson 1979;Vallortigara et al 1996). Nelini et al (2010) suggested that the bias for more left Mo-Un sleep of experimental chicks was associated with the consolidation of spatial memory in the right hemisphere, even though an additional process of recovery process after a higher activation (use eVect) of right hemisphere was not excluded.…”

“…It has been proposed that Mo-Un sleep of birds may be considered as a kind of local sleep. Nelini et al (2010) studied the relationship between the Mo-Un sleep pattern and spatial learning in domestic chicks using a paradigm of geometric modules (Vallortigara et al 1990). They reported that experimental chicks were able to learn the spatial task, subsequently showing a signiWcant bias towards more left Mo-Un sleep.…”

“…The rationale of present study would rely on two aims: (1) the association between spatial learning and sleep (MoUn sleep and Bin-sleep) was more precisely veriWed because training on the spatial task was performed monocularly thereby lateralized to only one eye-hemisphere system; (2) the training paradigm and subsequent sleep data could clarify the roles of learning and hemispheric activation (use eVect) on the pattern of Mo-Un sleep which was only assumed in the Nelini et al (2010) previous paper.…”