Monocular-unihemispheric sleep and visual discrimination learning in the domestic chick

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 contra-lateral to the open eye exhibited an EEG with fast waves typical of wakefulness, whereas the hemisphere contra-lateral to the closed eye exhibited an EEG typical of slow wave sleep. We investigated the pattern of monocular-unihemispheric sleep (Mo-Un sleep; i.e. selective preferential closure/opening of the left or right eye during sleep) following three types of visual learning tasks. The first group of chicks was submitted to a colour discrimination task (1), the second group to a spatial discrimination task with colour as a conspicuous, but irrelevant, cue (2), the third group to a spatial task without colour cue. After learning, the amount of binocular sleep and Mo-Un sleep patterns were recorded. The first and the second group of chicks exhibited more right Mo-Un sleep (right eye-closure/left unihemispheric sleep), suggesting that this pattern may be connected with prevalent engagement of left hemisphere during training trials. The third group showed a significant more left Mo-Un sleep (left eye-closure/right unihemispheric sleep) which would be associated with a prevalent engagement of right hemisphere during trials. Chicks of the control groups, did not learn the task, but were submitted to an equal number of trials. Controls of tasks 1 and 2 showed more left Mo-Un sleep suggesting a dominance of right hemisphere during exposure trials. Instead there was no eye-closure bias in controls of task 3, suggesting an absence of hemispheric dominance during trials. It is suggested that the Mo-Un sleep pattern may be a type of local sleep associated with a process of functional recovery in the hemisphere which was mainly engaged during training trials.

Unihemispheric sleep and asymmetrical sleep: behavioral, neurophysiological, and functional perspectives

“…Another group of chicks subjected to a spatial task showed subsequently more right Un-Mo sleep (left eye closure) related to a prevalent engagement of the right hemisphere in the task. 99 – 101 …”

“…Un-Mo sleep prevailed in the hemisphere that dominated during wakefulness, favoring a recovery process and consolidation of memory. 99 – 101 , 107 – 109 Because Un-Mo sleep episodes were intermingled with BSWS ones, the dominant hemisphere spent relatively more time sleeping (BSWS plus Un-Mo sleep) than the nondominant one. Concurrently, for the control of the environment, hen and antipredation chicks awoke the nondominant hemisphere and opened the contralateral eye.…”

“… 89 On the one hand, the reduction of sleep was lower in the dominant hemisphere, allowing for recovery process and memory consolidation. 89 , 99 On the other hand, the nondominant hemisphere showed a higher reduction of the time spent sleeping and had a greater role in the control of environment and vigilance.…”

Sleep as a fundamental property of neuronal assemblies

“…There are also several findings showing that during sleep cerebral blood flow is targeted to, and enhanced in, areas that were disproportionately stimulated during prior waking 27,28. Finally, findings from the developmental plasticity literature29–31 indicate that changes in the sleep EEG are targeted to areas that were activated during prior waking. In summary, sleep intensity, a characteristic of sleep that is determined from EEG delta-wave power, is dependent upon prior use and is enhanced in areas that were disproportionately used during prior wakefulness.…”

The Role of Cytokines in Sleep Regulation

“…There are also several findings showing that cerebral blood flow during sleep is enhanced in those areas disproportionately stimulated during prior waking [103,104]. Finally, the developmental plasticity literature [105][106][107] and the learning literature demonstrating replay of neuronal electrical patterns associated with waking learning tasks [108], indicate changes in the EEG during sleep are targeted to areas activated during prior waking.…”