Visually triggered K-complexes: a study in New Zealand rabbits

Abstract

K-complexes are the EEG elements recorded during the state of developing sleep and during slow wave sleep. They are the only EEG components which can be elicited by sensory stimulation during sleep. The peculiarity of New Zealand rabbits to sleep with their eyes open allows the use of visual stimuli to elicit K-complexes. Experiments were performed with three rabbits. For visual stimulation, an elongated screen illuminated by LED flashes was attached to an implant on the animal's skull. The screen covered 20-120° of the visual field of one eye, and moved with the head during animal motion. One-millisecond flashes (15-s interval) were used during daytime in an illuminated room. Flashes elicited evoked responses, which, during the first stages of sleep, were often accompanied by K-complexes. The induced K-complexes were recorded from electrodes located both above visual and somatosensory areas. Evoked responses to visual stimuli were also recorded from both pairs of electrodes, although they were generated exclusively in the visual cortex. Correlation analysis showed that visual evoked responses and K-complexes induced by this stimulation were generated in visual cortex, and passively spread to the electrodes above the somatosensory area. Investigation of the latencies of induced K-complexes revealed two time windows when these complexes could be seen. Within each window there was no correlation between latency and amplitude of K-complexes. There was also no correlation between amplitudes of the visual evoked responses and K-complexes elicited by these responses. We propose that visual stimulation in light sleep temporarily opens a gate for some independent external signals, which evoke activation of the visual cortex, reflected in K-complexes.

Ostriches Sleep like Platypuses

“…This wake-like sleep posture may explain why sleep is rarely reported in studies on time budgets and activity patterns in wild ostriches [27], [28]. SWS with open eyes has been reported in other avian [29]–[32] and mammalian [33], [34] species, and may allow for visual processing concurrent with sleep [32], [35]. During SWS, the EEG showed slow waves (Figure 2A, Figure S1) like those recorded from other birds engaged in SWS [36]–[38].…”

Cortical visual areas process intestinal information during slow‐wave sleep

“…In discussion of cortical visceral activation during sleep one often argues that these visceral responses can be of non-specific origin resembling sensory triggered K-complexes. This question was investigated in details in our recent study 55 where it was shown that visually induced K-complexes had absolutely specific origin. In addition, K-complexes could be induced by sensory stimuli only during short interval of developing sleep.…”

“…Cortical visceral responses on the contrary could be recorded during periods of deep slow-wave sleep when K-complexes could not be induced by any sensory stimulation. In our study of the induced K-complexes 55 we presented the arguments, which indicated that visually induced K-complexes also may reflect excitation coming from the visceral systems.…”

Sleepiness induced by sleep-debt enhanced amygdala activity for subliminal signals of fear

“…Furthermore, the subliminal process might work as a system that compensates for the decline seen in the level of consciousness with strong sleepiness, a situation that poses considerable danger to survival. For example, as a prey animal, a certain rabbit species sleeps with their eyes open in the wild, during which time their electroencephalograms show brain activation due to visual stimuli [18]. This is advantageous because it enables the animals to respond quickly to an attack by natural enemies, by waking up and engaging in avoidance behavior.…”