FIGURE 2.

Local sleep homeostasis in the avian brain. (A) Experimental design: a 12 h baseline night, 8 h period of bihemispheric sleep deprivation with unilateral visual stimulation (SD) and a 12 h recovery night. Photograph shows the experimental environment during the treatment. (B) Spectral power density (0.78–25.00 Hz) during NREM sleep for the first quarter of the baseline and recovery nights for the stimulated (dark blue) and visually deprived (light blue) hyperpallia and mesopallia. Data are presented as mean ± SE. Colored squares at the bottom of each recovery night plot reflect a significant pairwise comparison between the baseline and recovery night of the stimulated (dark blue) and visually deprived (light blue) hyperpallia; red squares denote a significant asymmetry between the left and right brain region during recovery sleep. Although the experimental treatment induced interhemispheric asymmetries across a wide range of frequencies, slow wave activity (yellow shading) in the hyperpallium showed the largest asymmetry. Insets: frontal view of a transverse section through the cerebrum of a pigeon highlighting the hyperpallium (H) and mesopallium (M). (C) Up slope of NREM sleep slow waves in the hyperpallium and mesopallium contralateral to the stimulated eye (dark blue) and deprived eye (light blue) during the first quarter of the baseline and recovery night. Data are presented as mean ± SE. Significant changes in slope between the baseline and recovery nights are marked with an asterisk (contralateral to the stimulated eye in dark blue; contralateral to the deprived eye, non-significant); significant asymmetries between the left and right hemisphere for a given brain region are denoted by a red asterisk. Note the asymmetry between the stimulated and visually deprived hyperpallia during recovery sleep, with the stimulated hyperpallium showing steeper slopes, and the symmetric mean increase in the mesopallium. Reproduced with permission from Lesku et al. (2011b).