Figure 3: Slow wave sleep electroencephalogram (EEG) asymmetry is related to circling flight.
(a) Distribution of awake and SWS 4 s epochs (all birds combined) occurring at different sway accelerations (0.02g0 bins) on land and in flight at night. On land (top), the values were clustered around zero while awake and in SWS indicating that the birds held their head straight during both states. Although the birds also held their head and wings straight while awake in flight, SWS, in most cases (70.57%), occurred with circling flight to the left and right, as reflected by sway acceleration <−0.175g0 and >0.175g0 (dashed vertical lines). (b) Diagram showing the wing and head angle relative to the horizon during circling flight to the left calculated from the accelerometry. The corresponding brain state (see below) is also shown. (c) Recording showing the relationship between asymmetric SWS (ASWS) and acceleration along the sway axis; during ASWS with greater EEG slow wave activity (SWA; 0.75–4.5 Hz power) in the left hemisphere (ASWS-L) the sway axis showed high values corresponding to circling to the left, and when SWA was greater in the right hemisphere (ASWS-R), the sway axis showed low values corresponding to circling to the right. Same bird as in Fig. 2. (d) The relationship between sway acceleration and type of SWS in flight for all birds combined. Data from (a) are partitioned according to the type of SWS as defined in the main text; ASWS-L, ASWS-R and bihemispheric SWS (BSWS). (e) Relationship between flight mode (sway acceleration) and SWS in flight for data from (a) partitioned according to the interhemispheric asymmetry in gamma activity (30–80 Hz power); asymmetric gamma with greater gamma in the left (AGamma-L; AI⩾0.1) or right (AGamma-R; AI≤−0.1) hemisphere and bihemispheric (symmetric) gamma (BGamma; −0.118 is summarized in (b); awake hyperpallium (green) and sleeping hyperpallium (blue) and the corresponding relative difference in EEG SWA. The green arrows show the general direction of visual flow while circling to the left.
