Around the saccade on swap trials—when WM trace transfer putatively occurs—interhemispheric theta (~4–10 Hz) and high-beta (~18–40 Hz) synchrony both exhibited a transient peak (Figure 7A; p < 0.01, paired t test versus pre-sample baseline). No such peaks were observed at analogous time points on no-swap trials (Figure 7B). These differences were confirmed by examining the contrast between swap and no-swap trials (Figure 7C; p < 0.01, paired t test). In contrast, during this period there was a suppression of interhemispheric synchrony relative to baseline within the alpha/low-beta band (~11–17 Hz), which extended into the post-saccade delay period (Figure 7C). Similar results, but with higher frequency positive effects extending into the gamma band (~40–100 Hz), were observed for synchrony between LFPs at distinct sites within each hemisphere (Figures 7D–7I). Theta and gamma increases were stronger in the sender hemisphere (Figures 7D, 7F, and 7H). Alpha/beta suppression from baseline, like beta power, was more similar in strength between hemispheres. These results suggest evidence for interhemispheric signal communication underlying memory trace transfer and that communication occurs via theta and high-beta but not alpha/beta synchrony.
