Effects of theta burst stimulation on the coherence of local field potential during working memory task in rats.

Theta burst stimulation (TBS), a highly efficient repetitive transcranial magnetic stimulation (rTMS) paradigm, has been widely used to modulate the working memory (WM) ability in experimental and clinical study. However, the underly neuroelectrophysiological mechanism remains unclear. The aim of this study was to compare the effect of iTBS, cTBS and rTMS on WM and explore the neural oscillatory communication changes in PFC involved in spatial WM task. 18 rats were treated by iTBS, cTBS and rTMS respectively (n = 6 each), while the rats in control group (n = 6) received no stimulation. T-maze WM task was used to assess the rats' performance of WM after stimulation. Local field potentials (LFPs) were recorded from a microelectrode array implanted in the medial prefrontal cortex (mPFC) while the rats were performing the WM task. Functional connectivity (FC) strength was assessed by LFP-LFP coherence calculations. The results showed that the rats from the rTMS group and iTBS group are able to reach criteria in less time than the control group's duration of the T-maze task. The power and the coherence value of rTMS and iTBS groups show a significant increase in the theta-band and gamma-band activity, wheras there are no significant differences of the energy and the coherence value between the cTBS group and the control group in theta-band. Furthermore, significantly positive correlations were observed between changes of memory performance during the WM task and the changes of the coherence value of the LFPs. In conclusion, these results indicate that rTMS and iTBS may improve the ability of WM by modulating the neural activity and connectivity in PFC.