Working memory (WM) refers to a brain system that provides temporary storage and manipulation of the information. 16-channel spike trains were extracted from neural activities recorded in medial prefrontal cortex (mPFC) during the WM tasks on a Y-maze. The Granger causality analysis was applied to measure the functional connectivity between the spike trains. The aim of this study is to quantitatively characterize the functional connectivity among the mutiple spike trains during the WM tasks. The global efficiency (E) and causal density (CD) in the network among spike trains were calculated to descript the functional connectivity quantitatively. T he statistical results of E and CD were calculated from 4 rats, and 10 tasks for each rat. The results show that E was 0.484±0.031 at the WM state, and 0.306±0.037 at the resting state (p<0.01). CD was 0.312±0.028 at the WM state and 0.220±0.030 at the resting state (p<0.01). Furthermore, E was variational from 0.406±0.036 to 0.484±0.032 during the WM task, and CD was variational from 0.267±0.027 to 0.312±0.028 during the WM tasks, where the maximums of E and CD were at the WM state. The conclusion is that the strong functional connectivity existed at WM state, and the connectivity increased until WM formed.
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