Working memory (WM) plays a crucial role in human brain functions. The application of brain connectivity analysis helps to understand the brain network properties in WM. Combination of functional and effective connectivity can provide new insights for exploring network attributes. Nevertheless, few studies have combined these two modes in WM. Near-infrared spectroscopy was used to investigate the connectivity properties in the prefrontal cortex (PFC) during n-back (0-back and 2-back) tasks by combining functional and effective connectivity analysis. Our results demonstrated that the PFC network showed small-world properties in both WM tasks. The characteristic path length was significantly longer in the 2-back task than in the 0-back task, while there was no obvious difference in the clustering coefficient between two tasks. Regarding the effective connectivity, the Granger causality (GC) was higher for right PFC→left PFC than for left PFC→right PFC in the 2-back task. Compared with the 0-back task, GC of right PFC→left PFC was higher in the 2-back task. Our findings show that, along with memory load increase, long range connections in PFC are enhanced and this enhancement might be associated with the stronger information flow from right PFC to left PFC.
Cerebral edema, as an acute head injury, has been of great interest over decades in clinical neurosurgery research. Many patients exhibited extensor motor abnormalities in the acute phase because their cerebral lose control of brainstem and spinal cord. These phenomenon, which is called “decerebrate rigidity”, showed up spontaneously or when their bodies were stimulated by external forces. Neuro imaging methods provide a new perspective in cerebral edema with decerebrate rigidity. Functional near infrared spectroscopy (fNIRS), as a novel optical detection method, has been widely used in monitoring changes of cerebral cortex blood oxygen concentration. Here, we utilized a self-made fNIRS detecting instrument with 4 channels fixed in forehead to monitor cerebral hemodynamic changes of patients with cerebral edema. The instrument has three waveforms (735nm, 805nm and 850nm) to detect concentration changes of oxygenated hemoglobin (HbO, deoxy hemoglobin (Hb), and blood volume (HbT). During the monitoring period, we captured two typical decerebrate rigidity in a patient (caused by external stimulation). At the beginning of decerebrate rigidity, Hb and HbT increased rapidly along with HbO decreased. The stage of this change lasts about 3s. Then the three hemodynamic parameters keep stable for about 6s. Finally, the three hemodynamic parameters return to the initial stage slowly (about 10s). The change amplitude of decerebrate rigidity caused by external stimulation were significantly higher than spontaneous situation. The results indicate that decerebrate rigidity caused acute hypoxia and congestion in patients’ cerebral cortex.