Primary microglia spontaneously migrate in microfluidic channels. After plating primary microglia in microfluidic devices for 30 min, time-lapse recording is performed every 30 min for 20 h. Arrows represent microglial processes and arrowheads indicate microglial cells. The different colors point to different forward- or backward-displacement of the cells inside the microchannels. The total migration path is: length 500 μm (white dotted arrow), width 12 μm, height 10 μm. The scale bar is 50 μm.