We introduce a transgenic mouse that can be a useful resource for cortical functional mapping. Transgenic mice were generated using a BAC transgene construct containing the murine glutamate transporter-1 (GLT1) promoter to express G-CaMP7. Of the resulting transgenic lines, the #817 line had bright ectopic expression of G-CaMP7 in a large set of neurons and glia. Using this mouse, we demonstrate in vivo mapping of cortical functions by presenting sensory stimuli of various modalities in urethane anesthesia. Of note, a brief tail pinch resulted in an elevation of long lasting (> 50 s) calcium signal across wide cortical areas in both neurons and glia, resembling GPCR activation by volume-transmitted subcortical neuromodulators. Finally, we monitored the entire dorsal cortical surface during transcranical direct current stimulation (tDCS). For tDCS, an anode was placed on the skull above the primary visual cortex with a conductive gel interface spreading over an area of 2 mm2 and a cathode was inserted to the neck muscle. A DC current of 100 μA was passed through the electrodes for 600 s. Although this is a well-accepted range of current in published literature, we could observe a large amplitude calcium wave originating near the anode that traveled radially covering the entire hemisphere, but not across the midline. The speed of the traveling wave was 0.23 ± 0.02 mm/s, similar to cortical spreading depression (CSD). Our results suggest that tDCS stimulation parameter should be carefully chosen for rodent experiments with electrodes directly contacting the skull. Alternatively, the CSD-like activity propagation maybe a mechanism that contributes to enhanced learning.