To investigate neural source of positive and negative BOLD signals, we modulated a balance of excitatory and inhibitory activity (EI) within the same somatosensory area to determine whether the polarity of evoked BOLD response is reversed. We measured BOLD fMRI at 15.2T and calcium photometry of ketamine/xylazine-anesthetized mice in response to frequency dependent whisker pad stimulation. At 4 Hz, positive BOLD and increased calcium activity were observed in the barrel cortex, whereas at 20 Hz stimulation, negative BOLD and decreased calcium activity were detected. This indicates that the BOLD polarity closely links to the EI balance.
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