Neurovascular coupling in primary auditory cortex investigated with voltage-sensitive dye imaging and laser-Doppler flowmetry

The spatiotemporal dynamics of the neurovascular response to brief acoustic stimuli were investigated in guinea pig primary auditory cortex. Neural activity and cortical tonotopic organization were measured with a voltage-sensitive dye (VSD) technique, whereas cerebral blood flow (CBF) response to neural stimulation was measured with laser-Doppler flowmetry (LDF). The acoustic stimulus was given as a wide band sound (click), which induced global activation or as one of two pure tones (1 kHz and 12 kHz), which induced distinct localizations in the auditory cortex. The VSD imaging showed that the sound-induced activation area varied dynamically, and that the spatial extent had peaks at 37 ± 3 ms and 38 ± 8 ms after the onset of stimulation during 1-kHz and 12-kHz tones, respectively. We observed that the average CBF response had a similar peak intensity irrespective of the type of stimuli: 16 ± 9%, 18 ± 11%, and 16 ± 8% for click, 1-kHz, and 12-kHz tones, respectively. No significant differences in the CBF time course, time-to-onset (∼ 0.6 s), or time-to-peak (∼ 3.3 s) were found across the recording sites and stimulus types. These results showed that the CBF response measured with LDF produced a less specific spatial pattern relative to the neural map determined with VSD. The findings can be explained by the methodological limitations of LDF and/or neurovascular regulatory systems in the auditory cortex.