Optical microangiography reveals temporal and depth-resolved hemodynamic change in mouse barrel cortex during whisker stimulation

Abstract

Significance: Cerebral blood flow (CBF) regulation at neurovascular coupling (NVC) plays an important role in normal brain functioning to support oxygen delivery to activating neurons. Therefore, studying the mechanisms of CBF adjustment is crucial for the improved understanding of brain activity.

Aim: We investigated the temporal profile of hemodynamic signal change in mouse cortex caused by neural activation and its variation over cortical depth.

Approach: Following the cranial window surgery, intrinsic optical signal imaging (IOSI) was used to spatially locate the activated region in mouse cortex during whisker stimulation. Optical microangiography (OMAG), the functional extension of optical coherence tomography, was applied to image the activated and control regions identified by IOSI. Temporal profiles of hemodynamic response signals obtained by IOSI and OMAG were compared, and OMAG signal was analyzed over cortical layers.

Results: Our results showed that the hemodynamic response to neural activity revealed by blood flow change signal signal through IOSI is slower than that observed by OMAG signal. OMAG also indicated the laminar variation of the response over cortical depth, showing the largest response in cortical layer IV.

Conclusions: Overall, we demonstrated the development and application of dual-modality imaging system composed of IOSI and OMAG, which may have potential to enable the future investigations of depth-resolved CBF and to provide the insights of hemodynamic events associated with the NVC.

Keywords: cerebral blood flow; hemodynamic response; intrinsic optical signal imaging; neurovascular coupling; optical coherence tomography; optical microangiography.

Fig. 1

Schematic diagram of IOSI and OCT systems and data processing. (a) IOSI system setup, (b) IOSI data processing steps, (c) OMAG data processing steps, and (d) OCT system setup. SLD, superluminescent diode; PC, polarization controller.

Fig. 2

IOSI identifies the activation region in the brain cortex upon whisker stimulation. (a) Microscope image of cranial window at somatosensory cortex. (b) Reflectance map of cranial window area at resting (2nd s). (c) Reflectance map of cranial window area at stimulation (12th s). R1 indicates the activated region and R2 indicates the control region. (d) Temporal profile of reflectance signal change in response to whisker stimulation at activated (red curve) and control (black curve) regions. $\mathrm{\Delta }R$ is a change in reflectance signal, $R$ is a baseline reflectance signal. Dashed lines indicate the start and the end of stimulation time.

Fig. 3

OMAG provides an ability to detect the localized hemodynamic response within the brain cortex upon whisker stimulation. (a) Reflectance IOSI map of the cortical tissue at cranial window, where the dashed line indicates the cross-section position for OCT imaging. (b) Cross-section of OCT structural image. (c) Cross-section of OMAG blood flow image. R1 indicates the activated region and R2 indicates the control region. (d) Temporal profile of OMAG signal change in response to whisker stimulation at activated (red curve) and control (black curve) regions. $\mathrm{\Delta }I$ is the change in OMAG signal, and I is the baseline OMAG signal. Dashed lines indicate the start and the end of stimulation time.

Fig. 4

OMAG provides an ability to detect the variation of hemodynamic response over cortical depth upon whisker stimulation. (a) OMAG cross-sectional blood flow image with activated region indicated (red rectangle). (b) OMAG cross-sectional blood flow image of activated region indicated in A with layers’ location indicated. (c) Difference in OMAG signal intensity between rest and functional activation states over cortical depth averaged over six animals. Error bars represent the standard deviation. *$p\text{-value}<0.02$, **$p\text{-value}<0.03$.