人腦血氧動態反應和行為的關聯與其結構基礎

Abstract

血氧水平依賴（BOLD）信號反映了潛在的神經活動和內在腦血管反應性（CVR）的組合。因此，使用BOLD信號偵測神經活動同步性以及推斷腦區間因果關係可能是有偏差的。可以透過閉氣（BH）任務來估計血液動力學延遲時間，得到測量BOLD信號中的純血管（非神經）延遲時間來解決這個問題。 本研究使用快速功能性磁振造影（取樣頻率 = 10 Hz）量測當受試者參與視覺運動（VM）任務時視覺區和感覺運動區之間的BOLD時間差。透過減去由CVR引起的時間差來進一步校正腦區間的BOLD時間差，而CVR是透過相同受試者族群的BH任務量測的。同時，我們還透過高空間解析度磁敏感加權成像（立體像素大小 = 0.78 × 0.78 × 1mm3）估計了受試者族群內的靜脈機率（VP）圖。透過計算這些結構和生理測量之間的相關性，我們目標是要顯示區域性的靜脈血管分佈與BOLD信號的動態變化及其變異性是否有關聯。 結果顯示，校正CVR造成的延遲時間，會使腦區間時間差呈現顯著差異（外側膝狀體早於視覺區，視覺區早於感覺運動區）。透過CVR校正，消除了原先在VP和BOLD延遲時間以及延遲時間變異性的顯著相關性。此外，在校正後，受試者之間和受試者自身重複量測皆發現任務反應時間（428 ± 41 ms）與腦區間BOLD時間差（432 ± 149 ms）之間呈現顯著正相關。研究結果顯示可以透過校正個體的CVR來改善BOLD信號的時間穩定性，此結果可由受試者族群的VP與BOLD延遲時間以及延遲時間變異性在校正後呈現無相關來驗證。

The blood-oxygen level dependent (BOLD) signal reflects the combination of both underlying neural activity and the intrinsic cerebral vascular reactivity (CVR). Thus detecting neuronal synchrony as well as inferring inter-regional causal modulation using BOLD signal can be biased. Mapping the hemodynamic latency using a breath-holding (BH) task provides a way to mitigate this issue by measuring the pure vascular (non-neural) latency component in the BOLD signal. Here we used fast fMRI measurements (sampling rate=10 Hz) to measure the BOLD timing difference between visual and sensorimotor areas when subjects engaged a visuomotor (VM) task. The inter-regional BOLD timing difference was further calibrated by subtracting the timing difference caused by CVR, which was measured by a BH task on the same subject group. Meanwhile, we also estimated a venous probability (VP) map within subject group by the high spatial resolution susceptibility-weighted image (voxel size=0.78×0.78×1mm3). Via the correlation between these structural and physiological measures, we aimed to reveal how the regional venous vasculature is related to the dynamics and variability of the BOLD signal. Calibrating the CVR led to the significant inter-regional BOLD timing difference (lateral geniculate nucleus before visual cortex, visual cortex before sensorimotor cortex). The significant correlation between VP and BOLD latencies as well as the latency variabilities were eliminated by CVR calibration. Further, significant positive correlation between task reaction time (428 ± 41 ms) and the within- as well as the cross-subject inter-regional BOLD timing difference (432 ± 149 ms) was revealed after calibration. The results supported that the temporal stability of BOLD signal can be empirically improved by calibrating individual’s CVR, which is underpinned by VP within the subject group.