Hodono Shota, Rideaux Reuben, van Kerkoerle Timo, Cloos Martijn A
Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia.
Queensland Brain Institute, The University of Queensland, Brisbane, Australia.
Imaging Neurosci (Camb). 2023 Sep 6;1. doi: 10.1162/imag_a_00013. eCollection 2023.
Functional MRI (fMRI) has been widely used to study activity patterns in the human brain. It infers neuronal activity from the associated hemodynamic response, which fundamentally limits its spatiotemporal specificity. In mice, the Direct Imaging of Neuronal Activity (DIANA) method revealed MRI signals that correlated with extracellular electric activity, showing high spatiotemporal specificity. In this work, we attempted DIANA in humans. Five experimental paradigms were tested, exploring different stimulus types (flickering noise patterns, and naturalistic images), stimulus durations (50-200 ms), and imaging resolution (2 × 2 × 5 mm and 1 × 1 × 5 mm). Regions of interest (ROI) were derived from Blood Oxygen Level Dependent (BOLD) fMRI acquisitions (both EPI and FLASH based) and T1-weighted anatomical scans. In Paradigm I ( = 1), using flickering noise patterns, signals were detected that resembled possible functional activity from a small ROI. However, changes in stimulus duration did not lead to corresponding signal changes (Paradigm II; = 1). Therefore, care should be taken not to mistake artifacts for neuronal activity. In Paradigm III ( = 3), when averaged across multiple subjects, a ~200 ms long 0.02% signal increase was observed ~100 ms after the stimulus onset (10x smaller than the expected signal). However, white matter control ROIs showed similarly large signal fluctuations. In Paradigm IV ( = 3), naturalistic image stimuli were used, but did not reveal signs of a potential functional signal. To reduce partial voluming effects and improve ROI definition, in Paradigm V ( = 3), we acquired data with higher resolution (1 × 1 × 5 mm) using naturalistic images. However, no sign of activation was found. It is important to note that repetitive experiments with short interstimulus intervals were found to be strenuous for the subjects, which likely impacted data quality. To obtain better data, improvements in sequence and stimulus designs are needed to maximize the DIANA signal and minimize confounds. However, without a clear understanding of DIANA's biophysical underpinnings it is difficult to do so. Therefore, it may be more effective to first investigate DIANA signals with simultaneously recorded electrophysiological signals in more controlled settings, e.g., in anesthetized mice.
功能磁共振成像(fMRI)已被广泛用于研究人类大脑中的活动模式。它从相关的血液动力学反应推断神经元活动,这从根本上限制了其时空特异性。在小鼠中,神经元活动直接成像(DIANA)方法揭示了与细胞外电活动相关的磁共振信号,显示出高时空特异性。在这项工作中,我们尝试在人类中进行DIANA实验。测试了五种实验范式,探索了不同的刺激类型(闪烁噪声模式和自然图像)、刺激持续时间(50 - 200毫秒)和成像分辨率(2×2×5毫米和1×1×5毫米)。感兴趣区域(ROI)来自基于血氧水平依赖(BOLD)的fMRI采集(包括基于EPI和FLASH的)以及T1加权解剖扫描。在范式I(n = 1)中,使用闪烁噪声模式,检测到的信号类似于来自一个小ROI的可能功能活动。然而,刺激持续时间的变化并未导致相应的信号变化(范式II;n = 1)。因此,应注意不要将伪影误认为是神经元活动。在范式III(n = 3)中,当对多个受试者的数据进行平均时,在刺激开始后约100毫秒观察到约200毫秒长的0.02%的信号增加(比预期信号小10倍)。然而,白质对照ROI也显示出类似大小的信号波动。在范式IV(n = 3)中,使用了自然图像刺激,但未发现潜在功能信号的迹象。为了减少部分容积效应并改善ROI定义,在范式V(n = 3)中,我们使用自然图像以更高分辨率(1×1×5毫米)采集数据。然而,未发现激活迹象。需要注意的是,发现短刺激间隔的重复实验对受试者来说很费力,这可能影响了数据质量。为了获得更好的数据,需要改进序列和刺激设计,以最大化DIANA信号并最小化干扰因素。然而,在没有清楚了解DIANA的生物物理基础的情况下,很难做到这一点。因此,首先在更可控的环境中,例如在麻醉小鼠中,将DIANA信号与同时记录的电生理信号一起进行研究,可能会更有效。