Cellular and Systems Neurobiology, Institute of Neurosciences, Spanish National Research Council-Miguel Hernandez University, Alicante, Spain.
Department of Physiology, Miguel Hernandez University, Alicante, Spain.
Psychophysiology. 2022 Oct;59(10):e14063. doi: 10.1111/psyp.14063. Epub 2022 Apr 8.
Functional near-infrared spectroscopy (fNIRS) is an increasingly used technology for imaging neural correlates of cognitive processes. However, fNIRS signals are commonly impaired by task-evoked and spontaneous hemodynamic oscillations of non-cerebral origin, a major challenge in fNIRS research. In an attempt to isolate the task-evoked cortical response, we investigated the coupling between hemodynamic changes arising from superficial and deep layers during mental effort. For this aim, we applied a rhythmic mental arithmetic task to induce cyclic hemodynamic fluctuations suitable for effective frequency-resolved measurements. Twenty university students aged 18-25 years (eight males) underwent the task while hemodynamic changes were monitored in the forehead using a newly developed NIRS device, capable of multi-channel and multi-distance recordings. We found significant task-related fluctuations for oxy- and deoxy-hemoglobin, highly coherent across shallow and deep tissue layers, corroborating the strong influence of surface hemodynamics on deep fNIRS signals. Importantly, after removing such surface contamination by linear regression, we show that the frontopolar cortex response to a mental math task follows an unusual inverse oxygenation pattern. We confirm this finding by applying for the first time an alternative method to estimate the neural signal, based on transfer function analysis and phasor algebra. Altogether, our results demonstrate the feasibility of using a rhythmic mental task to impose an oscillatory state useful to separate true brain functional responses from those of non-cerebral origin. This separation appears to be essential for a better understanding of fNIRS data and to assess more precisely the dynamics of the neuro-visceral link.
功能性近红外光谱（fNIRS）是一种越来越常用的技术，用于对认知过程的神经相关物进行成像。然而，fNIRS 信号通常会受到非脑部起源的任务诱发和自发性血液动力学波动的影响，这是 fNIRS 研究中的一个主要挑战。为了尝试分离任务诱发的皮质反应，我们研究了在脑力劳动过程中来自浅层和深层的血液动力学变化之间的耦合。为此，我们应用了一种有节奏的心理算术任务来诱发适合有效频率分辨测量的周期性血液动力学波动。二十名 18-25 岁的大学生（八名男性）接受了任务，同时使用新开发的 NIRS 设备在额头上监测血液动力学变化，该设备能够进行多通道和多距离记录。我们发现了与任务相关的显著的氧合血红蛋白和脱氧血红蛋白波动，在浅层和深层组织层之间高度一致，这证实了表面血液动力学对深部 fNIRS 信号的强烈影响。重要的是，通过线性回归去除这种表面污染后，我们表明，额叶前极皮质对心理数学任务的反应遵循一种不寻常的反氧合模式。我们通过首次应用基于传递函数分析和相量代数的替代方法来估计神经信号，从而证实了这一发现。总的来说，我们的结果证明了使用有节奏的心理任务来施加有用的振荡状态的可行性，这种状态可用于从非脑部起源的真实大脑功能反应中分离出来。这种分离对于更好地理解 fNIRS 数据并更精确地评估神经-内脏联系的动态性似乎是必不可少的。
