【作者】 李成军；

【导师】 骆清铭；

【作者基本信息】 华中科技大学 ， 生物医学工程， 2005， 博士

【摘要】 工作记忆是一种对信息进行暂时性储存和加工的机制,它能够保存被激活的信息表征,以备进一步加工之用,对于学习、推理、问题解决及语言理解等高级认知功能的完成起着重要作用。来自正电子发射层析成像（PET）和功能磁共振成像（fMRI）的研究证据表明,前额叶皮层（PFC）是在工作记忆中起关键作用的脑区。近红外光谱技术（NIRS）是近年来快速发展起来的一项非侵入光学测量方法。在700⁹00nm的近红外光谱范围内,生物组织具有高散射、低吸收的特性,近红外光可以穿过头皮和颅骨深入脑组织,并由漫射光携带出反映大脑皮层激活状况的血液动力学变化信息。基于氧合血红蛋白（HbO₂）和脱氧血红蛋白（Hb）对多个波长的近红外光的不同吸收,NIRS可以提供对脑组织中HbO₂和Hb浓度相对变化的独立测量,因而在大脑功能活动的检测领域表现出了巨大潜能。本论文在阐述NIRS 基本测量原理和大脑具体生理特性的基础上,设计并建立了一套多通道近红外光谱检测系统。作为系统的主要应用,通过对两种工作记忆任务下PFC 激活状况的检测,探讨了PFC 在工作记忆中的作用。1)以光与生物组织的相互作用规律为基础,结合脑的具体生理特性,设计并实现了一套24 通道基于三波长连续光类型的脑功能近红外光谱检测系统。系统的时间分辨率取决于采样频率,因此是可调的,应用中设定的分辨率为1 秒; 成像器（探头）探测面积为6cm×12cm,实际应用中,成像器对称地置于被试眉骨以上、前额中线左右两侧,这样,成像器所检测的脑区范围为前部前额区（Anterior PFC）,背外侧前额区（DLPFC）及腹外侧前额（VLPFC）的部分区域。系统实现的主要功能包括获取三种波长的光强变化数据,计算并显示HbO₂、Hb和总血红蛋白（HbT）的相对浓度变化量。离体血液模型实验结果表明该系统可以较为准确地测量组织中HbO₂、Hb和HbT相对浓度的变化。2)利用NIRS系统对被试在执行基于项目再认范式的言语和空间工作记忆任更多还原

【Abstract】 Working memory （WM） refers to a mental system that provides temporary storage and manipulation of the information necessary for such high-level cognitive tasks as learning, reasoning, problem-solving, and language comprehension. The system can provide the short-term maintenance of an active representation of information so that it is available for further processing. There are abundant evidences coming from positron emission tomography （PET） and functional magnetic resonance imaging （fMRI） studies accumulated to support a key role of prefrontal cortex （PFC） in different WM processes. Near-infrared spectroscopy （NIRS） is a noninvasive optical approach under fast development in recent years. Biological tissues characters low absorption and high scattering in near-infrared range from 700 to 900nm, which allows near-infrared light to probe the human cortex through the intact scalp and skull and carry out the functional information. NIRS has shown great potential in examining functional brain activity during cognitive tasks by enabling an independent measurement of changes in the concentration of the oxygenated hemoglobin （HbO2） and the deoxygenated hemoglobin （Hb） in cortex tissue based on differential absorption at multiple wavelengths. In this thesis, the basic principle of NIRS and the characteristic of brain are introduced. A multi-channel and multi-wavelength NIRS monitoring system is designed and built. As the main application of the system, the PFC functions during two working memory tasks are discussed in detail. 1)Based on the law of the photo-tissue interaction and the characteristic of brain,a 24-channel and three-wavelength continuous-wave-type NIRS monitoring system is designed and built. In the system, the temporal resolution is adjustable and determined by the sampling frequency. Here, we take 1 second as the temporal resolution. The imager possesses a detection area of 6 cm ×12cmcovering most part of PFC. In practical application, the imager is placed on the center of the forehead right above the eyebrow line to the upper and lateral sides. Thus, the detection area corresponds loosely to anterior PFC, dorsolateral PFC （DLPFC） and partial ventrolateral PFC （VLPFC）. The main functions can be achieved as follows: sampling the data of light’s intensity; calculating and displaying the relative concentration changes of HbO2, Hb and HbT. The capability of the system was validated by the blood model test in vitro. The results indicate that the concentration changes in HbO₂, Hb and HbT can be measured by the NIRS system. 2)PFC activations during verbal and spatial working memory tasks based on item-recognition paradigm were monitored by the NIRS system. On the base of the measurements, both the temporal characteristics of hemodynamic changes in PFC activation and the distributing diversity of the activated cortex area under two different tasks were investigated. The results revealed that there exists a typical activation pattern in which the concentration increases in HbO2 and HbT were frequently accompanied by concentration decrease in Hb. The activations in PFC present a lateral trend. The verbal task mainly activated the left VLPFC and the spatial material activated the right VLPFC. 3)During the verbal n-back task, the PFC activations were also monitored and the behavioral data were recorded by the system above. The effects of the working memory load on subjects’behavioral performances and PFC activation were investigated respectively. The relationships among the response time, accuracy and the PFC activation at higher memory load level were discussed. The results indicated as follow: i) Both the behavioral performances and PFC activation presented significant effects of working memory load. As WM task became more difficult, the activation in activated brain area and the response time increased and the accuracy decreased. ii) The activation in left PFC was obviously larger than that in the right, especially in VLPFC. iii) At higher memory load level, there existed a well-regulated relation among the response time, accuracy and the PFC activation: shorter response time being frequently companied by higher accuracy and smaller activation, in other words, longer response time being frequently companied by lower accuracy and larger activation. Overall, NIRS was firstly applied to the study on working memory in this thesis and thus a new method was provided for the project. In virtue of the characteristics of the high temporal resolution and multi-index measures in NIRS monitoring, we found that there exists a typical activation pattern in the activated cerebral area during the working memory task. The relationship between the PFC activation and the behavior parameters was also firstly investigated in the thesis and the fact was found that there exists a well-regulated relation among the response time, accuracy and the PFC activation at higher memory load level. The findings above provide new evidences for PFC function in working memory and are important for exploring the brain mechanism of the working memory.更多还原