观看虚化手动作时人类镜像神经系统的激活

doi:10.3969/j.issn.1673-5374.2013.03.007

摘要/Abstract

摘要：

研究证实，手的阴影能激活人脑与镜像神经元区域相关的运动皮质，但是比手的阴影更抽象的基于线条的非及物的手指运动（比手影还缺少填充物）能否激活人类镜像神经元还未见报道。实验应用脑电技术检测18名健康大学生在观看真实手动作、虚化的手（阴影手和线条手）动作刺激时，脑电mu节律的抑制程度。证实当观察三类手动作时，mu节律（8-13Hz）的去同步化现象（又称mu抑制）存在于感觉运动皮质（C3, Cz和C4电极记录），额叶皮质（F3, Fz 和F4记录）和中央及右后顶叶皮质（Pz和P4记录）。实验结果说明，仅仅观察不及物的虚化手部动作，如阴影和线条表达的手部动作，能激活广泛的与人类镜像神经系统相关的脑皮质。

关键词: 神经再生, 临床实践, 镜像神经系统, 手动作, 阴影手, 线条手, mu节律, mu节律去同步化, mu抑制, 脑电图, 虚化手动作, 基金资助文章, 图片文章

Abstract:

Previous studies have demonstrated that hand shadows may activate the motor cortex associated with the mirror neuron system in human brain. However, there is no evidence of activity of the human mirror neuron system during the observation of intransitive movements by shadows and line drawings of hands. This study examined the suppression of electroencephalography mu waves (8–13 Hz) induced by observation of stimuli in 18 healthy students. Three stimuli were used: real hand actions, hand shadow actions and actions made by line drawings of hands. The results showed significant desynchronization of the mu rhythm (“mu suppression”) across the sensorimotor cortex (recorded at C3, Cz and C4), the frontal cortex (recorded at F3, Fz and F4) and the central and right posterior parietal cortex (recorded at Pz and P4) under all three conditions. Our experimental findings suggest that the observation of “impoverished hand actions”, such as intransitive movements of shadows and line drawings of hands, is able to activate widespread cortical areas related to the putative human mirror neuron system.

Key words: neural regeneration, clinical practice, mirror neuron system, action understanding, direct matching hypothesis, mu suppression, event-related desynchronization, mu rhythm, electroencephalogram, impoverished hand actions, grants-supported paper, photographs-containing paper, neuroregeneration

. 观看虚化手动作时人类镜像神经系统的激活[J]. 中国神经再生研究(英文版), 2013, 8(3): 251-257.

Huaping Zhu, Yaoru Sun, Fang Wang. Electroencephalogram evidence for the activation of human mirror neuron system during the observation of intransitive shadow and line drawing actions[J]. Neural Regeneration Research, 2013, 8(3): 251-257.

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引言

材料方法

Design

An observational study with randomized stimuli.

Time and setting

The experiments were performed at the Department of Computer Science and Technology, Tongji University, China, from June to July 2011.

Subjects

Eighteen healthy graduate students at Tongji University in China (two female, 16 male; average age 25 years; range 22–29 years) were recruited by signs posted on campus. All participants were right-handed, had normal or corrected-to-normal vision, and were naïve with respect to the purpose of the experiments. The experimental protocol was in accordance with the Regulations for the Administration of Medical Institutions, formulated by the State Council of China^[34]. All participants provided written informed consent before experiments began.

Methods

Stimuli

The stimuli used in our four experiments are as follows:

(1) Hand shadow actions (shadow condition). In this condition, three different actions were made by the shadow of a right hand. The actions involved the rhythmic (1 Hz) movement of the thumb, forefinger or little finger between 0° (adducted) and approximately 40° (abducted). It was easy to recognize the movement of the hand-like shadow (Figure 3A).

(2) Line drawing actions (line drawing condition). In this condition, a line drawing of a right hand made the same movements as described for the shadow condition (Figure 3B).

(3) Real hand actions (real hand condition). In this condition, the actions were performed by a real human hand (Figure 3C).

(4) Bidirectional movements of two or three black circles on a white background (baseline condition). In this condition, the movement of the circles mimicked the trajectories of the static and moving finger tips. As shown in Figure 3, the movement D-D1-D was visually equivalent to the trajectory of A-A1-A; the movement D-D2-D was visually equivalent to the trajectory of B-B2-B; and the movement D-D3-D was visually equivalent to the trajectory of C-C3-C. Importantly, these circle movements were not perceived as animate.

Procedure

The four different stimuli were presented in a random order across subjects. Subjects observed the stimuli on a color monitor (Lenovo, Beijing, China) at a viewing distance of 1 000 mm. The stimuli were presented continuously within an 80 × 80 mm window centered on the screen for 80 seconds (24 frames per second) with a 2-minute rest period between blocks. The stimuli subtended approximately 4.6° of visual angle against a uniform white background. There was no abrupt change in the location of the hand actions in the transition from the final frame to the first frame of the animation, so the natural flow of movements was preserved. Thus, the subjects saw the same pattern (hand, shadow of a hand or line drawing of a hand) in the first frame and the final frame in each 1-second animation.

Subjects were explicitly instructed to pay attention to the stimuli and to limit their eye and head movements. To ensure that subjects were paying continuous attention to the stimuli, they were asked to engage in a counting task. In each 80-second period of stimulus presentation, the animation would stop moving for 1–2 seconds between four and six times, and the subjects were asked to count the number of times the stimuli stopped and report it at the end of each block.

EEG recordings

The EEG was recorded by 11 Ag/AgCl electrodes from F3, Fz, F4, C3, Cz, C4, P3, Pz, P4, O1 and O2, using the international 10-20 method of electrode placement. The signal power of the mu rhythm at three overlapping electrodes over the motor cortex is shown in Figure 1. Horizontal electrooculogram recording electrodes were positioned at the outer canthi of both eyes and vertical electrooculogram recording electrodes were placed approximately 2 cm above and below the left eye. Electrodes placed behind each ear (mastoid bones) were electronically linked and served as the reference electrode. All channels were amplified using the SynAmps (Neuroscan, Texas, USA) (bandpass: 0.05–30 Hz, sampling rate: 1 000 Hz). The impedances of all electrodes were measured and confirmed to be less than 10 kΩ both before and after testing. Once the electrodes were in place, subjects comfortably sat in an acoustically and electromagnetically shielded testing chamber.

EEG data processing

To reduce muscle artifacts in the EEG signal, the subjects were instructed to assume a comfortable position and to avoid movements. Ocular artifacts in the continuous EEG data for each subject were removed offline prior to analysis by the automatic application of a voltage threshold procedure provided in the Neuroscan 4.3 software. EEG oscillations in the mu frequency band (8–13 Hz) recorded over occipital cortex have been reported to be affected by states of expectancy and awareness^[35] so recordings from C3, Cz and C4 may be contaminated by this posterior activity. Therefore, as in previous EEG studies^{[14, 36-37]}, the first and last 10 seconds of data in each block were removed in all subjects, to eliminate this possible contamination. A 1-minute segment of data following the initial 10 seconds was obtained for each condition. EEG data were analyzed only if the data were sufficiently “clean”, with no subject movement or eye blink artifacts. For each clean segment, the integrated power in the 8–13 Hz range was calculated using a Fast Fourier Transform. Data were partitioned into epochs of 1 second from the start of the segment, and Fast Fourier Transform was performed on the segmented data (1 024 points). A cosine window was used to minimize artifacts resulting from data splicing.

Computation of mu suppression

The mu suppression was calculated as the ratio of the power in the experimental conditions (shadow action, line drawing action and real hand action) to the power in the baseline condition. As is common in this type of study^{[22, 38-39]}, a ratio was used to control for variability in the absolute mu power as a result of individual differences such as scalp thickness and electrode placement and impedance. A log transformation was applied to each ratio because of the non-normal distribution of the ratios. Thus, negative and positive log ratios are indicative of mu suppression and enhancement, respectively.

Statistical analysis

The data were analyzed with SPSS 17.0 software (SPSS, Chicago, IL, USA). Mu suppression was analyzed using three-way repeated measures analysis of variance with the following factors: condition (shadow, line drawing, real hand), moving object (thumb, forefinger, little finger) and electrode site (F3, Fz, F4, C3, Cz, C4, P3, Pz, P4, O1 and O2). A Greenhouse-Geisser correction was applied to the degrees of freedom and the corrected probability values were reported. Two-tailed t-tests were used to test whether each condition (shadow, line drawing, real hand) suppressed the mu rhythm relative to the baseline. A value of P < 0.05 was considered statistically significant.