Original articleRegional cerebral blood flow changes associated with emotions in children
Introduction
Emotion, which has an important role in higher cognition, especially attention, volition, and planning, is a complex mental function that reflects the coordinated activities of many parts of the brain. Benson separated the multiple facets of emotion into four subunits: mood, affect, drive, and cognitive control [1]. Clinical, experimental, and neuroimaging studies have explored neuroanatomic correlates of various emotions [2], [3], [4], and it has been thought that the prefrontal cortex has an important role in emotional responses that require cognitive control [1]. In contrast with adults, however, little is known about the neural substrates of emotion in preschool children. The facets of emotion, especially drive and cognitive control, are likely to be age-dependent functions. Modern neuroimaging techniques, such as positron emission tomography and functional magnetic resonance imaging, are expected to provide further insights into brain functions of children. However, because radioactive substances are used in positron emission tomography studies and strict motion restriction is required in both functional magnetic resonance imaging and positron emission tomography studies, it is difficult to apply these techniques to children.
Near-infrared spectroscopy (NIRS), a noninvasive optical technique, can measure changes in the hemoglobin oxygenation state and the redox state of cytochrome oxidase in the human brain [5]. NIRS is developing into a useful tool for clinical monitoring of tissue oxygenation [6], [7]. The validity and utility of this technique have been reported in laboratory and clinical applications [8], [9], although the measurement of cytochrome oxidase is still controversial [10], [11]. Although NIRS has been oriented toward use for clinical monitoring, we and others have recently demonstrated that NIRS has potential for neuroimaging of the human brain [12], [13], [14]. Simultaneous measurements with NIRS and other techniques, such as positron emission tomography, have confirmed its reliability in estimating cerebral blood flow [15], [16], [17]. NIRS instruments of several types are commercially available. Among them, a portable NIRS instrument allows patients to move about during measurement just as with portable EKG and electroencephalogram instruments. Because data are recorded into a memory card interface in this system, however, they are not displayed in real time. We therefore combined a wireless system with this portable NIRS instrument so that we could see data in real time at a place that was distant from the patient. It was expected that this NIRS system would enable neuroimaging studies on freely moving patients outside of laboratories, which is crucial to studies of children. Thus we used this system for evaluating hemodynamic changes associated with emotions in the bilateral frontal regions of preschool children. A 21-minute video clip consisting of various scenes was used to elicit emotions of various types and valences. Among the expected emotions elicited, hemodynamic changes associated with being startled, anticipation (prediction, expectation), and pleasant and unpleasant emotions were examined. The aims of this study were to investigate the neural substrates of emotion in younger children and the relationship between emotional response and age. The performance and possibilities of the portable NIRS system were also examined.
Section snippets
Portable NIRS measurement system
The details of the portable NIRS instrument (Fig 1) (HEO 200, Omron Ltd. Inc., Tokyo, Japan) used in this study have been reported elsewhere [18]. Briefly, it consists of a main unit and a probe unit. The main unit consists of a one-chip central processing unit, a light-emitting diode (LED) driver, an amplifier, a memory card interface, a liquid crystal display, and a power source. The probe unit, molded in elastic black silicon rubber, has a photodiode (the detector) in the center and
Results
No children felt uncomfortable during measurements, and all were cooperative, which was attributed to the fact that children’s motion was not restricted and measurements were performed in an examination room not so different from an ordinary living room. Fig 2 depicts an example of a NIRS trace obtained from the left side of a 5-year-old female while she was watching the 21-minute video.
Discussion
The neural substrates of emotion have not been fully elucidated even in adults. As far as we know, there is no study on the details of the neural network of the visual startle response. A study on the acoustic startle response in humans reported that the activity responsible for the startle response originated within the lower brainstem [23]. However, we had previously observed that cerebral blood flow increased in the frontal region of the adult brain responding to being startled, which was
Acknowledgements
This work has been supported by the Japan Society for the Promotion of Science project (RFTR-97L0025).
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