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Functional decline in locomotion is common among the elderly, and the prevalence of gait disorders increases with age. Recently, increasing interest has been focused on the influence of age-related decline in brain function and neurological disorders such as dementia and Alzheimer's disease on gait capacity. However, the neural mechanisms underlying gait control in the elderly remain poorly understood. We examined whether cortical activation patterns associated with the control of gait speed were related to the walking capacity in elderly subjects. Fifteen healthy elderly subjects participated in the study (mean +/- SD 63 +/- 4). Using functional near-infrared spectroscopy, we measured the changes in the cortical oxygenated hemoglobin (oxyHb) while the subjects walked on a treadmill at low, moderate, and high speeds corresponding to 30, 50, and 70% intensity of work load in each subject. We found a greater increase in oxyHb in the left prefrontal cortex (PFC) and the supplementary motor area (SMA) during walking at 70% intensity than at 50 or 30%. The degree of medial sensorimotor cortex (mSMC) and SMA activations was correlated with the locomotor speed and cadence. Heart rate response was only related with left PFC activation. Furthermore, at the highest speed, the change in the PFC activation was greater in subjects with low gait capacity than in those with high gait capacity. Our results indicate that the left PFC, SMA, and SMC control gait speed, and that the involvement of the left PFC might depend on an age-related decline in gait capacity in the elderly.

Locomotor recovery after stroke may be associated with improvement of asymmetry in SMC activation and enhanced PMC activation in the affected hemisphere.

Abstract. The brain activity during cooperation as a form of social process is studied. We investigate the relationship between coinstantaneous brain-activation signals of multiple participants and their cooperative-task performance. A wearable near-infrared spectroscopy (NIRS) system is used for simultaneously measuring the brain activities of two participants. Each pair of participants perform a cooperative task, and their relative changes in cerebral blood are measured with the NIRS system. As for the task, the participants are told to count 10 s in their mind after an auditory cue and press a button. They are also told to adjust the timing of their button presses to make them as synchronized as possible. Certain information, namely, the "intertime interval" between the two button presses of each participant pair and which of the participants was the faster, is fed back to the participants by a beep sound after each trial. When the spatiotemporal covariance between the activation patterns of the prefrontal cortices of each participant is higher, the intertime interval between their button-press times was shorter. This result suggests that the synchronized activation patterns of the two participants' brains are associated with their performance when they interact in a cooperative task. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

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