Neurofeedback using real-time near-infrared spectroscopy enhances motor imagery related cortical activation.

Accumulating evidence indicates that motor imagery and motor execution share common neural networks. Accordingly, mental practices in the form of motor imagery have been implemented in rehabilitation regimes of stroke patients with favorable results. Because direct monitoring of motor imagery is difficult, feedback of cortical activities related to motor imagery (neurofeedback) could help to enhance efficacy of mental practice with motor imagery. To determine the feasibility and efficacy of a real-time neurofeedback system mediated by near-infrared spectroscopy (NIRS), two separate experiments were performed. Experiment 1 was used in five subjects to evaluate whether real-time cortical oxygenated hemoglobin signal feedback during a motor execution task correlated with reference hemoglobin signals computed off-line. Results demonstrated that the NIRS-mediated neurofeedback system reliably detected oxygenated hemoglobin signal changes in real-time. In Experiment 2, 21 subjects performed motor imagery of finger movements with feedback from relevant cortical signals and irrelevant sham signals. Real neurofeedback induced significantly greater activation of the contralateral premotor cortex and greater self-assessment scores for kinesthetic motor imagery compared with sham feedback. These findings suggested the feasibility and potential effectiveness of a NIRS-mediated real-time neurofeedback system on performance of kinesthetic motor imagery. However, these results warrant further clinical trials to determine whether this system could enhance the effects of mental practice in stroke patients.

Cortical control of postural balance in patients with hemiplegic stroke.

Despite its remarkable effect on the activities of daily living, the precise mechanism underlying balance control after stroke remains to be elucidated. In this study, we investigated the cortical activation induced by postural perturbation in 20 patients with stroke using a 50-channel event-related functional near-infrared spectroscopy. A combination of brisk forward and backward movements of a platform without any prior cue was used as an external postural perturbation. Multi-participant analysis of oxygenated hemoglobin signals showed postural perturbation-related cortical activation in the prefrontal cortical areas in both hemispheres as well as the premotor and parietal association cortical areas in the unaffected hemisphere. Regression analysis using the individual Berg Balance Scale as the regressor showed a significant positive correlation between balance ability and the postural perturbation-related changes in oxygenated hemoglobin signals in the supplementary motor areas and prefrontal cortical areas in both hemispheres. Consistent with the previous findings in healthy participants, these findings suggest that the broad cortical network, including the prefrontal, premotor, supplementary motor, and parietal cortical areas in both hemispheres, was essential for balance control even in poststroke patients.

Synchronous activity of two people's prefrontal cortices during a cooperative task measured by simultaneous near-infrared spectroscopy.

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.

Application of near-infrared spectroscopy to measurement of hemodynamic signals accompanying stimulated saliva secretion.

We aim to test the feasibility of using near-infrared spectroscopy (NIRS) for indirect measurement of human saliva secretion in response to taste stimuli for potential application to organoleptic testing. We use an NIRS system to measure extracranial hemodynamics (Hb-signals around the temples) of healthy participants when taste stimuli are taken in their mouths. First, the Hb-signals and volume of expelled saliva (stimulated by distilled-water or sucrose-solution intake) are simultaneously measured and large Hb-signal changes in response to the taste stimuli (Hb-responses) are found. Statistical analysis show that both the Hb response and saliva volume are larger for the sucrose solution than for the distilled water with a significant correlation between them (r = 0.81). The effects of swallowing on the Hb-signals are investigated. Similar Hb responses, differing from the sucrose solution and distilled water, are obtained even though the participants swallow the mouth contents. Finally, functional magnetic resonance imaging is used to identify possible sources of the Hb signals corresponding to salivation. Statistical analysis indicates similar responses in the extracranial regions, mainly around the middle meningeal artery. In conclusion, the identified correlation between extracranial hemodynamics and the saliva volume suggests that NIRS is applicable to the measurement of hemodynamic signals accompanying stimulated saliva secretion.

Noninvasive imaging of prefrontal activation during attention-demanding tasks performed while walking using a wearable optical topography system.

Optical topography (OT) based on near-infrared spectroscopy is a noninvasive technique for mapping the relative concentration changes in oxygenated and deoxygenated hemoglobin (oxy- and deoxy-Hb, respectively) in the human cerebral cortex. In our previous study, we developed a small and light wearable optical topography (WOT) system that covers the entire forehead for monitoring prefrontal activation. In the present study, we examine whether the WOT system is applicable to OT measurement while walking, which has been difficult with conventional OT systems. We conduct OT measurements while subjects perform an attention-demanding (AD) task of balancing a ping-pong ball on a small card while walking. The measured time course and power spectra of the relative concentration changes in oxy- and deoxy-Hb show that the step-related changes in the oxy- and deoxy-Hb signals are negligible compared to the task-related changes. Statistical assessment of the task-related changes in the oxy-Hb signals show that the dorsolateral prefrontal cortex and rostral prefrontal area are significantly activated during the AD task. These results suggest that our functional imaging technique with the WOT system is applicable to OT measurement while walking, and will be a powerful tool for evaluating brain activation in a natural environment.

Gait capacity affects cortical activation patterns related to speed control in the elderly.

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.

Role of the prefrontal cortex in human balance control.

Although recent studies have demonstrated cortical involvement in human balance control, there is insufficient information regarding the regions of the cerebral cortex that contribute to human balance control and their mechanism of action. Using a functional near-infrared spectroscopic system, we investigated perturbation-related cortical activation. External perturbations were provided with and without the preceding auditory warning signals 2 s before the perturbation. Statistical analysis by applying the general linear model showed significant activation in the prefrontal cortex, including the dorsolateral prefrontal cortex and frontal eye field after external perturbation, regardless of the preceding auditory warning signals. A time-line analysis revealed similar temporal profiles for prefrontal activation in 2 different conditions. Based on the contrast between the 2 conditions, we detected enhanced activation in the right posterior parietal cortex and supplementary motor area in the condition where the auditory warning signals were provided. We presumed that prefrontal involvement may be relevant to adequate allocation of visuospatial attention. Our results may facilitate the understanding of cortical mechanisms for balance control in humans and the underlying pathophysiology of falls.

Activities in the frontal cortex and gait performance are modulated by preparation. An fNIRS study.

Neural activities in the primary motor cortex and supplementary motor area increase during the preparation as well as execution of voluntary movements of the hand and foot. However, there are few studies concerning preparatory activities of the brain preceding walking performance. We investigated how a verbal instruction "ready" before walking affected cortical activations and walking performances using a functional near-infrared spectroscopy. Seven healthy subjects performed two locomotor tasks on a treadmill with a verbal instruction "ready" before the treadmill was started (prepared walking; PW) and without it (simple walking; SW). Cadence was smaller and stride length was longer in PW than in SW. Increases of oxygenated hemoglobin (oxyHb) in the frontal regions especially in the prefrontal and premotor cortices were greater in PW than in SW both during the preparation and walking periods. These results suggested that preparation for walking cued by a verbal instruction enhanced frontal activations both during the preparation and execution of walking as well as walking performance.

Sustained prefrontal activation during ataxic gait: a compensatory mechanism for ataxic stroke?

There is accumulated evidence that cortical reorganization plays an important role in motor recovery after supratentorial stroke. However neural mechanisms underlying functional recovery of ataxia after infratentorial stroke remain unclear. We investigated cortical activations during ataxic gait in patients with infratentorial stroke to test the hypothesis that cerebral cortices were involved in compensatory mechanisms for ataxic gait. Twelve patients with infratentorial stroke (mean duration+/-S.D. from the onset: 88.3+/-44.8 days) and 11 age-matched healthy subjects participated in this study. All patients had predominant ataxia without severe hemiparesis. We measured cortical activation as assessed by task-related increase of oxygenated hemoglobin during gait on a treadmill using functional near-infrared spectroscopy. Task consisted of three repetitions of gait period alternated with rest period. In controls, cortical activations in the lateral and medial prefrontal cortex during the acceleration phase tended to be attenuated during the steady phase of the gait period while these activations were sustained throughout the gait period in ataxic patients. Repeated measures ANOVA for cortical activation revealed significant interactions (p<0.005) between phase (acceleration/steady) and group (control/stroke) in the medial and lateral prefrontal regions. These results suggest that sustained prefrontal activation during ataxic gait might be relevant to compensatory mechanisms for ataxic gait after infratentorial stroke.

Frontal regions involved in learning of motor skill--A functional NIRS study.

To investigate cerebral mechanisms underlying learning of motor skill, we assessed serial changes of cortical activation patterns during a pursuit rotor (PR) task in 18 right-handed, healthy subjects using a functional near-infrared spectroscopy (fNIRS) system. Subjects performed the task with the right hand for 30 s alternated with 30-s rest for 8 repetitions (cycle1 to 8). Gains in motor skill were evaluated by time for keeping the stylus on the target (max 30 s), surface EMG patterns and trajectories of the arm. Performance improved with repetitions of the task cycles (12.9/17.1/19.3/20.0/21.1/22.2/23.6/23.9 s on average) and reached plateau at the 7th cycle. Reciprocal EMG patterns and steady trajectories were associated with acquisition of the motor skill. Task-related increases of oxygenated hemoglobin (oxyHb) were observed in the channels covering the sensorimotor cortex (SMC), premotor and prefrontal regions. There were also task-related decreases of deoxygenated hemoglobin (deoxyHb) in these areas although the changes were smaller compared with those of oxyHb. The center of task-related increases of oxyHb was initially located in the presupplementary motor area (preSMA) and shifted caudally to the supplementary motor area (SMA) with cycle repetitions. The ratios of oxyHb changes in preSMA to SMA significantly decreased with task repetitions. DeoxyHb changes confirmed the activation patterns. These data suggest that preSMA plays an important role in the early phase of motor learning while the SMA might be more involved in the late learning phase of the motor skill.

Effect of body weight support on cortical activation during gait in patients with stroke.

Treadmill training with body weight support (BWS) was shown to improve locomotion after stroke. We investigated whether BWS affected cortical activation during gait using an optical imaging system. In six patients with subcortical stroke, BWS lowered activation in the sensorimotor cortex (SMC) as assessed by task-related changes of oxygenated hemoglobin levels (P<0.01). The changes of SMC activation correlated with those of cadence (P<0.05). Improvement of asymmetry in SMC activation also correlated with improvement of asymmetric gait (P<0.05). In five age-matched controls, BWS increased overall activation (P<0.05) but did not modify gait parameters and there was no correlation between gait parameters and SMC activation. It is suggested that BWS might improve efficacy of SMC function in patients with stroke.

Prefrontal and premotor cortices are involved in adapting walking and running speed on the treadmill: an optical imaging study.

We investigated changes of regional activation in the frontal cortices as assessed by changes of hemoglobin oxygenation during walking at 3 and 5 km/h and running at 9 km/h on a treadmill using a near-infrared spectroscopic (NIRS) imaging technique. During the acceleration periods immediately preceded reaching the steady walking or running speed, the levels of oxygenated hemoglobin (oxyHb) increased, but those of deoxygenated hemoglobin (deoxyHb) did not in the frontal cortices. The changes were greater at the higher locomotor speed in the bilateral prefrontal cortex and the premotor cortex, but there were less speed-associated changes in the sensorimotor cortices. The medial prefrontal activation was most prominent during the running task. These results indicate that the prefrontal and premotor cortices are involved in adapting to locomotor speed on the treadmill. These areas might predominantly participate in the control of running rather than walking.

Jogging improved performance of a behavioral branching task: implications for prefrontal activation.

We studied the effect of habitual jogging on the performance of a frontal lobe functioning test. Fourteen subjects were divided into a jogging trained group (TG) or a jogging untrained group (NG). The TG jogged for 12 weeks, for 30 min, 2.6 times per week, while the NG did not. We administered a prefrontal branching task (BR) combining a Spatial Delayed-Response Test (DR) and a Go/No-Go Test (GNG). Each test alone and a Simple Reaction Time Test (SR) were given as controls. All tests were given three times at 6 week intervals over 12 weeks in both groups. In the TG, the tests were given two times after termination of the jogging. The maximal oxygen uptake (VO2max) was measured in the TG during the 12 weeks. After 12 weeks, the correct performance rates in the BR task were more improved in the TG than in the NG. The control and reaction time tests were unchanged in both groups. The improved performance in the BR task in the TG decreased after stopping the jogging. The VO2max increased significantly during the 12 weeks of jogging in the TG. Thus, the habitual jogging improved performance in a prefrontal BR.

Longitudinal optical imaging study for locomotor recovery after stroke.

BACKGROUND AND PURPOSE: We sought to investigate cerebral mechanisms underlying locomotor recovery after stroke. METHODS: We measured cortical activities during hemiparetic gait on the treadmill before and after 2 months of inpatient rehabilitation in 8 patients with initial stroke (5 men, 3 women; 4 with right and 4 with left hemiparesis; aged 57 years; 3 months after stroke on average), using an optical imaging system. RESULTS: On the initial evaluation, hemiparetic gait was associated with increased oxygenated hemoglobin levels in the medial primary sensorimotor cortex (SMC) that were greater in the unaffected hemisphere than in the affected hemisphere as well as in the premotor cortex (PMC) and supplementary motor area. On the second examination, the asymmetry in SMC activation significantly improved, and there was enhanced PMC activation in the affected hemisphere. Improvement of the asymmetrical SMC activation significantly correlated with improvement of gait parameters. CONCLUSIONS: Locomotor recovery after stroke may be associated with improvement of asymmetry in SMC activation and enhanced PMC activation in the affected hemisphere.

Premotor cortex is involved in restoration of gait in stroke.

Cortical activation during hemiplegic gait was assessed in six nonambulatory patients with severe stroke (four men, two women; four with right and two with left hemiplegia; 57 years old and 3 months after stroke on average), using a near-infrared spectroscopic imaging system. Each patient performed tasks of treadmill walking (0.2km/hr), alternated with rest every 30 seconds for four repetitions, under partial body weight support, either with mechanical assistance in swinging the paretic leg control (CON) or with a facilitation technique that enhanced swinging of the paretic leg (FT), provided by physical therapists. Gait performance was associated with increased oxygenated hemoglobin levels in the medial primary sensorimotor cortex in the unaffected hemisphere greater than in the affected hemisphere. Both cortical mappings and quantitative data showed that the premotor activation in the affected hemisphere was enhanced during hemiplegic gait. There was also a prominent activation in the presupplementary motor area. Overall cortical activations and gait performance were greater in walking with FT than with CON. These indicate that multiple motor areas including the premotor cortex and presupplementary motor area might play important roles in restoration of gait in patients with severe stroke.