Testing the potential of a virtual reality neurorehabilitation system during performance of observation, imagery and imitation of motor actions recorded by wireless functional near-infrared spectroscopy (fNIRS)

Background Several neurorehabilitation strategies have been introduced over the last decade based on the so-called simulation hypothesis. This hypothesis states that a neural network located in primary and secondary motor areas is activated not only during overt motor execution, but also during observation or imagery of the same motor action. Based on this hypothesis, we investigated the combination of a virtual reality (VR) based neurorehabilitation system together with a wireless functional near infrared spectroscopy (fNIRS) instrument. This combination is particularly appealing from a rehabilitation perspective as it may allow minimally constrained monitoring during neurorehabilitative training. Methods fNIRS was applied over F3 of healthy subjects during task performance in a virtual reality (VR) environment: 1) 'unilateral' group (N = 15), contralateral recording during observation, motor imagery, observation & motor imagery, and imitation of a grasping task performed by a virtual limb (first-person perspective view) using the right hand; 2) 'bilateral' group (N = 8), bilateral recording during observation and imitation of the same task using the right and left hand alternately. Results In the unilateral group, significant within-condition oxy-hemoglobin concentration Δ[O2Hb] changes (mean ± SD μmol/l) were found for motor imagery (0.0868 ± 0.5201 μmol/l) and imitation (0.1715 ± 0.4567 μmol/l). In addition, the bilateral group showed a significant within-condition Δ[O2Hb] change for observation (0.0924 ± 0.3369 μmol/l) as well as between-conditions with lower Δ[O2Hb] amplitudes during observation compared to imitation, especially in the ipsilateral hemisphere (p < 0.001). Further, in the bilateral group, imitation using the non-dominant (left) hand resulted in larger Δ[O2Hb] changes in both the ipsi- and contralateral hemispheres as compared to using the dominant (right) hand. Conclusions This study shows that our combined VR-fNIRS based neurorehabilitation system can activate the action-observation system as described by the simulation hypothesis during performance of observation, motor imagery and imitation of hand actions elicited by a VR environment. Further, in accordance with previous studies, the findings of this study revealed that both inter-subject variability and handedness need to be taken into account when recording in untrained subjects. These findings are of relevance for demonstrating the potential of the VR-fNIRS instrument in neurofeedback applications

How to detect and reduce movement artifacts in near-infrared imaging using moving standard deviation and spline interpolation

Near-infrared imaging (NIRI) is a neuroimaging technique which enables us to non-invasively measure hemodynamic changes in the human brain. Since the technique is very sensitive, the movement of a subject can cause movement artifacts (MAs), which affect the signal quality and results to a high degree. No general method is yet available to reduce these MAs effectively. The aim was to develop a new MA reduction method. A method based on moving standard deviation and spline interpolationwas developed. It enables the semi-automatic detection and reduction of MAs in the data. It was validated using simulated and real NIRI signals. The results show that a significant reduction ofMAs and an increase in signal quality are achieved. The effectiveness and usability of themethod is demonstrated by the improved detection of evoked hemodynamic responses. The present method can not only be used in the postprocessing of NIRI signals but also for other kinds of data containing artifacts, for example ECG or EEG signals

In vivo functional near-infrared spectroscopy measures mood-modulated cerebral responses to a positive emotional stimulus in sheep

The affective state of an animal, which is thought to reflect its welfare, consists of both short-term emotional reactions and long-term general mood. Because this state is generated and processed by the brain, we used non-invasive measurement of such brain activity as a novel indicator variable and investigated the interplay of mood and short-term emotional reactions in animals. We developed a wireless sensor for functional near-infrared spectroscopy (fNIRS), which assesses cortical perfusion changes, and consequently neuronal activity. Mood differences were induced by barren and enriched housing in a total of nine sheep and we observed their brain reaction in response to the positive situation of being groomed. We detected a decrease in cerebral oxyhaemoglobin concentration ([O(2)Hb]) which persisted during grooming. The localisation of the decrease in the brain did not depend on the site where the stimulus was applied. Also, the intensity of the response did not depend on the intensity of the grooming stimulus and a sham stimulus did not evoke an [O(2)Hb] response as seen with a grooming stimulus. Thus, we conclude that the observed haemodynamic brain response was unlikely to reflect pure somato-sensory information. We then found that the amplitude of the [O(2)Hb] response was larger if sheep were in a supposedly more negative mood. This contradicts the common assumption that negative mood generally taints reactions to emotional stimuli. Our results also demonstrate the potential of fNIRS for assessing affective states in freely moving animals

Angiotensin II is an endogenous neurotransmitter for rat and human mesenteric resistance blood vessels

Angiotensin II (Ang II) is one of the most potent vasoconstrictors. We document here the innervation of rat and human mesenteric resistance arteries (MRA) by angiotensinergic neurons of the rat and human sympathetic coeliac ganglia. Angiotensinogen (Ang-N)-mRNA and angiotensin converting enzyme-mRNA but no renin-mRNA were detected by using quantitative real time polymerase chain reaction in total RNA extracts of rat coeliac ganglia. In the same extracts, cathepsin D-mRNA was detected: This protease also cleaves Ang I from Ang-N and could therefore account for the generation of neuronal Ang peptides in the absence of renin. In situ hybridization confirmed the presence of Ang-N-mRNA in the cytoplasm of rat coeliac ganglia. By using solid-phase extraction, high performance liquid chromatography and subsequent radioimmunoassay, Ang II and its metabolites were detected in rat and also in human coeliac ganglia. Immunoreactivity for Ang II was demonstrated in rat and human coeliac ganglia neurons and their projections innervating MRA. In addition, segmental angiotensinergic innervation of MRA was also observed. By means of confocal laser scanning microscopy we were able to demonstrate the presence of angiotensinergic synapses en passant along side of vascular smooth muscle cells. Our findings could indicate that Ang II is synthesized inside the neurons of sympathetic coeliac ganglia and may act as an endogenous neurotransmitter locally in MRA

Place de la clinique en médecine ambulatoire--les enseignements de l'etude TOPIC [The place of the clinic in primary case--the TOPIC study].

We know very little about the importance of history and physical examination compared to the importance of paraclinical tests in the diagnostic process in primary care. To answer this question, we examined prospectively 672 consecutive patients with chest pain in primary care. We recorded the timing and the clinical characteristics of the most frequent diagnosis. The resort to laboratory or other clinical tests and reference to specialist were influenced by: emergency consultation, potentially life-threatening aetiology, personal characteristics of the general practitioners' (GP) and patients' anxiety. GPs attributed the diagnosis to history and physical examination alone in 66% and to the association of history, physical examination and tests in 31% cases. This, clinical strategy remains the most important factor in the diagnostic process; even when they are insufficient, they allowed to generate hypotheses and guide investigations

Brain tissue oxygen saturation increases during the night in adolescents

How does the oxygen metabolism change during sleep? We aimed to measure the change in brain tissue oxygen saturation (StO2) before and after sleep with near-infrared spectroscopy (NIRS) using an in-house developed sensor. According to the synaptic homeostasis hypothesis [1], synaptic downscaling during sleep would result in reduced energy consumption. Thus, this reduced energy demands should be reflected in the oxygen metabolism and StO2. Thirteen nights of 7 male subjects (age 11-16 years, one subject contributed only one night, all others two) were included in the analysis. We performed NIRS measurements throughout the entire night. The NIRS sensor was placed close to electrode position Fp1 (international 10/20 system), over the left frontal cortex. Absolute StO2 and total haemoglobin (tHb) were calculated from the NIRS measurements using a self-calibrating method [2]. StO2 and tHb during the awake period prior to sleep and after awakening were compared. The subjects were instructed to lie in bed in the same position before and after sleep. Values of the two nights were averaged for each subject. Furthermore, a linear regression line was fit through the all-night StO2 recordings. We found an increase in StO2 by 4.32 ± 1.76 % (mean ± SD, paired t-test p < 0.001, n = 7) in the morning compared to evening, while tHb did not change (1.02 ± 6.81 μM p = 0.704, n = 7). Since the tHb remained at a similar level after sleep, this increase in StO2 indicates that in the morning more oxygenated blood and less deoxygenated blood was present in the brain compared to the evening. The slope of the regression line was 0.37 ± 0.13 % h(-1) leading to a similar increase of StO2 in the course of sleep. This may be interpreted as a reduced oxygen consumption or energy metabolism after sleep

The effect of basic assumptions on the tissue oxygen saturation value of near infrared spectroscopy

Tissue oxygen saturation (StO(2)), a potentially important parameter in clinical practice, can be measured by near infrared spectroscopy (NIRS). Various devices use the multi-distance approach based on the diffusion approximation of the radiative transport equation [1, 2]. When determining the absorption coefficient (μ (a)) by the slope over multiple distances a common assumption is to neglect μ (a) in the diffusion constant, or to assume the scattering coefficient [Formula: see text] to be constant over the wavelength. Also the water influence can be modeled by simply subtracting a water term from the absorption. This gives five approaches A1-A5. The aim was to test how these different methods influence the StO(2) values. One data set of 30 newborn infants measured on the head and another of eight adults measured on the nondominant forearm were analyzed. The calculated average StO(2) values measured on the head were (mean ± SD): A1: 79.99 ± 4.47%, A2: 81.44 ± 4.08%, A3: 84.77 ± 4.87%, A4: 85.69 ± 4.38%, and A5: 72.85 ± 4.81%. The StO(2) values for the adult forearms are: A1: 58.14 ± 5.69%, A2: 73.85 ± 4.77%, A3: 58.99 ± 5.67%, A4: 74.21 ± 4.76%, and A5: 63.49 ± 5.11%. Our results indicate that StO(2) depends strongly on the assumptions. Since StO(2) is an absolute value, comparability between different studies is reduced if the assumptions of the algorithms are not published