Satoru Kohno

Three-dimensional probabilistic anatomical cranio-cerebral correlation via the international 10–20 system oriented for transcranial functional brain mapping

The recent advent of multichannel near-infrared spectroscopy (NIRS) has expanded its technical potential for human brain mapping. However, NIRS measurement has a technical drawback in that it measures cortical activities from the head surface without anatomical information of the object to be measured. This problem is also found in transcranial magnetic stimulation (TMS) that transcranially activates or inactivates the cortical surface. To overcome this drawback, we examined cranio-cerebral correlation using magnetic resonance imaging (MRI) via the guidance of the international 10-20 system for electrode placement, which had originally been developed for electroencephalography. We projected the 10-20 standard cranial positions over the cerebral cortical surface. After examining the cranio-cerebral correspondence for 17 healthy adults, we normalized the 10-20 cortical projection points of the subjects to the standard Montreal Neurological Institute (MNI) and Talairach stereotactic coordinates and obtained their probabilistic distributions. We also expressed the anatomical structures for the 10-20 cortical projection points probabilistically. Next, we examined the distance between the cortical surface and the head surface along the scalp and created a cortical surface depth map. We found that the locations of 10-20 cortical projection points in the standard MNI or Talairach space could be estimated with an average standard deviation of 8 mm. This study provided an initial step toward establishing a three-dimensional probabilistic anatomical platform that enables intra- and intermodal comparisons of NIRS and TMS brain imaging data.

Removal of the skin blood flow artifact in functional near-infrared spectroscopic imaging data through independent component analysis.

We investigate whether the functional near-infrared spectroscopic (fNIRS) signal includes a signal from the changing skin blood flow. During a locomotor task on a treadmill, changes in the hemodynamic response in the front-parietal area of healthy human subjects are simultaneously recorded using an fNIRS imaging system and a laser Doppler tissue blood flow meter. Independent component analysis (ICA) for fNIRS signals is performed. The skin blood flow changes during locomotor tasks on a treadmill. The activated spatial distribution of one of the components separated by ICA reveals an overall increase in fNIRS channels. To evaluate the uniformity of the activated spatial distribution, we define a new statistical value-the coefficient of spatial uniformity (CSU). The CSU value is a highly discriminating value (e.g., 2.82) compared with values of other components (e.g., 1.41, 1.10, 0.96, 0.61, and 0.58). In addition, the independent component signal corresponding to the activated spatial distribution is similar to changes in skin blood flow measured with the laser Doppler tissue blood flow meter. The coefficient of correlation indicates strong correlation. Localized activation areas around the premotor and medial somatosensory cortices are shown more clearly by eliminating the extracted component.

Water-diffusion slowdown in the human visual cortex on visual stimulation precedes vascular responses

We used magnetic resonance imaging (MRI) to investigate the temporal dynamics of changes in water diffusion and blood oxygenation level-dependent (BOLD) responses in the brain cortex of eight subjects undergoing visual stimulation, and compared them with changes of the vascular hemoglobin content (oxygenated, deoxygenated, and total hemoglobin) acquired simultaneously from intrinsic optical recordings (near infrared spectroscopy). The group average rise time for the diffusion MRI signal was statistically significantly shorter than those of the BOLD signal and total hemoglobin content optical signal, which is assumed to be the fastest observable vascular signal. In addition, the group average decay time for the diffusion MRI also was shortest. The overall time courses of the BOLD and optical signals were strongly correlated, but the covariance was weaker with the diffusion MRI response. These results suggest that the observed decrease in water diffusion reflects early events that precede the vascular responses, which could originate from changes in the extravascular tissue.

Broad cortical activation in response to tactile stimulation in newborns.

Tactile sensation, which is one of the earliest developing sensory systems, is very important in the perception of an individual’s body and the surrounding physical environment, especially in newborns. However, currently, only little is known about the response of a newborn’s brain to tactile sensation. The objective of the present study was to determine the response of a newborn’s brain to tactile sensation and to compare the brain responses to various sensory stimuli. Ten healthy newborns, 2–9 days after birth, were enrolled. A multichannel near-infrared spectroscopy system was used to measure brain responses. The probe array covered broad cortical areas, including the parietal, temporal, and occipital areas. We measured cortical hemodynamic changes in response to three different types of stimuli: tactile, auditory, and visual. Activated areas were analyzed by t-tests, and the number of activated channels among the three different stimuli was compared by &khgr;2-tests. The results showed that when the brain responded to each type of stimulation, the corresponding primary sensory area was activated, and tactile stimuli induced broader areas of brain activation than the other two types of stimuli (auditory or visual). Thus, broad brain areas, including the temporal and parietal areas, were activated by tactile stimuli in early newborn periods. These results suggest that there are differences in newborns’ reactions to various types of sensory stimuli, which may reflect the importance of tactile sensation in the early newborn period.

Emotional discrimination during viewing unpleasant pictures: timing in human anterior ventrolateral prefrontal cortex and amygdala

The ventrolateral prefrontal cortex (VLPFC) and amygdala have critical roles in the generation and regulation of unpleasant emotions, and in this study the dynamic neural basis of unpleasant emotion processing was elucidated by using paired-samples permutation t-tests to identify the timing of emotional discrimination in various brain regions. We recorded the temporal dynamics of blood-oxygen-level-dependent (BOLD) signals in those brain regions during the viewing of unpleasant pictures by using functional magnetic resonance imaging (fMRI) with high temporal resolution, and we compared the time course of the signal within the volume of interest (VOI) across emotional conditions. Results show that emotional discrimination in the right amygdala precedes that in the left amygdala and that emotional discrimination in both those regions precedes that in the right anterior VLPFC. They support the hypotheses that the right amygdala is part of a rapid emotional stimulus detection system and the left amygdala is specialized for sustained stimulus evaluation and that the right anterior VLPFC is implicated in the integration of viscerosensory information with affective signals between the bilateral anterior VLPFCs and the bilateral amygdalae.

Development of double density whole brain fNIRS with EEG system for brain machine interface

Brain-machine interfaces (BMI) are expected as new man-machine interfaces. Non-invasive BMI have the potential to improve the quality of life of many disabled individuals with safer operation. The non-invasive BMI using the functional functional near-infrared spectroscopy (fNIRS) with the electroencephalogram (EEG) has potential applicability beyond the restoration of lost movement and rehabilitation in paraplegics and would enable normal individuals to have direct brain control of external devices in their daily lives. To shift stage of the non-invasive BMI from laboratory to clinical, the key factor is to develop high-accuracy signal decoding technology and highly restrictive of the measurement area. In this article, we present the development of a high-accuracy brain activity measurement system by combining fNIRS and EEG. The new fNIRS had high performances with high spatial resolution using double density technique and a large number of measurement channels to cover a whole human brain.

Spatial distributions of hemoglobin signals from superficial layers in the forehead during a verbal-fluency task.

Abstract. Functional near-infrared spectroscopy (fNIRS) signals originate in hemoglobin changes in both the superficial layer of the head and the brain. Under the assumption that the changes in the blood flow in the scalp are spatially homogeneous in the region of interest, a variety of methods for reducing the superficial signals has been proposed. To clarify the spatial distributions of the superficial signals, the superficial signals from the forehead during a verbal-fluency task were investigated by using ten source–detector pairs separated by 5 mm, whereas fNIRS signals were also detected from two source–detector pairs separated by 30 mm. The fNIRS signals strongly correlated with the superficial signals at some channels on the forehead. Hierarchical cluster analysis was performed on the temporal cross-correlation coefficients for two channels of both the NIRS signals, and the analysis results demonstrate spatially heterogeneous distributions and network structures of the superficial signals from within the forehead. The results also show that the assumption stated above is invalid for homogeneous superficial signals from any region of interest of 15-mm diameter or larger on the forehead. They also suggest that the spatially heterogeneous distributions may be attributable to vascular networks, including supraorbital, supratrochlear, and superficial temporal vessels.

Numerical modeling of photon propagation in biological tissue based on the radiative transfer equation

Recently, numerical models for photon propagation inside the living tissues have extensively been discussed based on the radiative transfer (RTE) and diffusion equations (DE). In this paper, we propose a hybrid model based on the RTE and DE for photon propagation in a turbid medium with an anisotropic source and refractive-index-mismatched boundaries. At first, we examine the validity of the diffusion approximation by comparing calculated fluence rates between the RTE and DE. The accuracy of the diffusion approximation is confirmed when the detector is placed far from the source and boundaries. These length scales are estimated at ∼10/μt from the source and ∼3/μt from the boundaries with the transport coefficient μt. By using the two length scales, we can construct a hybrid model successfully. Our hybrid model recovers photon propagation based on the RTE, and effectively reduces computation costs by approximately half.

FASCINATE: a pulse sequence for simultaneous acquisition of T2-weighted and fluid-attenuated images.

A pulse sequence that enables simultaneous acquisition of T2‐weighted and fluid‐attenuated images is presented. This sequence is referred to as FASCINATE (Fluid‐Attenuated Scan Combined with Interleaved Non‐ATtEnuation). In this new technique, the inversion pulse of conventional fast fluid‐attenuated inversion recovery (FLAIR) is replaced with a fast spin echo (FSE) acquisition that has an additional 180(y)–90(x) pulse train for driven inversion. By using appropriate scan parameters, the first part of the sequence provides T2‐weighted images and the second part provides fluid‐attenuated images, thus allowing simultaneous acquisition in a single scan time comparable to that of fast FLAIR. FASCINATE was compared with conventional scanning techniques using a normal volunteer and a patient. A signal simulation was also conducted. In the human study, both T2‐weighted and fluid‐attenuated images from FASCINATE showed the same image quality as conventional images, suggesting the potential for this technique to replace the combination of fast FLAIR and T2‐weighted FSE for scan time reduction. Magn Reson Med 51:205–211, 2004.

Hybrid model for photon propagation in random media based on the radiative transfer and diffusion equations

For improvement of diffuse optical tomography, one needs a numerical model to compute photon propagation accurately and efficiently. Thus, in the paper, we construct a hybrid model based on the radiative transfer equation (RTE) and diffusion equation (DE) in the time domain under the refractive-index-mismatching at boundary. At first, a fictive interface between the RTE and DE regions is determined, which is characterized by a length scale ρDA. By comparing the fluence rate calculated based on the RTE to that on the DE, we estimate ρDA at ~10/μt, where μt denotes the extinction coefficient. Next, we determine a coefficient representing the reflectivity in the Robin boundary condition of the DE by analyzing the fluence rates in the domain outside ρDA. Then, the hybrid model is constructed by using the determinations. The fluence rates based on this hybrid algorithm is consistent with those on the RTE in a whole range of the medium and computational costs are reduced efficiently.