Yukiko Hirabayashi

Cerebral hemodynamics in newborn infants exposed to speech sounds: a whole-head optical topography study.

Considerable knowledge on neural development related to speech perception has been obtained by functional imaging studies using near‐infrared spectroscopy (optical topography). In particular, a pioneering study showed stronger left‐dominant activation in the temporal lobe for (normal) forward speech (FW) than for (reversed) backward speech (BW) in neonates. However, it is unclear whether this stronger left‐dominant activation for FW is equally observed for any language or is clearer for the mother tongue. We hypothesized that the maternal language elicits clearer activation than a foreign language in newborns because of their prenatal and/or few‐day postnatal exposure to the maternal language. To test this hypothesis, we developed a whole‐head optode cap for 72‐channel optical topography and visualized the spatiotemporal hemodynamics in the brains of 17 Japanese newborns when they were exposed to FW and BW in their maternal language (Japanese) and in a foreign language (English). Statistical analysis showed that all sound stimuli together induced significant activation in the bilateral temporal regions and the frontal region. They also showed that the left temporal‐parietal region was significantly more active for Japanese FW than Japanese BW or English FW, while no significant difference between FW and BW was shown for English. This supports our hypothesis and suggests that the few‐day‐old brain begins to become attuned to the maternal language. Together with a finding of equivalent activation for all sound stimuli in the adjacent measurement positions in the temporal region, these findings further clarify the functional organization of the neonatal brain. Hum Brain Mapp 33:2092–2103, 2012.

Wavelet analysis for detecting body-movement artifacts in optical topography signals.

We have developed a wavelet-based method of detecting body-movement artifacts in optical topography (OT) signals. Although OT, which is a noninvasive imaging technique for measuring hemodynamic response related to brain activation, is particularly useful for studying infants, the signals occasionally contain undesirable artifacts caused by body movements, so data corrupted by body-movement artifacts must be eliminated to obtain reliable results. For this purpose, we applied a wavelet transform to automatically detect body-movement artifacts in OT signals. We measured OT signals from nine healthy infants in response to speech stimuli. After the continuous signals had been divided into blocks (a block is a time series of OT signal in a 30-s period including a 10-s stimulation period), they were classified into two groups (movement blocks and non-movement blocks) according to whether the participants moved or not by video judgment. Using those data, we developed a wavelet-based algorithm for detecting body-movement artifacts at a high discrimination rate being consistent with the actual body-movement state. The wavelet method has two parameters (scale and threshold), and a Monte Carlo analysis gave the mean optimal parameters as 9+/-1.9 (mean+/-standard deviation) for the scale and as 42.7+/-1.9 for the threshold. Our wavelet method with the mean optimal parameters (scale=9, threshold=43) achieved a higher discrimination rate (mean+/-standard deviation: 86.3+/-8.8%) for actual body movement than a previous method (mean+/-standard deviation: 80.6+/-8.7%) among different participants (paired t test: t(8)=2.92, p<0.05). These results demonstrate that our wavelet method is useful in practice for eliminating blocks containing body-movement artifacts in OT signals. It will contribute to obtaining reliable results from OT studies of infants.

A sonic spray interface for the mass analysis of highly charged ions from protein solutions at high flow rates.

We have improved the sonic spray interface to enable the analysis of multiply charged ions of protein from a solution at a flow rate of 1 mL/min using a conventional liquid chromatograph/mass spectrometer. In this interface, we added a multihole plate in front of the sampling orifice of a mass spectrometer. This plate does not have a hole coaxial to the sampling orifice but has small holes around the central region of the plate. The plate reduces the density of the solvent molecules in the sprayed gas introduced into the vacuum region through the sampling orifice from the atmosphere and prevents the ions from being solvated and becoming charged droplets due to the cooling that follows adiabatic expansion of the sprayed gas. With this improvement, multiply charged ions whose charge distribution ranged from 11+ to 16+ were analyzed from a 1 μM cytochrome c solution at a high flow rate of 1 mL/min without using a splitter.

Multiply-charged Ion Formation by Sonic Spray

In sonic spray ionization technique, a solution from a fused-silica capillary is sprayed with a sonic gas flow coaxial to the capillary. The current for the ions produced and for the charged droplets is found to be dramatically enhanced when a voltage is applied to a surrounding metal piece, which is isolated from the solution by the fused-silica capillary. This can be ascribed to the induced concentration difference between positive and negative ions in the solution near the surface. Furthermore, multiply-protonated molecules produced in this way from protein solutions are analyzed with a quadrupole mass spectrometer. The ion intensity shows a strong dependence on the voltage but the diameter of the droplet produced by the spray is likely to be independent of the voltage. Thus, we conclude that the charge density of the droplet is regulated by the voltage.

Tutorial on platform for optical topography analysis tools

Abstract. Optical topography/functional near-infrared spectroscopy (OT/fNIRS) is a functional imaging technique that noninvasively measures cerebral hemoglobin concentration changes caused by neural activities. The fNIRS method has been extensively implemented to understand the brain activity in many applications, such as neurodisorder diagnosis and treatment, cognitive psychology, and psychiatric status evaluation. To assist users in analyzing fNIRS data with various application purposes, we developed a software called platform for optical topography analysis tools (POTATo). We explain how to handle and analyze fNIRS data in the POTATo package and systematically describe domain preparation, temporal preprocessing, functional signal extraction, statistical analysis, and data/result visualization for a practical example of working memory tasks. This example is expected to give clear insight in analyzing data using POTATo. The results specifically show the activated dorsolateral prefrontal cortex is consistent with previous studies. This emphasizes analysis robustness, which is required for validating decent preprocessing and functional signal interpretation. POTATo also provides a self-developed plug-in feature allowing users to create their own functions and incorporate them with established POTATo functions. With this feature, we continuously encourage users to improve fNIRS analysis methods. We also address the complications and resolving opportunities in signal analysis.

Technique for designing and evaluating probe caps used in optical topography of infants using a real head model based on three dimensional magnetic resonance images

We have developed an effective technique for aiding the design and evaluating the performance of the probe caps used to perform optical topography (OT) on infants. To design and evaluate a probe cap, it is necessary to determine the measurement positions for conducting OT on the brain surface of subjects. One technique for determining these positions on the brain surface is to find their three-dimensional (3D) coordinates using a 3D magnetic space digitizer, which consists of a 3D magnetic source and a 3D magnetic sensor. The problem with this technique is that it takes a long time to determine all the measurement points on the subjects head and it is difficult to use with infants. It is a particular problem with infants who cannot support their own heads. Therefore, we have developed a real model of an infant subjects head based on 3D magnetic resonance (MR) images. The model is made from an optical-curable resin using 3D computer-aided-format coordinate data taken from 3D MR image-format coordinate data. We have determined the measurement positions on the surface of the model corresponding to a scalp using a 3D magnetic space digitizer and displayed the positions on a 3D MR image of the infants brain. Using this technique, we then determined the actual 72 measurement positions located over the entire brain surface area for use with our new whole-head probe cap for neonates and infants. This method is useful for evaluating the performance of and designing probe caps.

Development of near infrared-light spectroscopic topography: novel imaging modality for higher order function of the human brain

A new neuro-imaging technique based on near-infrared spectroscopy has been developed in Japan. The technique comes into usage in order to elucidate and diagnose the brain function in baby to adult.

The Application of Sonic Spray Ionization. A Sonic Spray Interface for Capillary Electrophoresis/Mass Spectrometry.

An interface for capillary electrophoresis/mass spectrometry (CE/MS) using sonic spray ionization (SSI) was developed. In the SSI technique, a sample solution is sprayed at any solution-flow rate from a sample-introduction capillary with a high-speed gas flow coaxial to the capillary and ions are formed at atmospheric pressure. Therefore, it can be used with a wide range of buffer solutions regardless of the conductivity of the solutions. SSI is now being used as an interface in semi-micro and conventional liquid chromatography/mass spectrometry (LC/MS). However, the pressure around the tip of the sample-introduction capillary is reduced by the high-speed gas flow, so the solution is pumped into the capillary at a flow rate above 0.1 μL/min due to the difference of pressure between the two ends of the capillary. Since the solution-flow rate in CE is much lower than this pumping rate, the resolution of CE separation is expected to be decreased by the pumping effect when an electrophoresis capillary is connected directly with the sample-introduction capillary. To prevent this in CE/MS, the author has set a buffer reservoir between the sample-injection capillary and the electrophoresis capillary. Using this interface, the author has demonstrated CE/MS analysis with a mobile-phase buffer containing 15 mM of phosphate by filling the buffer reservoir with an acetic-acid solution as a substitute for the mobile-phase buffer. This increased the ion intensity 100-fold by enhancing the evaporation of charged droplets produced by the spray.