Biomedical subjects

Yoko Hoshi

Publications and source records attributed to Yoko Hoshi.

23 records · Page 2Linked to original sources

PubMed2002

Movement interference attenuates somatosensory high-frequency oscillations: contribution of local axon collaterals of 3b pyramidal neurons.

OBJECTIVES: We examined the effects of movement interference on high-frequency oscillations (HFOs) and N20m in 10 healthy subjects. METHODS: For the movement interference condition, somatosensory evoked magnetic fields (SEFs) following electric median nerve stimulation were recorded during voluntary movement of the digits. For the control condition, the SEFs were recorded without interference. The N20m and HFOs were separated by 3-300Hz and 300-900Hz bandpass filtering. Then, the peak-to-peak amplitudes were measured. RESULTS: Both interference/control amplitude ratios for the N20m and HFOs were smaller than 100%. In contrast, the HFO/N20m amplitude index, which was calculated by dividing the interference/control amplitude ratio for the HFOs with that for the N20m, was significantly greater in the movement interference condition than in the control condition. CONCLUSIONS: Although the overall amplitude of the HFOs was decreased by movement, enhancement of the HFOs by the movement was revealed by the HFO/N20m amplitude index. Thus, we suggest that the HFOs represent activity of the inhibitory interneurons excited by both thalamocortical afferent impulses and excitatory synaptic inputs from pyramidal neurons in area 3b through their local axon collaterals, thereby reflecting both feed-forward and feedback inhibitory effects onto the post-synaptic pyramidal neurons.

Adult↗

PubMed2002

Quantitative evaluation of the relative contribution ratio of cerebral tissue to near-infrared signals in the adult human head: a preliminary study.

Combining spatially- and time-resolved spectroscopies. we attempted to quantitatively evaluate the contribution ratio of the partial mean pathlength of cerebral tissue to the observed overall mean pathlength, in which haemoglobin concentrations were selectively changed by administration of acetazolamide. When acetazolamide was administered, the observed increases in oxygenated haemoglobin depended on the probe distance, which became progressively larger at distances of 2, 3 and 4 cm. Increases in oxygen saturation were detected at 3 and 4 cm spacing, but not at 2 cm. Assuming that the modified Lambert-Beer's law can exist in the inhomogeneous structure of the head, then, we could estimate the contribution ratio of the cerebral tissue to optical signals at the probe distances of 2, 3 and 4 cm as 33%, 55% and 69%, respectively. Using these values, we recalculated acetazolamide-induced concentration changes in oxygenated-haemoglobin in the cerebral tissue, which resulted in the same values at distances of 2, 3 and 4 cm as expected. Thus, our present method opened the door to the possibility of selectively obtaining optical signals attributed to cerebral tissue.

Adult↗

PubMed2002

[Near-infrared optical imaging of human brain function--a novel approach to the brain and the mind].

Near-infrared spectroscopy (NIRS) can measure changes in the hemoglobin oxygenation state in the human brain. NIRS has been oriented toward use for clinical monitoring of tissue oxygenation. However, we and others have recently demonstrated that NIRS also has the potential for neuroimaging. NIRS instruments, which use continuous wave light (CW) as a light source, are now commercially available. These CW-type NIRS instruments have high temporal resolution (less than 1 second) and allow long-term and continuous measurements, though they do not provide absolute values of changes in hemoglobin concentrations. In contrast, time-resolved spectroscopy (TRS), which uses short pulsed laser diodes as light sources, makes quantification possible. Quantification is necessary for the imaging of brain activity. Topographical images can be obtained by the use of our recently developed 64-channel time-resolved optical tomographic imaging system (optical CT) or by combining the 1 channel TRS instrument with the multichannel CW-type NIRS instrument. NIRS is completely non-invasive and does not require strict motion restriction during measurements unlike PET and fMRI. It is, thus, expected that NIRS will open a window into brain physiology in subjects who are difficult to examine with PET and fMRI such as children, the elderly, and patients with psychoneurological problems.

Brain↗

PubMedDate not supplied

Extraction of depth-dependent signals from time-resolved reflectance in layered turbid media.

We try a new approach with near-IR time-resolved spectroscopy, to separate optical signals originated in the upper layer from those in the lower layer and to selectively determine the absorption coefficient (mu(a)) of each layer in a two-layered turbid medium. The difference curve in the temporal profiles of light attenuation between a target and a reference medium is divided into segments along the time axis, and a slope of each segment is calculated to determine the depth-dependent mu(a). The depth-dependent mu(a) values are estimated under various conditions in which mu(a) and the reduced scattering coefficient (mu(s)') of each layer are changed with a Monte Carlo simulation and in phantom experiments. Temporal variation of them represents the difference in mu(a) between two layers when mu(s)' of a reference is the same as that of the upper layer of the target. The discrepancies between calculated mu(a) and the real mu(a) depend on the ratio of the real mu(a) of the upper layer to that of the lower layer, and our approach enables us to estimate the ratio of mu(a) between the two layers. These results suggest the potential that mu(a) of the lower layer can be determined by our procedure.

Algorithms↗

PubMedDate not supplied

Reevaluation of near-infrared light propagation in the adult human head: implications for functional near-infrared spectroscopy.

Using both experimental and theoretical methods, we examine the contribution of different parts of the head to near-IR (NIR) signal. Time-resolved spectroscopy is employed to measure the mean optical path length (PL), and the absorption (mu(a)) and reduced scattering (mu(s)') coefficients in multiple positions of the human head. Monte Carlo simulations are performed on four-layered head models based on an individual magnetic resonance imaging (MRI) scan to determine mu(a) and mu(s)' in each layer of the head by solving inverse problems, and to estimate the partial path length in the brain (p-PL) and the spatial sensitivity to regions in the brain at the source-detector separation of 30 mm. The PL is closely related to the thickness of the scalp, but not to that of other layers of the head. The p-PL is negatively related to the PL and its contribution ratio to the PL is 5 to 22% when the differential path length factor is 6. Most of the signal attributed to the brain comes from the upper 1 to 2 mm of the cortical surface. These results indicate that the NIR signal is very sensitive to hemodynamic changes associated with functional brain activation in the case that changes in the extracerebral tissue are ignorable.

Adult↗