Summary: Near-infrared spectroscopy (NIRS) was used to monitor human visual cortical function during and after photic stimulation (PS) in five adult volunteers. Cerebral blood volume (CBV) increased on the occipital surface during PS, but NIRS parameters did not change on the frontal surface. The increase in CBV was caused by a rapid increase in oxyhemoglobin with but a small increase in deoxyhemoglobin, suggesting cerebral vascular dilata tion with decreased oxygen consumption. After PS A study of human subjects using positron emis sion tomography (PET) indicated that photic stim ulation (PS) raises blood flow and glucose consump tion in the visual cortex by about 50%, whereas oxygen consumption increases only 5% (Fox et al., 1988). Using proton magnetic resonance spectros copy, Prichard et al. (1991) demonstrated that PS causes an increase in brain lactate in the human visual cortex. However, the mechanism of PS ac tion on human visual cortical function is still not clear. Near-infrared spectroscopy (NIRS) is a non invasive tool for the continuous monitoring of changes in cerebral blood volume (CBV), oxyhemo globin (Hb02), deoxyhemoglobin (HbR) and redox state of cytochrome aa3 (Cyt). Voluntary hypervenReceived February 11, 1992; final revision received October 27, 1992; accepted October 27, 1992.Address correspondence and reprint requests to Dr. Toshinori Kato, Mental Retardation and Birth Defect Research Division, National Institute of Neuroscience, NCNP, 4-1-1 Ogawahigashi cho, Kodaira, Tokyo, Japan.Abbreviations used: CBV, cerebral blood volume; Cyt, cy tochrome aa3; DPF, differential path length factor; HbR, de oxyhemoglobin; Hb02, oxyhemoglobin; HbT, total hemoglobin (Hb02 + HbR); MRI, magnetic resonance imaging; NIRS, near infrared spectroscopy; PET, positron emission tomography; PC, photon count; PS, photic stimulation. 516stopped, CBV promptly decreased and then slightly in creased again. Cytochrome aa3 did not show any change during and after PS. These phenomena reappeared fol lowing repeated PS in all five subjects. These results may represent the first step in the development of NIRS im aging.

The gel-melting temperatures of branched polyethylene-cyclohexane-carbon disulfide gels were measured. Branched polyethylenes having a different number of long-branching points were used. The reciprocal of the gel-melting temperature is a linear function of the logarithm of the polymer concentration. A theory which predicts the gel-melting temperature of branched crystalline copolymers is given. Analysis of the experimental data suggests that the size of the crystalline junction decreases with an increase in the number of long-branching points. KEY WORDS Sol-Gel Transition I Branched Polyethylene I Gel I Gel-Melting Temperature I Polyethylene I

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Signal increases in functional magnetic resonance imaging (fMRI) are believed to be a result of decreased paramagnetic deoxygenated haemoglobin (deoxyHb) content in the neural activation area. However, discrepancies in this canonical blood oxygenation level dependent (BOLD) theory have been pointed out in studies using optical techniques, which directly measure haemoglobin changes. To explain the discrepancies, we developed a new theory bridging magnetic resonance (MR) signal and haemoglobin changes. We focused on capillary influences, which have been neglected in most previous fMRI studies and performed a combined fMRI and near-infrared spectroscopy (NIRS) study using a language task. Paradoxically, both the MR signal and deoxyHb content increased in Broca's area. On the other hand, fMRI activation in the auditory area near large veins correlated with a mirror-image decrease in deoxyHb and increase in oxygenated haemoglobin (oxyHb), in agreement with canonical BOLD theory. All fMRI signal changes correlated consistently with changes in oxyHb, the diamagnetism of which is insensitive to MR. We concluded that the discrepancy with the canonical BOLD theory is caused by the fact that the BOLD theory ignores the effect of the capillaries. Our theory explains the paradoxical phenomena of the oxyHb and deoxyHb contributions to the MR signal and gives a new insight into the precise haemodynamics of activation by analysing fMRI and NIRS data.