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| 光学的技術 Optical methods | |
| P2-2-239 光源にLEDを用いたNIRSにおけるクロストークの光子伝播モンテカルロシミュレーションによる推定 Estimation of Crosstalk in NIRS using LED by Photon Propagation Monte Carlo Simulation ○岩野孝之1, 梅山伸二1 ○Takayuki Iwano1, Shinji Umeyama1 産業技術総合研究所 脳機能計測研究G1 AIST, Tsukuba, Japan1 NIRS(near infrared spectroscopy) is a method which can measure brain activity non-invasively. It estimates change of oxy-hemoglobin and deoxy-hemoglobin concentration in blood in the cortex by emitting near infrared light into head and detecting the reflected light. Laser light is conventionally used but its cost is high. If LEDs can be used instead, its cost is much lower than that of laser light. However, because of the wide spectrum range of LED light, if analyzing in the same way of laser light, it may cause crosstalk of estimated concentration of oxy-hemoglobin and deoxy-hemoglobin. So, in order to assess the amount and property of the crosstalk, we performed Monte Carlo simulations of propagation of infrared photons in a head model and calculated the pathlength of photons in each layer in the head. Using simulated data of the pathlength of photons and absorption coefficient of infrared light in each layer of head model, we calculated change of light attenuation at each wavelength every 1 nm. And using spectrum of LED light, we estimated the intensity of reflected light and calculated the amount of crosstalk when adopting a conventional analyzing method using an inverse matrix of extinction coefficient. In addition, we investigated the crosstalk when using an inverse matrix of weight averaged extinction coefficient. As a result, we found that when using LEDs the amount of crosstalk increased in most of combinations of wavelength, but the amount of increase is not so large and when using an inverse matrix of weight averaged extinction coefficient the increase of crosstalk is reduced. This result supports the use of LEDs in NIRS whose cost is much lower than laser. |
P2-2-240 in vivo脳情報解読を目指した光操作によるAMPA受容体機能破壊技術の開発 Light induced inactivation of AMPA receptors towards an artificial memory erasure ○竹本研1, 永井健治3, 高橋琢哉1 ○Kiwamu Takemoto1, Takeharu Nagai3, Takuya Takahashi1 横浜市大・医・生理学1, JSTさきがけ2, 阪大・産研3 Dept Physiol, Yokohama City Univ, Yokohama1, JST, PRESTO2, ISIR, Osaka Univ3 Hippocampus is an essential brain region for memory formation. While many analyses for hippocampus synaptic response in vitro have been reported, mechanism of memory formation in vivo is poorly understood. If we could inactivate synaptic function to induce "artificial memory erasure" in vivo, it should be strong strategy for decoding of brain information in living animals. Among molecules in synaptic function, AMPA type glutamate receptors, GluR1 are especially known as important molecules for memory formation that are transported into synapse in response to many types of learning and experience (Takahashi et al. Science 2003, Rumpel et al. Science 2005. etc.). Towards development of "artificial memory erasure" technology, we are now trying to develop a new technique for inactivation of synaptic GluR1 receptors in vivo with light irradiation. Because this technology could be used in combination with in vivo live imaging, we could make a functional map in synaptic highway in living animals. In this session, we will report detail properties, specificity and validity. Finally, we will also hope to discuss a future of this technology. |
| P2-2-241 スキャン式顕微鏡画像時系列のサブフレーム単位レジストレーションについて Sub-frame-wise image registration for time-lapse scanning microscopy ○大羽成征1,2, 平理一郎3, 田中康裕3, 和氣弘明3, 正水芳人3, 岡田尚巳4, 松崎政紀2, 石井信1 ○Shigeyuki Oba1,2, Riichiro Hira3, Yasuhiro Tanaka3, Hiroaki Wake3, Yoshito Masamizu3, Takashi Okada4, Masanori Matsuzaki2, Shin Ishii1 京大院・情1, 科学技術振興機構2, 国立基礎生物学研究所3, 国立精神・神経医療研究センター4 Info., Kyoto univ., Kyoto1, JST, PRESTO2, National Institute for Basic Biology, Okazaki3, National Center of Neurology and Psychiatry, Tokyo4 Time-lapse observation of laser scan microscopy often suffers from severe motion artifacts that cannot be well corrected by existing frame-wise registration processes. We developed an image registration algorithm considering sequential data acquisition process of scanning microscopy. A single frame is divided into multiple subframes along time-course of scanning process so that each subframe is registered based on a template. In the estimation of subframe-wise registration parameters, we designed a linear dynamical model which can deal with fitting error possibly by large observation noise, and, so called, aperture problem. We show that our subframe-wise registration algorithm improved the performance of motion artifact removal which is crucial for imaging of live animals, by means of confocal or two-photon microscopy. We also show that high-quality super-resolution images can also be obtained by our subframe-wise registration algorithm, owing to the fine and sub-pixel level registration. |
P2-2-242 高密度ファイバー束による細胞イメージング Cellular imaging with a high density fiber-coupled microscope ○鯉田孝和1, 櫻井孝司1 ○Kowa Koida1, Takashi Sakurai1 豊橋技術科学大学 エレクトロニクス先端融合研究所1 EIIRIS, Toyohashi Tech, Toyohashi1 By using the fiber-coupled microscope (FCM), in vivo imaging is possible at the deep site in the tissues or organs where other optical techniques are difficult to reach. The optical performance of the FCM highly depends on the properties of the fiber bundle which detects an emitting light from cells. However, the quality and resolution of the images obtained by the conventional FCM was low to examine the neuronal signals. To improve the spatial resolution of the FCM, we used a high density type of the imaging fiber (HDI) which included 3×104 unit fibers and each diameter was less than 1.8 μm. The HDI composed a circular field of view of about 300 μm wide, thus spatial resolution was 1.8 μm/unit on average. The tip of the HDI was tangentially trimmed and either an optical lens was attached (gradient index lenses; GRIN fiber) or not (bare fiber). Total diameter of the HDI was less than 450 μm in either case. The HDI we employed here produced a spatial-resolution 1.7 fold higher than the conventional fibers we used before. The activity-dependent signals of each neuron were successfully detected from in vitro preparation of the rodents' cortex by using the HDI with a fluorescence imaging system consisting of laser, objective lens and CCD camera. The intracellular details of fluorescence pattern and their temporal changes, difficult to observe with the former system, were easily detected by using the new FCM system. We also observed the intrinsic signals of individual neurons which reflected metabolic states of the cells and found that the HDI was capable as real-time (10 frames per s) label-free cellular imaging probes. These fibers can penetrate deeper than 1 mm from the surface of the cortex. The potential power of the FCM will be expected to rise continuously for the analysis of a fine structure of the cells and an organization of certain functions in vivo. |
| P2-2-243 ラット上丘における層間抑制回路の集団神経活動イメージングによる解析 Analysis of the interlaminar inhibitory circuit in the rat superior colliculus by the imaging of population activity with the optical imaging ○森田奈々1, 長谷川良平1,2, 村瀬一之1, 池田弘1 ○Nana Morita1, Ryohei P. Hasegawa1,2, Kazuyuki Murase1, Hiroshi Ikeda1 福井大学大学院 工学研究科 知能システム工学1, 産業技術総合研究所ヒューマンライフテクノロジー研究部門2 Grad. Sch. of Engineering, Univ. of Fukui, Fukui1, Human Tech RI, AIST, Tsukuba, Japan2 Optical methods have been used as a powerful tool to study neural activity with a high spatiotemporal resolution, but not often apply to discover inhibitory circuits. We devised the experiment method to examine the neural connection of inhibitory circuits by using optical imaging with sequential delivery of two stimuli in twosites. The inhibitory signal by first stimulation was decrease neuronal activity by next stimulation in another site. In this study, we studied local circuits of superior colliculus (SC), which is a center orientation bivabior. We especially focused on that from the intermediate layer (SGI) to the superficial layer (SGS), which is thought to be inhibitory. We examined the influence of stimulation to the SGI on population activity of SGS neurons and the contribution of GABAergic neurons by using optical imaging with voltage-sensitive dye RH482. The optical response evoked by stimulation to the SGS was propagated within SGS, and this optical response was decreased by pre-stimulation to the SGI. The inhibition of optical response in the SGS by stimulation to the SGI was not observed by perfusion with a solution containing a GABAA receptor antagonist picrotoxin. These results indicate that the population activity of SGS neurons is inhibited by the activation of GABAergic neurons in SGI which terminate to the excitatory neurons in the SGS and/or by the activation of excitatory neurons in SGI which terminate to inhibitory neurons in the SGS.This study suggests that it is possible to discover inhibitory circuits by the method using optical imaging. Furthermore, we make the proposal that the inhibitory circuits is the visual input feedback. This feedback circuit may play a role in controlling orientation behaviors. |
P2-2-244 狂犬病ウイルスベクターとカルシウムセンサーを用いた異なる神経細胞群からの同時光計測法の開発 Simultaneous optical monitoring of activity from different neural population using rabies virus vectors and genetically-encoded calcium indicator ○佐藤翔1, 大原慎也1, 加藤智也1, 菩提寺誉子1, 筒井健一郎1, 飯島敏夫1 ○Sho Sato1, Shinya Ohara1, Tomoya Kato1, Motoko Bodaiji1, Ken-Ichiro Tsutsui1, Toshio Iijima1 東北大学大学院 生命科学研究科 脳情報処理分野1 Division of Systems Neuroscience, Graduate School of Life Science, Tohoku University, Sendai, Japan1 The brain is a complicated system consisting of multiple types of neurons. Even neurons that are located close by in the same brain region have different connectivity and functional properties. Monitoring of activity from different such neural population is an essential step to understand the information processing of the brain. However, complicated structure of the brain makes it difficult to record the activity only from the neuron of our interest. We previously developed double-labeling method using two strains of recombinant rabies virus vector, each expressing a different fluorescent protein. Since this virus vector can infect neurons retrogradely, this method allows us to detect neurons that project to different brain regions by expression of different fluorescent protein. Here we present the development of a novel method that enables us to monitor the neural activity from two groups of specific projection neurons at the same time. We used a glycoprotein-deleted (ΔG) rabies virus vector known as non-transsynaptic retrograde tracer which expresses genetically-encoded calcium indicator in addition to fluorescent protein (rHEP3.0-ΔG-GCaMP6-BFP, rHEP3.0-ΔG-GCaMP6-mRFP). This virus allows us to monitor the neural activity by the fluorescence of calcium indicator, and to detect the neurons which project to specific brain region by the fluorescence of fluorescent protein. We used GCaMP6 as a genetically-encoded calcium indicator. GCaMP6 is a fluorescent protein which modulates their fluorescence intensity in response to changes in calcium ion concentration. The sensitivity, dynamics range and speed of the GCaMP6 exceed those of the synthetic indicator OGB-1. These virus vectors would be a useful tool to monitor the activity of specific group of neurons with different connectivity. |
| P2-2-245 in vivo 2光子顕微鏡法による生体マウス脳深部観察の為の光学条件の最適化 Optimization of laser illumination in two-photon microscopy for in vivo deep imaging in mouse brain ○澤田和明1, 川上良介1,2, 根本知己1,2 ○Kazuaki Sawada1, Ryosuke Kawakami1,2, Tomomi Nemoto1,2 北海道大学 情報科学院 生命人間情報科学専攻 脳機能研究室1, 北海道大学 電子科学研究所 光細胞生理研究分野2 Laboratory of functional neuroimaging, Graduate school of information science and technology, Hokkaido University, Hokkaido, Japan1, Laboratory of Molecular and Cellular Biophysics, RIES, Hokkaido University, Hokkaido, Japan2 In vivo two-photon microscopy has revealed many essential properties of neural circuits for brain functions, though it enabled to observe spines within deeper layer less than a several hundred micrometers from the brain surface. This penetration depth should be improved for the further elucidation. Our preliminary experiments suggest that properties of the excitation laser beam can be modified to improve the penetration depth. Thus, we compared penetration depths in the cortex at various diameters of the excitation laser beam and/or at different positions of the correction ring of the objective lens. The beam diameter was adjusted to full fill, 1/2, 1/3, or 1/4 of the objective pupil diameter via a Kepler's optics. The correction ring, which compensates for spherical aberrations, was positioned at 0.17 or maximum. H-line (Thy1-eYFP) mice were used in the experiments. The mouse was anesthetized and a part of the skull was replaced with a cover slip. For two-photon microscopy, the mouse was held under the upright microscope stage. We found that eYFP fluorescence signal intensities and the depth limits of detection were increased when the beam diameter was reduced from the full-fill over the pupil, and the correction ring was positioned at maximum. In addition, the position of the correction ring affected the spatial resolution of fluorescent images depending on the depth of brain. At the maximum position, higher resolution was achieved at 400 um depth. On the other hand, the 0.17 position resulted in higher resolution at the surface of brain. Under optimized laser condition for deep layer, we visualized the morphology of single spines in basal dendrites of layer V pyramidal neurons. Our results indicate that optimizing the illumination parameters improved the penetration depth in the cortex, even in a conventional two-photon microscope. We anticipate that this optimization will benefit future investigation on the function of neural circuits in live specimens. |
P2-2-246 Yellow Cameleon 2.60トランスジェニックマウスと広視野顕微鏡を用いた細胞種選択的広域カルシウムイメージング Cell-type selective wide-field calcium imaging combined with Yellow Cameleon 2.60 transgenic mice and macromicroscopy ○黒木暁1,2, 筒井秀和3,4, 道川貴章1,5, 岩間瑞穂6, 宮脇敦史4, 糸原重美1 ○Satoshi Kuroki1,2, Hidekazu Tsutsui3,4, Takayuki Michikawa1,5, Mizuho Iwama6, Atsushi Miyawaki4, Shigeyoshi Itohara1 理研・BSI・行動遺伝1, 早大・先進理工・生医・学振DC2, 阪大・医・統合生理3, 理研・BSI・細胞機能探索4, 埼玉大・脳科学融合研究センター5, 理研・バイオリソースセンター6 Behav Genet, BSI, RIKEN, Saitama1, JSPS Research Fellow, Life Sci. & Med, Waseda Univ, Tokyo2, Med & Front Biosci, Osaka Univ, Osaka3, Cell Func Dyn, RIKEN, Saitama4, BSI, Saitama Univ., Saitama5, BRC, RIKEN, Tsukuba6 The development of new techniques for recording neural population activities during behavioral tasks is important toward gaining a better understanding of how the brain controls behavior. A -new imaging technique using two-photon microscopy was recently developed to record the calcium dynamics of tiny structures, such as dendritic spines and axonal boutons, during behavior. Currently, little is known about wide-field neural activities, such as the interactions between different cortical areas during behavior, especially in rodents. To record wide-field neural activities during behavior in mice, we established a wide-field calcium imaging system combined with a genetically-encoded calcium indicator (GECI) in transgenic (Tg) mice and macromicroscopy. First, we established Tg mice expressing a GECI, Yellow Chameleon 2.60 (YC2.60), in a cell-type specific manner under the Tet-on/off or Cre/LoxP system. Next, we recorded transcranial images of the calcium dynamics of the Tg mice with whisker stimulation at either the hemisphere or whole brain scale. Both excitatory and inhibitory responses to whisker stimulation were separately detected in awake and anesthetized mice, and spontaneous activities were recorded. This system allowed us to visualize functional brain maps of cerebral excitatory and inhibitory neurons at the whole hemisphere scale. We also detected neural activity at the cellular level using two-photon microscopy. We established a novel imaging method with a wide-field, low invasiveness, high spatiotemporal resolution, and cell-type selectivity. This system can be applied to record wide-field neural activities over several days during a behavioral task and can be combined with microcircuit analysis using two-photon microscopy. Application of this method will be especially useful for studies of the control of perception and attention by allowing for the analysis of interactions among different cortical areas. |
| P2-2-247 脳機能イメージングのための極微細内視鏡イメージングシステムの開発 Development of a micro-imaging probe system for functional brain imaging ○小山内実1,2, 鈴木太郎3, 田村篤史1,2, 米村次男3, 森一生1, 柳川右千尾4, 八尾寛5, 虫明元1,2 ○Makoto Osanai1,2, Taro Suzuki3, Atsushi Tamura1,2, Tsugio Yonemura3, Issei Mori1, Yuchio Yanagawa4, Hiromu Yawo5, Hajime Mushiake1,2 東北大院・医1, 東洋ガラス株式会社3, 群馬大院・医4, 東北大院・生命科学5 Tohoku Univ Grad Sch Med, Sendai1, JST, CREST, Tokyo2, TOYO GLASS Co, Ltd, Kawasaki3, Gunma Univ Grad Sch Med, Maebashi4, Tohoku Univ Grad Sch Life Sci, Sendai5 Multicellular neuronal activities should be characterized to understand the mechanisms underlying information processing and the dynamics of the neuronal circuit. Optical imaging methods are suitable for recording multicellular activities. For in vivo functional imaging, many types of imaging probes were made. However, the issue of invasiveness has to be considered. Thus, to reduce the invasiveness of the insertion site of the probe, we have designed and fabricated a new type of fiber optics, the micro-imaging probe. This micro-imaging probe is composed of a small diameter GRIN lens and a high-resolution image fiber. These two components are optically connected within a thin metal tube generated using a micro fabrication technique. We found an optimal optical configuration for maximizing the efficiency of the imaging probe. The spatial resolution of this imaging probe was about 5 μm in x-y plane. Using this optical configuration with the micro-imaging probe, we could captured the fluorescence images from neurons expressing green fluorescent protein in a cerebellar block preparation, and the evoked cellular calcium elevation in a mouse brain slice preparation. Our optical system would facilitate the in vivo imaging studies with less invasive manners using thinner optic fiber than previously made. |
P2-2-248 |
| P2-2-249 高感度な改良G-CaMPカルシウムプローブを用いた樹状突起棘における発火閾値下のシナプス入力の可視化 Imaging of sub-threshold synaptic inputs into dendritic spines with a high-sensitivity G-CaMP calcium indicator ○貞苅純子1, 大倉正道1, 佐々木拓哉1, 安藤恵子1, 永村ゆう子1, 小林千晃2, 池谷裕二2, 中井淳一1 ○Junko Sadakari1, Masamichi Ohkura1, Takuya Sasaki1, Keiko Gengyo-Ando1, Yuko Kagawa-Nagamura1, Chiaki Kobayashi2, Yuji Ikegaya2, Junichi Nakai1 埼玉大・脳センター1, 東京大院・薬・薬品作用2 Brain Sci. Inst., Saitama Univ. Saitama, Japan1, Lab. Chem. Pharmacol., Grad. Sch. Pharm. Sci., Univ. Tokyo, Tokyo, Japan2 Imaging the activities of individual synapses with genetically encoded Ca2+ indicators (GECIs) is a promising technique for understanding the integration mechanisms of synaptic inputs. Recently, we developed high-sensitivity and fast-responsivity GECIs, termed G-CaMP6/7/8 (Ohkura, M. et al., PLoS One 7, e51286, 2012). These three GECIs could reliably detect individual spikes from pyramidal neurons of cultured hippocampal slices or acute cortical slices. Because G-CaMP6 showed the highest sensitivity among G-CaMP6/7/8, we sought to image Ca2+ activities induced by excitatory synaptic inputs into dendritic spines, the main postsynaptic sites, using G-CaMP6. By fusing G-CaMP6 with actin, a major cytoskeletal protein within dendritic spines, we constructed a spine Ca2+ indicator, G-CaMP6-actin. Then we expressed G-CaMP6-actin in CA3 pyramidal neurons of cultured hippocampal slices. By electrically stimulating granule cells of the dentate gyrus, which innervate CA3 pyramidal neurons, we demonstrated that supra-threshold stimulation triggered large fluorescence responses in virtually all of the spines with a 100% activity rate, whereas sub-threshold stimulation triggered small Ca2+ responses in a limited number of spines with a low response rate in active spines. We expect that spine Ca2+ imaging with G-CaMP6-actin will facilitate our understanding of integration mechanisms of synaptic inputs. |
P2-2-250 自由運動中の線虫の光刺激とカルシウムイメージングを可能とするシステムの開発 Real-time optogenetic control and imaging of neuromuscular activity in freely moving Caenorhabditis elegans ○永村ゆう子1, 安藤恵子1, 大澤明香音1, 橋本浩一2, 大倉正道1, 中井淳一1 ○Yuko Kagawa-Nagamura1, Keiko Gengyo-Ando1, Akane Osawa1, Kouichi Hashimoto2, Masamichi Ohkura1, Junichi Nakai1 埼玉大・脳セ1, 東北大・情報科学2 Saitama Univ Brain Sci Ins1, Grad Sch Info Sci, Tohoku Univ2 The recent development of optogenetics and imaging technology has enabled quantitative neurophysiology in many model organisms including the small, transparent and genetically tractable model organism such as Caenorhabditis elegans. However, the optical stimulation and simultaneous recording from cells of interest in moving small model animals remain largely elusive. Here we developed a system that allowed both confocal Ca2+ imaging at the high spatiotemporal resolution and real-time optogenetic manipulation of the neural circuits in a freely moving C. elegans, which was automatically kept in the field of view by an auto-tracking unit. Photostimulation of the worm coexpressing both channelrhodopshin-2 (ChR2) and our newly designed RFP-based Ca2+ probe R-CaMP in the GABAergic motor neurons and expressing GFP-based Ca2+ probe G-CaMP in the postsynaptic body wall muscle cells induced the R-CaMP fluorescence increase in the GABAergic motor neurons and the G-CaMP fluorescence decrease in the body wall muscles. The results indicated that our system is a powerful tool for investigating the motor circuits in a freely moving C. elegans. |
| P2-2-251 量子ドットで標識した神経細胞接着分子動態の光操作 Optical manipulation of neural cell adhesion molecules labeled with quantum-dots in living neurons ○武田尚子1,2, 工藤卓1,2, 田口隆久1, 細川千絵1,2 ○Naoko Takeda1,2, Suguru N. Kudoh1,2, Takahisa Taguchi1, Chie Hosokawa1,2 産業技術総合研究所 健康工学研究部門1, 関西学院大学大学院 理工学研究科2 Health Research Institute, AIST, Ikeda, Osaka, Japan1, School of Sci. and Tech., Kwansei Gakuin Univ., Sanda, Hyogo, Japan2 Neuronal networks in brain systems communicate through synaptic connections of each neuron. For aiming optical control of synaptic transmission in a neuronal network, we applied optical tweezers to intracellular manipulation of neural cell adhesion molecules (NCAMs) labeled with quantum-dots (Q-dots) in living neurons. The optical trapping and assembling dynamics of NCAMs labeled with Q-dots in hippocampal neurons was investigated by fluorescence analysis. When a 1064-nm laser beam for optical tweezers focused on NCAMs labeled with Q-dots at plasma membrane of a neuronal cell, the fluorescence intensity of Q-dots gradually increased at the laser focus, suggesting that Q-dots attached to NCAMs were optically trapped and assembled at the focal spot within the laser irradiation time. The dynamics of NCAMs labeled with Q-dots in an optical trap was evaluated by fluorescence correlation spectroscopy. The decay time of autocorrelation function of fluorescence intensity obtained from the Q-dots attached to NCAMs in neurons increased with the trapping laser power. This suggests that the particle motion of Q-dots attached to NCAMs was constrained at the focal spot due to optical trapping force. Our method can be applied to intracellular manipulation of the molecular assembly at plasma membrane of living neuronal cells. |
P2-2-252 近赤外および赤色レーザ照射による聴覚皮質活動の抑制効果 Suppressive effect of auditory cortical activity by near-infrared and red laser irradiation ○池田聡1, 沼田亮太1, 古川茂人2, 杉本俊二1, 堀川順生1 ○So Ikeda1, Ryota Numata1, Shigeto Furukawa2, Shunji Sugimoto1, Junsei Horikawa1 豊橋技術科学大学大学院 工学研究科 情報・知能工学専攻1, 日本電信電話株式会社 NTTコミュニケーション科学基礎研究所 人間情報研究部2 Computer Science and Engineering, Graduate school of Engineering, Toyohashi University of Technology ,Aichi ,Japan1, Human Information Science Laboratories, NTT Communication Science Laboratories, NTT Corporation, Kanagawa, Japan2 Irradiation of near-infrared laser (NIR) has been reported to affect reversibly on neural activity measured by single-unit or field-potential recording from the auditory or somatosensory cortex of rats and gerbils. In this study, wavelength- and cortical-temperature-dependency of the effects of laser irradiation was investigated by recording the auditory-evoked field potentials (AEP) from the core auditory cortex of guinea pigs. AEP in response to white-noise bursts (200-ms long, 5-ms rise-fall time, 75 dBSPL, presented contralaterally) were recorded every 2 s before (5 min), during (5 min) and after (5 min) the NIR (wavelength 830 nm) and red (RED, 650 nm) laser irradiation to the cortex including the recording location. The peak-to-peak amplitude of AEP reduced with the increase of the NIR and RED laser intensity. This suppressive effect was reversible for the laser intensity up to a certain limit. At a given laser intensity, the suppressive effect was greater for RED than for NIR. The cortical temperature increased after the laser irradiation and the extent of the temperature increase was nearly proportional to the laser intensity. When the peak-to-peak amplitude of AEP was plotted as a function of the temperature, the functions for NIR and RED were essentially identical. The NIR irradiation suppressed the positive component of AEP more strongly than the negative component, whereas the RED irradiation suppressed the both components to the same extent. This tendency was the same when they were plotted with respect to the temperature. These results suggest that the irradiation-induced temperature change of the cortex, rather than the laser intensity per se, is the crucial parameter for AEP reduction. However the differential suppression of the positive and negative components of AEP by the NIR and RED laser irradiation indicates that the effect is also wavelength-dependent. |
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