Wakate Dojo
Sensory System 1
若手道場口演
感覚系1 |
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| 7月25日（木）9:00～9:20 第10会場（万代島ビル 6F 会議室）
1WD10bm1-1
皮質聴覚受容野は音情報処理能力を改善するよう背景ノイズ音に依存的に発達する
Natsumi Homma（本間 夏美），Christoph E Schreiner（Schreiner E Christoph）
Dept OHNS, Univ of California, San Francisco, USA
During critical periods, receptive fields (RFs) develop to adapt to the sensory environment by forming neural circuits that optimally process relevant stimuli. In humans, this developmental stage is essential for acquiring language. It has been shown that sound exposure during a critical period dynamically altered the RF properties in the auditory cortex such as frequency tuning, tuning bandwidth, or temporal resolution (de Villers-Sadani and Merzenich, 2011). However, the relationship between this altered neural coding and perceptual abilities is yet largely unknown. In this study, we tested the hypothesis that exposure to moderate levels of structured background noise during the critical period enhances the ability of adult animals to process vocalization in noise. We raised rat pups in moderate noises (~60 dB SPL) of different spectro-temporal statistics during their auditory critical period (P6-45). Once these animals reached adulthood, we trained them, as well as an unexposed control group, to detect vocalizations presented in these noises using a go/no-go behavioral paradigm. Based on signal detection theory, the sensitivity index (d') was obtained for several signal-to-noise ratios. Noise exposure enhanced the behavioral performance of detecting rat vocalizations in background noise. Improvement depended on the stimulus statistics of the exposure noise. In addition, we estimated neural discriminability of rat vocalizations in noise using Euclidean distance-based spike train classifiers and obtained spectro-temporal RFs based on the spike-triggered average. We found that cortical signal encoding of vocalizations was improved in noise-exposed animals accompanied by specific shifts in RF properties compared to unexposed animals. To capture additional aspects of altered neural coding, we used a two-filter linear-nonlinear approach (Sharpee et al., 2004) and estimated RFs. Preliminary data showed that noise exposure i) increased mutual information captured by the first filter, which is thought to act as a feature detector, and ii) modulated synergy between the first and weaker, secondary filters. These findings support the idea that maturational noise exposure can alter cortical RF properties to enhance information extraction in noisy environment thus reducing the impact of background noise masking and helping the animals to perceptually segregate signals from noise background. | | 7月25日（木）9:20～9:40 第10会場（万代島ビル 6F 会議室）
1WD10bm1-2
マイクログリアのシナプス·ストリッピングによる聴覚情報の制御
Toshimitsu Hiragi（平木 俊光），Yuji Ikegaya（池谷 裕二），Ryuta Koyama（小山 隆太）
東京大院薬薬品作用
Disrupted processing of auditory information including auditory hallucination is a challenging problem that affects both the quality of life and treatment of patients with epilepsy. Here we report that microglia, the brain resident immune cells, play a key role in the disruption of auditory information processing in a mouse model of adult temporal lobe epilepsy (TLE). We found that the chemoconvulsant kainic acid (KA)-induced status epilepticus significantly activated microglia in the medial geniculate nucleus (MGN), a brain region which sends ascending projection to the auditory cortex. In the MGN, microglia wrapped the soma of MGN neurons and stripped axosomatic inhibitory synapses to these neurons. The synaptic striping by microglia reduced the density of inhibitory synapses, inducing the elevation of c-fos expression, which is the indicative of increased neuronal activity, in neurons of the MGN, as well as the auditory cortex. Furthermore, after KA-induced prolonged status epilepticus, mice exhibited deficits in an auditory perception test to discriminate whether or not sound stimuli are presented; mice behaved as if the sound stimuli were presented when the stimuli were not actually presented. These results suggest that mice experienced auditory hallucination after KA-induced status epilepticus. Similarly, mice exhibited deficits in an auditory avoidance task to discriminate two tones with differently modulated frequencies. Thus, our study provides a novel mechanism by which microglia exclusively strip inhibitory synapses in the MGN, disrupting the processing of auditory information in the epileptic brain. | | 7月25日（木）9:40～10:00 第10会場（万代島ビル 6F 会議室）
1WD10bm1-3
新型補聴器の開発：フラビン蛋白蛍光イメージングによる経鼓膜レーザー刺激が誘発する聴覚皮質応答の解明
Yuta Tamai（玉井 湧太），Yuki Ito（伊藤 優樹），Takafumi Furuyama（古山 貴文），Shizuko Hiryu（飛龍 志津子），Kohta I Kobayasi（小林 耕太）
同志社大院生命医科学
Cochlear implants bypass damaged hair cells in a cochlea and stimulate cochlear nerves electrically. One of the greatest drawbacks of the cochlear implant is that the devices require surgical intervention. Pulsed infrared laser has been proposed as a novel neural stimulation. It stems from optical absorption of water. The laser causes instantiable temperature rise and opening of heat-sensitive ion channel. In contrast to electric stimulation, infrared neural stimulation (INS) evokes spatially precise neural activity without tissue contact. Our goal is to develop a novel auditory prosthesis by applying INS to a hearing aid. The auditory prosthesis with the infrared laser does not need invasive surgery because INS does not require direct contact with neural tissue. For clinical application of INS to an auditory prosthesis, study of peripheral nervous system response (e.g. auditory ganglion cells) is well conducted; however, research of central nervous system response has been rarely reported. The purpose of our study was to investigate whether auditory cortical response was observed by laser irradiation to cochlear nerves. Flavoprotein fluorescence imaging of left hemisphere of the brain was performed to assess laser evoked cortical response. Mongolian gerbil (Meriones unguiculatus) were anesthetized with urethane (1.5 g/kg, i.p.). Cortical images of endogenous green fluorescence in blue light were captured by a cooled CCD camera through the intact skull. An optic fiber was inserted into subject's ear canals and the infrared laser irradiated cochlear nerves through their tympanic membranes. Click train with repletion rate of 4000 Hz and red light-emitting diode light was used as auditory and visual stimuli respectively. Repetitive pulsed infrared laser (Radiant exposure: 0.5-12.8 mJ/cm2; Repetition rate: 4000 Hz) was presented. As results, laser stimulation did not activate visual cortex but auditory cortex as with auditory stimulation, and the greater response was recorded as radiant exposure increased (ΔF/F0: 0.07-0.38). These results suggest that peripheral nervous system response with laser irradiation to cochlear nerves was processed in an auditory cortex, and that the laser evoked cortical response depends on radiant exposure. | | | |
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