2000 Fiscal Year Final Research Report Summary
Feature extraction of auditory information
| Project/Area Number |
10480231
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| Research Category |
Grant-in-Aid for Scientific Research (B).
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
神経・脳内生理学
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
OHMORI Harunori Kyoto Univ.Fac.Medicine, Professor, 医学研究科, 教授 (30126015)
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| Project Period (FY) |
1998 – 2000
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| Keywords | feature extraction / auditory / magnocellular nucleus / angular nucleus / phasic information / sound intensity |
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| Research Abstract |
Sound frequency is coded along the tonotopy in the cochlea, and each ANF has the characteristic frequency. Sound intensity and timing information are coded as a sequence of action potentials. In the avian cochlear nucleus the pathway to extract temporal information starts at Ncl. Magnocellularis (NM) and intensity information at Ncl.Angularis (NA). We have compared the nature of synaptic transmission and postsynaptic membrane excitability in these two nuclei and found target specific differentiation. The membrane excitability of NM is characterized by the presence of both the low threshold voltage activated K+ conductance (LT) and high threshold voltage activated K+ conductance (HT). NM neuron generates a single action potential at the onset of a burst of synaptic inputs or at the beginning of current injection. The neuron in NA is characterized by a regular spike generation in response to current injection or to the burst of synaptic inputs. These neurons do not have LT.K+ currents bu
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t have large quantity of HT K+ currents and Ca2+ activated K+ currents . The frequency of burst firing was reduced by the activity of Ca2+ activated K+ currents. When a train of synaptic inputs were made, the EPSC size depressed drastic in NM neuron while the depression was moderate in NA neuron. By applying a pair of stimulus at various intervals, the NM EPSC depressed in two phases. The first phase is CTZ sensitive, therefore due to desensitization of postsynaptic AMPA receptors, and the 2nd slower phase was CTZ resistive. In NA, EPSC was not affected by CTZ at normal 2mM Ca2+ concentration, however at 5 mM Ca2+ CTZ increased the EPSC size and prolonged decay kinetics as in NM.This might indicate larger quantity of transmitter released from the presynaptic terminals to NM due to larger Ca2+ influx there than to NA.In NM only a few presynaptic terminals are made and they are known as end bulbs of Held, while in NA a large number of small bouton type terminals are formed. Therefore, presynapitc terminals and postsynaptic neurons are likely differentiated target specifically both in morphology and in function. Less
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