| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2000: ¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 1999: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
The auditory cortex of all mammals consists of multiple fields. However, the functional parcellation of the auditory cortex, especially of the higher auditory fields, is still not clearly established and neural interaction within and between the fields has not been studied well. In order to study the neural interaction in those fields, we have investigated the response properties of the multiple fields of the guinea-pig auditory cortex using a voltage-sensitive-dye optical reording method (RH795) and a multi-electrode method. All experiments were conducted under anesthesia (sodium pentobarbital) and neuroleptanalgesia.
Optical responses in 3mmx3mm area were recorded by a photodiode array (464 or. 144 channels. 0.6 ms/frame) and were averaged over 5 trials. In order to record the responses from the wide cortical areas, the recording location was shifted systematically. These data were combined by computer and were converted into large spatiotemporal images. The combined images clearly sh
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owed differences in response properties (tonotopicity, latency and duration )among multi-fields. Based on the response properties, we could distinguish the following auditory fields : the core fields consisting of the primary (AI) and secondary (AII) fields and the surrounding fields consisting of the posterior (P), ventroposterior (VP), dorsoanterior (DA), dorsal (D), dorsoposterior (DP), and ventroanterior (VA) fields. Interestingly, excitation evoked by contralateral sounds in the fields posterior to AII was strongly suppressed when ipsilateral sounds were simultancously presented. This finding suggests that the caudal fields is concerned with sound localization.
In order to study neural interaction in the auditory cortex, a custom-made multi-electrode system was used. Single-line electrodes (4x1) were positioned across or along the isofrequency band (IFB) and were inserted into the core and surrounding fields at depths of 0.2-0.6 mm. Each electrode was separately advanced by each micromanipulator and recorded single- or multi- unit responses simultaneously. Cross-correlograms were obtained during tone-stimulus periods of no-stimulus (spontaneous) periods. Generally, the cross-correlation decreased with the distance between the electrodes. However, the rate of decrease differed between the stimulus and no-stimulus conditions and between along and across the IFBs. In the core fields, the rate of decrease in cross-correlation of spontancous activities showed no difference between across and along the IFBs. During the sound stimulation, the decrease rate was much larger across the IFB than along the IFB.and the decrease rate along the IFB became smaller with the increase in the stimulus intensity. These results suggest that the neural activity along the IFB was synchronized more widely than that across the IFB during the stimulation and that the neural activity along the IFB was more synchronized at the higher sound pressure levels. In the surrounding fields, cross-correlation of spontaneous activities were decreased with the electrode distance, but the amplitude of cross-correlation were larger than that during the sound stimulation. At the 750-900 μm of the distance, the second peak of cross-correlation was observed. These results suggest that the neural interaction in the surroundings fields during the stimulus differs from and is more complicate than that in the core fields and that the neural projection between the fields is patch-like, each patch being separated by 750-900 μm. Less
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