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S191 1706 SONAGRAPIIIC REPRESENTATION OF F31 SOUNDS IN THE GUINEA CORTEX OBSERVED BY OPTICAL RECORDING IKUO TANIGUCHI, MASAHIRO NASU AND JUNSEI HORIKAWA Department of Neurophysiology. Medical Research Institute. Tokyo Dental University, Kanda-surugadai, Chiyoda-ku, Tokyo i01, Japan PIG AUDITORY Medical and Little is known of organizational principles of the auditory cortex, except for bats, which processes frequency-modulated (FM) sounds. By using optical recording with the aid of a voltage-sensltivedye (RH795), we observed the spat~b-temporal pattern of neural activity evoked by FM sounds in the guinea plg auditory cortex. Animals were anesthetized with intraperitoneal Nembutal (30 mg/kg). The cortex was stained with RH795. The fluorescence emitted from dyed neurons were detected by a 12x12 photodiode array. Responses were color-coded and transformed to sequential images. For sound stimulation, we used FM sounds with different frequency-sweeplng directions. Physical parameters of F31 sounds were represented as a trajectory of sound-lnduced neural activity which propa- gated obliquely across different iso-frequency contours in the tonotopically organized fields. Such sonagraphic images suggest that processlng of F51 sounds is primarily done by an ensemble of simple neurons responsible for pure tones. Further information processing will be transferred to specialists or detectors, if there are, In hierarchically higher order fields. 17o7 CODINGS OF THE VIRTUAL PITCH INFORMATION IN THE PRIMARY AUDITORY CORTEX OF THE JAPANESE MONKEY. HtROSHI RIQUIMAROUX 1 . TETSUYA TAKAHASHI 2 and TSUTOMU HASHIKAWA 1, Labs. for 1Neural Systems and 2Neural Networks, Frontier Research Prooram, The Institute of Physical and Chemical Resea, rch IRIKEN). Wako. Saitama 351-01, ~laoan. The present study has examined whether the temporal pitch, known as the virtual pitch or missing fundamental, is co-place- coded with the p~acepitch, corresponding to a pTace a~ongthe basilar membrane in the cochlea, by the same neuron in the auditory cortex. Adult Japanese monkeys (Macaca fuscata) were used. All surgeries were aseptically performed with anesthesia. A chamber was placed for chronic recordings on the left temporal part of the skull. The stimuli used were white noise bursts, tone bursts and bursts of a combination of higher harmonics of a low frequency. They were presented to the animal's right ear in a sound;proof room. Unit recordings were made with glass-coated Elgiloy electrodes from the left primary auditory cortex (AI). During recordings, the animal was anesthetized with a mixture of nitrous oxide and oxygen, supplemented by ketamine and xylazine iniections. PST (post-stimulus- time) histograms were constructed by a computer on line and then analyzed. The present data have confirmed a tonotopicity, low frequency anteriorly while high frequency posteriorly, in the Japanese macaque's AI when the recording time window was short (< 20 msec) and the stimulus level was close to threshold levels. In the low frequency area (< 500 Hz), the same neuron responded both to the best frequency (BF) and to combinations of successive higher harmonics which create a temporal periodicity identical to the BF. However, these neurons did not or little respond to the higher harmonics themselves when they were presented alone. The findings suggest that the temporally-codedpitch in the periphery appears to be already place-coded together with the place pitch by the same neuron at the level of AI to produce an identical pitch. Thus, this evidence agrees well with previous psychoacoustical findings in human studies. J 708 OPTICAL IMAGING OF AUDITORY CORTICAL ACTIVITY IN THE GUINEA PIG. HASHIMOTO, T. Inst Med. Dent. Engin., Tokyo Med. Dent. Univ. Chiyoda-ku, Tokyo I01, JaDan The pattern of population activity of the auditory cortex in response to sound stimulation was mapped with a newly developed video method imaging the epl-fluorescence of a voltage-sensitive dye(RH795). The animals were lightly anesthetized with Nembutal. The fluorescent images were sampled through pulse d illuminatlon by a Xenon lamp lightened id synchrony with the stimulus presentation. The responsive image was accumulated over the electric charge pattern on the CCD video camera. The background images were subtracted from the responsive images and the resultant difference images were integrated in the video frame memory to visualize the specific cortical activity in response to the stimulus sound. The excitation loci in the optical record were analyzed in correlation with a spectrographic survey of the stimulus. The spatio-temporal patterns of auditory cortical activity were surveyed by a train of sequentially recorded stroboscopic images. A spot or stripe pattern of excitation was found in the optical records. It would be due to the columnar structure in the auditory cortex. The time series of the optical records would play an important role in analyzing the global f~nctlonal structure of the audltory cortex in response to sound stimulation. The functioning of the auditory cortex could be elucidated 5y the time series analysis of the global population activity with the present optical recording method.

1708 Optical imaging of auditory cortical activity in the guinea pig

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S191

1706 SONAGRAPIIIC REPRESENTATION OF F31 SOUNDS IN THE GUINEA CORTEX OBSERVED BY OPTICAL RECORDING IKUO TANIGUCHI, MASAHIRO NASU AND JUNSEI HORIKAWA

D e p a r t m e n t o f N e u r o p h y s i o l o g y . M e d i c a l R e s e a r c h I n s t i t u t e . T o k y o Dental Univers i ty , Kanda-surugadai, Chiyoda-ku, Tokyo i01, Japan

PIG AUDITORY

Medical and

L i t t l e is known of organizat ional p r inc ip les of the auditory cortex, except for bats, which processes frequency-modulated (FM) sounds. By using op t ica l recording with the aid of a v o l t a g e - s e n s l t i v e dye (RH795), we observed the spat~b-temporal pa t te rn of neural a c t i v i t y evoked by FM sounds in the guinea plg auditory cortex. Animals were anesthet ized with i n t r ape r i t onea l Nembutal (30 mg/kg). The cortex was stained with RH795. The fluorescence emitted from dyed neurons were detected by a 12x12 photodiode array. Responses were color-coded and transformed to sequent ia l images. For sound s t imulat ion, we used FM sounds with d i f f e r e n t frequency-sweeplng d i r ec t ions . Physical parameters of F31 sounds were represented as a t r a j e c t o r y of sound-lnduced neural a c t i v i t y which propa- gated obl iquely across d i f f e r e n t iso-frequency contours in the tonotopica l ly organized f i e l d s . S u c h sonagraphic images suggest that processlng of F51 sounds is pr imar i ly done by an ensemble of simple neurons responsible for pure tones. Further information processing w i l l be t ransfer red to s p e c i a l i s t s or detectors , i f there are, In h i e r a r c h i c a l l y higher order f i e l d s .

17o7 CODINGS OF THE VIRTUAL PITCH INFORMATION IN THE PRIMARY AUDITORY CORTEX OF THE JAPANESE MONKEY. HtROSHI RIQUIMAROUX 1 . TETSUYA TAKAHASHI 2 and TSUTOMU HASHIKAWA 1, Labs. for 1Neural Systems and 2Neural

Networks, Frontier Research Prooram, The Institute of Physical and Chemical Resea, rch IRIKEN). Wako. Saitama 351-01, ~laoan.

The present study has examined whether the temporal pitch, known as the virtual pitch or missing fundamental, is co-place- coded with the p~ace pitch, corresponding to a pTace a~ong the basilar membrane in the cochlea, by the same neuron in the auditory cortex. Adult Japanese monkeys (Macaca fuscata) were used. All surgeries were aseptically performed with anesthesia. A chamber was placed for chronic recordings on the left temporal part of the skull. The stimuli used were white noise bursts, tone bursts and bursts of a combination of higher harmonics of a low frequency. They were presented to the animal's right ear in a sound;proof room. Unit recordings were made with glass-coated Elgiloy electrodes from the left primary auditory cortex (AI). During recordings, the animal was anesthetized with a mixture of nitrous oxide and oxygen, supplemented by ketamine and xylazine iniections. PST (post-stimulus- time) histograms were constructed by a computer on line and then analyzed. The present data have confirmed a tonotopicity, low frequency anteriorly while high frequency posteriorly, in the Japanese macaque's AI when the recording time window was short (< 20 msec) and the stimulus level was close to threshold levels. In the low frequency area (< 500 Hz), the same neuron responded both to the best frequency (BF) and to combinations of successive higher harmonics which create a temporal periodicity identical to the BF. However, these neurons did not or little respond to the higher harmonics themselves when they were presented alone. The findings suggest that the temporally-coded pitch in the periphery appears to be already place-coded together with the place pitch by the same neuron at the level of AI to produce an identical pitch. Thus, this evidence agrees well with previous psychoacoustical findings in human studies.

J 708 OPTICAL IMAGING OF AUDITORY CORTICAL ACTIVITY IN THE GUINEA PIG.

HASHIMOTO, T. Inst Med. Dent. Engin., Tokyo Med. Dent. Univ.

Chiyoda-ku, Tokyo I01, JaDan

The pattern of population activity of the auditory cortex in response to sound stimulation was mapped with a newly developed video method imaging the epl-fluorescence of a voltage-sensitive dye(RH795). The animals were lightly anesthetized with Nembutal. The fluorescent images were sampled through pulse d illuminatlon by a Xenon lamp lightened id synchrony with the stimulus presentation. The responsive image was accumulated over the electric charge pattern on the CCD video camera. The background images were subtracted from the responsive images and the resultant difference images were integrated in the video frame memory to visualize the specific cortical activity in response to the stimulus sound. The excitation loci in the optical record were analyzed in correlation with a spectrographic survey of the stimulus. The spatio-temporal patterns of auditory cortical activity were surveyed by a train of sequentially recorded stroboscopic images. A spot or stripe pattern of excitation was found in the optical records. It would be due to the columnar structure in the auditory cortex. The time series of the optical records would play an important role in analyzing the global f~nctlonal structure of the audltory cortex in response to sound stimulation. The functioning of the auditory cortex could be elucidated 5y the time series analysis of the global population activity with the present optical recording method.