Introduction to synaptic circuits, Gordon M.Shepherd and Christof Koch membrane properties and neurotransmitter actions, David A.McCormick peripheral ganglia, Paul R.Adams and Christof Koch spinal cord - ventral horn, Robert E.Burke olfactory bulb, Gordon M.Shepherd, and Charles A.Greer retina, Peter Sterling cerebellum, Rodolfo R.Llinas and Kerry D.Walton thalamus, S.Murray Sherman and Christof Koch basal ganglia, Charles J.Wilson olfactory cortex, Lewis B.Haberly hippocampus, Thomas H.Brown and Anthony M.Zador neocortex, Rodney J.Douglas and Kevan A.C.Martin Gordon M.Shepherd. Appendix: Dendretic electrotonus and synaptic integration.

The synaptic organization of the brain

中枢神経系疾患の治療は正常細胞（ニューロン）の機能維持を目的とするが，脳血管障害のように機能障害の原因が細胞の死滅に基づくことは多い．一方，脳腫瘍の治療においては薬物療法や放射線療法といった腫瘍細胞の死滅を目標とするものが大きな位置を占める．いずれの場合にも，細胞死の機序を理解することは各種病態や治療法の理解のうえで重要である．現在のところ最も研究の進んでいる細胞死の型はアポトーシスである．そのなかで重要な位置を占めるミトコンドリアにおける反応および抗アポトーシス因子について概要を紹介する．

Neuroscience 細胞死：最近の知見

In mammals, environmental sounds stimulate the auditory receptor, the cochlea, via vibrations of the stapes, the innermost of the middle ear ossicles. These vibrations produce displacement waves that travel on the elongated and spirally wound basilar membrane (BM). As they travel, waves grow in amplitude, reaching a maximum and then dying out. The location of maximum BM motion is a function of stimulus frequency, with high-frequency waves being localized to the “base” of the cochlea (near the stapes) and low-frequency waves approaching the “apex” of the cochlea. Thus each cochlear site has a characteristic frequency (CF), to which it responds maximally. BM vibrations produce motion of hair cell stereocilia, which gates stereociliar transduction channels leading to the generation of hair cell receptor potentials and the excitation of afferent auditory nerve fibers. At the base of the cochlea, BM motion exhibits a CF-specific and level-dependent compressive nonlinearity such that responses to low-level, near-CF stimuli are sensitive and sharply frequency-tuned and responses to intense stimuli are insensitive and poorly tuned. The high sensitivity and sharp-frequency tuning, as well as compression and other nonlinearities (two-tone suppression and intermodulation distortion), are highly labile, indicating the presence in normal cochleae of a positive feedback from the organ of Corti, the “cochlear amplifier.” This mechanism involves forces generated by the outer hair cells and controlled, directly or indirectly, by their transduction currents. At the apex of the cochlea, nonlinearities appear to be less prominent than at the base, perhaps implying that the cochlear amplifier plays a lesser role in determining apical mechanical responses to sound. Whether at the base or the apex, the properties of BM vibration adequately account for most frequency-specific properties of the responses to sound of auditory nerve fibers.

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Mechanics of the Mammalian Cochlea

Phantom auditory perception (tinnitus): mechanisms of generation and perception

The temporal properties of speech appear to play a more important role in linguistic contrasts than has hitherto been appreciated. Therefore, a new framework for describing the acoustic structure of speech based purely on temporal aspects has been developed. From this point of view, speech can be said to be comprised of three main temporal features, based on dominant fluctuation rates: envelope, periodicity, and fine-structure. Each feature has distinct acoustic manifestations, auditory and perceptual correlates, and roles in linguistic contrasts. The applicability of this three-featured temporal system is discussed in relation to hearing-impaired and normal listeners.

Temporal Information in Speech: Acoustic, Auditory and Linguistic Aspects

The representation of speech-like stimuli in the auditory nerve and cochlear nucleus have been the subject of numerous studies over the past 20 years (Blackburn and Sachs, 1990; Geisler, 1988; Kiang and Moxon, 1974; Palmer, et al, 1986; Sachs and Young, 1979; Young and Sachs, 1979) In both the auditory nerve and cochlear nucleus, for exam- ple, the spectra of vowels can be represented in terms of average rate (Sachs and Young, 1979) or the temporal patterns of firing (phase-locking; Blackburn and Sachs, 1990; Young and Sachs, 1979) or a combination of the two (Blackburn and Sachs, 1990; Young and Sachs, 1979) In this chapter we focus on average rate representations

Speech Representation in the Auditory Nerve and Ventral Cochlear Nucleus

Classification of Complex Nonspeech Sounds

Steady-state vowels can be discriminated in background noise at signal to noise ratios of less than -15 dB (Dewson, 1968). Thus, the information relating to the spectrum of a vowel stimulus which is contained in the firing patterns of the ensemble of auditory-nerve fibers must remain when the vowels are presented in background noise. Spectral features may be encoded in auditory-nerve discharge patterns in at least two ways: One in terms of the distribution of average discharge rate as a function of fibers’ characteristic frequencies (CF) (rate-place representation, Sachs and Young, 1979), and the other in terms of temporal or phase-locked responses (temporal-place representation, Young and Sachs, 1979). We have shown previously (Young and Sachs, 1979) that the temporal-place code provides a more robust representation of vowel formant frequencies than does the rate-place code. In this paper we shall compare the effects of broad-band noise on these two representations of the spectrum of the vowel /e/.

Effects of Masking Noise on the Representation of Vowel Spectra in the Auditory Nerve

The intelligibility of speech transmitted through an acoustic channel such as the ocean is limited by multipath “time smearing.” The purpose of this study has been to obtain a quantitative measure of the effects of such time smearing on speech intelligibility. A linear, time‐invariant channel was used as a model of the ocean. The impulse response of this channel was a sample of band‐limited Gaussian noise. Using fast Fourier transform techniques, words of the modified rhyme test were convolved with (“smeared by”) this channel impulse response. The intelligibility of these “smeared” words was measured as a function of the impulse response duration T. Intelligibility was found to decrease monotonically as a function of T over the range T = 0 to T = 150 msec. Increasing T beyond 150 msec caused little change in intelligibility. With rhyme‐test words used in a 6AFC test, average scores of 75%–80% were obtained for T between 150 and 665 msec.

Speech Intelligibility in a Stationary Multipath Channel

Representations of the syllables [ba] and [da] based on the temporal response properties of populations of auditory‐nerve fibers were studied. Post‐stimulus time histograms and interval histograms were computed from 20‐ms segments of fiber spike trains occurring in response to each stimulus. Discrete Fourier transforms with a resolution of 50 Hz were computed from each histogram. As a measure of the response of the population of fibers to each harmonic of the 50‐Hz resolution frequency, the magnitude of the response to that frequency was averaged across all fibers whose characteristic frequencies were within one‐fourth octave of that harmonic. We have previously called this measure the average localized synchronized rate (ALSR). Response profiles for the 20‐ms segments of the stimulus were generated by plotting the ALSR versus stimulus frequency. Time‐varying spectral features of the stimulus are well preserved by such profiles. For example, the onset spectra and formant transitions of the stop consonants...

Murray B. Sachs

Papers

Speech Representation in the Auditory Nerve and Ventral Cochlear Nucleus

Classification of Complex Nonspeech Sounds

Effects of Masking Noise on the Representation of Vowel Spectra in the Auditory Nerve

Speech Intelligibility in a Stationary Multipath Channel

Temporal representation of CV syllables in populations of auditory‐nerve fibers