Summary
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1.
In the cochlear nucleus (CN) of Horseshoe bats, recordings were made from 148 single neurons to constant frequency (CF) signals and to sinusoidally frequency modulated (SFM) and sinusoidally amplitude modulated (SAM) signals, which in a first approximation simulate the periodic modulations of echoes returning from wing beating insects.
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2.
The probability of obtaining synchronized discharge activity to modulations was independent of the neurons' best frequencies (BFs). Neurons belonging to separate response pattern categories to CF-signals differed in the synchronization pattern to periodic modulations. While the response patterns of tonic neurons were characterized by an image-like reproduction of the time course of frequency or amplitude changes, phasic neurons respond with an activity peak to distinct portions of the modulation cycles. Neurons with build up patterns to CF-signals (n= 8) and three phasic neurons did not lock their discharges to SFM- or SAM-signals. Response patterns were essentially similar for SFM- and SAM-signals and systematically depended on modulation magnitude, carrier frequency and intensity parameters of the signals.
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3.
The effects of decreasing modulation magnitude were tested for 45 neurons with SFM- and for 46 neurons with SAM-signals. Asymmetries in the response patterns present at high modulation magnitudes disappeared with smaller modulation magnitudes and histogram envelopes approach sinusoidal form. Synchronized responses to SFM-signals were present down to modulation heights of ±20 Hz and to SAM-signals of 6%. Sensitivity for small modulation heights of the SFM-signal was highest in sharply tuned neurons in the frequency range of 81–88 kHz (‘filter neurons’). No correlations between minimum modulation depth of the SAM-signal and the neurons' BFs were found.
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4.
The carrier frequency of the SFM-signal was systematically varied in 19 neurons. Sensitivity for small modulation heights could be improved by positioning the carrier frequency near the flanks of the excitatory response area. The response to SAM-signals was less influenced by the carrier frequency.
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5.
The intensity parameter was studied in 18 neurons with SFM- and 25 neurons with SAM-signals. While synchronization was clearly present in the range of 10 to 30 dB SPL above minimum threshold, the response peaks to individual modulation cycles of tonic neurons tended to fuse at higher intensities. In sharply tuned neurons, individual response peaks to SFM-signals could be distinguished over wider intensity ranges than with SAM-signals.
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6.
Periodically amplitude modulated SFM-signals with different phase relations between amplitude maximum and particular frequency components were used for stimulation of 22 neurons. Due to their sharp tuning properties, the response pattern of filter neurons systematically changed depending on the phase relations of AM and FM, whereas the response pattern of neurons in other frequency ranges resembled the pattern to SAM-stimuli.
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7.
In order to determine the limiting rate of frequency and amplitude change for synchronization of response activity, the modulation frequency was varied between 50 Hz and 2,000 Hz in 59 neurons with SFM- and 46 neurons with SAM-stimuli. The range of modulation frequencies covered by synchronized activity was broad, with most neurons (n=41 SFM,n=28 SAM) reaching upper rates between 400 and 800 Hz, or even higher (n=6 SFM,n=14 SAM). Neurons with limiting rates below 400 Hz were rare (n=12 SFM,n=4 SAM). Low, medium and high limiting rates were found in tonic as well as phasic neurons. Some phasic neurons (n=3), required minimum modulation frequencies of 200 Hz to start synchronization. Synchronization behavior depended on intensity, center frequency, modulation magnitude and could be different for SFM- and SAM-signals in the same unit.
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8.
Data are discussed in relation to single unit recordings to periodically modulated signals in CN of other mammals and to results obtained from higher order auditory nuclei of Horseshoe bats.
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Abbreviations
- AC :
-
auditory cortex
- BF :
-
best frequency
- CF :
-
constant frequency
- CN :
-
cochlear nucleus
- df :
-
modulation height
- FM :
-
frequency modulation
- IC :
-
inferior colliculus
- MGB :
-
medial geniculate body
- PST :
-
post stimulus time
- Rf :
-
Rhinolophus ferrumequinum
- Rr :
-
Rhinolophus rouxi
- SAM :
-
sinusoidal amplitude modulation
- SFM :
-
sinusoidal frequency modulation
References
Britt RH (1976) Intracellular study of synaptic events related to phase-locking responses of cat cochlear nucleus cells to low frequency tones. Brain Res 112:313–327
Britt R, Starr A (1976a) Synaptic events and discharge patterns of cochlear nucleus cells. I. Steady frequency tone bursts. J Neurophysiol 39:162–178
Britt R, Starr A (1976b) Synaptic events and discharge patterns of cochlear nucleus cells. II. Frequency-modulated tones. J Neurophysiol 39:179–194
Bruns V (1976a) Peripheral auditory tuning for fine frequency analysis by the CF-FM bat,Rhinolophus ferrumequinum. I. Mechanical specializations of the cochlea. J Comp Physiol 106:77–86
Bruns V (1976b) Peripheral auditory tuning for fine frequency analysis by the CF-FM bat,Rhinolophus ferrumequinum. II. Frequency mapping in the cochlea. J Comp Physiol 106:87–97
Caspary DM, Rupert AL, Moushegian G (1977) Neuronal coding of vowel sounds in the cochlear nuclei. Exp Neurol 54:414–431
Creutzfeldt O, Hellweg FC, Schreiner C (1980) Thalamo-cortical transformation of response to complex auditory stimuli. Exp Brain Res 39:87–104
Engelstätter R (1981) Hörphysiologische Untersuchungen an Neuronen der aufsteigenden Hörbahn der echoortenden FledermausRhinolophus rouxi. Inaugural Dissertation, Frankfurt
Evans EF (1975) Cochlear nerve and cochlear nucleus. In: Keidel WD, Neff WD (eds) Handbook of sensory physiology, vol 2. Springer, Berlin Heidelberg New York, pp 1–109
Evans EF, Nelson PG (1973) The responses of single neurons in the cochlear nucleus of the cat as a function of their location and the anaesthetic state. Exp Brain Res 17:402–427
Godfrey DA, Kiang NYS, Norris BE (1975a) Single unit activity in the posteroventral cochlear nucleus of the cat. J Comp Neurol 162:247–268
Godfrey DA, Kiang NYS, Norris BE (1975b) Single unit activity in the dorsal cochlear nucleus of the cat. J Comp Neurol 162:269–284
Goldman LJ, Henson OW (1977) Prey recognition and selection by the constant frequency bat,Pteronotus p. parnellii. Behav Ecol Sociobiol 2:411–419
Harnischfeger G (1979) An improved method for extracellular marking of electrode tip positions in nervous tissue. J Neurosci Methods 1:195–200
Hirsch HR, Morton Gibson M (1976) Responses of single units in the cat cochlear nucleus to sinusoidal amplitude modulations of tones and noise: Linearity and relation to speech perception. J Neurosci Res 2:337–356
Machmerth H, Theiss D, Schnitzler H-U (1975) Konstruktion eines Luftultraschallgebers mit konstantem Frequenzgang im Bereich von 15 kHz-130 kHz. Acustica 34:81–85
Möller J, Neuweiler G, Zoeller H (1978) Response characteristics of inferior colliculus neurons of the awake CF-FM bat,Rhinolophus ferrumequinum. I. Single tone stimulation. J Comp Physiol 125:217–225
Møller AR (1969) Unit responses in the rat cochlear nucleus to repetitive, transient sounds. Acta Physiol Scand 75:542–551
Møller AR (1972) Coding of amplitude and frequency modulated sounds in the cochlear nucleus of the rat. Acta Physiol Scand 86:223–238
Møller AR (1974) Coding of sounds with rapidly varying spectrum in the cochlear nucleus. J Acoust Soc Am 55:631–640
Nelson PG, Erulkar SD, Bryan JS (1966) Responses of units of the inferior colliculus to time-varying acoustic stimuli. J Neurophysiol 29:834–860
Neuweiler G, Vater M (1977) Response patterns to pure tones of cochlear nucleus units in the CF-FM bat,Rhinolophus ferrumequinum. J Comp Physiol 115:119–133
Neuweiler G, Brans V, Schuller G (1980) Ears adapted for the detection of motion, or how echolocating bats have exploited the capacities of the mammalian auditory system. J Acoust Soc Am 68:741–753
Ostwald J (1980) Die funktionelle Organisation des Hörcortex der großen Hufeisennase,Rhinolophus ferrumequinum. Inaugural Dissertation, University of Marburg
Pfeiffer RR (1966) Classification of response patterns of spike discharges for units in the cochlear nucleus: Tone burst stimulation. Exp Brain Res 1:220–235
Pollak GD, Schuller G (1981) Tonotopic organization and encoding features of single units in the inferior colliculus of Horseshoe bats: Functional implications for prey identification. J Neurophysiol 45:208–226
Ribeaupierre F De, Goldstein MH, Yeni Komishan G (1972) Cortical coding of repetitive acoustic pulses. Brain Res 48:205–225
Romand R (1978) Survey of intracellular recording in the cochlear nucleus of the cat. Brain Res 148:43–65
Schnitzler H-U (1968) Die Ultraschall-Ortungslaute der Hufeisenfledermäuse (Chiroptera, Rhinolophidae) in verschiedenen Ortungsituationen. Z Vergl Physiol 57:376–408
Schnitzler H-U (1978) Die Detektion von Bewegungen durch Echoortung bei Fledermäusen. Verh Dtsch Zool Ges 1978:16–33
Schuller G (1979) Coding of small sinusoidal frequency and amplitude modulations in the inferior colliculus of the ‘CF-FM’ bat,Rhinolophus ferrumequinum. Exp Brain Res 34:117–132
Schuller G, Pollak GD (1979) Disproportionate frequency representation in the inferior colliculus of Horseshoe bats: evidence for an “acoustic fovea”. J Comp Physiol 132:47–54
Schuller G, Beuter K, Schnitzler H-U (1974) Responses to frequency-shifted artificial echoes in the bat,Rhinolophus ferrumequinum. J Comp Physiol 89:275–286
Schweizer H (1981) The connections of the inferior colliculus and the organization of the brainstem auditory system in the Greater Horseshoe bat (Rhinolophus ferrumequinum). J Comp Neurol 201:25–49
Suga N (1973) Feature extraction in the auditory system of bats. In: Møller A (ed) Basic mechanisms in hearing. Academic Press, New York, pp 675–745
Suga N, Jen PH, Jen H-S (1977) Further studies on the peripheral auditory system of ‘CF-FM’ bats specialized for fine frequency analysis of Doppler-shifted echoes. J Exp Biol 69:207–232
Suga N, Neuweiler G, Møller J (1976) Peripheral auditory tuning for fine frequency analysis by the CF-FM bat,Rhinolophus ferrumequinum. IV. Properties of peripheral auditory neurons. J Comp Physiol 106:111–125
Whitfield IC, Evans EF (1965) Responses of auditory cortical neurons to stimuli of changing frequency. J Neurophysiol 28:655–672
Young ED, Brownell WE (1976) Responses to tones and noise of single cells in dorsal cochlear nucleus of unanesthetized cats. J Neurophysiol 39:282–300
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Vater, M. Single unit responses in cochlear nucleus of horseshoe bats to sinusoidal frequency and amplitude modulated signals. J. Comp. Physiol. 149, 369–388 (1982). https://doi.org/10.1007/BF00619153
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DOI: https://doi.org/10.1007/BF00619153