The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 6, 2016
Electroacoustic stimulation in subjects with residual hearing is becoming more widely used in cli... more Electroacoustic stimulation in subjects with residual hearing is becoming more widely used in clinical practice. However, little is known about the properties of electrically induced responses in the hearing cochlea. In the present study, normal-hearing guinea pig cochleae underwent cochlear implantation through a cochleostomy without significant loss of hearing. Using recordings of unit activity in the midbrain, we were able to investigate the excitation patterns throughout the tonotopic field determined by acoustic stimulation. With the cochlear implant and the midbrain multielectrode arrays left in place, the ears were pharmacologically deafened and electrical stimulation was repeated in the deafened condition. The results demonstrate that, in addition to direct neuronal (electroneuronal) stimulation, in the hearing cochlea excitation of the hair cells occurs ("electrophonic responses") at the cochlear site corresponding to the dominant temporal frequency components of ...
Optical stimulation of the inner ear, the cochlea, is discussed as a possible alternative to conv... more Optical stimulation of the inner ear, the cochlea, is discussed as a possible alternative to conventional cochlear implants with the hypothetical improvement of dynamic range and frequency resolution. In this study nanosecond-pulsed optical stimulation of the hearing and non-hearing inner ear is investigated in vivo over a wide range of optical wavelengths and at different beam delivery locations. Seven anaesthetized guinea pigs were optically stimulated before and after neomycin induced destruction of hair cells. An optical parametric oscillator was tuned to different wavelengths (420 nm-2150 nm, ultraviolet to near-infrared) and delivered 3-5 ns long pulses with 6 ĀµJ pulse energy via a multimode optical fiber located either extracochlearly in front of the intact round window membrane or intracochlearly within the scala tympani. Cochlear responses were measured using registration of compound action potentials (CAPs). With intact hair cells CAP similar to acoustic stimulation were measured at both locations, while the neomycin treated cochleae did not show any response in any case. The CAP amplitudes of the functional cochleae showed a positive correlation to the absorption coefficient of hemoglobin and also to moderate water absorption. A negative correlation of CAP amplitude with a water absorption coefficient greater than 5.5 cm ā1 indicates additional phenomena. We conclude that in our stimulation paradigm with ns-pulses the most dominant stimulation effect is of optoacoustic nature and relates to functional hair cells.
Congenital sensory deprivation can lead to reorganization of the deprived cortical regions by ano... more Congenital sensory deprivation can lead to reorganization of the deprived cortical regions by another sensory system. Such cross-modal reorganization may either compete with or complement the "original" inputs to the deprived area after sensory restoration and can thus be either adverse or beneficial for sensory restoration. In congenital deafness, a previous inactivation study documented that supranormal visual behavior was mediated by higher-order auditory fields in congenitally deaf cats (CDCs). However, both the auditory responsiveness of "deaf" higher-order fields and interactions between the reorganized and the original sensory input remain unknown. Here, we studied a higher-order auditory field responsible for the supranormal visual function in CDCs, the auditory dorsal zone (DZ). Hearing cats and visual cortical areas served as a control. Using mapping with microelectrode arrays, we demonstrate spatially scattered visual (cross-modal) responsiveness in the DZ, but show that this did not interfere substantially with robust auditory responsiveness elicited through cochlear implants. Visually responsive and auditory-responsive neurons in the deaf auditory cortex formed two distinct populations that did not show bimodal interactions. Therefore, cross-modal plasticity in the deaf higher-order auditory cortex had limited effects on auditory inputs. The moderate number of scattered cross-modally responsive neurons could be the consequence of exuberant connections formed during development that were not pruned postnatally in deaf cats. Although juvenile brain circuits are modified extensively by experience, the main driving input to the cross-modally (visually) reorganized higher-order auditory cortex remained auditory in congenital deafness.
Extracellular local field potentials (LFPs) and multiunit activity (MUA) reflect the spatially in... more Extracellular local field potentials (LFPs) and multiunit activity (MUA) reflect the spatially integrated activity of multiple neurons in a given cortical structure. In the cat and primate visual cortices, these signals exhibit selectivity for visual stimulus features, such as orientation, direction of motion or spatial frequency. In the mouse visual cortex, a model which has been increasingly used in visual neuroscience, the visual stimulus selectivity of population signals has not been examined in detail. We recorded LFPs and MUA using multielectrode arrays and two derived measures, the high-pass filtered continuous MUA and the bipolar first spatial derivative of the LFP, in the visual cortex of isoflurane-anesthetized C57Bl/6 mice. We analyzed the onset latency and characterized the receptive fields in addition to the direction, orientation, and spatial and temporal frequency preferences of these signals. Population signals exhibited onset latencies as short as ā¼30 ms and possessed receptive fields as large as ā¼38Ā° with MUA receptive fields smaller than those of LFPs. All four population signals exhibited similar spatial frequency preferences (ā¼0.1 cycles per degree) and temporal frequency preferences (ā¼1 cycle per second). However, for all population signals, spatial and frequency tunings were broad and orientation and direction of motion preferences were absent. The characterization of the visual stimulus selectivity of LFPs and MUA in the mouse visual cortex should provide information regarding their usability in characterizing stimulus properties and disclose possible limitations.
This article reviews the studies on functional deficits in the auditory cortex of congenitally de... more This article reviews the studies on functional deficits in the auditory cortex of congenitally deaf animals. It compares their results with psychophysical and imaging data obtained from prelingually deaf humans. The studies demonstrate that the development of the auditory cortex is affected by the absence of hearing experience. In humans, the restoration of hearing after congenital deafness shows a sensitive period of 4 years, whereas even within this sensitive period cortical plasticity is already decreasing with increasing age. The reasons for the sensitive period are developmental changes of synaptic plasticity, developmentally modified synaptogenesis and synaptic pruning as well as changes in connectivity of the auditory cortex. Absence of top-down interactions from higher order auditory areas is another cardinal reason for the sensitive period. All these mechanisms contribute to the decreasing capacity for cortical plasticity during postnatal development. From the developmental...
Tinnitus is the conscious perception of sound heard in the absence of physical sound sources inte... more Tinnitus is the conscious perception of sound heard in the absence of physical sound sources internal or external to the body. The characterization of tinnitus by its spectrum reflects the missing frequencies originally represented in the hearing loss, i.e., partially or completely deafferented, region. The tinnitus percept, despite a total hearing loss, may thus be dependent on the persisting existence of a somatic memory for the "lost" frequencies. Somatic memory in this context is the reference for phantom sensations attributed to missing sensory surfaces or parts thereof. This raises the question whether tinnitus can exist in congenital deafness, were somatic representations have not been formed. We review the development of tonotopic maps in altricial and precocial animals evidence for a lack of tinnitus in congenital deafness and the effects of cochlear implants on the formation of tonotopic maps in the congenitally deaf. The latter relates to the emergence of tinnitus in these subjects. The reviewed material is consistent with the hypothesis that tinnitus requires an established and actively used somatotopic map that leads to a corresponding somatic memory. The absence of such experience explains the absence of tinnitus in congenital bilateral and unilateral deafness.
The present paper introduces a registration method for the electrical field produced by a cochlea... more The present paper introduces a registration method for the electrical field produced by a cochlear implant in the scala tympani in vitro. It was possible to determine the electrical potentials with high spatial resolution using an additional recording electrode. The results indicate that the efficacy of the stimulation by the more apical electrodes is higher than by the more basal ones. The reason is the decreasing cross-sectional area of the scala tympani, which represents a decreasing shunt between the stimulation electrodes.
We examined the longitudinal development of the cortical auditory evoked potential (CAEP) in 21 c... more We examined the longitudinal development of the cortical auditory evoked potential (CAEP) in 21 children who were Wtted with unilateral cochlear implants and in two children who were Wtted with bilateral cochlear implants either before age 3.5 years or after age 7 years. The age cut-oVs (<3.5 years for early-implanted and >7 years for late-implanted) were based on the sensitive
Die neuronale Entwicklung ist eine progressive Sequenz von umfangreichen konstruktiven und redukt... more Die neuronale Entwicklung ist eine progressive Sequenz von umfangreichen konstruktiven und reduktiven Prozessen (Zellteilung, Zellakkumulation, Zelldifferenzierung und Ausbildung von neuronalen Schaltkreisen) mit dem finalen Ziel der Etablierung adaptiver neuronaler Schaltkreise, welche zum adƤquaten Verhalten fĆ¼hren. Die Entwicklung des Gehirns verlƤuft in mehreren Phasen, von denen einige erst postnatal ablaufen. Sie finden ihren Abschluss nach dem 18. Lebensjahr. Zur Erlangung der alltagstauglichen HƶrfƤhigkeit ist die Hƶrerfahrung noch in der sensiblen Phase bis zum 4. Lebensjahr notwendig. Nachdem die Kochlea ihre FunktionalitƤt erlangt hat (beim Menschen um die 26. Schwangerschaftswoche; [47, 58, 88]) wird ein Teil der Entwicklungsprozesse durch akustische Reize mitgesteuert. Die protrahierteste Entwicklung zeigt die Hirnrinde. Diese ist auch fĆ¼r die komplexesten Leistungen des Gehirns verantwortlich, zu denen u. a. bewusste Wahrnehmung und das Lernen zƤhlen.
Cortical development is dependent on stimulus-driven learning. The absence of sensory input from ... more Cortical development is dependent on stimulus-driven learning. The absence of sensory input from birth, as occurs in congenital deafness, affects normal growth and connectivity needed to form a functional sensory system, resulting in deficits in oral language learning. Cochlear implants bypass cochlear damage by directly stimulating the auditory nerve and brain, making it possible to avoid many of the deleterious effects of sensory deprivation. Congenitally deaf animals and children who receive implants provide a platform to examine the characteristics of cortical plasticity in the auditory system. In this review, we discuss the existence of time limits for, and mechanistic constraints on, sensitive periods for cochlear implantation and describe the effects of multimodal and cognitive reorganization that result from long-term auditory deprivation.
Congenital auditory deprivation leads to deficits in the auditory cortex. The present review focu... more Congenital auditory deprivation leads to deficits in the auditory cortex. The present review focuses on central aspects of auditory deprivation: development, plasticity, corticocortical interactions, and cross-modal reorganization. We compile imaging data from human subjects, electroencephalographic data from cochlear implanted children, and animal research on congenital deafness. Behavioral, electroencephalographic, and imaging data in humans correspond well to behavioral and neurophysiological data obtained from congenitally deaf cats. The available data indicate that auditory deprivation leads to 'decoupling' of the primary auditory cortex from cognitive modulation of higher-order auditory areas. Higherorder auditory areas undergo a strong cross-modal reorganization and take-over new functions. Due to these and other deficits of intrinsic microcircuitry, the cortical column can not integrate bottom-up and top-down influences in deaf auditory cortex. In the ultimate consequence perceptual learning is compromised, resulting in sensitive periods.
We examined the longitudinal development of the cortical auditory evoked potential (CAEP) in 21 c... more We examined the longitudinal development of the cortical auditory evoked potential (CAEP) in 21 children who were Wtted with unilateral cochlear implants and in two children who were Wtted with bilateral cochlear implants either before age 3.5 years or after age 7 years. The age cut-oVs (<3.5 years for early-implanted and >7 years for late-implanted) were based on the sensitive period for central auditory development described in [Ear Hear. 23 (6), 532.] Our results showed a fundamentally diVerent pattern of development of CAEP morphology and P1 cortical response latency for early-and late-implanted children. Early-implanted children and one child who received bilateral implants by age 3.5 years showed rapid development in CAEP waveform morphology and P1 latency. Late-implanted children showed aberrant waveform morphology and signiWcantly slower decreases in P1 latency postimplantation. In the case of a child who received his Wrst implant by age 3.5 years and his second implant after age 7 years, CAEP responses elicited by the second implant were similar to late-implanted children. Our results are consistent with animal models of central auditory development after implantation and conWrm the presence of a relatively brief sensitive period for central auditory development in young children. ļ
This paper addresses the question of frequency discrimination of hearing for non-stationary (shor... more This paper addresses the question of frequency discrimination of hearing for non-stationary (short) tone stimuli (duration ~< 125 ms). Shortening of the stimulus duration leads to widening of the frequency spectrum of the tone. It can be shown that for hearing no acoustical uncertainty relation holds and thus some nonlinear elements must be present in hearing physiology. We present neurophysiological and psychoacoustical findings supporting the hypothesis that frequency discrimination of non-stationary short tone stimuli is performed in neural networks of the auditory system. Neural network architectures that could process the temporal and place excitation patterns originating in the cochlea are suggested. We show how these networks (temporal coincidence network processing the temporal code and lateral inhibition network processing the place code) can be combined to show performance consistent with auditory physiology. They might explain the frequency discrimination of hearing for non-stationary short tone stimuli. We show the fitting of psychophysical relations based on these networks with the experimentally determined data.
The hypothesis that temporal code is mainly responsible for speech recognition is discussed. Data... more The hypothesis that temporal code is mainly responsible for speech recognition is discussed. Data from cochlear implant research demonstrate that single-channel speech processors, supplying only temporal code, enable understanding of spoken language. Physiological findings supporting the observation are presented. A temporal theory of tone pitch perception is discussed.
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 6, 2016
Electroacoustic stimulation in subjects with residual hearing is becoming more widely used in cli... more Electroacoustic stimulation in subjects with residual hearing is becoming more widely used in clinical practice. However, little is known about the properties of electrically induced responses in the hearing cochlea. In the present study, normal-hearing guinea pig cochleae underwent cochlear implantation through a cochleostomy without significant loss of hearing. Using recordings of unit activity in the midbrain, we were able to investigate the excitation patterns throughout the tonotopic field determined by acoustic stimulation. With the cochlear implant and the midbrain multielectrode arrays left in place, the ears were pharmacologically deafened and electrical stimulation was repeated in the deafened condition. The results demonstrate that, in addition to direct neuronal (electroneuronal) stimulation, in the hearing cochlea excitation of the hair cells occurs ("electrophonic responses") at the cochlear site corresponding to the dominant temporal frequency components of ...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 6, 2016
Electroacoustic stimulation in subjects with residual hearing is becoming more widely used in cli... more Electroacoustic stimulation in subjects with residual hearing is becoming more widely used in clinical practice. However, little is known about the properties of electrically induced responses in the hearing cochlea. In the present study, normal-hearing guinea pig cochleae underwent cochlear implantation through a cochleostomy without significant loss of hearing. Using recordings of unit activity in the midbrain, we were able to investigate the excitation patterns throughout the tonotopic field determined by acoustic stimulation. With the cochlear implant and the midbrain multielectrode arrays left in place, the ears were pharmacologically deafened and electrical stimulation was repeated in the deafened condition. The results demonstrate that, in addition to direct neuronal (electroneuronal) stimulation, in the hearing cochlea excitation of the hair cells occurs ("electrophonic responses") at the cochlear site corresponding to the dominant temporal frequency components of ...
Optical stimulation of the inner ear, the cochlea, is discussed as a possible alternative to conv... more Optical stimulation of the inner ear, the cochlea, is discussed as a possible alternative to conventional cochlear implants with the hypothetical improvement of dynamic range and frequency resolution. In this study nanosecond-pulsed optical stimulation of the hearing and non-hearing inner ear is investigated in vivo over a wide range of optical wavelengths and at different beam delivery locations. Seven anaesthetized guinea pigs were optically stimulated before and after neomycin induced destruction of hair cells. An optical parametric oscillator was tuned to different wavelengths (420 nm-2150 nm, ultraviolet to near-infrared) and delivered 3-5 ns long pulses with 6 ĀµJ pulse energy via a multimode optical fiber located either extracochlearly in front of the intact round window membrane or intracochlearly within the scala tympani. Cochlear responses were measured using registration of compound action potentials (CAPs). With intact hair cells CAP similar to acoustic stimulation were measured at both locations, while the neomycin treated cochleae did not show any response in any case. The CAP amplitudes of the functional cochleae showed a positive correlation to the absorption coefficient of hemoglobin and also to moderate water absorption. A negative correlation of CAP amplitude with a water absorption coefficient greater than 5.5 cm ā1 indicates additional phenomena. We conclude that in our stimulation paradigm with ns-pulses the most dominant stimulation effect is of optoacoustic nature and relates to functional hair cells.
Congenital sensory deprivation can lead to reorganization of the deprived cortical regions by ano... more Congenital sensory deprivation can lead to reorganization of the deprived cortical regions by another sensory system. Such cross-modal reorganization may either compete with or complement the "original" inputs to the deprived area after sensory restoration and can thus be either adverse or beneficial for sensory restoration. In congenital deafness, a previous inactivation study documented that supranormal visual behavior was mediated by higher-order auditory fields in congenitally deaf cats (CDCs). However, both the auditory responsiveness of "deaf" higher-order fields and interactions between the reorganized and the original sensory input remain unknown. Here, we studied a higher-order auditory field responsible for the supranormal visual function in CDCs, the auditory dorsal zone (DZ). Hearing cats and visual cortical areas served as a control. Using mapping with microelectrode arrays, we demonstrate spatially scattered visual (cross-modal) responsiveness in the DZ, but show that this did not interfere substantially with robust auditory responsiveness elicited through cochlear implants. Visually responsive and auditory-responsive neurons in the deaf auditory cortex formed two distinct populations that did not show bimodal interactions. Therefore, cross-modal plasticity in the deaf higher-order auditory cortex had limited effects on auditory inputs. The moderate number of scattered cross-modally responsive neurons could be the consequence of exuberant connections formed during development that were not pruned postnatally in deaf cats. Although juvenile brain circuits are modified extensively by experience, the main driving input to the cross-modally (visually) reorganized higher-order auditory cortex remained auditory in congenital deafness.
Extracellular local field potentials (LFPs) and multiunit activity (MUA) reflect the spatially in... more Extracellular local field potentials (LFPs) and multiunit activity (MUA) reflect the spatially integrated activity of multiple neurons in a given cortical structure. In the cat and primate visual cortices, these signals exhibit selectivity for visual stimulus features, such as orientation, direction of motion or spatial frequency. In the mouse visual cortex, a model which has been increasingly used in visual neuroscience, the visual stimulus selectivity of population signals has not been examined in detail. We recorded LFPs and MUA using multielectrode arrays and two derived measures, the high-pass filtered continuous MUA and the bipolar first spatial derivative of the LFP, in the visual cortex of isoflurane-anesthetized C57Bl/6 mice. We analyzed the onset latency and characterized the receptive fields in addition to the direction, orientation, and spatial and temporal frequency preferences of these signals. Population signals exhibited onset latencies as short as ā¼30 ms and possessed receptive fields as large as ā¼38Ā° with MUA receptive fields smaller than those of LFPs. All four population signals exhibited similar spatial frequency preferences (ā¼0.1 cycles per degree) and temporal frequency preferences (ā¼1 cycle per second). However, for all population signals, spatial and frequency tunings were broad and orientation and direction of motion preferences were absent. The characterization of the visual stimulus selectivity of LFPs and MUA in the mouse visual cortex should provide information regarding their usability in characterizing stimulus properties and disclose possible limitations.
This article reviews the studies on functional deficits in the auditory cortex of congenitally de... more This article reviews the studies on functional deficits in the auditory cortex of congenitally deaf animals. It compares their results with psychophysical and imaging data obtained from prelingually deaf humans. The studies demonstrate that the development of the auditory cortex is affected by the absence of hearing experience. In humans, the restoration of hearing after congenital deafness shows a sensitive period of 4 years, whereas even within this sensitive period cortical plasticity is already decreasing with increasing age. The reasons for the sensitive period are developmental changes of synaptic plasticity, developmentally modified synaptogenesis and synaptic pruning as well as changes in connectivity of the auditory cortex. Absence of top-down interactions from higher order auditory areas is another cardinal reason for the sensitive period. All these mechanisms contribute to the decreasing capacity for cortical plasticity during postnatal development. From the developmental...
Tinnitus is the conscious perception of sound heard in the absence of physical sound sources inte... more Tinnitus is the conscious perception of sound heard in the absence of physical sound sources internal or external to the body. The characterization of tinnitus by its spectrum reflects the missing frequencies originally represented in the hearing loss, i.e., partially or completely deafferented, region. The tinnitus percept, despite a total hearing loss, may thus be dependent on the persisting existence of a somatic memory for the &amp;amp;amp;amp;quot;lost&amp;amp;amp;amp;quot; frequencies. Somatic memory in this context is the reference for phantom sensations attributed to missing sensory surfaces or parts thereof. This raises the question whether tinnitus can exist in congenital deafness, were somatic representations have not been formed. We review the development of tonotopic maps in altricial and precocial animals evidence for a lack of tinnitus in congenital deafness and the effects of cochlear implants on the formation of tonotopic maps in the congenitally deaf. The latter relates to the emergence of tinnitus in these subjects. The reviewed material is consistent with the hypothesis that tinnitus requires an established and actively used somatotopic map that leads to a corresponding somatic memory. The absence of such experience explains the absence of tinnitus in congenital bilateral and unilateral deafness.
The present paper introduces a registration method for the electrical field produced by a cochlea... more The present paper introduces a registration method for the electrical field produced by a cochlear implant in the scala tympani in vitro. It was possible to determine the electrical potentials with high spatial resolution using an additional recording electrode. The results indicate that the efficacy of the stimulation by the more apical electrodes is higher than by the more basal ones. The reason is the decreasing cross-sectional area of the scala tympani, which represents a decreasing shunt between the stimulation electrodes.
We examined the longitudinal development of the cortical auditory evoked potential (CAEP) in 21 c... more We examined the longitudinal development of the cortical auditory evoked potential (CAEP) in 21 children who were Wtted with unilateral cochlear implants and in two children who were Wtted with bilateral cochlear implants either before age 3.5 years or after age 7 years. The age cut-oVs (<3.5 years for early-implanted and >7 years for late-implanted) were based on the sensitive
Die neuronale Entwicklung ist eine progressive Sequenz von umfangreichen konstruktiven und redukt... more Die neuronale Entwicklung ist eine progressive Sequenz von umfangreichen konstruktiven und reduktiven Prozessen (Zellteilung, Zellakkumulation, Zelldifferenzierung und Ausbildung von neuronalen Schaltkreisen) mit dem finalen Ziel der Etablierung adaptiver neuronaler Schaltkreise, welche zum adƤquaten Verhalten fĆ¼hren. Die Entwicklung des Gehirns verlƤuft in mehreren Phasen, von denen einige erst postnatal ablaufen. Sie finden ihren Abschluss nach dem 18. Lebensjahr. Zur Erlangung der alltagstauglichen HƶrfƤhigkeit ist die Hƶrerfahrung noch in der sensiblen Phase bis zum 4. Lebensjahr notwendig. Nachdem die Kochlea ihre FunktionalitƤt erlangt hat (beim Menschen um die 26. Schwangerschaftswoche; [47, 58, 88]) wird ein Teil der Entwicklungsprozesse durch akustische Reize mitgesteuert. Die protrahierteste Entwicklung zeigt die Hirnrinde. Diese ist auch fĆ¼r die komplexesten Leistungen des Gehirns verantwortlich, zu denen u. a. bewusste Wahrnehmung und das Lernen zƤhlen.
Cortical development is dependent on stimulus-driven learning. The absence of sensory input from ... more Cortical development is dependent on stimulus-driven learning. The absence of sensory input from birth, as occurs in congenital deafness, affects normal growth and connectivity needed to form a functional sensory system, resulting in deficits in oral language learning. Cochlear implants bypass cochlear damage by directly stimulating the auditory nerve and brain, making it possible to avoid many of the deleterious effects of sensory deprivation. Congenitally deaf animals and children who receive implants provide a platform to examine the characteristics of cortical plasticity in the auditory system. In this review, we discuss the existence of time limits for, and mechanistic constraints on, sensitive periods for cochlear implantation and describe the effects of multimodal and cognitive reorganization that result from long-term auditory deprivation.
Congenital auditory deprivation leads to deficits in the auditory cortex. The present review focu... more Congenital auditory deprivation leads to deficits in the auditory cortex. The present review focuses on central aspects of auditory deprivation: development, plasticity, corticocortical interactions, and cross-modal reorganization. We compile imaging data from human subjects, electroencephalographic data from cochlear implanted children, and animal research on congenital deafness. Behavioral, electroencephalographic, and imaging data in humans correspond well to behavioral and neurophysiological data obtained from congenitally deaf cats. The available data indicate that auditory deprivation leads to 'decoupling' of the primary auditory cortex from cognitive modulation of higher-order auditory areas. Higherorder auditory areas undergo a strong cross-modal reorganization and take-over new functions. Due to these and other deficits of intrinsic microcircuitry, the cortical column can not integrate bottom-up and top-down influences in deaf auditory cortex. In the ultimate consequence perceptual learning is compromised, resulting in sensitive periods.
We examined the longitudinal development of the cortical auditory evoked potential (CAEP) in 21 c... more We examined the longitudinal development of the cortical auditory evoked potential (CAEP) in 21 children who were Wtted with unilateral cochlear implants and in two children who were Wtted with bilateral cochlear implants either before age 3.5 years or after age 7 years. The age cut-oVs (<3.5 years for early-implanted and >7 years for late-implanted) were based on the sensitive period for central auditory development described in [Ear Hear. 23 (6), 532.] Our results showed a fundamentally diVerent pattern of development of CAEP morphology and P1 cortical response latency for early-and late-implanted children. Early-implanted children and one child who received bilateral implants by age 3.5 years showed rapid development in CAEP waveform morphology and P1 latency. Late-implanted children showed aberrant waveform morphology and signiWcantly slower decreases in P1 latency postimplantation. In the case of a child who received his Wrst implant by age 3.5 years and his second implant after age 7 years, CAEP responses elicited by the second implant were similar to late-implanted children. Our results are consistent with animal models of central auditory development after implantation and conWrm the presence of a relatively brief sensitive period for central auditory development in young children. ļ
This paper addresses the question of frequency discrimination of hearing for non-stationary (shor... more This paper addresses the question of frequency discrimination of hearing for non-stationary (short) tone stimuli (duration ~< 125 ms). Shortening of the stimulus duration leads to widening of the frequency spectrum of the tone. It can be shown that for hearing no acoustical uncertainty relation holds and thus some nonlinear elements must be present in hearing physiology. We present neurophysiological and psychoacoustical findings supporting the hypothesis that frequency discrimination of non-stationary short tone stimuli is performed in neural networks of the auditory system. Neural network architectures that could process the temporal and place excitation patterns originating in the cochlea are suggested. We show how these networks (temporal coincidence network processing the temporal code and lateral inhibition network processing the place code) can be combined to show performance consistent with auditory physiology. They might explain the frequency discrimination of hearing for non-stationary short tone stimuli. We show the fitting of psychophysical relations based on these networks with the experimentally determined data.
The hypothesis that temporal code is mainly responsible for speech recognition is discussed. Data... more The hypothesis that temporal code is mainly responsible for speech recognition is discussed. Data from cochlear implant research demonstrate that single-channel speech processors, supplying only temporal code, enable understanding of spoken language. Physiological findings supporting the observation are presented. A temporal theory of tone pitch perception is discussed.
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 6, 2016
Electroacoustic stimulation in subjects with residual hearing is becoming more widely used in cli... more Electroacoustic stimulation in subjects with residual hearing is becoming more widely used in clinical practice. However, little is known about the properties of electrically induced responses in the hearing cochlea. In the present study, normal-hearing guinea pig cochleae underwent cochlear implantation through a cochleostomy without significant loss of hearing. Using recordings of unit activity in the midbrain, we were able to investigate the excitation patterns throughout the tonotopic field determined by acoustic stimulation. With the cochlear implant and the midbrain multielectrode arrays left in place, the ears were pharmacologically deafened and electrical stimulation was repeated in the deafened condition. The results demonstrate that, in addition to direct neuronal (electroneuronal) stimulation, in the hearing cochlea excitation of the hair cells occurs ("electrophonic responses") at the cochlear site corresponding to the dominant temporal frequency components of ...
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Papers by Andrej Kral