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PubMed2001

Between sound and perception: reviewing the search for a neural code.

This review investigates the roles of representation, transformation and coding as part of a hierarchical process between sound and perception. This is followed by a survey of how speech sounds and elements thereof are represented in the activity patterns along the auditory pathway. Then the evidence for a place representation of texture features of sound, comprising frequency, periodicity pitch, harmonicity in vowels, and direction and speed of frequency modulation, and for a temporal and synchrony representation of sound contours, comprising onsets, offsets, voice onset time, and low rate amplitude modulation, in auditory cortex is reviewed. Contours mark changes and transitions in sound and auditory cortex appears particularly sensitive to these dynamic aspects of sound. Texture determines which neurons, both cortical and subcortical, are activated by the sound whereas the contours modulate the activity of those neurons. Because contours are temporally represented in the majority of neurons activated by the texture aspects of sound, each of these neurons is part of an ensemble formed by the combination of contour and texture sensitivity. A multiplexed coding of complex sound is proposed whereby the contours set up widespread synchrony across those neurons in all auditory cortical areas that are activated by the texture of sound.

Animals↗
PubMed1999

Sound lateralisation in patients with left or right cerebral hemispheric lesions: relation with unilateral visuospatial neglect.

OBJECTIVES: To localise the brain lesion that causes disturbances of sound lateralisation and to examine the correlation between such deficit and unilateral visuospatial neglect. METHOD: There were 29 patients with right brain damage, 15 patients with left brain damage, and 22 healthy controls, who had normal auditory and binaural thresholds. A device was used that delivered sound to the left and right ears with an interaural time difference using headphones. The amplitude (an index of ability to detect sound image shifts from the centre) and midpoint (an index of deviation of the interaural time difference range perceived as the centre) parameters of interaural time difference were analysed in each subject using 10 consecutive stable saw toothed waves. RESULTS: The amplitude of interaural time difference was significantly higher in patients with right brain damage than in controls. The midpoint of the interaural time difference was significantly more deviated in patients with right brain damage than in those with left brain damage and controls (p<0. 05). Patients with right brain damage with lesions affecting both the parietal lobe and auditory pathway showed a significantly higher amplitude and deviated midpoint than the controls, whereas right brain damage with involvement of only the parietal lobe showed a midpoint significantly deviated from the controls (p<0.05). Abnormal sound lateralisation correlated with unilateral visuospatial neglect (p<0.05). CONCLUSIONS: The right parietal lobe plays an important part in sound lateralisation. Sound lateralisation is also influenced by lesions of the right auditory pathway, although the effect of such lesions is less than that of the right parietal lobe. Disturbances of sound lateralisation correlate with unilateral visuospatial neglect.

Analysis of Variance↗
PubMed1989

Middle-latency responses. II. Variation among stimulation sites.

We investigated the relationship between thresholds of the electrically evoked auditory brain-stem response (EABR) and the electrically evoked middle-latency response (EMLR), and the variation in EMLR thresholds and dynamic ranges with site of stimulation. The EABRs and EMLRs were recorded in albino guinea pigs in response to electrical stimulation at the round window, promontory, scala tympani, and modiolus. The EABR and EMLR thresholds were similar. There was no significant difference between thresholds for round-window and scala tympani stimulation. Amplitude/intensity functions for the EMLR differed with site of stimulation. The EMLR seems to be comparable with the EABR for assessing the electrical excitability of the auditory pathway with less electrical artifact contamination. In this respect, round-window and scala tympani stimulation sites are equally efficacious.

Animals↗
PubMed1996

The development of auditory behavior (or what the anatomists and physiologists have to explain).

OBJECTIVE: Infants' and children's performance in detecting and discriminating between sounds is often poorer than that of adults. Behavioral immaturity often coexists with mature-looking morphology and physiological responses from the peripheral and brain stem structures that limit performance among adults. One interpretation of this pattern of results is that "hearing" is mature but some unnamed central process is immature. DESIGN: The approach to the problem taken here is to view auditory behavior as the process to be explained and physiological or anatomical measurements as giving us clues about the underlying processes. The development of four aspects of hearing-frequency resolution, detection, temporal resolution, and intensity resolution-is reviewed in this paper, and new data addressing these topics are presented. RESULTS: Frequency resolution, detection, temporal resolution, and intensity resolution all undergo development during infancy and childhood, although the mechanisms underlying development vary across capacity and developmental period. CONCLUSIONS: A coherent argument can be made that both primary auditory pathway maturation and maturation of specific central processes are involved in development. Both types of maturation continue into childhood, and both types of maturation can influence hearing directly.

Age Factors↗
PubMed2003

The psychophysics and physiology of comodulation masking release.

The ability to detect auditory signals from background noise may be enhanced by the addition of energy in frequency regions well removed from the frequency of the signal. However, it is important that this energy is amplitude-modulated in a coherent way across frequencies, i.e. comodulated. This enhancement of signal detectability is known as comodulation masking release (CMR), and in this review we show that CMR is largest if: (1) the total masker's bandwidth is large, (2) the modulation frequency is low, (3) the modulation depth is high, (4) the envelope is regular and, (5) the masker's spectrum level is high. Possible physiological correlates of CMR have been found at different levels of the auditory pathway. Current hypotheses for the underlying physiological mechanisms, including wide-band inhibition or the disruption of masker modulation envelope response, are discussed.

Action Potentials↗
PubMed1993

Auditory evoked potentials in epileptic patients.

Auditory brain stem response (ABR) and middle latency response (MLR) were recorded in 49 epileptic patients. Responses were evoked and recorded at 90 dB nHL down to threshold. A statistically significant number of epileptic patients showed elevated ABR (30.1%) and MLR (40.7%) thresholds, even though their pure-tone audiograms showed normal hearing sensitivity. Threshold elevation was more frequent in subjects with grand mal epilepsy compared to subjects with temporal lobe epilepsy reflecting poorer response in the former subgroup. Furthermore, chronicity of illness was significantly related to the elevated ABR and MLR thresholds in grand mal patients in contrast to patients with temporal lobe epilepsy. On the other hand, the effect of antiepileptic drugs did not seem to be significantly related to the elevated thresholds in both subgroups. Threshold elevation was attributed to a disturbance in the neurotransmitters of the brain stem as well as other subcortical structures. The inhibitory effect of the efferent auditory pathway on the incoming neural signals was also suggested to explain such elevated thresholds.

Acoustic Stimulation↗
PubMed2002

Excitatory action of an immature glycinergic/GABAergic sound localization pathway.

Most mammals determine the azimuthal direction of incoming sound using auditory cues arising from differences in interaural sound intensity. The first station in the ascending auditory pathway, which processes interaural intensity differences, is the lateral superior olive (LSO), a binaural nucleus in the auditory brainstem. LSO neurons encode interaural intensity differences by integrating excitatory input from the ipsilateral cochlea and inhibitory input from the contralateral cochlea. Both inputs converge on single neurons in a highly organized, frequency-specific manner. The correct development of the precise arrangement of these inputs and their physiological properties depends on neuronal activity. Previous studies have shown that inhibitory, glycinergic/GABAergic inputs to the LSO are transiently depolarizing, and it has been hypothesized that this depolarizing action enables developing inhibitory inputs to act as excitatory inputs. In support of this hypothesis, we recently demonstrated that depolarizing glycinergic/GABAergic inputs can increase the intracellular calcium concentration in immature LSO neurons and elicit action potentials. These results provide support for the notion that the influence of glycinergic/GABAergic synaptic activity on development of the LSO involves calcium-dependent signaling mechanisms.

Animals↗
PubMed1982

Preservation of central auditory function in the deafness mouse.

Deafness mice are profoundly deaf from birth as a result of genetically determined cochlear dysfunction. Evoked potentials in response to direct electrical stimulation of the cochlear nerve can readily be recorded in the inferior colliculus of deafness mice, and such responses are larger in amplitude than those in control mice. These observations indicate that at least some central connections become functional in the deafness central auditory pathway in the absence of peripheral stimulation, and are relevant to the general problem of restoring function by direct nerve stimulation in the profoundly deaf.

Animals↗
PubMed2006

Inhibition of the c-Jun N-terminal kinase-mediated mitochondrial cell death pathway restores auditory function in sound-exposed animals.

We tested and characterized the therapeutic value of round window membrane-delivered (RWM) d-JNKI-1 peptide (Bonny et al., 2001) against sound trauma-induced hearing loss. Morphological characteristics of sound-damaged hair cell nuclei labeled by Hoechst staining show that apoptosis is the predominant mode of cell death after sound trauma. Analysis of the events occurring after sound trauma demonstrates that c-Jun N-terminal kinase (JNK)/stress-activated protein kinase activates a mitochondrial cell death pathway (i.e., activation of Bax, release of cytochrome c, activation of procaspases, and cleavage of fodrin). Fluorescein isothiocyanate (FITC)-conjugated d-JNKI-1 peptide applied onto an intact cochlear RWM diffuses through this membrane and penetrates cochlear tissues with the exception of the stria vascularis. A time sequence of fluorescence measurements demonstrates that FITC-labeled d-JNKI-1 remains in cochlear tissues for as long as 3 weeks. In addition to blocking JNK-mediated activation of a mitochondrial cell death pathway, RWM-delivered d-JNKI-1 prevents hair cell death and development of a permanent shift in hearing threshold that is caused by sound trauma in a dose-dependent manner (EC50 = 2.05 microM). The therapeutic window for protection of the cochlea from sound trauma with RWM delivery of d-JNKI-1 extended out to 12 h after sound exposure. These results show that the mitogen-activated protein kinase/JNK signaling pathway plays a crucial role in sound trauma-initiated hair cell death. Blocking this signaling pathway with RWM delivery of d-JNKI-1 may have significant therapeutic value as a therapeutic intervention to protect the human cochlea from the effects of sound trauma.

Animals↗
PubMed1992

The ontogeny of homeothermic regulation in post-hatching chicks: its influence on the development of hearing.

1. The maturation of homeothermy in chicks from day 0 to day 30 after hatching (P0-P30) was studied by measuring rectal temperatures following different environmental exposures. 2. Body temperature regulation and an adult-like temperature (41.5 degrees C) develop with different time courses, being mature on days P4 and P23, respectively. After 1 hr at 20 degrees C, P0 chicks were 4.5-6.5 degrees C cooler than P30 animals. 3. A temperature effect shifts frequency in the auditory pathway up to 0.5 octaves to lower values. Some shifts in tonotopic maps observed in developmental studies of frequency representation in awake chicks can be fully explained by this temperature effect.

Animals↗
PubMed1984

Developmental and aging changes in somatosensory, auditory and visual evoked potentials.

To assess developmental and aging changes in human sensory systems, components of short-latency somatosensory, brain-stem auditory and pattern-reversal visual evoked potentials, thought to originate in specific structures of these systems, were recorded in 286 normal subjects ranging in age from 4 to 95 years. Analysis was primarily restricted to peak and interpeak latencies; visual evoked potential amplitudes were also analyzed. Major results and conclusions are: (1) 'Developmental' changes (that is, decreases in latency attributable to decreased conduction time in younger subjects) were not seen in the median nerve, in brain-stem auditory pathways, or in some portions of visual cortex. Small developmental changes were seen in the somatosensory afferent pathway from the cervical spinal cord to thalamus, and large changes were seen in somatosensory and visual cortex. Cortical developmental changes appeared not to be complete until 17 years of age or later. (2) 'Aging' changes (that is, increases in latency attributable to increased conduction time in older subjects) were observed in the median nerve, cervical spinal cord, brain-stem auditory pathways, and somatosensory and visual cortex. (3) Visual evoked potential amplitudes tended to decrease with age, particularly during development; amplitude and latency effects were dissimilar for most components. (4) Males tended to show larger aging effects than females. (5) The results suggest that age-related changes in human sensory systems are not uniform, but rather are different in specific portions of these systems, different at particular epochs of the life span, and stronger in males than in females.

Adolescent↗
PubMed1989

A study of proteins in the auditory system of rabbits using two-dimensional gels: identification of glial fibrillary acidic protein and vitamin D-dependent calcium binding protein.

Two-dimensional gel electrophoresis and computerized optical densitometry were employed to compare the relative content of proteins across major auditory brain regions in rabbits. Areas examined included the dorsal and ventral cochlear nuclei which receive the primary afferents from the organ of Corti, the lateral superior olivary nucleus which has strong reciprocal relationships with the cochlear nucleus, and the successively more rostral projections of the auditory pathways to inferior colliculus, medial geniculate and auditory cortex. Twelve proteins demonstrated significant decreases and 5 proteins significant increases in content at successively more rostral levels of the auditory system, including 2 proteins which were highly localized to the cochlear nuclei and 2 proteins greatest in amounts in the auditory cortex. One protein which was localized to the cochlear nuclei and lateral superior olive (molecular weight (MW) = 50.3, isoelectric point (pI) = 5.7) was identified as the glial fibrillary acidic protein by reaction of specific antisera on blots. Antisera to the vitamin D-dependent calcium binding protein reacted specifically with one protein (MW = 27.2, pI = 4.8) which was greatest in amount in the lateral superior olive (LSO) versus other auditory regions examined. The significance of these findings rests in the potential for identifying specific markers for cellular elements that are important in auditory function and which might be lost as a consequence of developmental abnormalities or other traumas.

Animals↗
PubMed2001

Development and plasticity of cortical areas and networks.

The development of cortical layers, areas and networks is mediated by a combination of factors that are present in the cortex and are influenced by thalamic input. Electrical activity of thalamocortical afferents has a progressive role in shaping cortex. For early thalamic innervation and patterning, the presence of activity might be sufficient; for features that develop later, such as intracortical networks that mediate emergent responses of cortex, the spatiotemporal pattern of activity often has an instructive role. Experiments that route projections from the retina to the auditory pathway alter the pattern of activity in auditory thalamocortical afferents at a very early stage and reveal the progressive influence of activity on cortical development. Thus, cortical features such as layers and thalamocortical innervation are unaffected, whereas features that develop later, such as intracortical connections, are affected significantly. Surprisingly, the behavioural role of 'rewired' cortex is also influenced profoundly, indicating the importance of patterned activity for this key aspect of cortical function.

Animals↗
PubMed2003

Corollary discharge inhibition of ascending auditory neurons in the stridulating cricket.

Acoustically communicating animals are able to process external acoustic stimuli despite generating intense sounds during vocalization. We have examined how the crickets' ascending auditory pathway copes with self-generated, intense auditory signals (chirps) during singing (stridulation). We made intracellular recordings from two identified ascending auditory interneurons, ascending neuron 1 (AN1) and ascending neuron 2 (AN2), during pharmacologically elicited sonorous (two-winged), silent (one-winged), and fictive (isolated CNS) stridulation. During sonorous chirps, AN1 responded with bursts of spikes, whereas AN2 was inhibited and rarely spiked. Low-amplitude hyperpolarizing potentials were recorded in AN1 and AN2 during silent chirps. The potentials were also present during fictive chirps. Therefore, they were the result of a centrally generated corollary discharge from the stridulatory motor network. The spiking response of AN1 and AN2 to acoustic stimuli was inhibited during silent and fictive chirps. The maximum period of inhibition occurred in phase with the maximum spiking response to self-generated sound in a sonorously stridulating cricket. In some experiments (30%) depolarizing potentials were recorded during silent chirps. Reafferent feedback elicited by wing movement was probably responsible for the depolarizing potentials. In addition, two other sources of inhibition were present in AN1: (1) IPSPs were elicited by stimulation with 12.5 kHz stimuli and (2) a long-lasting hyperpolarization followed spiking responses to 4.5 kHz stimuli. The hyperpolarization desensitized the response of AN1 to subsequent quieter stimuli. Therefore, the corollary discharge will reduce desensitization by suppressing the response of AN1 to self-generated sounds.

Acoustic Stimulation↗
PubMed1992

[Critical ratio: effects of contralateral masking on normal and pathological ears].

In order to evaluate the central interferences on the auditory efficiency, the effect of contralateral masking noise on Critical Ratio (CR) has been studied in 14 normal ears (control group), in 12 ears with cochlear disorders and in 6 with retrocochlear lesion (acoustic neuromas); in all cases the impairment was unilateral, while the other ear was normal. CR values were calculated for 1 KHz pulsed tones (duration 500 ms, rise/fall 25 ms, duty cycle of 50%); the masking noise was a wide band (90-20,000 Hz) delivered at 40 dB SL. The results have demonstrated that in the presence of contralateral masking noise, CRs don't modify both in the normal ears and in those with retrocochlear disorder, whereas they increase, almost always, in ears with cochlear deafness. These results demonstrate that the involvement of central auditory pathways, because of contralateral noise, makes the auditory efficiency worse, only in ears with cochlear dysfunctions; this behaviour seems to confirm the peripheral origin of CR.

Adolescent↗
PubMed1997

Temporal integration and duration tuning in the dorsal zone of cat auditory cortex.

The present study examined auditory cortical neurons, the responses of which depended on the duration of noise bursts. We recorded from 150 neurons with response latencies exceeding 30 msec and from 28 neurons with OFF responses to auditory stimuli in the dorsal zone of cat auditory cortex. Of 150 long-latency neurons, 132 displayed some form of duration selectivity. Seventy-eight were classified as selective for long durations. Among the long-duration-selective neurons, 30 responded only to noise burst stimuli with durations longer than a minimal threshold and were classified further as duration threshold neurons. Of 132 duration-selective neurons, 41 responded selectively to noise bursts of short duration; 13 showed maximal responses to noise bursts of a particular duration and could be regarded as duration-tuned neurons. OFF-response neurons included ones that were long-duration-selective, duration-tuned, and nonduration-selective. Duration tuning has been described previously only at the midbrain level in amphibians and bats. The present finding of sensitivity to sound duration in at least one region of cat auditory cortex indicates that this form of neural tuning may be important for hearing in all vertebrates, and for processing of sound at multiple levels in the auditory pathway. The duration tuning in the cat auditory cortex was much broader, and the best duration was distributed over a wider range than in the bat inferior colliculus. We suggest that the duration selectivity of the long-latency neurons results from integration along the time domain of a stimulus during the latent period.

Acoustic Stimulation↗
PubMed2003

A corollary discharge mechanism modulates central auditory processing in singing crickets.

Crickets communicate using loud (100 dB SPL) sound signals that could adversely affect their own auditory system. To examine how they cope with this self-generated acoustic stimulation, intracellular recordings were made from auditory afferent neurons and an identified auditory interneuron-the Omega 1 neuron (ON1)-during pharmacologically elicited singing (stridulation). During sonorous stridulation, the auditory afferents and ON1 responded with bursts of spikes to the crickets' own song. When the crickets were stridulating silently, after one wing had been removed, only a few spikes were recorded in the afferents and ON1. Primary afferent depolarizations (PADs) occurred in the terminals of the auditory afferents, and inhibitory postsynaptic potentials (IPSPs) were apparent in ON1. The PADs and IPSPs were composed of many summed, small-amplitude potentials that occurred at a rate of about 230 Hz. The PADs and the IPSPs started during the closing wing movement and peaked in amplitude during the subsequent opening wing movement. As a consequence, during silent stridulation, ON1's response to acoustic stimuli was maximally inhibited during wing opening. Inhibition coincides with the time when ON1 would otherwise be most strongly excited by self-generated sounds in a sonorously stridulating cricket. The PADs and the IPSPs persisted in fictively stridulating crickets whose ventral nerve cord had been isolated from muscles and sense organs. This strongly suggests that the inhibition of the auditory pathway is the result of a corollary discharge from the stridulation motor network. The central inhibition was mimicked by hyperpolarizing current injection into ON1 while it was responding to a 100 dB SPL sound pulse. This suppressed its spiking response to the acoustic stimulus and maintained its response to subsequent, quieter stimuli. The corollary discharge therefore prevents auditory desensitization in stridulating crickets and allows the animals to respond to external acoustic signals during the production of calling song.

Acoustic Stimulation↗
PubMed1979

Middle-ear structures contribute little to auditory perception of microwaves.

The contribution of the ossicles (middle-ear bones) to auditory perception of microwaves was evaluated by the brain-stem evoked response (BER). Amplitude and latency of BERs were recorded from guinea pigs that were stimulated at various intensities by acoustic pulses coupled to the auditory canal or via bone conduction, and by microwave pulses. Blocking of the external ear, middle-ear damping, and middle-ear destruction produced little change in the BERs that were elicited by microwave pulses. Results indicate that activity in the central auditory pathway as induced by pulsed microwaves only requires stimulation of the cochlea. Conduction of pressure waves through the bones of the calvarium appears to be the mechanism responsible in perception of pulsed microwaves.

Animals↗