Receptive-field nonlinearities in primary auditory cortex: a comparative perspective.

Cortical processing of auditory information can be affected by interspecies differences as well as brain states. Here we compare multifeature spectro-temporal receptive fields (STRFs) and associated input/output functions or nonlinearities (NLs) of neurons in primary auditory cortex (AC) of four mammalian species. Single-unit recordings were performed in awake animals (female squirrel monkeys, female, and male mice) and anesthetized animals (female squirrel monkeys, rats, and cats).

Spectral plasticity in monkey primary auditory cortex limits performance generalization in a temporal discrimination task.

Auditory experience and behavioral training can modify perceptual performance. However, the consequences of temporal perceptual learning for temporal and spectral neural processing remain unclear. Specifically, the attributes of neural plasticity that underlie task generalization in behavioral performance remain uncertain.

Background noise exerts diverse effects on the cortical encoding of foreground sounds.

In natural listening conditions, many sounds must be detected and identified in the context of competing sound sources, which function as background noise. Traditionally, noise is thought to degrade the cortical representation of sounds by suppressing responses and increasing response variability. However, recent studies of neural network models and brain slices have shown that background synaptic noise can improve the detection of signals.

Passive stimulation and behavioral training differentially transform temporal processing in the inferior colliculus and primary auditory cortex.

Unlabelled: In profoundly deaf cats, behavioral training with intracochlear electric stimulation (ICES) can improve temporal processing in the primary auditory cortex (AI). To investigate whether similar effects are manifest in the auditory midbrain, ICES was initiated in neonatally deafened cats either during development after short durations of deafness (8 wk of age) or in adulthood after long durations of deafness (≥3.5 yr).

Modulation-frequency-specific adaptation in awake auditory cortex.

Amplitude modulations are fundamental features of natural signals, including human speech and nonhuman primate vocalizations. Because natural signals frequently occur in the context of other competing signals, we used a forward-masking paradigm to investigate how the modulation context of a prior signal affects cortical responses to subsequent modulated sounds. Psychophysical "modulation masking," in which the presentation of a modulated "masker" signal elevates the threshold for detecting the modulation of a subsequent stimulus, has been interpreted as evidence of a central modulation filterbank and modeled accordingly.

Spectral context affects temporal processing in awake auditory cortex.

Amplitude modulation encoding is critical for human speech perception and complex sound processing in general. The modulation transfer function (MTF) is a staple of auditory psychophysics, and has been shown to predict speech intelligibility performance in a range of adverse listening conditions and hearing impairments, including cochlear implant-supported hearing. Although both tonal and broadband carriers have been used in psychophysical studies of modulation detection and discrimination, relatively little is known about differences in the cortical representation of such signals.

Behavioral training restores temporal processing in auditory cortex of long-deaf cats.

Temporal auditory processing is poor in prelingually hearing-impaired patients fitted with cochlear prostheses as adults. In an animal model of prelingual long-term deafness, we investigated the effects of behavioral training on temporal processing in the adult primary auditory cortex (AI). Neuronal responses to pulse trains of increasing frequencies were recorded in three groups of neonatally deafened cats that received a cochlear prosthesis after >3 yr of deafness: 1) acutely implanted animals that received no electric stimulation before study, 2) animals that received chronic-passive stimulation for several weeks to months before study, and 3) animals that received chronic-passive stimulation and additional behavioral training (signal detection).

Behavioral training enhances cortical temporal processing in neonatally deafened juvenile cats.

Deaf humans implanted with a cochlear prosthesis depend largely on temporal cues for speech recognition because spectral information processing is severely impaired. Training with a cochlear prosthesis is typically required before speech perception shows improvement, suggesting that relevant experience modifies temporal processing in the central auditory system. We tested this hypothesis in neonatally deafened cats by comparing temporal processing in the primary auditory cortex (AI) of cats that received only chronic passive intracochlear electric stimulation (ICES) with cats that were also trained with ICES to detect temporally challenging trains of electric pulses.

Spatial selectivity to intracochlear electrical stimulation in the inferior colliculus is degraded after long-term deafness in cats.

In an animal model of electrical hearing in prelingually deaf adults, this study examined the effects of deafness duration on response thresholds and spatial selectivity (i.e., cochleotopic organization, spatial tuning and dynamic range) in the central auditory system to intracochlear electrical stimulation.

Functional organization and hemispheric comparison of primary auditory cortex in the common marmoset (Callithrix jacchus).

Hemispheric fine-grain maps of primary auditory cortex (AI) were derived from microelectrode penetrations in the temporal gyrus of the common marmoset (Callithrix jacchus) to 1) compare the functional organization of AI in the marmoset with other mammalian species and 2) compare the right and left AI maps in individual monkeys. Frequency receptive fields (FRFs) were recorded with pure tones. Five FRF parameters were analyzed: characteristic frequency, threshold, sharpness of tuning 10 dB and 40 dB above threshold, and minimum response latency.

Degradation of temporal resolution in the auditory midbrain after prolonged deafness is reversed by electrical stimulation of the cochlea.

In an animal model of prelingual deafness, we examined the anatomical and physiological effects of prolonged deafness and chronic electrical stimulation on temporal resolution in the adult central auditory system. Maximum following frequencies (Fmax) and first spike latencies of single neurons responding to electrical pulse trains were evaluated in the inferior colliculus of two groups of neonatally deafened cats after prolonged periods of deafness (>2.5 yr): the first group was implanted with an intracochlear electrode and studied acutely (long-deafened unstimulated, LDU); the second group (LDS) received a chronic implant and several weeks of electrical stimulation (pulse rates > or =300 pps).

Reward-dependent plasticity in the primary auditory cortex of adult monkeys trained to discriminate temporally modulated signals.

Adult owl monkeys were trained to detect an increase in the envelope frequency of a sinusoidally modulated 1-kHz tone. Detection was positively correlated with the magnitude of the change in the envelope frequency. Surprisingly, neuronal responses recorded in the primary auditory cortex of trained monkeys were globally suppressed by the modulated tone.

Representation of spectral and temporal envelope of twitter vocalizations in common marmoset primary auditory cortex.

Cortical sensitivity in representations of behaviorally relevant complex input signals was examined in recordings from primary auditory cortical neurons (AI) in adult, barbiturate-anesthetized common marmoset monkeys (Callithrix jacchus). We studied the robustness of distributed responses to natural and degraded forms of twitter calls, social contact vocalizations comprising several quasi-periodic phrases of frequency and AM. We recorded neuronal responses to a monkey's own twitter call (MOC), degraded forms of their twitter call, and sinusoidal amplitude modulated (SAM) tones with modulation rates similar to those of twitter calls.

Auditory detection and discrimination in deaf cats: psychophysical and neural thresholds for intracochlear electrical signals.

More than 30,000 hearing-impaired human subjects have learned to use cochlear implants for speech perception and speech discrimination. To understand the basic mechanisms underlying the successful application of contemporary speech processing strategies, it is important to investigate how complex electrical stimuli delivered to the cochlea are processed and represented in the central auditory system. A deaf animal model has been developed that allows direct comparison of psychophysical thresholds with central auditory neuronal thresholds to temporally modulated intracochlear electrical signals in the same animals.

Responses of inferior colliculus neurons to amplitude-modulated intracochlear electrical pulses in deaf cats.

Current cochlear prostheses use amplitude-modulated pulse trains to encode acoustic signals. In this study we examined the responses of inferior colliculus (IC) neurons to sinusoidal amplitude-modulated pulses and compared the maximum unmodulated pulse rate (Fmax) to which they responded with the maximum modulation frequency (maxFm) that they followed. Consistent with previous results, responses to unmodulated pulses were all low-pass functions of pulse rate.

Electrical cochlear stimulation in the deaf cat: comparisons between psychophysical and central auditory neuronal thresholds.

Cochlear prostheses for electrical stimulation of the auditory nerve ("electrical hearing") can provide auditory capacity for profoundly deaf adults and children, including in many cases a restored ability to perceive speech without visual cues. A fundamental challenge in auditory neuroscience is to understand the neural and perceptual mechanisms that make rehabilitation of hearing possible in these deaf humans. We have developed a feline behavioral model that allows us to study behavioral and physiological variables in the same deaf animals.

Behavioral and neurophysiological thresholds for electrical cochlear stimulation in the deaf cat.

Psychophysical detection thresholds for unmodulated electrical pulse trains or for sinusoidally amplitude-modulated (SAM) pulse trains were estimated in deaf juvenile cats using a conditioned avoidance paradigm. Biphasic current pulses (0.2 ms/phase) were delivered by scala tympani electrodes consisting of 4-8 electrode contacts driven as bipolar pairs.

Temporal properties of chronic cochlear electrical stimulation determine temporal resolution of neurons in cat inferior colliculus.

As cochlear implants have become increasingly successful in the rehabilitation of adults with profound hearing impairment, the number of pediatric implant subjects has increased. We have developed an animal model of congenital deafness and investigated the effect of electrical stimulus frequency on the temporal resolution of central neurons in the developing auditory system of deaf cats. Maximum following frequencies (Fmax) and response latencies of isolated single neurons to intracochlear electrical pulse trains (charge balanced, constant current biphasic pulses) were recorded in the contralateral inferior colliculus (IC) of two groups of neonatally deafened, barbiturate-anesthetized cats: animals chronically stimulated with low-frequency signals (< or = 80 Hz) and animals receiving chronic high-frequency stimulation (> or = 300 pps).

Functional organization of spectral receptive fields in the primary auditory cortex of the owl monkey.

Recent experiments in the cat have demonstrated that several response parameters, including frequency tuning, intensity tuning, and FM selectivity, are spatially segregated across the isofrequency axis. To investigate whether a similar functional organization exists in the primate, we have studied the spatial distribution of pure-tone receptive field parameters across the primary auditory cortex (AI) in six owl monkeys (Aotus trivirgatus). The distributions of binaural interaction types and onset latency were also examined.

Acoustic pursuit of invisible moving targets by cats.

Head movements evoked by an invisible acoustic target were used as a metric to analyze localization of moving sources of sound in naive cats. The target was presented in the lateral sound field and moved along an arc at constant angular speeds. Head-movement trajectories were characterized by a large-magnitude orienting component that undershot the target, and a tracking component elicited by the target during acoustic pursuit.

Contribution of auditory cortex to acoustical orientation in cats under conditions of discordant auditory reafference.

Head-orienting responses (ORs) evoked by a stationary source of sound typically terminate in small undershoots in normal hearing cats or in large undershoots (hypometria) if the auditory cortex is ablated bilaterally. In the present study, ORs executed by cats were studied using a procedure in which the OR produced an isogonal rotation of the sound source, i.e.

Representation of a species-specific vocalization in the primary auditory cortex of the common marmoset: temporal and spectral characteristics.

1. The temporal and spectral characteristics of neural representations of a behaviorally important species-specific vocalization were studied in neuronal populations of the primary auditory cortex (A1) of barbiturate-anesthetized adult common marmosets (Callithrix jacchus), using both natural and synthetic vocalizations. The natural vocalizations used in electrophysiological experiments were recorded from the animals under study or from their conspecifics.

Temporal resolution of neurons in cat inferior colliculus to intracochlear electrical stimulation: effects of neonatal deafening and chronic stimulation.

1. Cochlear implants have been available for > 20 yr to profoundly deaf adults who have lost their hearing after acquiring language. The success of these cochlear prostheses has encouraged the application of implants in prelingually deaf children as young as 2 yr old.

Effects of bilateral and unilateral ablation of auditory cortex in cats on the unconditioned head orienting response to acoustic stimuli.

1. Reflexive head orienting responses (ORs) elicited by bursts of wide-band noise were investigated in cats after bilateral or unilateral ablation of the auditory cortex, and the cats' performance was compared with that of control cats. The OR was used as an indication of ability to orient toward the azimuthal direction of a source of sound.