Effects of visual attention on the intensity of auditory evoked potentials.

Click-evoked potentials were recorded from the round window (cochlear microphonic and auditory nerve), cochlear nucleus, and auditory cortex of unanesthetized cats during periods of visual attention and increased auditory intensity. The clicks (irrelevant stimuli) were presented continuously as background before, during, and after the presentation of a visual discrimination task (relevant stimuli) which attempted to alter the attentive state of the animals. At all electrode sites, the mean peak-to-peak amplitudes of click-evoked potentials were significantly smaller during attention to the visual discrimination stimuli when compared with the pretest and posttest control periods. Although the amplitudes of the click-evoked potentials were suppressed at all intensities during visual attention, much greater suppression occurred at low auditory intensities than at high auditory intensities. The results suggest that during attention, a central inhibitory mechanism suppresses irrelevant auditory stimuli presumably via the olivo-cochlear bundle at the peripheral stages in the afferent auditory pathways.     

Intraoperative electrophysiological monitoring for hearing preservation in acoustic neurinoma surgery

Five acoustic neurinomas have been operated with hearing preservation as a goal. We monitored intraoperative brainstem auditory evoked potentials (BAEP) in all five cases, electrocochleogram (ECoG) using needle electrode in external auditory meatus in four, and compound action potentials directly recorded from the cochlear nerve (CAP VIII) in three. In all five cases the tumor was totally resected and cochlear nerve was anatomically preserved. However, in only one case useful hearing was preserved with preservation of all wave forms of the BAEP. Another patient with preservation of all wave forms of BAEP and the ECoG showed postoperative severe hearing loss. Other three patients showed postoperative severe hearing loss: only Wave I of BAEP and ECoG were preserved without preservation of the CAP VIII in one whose cochlear nerve was thought to be damaged in cerebellopontine angle cistern; Wave I of BAEP, ECoG and CAP VIII were preserved in one in whom it was suggested cochlear nerve near brainstem or cochlear nucleus was damaged; none of the BAEP, ECoG and CAP VIII was preserved in one in whom it was suggested distal cochlear nerve, or internal auditory artery was damaged. These different patterns of changes suggested that different causes for the hearing loss and difficulties in hearing preservation during acoustic neurinoma surgery. Having identified the putative mechanism of the hearing loss by monitoring those potentials, suggestions are made about how such hearing loss might be avoided. For preservation of the hearing in acoustic neurinoma surgery, all of those potentials including all wave forms of BAEP, ECoG and CAP VIII should be preserved during surgery.(ABSTRACT TRUNCATED AT 250 WORDS)     

Short latency vestibular potentials evoked by electrical round window stimulation in the guinea pig

Short-latency potentials evoked by round window electrical stimulation were recorded in guinea pig by means of vertex-pinna skin electrodes using averaging techniques. Constant current shocks of 20 microseconds or 50 microseconds (25-300 microA) were used to evoke both auditory and vestibular brain-stem potentials. Pure auditory potentials, comparable to those evoked by acoustic clicks, were obtained by 20 microseconds electrical stimuli and disappeared during an auditory masking procedure made with a continuous white noise (110 dB SPL). Short latency potentials labeled V1, V2 and V3 were obtained by 50 microseconds electrical stimuli during an auditory masking procedure. This response disappeared after specific vestibular neurectomy, whereas the auditory response evoked by acoustic clicks or by electrical stimulation remained unchanged, suggesting that these latter potentials had a vestibular origin.     

Selective attention affects human brain stem frequency-following response

Selective attention modifies long-latency cortical event-related potentials. Amplitudes are typically enhanced and/or latencies reduced when evoking stimuli are attended. However, there is controversy concerning the effects of selective attention on short-latency brain stem evoked potentials. The objective of the present study was to assess possible attention effects on the brain stem auditory frequency-following response (FFR) elicited by a periodic tone. Young adult subjects heard a repetitive auditory stimulus while detecting infrequent target stimuli in either an auditory or visual detection task. Five channels of high frequency electroencephalographic (EEG) activity were recorded along the scalp midline with the center electrode positioned at the vertex. The FFR was elicited by the repetitive tone during both tasks. There were significant individual differences in the electrode sites yielding maximum response amplitudes, but overall FFR amplitudes were significantly larger during the auditory attention task. These results suggest that selective attention in humans can modify signal processing in sensory (afferent) pathways at the level of the brain stem. This may reflect top-down perceptual preprocessing mediated by extensive descending (efferent) pathways that originate in the cortex. Overall, the FFR appears to be a robust indicator of early auditory neural processing and shows effects not seen in brain stem auditory evoked response studies employing transient (click) acoustic stimuli.     

Unit activity to click CS changes in dorsal cochlear nucleus after conditioning.

Recordings were made of single unit activity (n = 360 units) from the dorsal cochlear nucleus of cats. Different patterns of activity were elicited by acoustic stimuli before and after Pavlovian conditioning. The peak response to a forward paired click conditioned stimulus (CS) increased whereas that to a backward paired hiss discriminative stimulus (DS) did not. The percentage of units responding to the CS increased from 34% to 46% after conditioning. The findings do not support the widely accepted hypothesis that learning has no effect on transmission through the first brain stem relay of the auditory system and indicate, instead, that the cochlear nucleus can participate in complex adaptive acoustic signal processing.     

Developmental changes in auditory evoked potentials in the inferior colliculi of mice during periods of susceptibility to priming

In mice, which are not normally susceptible to audiogenic seizures, a single exposure to an intense acoustic stimulus between the ages of 12 and 26 days renders the animals susceptible thereafter to audiogenic seizures. This phenomenon is known as “acoustic priming”. In the present study, auditory evoked potentials were recorded from the inferior colliculi of 116 unanaesthetized mice bearing chronically implanted electrodes. The amplitude of the evoked potentials increased sharply between approximately 15 and 22 days of age, suggesting that the “critical period” for priming coincides with a period of rapid development in the auditory system. Since there is substantial evidence from the work of other investigators that priming is due to disuse of the auditory pathways resulting from sound-induced cochlear damage (and can be mimicked by puncturing the eardrum or stoping up the auditory meatus). A plausible hypothesis is that the development of the auditory pathways is modulated by input, as if damage to the receptors during the “critical period” of development leads to proliferation of functional connections.     

Sound-induced changes of infraslow brain potential fluctuations in the medial geniculate nucleus and primary auditory cortex in anaesthetized rats

Recent publications indicate the presence of infraslow activity (<0.5 Hz) in subcortical and cortical sites of the auditory system of the brain. It has been reported that this activity might be sensitive to acoustic stimuli. Yet the dynamics of infraslow brain potential (ISBP) fluctuations in these structures and their potential sensitivity to auditory stimuli are unknown. The present study was performed in order to test the hypothesis that extracellular ISBP activity in the medial geniculate nucleus (MGN) and the primary auditory cortex (A1) responds concurrently to acoustic stimuli. The experimental subjects were 5 adult rats with chronic stereotaxic electrodes implanted in MGN and A1. The animals were anesthetized and recordings were made in both sites during both silence and rhythmical acoustic stimulation. Our results support the hypothesis that these fluctuations are sensitive to acoustic stimuli. There were similar changes in ISBP activity in the MGN and A1 in response to rhythmic acoustic stimulation. Specifically, there were significant increases in the frequency range of seconds. Based on these findings, we suggest that sound-correlated changes in infraslow activity in the range of seconds in the MGN and A1 reflect specific mechanisms of neural processing of acoustic information in the auditory system of the brain.     

Short-latency auditory projection to the frontal telencephalon of the pigeon

An auditory projection to the frontolateral telencephalon of birds, originally described by Iljitschew, is confirmed for the pigeon. Potentials evoked by acoustic stimuli were recorded from the neostriatum frontale closely surrounding the nucleus basalis, in anesthetized and awake subjects. The latency of these responses was short (5 to 8 ms) compared to that of responses recorded from the orthodox avian telencephalic auditory projection in the neostriatum caudale, field L (12 to 14 ms). The intensity and frequency sensitivities of the frontal auditory potentials, however, were similar to those of the area L responses. Clicks delivered to the auditory meati were more effective than the same stimuli directed at other parts of the head or beak. Ipsilateral and contralateral auditory stimuli were equally effective. Occlusion of the ear openings attenuated the responses; thick pasting of the remainder of the head or beak did not affect them. Trigeminal deafferentation similarly did not attenuate the frontal auditory potentials, but alblation of the cochleae totally abolished them. The hypothesis that the frontal auditory responses are due to an artifactual stimulation of trigeminal mechanoreceptors projecting to the nucleus basalis is thus rejected. The neural pathway subserving this projection and the functional role that it may play are discussed.     

Visual processing affects the neural basis of auditory discrimination

The interaction between auditory and visual speech streams is a seamless and surprisingly effective process. An intriguing example is the "McGurk effect": The acoustic syllable /ba/ presented simultaneously with a mouth articulating /ga/ is typically heard as /da/ [McGurk, H., & MacDonald, J. Hearing lips and seeing voices. Nature, 264, 746-748, 1976]. Previous studies have demonstrated the interaction of auditory and visual streams at the auditory cortex level, but the importance of these interactions for the qualitative perception change remained unclear because the change could result from interactions at higher processing levels as well. In our electroencephalogram experiment, we combined the McGurk effect with mismatch negativity (MMN), a response that is elicited in the auditory cortex at a latency of 100-250 msec by any above-threshold change in a sequence of repetitive sounds. An "odd-ball" sequence of acoustic stimuli consisting of frequent /va/ syllables (standards) and infrequent /ba/ syllables (deviants) was presented to 11 participants. Deviant stimuli in the unisensory acoustic stimulus sequence elicited a typical MMN, reflecting discrimination of acoustic features in the auditory cortex. When the acoustic stimuli were dubbed onto a video of a mouth constantly articulating /va/, the deviant acoustic /ba/ was heard as /va/ due to the McGurk effect and was indistinguishable from the standards. Importantly, such deviants did not elicit MMN, indicating that the auditory cortex failed to discriminate between the acoustic stimuli. Our findings show that visual stream can qualitatively change the auditory percept at the auditory cortex level, profoundly influencing the auditory cortex mechanisms underlying early sound discrimination.     

Differential auditory processing continues during sleep.

Auditory evoked potentials (AEPs) were used to examine selective stimulus processing in sleep. In waking, repetitive stimuli generate exogenous P1, N1 and P2 components of the auditory evoked potential (AEP). Deviant stimuli generate endogenous cognitive components including the mismatch negativity (MMN), N2 and P3 components. We examined long-latency auditory evoked potentials elicited by repetitive and deviant stimuli during waking and stage II-IV sleep to assess whether stimulus deviance is detected during sleep. The waking P1, N1b and P2 had maximal amplitudes at fronto-central scalp sites, with additional peaks (N1a, N1c) at temporal sites. Deviant tones generated a frontal maximal MMN, and complex novel tones generated an additional P3 component maximal at centro-parietal sites. During stages II-IV sleep N1a, b, c amplitudes were reduced. During stage II sleep all stimuli generated increased P2 amplitudes and a late negative component (N340). Deviant stimuli generated greater P2 and N340 amplitudes than frequent stimuli in stage II sleep, as well as an additional P420 component. In stage III-IV sleep the P420 was absent and the AEP was dominated by a negativity of long duration whose amplitude increased in response to deviant stimuli. These data indicate that auditory evoked activity changes from wakefulness to sleep. The differential response to deviant sounds observed during waking and all sleep stages supports the theory that selective processing of auditory stimuli persists during sleep.     

Neural activity associated with binaural processes for the perceptual segregation of pitch

OBJECTIVE: We measured late cortical potentials in a psychophysical procedure for binaural unmasking of a dichotically-embedded pitch. METHODS: Late-latency auditory evoked potentials were measured from 128 recording channels in 13 healthy subjects. Control stimuli consisted of 500 ms segments of broadband acoustic noise presented identically to both ears via earphones, evoking a perception of noise localized in the centre of the head. Dichotic pitch stimuli were created by introducing a dichotic delay to a narrow frequency region of the same noise segments, and resulted in a perception of both the centrally-located noise and a right-lateralized pitch. RESULTS: Both stimuli evoked late auditory event-related potentials (ERPs) characterized by a P1-N1-P2 complex of waves between 60 and 180 ms after stimulus onset. ERPs associated with the control and dichotic pitch stimuli showed no amplitude differences for the P1 and N1 waves. ERPs to dichotic pitch stimuli became significantly more negative beginning at a latency around 150 ms, an effect that was maximal between 210 and 280 ms. Topographic mapping showed that this late negativity was lateralized to the left hemisphere. CONCLUSIONS: The late negative wave elicited by the dichotic pitch stimulus reflects neural processing that is dependent upon binaural fusion within the auditory system. SIGNIFICANCE: The dichotic pitch paradigm may provide a useful tool for the electrophysiological assessment and study of the temporal processing capabilities of the auditory system. This paradigm may also be useful for the study of binaural mechanisms for the perceptual segregation of concurrent sound sources.     

Cortical responsiveness during inner speech in schizophrenia: an event-related potential study.

OBJECTIVE: The study assessed the effects of inner speech on auditory cortical responsiveness in schizophrenia. METHOD: Comparison subjects (N=15) and patients with schizophrenia (N=15) were presented with acoustic and visual stimuli during three conditions: while subjects were silent, when spontaneous inner speech might occur; during directed inner speech, while subjects repeated a statement silently to themselves; and while subjects listened to recorded speech. N1 event-related potentials were recorded during the three conditions. RESULTS: N1 event-related potentials elicited by acoustic stimuli, but not by visual stimuli, were lower during directed inner speech than during the silent baseline condition in the comparison subjects but not in the patients. CONCLUSIONS: Abnormal auditory cortical responsiveness to inner speech in patients with schizophrenia may be a sign of corollary discharge dysfunction, which may potentially cause misattribution of inner speech to external voices.     

Opioid modulation of cochlear auditory responses in the rat inner ear

The auditory system has an extensive efferent innervation, which contributes to processes of control and regulation of the afferent input. The expression of receptors to various neurotransmitters and neuropeptides in the inner ear has been described, among which endogenous opioid receptors are found. The role of opioid receptors in the cochlea is not yet fully defined, it has been reported that opioid agonists and antagonists modulate the response to auditory stimuli and in clinical practice, multiple cases have been reported in which the consumption of opioid derivatives induce sensorineural hearing loss. In this work, we evaluated the effects of acute treatment with morphine, fentanyl, tramadol, and naloxone, in the auditory brain stem potentials (ABR), the compound action potential (CAP), and distortion products otacoustic emissions (DPOAE), across a wide range of stimulus frequencies and amplitudes. Adult Long-Evans rats of the strain CII/ZV weighing 180–220 g were used. For the ABR recording drugs were administered intraperitoneally or intravenously. For the CAP and DPOAE drugs were applied by direct perfusion in the middle ear. The opioid agonists produced a consistent increase in the amplitude of the PI component of the ABR and of the N1-P1 amplitude of the CAP. Naloxone produced no significant changes in the ABR and a reduction of the CAP N1-P1 amplitude. Also, opioid agonists induced a decrease in the amplitude of the DPOAE. These results show that the opioid receptor activation modulates both the afferent response at both the afferent response to acoustic stimuli, and also at the cochlear mechanics as revealed by DPOAE changes. These results present a significant step in understanding how opioid modulation of auditory responses may contribute to the auditory processing and to sensorineural hearing loss produced by opioids.     

Physiological abnormalities in hereditary hyperekplexia.

Five patients from a kindred with hereditary hyperekplexia had physiological testing. The surface-recorded electromyographic pattern of audiogenic muscle jerks was identical to that of the normal acoustic startle reflex. Testing at graded stimulus intensities indicated an increase in the gain of the acoustic startle reflex. Nose-tap stimuli resulted in short-latency generalized electromyographic bursts that were similar to the R1 component of the blink reflex. Electrical stimulation of peripheral nerves elicited a pattern of generalized muscle jerks that was similar to that of the acoustic startle reflex. Somatosensory evoked potentials, brainstem auditory evoked potentials, and cortical auditory evoked potentials were normal. The primary physiological abnormality in hereditary hyperekplexia is widespread elevated gain of vestigial withdrawal reflexes in the brainstem and possibly the spinal cord, most likely resulting from increased excitability of reticular neurons.     

Learning-related activation in the auditory system of the rat produced by long-term habituation: a 2-deoxyglucose study

Autoradiography with [14C]2-deoxyglucose (2-DG) was used to examine the functional activity of the rat auditory system during long- and short-term habituation of the acoustic startle reflex. The data showed that presentation of the acoustic stimulus to long-term habituated rats resulted in a learning-related metabolic enhancement that was significantly greater than the response evoked by the same acoustic stimulus in the inexperienced rats. This enhancement was localized to brainstem and midbrain auditory nuclei and no significant changes occurred at thalamocortical levels of the auditory pathway. The largest difference in 2-DG uptake between long- and short-term habituated rats was in the lateral superior olivary nucleus (LSO). The LSO activation suggests that olivocochlear efferents may operate in a central feedback control of peripheral auditory input during long-term habituation. Findings of enhanced metabolism from the cochlear nuclei to the central nucleus of the inferior colliculus indicated that active processes of neuronal plasticity take place in the lower auditory system during long-term habituation. The results provide the first demonstration of how a nonassociative learning experience such as long-term habituation modifies the metabolic activity of the auditory system. The findings support the conclusion that auditory responses of behaving animals to acoustic stimuli are dependent not only on the physical parameters of a stimulus, but also on its learned behavioral significance.     

Clinical neurophysiology of visual and auditory processing in dyslexia: A review

Neurophysiological studies on children and adults with dyslexia provide a deeper understanding of how visual and auditory processing in dyslexia might relate to reading deficits. The goal of this review is to provide an overview of research findings in the last two decades on motion related and contrast sensitivity visual evoked potentials and on auditory event related potentials to basic tone and speech sound processing in dyslexia. These results are particularly relevant for three important theories about causality in dyslexia: the magnocellular deficit hypothesis, the temporal processing deficit hypothesis and the phonological deficit hypothesis. Support for magnocellular deficits in dyslexia are primarily provided from evidence for altered visual evoked potentials to rapidly moving stimuli presented at low contrasts. Consistently ERP findings revealed altered neurophysiological processes in individuals with dyslexia to speech stimuli, but evidence for deficits processing certain general acoustic information relevant for speech perception, such as frequency changes and temporal patterns, are also apparent.     

Auditory and visual event-related perturbations in the 40 Hz auditory steady-state response.

The effects of salient auditory and visual 'foreground' stimuli on responses to 'background' probe stimuli were investigated. The foreground stimuli were given at long and aperiodic intervals and required a discriminative judgment. Simultaneously, evoked potentials were obtained in response to background probe auditory stimuli presented in a continuous train at about 40/sec. The 40 Hz steady-state rhythm (SSR) evoked under such conditions was extracted using digital averaging and filtering techniques and examined continuously for evidence of change in latency or amplitude during the period surrounding the foreground stimulus. Within the first 200-300 msec after the onset of an acoustic foreground stimulus the latencies of individual peaks in the rhythm were momentarily reduced by a mean of 5.5 msec. A shift in the 40 Hz rhythm was also seen following visual foreground stimuli, although the shift was about one-third that following acoustic stimuli. A latency shift of comparable magnitude was not produced by deliberate manipulation of intensity or signal-to-noise ratio of the stimuli used to evoke the rhythm. The latency shift response is discussed in terms of a transient period of sensory facilitation during orienting or alerting associated with the foreground stimuli.     

Emotional context enhances auditory novelty processing: behavioural and electrophysiological evidence

Viewing emotionally negative pictures has been proposed to attenuate brain responses towards sudden auditory events, as more attentional resources are allocated to the affective visual stimuli. However, peripheral reflexes have been shown intensified. These observations have raised the question of whether an emotional context actually facilitates or attenuates processing in the auditory novelty system. Using scalp event-related potentials we measured brain responses induced by novel sounds when participants responded to visual stimuli displaying either threatening or neutral sceneries. We then tested the modulatory effect of the emotional task conditions on auditory responses. Novel sounds yielded a stronger behavioural disruption on subjects' visual task performance when responding to negative pictures compared with when responding to the neutral ones. Accordingly, very early novelty-P3 responses to novel sounds were enhanced in negative context. These results provide strong evidence that the emotional context enhances the activation of neural networks in the auditory novelty system, gating acoustic novelty processing under potentially threatening conditions.     

Neural and receptor cochlear potentials obtained by transtympanic electrocochleography in auditory neuropathy

OBJECTIVE: Transtympanic electrocochleography (ECochG) was recorded bilaterally in children and adults with auditory neuropathy (AN) to evaluate receptor and neural generators. METHODS: Test stimuli were clicks from 60 to 120dB p.e. SPL. Measures obtained from eight AN subjects were compared to 16 normally hearing children. RESULTS: Receptor cochlear microphonics (CMs) in AN were of normal or enhanced amplitude. Neural compound action potentials (CAPs) and receptor summating potentials (SPs) were identified in five AN ears. ECochG potentials in those ears without CAPs were of negative polarity and of normal or prolonged duration. We used adaptation to rapid stimulus rates to distinguish whether the generators of the negative potentials were of neural or receptor origin. Adaptation in controls resulted in amplitude reduction of CAP twice that of SP without affecting the duration of ECochG potentials. In seven AN ears without CAP and with prolonged negative potential, adaptation was accompanied by reduction of both amplitude and duration of the negative potential to control values consistent with neural generation. In four ears without CAP and with normal duration potentials, adaptation was without effect consistent with receptor generation. In five AN ears with CAP, there was reduction in amplitude of CAP and SP as controls but with a significant decrease in response duration. CONCLUSIONS: Three patterns of cochlear potentials were identified in AN: (1) presence of receptor SP without CAP consistent with pre-synaptic disorder of inner hair cells; (2) presence of both SP and CAP consistent with post-synaptic disorder of proximal auditory nerve; (3) presence of prolonged neural potentials without a CAP consistent with post-synaptic disorder of nerve terminals. SIGNIFICANCE: Cochlear potential measures may identify pre- and post-synaptic disorders of inner hair cells and auditory nerves in AN.     

Anatomical and physiological evidence for auditory specialization in the mountain beaver (Aplodontia rufa)

On examination of brain stem auditory nuclei in a comparative series of over 100 mammals, the mountain beaver (Aplodontia rufa) was discovered to have a very large and unique cochlear nuclear complex. The dorsal cochlear nucleus in this species is 4–7 times larger than in any of 17 other rodent species examined. While there is a very small laminated region of the nucleus, its main bulk lacks the laminar organization so characteristic of the nucleus in other mammals. The cochlear granule field is extraordinarily large, comprising nearly half of the volume of this enlarged cochlear nuclear complex. The ventral cochlear nucleus is similar in size and organization to the nucleus in other mammals.Study of single units in the specialized dorsal cochlear nucleus revealed that many neurons responded to exceptionally low frequency stimuli (below 10 Hz). Thresholds of neurons were relatively high and response areas relatively flat in comparison with responses of neurons in the ventral nucleus. Neurons isolated within the large granule cell field could not be excited by tonal or other simple acoustic stimuli. These data suggest that part of the unique auditory system in the mountain beaver is specialized for the detection of slow changes in air pressure.