Search

Background: Auditory Brainstem Response (ABR) recording in awake is essential to detect off-responses. This study clarified whether after-termination responses on ABR were offset responses, off-responses or a mixture of the two., Methods: Evoked potentials in the auditory cortex of cats in response to tone burst stimuli were recorded, and off responses were examined with chronically implanted electrodes., Results: When the fall time at the end of sound stimuli was 5ms or longer, the amplitude of click responses was extremely small. Under this condition, evoked potentials in response to two types of tone bursts (long and short) were recorded.By calculating the differences in evoked potentials between the two-tone bursts, off responses were separated. Off responses were generated during wakefulness by auditory cortex stimulation but were not observed under anesthesia. Pronounced off responses, which were middle latency responses exhibiting bis positive waves, were obtained in response to sound stimuli with a frequency of 2 kHz or higher. Vertex stimulation did not induce off responses either during wakefulness or under anesthesia., Conclusion: Off responses are derived from synchronous responses of neurons in the auditory cortex, which are generated when the neurons detect attenuation in the stimulus strength at the end of tone burst stimuli.

Responding to multiple stimuli of different modalities has been shown to reduce reaction time (RT), yet many different processes can potentially contribute to multisensory response enhancement. To investigate the neural circuits involved in voluntary response initiation, an acoustic stimulus of varying intensities (80, 105, or 120 dB) was presented during a visual RT task to a patient with profound bilateral cortical deafness and an intact auditory brainstem response. Despite being unable to consciously perceive sound, RT was reliably shortened (~100 ms) on trials where the unperceived acoustic stimulus was presented, confirming the presence of multisensory response enhancement. Although the exact locus of this enhancement is unclear, these results cannot be attributed to involvement of the auditory cortex. Thus, these data provide new and compelling evidence that activation from subcortical auditory processing circuits can contribute to other cortical or subcortical areas responsible for the initiation of a response, without the need for conscious perception.

Conclusion: A right-handed 38-year-old man's complete loss of hearing could be diagnosed as cortical deafness caused by cerebral vascular lesions in bilateral auditory cortices., Objective: The aim of this case report was to study the pathophysiology of a particular patient who manifested deafness without residual hearing and lost somatosensory sensation, vestibular sensation, and articulation ability after a right internal carotid-posterior communicating artery (IC-PC) aneurysm and subarachnoidal hemorrhage., Methods: MRI, aphasia and neurological tests, subjective and objective audiometry, and vestibular function tests were performed., Results: The neurological test revealed system loss of somatosensory sensation with normal motor function and articulation ability. Brain imaging revealed extensive infarction in the bilateral primary auditory cortices, postcentral gyruses, and the bilateral partial third frontal gyruses. Pure-tone audiometry of both ears revealed off-the-scale results and speech audiometry demonstrated 0% maximum speech discrimination. However, objective audiometry showed normal distortion product otoacoustic emissions (DPOAE) and normal auditory brainstem response (ABR). The patient showed 0% perception of environmental, speech, and music sounds in both ears. He was unable to feel vestibular sensation despite normal caloric nystagmus. He showed no damage to his larynx or articulation organs.

Conclusions: The functional connectivity (FC) between the right and left auditory cortex is weak in tinnitus patients. Transcranial direct current stimulation (tDCS) over the auditory cortex has potential as a tool to modulate auditory-based FC., Objective: This study investigated the effects of applying tDCS in tinnitus patients, and searched for modulation of brain networks in resting-state functional magnetic resonance imaging (rs-fMRI) through an analysis of FC with the stimulated brain region., Subjects and Methods: Nine male patients with chronic tinnitus and 10 male volunteers with normal hearing were enrolled. The subjects were evaluated with rs-fMRI immediately before and after tDCS. The tinnitus patients filled out the self-evaluation questionnaires designed to measure tinnitus conditions before tDCS treatment and 1 week afterwards., Results: The FC between the right and left auditory cortex was significantly weaker in tinnitus patients than in controls. After tDCS treatment, in the tinnitus group, the primary auditory cortex showed a reduction in the amount of statistically significant connectivity with the somatosensory area and motor area, but maintained strong significant connectivity (p < 0.005) with the auditory area and insular cortex. In contrast, in the control group, there remained strong significant connectivity between the primary auditory cortex and the somatosensory area, motor area, insular cortex, and auditory area.

We understand from experience that musical contexts are formed when chords are combined according to the rules of harmony. In this study, the N1 component of the auditory-evoked potential was measured using comparable three-chord sequences; these sequences were constructed as a consecutive task (cf. C-C-C vs. Cm-Cm-Cm; control) and a cadence task (cf. C-G-C vs. C-G-Cm). In the cadence task, compared with cadences ending with a major chord (anticipated chord), those ending with a minor chord (unanticipated chord) showed a significantly larger amplitude of N1 waves. These components of auditory-evoked potentials reflect the effect of chord progression in musical perception and suggest that the musical context is recognized at least 100 ms after a chord is played.

Using magnetoencephalography (MEG), we report here the hemispheric dominance of the auditory cortex that is selectively modulated by unexpected errors in the lyrics and melody of songs (lyrics and melody deviants), thereby elucidating under which conditions the lateralization of auditory processing changes. In experiment 1 using familiar songs, we found that the dipole strength of responses to the lyrics deviants was left-dominant at 140 ms (M140), whereas that of responses to the melody deviants was right-dominant at 130 ms (M130). In experiment 2 using familiar songs with a constant syllable or pitch, the dipole strength of frequency mismatch negativity elicited by oddballs was left-dominant. There were significant main effects of experiment (1 and 2) for the peak latencies and for the coordinates of the dipoles, indicating that the M140 and M130 were not the frequency mismatch negativity. In experiment 3 using newly memorized songs, the right-dominant M130 was observed only when the presented note was unexpected one, independent of perceiving unnatural pitch transitions (i.e., perceptual saliency) and of selective attention to the melody of songs. The consistent right-dominance of the M130 between experiments 1 and 3 suggests that the M130 in experiment 1 is due to unexpected notes deviating from well-memorized songs. On the other hand, the left-dominant M140 was elicited by lyrics deviants, suggesting the influence of top-down linguistic information and the memory of the familiar songs. We thus conclude that the left- lateralized M140 and right-lateralized M130 reflect the expectation based on top-down information of language and music, respectively.

The dichotic presentation of two sinusoids with a slight difference in frequency elicits subjective fluctuations called binaural beat (BB). BBs provide a classic example of binaural interaction considered to result from neural interaction in the central auditory pathway that receives input from both ears. To explore the cortical representation of the fluctuation of BB, we recorded magnetic fields evoked by slow BB of 4.00 or 6.66 Hz in nine normal subjects. The fields showed small amplitudes; however, they were strong enough to be distinguished from the noise accompanying the recordings. Spectral analyses of the magnetic fields recorded on single channels revealed that the responses evoked by BBs contained a specific spectral component of BB frequency, and the magnetic fields were confirmed to represent an auditory steady-state response (ASSR) to BB. The analyses of spatial distribution of BB-synchronized responses and minimum-norm current estimates revealed multiple BB ASSR sources in the parietal and frontal cortices in addition to the temporal areas, including auditory cortices. The phase of synchronized waveforms showed great variability, suggesting that BB ASSR does not represent changing interaural phase differences (IPD) per se, but instead it reflects a higher-order cognitive process corresponding to subjective fluctuations of BB. Our findings confirm that the activity of the human cerebral cortex can be synchronized with slow BB by using information on the IPD.

Auditory evoked potentials (AEPs) in the temporal cortex have typical slow positive/negative (P1/N1) biphasic waves, which are occasionally associated with an additional earlier small deflection (P0/N0). In the present paper, we attempted to address the neural origin of P0/N0 deflection by the independent component analysis (ICA) of densely mapped cortical AEPs of rats. The ICA results suggest that the deflection appears when subcortical contribution to AEP is equal to or larger than cortical contribution.

Existing studies have demonstrated interfield differences in functional organizations and neuronal responsive properties at a single neuron level in the auditory cortex, suggesting complicated encoding of sound frequency and intensity. The objective of present work is, by characterizing cortical auditory evoked potentials (AEPs), to bridge neural characteristics between a single neuron and field levels and to identify the interfield differences in the auditory cortex specifically in terms of spatial representation, which will be useful in guiding future unit studies. The AEP mapping found that each of auditory fields, which could be identified by a different tonotopic representation, showed interfield differences in an intensity-dependent spatial change, amplitude, latency, and amplitude-SPL (sound pressure level) function. These results also showed that many aspects of cortical representation were based on the cochlear properties, yet some were inconsistent. The intensity-dependent shift of activation in AI paralleled the tonotopic axis, which was similar to the place code in cochlea, while the shift in AAF and VAF did not parallel. Nevertheless, the amplitude-SPL function suggested that an underlying mechanism of all these shifts can be a compressive nonlinearity to CF tone, which is possibly formed in the cochlea and still preserved in the cortex. These results suggest that each field modifies the representation to handle a different aspect of sound information, which can be better analyzed than the cochlear representation.

A mismatch between auditory sensation and expectant imagery of syllables elicited a possible equivalent of mismatch negativity in a previous study. The purpose of this study was to verify whether auditory imagery from musical notation could also mediate such imagery-based mismatch negativity. Neuromagnetic recording was obtained from eight musicians, who were instructed to identify unpredictably occurring pitch mismatches between a random tone sequence and a visually presented musical score. The difference between incongruent and congruent responses showed a magnetic distribution consistent with two frontal-negative current dipoles bilaterally located in the vicinity of Heschl's gyrus, peaking at approximately 150 ms in latency. This imagery-based mismatch negativity may represent an early neural process of deviance detection between the sensory input and expectant imagery.

Auditory brainstem implants (ABI) that electrically stimulate the surface of cochlear nucleus have been clinically used for the rehabilitation of deaf patients with bilateral vestibular schwannomas. The change of pitch perception with an active electrode location is not as clear in ABIs as in cochlear implants, a factor which might play a role in poorer speech performance in ABIs. The objective of present work was to develop an animal ABI model that could provide physiological data for future ABI development and optimization. The experimental system included a penetrating microelectrode array for microstimulation of the cochlear nucleus and a surface microelectrode array for mapping evoked potentials over the auditory cortex. We first obtained tone-evoked cortical activation patterns, which represented a place code of the frequency and intensity of test tones, i.e., the ampli-tonotopic organization, and compared the patterns with those evoked by cochlear nuclear microstimulation. Our experimental results demonstrated that microstimulation of both the dorsal and ventral cochlear nucleus (DCN and VCN) could access the cortical ampli-tonotopic organization as acoustic stimuli did. We also found that the cortical dynamic range was wider for the DCN than VCN stimulation and for the low-frequency than for the high-frequency pathway. The present results have great implications for improved ABI performance.

During silent reading, visual information provided by letters is converted to auditory information in the mind. The purpose of this study was to identify the primary locus for auditory verbal imagery in the brain. Neuromagnetic recording was obtained from 10 right-handed study participants, who were instructed to identify infrequently occurring phonological mismatches between a random-ordered sequence of syllable sounds and a visually presented syllabogram sequence. The activity difference in early latency, calculated by subtracting the averaged responses to matched syllables from the averaged responses to mismatched syllables, showed a spatiotemporal profile strikingly similar to that of mismatch negativity. Auditory imagery of forthcoming verbal sounds may establish a memory trace as a template for imagery-based mismatch negativity generation in the auditory cortex.

This paper provides a detailed process flow for fabricating an easy-to-prepare, inexpensive, dense array of tungsten microelectrodes. We designed the process flow to minimize routine tasks by separating an initial preparation of a master mold from a routine preparation of substrate replication, array assembly and tip processing. Sandblast processing first produced a glass mold with a pattern of a series of protruding lines at a requested interval of a few hundred micrometers. Copying the groove pattern onto polystyrene mass-produced a replica substrate. Tungsten probes were then aligned on the substrate, and the tips of probes were finely processed in the block.

Magnetic responses to periodic complex sounds with equivalent acoustic parameters except for two different fundamental frequencies (F0) and 12 different spectral envelopes of vocal, instrumental, and linear shapes were recorded to determine the cortical representation of timbre categorization in humans. Responses at approximately 100 ms (N1m) to vocal and instrumental (nonlinear) sounds were localized significantly anterior to linear sound responses. N1m source strength for nonlinear sounds was significantly larger than that for linear sounds, and this difference was more marked in the left hemisphere than in the right. N1m peak latency only for vocal sounds was not affected by F0. Perceptual categorization was reflected in N1m source strength and location (linear or nonlinear), and in N1m latency (vocal or nonvocal).

Prevailing studies of auditory systems pay most attention to the dynamic temporal changes of sound intensity, but poorly enlighten the encoding of steady-state aspects. Using tone bursts as test stimuli, we epipially map auditory evoked potentials over the rat auditory cortex and investigate how the cortex represents the dynamic and steady states. Our results demonstrate that all of the auditory fields investigated potentially have at least two strategies to represent the two states; a temporal combination of early and late components of the potentials, and a spatial combination of an arbitrary component. In addition, the optimal combination that can distinguish between the two states differs across auditory fields, suggesting robust analyses of sound intensity in the auditory cortex.

We epipially mapped tone-burst-evoked potentials over the rat auditory cortex, and investigated the representation of intensity information. The experiments were designed to elucidate how the auditory cortex represents a steady-state plateau sound pressure level (SPL) and dynamic onset temporal structure, i.e., the rate of pressure change (in Pa/s), and how the representations differ across the auditory fields. The anterior and ventral fields have spatial axes of the rate of pressure change. Characteristic frequency (CF) locations mainly handle the dynamic state, while off-CF locations have the potential to code the steady state. Each field represents the intensity information differently, particularly at the off-CF locations. These results suggest that intensity information is distributed in various aspects in the multiple auditory fields.

We evaluated the cortical activations in postlingually deaf cochlear implant (CI) users in the early period (0-2 months) of CI usage. The subjects were 8 early CI users and 8 normal subjects. With tone burst stimuli (1 kHz) delivered to the right side, strong and broad activation of the ipsilateral (right) primary auditory cortex with 2 peaks and weaker activation of the contralateral (left) temporal lobe were observed in early CI users, in a clear contrast with the normal subjects in whom activation was observed in a small area of the contralateral (left) primary cortex. With word stimuli, activation of the superior frontomedian cortex presumably including the supplementary motor area and the neighboring cingulate gyri was observed in early CI users, which was absent in normal subjects. The activation in the immediate association cortices near the primary area was lower in early CI users, while the periphery of the association cortex seemed to be more mobilized., (Copyright 2004 S. Karger AG, Basel)

We characterized the auditory-evoked offset responses of the rat auditory cortex by multiple-site surface microelectrode recording. Tone bursts served as test stimuli. Offset responses did not appear tonotopically, but at the fringe of tonotopic onset distributions. Offset amplitude was significantly sensitive to sound intensity, fall time at tone termination, and duration. These results suggest that offset responses are associated with inhibitory responses surrounding excitatory onset responses, and offset responses become large when inhibition becomes strong and long or terminates synchronously. Thus, the rebound after the inhibition in the presence of a stimulus is likely to be a major cause of offset responses in the auditory cortex.

Objective: To demonstrate the influence of auditory cortex lesions on auditory middle-latency responses (AMLRs) and middle-latency auditory-evoked magnetic fields (MLAEFs) in humans., Material and Methods: A total of 15 normal subjects, 9 patients with left auditory cortex lesions and 1 patient with a right auditory cortex lesion were studied. MLAEFs were recorded from each hemisphere of the brain in a magnetically shielded room using a 37-channel SQUID gradiometer. Simultaneously, AMLRs were recorded from the scalp at the vertex, C3 and C4. Tone bursts were used as auditory stimuli., Results: Pam responses of the MLAEF, which are typically evoked in the latency range of the Pa of the AMLR, and are localized at the auditory cortex as dipoles, were impaired or abolished over the left auditory cortex lesion in the patients with left-hemisphere lesions, but the Pa of the AMLR persisted., Conclusion: The main generator of the Pam in MLAEF was demonstrated to be the auditory cortex. The results also show that the Pa of the AMLR is evoked only partly from the auditory cortex.

Generally, cortical deafness is not complicated by anarthria and cortical anarthria does not affect auditory perception. We report a case of simultaneous progressive cortical deafness and anarthria. At the age of 70 years, the patient, a woman, noticed hearing problems when using the telephone, which worsened rapidly over the next 2 years. She was then referred to our hospital for further examinations of her hearing problems. Auditory tests revealed threshold elevation in the low and middle frequencies on pure-tone audiometry, a maximum speech discrimination of 25% and normal otoacoustic emissions and auditory brainstem, middle- and long-latency responses. An articulation test revealed abnormal pronunciation. Because of these problems only written and not verbal communication was possible; her ability to read and write was unimpaired. She showed no other neurological problems. Brain MRI demonstrated atrophic changes of the auditory cortex and Wernicke's language center and PET suggested low uptake of (18F) 2-fluoro-2-deoxy-d-glucose around the Sylvian fissures in both hemispheres. Neurologically, the patient was suspected of having progressive aphasia or frontotemporal dementia. Her cortical deafness and anarthria are believed to be early signs of this entity.

This paper describes a flexible polyimide microelectrode ribbon with a bending structure for epidural recording. Bending the ribbon establishes good electro-mechanical contact of the electrodes to the cortex. Impedance spectroscopy and noise measurements in vitro were used to characterize the electrodes. Our in vivo experiments then successfully achieved synchronized neuronal activity and evoked potential patterns useful for understanding brain function and for finding cortical function.

Four pediatric patients whose bilateral auditory cortices were damaged by herpes encephalitis at an early age were studied. Their brain CT and MRI scans demonstrated common bilateral lesions of the auditory cortices. Their auditory perception was investigated by means of behavioral and objective hearing tests and auditory perception tests. All four patients showed mild or moderate hearing loss in the behavioral hearing test and normal auditory brainstem responses but did not manifest total deafness. Moreover, perception tests involving speech, environmental sounds and music demonstrated that most auditory perception ability had been lost in all patients. On reaching school age, the patients were enrolled in schools for the deaf or special schools for handicapped children.

Conclusion: In patients with unilateral microtia and atresia after reconstruction of the auricle and external canal and fitting of a canal-type hearing aid for the operated ear, the ability to discriminate the inter-aural intensity difference (IID) was acquired in all of the patients, whereas that to discriminate inter-aural time difference (ITD) was acquired in one-half of the patients. Objective: To study the post-operative sound lateralization ability in patients with unilateral microtia and atresia after reconstruction surgery of the auricle and external canal and fitting of a canal-type hearing aid of the operated ear. Methods: Eighteen patients with unilateral microtia and atresia ranging from 13–24 years of age were recruited in this study. All of them underwent reconstruction of the auricle and external canal and were fitted a canal-type hearing aid for the operated ear. The sound lateralization test was conducted to determine IID and ITD using a self-recording apparatus. The test stimulus was a continuous narrow-band noise at 500 Hz and 50 dBHL presented to the right and left ears through the air conduction receivers. Results: IID could be measured in all of the patients, whereas ITD could be measured in only nine out of the 18 patients. Post-operative binaural hearing could be acquired in all the patients. [ABSTRACT FROM AUTHOR]

Short- and long-term changes in the middle latency response (MLR) after bilateral ablation of the auditory cortices were studied in awake cats. The amplitude of the negative peak with a latency of about 15 ms (NA) decreased to 60% of the original value 1 week after ablation (short-term change). In the long term, i.e. 11-30 months, NA either decreased further (decreased group) or remained unchanged (non-decreased group). A histological study with light microscopy revealed degeneration of neurons in the ventral nucleus of the medial geniculate body (MGv) in the decreased group, whereas the neurons in this region were preserved in the non-decreased group. This study suggests that long-term changes in NA reflect retrograde degeneration in the MGv after auditory cortical ablation. [ABSTRACT FROM AUTHOR]

Summary: Objective: To investigate the myelination progression course in language-correlated regions of children with normal brain development by quantitative magnetic resonance imaging (MRI) analysis compared with histological studies. Methods: The subjects were 241 neurologically intact neonates, infants and young children (128 boys and 113 girls) who underwent MRI between 2001 and 2007 at the University of Tokyo Hospital, ranging in age from 0 to 429 weeks corrected by postnatal age. To compare their data with adult values, 25 adolescents and adults (14 men and 11 women, aged from 14 to 83 years) were examined as controls. Axial T2-weighted images were obtained using spin-echo sequences at 1.5T. Subjects with a history of prematurity, birth asphyxia, low Apgar score, seizures, active systemic disease, congenital anomaly, delayed development, infarcts, hemorrhages, brain lesions, or central nervous system malformation were excluded from the analysis. Seven regions of interest in language-correlated areas, namely Broca’s area, Wernicke’s area, the arcuate fasciculus, and the angular gyrus, as well as their right hemisphere homologous regions, and the auditory cortex, the motor cortex, and the visual cortex were examined. Signal intensity obtained by a region-of-interest methodology progresses from hyper- to hypointensity during myelination. We chose the inferior cerebellar peduncle as the internal standard of maturation. Results: Myelination in all these seven language-correlated regions examined in this study shared the same curve pattern: no myelination was observed at birth, it reached maturation at about 1.5 years of age, and it continued to progress slowly thereafter into adult life. On the basis of scatter plot results, we put these areas into three groups: Group A, which included the motor cortex, the auditory cortex, and the visual cortex, myelinated faster than Group B, which included Broca’s area, Wernicke’s area, and the angular gyrus before 1.5 years old; Group C, consisting of the arcuate fasciculus, has similar degree of myelination as Group B before 1.5 years but then myelinated more slowly after 3 years of age. No gender or left-right differences between homologous regions were found. Conclusions: In this study, we determined the sequence of myelination of language-correlated regions in infants and children by quantitative MRI assessment. The higher cortical areas matured later than the primary cortical areas, and the arcuate fasciculus matured last. The observation that myelination reaches maturity after 18 months suggests that myelination may be a reason for the acceleration in vocabulary acquisition observed in children from that age. The slow pace of myelination also suggested the possibility of language development’s continuation into early adult life. Myelination assessed by MRI was at least 1 month behind that assessed by histological staining. No gender or left-right hemisphere differences in myelination were noted. [Copyright &y& Elsevier]

Presentation of one sinusoid to each ear with a small difference of frequency elicits subjective fluctuations called binaural beat (BB). BB is a classic example of binaural interaction and provides a typical demonstration that the discharges of the auditory nerve fibers preserve information on the phase of the acoustic stimuli. Neural spikes tend to occur at a particular phase of the sinusoidal waveform (phase locking). The central auditory system utilizes the information of interaural phase difference (IPD) with continuous and periodical oscillation. The apparent beat frequency heard is equal to the IPD provided. In order to confirm the cortical representation of fluctuation of BB, we recorded the magnetic field of the auditory steady-state response (SSR) evoked by BBs in six normal-hearing right-handed subjects. Periodical responses with small amplitude were recorded around the bilateral temporal areas by a wholescalp neuromagnetometer under presentation of slow BB (4 and 6.66 Hz). Spectral analysis detected peaks of the BB frequency in the channels of bilateral temporal areas. These results suggested that activity of cerebral cortex, especially auditory cortex, can be synchronized with slow BB and have capacity for preserving the information of IPD. [Copyright &y& Elsevier]