Speech Perception Growth Patterns in Prelingual Deaf Children With Bilateral Sequential Cochlear Implantation.

OBJECTIVE: To evaluate speech perception following the first (CI-1) and second (CI-2) cochlear implantation (CI) in children with sequential bilateral CI. STUDY DESIGN: Retrospective. PATIENTS: Seventy children with follow-up for 60 months post CI-1 and 36 months post CI-2. MAIN OUTCOME MEASURES: Word recognition score (WRS) was the main outcome. WRSs were compared by age at CI operation (group A ≤ 3.5 yr, B 3.6-8.6, for CI-1; group I ≤ 3.5 yr, II 3.6-7.0, III 7.1-13, IV > 13, for CI-2). RESULTS: For CI-1, the WRS of group A exceeded 80% at 24 months post procedure, earlier than group B (54 mo). Group A also had a shorter period of CI-1 use up to the WRS plateau than group B. CI-2 showed an initial burst of WRS growth much earlier than CI-1. This initial burst was most robust within 3 months in group II, but modest in group IV. The periods of CI-2 use (11-17 mo) up to the WRS plateau were much shorter than CI-1 (40-64 mo). Group I did not show the best WRS at 1 month post CI but later exceeded the other groups. CONCLUSION: Children received an immediate benefit by a burst of WRS growth from CI-2 earlier than CI-1, even within 3 months, suggesting that CI-1 gets the auditory cortex ready to foster speech processing from CI-2. The CI-2 performance depends on age at CI-2 implantation and on CI-1 performance. Our current findings will be relevant for clinicians who are counselling parents on CI-2 surgery.

The use of animal models to study cell transplantation in neuropathic hearing loss.

Auditory neuropathy (AN) is a form of sensorineural deafness specifically affecting the conduction of the nerve impulse from the cochlear hair cells to the auditory centres of the brain. As such, the condition is a potential clinical target for 'cell replacement therapy', in which a functioning auditory nerve is regenerated by transplanting an appropriated neural progenitor. In this review, we survey the current literature and examine possible experimental models for this condition, with particular reference to their compatibility as suitable hosts for transplantation. The use of exogenous neurotoxic agents such as ouabain or ß-bungarotoxin is discussed, as are ageing and noise-induced synaptopathy models. Lesioning of the nerve by mechanical damage during surgery and the neuropathy resulting from infectious diseases may be very relevant clinically, and we discuss whether there are good models for these situations. We also address genetic models for AN, examining whether the phenotypes truly model the clinical situation in their human counterpart syndromes - we use the example of the hyperbilirubinaemic Gunn rat as a particular instance in this regard.

Flavoprotein fluorescence imaging-based electrode implantation for subfield-targeted chronic recording in the mouse auditory cortex.

BACKGROUND: Chronic neural recording in freely moving animals is important for understanding neural activities of cortical neurons associated with various behavioral contexts. In small animals such as mice, it has been difficult to implant recording electrodes into exact locations according to stereotactic coordinates, skull geometry, or the shape of blood vessels. The main reason for this difficulty is large individual differences in the exact location of the targeted brain area. NEW METHODS: We propose a new electrode implantation procedure that is combined with transcranial flavoprotein fluorescence imaging. We demonstrate the effectiveness of this method in the auditory cortex (AC) of mice. RESULTS: Prior to electrode implantation, we executed transcranial flavoprotein fluorescence imaging in anesthetized mice and identified the exact location of AC subfields through the skull in each animal. Next, we surgically implanted a microdrive with a tungsten electrode into exactly the identified location. Finally, we recorded neural activity in freely moving conditions and evaluated the success rate of recording auditory responses. COMPARISON WITH EXISTING METHOD(S): These procedures dramatically improved the success rate of recording auditory responses from 21.1% without imaging to 100.0% with imaging. We also identified large individual differences in positional relationships between sound-driven response areas and the squamosal suture or blood vessels. CONCLUSIONS: Combining chronic electrophysiology with transcranial flavoprotein fluorescence imaging before implantation enables the realization of reliable subfield-targeted neural recording from freely moving small animals.

Synchrony, connectivity, and functional similarity in auditory midbrain local circuits.

The central nucleus of the inferior colliculus (ICC) contains a laminar structure that functions as an organizing substrate of ascending inputs and local processing. While topographic distributions of ICC response parameters within and across laminae have been reported, the functional micro-organization of the ICC is less well understood. For pairs of neighboring ICC neurons, we examined the nature of functional connectivity and receptive field preferences to gain a better understanding of the structure and function of local circuits. By recording from pairs of adjacent neurons and presenting pure-tone and dynamic broad-band stimulation, we estimated functional connectivity and local differences in frequency response areas (FRAs), spectrotemporal receptive fields (STRFs), nonlinear input/output functions, and single-spike information. From the cross-covariance functions we identified putative unidirectional as well as bidirectional excitatory/inhibitory interactions. STRFs of neighboring neurons strongly conserve best frequency, and moderately agree in STRF similarity, bandwidth, temporal response type, best modulation frequency, nonlinearity structure, and degree of information processing. Excitatory connectivity was stronger and temporally more precise than for inhibitory connections. Neither connection strength nor degree of synchrony correlated with receptive field parameters. The functional similarity of local pairs of ICC neurons was substantially less than for local pairs in the granular layers of primary auditory cortex (AI). These results imply that while the ICC is an obligatory nexus of ascending information, local neurons are comparatively weakly connected and exhibit considerable receptive field variability, potentially reflecting the heterogeneity of converging inputs to ICC functional zones.

Impact of Elevation of Temporal Lobe During Middle Fossa Acoustic Neuroma Surgery on Contralateral Speech Discrimination.

AIM: For middle fossa acoustic neuroma approach, retractors are needed to elevate the temporal lobe to be able to access the internal auditory meatus. The temporal lobe hosts the primary and secondary auditory fields. The question arises regarding whether this elevation affects the functionality of the auditory cortex. MATERIAL AND METHODS: In patients, who underwent acoustic neuroma surgery, contralateral speech discrimination was tested pre- and postsurgery using different speech discrimination tests. Results of patients with a middle fossa approach were compared with patients with a translabyrinthine approach. RESULTS: No major differences between the translabyrinthine and the middle fossa approach could be detected. CONCLUSION: Elevation of the temporal lobe during middle fossa approach for acoustic neuroma surgery does not lead to short-term impaired contralateral speech discrimination compared with translabyrinthine approach.

Positron Emission Tomography Imaging Reveals Auditory and Frontal Cortical Regions Involved with Speech Perception and Loudness Adaptation.

Considerable progress has been made in the treatment of hearing loss with auditory implants. However, there are still many implanted patients that experience hearing deficiencies, such as limited speech understanding or vanishing perception with continuous stimulation (i.e., abnormal loudness adaptation). The present study aims to identify specific patterns of cerebral cortex activity involved with such deficiencies. We performed O-15-water positron emission tomography (PET) in patients implanted with electrodes within the cochlea, brainstem, or midbrain to investigate the pattern of cortical activation in response to speech or continuous multi-tone stimuli directly inputted into the implant processor that then delivered electrical patterns through those electrodes. Statistical parametric mapping was performed on a single subject basis. Better speech understanding was correlated with a larger extent of bilateral auditory cortex activation. In contrast to speech, the continuous multi-tone stimulus elicited mainly unilateral auditory cortical activity in which greater loudness adaptation corresponded to weaker activation and even deactivation. Interestingly, greater loudness adaptation was correlated with stronger activity within the ventral prefrontal cortex, which could be up-regulated to suppress the irrelevant or aberrant signals into the auditory cortex. The ability to detect these specific cortical patterns and differences across patients and stimuli demonstrates the potential for using PET to diagnose auditory function or dysfunction in implant patients, which in turn could guide the development of appropriate stimulation strategies for improving hearing rehabilitation. Beyond hearing restoration, our study also reveals a potential role of the frontal cortex in suppressing irrelevant or aberrant activity within the auditory cortex, and thus may be relevant for understanding and treating tinnitus.

Multitarget surgical neuromodulation: Combined C2 and auditory cortex implantation for tinnitus.

Tinnitus, as a phantom sound can express itself as a pure tone and as a noise-like sound. It is notoriously difficult to treat, and in medically, psychologically and audiologically intractable tinnitus patients sometimes intracranial electrodes overlying the auditory cortex are implanted. In this case report, we describe a patient who had a complete resolution of the pure tone component of his tinnitus by an auditory cortex implant, without any beneficial effect on the noise-like aspect of his tinnitus, even after changing the stimulation design to burst stimulation, which is known to treat noise-like tinnitus better than tonic stimulation. After an initial successful treatment of his noise-like component with transcutaneus electrical nerve stimulation, a wire electrode is inserted subcutaneously and connected to his internal pulse generator. With the dual stimulation his pure tone tinnitus remains abolished after 5 years of stimulation and his noise-like tinnitus is improved by 50%, from 8/10 to 4/10. This case report suggests that multi-target stimulation might be better than single target implantation in selected cases.

Uncovering auditory evoked potentials from cochlear implant users with independent component analysis.

Auditory evoked potentials (AEPs) provide an objective measure of auditory cortical function, but AEPs from cochlear implant (CI) users are contaminated by an electrical artifact. Here, we investigated the effects of electrical artifact attenuation on AEP quality. The ability of independent component analysis (ICA) in attenuating the CI artifact while preserving the AEPs was evaluated. AEPs recovered from CI users were systematically correlated with age, demonstrating that individual differences were well preserved. CI users with high-quality AEPs were characterized by a significantly shorter duration of deafness. Finally, a simulation study revealed very high spatial correlations between original and recovered normal hearing AEPs (r>.95) that were previously contaminated with CI artifacts. The results confirm that after ICA, good quality AEPs can be recovered, facilitating the objective, noninvasive study of auditory cortex function in CI users.

Surgical treatment by electrical stimulation of the auditory cortex for intractable tinnitus.

Tinnitus is a public health issue in France. Around 1% of the population is affected and 30,000 people are handicapped in their daily life. The treatments available for disabling tinnitus have until now been disappointing. We are reporting on the surgical treatment by electrical stimulation of the auditory cortex of a female patient affected by disabling tinnitus that resisted classical treatments. The tinnitus appeared suddenly 10 years ago after a left ear tympanoplasty. The acouphenometry measures revealed a bilateral tinnitus, predominant on the right side, constant, with high frequency (6000 Hz). Transcranial magnetic stimulation (TMS) was performed at first with several supraliminal and infraliminal protocols. This showed promising results. Anatomic and functional magnetic resonance imaging (fMRI) of the auditory cortex before and after repetitive TMS (rTMS) demonstrated a modification of the cortical activity and where the ideal location for a cortical electrode might be, to straddle primary and secondary auditory cortex. After these investigations, two quadra polar electrodes (Resume, Medtronic Ltd, Hertfordshire, UK), connected to a stimulating device implanted under the skin (Synergy, Medtronic Ltd), were extradurally implanted. The surgical procedure was similar to the one performed for analgesic cortical stimulation. No surgical complications were reported. The activation of the stimulator provided a reduction of 65% of the tinnitus impact, with a persistent effect on the right side. The feasibility of the cortical stimulation in symptomatic treatment of tinnitus was proven by this preparatory work. The middle- and long-term therapeutic effects remain to be evaluated.

Reversible deficit affecting the perception of tone of a human voice after tumour resection from the right auditory cortex.

We report on a young woman operated for a ganglioglioma involving the right auditory cortex (AC), presenting with auditory seizures. Despite a normal pre-operative examination, a specific post-operative disorder affecting the perception of a human voice occurred. The patient was unable to recognise the tone of familiar voices while she recognised the expressed content. A temporal lobectomy for recurrence was performed two years later. The patient recovered from the voice perception deficit. This report shows that (1) a discrete site within the AC is specifically involved in the perception of tone of the human voice (2) functional compensation is possible.

Detection of sinusoidal amplitude modulated sounds: deficits after bilateral lesions of auditory cortex in the rat.

The ability of rats to detect the presence of sinusoidal amplitude modulation (AM) of a broadband noise carrier was determined before and after bilateral ablation of auditory cortex. The rats were trained to withdraw from a drinking spout to avoid a shock when they detected a modulation of the sound. Sensitivity was evaluated by testing the rats at progressively smaller depths of modulation. Psychophysical curves were produced to describe the limits of detection at modulation rates of 10, 100 and 1000Hz. Performance scores were based on the probability of withdrawal from the spout during AM (warning periods) relative to withdrawal during the un-modulated noise (safe periods). A threshold was defined as the depth of modulation that produced a score halfway between perfect avoidance and no avoidance (performance score=0.5). Bilateral auditory cortical lesions resulted in significant elevations in threshold for detection of AM at rates of 100 and 1000Hz. No significant shift was found at a modulation rate of 10Hz. The magnitude of the deficit for AM rates of 100 and 1000Hz was positively correlated with the size of the cortical lesion. Substantial deficits were found only in animals with lesions that included secondary as well as primary auditory cortical areas. The results show that the rat's auditory cortex is important for processing sinusoidal AM and that its contribution is most apparent at high modulation rates. The data suggest that the auditory cortex is a crucial structure for maintaining normal sensitivity to temporal modulation of an auditory stimulus.

[Application of functional MR-images acquired at low field in planning of neurosurgical operation close to an eloquent brain area]. / Alacsony téreron nyert funkcionalis MR-képek alkalmazása elokvens terület közelében végzett idegsebészeti mutétek tervezésénél.

AIM OF THE STUDY: Presentation of functional MRI performed at low magnetic field (1 Tesla) for planning microsurgical operation in a patient suffering from tumor close to an eloquent brain area. METHODS: Microsurgical removal navigated by frameless stereotaxy of an intrinsic tumor located in eloquent area is indicated if speech function is not damaged, i.e. exact localisation and relationship of the tumor and speech area can be defined. Before operation an optimized EPI based 2D sequence was applied to yield functional MR images. At the planning of the operation the paradigm used for the localization of the sensory language cortex contained passive listening to a text. Control investigations were performed one month postoperatively. A specific psychological test, as an additional investigation to estimate the accurate level of the sensory language function, was also conducted. RESULTS: Low resolution (matrix of 64x 64) functional MR images visualized sensory speech center and auditory cortex satisfactorily. The scans showed clearly that the Wernicke's region was situated just above the tumor (WHO grade II glioma), and this finding increased the safety of intraoperative localization and reduced the risk of morbidity. Control examinations revealed minimal decrease in sensory language function, however, it was not noticeable for either the patient or her surroundings. CONCLUSION: Optimized functional MR imaging performed at low magnetic field can support planning of neurosurgical operations and reduce the morbidity of microsurgical interventions.

Auditory and tactile processing in a postmeningitic deaf-blind patient with a cochlear implant.

The authors examined the neural function of a postmeningitic deaf-blind patient who regained his hearing with a multichannel cochlear implant. Auditory stimuli activated the temporal cortices of both sides in a manner similar to that of controls, reflecting the successful recruitment of the auditory cortex after implantation. The patient's occipital lobes were deactivated during the tactile language task, the results of which were completely different from those before cochlear implantation.

Magnetic and electrical stimulation of the auditory cortex for intractable tinnitus. Case report.

Tinnitus is a distressing symptom that affects up to 15% of the population for whom no satisfactory treatment exists. The authors present a novel surgical approach for the treatment of intractable tinnitus, based on cortical stimulation of the auditory cortex. Tinnitus can be considered an auditory phantom phenomenon similar to deafferentation pain, which is observed in the somatosensory system. Tinnitus is accompanied by a change in the tonotopic map of the auditory cortex. Furthermore, there is a highly positive association between the subjective intensity of the tinnitus and the amount of shift in tinnitus frequency in the auditory cortex, that is, the amount of cortical reorganization. This cortical reorganization can be demonstrated by functional magnetic resonance (fMR) imaging. Transcranial magnetic stimulation (TMS) is a noninvasive method of activating or deactivating focal areas of the human brain. Linked to a navigation system that is guided by fMR images of the auditory system, TMS can suppress areas of cortical plasticity. If it is successful in suppressing a patient's tinnitus, this focal and temporary effect can be perpetualized by implanting a cortical electrode. A neuronavigation-based auditory fMR imaging-guided TMS session was performed in a patient who suffered from tinnitus due to a cochlear nerve lesion. Complete suppression of the tinnitus was obtained. At a later time an extradural electrode was implanted with the guidance of auditory fMR imaging navigation. Postoperatively, the patient's tinnitus disappeared and remains absent 10 months later. Focal extradural electrical stimulation of the primary auditory cortex at the area of cortical plasticity is capable of suppressing contralateral tinnitus completely. Transcranial magnetic stimulation may be an ideal method for noninvasive studies of surgical candidates in whom stimulating electrodes might be implanted for tinnitus suppression.

Amusia following resection of a Heschl gyrus glioma. Case report.

The incidence and character of neurological deficits following resection of glial neoplasms localized to the Heschl gyrus are currently unknown. In this series, the authors report the clinical presentation, management, and postoperative course of three patients with right hemisphere Heschl gyrus gliomas, one of whom developed difficulty with music production and comprehension postoperatively. Resection of right hemisphere Heschl gyms gliomas can result in deficits involving music comprehension. Preliminary evidence suggests that when these deficits occur, they may be transient in nature.

An animal model of auditory cortex prostheses.

Experiments aimed at rehabilitating deaf and blind patients with cortical prostheses were first conducted decades ago, but epicortical electrodes allowed only crude information transfer. Here we report that in Mongolian gerbils with electrodes implanted in input layers of the primary auditory cortex, spatial, temporal and spatiotemporal variations in intracortical stimulation all lead to perceptual differences as evidenced by discrimination training. For some stimulus regimes discrimination learning was as fast as with intracochlear stimulation in this animal. Intracortical stimulation induced field potentials and 2-deoxyglucose labeling patterns in primary auditory cortex similar to those induced by auditory click or tone stimuli, respectively. Given the common organization principles of neocortical areas, these results are presumably also of significance to prostheses interfacing with visual cortex.

[Heschl's gyrus identification using functional MRI: neurosurgical issue]. / Identification du gyrus de heschl en IRM fonctionnelle.

AIM: Localizing Heschl's gyrus with functional MRI (fMRI) is a particularly difficult challenge due to the noise of the echo planar sequences and the frequent activation of language areas during auditory paradigms. The goal of this study was to search for a paradigm capable of assessing only pure primary auditory cortex activation with fMRI. MATERIAL AND METHOD: Ten healthy adults were studied. Subjects were asked to continuously perform a visual decisional task while passively listening to an ON-OFF randomized paradigm of tones and rhythmic stimuli. Data were analyzed with SPM. RESULTS: Auditory cortex activation was assessed by observing activated pixels in functional images. Due to the distraction effect of the visual decisional task, functional images of pure primary auditory cortex were obtained in all subjects, with strong and selective activation in the Heschl's gyrus. CONCLUSION: This technique, coupled with fMRI data of language areas can be used as a preoperative tool for surgical preplanning in the left superior temporal region. It shows a clear distinction between resectable areas (primary auditory cortex) and not resectable essential areas (language areas).

Spatial localization after excision of human auditory cortex.

Neurophysiological and animal ablation studies concur that primary auditory cortex is necessary for computation of the spatial coordinates of a sound source. Human studies have reported conflicting findings but have often suffered from inadequate psychophysical measures and/or poor lesion localization. We tested patients with unilateral temporal lobe excisions either encroaching on or sparing Heschl's gyrus (HG), quantifying lesion extent using anatomical magnetic resonance imaging measures. Subjects performed two tasks. In the localization task, they heard single clicks in a free-field spatial array subtending 180 degrees of azimuth and indicated the perceived location with a laser pointer. In the discrimination task, two clicks were presented, and subjects indicated if they were in the same or different position. As a group, patients with right temporal excision, either encroaching onto HG or not, were significantly impaired in both hemifields in both tasks, although this was not true for all individuals. Patients with left temporal resections generally performed normally, although some of the patients with left HG excision showed impaired performance bilaterally, especially in the discrimination task. This pattern stands in marked contrast to previous studies showing significant preservation of localization in hemispherectomized patients. We conclude that (1) contrary to hypotheses derived from animal studies, human auditory spatial processes are dependent primarily on cortical areas within right superior temporal cortex, which encompass both spatial hemifields; (2) functional reorganization may not take place after restricted focal damage but only after more extensive early damage; and (3) the existence of individual differences likely illustrates differential patterns of functional lateralization and/or recovery.

An investigation of sensory deficits underlying the aphasia-like behavior of macaques with auditory cortex lesions.

Bilateral auditory cortex lesions in Japanese macaques result in an aphasia-like deficit in which the animals are unable to discriminate two forms of their coo vocalizations. To determine whether this deficit is sensory in nature, two monkeys with bilateral lesions were tested for their ability to discriminate frequency and frequency change. The results indicated that although the animals were able to discriminate between sounds of different frequencies, they were unable to determine whether a sound was changing in frequency. Because the animals' coo vocalizations differ primarily in the predominant direction of their frequency change and not in their absolute frequency content, the aphasia-like deficit of animals with bilateral auditory cortex lesions appears to be a sensory disorder.