Auditory cortex activation in deaf subjects during cochlear electrical stimulation. Evaluation by functional magnetic resonance imaging

Soft Fiber Electronics Based on Semiconducting Polymer

Fibers, originating from nature and mastered by human, have woven their way throughout the entire history of human civilization. Recent developments in semiconducting polymer materials have further endowed fibers and textiles with various electronic functions, which are attractive in applications such as information interfacing, personalized medicine, and clean energy. Owing to their ability to be easily integrated into daily life, soft fiber electronics based on semiconducting polymers have gained popularity recently for wearable and implantable applications. Herein, we present a review of the previous and current progress in semiconducting polymer-based fiber electronics, particularly focusing on smart-wearable and implantable areas. First, we provide a brief overview of semiconducting polymers from the viewpoint of materials based on the basic concepts and functionality requirements of different devices. Then we analyze the existing applications and associated devices such as information interfaces, healthcare and medicine, and energy conversion and storage. The working principle and performance of semiconducting polymer-based fiber devices are summarized. Furthermore, we focus on the fabrication techniques of fiber devices. Based on the continuous fabrication of one-dimensional fiber and yarn, we introduce two- and three-dimensional fabric fabricating methods. Finally, we review challenges and relevant perspectives and potential solutions to address the related problems.

Long-term Outcomes in Down Syndrome Children After Cochlear Implantation: Particular Issues and Considerations

OBJECTIVE

The aim of the study was to analyze the long-term outcomes after cochlear implantation in deaf children with Down syndrome (DS) regarding age at the first implantation and refer the results to preoperative radiological findings as well as postoperative auditory and speech performance. Additionally, the influence of the age at implantation and duration of CI use on postoperative hearing and language skills were closely analyzed in children with DS.

STUDY DESIGN

Retrospective analysis.

SETTING

Referral center (Cochlear Implant Center).

MATERIALS AND METHODS

Nine children with Down syndrome were compared with 220 pediatric patients without additional mental disorders or genetic mutations. Patients were divided into four categories depending on the age of the first implantation: CAT1 (0-3 yr), CAT2 (4-5 yr), CAT3 (6-7 yr), and CAT4 (8-17 yr). The auditory performance was assessed with the meaningful auditory integration scales (MAIS) and categories of auditory performance (CAP) scales. The speech and language development were further evaluated with meaningful use of speech scale (MUSS) and speech intelligibility rating (SIR). The postoperative speech skills were analyzed and compared between the study group and the reference group by using nonparametric statistical tests. Anatomic abnormalities of the inner ear were examined using magnetic resonance imaging (MRI) and high-resolution computed tomography of the temporal bones (HRCT).

RESULTS

The mean follow-up time was 14.9 years (range, 13.1-18.3 yr). Patients with DS received a multichannel implant at a mean age of 75.3 months (SD 27.9; ranging from 21 to 127 mo) and 220 non-syndromic children from reference group at a mean age of 51.4 months (SD 34.2; ranging from 9 to 167 mo). The intraoperative neural response was present in all cases. The auditory and speech performance improved in each DS child. The postoperative mean CAP and SIR scores were 4.4 (SD 0.8) and 3.2 (SD 0.6), respectively. The average of scores in MUSS and MAIS/IT-MAIS scales was 59.8% (SD 0.1) and 76.9% (SD 0.1), respectively. Gathered data indicates that children with DS implanted with CI at a younger age (<6 years of age) benefited from the CI more than children implanted later in life, similarly in a control group. There were additional anomalies of the temporal bone, external, middle, or inner ear observed in 90% of DS children, basing on MRI or HRCT.

CONCLUSIONS

The early cochlear implantation in children with DS is a similarly useful method in treating severe to profound sensorineural hearing loss (SNHL) as in non-syndromic patients, although the development of speech skills present differently. Due to a higher prevalence of ear and temporal bone malformations, detailed diagnostic imaging should be taken into account before the CI qualification. Better postoperative outcomes may be achieved through comprehensive care from parents/guardians and speech therapists thanks to intensive and systematic rehabilitation.

P300 in individuals with sensorineural hearing loss

Introduction

Behavioral and electrophysiological auditory evaluations contribute to the understanding of the auditory system and of the process of intervention.

Objective

To study P300 in subjects with severe or profound sensorineural hearing loss.

Methods

This was a descriptive cross-sectional prospective study. It included 29 individuals of both genders with severe or profound sensorineural hearing loss without other type of disorders, aged 11 to 42 years; all were assessed by behavioral audiological evaluation and auditory evoked potentials.

Results

A recording of the P3 wave was obtained in 17 individuals, with a mean latency of 326.97 ms and mean amplitude of 3.76 V. There were significant differences in latency in relation to age and in amplitude according to degree of hearing loss. There was a statistically significant association of the P300 results with the degrees of hearing loss (p = 0.04), with the predominant auditory communication channels (p < 0.0001), and with time of hearing loss.

Conclusions

P300 can be recorded in individuals with severe and profound congenital sensorineural hearing loss; it may contribute to the understanding of cortical development and is a good predictor of the early intervention outcome.

Neuroimaging with near-infrared spectroscopy demonstrates speech-evoked activity in the auditory cortex of deaf children following cochlear implantation

Cochlear implants (CI) are commonly used to treat deafness in young children. While many factors influence the ability of a deaf child who is hearing through a CI to develop speech and language skills, an important factor is that the CI has to stimulate the auditory cortex. Obtaining behavioral measurements from young children with CIs can often be unreliable. While a variety of noninvasive techniques can be used for detecting cortical activity in response to auditory stimuli, many have critical limitations when applied to the pediatric CI population. We tested the ability of near-infrared spectroscopy (NIRS) to detect cortical responses to speech stimuli in pediatric CI users. Neuronal activity leads to changes in blood oxy- and deoxy-hemoglobin concentrations that can be detected by measuring the transmission of near-infrared light through the tissue. To verify the efficacy of NIRS, we first compared auditory cortex responses measured with NIRS and fMRI in normal-hearing adults. We then examined four different participant cohorts with NIRS alone. Speech-evoked cortical activity was observed in 100% of normal-hearing adults (11 of 11), 82% of normal-hearing children (9 of 11), 78% of deaf children who have used a CI > 4 months (28 of 36), and 78% of deaf children who completed NIRS testing on the day of CI initial activation (7 of 9). Therefore, NIRS can measure cortical responses in pediatric CI users, and has the potential to be a powerful adjunct to current CI assessment tools.

Neural prostheses and brain plasticity

The success of modern neural prostheses is dependent on a complex interplay between the devices' hardware and software and the dynamic environment in which the devices operate: the patient's body or 'wetware'. Over 120 000 severe/profoundly deaf individuals presently receive information enabling auditory awareness and speech perception from cochlear implants. The cochlear implant therefore provides a useful case study for a review of the complex interactions between hardware, software and wetware, and of the important role of the dynamic nature of wetware. In the case of neural prostheses, the most critical component of that wetware is the central nervous system. This paper will examine the evidence of changes in the central auditory system that contribute to changes in performance with a cochlear implant, and discuss how these changes relate to electrophysiological and functional imaging studies in humans. The relationship between the human data and evidence from animals of the remarkable capacity for plastic change of the central auditory system, even into adulthood, will then be examined. Finally, we will discuss the role of brain plasticity in neural prostheses in general.

Testing the diagnostic value of electrical ear canal stimulation in cochlear implant candidates by functional magnetic resonance imaging

Prior to cochlear implant (CI) surgery in children, the integrity of the auditory pathway is sometimes assessed by electrical ear canal stimulation (ECS). However, the evaluation of reactions as auditory is subjective. To test the prognostic value of ECS, functional magnetic resonance imaging (fMRI) was performed during ECS vicariously in 18 adult CI candidates. Activation of the primary auditory cortex was detected in 9 of 16 cases when auditory sensations during ECS occurred, and tended to be more bilaterally distributed in CI candidates than in normal-hearing controls. ECS sensations only tended to correlate with fMRI activations. However, solely frequency discrimination during electrical stimulation predicted CI outcome, but neither other auditory sensations nor fMRI activations did so satisfactorily, which limits the diagnostic value of these measures. Instead, preoperative residual hearing (nonamplified and amplified) was a robust predictor for CI benefit.

Cochlear implants and brain plasticity

Cochlear implants have been implanted in over 110,000 deaf adults and children worldwide and provide these patients with important auditory cues necessary for auditory awareness and speech perception via electrical stimulation of the auditory nerve (AN). In 1942, Woolsey and Walzl presented the first report of cortical responses to localised electrical stimulation of different sectors of the AN in normal hearing cats, and established the cochleotopic organization of the projections to primary auditory cortex. Subsequently, individual cortical neurons in normal hearing animals have been shown to have well characterized input-output functions for electrical stimulation and decreasing response latencies with increasing stimulus strength. However, the central auditory system is not immutable, and has a remarkable capacity for plastic change, even into adulthood, as a result of changes in afferent input. This capacity for change is likely to contribute to the ongoing clinical improvements observed in speech perception for cochlear implant users. This review examines the evidence for changes of the response properties of neurons in, and consequently the functional organization of, the central auditory system produced by chronic, behaviourally relevant, electrical stimulation of the AN in profoundly deaf humans and animals.

BOLD response to direct thalamic stimulation reveals a functional connection between the medial thalamus and the anterior cingulate cortex in the rat

Recent functional neuroimaging studies in humans and rodents have shown that the anterior cingulate cortex (ACC) is activated by painful stimuli, and plays an important role in the affective aspect of pain sensation. The aim of the present study was to develop a suitable stimulation method for direct activation of the brain in fMRI studies and to investigate the functional connectivity in the thalamo-cingulate pathway. In the first part of the study, tungsten, stainless steel, or glass-coated carbon fiber microelectrodes were implanted in the left medial thalamus (MT) of anesthetized rats, and T2*-weighted gradient-echo (GE) images were obtained in the sagittal plane on a 4.7 T system (Biospec BMT 47/40). Only the images obtained with the carbon fiber electrode were acceptable without a reduction of the signal-to-noise ratio (SNR) and image distortion. In the second part of the study, a series of two-slice GE images were acquired during electrical stimulation of the MT with the use of a carbon fiber electrode. A cross-correlation analysis showed that the signal intensities of activated areas in the ipsilateral ACC were significantly increased by about 4.5% during MT stimulation. Functional activation, as assessed by the distribution of c-Fos immunoreactivity, showed strong c-Fos expression in neurons in the ipsilateral ACC. The present study shows that glass-coated carbon fiber electrodes are suitable for fMRI studies and can be used to investigate functional thalamocortical activation.

A method for direct thalamic stimulation in fMRI studies using a glass-coated carbon fiber electrode

Recent fMRI studies are of interest in exploring long-range interactions between different brain structures and the functional activation of specific brain regions by known neuroanatomical pathways. One of the experimental approaches requires the invasive implantation of an intracranial electrode to excite specific brain structures. In the present report, we describe a procedure for the production of a glass-coated carbon fiber electrode and the use of this electrode for direct activation of the brain in fMRI studies. The glass-coated carbon fiber microelectrode was implanted in the medial thalamus of anaesthetized rats and T2*-weighted gradient echo images in the sagittal plane obtained on a 4.7 T system (Biospec BMT 47/40) during electrical stimulation of the medial thalamus. The image quality obtained using this electrode was acceptable without reduction of the signal-to-noise ratio and image distortion. Cross-correlation analysis showed that the signal intensities of activated areas in the ipsilateral anterior cingulate cortex were significantly increased by about 4-5% during medial thalamus stimulation. The present study shows that glass-coated carbon fiber electrodes are suitable for fMRI studies and can be used to investigate functional thalamocingulate activation.

Functional Magnetic Resonance Imaging of Activation in Subcortical Auditory Pathway

OBJECTIVES

Functional magnetic resonance imaging (fMRI) has been used to investigate activation of the auditory cortex; however, assessment of activation in the subcortical auditory pathway has been challenging. The aim of this study was to examine neural correlates of cortical and subcortical auditory activation evoked by pure-tone stimulus using silent fMRI.

STUDY DESIGN

Prospective analysis.

METHODS

Seventeen normal-hearing volunteers (7 male, 10 female; age range, 14-37 yrs) underwent silent fMRI. An audiometer was used to deliver pure tones of 1000 Hz to the left ear. Pure tones were presented at hearing thresholds determined in the scanner. Brain regions showing increased activation during pure-tone stimulus presentation were mapped and auditory activations exceeding P <.001 were included in the analysis.

RESULTS

Pure-tone stimuli evoked bilateral activation in cortical regions of the transverse and superior temporal gyri and the planum temporale. Activation in subcortical structures included the medial geniculate body, inferior colliculus, lateral lemniscus, superior olivary complex, and cochlear nucleus.

CONCLUSIONS

Silent functional magnetic resonance imaging findings documented the feasibility of detecting activation elicited by pure tone along the cortical and subcortical auditory pathway. The use of this technique in the assessment of disorders with auditory dysfunction merits further investigation.

A method for the direct electrical stimulation of the auditory system in deaf subjects: a functional magnetic resonance imaging study

PURPOSE

To develop a safe functional magnetic resonance imaging (fMRI) procedure for auditory assessment of deaf subjects.

MATERIALS AND METHODS

A gold-plated tungsten electrode has been developed which has zero magnetic susceptibility. Used with carbon leads and a carbon reference pad, it enables safe, distortion-free fMRI studies of deaf subjects following direct electrical stimulation of the acoustic nerve. Minor pickup of the radio frequency (RF) pulses by the electrode assembly is difficult to eliminate, and a SPARSE acquisition sequence is used to avoid any effects of unintentional auditory nerve stimulation.

RESULTS

The procedure is demonstrated in a deaf volunteer. Activation is observed in the contralateral but not the ipsilateral primary auditory cortex. This is in sharp contrast to studies of auditory processing in hearing subjects, but consistent with the small number of previous positron emission tomography (PET) and MR studies on adult deaf subjects.

CONCLUSION

The fMRI procedure is able to demonstrate whether the auditory pathway is fully intact, and may provide a useful method for preoperative assessment of candidates for cochlear implantation.

Cochlear implants and brain stem implants

This chapter describes the development of two implantable prosthetic neurostimulators which, in the last 20 years, have revolutionised the management of severe-to-profound sensorineural deafness. We have witnessed their rapid evolution from the realms of esoteric laboratory abstraction, with many critics and little perceived clinical use, to a routine treatment which is safe, effective and, indeed, cost effective. It is one of the great triumphs of biomedical and surgical collaboration, and is without any doubt the greatest ever advance in the treatment of deafness.

Functional MRI of congenital hyposmia: brain activation to odors and imagination of odors and tastes

PURPOSE

Our goal was to use functional MRI (fMRI) to define brain activation in response to odors and imagination ("memory") of odors and tastes in patients who never recognized odors (congenital hyposmia).

METHOD

Functional MR brain scans were obtained in nine patients with congenital hyposmia using multislice echo planar imaging (EPI) in response to odors of amyl acetate, menthone, and pyridine and to imagination ("memory") of banana and peppermint odors and to salt and sweet tastes. Functional MR brain scans were compared with those in normal subjects and patients with acquired hyposmia. Activation images were derived using correlation analysis, and ratios of areas of brain activated to total and hemispheric brain areas were calculated. Total and hemispheric activated pixel counts were used to quantitate regional brain activation.

RESULTS

Brain activation in response to odors was present in patients with congenital hyposmia. Activation was significantly lower than in normal subjects and patients with acquired hyposmia and did not demonstrate differential vapor pressure-dependent detection responsiveness or odor response lateralization. Regional activation localization was in anterior frontal and temporal cortex similar to that in normal subjects and patients with acquired hyposmia. Activation in response to presented odors was diverse, with a larger group exhibiting little or no activation with localization only in anterior frontal and temporal cortex and a smaller group exhibiting greater activation with localization extending to more complex olfactory integration sites. "Memory" of odors and tastes elicited activation in the same central nervous system (CNS) regions in which activation in response to presented odors occurred, but responses were significantly lower than in normal subjects and patients with acquired hyposmia and did not lateralize.

CONCLUSION

Odors induced CNS activation in patients with congenital hyposmia, which distinguishes olfaction from vision and audition since neither light nor acoustic stimuli induce CNS activation. Odor activation localized to anterior frontal and temporal cortex, consistent with the hypothesis that olfactory pathways are hard-wired into the CNS and that further pathways are undeveloped with primary olfactory system CNS connections but lack of secondary connections. However, some patients exhibited greater odor activation with response localization extending to cingulate and opercular cortex, indicating some olfactory signals impinge on and maintain secondary connections consistent with similar functions in vision and audition. Activation localization of taste "memory" to anterior frontal and temporal cortex is consistent with CNS plasticity and cross-modal CNS reorganization as described for vision and audition. Thus, there are differences and similarities between olfaction, vision, and audition, the differences dependent on unique qualities of olfaction, perhaps due to its diffuse, primitive, fundamental role in survival. Response heterogeneity to odors may reflect heterogeneous genetic abnormalities, independent of anatomic or hormonal changes but dependent on molecular abnormalities in growth factor function interfering with growth factor/stem cell interactions. Patients with congenital hyposmia offer an unique model system not previously explored in which congenital smell lack as measured by fMRI is reflective of congenital dysfunction of a major sensory system.

Imaging plasticity in cochlear implant patients

Auditory re-afferentation by cochlear implants (CI) offers a unique opportunity to study directly from within the auditory modality plastic changes taking place at organisational levels up to the supra- or polymodal level. These plastic changes resulting from deafness and chronic electrical stimulation can be studied using modern neuroimaging techniques. In this paper, we review the available techniques and the experimental approaches to human studies of plasticity, we discuss the different forms of plasticity that are associated with cochlear implantation and we point to the interest of imaging studies for providing a prognosis of functional outcome after implantation.

Safe electrical stimulation of the cochlear nerve at the promontory during functional magnetic resonance imaging

The purpose of this study was to evaluate possibilities and technical risks for combining intended electrical stimulation of the cochlear nerve and functional magnetic resonance imaging (fMRI). Theoretical considerations and experiments indicate that fMRI can be performed safely during electrical stimulation. A nerve stimulator was developed with minimized length of electrical conductors, current limiting resistance, high inner impedance of a current source, radio frequency (RF)-shielding, and avoidance of ferromagnetic materials. This nerve stimulator transfers the optically encoded stimulating current signal via a fiber optic cable located near the area of stimulation. There, the optical signal drives an MRI-compatible current source. This set-up was tested with transtympanic electrical stimulation of the cochlear nerve at the promontory during an fMRI examination. No hazardous effects could be detected. The stimulation resulted in activation of the Heschl's gyrus. Compared to the conventional promontory testing this method may allow a more objective examination of cochlear implant candidates. Magn Reson Med 42:371-378, 1999.

Neuro-functional imaging and profound deafness

This paper deals with the subject of the place of neuro-functional imaging in cochlear implantation. Neuro-functional imaging is a means to assess the functioning of the brain in some normal or pathological conditions. Deafness is a model of sensorineural deprivation. Cochlear implantation offers to clinicians and neuroscientists a model for understanding influence of deafness on cerebral connectivity, and to assess mechanisms of plasticity when the auditory inputs are given again to a deaf cochlea. This paper proposes a brief review of the literature on cochlear implantation and neuro-functional imaging. Patients can be scanned pre- or post-operatively, thus different questions can be investigated about neurobiology of the consequences of deafness and auditory rehabilitation by cochlear implantation, and about the possible role of neuro-functional imaging in cochlear implant candidates to predict the future benefit of the implantation.