Evaluation of electrode position in deep brain stimulation by image fusion (MRI and CT).

INTRODUCTION: Imaging has an essential role in the evaluation of correct positioning of electrodes implanted for deep brain stimulation (DBS). Although MRI offers superior anatomic visualization of target sites, there are safety concerns in patients with implanted material; imaging guidelines are inconsistent and vary. The fusion of postoperative CT with preoperative MRI images can be an alternative for the assessment of electrode positioning. The purpose of this study was to assess the accuracy of measurements realized on fused images (acquired without a stereotactic frame) using a manufacturer-provided software. METHODS: Data from 23 Parkinson's disease patients who underwent bilateral electrode placement for subthalamic nucleus (STN) DBS were acquired. Preoperative high-resolution T2-weighted sequences at 3 T, and postoperative CT series were fused using a commercially available software. Electrode tip position was measured on the obtained images in three directions (in relation to the midline, the AC-PC line and an AC-PC line orthogonal, respectively) and assessed in relation to measures realized on postoperative 3D T1 images acquired at 1.5 T. RESULTS: Mean differences between measures carried out on fused images and on postoperative MRI lay between 0.17 and 0.97 mm. CONCLUSION: Fusion of CT and MRI images provides a safe and fast technique for postoperative assessment of electrode position in DBS.

Effects of amygdala-hippocampal stimulation on synchronization.

Changes in EEG synchronization, i.e., spatio-temporal correlation, with amygdala-hippocampal stimulation were studied in patients with temporal lobe epilepsy. Synchronization was evaluated for high frequency, 130 Hz, pseudo-monophasic or biphasic charge-balanced pulses. Desynchronization was most frequently induced by stimulation. There was no correlation between the changes in synchronization and the changes in interictal epileptiform discharge rates. Changes in synchronization do not appear yet to be a marker of stimulation efficiency in reducing seizures.

Early-onset or rapidly progressive scoliosis in children: check the eyes!

Horizontal gaze palsy with progressive scoliosis (HGPPS) is a rare autosomal recessive disorder characterized by the absence of conjugate horizontal eye movements, and progressive scoliosis developing in childhood and adolescence, caused by mutations in the ROBO3 gene which has an important role in axonal guidance and neuronal migration. We describe two female children aged 12 years and 18 months, with progressive scoliosis, in whom the neurological examination showed absent conjugate horizontal eye movements, but preserved vertical gaze and convergence. Cerebral Magnetic resonance imaging findings included pontine hypoplasia, absent facial colliculi, butterfly configuration of the medulla and a deep midline pontine cleft, while Diffusion tensor imaging (DTI) maps showed the absence of decussating ponto-cerebellar fibers and superior cerebellar peduncles. Somatosensory and motor evoked potential studies demonstrated ipsilateral sensory and motor responses. The diagnosis was confirmed by the identification of bi-allelic mutations in the ROBO3 gene.

Effects of amygdala-hippocampal stimulation on interictal epileptic discharges.

Deep brain stimulation (DBS) of different nuclei is being evaluated as a treatment for epilepsy. While encouraging results have been reported, the effects of changes in stimulation parameters have been poorly studied. Here the effects of changes of pulse waveform in high frequency DBS (130 Hz) of the amygdala-hippocampal complex (AH) are presented. These effects were studied on interictal epileptic discharge rates (IEDRs). AH-DBS was implemented with biphasic versus pseudo monophasic charge balanced pulses, in two groups of patients: six with temporal lobe epilepsy (TLE) associated with hippocampal sclerosis (HS) and six with non lesional (NLES) temporal epilepsy. In patients with HS, IEDRs were significantly reduced with AH-DBS applied with biphasic pulses in comparison with monophasic pulse. IEDRs were significantly reduced in only two patients with NLES independently to stimulus waveform. Comparison to long-term seizure outcome suggests that IEDRs could be used as a neurophysiological marker of chronic AH-DBS and they suggest that the waveform of the electrical stimuli can play a major role in DBS. We concluded that biphasic stimuli are more efficient than pseudo monophasic pulses in AH-DBS in patients with HS. In patients with NLES epilepsy, other parameters relevant for efficacy of DBS remain to be determined.

Professional occupation after cochlear implantation.

The aims of this study were to verify whether cochlear implants helped profoundly deaf adults to maintain or even to develop their professional occupations, and to identify other elements that may contribute to or, on the contrary, impede such patients' professional success. All adult patients received a questionnaire concerning their professional activities before and after implantation. Demographic data, health information, hearing performance and degree of satisfaction with the implant were also considered. Sixty-seven adults had been implanted, with three different devices, since 1985. At the time of implantation, 34 had been professionally active. After implantation, 29 had remained professionally active, four of whom reported positive developments in their careers. Five patients had become professionally inactive. Those patients who had previously been professionally inactive remained so. There had been no difference in performance, either between different types of cochlear implants or between professionally active or inactive patients. The implanted patients had kept their jobs and many of them had developed their professional skills. In spite of this, cochlear implants may still be perceived as proving insufficiently satisfactory hearing to enable professionally inactive patients to reintegrate and to facilitate further learning or career developments.

Channel interactions with high-rate biphasic electrical stimulation in cochlear implant subjects.

Channel interactions were assessed using high-rate stimulation in cochlear implant subjects using the Ineraid electrode array. Stimulation currents were applied on one intracochlear electrode and their effects on psychophysical detection thresholds on an adjacent electrode were measured. Stimuli were trains of brief, biphasic, 50-micros/phase pulses presented at a rate of 2000 pulses per second per channel. In experiment I, we studied how the detection of a probe signal was influenced by a sub-threshold perturbation signal presented either simultaneously or non-simultaneously (with no overlap) on an adjacent electrode. Results showed that simultaneous activation led to strong channel interactions, producing threshold changes consistent with instantaneous electric field summation. Non-simultaneous activation revealed much weaker interactions, producing threshold changes of opposite sign. In experiment II, we studied how the temporal delay between perturbation and probe pulses, as well as how the level of the perturbation signal influenced non-simultaneous channel interactions. First, threshold changes when reversing the polarity of the perturbation did progressively vanish when increasing the delay between pulses. This suggested that non-overlapping stimulation of adjacent electrodes produced channel interactions that were in part due to residual polarization of the nerve membrane. Second, increasing the perturbation to supra-threshold levels produced threshold elevations that were independent of the interpulse interval. This suggested channel interactions due to neural masking. These results provide insights into the different concurrently active mechanisms of channel interactions in cochlear implant systems using this type of stimuli.

Speech recognition with a CIS strategy for the ineraid multichannel cochlear implant.

Wilson et al. proposed a new sound-processing strategy for multichannel cochlear implants, the Continuous Interleaved Sampling (CIS) strategy. Their study was performed on seven American patients, selected for their excellent performance with the Ineraid multichannel cochlear implant, and involved refined testing of several parameter modifications of the CIS strategy during a 1-week period. At the end of the week, the CIS strategy produced large improvements in speech-recognition tests for all subjects. To evaluate the generality of this promising result, the goal of this study was to assess whether similar improvements of performance could be observed in a typical population of Ineraid users and implemented as a clinical protocol. Therefore we designed one unique, predetermined CIS processor that could be temporarily fitted to the patients in < 2 h, and we evaluated speech recognition with consonant-and vowel-identification tests in a group of patients with performances ranging from star to almost chance levels and speaking six different native languages. Scores of vowel and consonant identifications obtained with this predetermined CIS processor and with the standard processor of the Ineraid system were compared in 15 Ineraid users. Fourteen of 15 patients had significantly better scores of consonant identification with the new CIS strategy. The group mean scores of vowel identification with either strategy were not statistically different. In agreement with these observations, most patients immediately reported that the CIS strategy sounded subjectively "more clear" for real-time speech recognition. It is now possible to implement a CIS speech-coding strategy as a standard clinical procedure to improve speech-recognition performances of all Ineraid users.

Ineraid cochlear implant in the ossified cochlea: surgical techniques and results.

Extensive ossification of the cochlea is a common finding in patients with total deafness caused by meningitis, labyrinthitis, or otosclerosis. When the cochlea is totally ossified, the prognosis for achieving free-running speech without lip reading is poor. However, subtotal ossification with residual cochlear patency in the upper basal turn, the middle turn, or the apical turn can be maximally exploited by selective insertion of electrodes. Results can be surprisingly adequate in spite of the poor anatomic conditions. Computed tomography and exploratory cochleotomy, in which electrically evoked auditory brainstem responses are elicited and recorded by intracochlear stimulation are good diagnostic indicators of ossification and residual auditory nerve excitability. "Apical cochleostomy" is an adequate procedure to help penetrate the basal turn in retrograde insertion of the cochlear implant electrode array. Results of this study indicate that the surgical technique and placement of the Ineraid electrode array play a major role in the ability of the patient to achieve understanding of free-running speech.

Low-pass filtering in amplitude modulation detection associated with vowel and consonant identification in subjects with cochlear implants.

Temporal auditory analysis of acoustic events in various frequency channels is influenced by the ability to detect amplitude modulations which for normal hearing involves low-pass filtering with a cutoff frequency around 100 Hz and a rejection slope of about 10 dB per decade. These characteristics were established in previous studies measuring modulation transfer functions. For cochlear implant subjects, the delivery of detailed amplitude modulation information has been recently shown to result in very significant improvements in speech understanding. Several previous studies on cochlear implant subjects have reported capacities for temporal resolution rather equivalent to those of normally hearing subjects but with some notable individual differences. Recently two studies on some cochlear implant subjects indicated modulation transfer functions often quite similar to those of normal hearing but exhibiting marked individual differences in shape and absolute sensitivity. The present study compared amplitude modulation detection and phonetic recognition in a group of cochlear implant subjects to determine the extent to which the two tasks are correlated. Nine individuals who had been implanted with an Ineraid device and who demonstrated open speech understanding ranging from excellent to poor were chosen and tested in the present study. For each subject modulation transfer functions were measured at the most apical electrode and phonetic recognition of isolated vowels and intervocalic consonants was assessed. Results showed a strong correlation between the depth of high-frequency rejection in modulation transfer functions and success in vowel and consonant intelligibility. These results emphasize the importance of temporal speech features and offer perspectives for customizing signal processing in cochlear implants.

Vowel and consonant identification tests can be used to compare performances in a multilingual group of cochlear implant patients.

Vowel and consonant identification tests were conducted in the sound-only condition in a multilingual group of 13 totally deaf patients who are users of the Ineraid multichannel cochlear implant. Native languages ranged across French, German, Italian, Spanish, Albanian and Swahili. We found high correlations (r > -0.83) among vowel or consonant identification scores and 'subjective ranking' scores established on the basis of a subjective evaluation of the patient's speech reception abilities in the sound-only condition. Detailed analysis demonstrates that the identification of vowel and consonant is dominated by the perception of acoustic cues characteristic of the set of stimuli used as well as by the strengths and weaknesses of the speech processing of the cochlear implant system. We did not find any systematic pattern in the results that could be related to the native language of the patients. These results suggest that vowel as well as consonant identification tests are effective means to compare the performance of cochlear implant patients even across different native languages. They also indicate that, in the future, one can conduct a fewer number of the many different (e.g. nonsense-syllable, word, sentence, speech-tracking) tests when evaluating the speech recognition abilities of patients with the implant.