IZ2M & IZ2MH Stimulators

Cochlear implants (CIs) have successfully restored hearing in more than one million patients with severe to profound hearing loss worldwide. Although CIs effectively restore speech perception in quiet environments, sound localization remains challenging for bilateral CI users, particularly their ability to utilize interaural time differences (ITDs). The majority of clinical CI processors use a coding strategy that encodes ITD information only in the envelope of electrical pulse trains rather than their pulse timing, which may contribute to the poorer spatial hearing perception of CI users. We recently demonstrated in a behavioural study on early deafened, bilaterally CI‐implanted rats that pulse timing ITDs completely dominate ITD perception, whereas sensitivity to envelope ITDs is almost negligible in comparison. Building on this, we here investigated the neurophysiological sensitivity of the inferior colliculus (IC) to envelope and pulse timing ITDs at two different pulse rates (900 and 4500 pulses/s) and three different stimulation modulations (5, 20 and 100 Hz) in CI rats with different hearing experiences. Our results indicate that IC neurons exhibit far greater sensitivity to pulse timing ITD than envelope ITD independent of pulse rate, modulation rate or hearing experience. These findings suggest that to improve binaural hearing outcomes in bilateral CI users, clinical stimulation strategies should provide informative pulse timing ITDs. image Key points Current bilateral cochlear implants mostly provide time cues of arriving sound in the envelope of stimulation rather than in the timing of pulses. A behavioural study on cochlear implanted rats has shown that pulse timing dominates binaural hearing. Here we examined the neural sensitivity to independent changes in time cues presented on the envelope or pulse timing, respectively, in rats with bilateral cochlear implants and different hearing experiences. Auditory midbrain neurons were consistently more sensitive to changes in pulse timing rather than envelope, irrespective of stimulus pulse rate, modulation rate or an animal's hearing experience.

Electrical brain stimulation (EBS) has been studied as a tool to improve speech perception. Available EBS methods compromise between precision and power and rarely consider temporal dynamics. Noninvasive EBS delivers currents to wide areas but may lack regional specificity and is susceptible to current shunting through the skin. We introduce a novel minimally-invasive electrical brain stimulation approach using clinically implanted epicranial electrodes and cranial bolts, circumventing the current shunting limitations of traditional transcranial stimulation. Two types of contacts were used in five epilepsy patients (one female) over six experimental sessions undergoing intracranial monitoring: epicranial electrodes (served as reference electrodes for clinical recordings) and cranial bolts (holding fixtures for depth electrodes). Participants monaurally listened to pseudo-randomly presented sentences from matrix sentence speech-in-noise task in 3 conditions: no-stimulation, 50 ms, or 200 ms stimulation lag relative to sentence onset. EBS parameters were 100 Hz, biphasic, amplitude-balanced, square-wave pulses where the amplitude (1-6 mA) was modulated by the ongoing speech envelope. Accuracy in the task improved in 5 of 6 sessions while not reaching significance across sessions possibly limited due to the limited number of sessions and trials (p = 0.087 and 0.068 for 50 ms and 200 ms delay, linear mixed-effects model). In 5/6 sessions, there was increased accuracy with 50 ms delay, and in 3 of those, there was further improvement with 200 ms delay. We successfully demonstrated the dynamic EBS patterns delivered through minimally-invasive electrodes during speech perception with 83% responder rate for improvement in speech perception with short latency (50 ms) and 50% with longer latency (200 ms) stimulation.

Most spinal cord injuries (SCI) spare descending and sublesional circuits that can be targeted through motor cortex and spinal cord stimulation to mitigate locomotor deficits. However, the potential synergy between cortical and spinal stimulation remains unknown. Here, we first investigated the phase-locked electrical stimulation of the motor cortex and lumbar spinal cord at 40 Hz in a rat model of unilateral SCI. Combining cortical and lumbar stimulation around the anticipated lift synergistically enhanced leg movements. When integrated into rehabilitation training, cortical stimulation proved essential for the recovery of skilled locomotion. We next investigated the effects of high-frequency (330 Hz) lumbar and sacral stimulation combined with cortical stimulation. Timely integration during the swing phase showed that cortical and lumbar stimulations enhance the initial and mid-swing phases, while sacral stimulation improves extension velocity in the late swing. These findings indicate that supraspinal and sublesional neuromodulation offer complementary neuroprosthetic effects in targeted SCI gait rehabilitation.