scholarly journals Cochlear-Implant High Pulse Rate and Narrow Electrode Configuration Impair Transmission of Temporal Information to the Auditory Cortex

2008 ◽  
Vol 100 (1) ◽  
pp. 92-107 ◽  
Author(s):  
John C. Middlebrooks
Keyword(s):  
Animal Model ◽  
Auditory Cortex ◽  
Cochlear Implant ◽  
Pulse Rate ◽  
Temporal Information ◽  
Electrode Configuration ◽  
Bipolar Electrode ◽  
Pulse Trains ◽  
Speech Reception ◽  
High Pulse

In the most commonly used cochlear prosthesis systems, temporal features of sound are signaled by amplitude modulation of constant-rate pulse trains. Several convincing arguments predict that speech reception should be optimized by use of pulse rates ≳2,000 pulses per second (pps) and by use of intracochlear electrode configurations that produce restricted current spread (e.g., bipolar rather than monopolar configurations). Neither of those predictions has been borne out in consistent improvements in speech reception. Neurons in the auditory cortex of anesthetized guinea pigs phase lock to the envelope of sine-modulated electric pulse trains presented through a cochlear implant. The present study used that animal model to quantify the effects of carrier pulse rate, electrode configuration, current level, and modulator wave shape on transmission of temporal information from a cochlear implant to the auditory cortex. Modulation sensitivity was computed using a signal-detection analysis of cortical phase-locking vector strengths. Increasing carrier pulse rate in 1-octave steps from 254 to 4,069 pps resulted in systematic decreases in sensitivity. Comparison of sine- versus square-wave modulator waveforms demonstrated that some, but not all, of the loss of modulation sensitivity at high pulse rates was a result of the decreasing size of pulse-to-pulse current steps at the higher rates. Use of a narrow bipolar electrode configuration, compared with the monopolar configuration, produced a marked decrease in modulation sensitivity. Results from this animal model suggest explanations for the failure of high pulse rates and/or bipolar electrode configurations to produce hoped-for improvements in speech reception.

scholarly journals Auditory Temporal Acuity Probed With Cochlear Implant Stimulation and Cortical Recording

2010 ◽  
Vol 103 (1) ◽  
pp. 531-542 ◽  
Author(s):  
Alana E. Kirby ◽  
John C. Middlebrooks
Keyword(s):  
Auditory Cortex ◽  
Pulse Rate ◽  
Auditory Nerve ◽  
Acoustic Noise ◽  
Forward Masking ◽  
Neural Mechanisms ◽  
Gap Detection ◽  
Temporal Acuity ◽  
Pulse Trains ◽  
Modulation Detection

Cochlear implants stimulate the auditory nerve with amplitude-modulated (AM) electric pulse trains. Pulse rates >2,000 pulses per second (pps) have been hypothesized to enhance transmission of temporal information. Recent studies, however, have shown that higher pulse rates impair phase locking to sinusoidal AM in the auditory cortex and impair perceptual modulation detection. Here, we investigated the effects of high pulse rates on the temporal acuity of transmission of pulse trains to the auditory cortex. In anesthetized guinea pigs, signal-detection analysis was used to measure the thresholds for detection of gaps in pulse trains at rates of 254, 1,017, and 4,069 pps and in acoustic noise. Gap-detection thresholds decreased by an order of magnitude with increases in pulse rate from 254 to 4,069 pps. Such a pulse-rate dependence would likely influence speech reception through clinical speech processors. To elucidate the neural mechanisms of gap detection, we measured recovery from forward masking after a 196.6-ms pulse train. Recovery from masking was faster at higher carrier pulse rates and masking increased linearly with current level. We fit the data with a dual-exponential recovery function, consistent with a peripheral and a more central process. High-rate pulse trains evoked less central masking, possibly due to adaptation of the response in the auditory nerve. Neither gap detection nor forward masking varied with cortical depth, indicating that these processes are likely subcortical. These results indicate that gap detection and modulation detection are mediated by two separate neural mechanisms.

scholarly journals Neural ITD coding with bilateral cochlear implants: effect of binaurally coherent jitter

2012 ◽  
Vol 108 (3) ◽  
pp. 714-728 ◽  
Author(s):  
Kenneth E. Hancock ◽  
Yoojin Chung ◽  
Bertrand Delgutte
Keyword(s):  
Pulse Rate ◽  
Interaural Time Difference ◽  
Time Difference ◽  
High Rate ◽  
Neural Responses ◽  
Neural Basis ◽  
Pulse Trains ◽  
Bilateral Cochlear Implants ◽  
Periodic Pulse ◽  
High Pulse

Poor sensitivity to the interaural time difference (ITD) constrains the ability of human bilateral cochlear implant users to listen in everyday noisy acoustic environments. ITD sensitivity to periodic pulse trains degrades sharply with increasing pulse rate but can be restored at high pulse rates by jittering the interpulse intervals in a binaurally coherent manner (Laback and Majdak. Binaural jitter improves interaural time-difference sensitivity of cochlear implantees at high pulse rates. Proc Natl Acad Sci USA 105: 814–817, 2008). We investigated the neural basis of the jitter effect by recording from single inferior colliculus (IC) neurons in bilaterally implanted, anesthetized cats. Neural responses to trains of biphasic pulses were measured as a function of pulse rate, jitter, and ITD. An effect of jitter on neural responses was most prominent for pulse rates above 300 pulses/s. High-rate periodic trains evoked only an onset response in most IC neurons, but introducing jitter increased ongoing firing rates in about half of these neurons. Neurons that had sustained responses to jittered high-rate pulse trains showed ITD tuning comparable with that produced by low-rate periodic pulse trains. Thus, jitter appears to improve neural ITD sensitivity by restoring sustained firing in many IC neurons. The effect of jitter on IC responses is qualitatively consistent with human psychophysics. Action potentials tended to occur reproducibly at sparse, preferred times across repeated presentations of high-rate jittered pulse trains. Spike triggered averaging of responses to jittered pulse trains revealed that firing was triggered by very short interpulse intervals. This suggests it may be possible to restore ITD sensitivity to periodic carriers by simply inserting short interpulse intervals at select times.

scholarly journals Auditory Cortex Phase Locking to Amplitude-Modulated Cochlear Implant Pulse Trains

2008 ◽  
Vol 100 (1) ◽  
pp. 76-91 ◽  
Author(s):  
John C. Middlebrooks
Keyword(s):  
Auditory Cortex ◽  
Cochlear Implant ◽  
Amplitude Modulation ◽  
Cortical Neurons ◽  
Modulation Depth ◽  
Phase Locking ◽  
Modulation Frequency ◽  
Electrical Pulse ◽  
Electrode Arrays ◽  
Pulse Trains

Cochlear implant speech processors transmit temporal features of sound as amplitude modulation of constant-rate electrical pulse trains. This study evaluated the central representation of amplitude modulation in the form of phase-locked firing of neurons in the auditory cortex. Anesthetized pigmented guinea pigs were implanted with cochlear electrode arrays. Stimuli were 254 pulse/s (pps) trains of biphasic electrical pulses, sinusoidally modulated with frequencies of 10–64 Hz and modulation depths of −40 to −5 dB re 100% (i.e., 1–56.2% modulation). Single- and multiunit activity was recorded from multi-site silicon-substrate probes. The maximum frequency for significant phase locking (limiting modulation frequency) was ≥60 Hz for 42% of recording sites, whereas phase locking to pulses of unmodulated pulse trains rarely exceeded 30 pps. The strength of phase locking to frequencies ≥40 Hz often varied nonmonotonically with modulation depth, commonly peaking at modulation depths around −15 to −10 dB. Cortical phase locking coded modulation frequency reliably, whereas a putative rate code for frequency was confounded by rate changes with modulation depth. Group delay computed from the slope of mean phase versus modulation frequency tended to increase with decreasing limiting modulation frequency. Neurons in cortical extragranular layers had lower limiting modulation frequencies than did neurons in thalamic afferent layers. Those observations suggest that the low-pass characteristic of cortical phase locking results from intracortical filtering mechanisms. The results show that cortical neurons can phase lock to modulated electrical pulse trains across the range of modulation frequencies and depths presented by cochlear implant speech processors.

Anatomical and Morphological study of the Heart's Chambers and valves in Iraqi ducks Anser platyrhuncha

2019 ◽  
Vol 43 (1) ◽  
pp. 21-25
Author(s):  
Mohammed Senna Hassan
Keyword(s):  
Blood Pressure ◽  
Anterior Chamber ◽  
High Blood Pressure ◽  
Pulse Rate ◽  
Morphological Study ◽  
Heart Valves ◽  
Simple Manner ◽  
High Pulse ◽  
The Right ◽  
High Pulse Rate

   Twenty Iraqi ducks hearts ( 10 male and 10 female ) have been  used for   demonstration  and illustration of heart's valves  and chambers  as well as  anatomical   and morphological site of view to explain what modifications had been take place for ducks heart  to perform  his normal life at the  circumstances  of  high  blood  pressure  and  pulse  rate. The heart  which has distinctly pointed  apex  was  built   in simple  manner located  in a transparent  taught  heart  pericardial  sac. It   was pyramidal in shape  externally  and  has a longitudinal  salcus  passing  to the  right  side, the  anterior of  the   heart  is  divided  into two  unequal  anterior  chamber  similar  to  those of mammalian  hear  .The heart valves are modified  in  order to  minimize  the  fraction  that occur as a result of  high  blood  pressure  and  pulse  rate  of  the  duck  heart , also  the  muscular  trabeculae   replace  the  chordate  tendineae  , which  were  present in the  mammalian    heart  in order to  minimize  the  fraction  resulting  from high  pulse  rate..    

scholarly journals Using Interleaved Stimulation to Measure the Size and Selectivity of the Sustained Phase-Locked Neural Response to Cochlear Implant Stimulation

2021 ◽  
Author(s):  
Robert P. Carlyon ◽  
François Guérit ◽  
John M. Deeks ◽  
Andrew Harland ◽  
Robin Gransier ◽  
...  
Keyword(s):  
Cochlear Implant ◽  
Group Delay ◽  
Acoustic Stimulation ◽  
Neural Response ◽  
Clinical Applications ◽  
Pulse Trains ◽  
Charge Integration ◽  
Recording Electrodes ◽  
Time Point ◽  
Do So

AbstractWe measured the sustained neural response to electrical stimulation by a cochlear implant (CI). To do so, we interleaved two stimuli with frequencies F1 and F2 Hz and recorded a neural distortion response (NDR) at F2-F1 Hz. We show that, because any one time point contains only the F1 or F2 stimulus, the instantaneous nonlinearities typical of electrical artefact should not produce distortion at this frequency. However, if the stimulus is smoothed, such as by charge integration at the nerve membrane, subsequent (neural) nonlinearities can produce a component at F2-F1 Hz. We stimulated a single CI electrode with interleaved sinusoids or interleaved amplitude-modulated pulse trains such that F2 = 1.5F1, and found no evidence for an NDR when F2-F1 was between 90 and 120 Hz. However, interleaved amplitude-modulated pulse trains with F2-F1~40 Hz revealed a substantial NDR with a group delay of about 45 ms, consistent with a thalamic and/or cortical response. The NDR could be measured even from recording electrodes adjacent to the implant and at the highest pulse rates (> 4000 pps) used clinically. We then measured the selectivity of this sustained response by presenting F1 and F2 to different electrodes and at different between-electrode distances. This revealed a broad tuning that, we argue, reflects the overlap between the excitation elicited by the two electrodes. Our results also provide a glimpse of the neural nonlinearity in the auditory system, unaffected by the biomechanical cochlear nonlinearities that accompany acoustic stimulation. Several potential clinical applications of our findings are discussed.

scholarly journals Evidence of a Tonotopic Organization of the Auditory Cortex in Cochlear Implant Users

2007 ◽  
Vol 27 (29) ◽  
pp. 7838-7846 ◽  
Author(s):  
J. Guiraud ◽  
J. Besle ◽  
L. Arnold ◽  
P. Boyle ◽  
M.-H. Giard ◽  
...  
Keyword(s):  
Auditory Cortex ◽  
Cochlear Implant ◽  
Tonotopic Organization
Sign in / Sign up

Export Citation Format

Share Document