PubMed Health⌕ Search

Biomedical subjects

C E Molnar

Publications and source records attributed to C E Molnar.

13 recordsLinked to original sources
PubMed1993

Effects of spike discharge history on discharge probability and latency in frog basilar papilla units.

Gaumond et al. [(1982) J. Neurophysiol. 48, 856-873] showed in the cat that a multiplicative-intensity model can generally account quite well for reduction of the probability of an auditory-nerve spike by another spike preceding it by 4 to 25 ms, and that for smaller separations there is also an increased latency of the following spike. Bosch [(1990) D. Sc. Dissertation, Washington University, St. Louis, MO] made important improvements in experimental design and estimation techniques for studying these effects, and confirmed their presence in the gerbil. However, direct application of these methods to the frog does not yield reliable estimates. A clearer separation of discharge probability and latency effects in frog basilar papilla units is provided by the paired-click paradigm used in this study, which is applicable to low-spontaneous-rate units that generally respond to click stimuli with zero or one spike within a short interval following the click. The results confirm the existence in the frog of both spike-probability and spike-latency effects that are qualitatively similar to those found in mammals, although the absolute refractory time is much longer in frog, and the relative refractory time usually shorter. The paired-click paradigm also reveals a stimulus-history effect at stimulus levels which are near threshold: when there is no response to the first click, responses to the second click occur with increased probability and reduced latency.

Acoustic Stimulation↗
PubMed1983

Response of cochlear nerve fibers to brief acoustic stimuli: role of discharge-history effects.

The probability that a cochlear nerve fiber spike discharge occurs during a time interval delta t depends on both the acoustic stimulus and on aftereffects from earlier spike discharges. We have examined the influence of discharge-history on post-stimulus time (PST) histogram responses to acoustic click and tone-burst stimuli. Discharge-history effects were found to include the modification of observed interpeak times of PST responses to clicks, a loss of distinct peaks in the click response of high characteristic frequency (CF greater than 5 kHz) fibers, and changes in the ratio of initial to steady-state response portions of tone-burst responses. The method used to separate discharge-history from stimulus-related factors is based on a model developed in Gaumond et al. [J. Neurophysiol. 48, 856-873 (1982)]. The results are in general agreement with those obtained by the method of Peter Gray [Biophys. J. 7, 759-777 (1967)], which discards from consideration those portions of the response record not preceded by a silent interval of 20 or 25 ms or more. Our method requires more assumptions about the spike train, but produces less variable results by utilizing more of the spike train data.

Acoustic Stimulation↗
PubMed1982

Effects of altering organ of Corti on cochlear distortion products f2 - f1 and 2f1 - f2.

1. Single cochlear nerve fiber recordings from unexposed chinchillas show spatial distributions of amplitude and phase of the distortion products f2 - f1 and 2f1 - f2 similar to those previously reported for the cat (35, 37, 42). 2. Damaging the organ of Corti in the region corresponding to the frequencies of a two-tone stimulus substantially reduces the amplitude of these distortion products at their characteristic places. 3. The distortion products 2f - f1 and 2f1 - f2 thus appear to be generated in the organ of Corti in the region of the primary-frequency places. 4. The neural responses suggest that the distortion products are propagated in the motion of the cochlear partition like externally applied stimulus tones at the distortion frequencies wih a similar spatial distribution of distortion product amplitude and phase. Models of the cochlea that assume nonlinear cochlear-partition dynamics can account for the similarity by demonstrating that distortion products generated by cochlear-partition nonlinearity can propagate apicalward in the motion of the cochlear partition. 5. Models of the cochlea using a linear-system model for cochlear partition motion, in cascade with a nonlinear transduction stage and a subsequent sharp filter, are inadequate to account for present observations, unless two currently implausible assumptions are made: a) stimulus tones near 4 kHz must propagate in normal cochleas at least as far apically as the 300-Hz place with sufficient amplitude to generate f2 - f1 there, and b) damage to the organ of Corti must interfere with this propagation of 4-kHz stimulus tones to the 300-Hz place. 6. Distortion generation in the cochlea is sensitive to delicate alterations of the organ of Corti. Short moderate-intensity exposures to sound can reversibly reduce the amplitudes of the distortion products f2 - f1 and 2f1 - f2 seen in responses from cochlear nerve fibers with characteristic frequencies (CF) near the distortion frequencies. Since such exposures do ot produce permanent structural changes visible under light microscopy, it seems most reasonable to believe that subtle changes in the organ of Corti (most likely in the hair cells themselves) in the region most responsive to f1 and f2 reduce the generation of mechanically present distortion products.

Acoustic Stimulation↗
PubMed1970

Cochlear nerve fiber discharge patterns: relationship to the cochlear microphonic.

Fourier analysis of discharge patterns in response to sinusoidal acoustic stimulation provides a consistent and repeatable measure of response phase and amplitude. The variation of the fundamental and harmonic components of the patterns as stimulus parameters are changed is strikingly similar to that of cochlear microphonics. The results are significantly different for single fibers with different characteristic frequencies; the variations parallel those of microphonics recorded from different cochlear turns.

Acoustics↗