PubMed Health⌕ Search

Biomedical subjects

R Patuzzi

Publications and source records attributed to R Patuzzi.

25 records · Page 2Linked to original sources
PubMed1983

Comparison between the tuning properties of inner hair cells and basilar membrane motion.

Measurements were made of inner hair cell receptor potentials and basilar membrane motion in the 17-21 kHz region of the guinea pig cochlea. The latter were made using the Mossbauer technique. Isoamplitude curves at 0.9 mV d.c. receptor potential were compared with isovelocity curves at 0.04 mm/s and the corresponding basilar membrane displacement at CF. The Mossbauer source (20 X 60 or 60 X 85 microns) was placed either in the middle of the basilar membrane or on the extreme modiolar edge. These two source positions yielded broad and narrow mechanical tuning curves, respectively. The latter approximated the receptor potential curves most closely but deviated by 10-15 dB on the low frequency side of the tuning curve tip.

Action Potentials↗
PubMed1983

The influence of Mossbauer source size and position on phase and amplitude measurements of the guinea pig basilar membrane.

Phase and amplitude measurements were made from the incus and basilar membrane in guinea pig using the Mossbauer technique. The basilar membrane/incus ratio had a maximum of about 60 dB and a phase accumulation of between 9 and 12 radians to CF. Two source sizes were used (60 X 85 and 20 X 60 microns) and the source was placed either on the modiolar edge of the basilar membrane or in the middle. Notches in plots of the basilar membrane/incus ratio occur at stimulus frequencies that appear to be associated with source size rather than position, suggesting that artefacts could be produced by the presence of the Mossbauer source.

Animals↗
PubMed1983

The alteration of the low frequency response of primary auditory afferents by cochlear trauma.

The response phase of primary auditory afferents in the first turn of the guinea pig cochlea to low frequency sinusoidal stimuli is altered by trauma to the cochlea. Loud sounds of sufficient intensity to produce temporary shifts in the thresholds of these cells at their characteristic frequency produce a reversal of the neural response from increased firing for basilar membrane displacements towards scala tympani before trauma to an increased firing towards scala vestibuli following trauma. These changes can be reversible.

Acoustic Stimulation↗
PubMed1983

A comparison between basilar membrane and inner hair cell receptor potential input-output functions in the guinea pig cochlea.

Intracellular recordings were made from inner hair cells and basilar membrane motion was measured at a similar place, but in different preparations, in the first turn of the guinea pig cochlea. Potential recordings were made using glass microelectrodes and mechanical measurements were made using the Mössbauer technique. Intensity functions of DC receptor potential and basilar membrane velocity in animals with good and poor thresholds are presented. In animals with good thresholds, stimuli at and above the characteristic frequency produce similarly compressive input-output functions for both inner hair cell receptor potentials and basilar membrane motion. However, for frequencies lower than the characteristic frequency, receptor potential input-output functions obtained from animals in good and poor condition show saturation at high stimulus intensities at which basilar membrane motion is linear. This discrepancy is believed to be due to a nonlinear inner hair cell transduction mechanism. We propose that nonlinearity observed in receptor potential input-output functions is a consequence of the simple cascading of a frequency-dependent nonlinear mechanical input and a frequency-independent nonlinear transduction process.

Action Potentials↗
PubMed1982

Modulation of responses of spiral ganglion cells in the guinea pig cochlea by low frequency sound.

Period histograms were generated from single unit data obtained from the spiral ganglion of the first turn of the guinea pig cochlea in response to continuous tones between 40 and 500 Hz. With the lowest intensities used, spontaneous activity was suppressed during basilar membrane displacement (inferred from cochlear microphonic phase) towards scala vestibula and activity was enhanced during displacement towards scala tympani. At higher intensities the response changed to excitation during maximal basilar membrane velocity towards scala vestibuli. These patterns were delayed by about 0.5 ms producing large phase delays at the higher frequencies. We postulate that the displacement response is produced by cochlear microphonic originating from the outer hair cells acting on the inner hair cell membrane. In contrast, the velocity response is produced by the inner hair cell receptor potential. The effect of a 40 Hz tone on activity evoked by tones above, at, and below the characteristic frequency was investigated by generating period histograms synchronous with the 40 Hz tone. We found that activity evoked by tones around the characteristic frequency of the cell was suppressed during displacement of the basilar membrane towards scala tympani and enhanced in the opposite direction at 40 Hz intensities that had no effect on spontaneous activity. Further increase in the 40 Hz intensity produced suppression during scala vestibuli displacement with activity remaining only during the zero crossings. Still further increase produces the 40 Hz tone alone response. Activity evoked by tones in the low frequency 'tails' of the frequency threshold curve was not similarly modulated. This phenomenon is though to be related to basilar membrane nonlinearity for frequencies close to the cut-off. Investigation of the effect of a 40 Hz tone on the threshold of the compound action potential confirmed data obtained from single units.

Animals↗
PubMed1982

Measurement of basilar membrane motion in the guinea pig using the Mössbauer technique.

Basilar membrane motion was measured at the 16-19 kHz place of the guinea pig cochlea using the Mössbauer technique. The threshold of the gross cochlear action potential (CAP) evoked by pure-tone bursts was used as an indication of neural threshold. CAP threshold deteriorated progressively after the cochlea was opened and the Mössbauer source placed on the basilar membrane. A close relationship was found between the amplitude of basilar membrane motion at the source place frequency and CAP threshold. Basilar membrane velocity at CAP threshold SPL was about 0.04 mm/s over a 60-dB range of CAP threshold. Intensity functions for basilar membrane motion were linear for frequencies more than an octave below the source place frequency but demonstrated progressive saturation for frequencies greater than an octave below the CF. This nonlinear behavior was eliminated as the CAP threshold became less sensitive and was absent post mortem. Isovelocity curves at the 0.04 mm/s criterion were remarkably similar to frequency threshold curves from primary afferent fibers innervating a similar place on the basilar membrane. The isovelocity curve was a better fit than the isoamplitude curve suggesting that inner hair cells respond to basilar membrane velocity. As the CAP threshold deteriorated, the isovelocit curves lost sensitivity around the best frequency, whereas sensitivity to frequencies below 10 kHz remained constant even after the animal was killed. We suggested that most of the frequency response and nonlinear behavior of inner hair cells and afferent fibers may be found in basilar motion.

Animals↗