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Biomedical subjects

F de Ribaupierre

Publications and source records attributed to F de Ribaupierre.

29 records · Page 2Linked to original sources
PubMed1985

Origin of afferents to physiologically defined regions of the medial geniculate body of the cat: ventral and dorsal divisions.

To study the origin of afferents to the medial geniculate body (MGB), single unit recordings were first conducted to define physiologically a given region in this auditory thalamic nucleus. Horseradish peroxidase (HRP) was then injected extracellularly, in order to label retrogradely the neurons whose axon terminals end in this region. The principal inputs to the MGB are coming from various nuclei of the brain stem, the auditory cortex and the reticular complex of the thalamus. The ventral division receives its cortical inputs principally from the primary (AI) and the posterior (PAF) auditory cortical fields, with a quantitatively smaller contribution of the secondary (AII) and anterior (AAF) cortical fields. On the other hand, the dorsal division receives a majority of its cortical inputs from AII, with a less important contribution of AI and PAF. The auditory cortex sends roughly as many axons to these two divisions as does the brain stem, mainly the inferior colliculus (IC). The analysis of ascending inputs to the same regions of the MGB reveals that, on the average, 88%, 7% and 5% of them are coming from the ipsilateral IC, the contralateral IC and other nuclei of the brain stem, respectively.

Animals↗
PubMed1983

Neural correlates of cubic difference tones in the medial geniculate body of the cat.

Single unit responses to the cubic difference tone CDT (2f1 - f2 = CF) and the difference tone DT (f2 - f1 = CF) were studied in the medial geniculate body (MGB) of the cat. Out of 66 units tested with CDT stimuli and having characteristic frequencies (CF) below 10 kHz, 77% gave a response to the two-tone combination stimulus. The component tones when presented alone evoked no responses, or in some cases a response pattern that was different from the one observed for the combination tone. The CDT response pattern was always similar to that seen for a pure tone at the CF. The threshold of response for the CDT was 10-70 dB higher than for a pure tone stimulus at the CF. The few units which were phase-locked could be synchronised with the CF, CDT, or DT, depending on the particular stimulus conditions. The index of synchrony was in many cases found to be higher for CDT responses than for a pure tone at CF.

Animals↗
PubMed1983

Intensity functions of single unit responses to tone in the medial geniculate body of cat.

Extracellular spike activity was recorded from single units in the medial geniculate body (MGB) of nitrous oxide anaesthetized cats. The responses of 291 units to tone bursts at the characteristic frequency (CF) were studied as a function of stimulus intensity, covering a range from 10 to 100 dB SPL. The proportion of MGB units characterized by a monotonic or a non-monotonic discharge rate--intensity function was 26% and 74%, respectively. In addition, changes of response latency as a function of tone levels were demonstrated to be either monotonic (38% of units) or non-monotonic (62% of units). One third Of MGB units showed a change of response pattern with increasing intensities, in similar proportion towards either prevailing excitatory or inhibitory components. The monotonic units tended to differ from non-monotonic ones in addition to their intensity function by showing shorter response latencies, a higher response probability to broad-band stimuli and simpler response patterns. The mean dynamic range of the monotonic unit population was 60 dB, with thresholds ranging from 10 to 90 dB SPL; most discharge rate--intensity functions did not saturate at sound levels of 100 dB SPL. In the population of non-monotonic units, the 'best' intensity, defined as th intensity giving the strongest response, ranged between 10 and 100 dB SPL. The present results suggest that the intensity could be signaled by the mean firing rate of a restricted population of monotonic units or place coded by the distribution of maximally activated non-monotonic units which are broadly tuned to different intensities.

Acoustic Stimulation↗
PubMed1982

Neurons sensitive to narrow ranges of repetitive acoustic transients in the medial geniculate body of the cat.

Neuronal activity was recorded in the medial geniculate body (MGB) of nitrous oxide anaesthetized, paralysed cats in response to click trains. For most cells responding to these stimuli the spike discharges are precisely time locked to individual clicks within the train. The present study has revealed that, apart from the normal "locker" response being characterized by a monotonic decrease in the entrainment as the frequency of the clicks within the train increases, there is a small population of "lockers" which show a non-monotonic response to increasing click frequency. 41% of these non-monotonic cells were not at all entrained by the lowest click rates and had time-locked responses for very restricted frequency ranges. These particular non-monotonic "lockers" were more commonly-found in the posterior part of the pars lateralis and in the suprageniculate nucleus. These cells might be involved in the temporal coding of natural sounds such as animal vocalizations and the cat's purr.

Acoustic Stimulation↗
PubMed1981

Neural coding of repetitive clicks in the medial geniculate body of cat.

The activity of 418 medial geniculate body (MGB) units was studied in response to repetitive acoustic pulses in 35 nitrous oxide anaesthetized cats. The proportion of MGB neurons insensitive to repetitive clicks was close to 30%. On the basis of their pattern of discharge, the responsive units were divided into three categories. The majority of them (71%), classified as "lockers', showed discharges precisely time-locked to the individual clicks of the train. A few units (8%), called "groupers', had discharges loosely synchronized to low-rate repetitive clicks. When the spikes were not synchronized, the cell had transient or sustained responses for a limited frequency range and was classified as a "special responder' (21%). Responses of "lockers' were time-locked up to a limiting rate, which varied between 10 and 800 Hz; half of the "lockers' had a limiting rate of locking equal to or higher than 100 Hz. The degree of entrainment, defined as the probability that each click evokes at least one spike, regularly decreases for increasing rates; on the other hand, the precision of locking increasing increases with frequency. The time jitter observed at 100 Hz might be as small as 0.2 ms and was 1.2 ms on average. The population of "lockers' can mark with precision the transients of complex sounds and has response properties still compatible with a temporal coding of the fundamental frequency of most animal vocalizations.

Animals↗
PubMed1980

Transmission delay of phase-locked cells in the medial geniculate body.

Over 4000 single unit recordings were obtained from the medial geniculate body (MGB) of nitrous oxide anaesthetized cats. Out of 1600 cells sensitive to tone bursts below 4 kHz, 10% were responding in a sustained manner. From these, 121 were tested for phase-locked responses. The general characteristics of these units have been described in a previous report. The central tendency of the discharges distribution within the period or mean phase angle was studied for many frequencies in 24 phase-locked units. For each of them, the mean phase angle shifts linearly with the frequency. The slope of these phase versus frequency lines is an accurate measure of the transmission delay from the cochlea to the MGB. This delay is a function of the unit's characteristic frequency and shows that the time spread introduced by the cochlea between the high and low frequency components of an acoustic signal is preserved up to the MGB. Subtracting the cochlear delay from this overall delay, the neural delay from the eighth nerve to the MGB was found to be 6.4 ms for neurons having a CF above 300 Hz; it was greater by 3 ms for cells with a CF below that frequency.

Acoustic Stimulation↗
PubMed1980

Functional ear asymmetry in vertical localization.

Vertical frontal mid-saggital plane localization was tested in binaural, monaural left and monaural right ear conditions. Band-pass noise stimuli were presented pseudorandomly through one of four loudspeakers set with an angular separation of 11 degrees. The subject's performance, based on reaction time and mistakes, was continuously recorded. The binaural performance was twice as high as the monaural performance, suggesting that the two ears treat the information in a different and complementary way. The left ear performance was higher than the right ear performance; this strongly suggests a right hemisphere superiority for vertical localization.

Auditory Perception↗
PubMed1979

Computer-controlled double-beam scanning microspectrophotometry for rapid microscopic image reconstructions.

A method for automated collection of various specific data from an entire microscopical preparation and their quantitative evaluation is described. Its application to the study of neuronal connections is discussed in some detail. Brain sections are scanned using a computer-controlled microscope for reflectance, fluorescences or absorbance signals. Two illuminating beams are used, one of them being amplitude modulated. By means of a synchronous detection the two signals are recorded simultaneously: for example, in an autoradiograph, the reflectance (measuring the density of the silver grains in emulsion) and the absorbance (allowing to localize the underlying counterstained cells). The data are stored in a computer. Various off-line processing schemes allow the reconstruction of the data with respect to the corresponding spatial coordinates. Thus pseudo-three-dimensional, analogue or digital, graphic displays may be obtained in which the patterns of neuronal connections can be recognized and interpreted. A method for the detection of weakly labelled nerve fibres based on digital filtering is presented. The whole processing for a frontal section of the mouse brain (7 X 10 mm area) takes less than 1 h. In addition to the evaluation of microscopically labelled material (grains of autoradiographs, horseradish peroxidase, nucleic acids) the technique described has been successfully used for the study of naturally fluorescent intracellular components in living tissue cultures.

Animals↗