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Biomedical subjects

S F Ronner

Publications and source records attributed to S F Ronner.

6 recordsLinked to original sources
PubMed1992

Preservation of hearing and facial nerve function in resection of acoustic neuroma.

The surgical results in 78 recent cases of total removal of unilateral acoustic neuroma in which an attempt was made to preserve cochlear function have been added to the authors' previous series of 66 cases to evaluate the factors influencing the ability to preserve useful hearing. Useful hearing was defined by speech reception threshold no poorer than 70 dB and a discrimination score of at least 15%. Analysis using a logistic regression model showed that certain preoperative clinical parameters such as tumor size, speech discrimination score, and gender were significantly correlated with hearing outcome. Favorable outcome was significantly correlated with smaller tumor size, higher preoperative speech discrimination score, and male sex. From this data, an explicit formula was devised for predicting hearing outcome for an individual patient. In four cases with useful hearing preserved, there was improvement of greater than 15 percentage points in speech discrimination scores. While preoperative auditory brainstem responses were not predictive of hearing preservation, monitoring of intraoperative auditory evoked potentials was predictive of hearing outcome in selected cases. Specifically, when wave V was unchanged at the end of the operation, even if it may have been transiently lost during surgery, useful hearing was invariably preserved.

Audiometry, Evoked Response↗
PubMed1990

Neurosurgical applications for intraoperative stimulation.

Intraoperative neurostimulation can be most useful to the surgeon whenever the need arises to assess physiological function or identify fiber pathways and/or neuronal populations in critical areas of brain, spinal cord, or peripheral nerve. Low-level (threshold) stimulation allows for the nearest populations of axons or neuronal cell bodies (in the vicinity of the electrode tip) to be activated in the safest possible fashion. When motor pathways are being tested, attention must be paid to the control and administration of muscle relaxant drugs, which can dampen or abolish muscle responsiveness during stimulation. Peripheral nerve conduction studies can be carried out intraoperatively and may be beneficial for assessing the physiological status of a section of traumatized nerve. Cortical mapping is valuable when surgical resections near motor or speech areas in the brain are contemplated and may help the surgeon avoid significant postoperative deficits in movement or language. Intraoperative stimulation for identifying spinal motor pathways may be used to guide surgical exploration. Finally, selective intraoperative stimulation for identifying nerve fibers encased in tumor may be useful for procedures involving difficult dissections along the brachial plexus or other major nerves in the arm or leg.

Brain Mapping↗
PubMed1976

Responses of complex cells in the visual cortex of the cat as a function of the length of moving slits.

(1) As a step towards specifying the spatial selectivity characteristics of complex cells with spatially periodic substructures, we have studied single cell responses to narrow slits of variable length moved across the receptive field in the preferred direction. In general, the length-response curves were linear over a considerable and sometimes full range until an optimal slit length was reached. (2) In those cells in which the rate of rise of the slit length-response functions decreased before the optimal length was reached, at least 3 factors contribute to the shape of the curve. First, the receptive field shapes of some complex cells are more ovoid or rounded than rectangular, and the summation of responses from excitatory zones of varying optimal lengths itself results in a nonlinear slit length-response function at long slit lengths. Second, central regions may contribute more to cell response than do more lateral regions along the length dimension. Third, a nonlinearity in the slit length-response curve may occur in the upper range of slit lengths as a saturation effect because discharge rates may reach 600/sec, which appears to be close to a limiting firing rate. (3) Some cells believed to be complex during preliminary receptive field testing showed weak inhibitory regions beyond the region of the optimal slit length. Many of these cells also displayed periodic average response histograms to moving slits. The extent and magnitude of the inhibition were variable from cell to cell. In terms of receptive field properties, these cells and 'regular' complex cells seem part of a continuum.

Animals↗
PubMed1975

Periodic excitability changes across the receptive fields of complex cells in the striate and parastriate cortex of the cat.

1. Complex cells in cortical areas 17 and 18 of the cat have been studied in response to narrow slits and edges moving across the receptive field in the preferred direction and also to stationary slits of different widths. 2. Average response histograms, recorded as a narrow slit was moved across the receptive field, displayed a periodic series of peaks above a base line level. The response histogram for most area 17 and 18 cells contained five principal peaks; sometimes one or two weaker peaks were present at receptive field borders. The histogram for one cell located at the area 17-18 border showed thirteen distinct peaks. Periodic response patterns were also generated as an extended edge was moved across the receptive field. Plots of cell responses versus slit width for stationary slits of different widths also indicated periodic response pattern. 3. The accuracy of determining the preferred slit orientation was the single most important requirement for demonstrating the periodic response pattern. Significant changes in the appearance of the periodic pattern occurred even upon 5 degrees rotations away from the preferred orientation. 4. Average response histograms were also studied over a wide range of moving slit velocities. The number of peaks across corresponding spacings within the recewptive field remained constant over a range of velocities. Response amplitudes, however, were velocity dependent. Thus the response peaks remain associated with fixed positions within visual space independent of stimulus velocity, even though temporal as well as spatial factors may be involved in response selectivity and the periodic modulation. The most striking periodic response histograms were generated at the velocities which produced the greatest cell firing rates. Area 17 complex cells responded well to velocities of less than 0-5 degrees to 6-0 degrees/sec, but cells in area 18 generally required higher velocities, sometimes as high as 20 degrees--30 degrees/sec, for a good response. 5. Spatial frequencies for the periodic component of the receptive field for area 17 cells in the central visual area covered a range of three octaves up to 5 cycles/degree, and area 18 cells included another octave on the low frequency side. The spatial frequency of a cell was found to be roughly inversely proportional to the receptive field width. Only a small sample of area 18 cells was studied, but these cells tended to represent low spatial frequencies and to respond selectively to high velocity stimuli...

Action Potentials↗