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J F Olsen

Publications and source records attributed to J F Olsen.

13 recordsLinked to original sources
PubMed2000

The corticofugal system for hearing: recent progress.

Peripheral auditory neurons are tuned to single frequencies of sound. In the central auditory system, excitatory (or facilitatory) and inhibitory neural interactions take place at multiple levels and produce neurons with sharp level-tolerant frequency-tuning curves, neurons tuned to parameters other than frequency, cochleotopic (frequency) maps, which are different from the peripheral cochleotopic map, and computational maps. The mechanisms to create the response properties of these neurons have been considered to be solely caused by divergent and convergent projections of neurons in the ascending auditory system. The recent research on the corticofugal (descending) auditory system, however, indicates that the corticofugal system adjusts and improves auditory signal processing by modulating neural responses and maps. The corticofugal function consists of at least the following subfunctions. (i) Egocentric selection for short-term modulation of auditory signal processing according to auditory experience. Egocentric selection, based on focused positive feedback associated with widespread lateral inhibition, is mediated by the cortical neural net working together with the corticofugal system. (ii) Reorganization for long-term modulation of the processing of behaviorally relevant auditory signals. Reorganization is based on egocentric selection working together with nonauditory systems. (iii) Gain control based on overall excitatory, facilitatory, or inhibitory corticofugal modulation. Egocentric selection can be viewed as selective gain control. (iv) Shaping (or even creation) of response properties of neurons. Filter properties of neurons in the frequency, amplitude, time, and spatial domains can be sharpened by the corticofugal system. Sharpening of tuning is one of the functions of egocentric selection.

Animals↗
PubMed1998

Distribution of response types across entire hemispheres of the mustached bat's auditory cortex.

AILDD1 AC'1 The responses of neurons in the mustached bat's auditory cortex are specialized to extract particular information from biosonar signals. For this study, we mapped response properties across entire hemispheres in several animals. These experiments enabled us to construct a standard map that aided in determining the connections among the areas, as described subsequently. The mapping also yielded quantitative data regarding the relative sizes of areas and the proportion of cortex devoted to different response types. We identified six response types that were distributed in 11 areas. Eight areas, comprising two-thirds of the auditory cortex, contained neurons sensitive to particular components in biosonar signals. Most were facilitated by combinations of frequency modulated and constant frequency biosonar signal components (FMs and CFs, respectively). There were three major types of combination-sensitive neurons: FM-FM, CF/CF, and FM-CF. Each type of combination sensitivity occurred in multiple areas. The largest proportion were FM-FM neurons (approximately 30% of all neurons in auditory cortex), followed by FM1-CF2 (approximately 23%) and CF/CF (approximately 11%). In the other three areas comprising approximately one-third of the auditory cortex, most neurons responded well to frequencies not contained in biosonar signals.

Animals↗
PubMed1998

Connections among functional areas in the mustached bat auditory cortex.

Connections among functional areas in the mustached bat's auditory cortex were examined by placing anatomical tracers in physiologically defined locations. We identified at least two and probably three channels connecting the various areas. One channel is formed by interconnections among areas containing neurons sensitive to frequency-modulated components (FMs) of the pulse and echo. These neurons are tuned to echo delay, a cue for target range, and thus define a ranging channel. An additional one or two channels are formed by interconnections among areas that contain neurons sensitive to the constant frequency components (CFs) of echoes. These neurons are of two main types: either sensitive to CFs of both pulse and echo (CF/CF neurons) or sensitive to a pulse FM and echo CF (FM-CF neurons). There was only a weak connection between the largest area of each type, suggesting they lie in different channels. Connections among areas in the ranging channel and echo CF-sensitive channel(s) were weak. Thus, the interconnections among functional areas in the mustached bat's auditory cortex define parallel channels for processing different types of biosonar information. Most corticocortical connections were patchy, in a manner suggestive of a columnar organization. The average width of the patches was approximately 360 microm. Based on the sizes of the functional areas, we estimate the auditory cortex contains a total of approximately 150 columns. Individual areas contain from as many as approximately 20 to as few as 1-4 columns. Each area had abundant projections outside of the auditory cortex. Connections within the cortex included the frontal, anterior cingulate, retrosplenial and perirhinal cortices, and the claustrum. Subcortical targets included the amygdyla, auditory thalamus, pons, pretectum, superior and inferior colliculi, and central gray. Projections within the cortex were of modest strength compared with several of the subcortical projections. Thus, the auditory areas themselves are the primary source of cortically processed biosonar information to the rest of the brain.

Animals↗
PubMed1997

Accuracy of the diagnosis of pleural effusion on supine chest X-ray.

Diagnosis of pleural effusion (PE) on supine chest X-ray (SCXR) is considered difficult. This study aimed at evaluating the accuracy of the diagnosis of PE on SCXR and was performed in two phases. At phase 1, a formula for the sonographic estimation of the volume of PE was established by correlating 24 measurements (in 7 patients in whom complete drainage was achieved) with the drained volumes. At phase two, 112 consecutive SCXRs were supplemented by sonography of the chest. The films were evaluated for the presence of PE and for the presence of different radiologic signs of PE. Sonography showed PE in 41 right and 30 left hemithoraces. The overall accuracy of the diagnosis of PE on SCXR was 82 %. Only one of the undiagnosed PEs had a volume of > 300 ml. The most accurate signs were increased density of the hemithorax, blunted costophrenic angle, and loss of the hemidiaphragm silhouette.

Adolescent↗
PubMed1994

Adaptive plasticity of the auditory space map in the optic tectum of adult and baby barn owls in response to external ear modification.

1. This study demonstrates the influence of experience on the establishment and maintenance of the auditory map of space in the optic tectum of the barn owl. Auditory experience was altered either by preventing the structures of the external ears (the facial ruff and preaural flaps) from appearing in baby barn owls (baby ruff-cut owls) or by removing these structures in adults (adult ruff-cut owls). These structures shape the binaural cues used for localizing sounds in both the horizontal and vertical dimensions. 2. The acoustic effects of removing the external ear structures were measured using probe tube microphones placed in the ear canals. In both baby and adult ruff-cut owls, the spatial pattern of binaural localization cues was dramatically different from normal: interaural level difference (ILD) changed with azimuth instead of with elevation, the rate of change of ILD across space was decreased relative to normal, and the rate of change of interaural time difference (ITD) across frontal space was increased relative to normal. 3. The neurophysiological representations of ITD and ILD in the optic tectum were measured before and > or = 3 mo after ruff removal in adults and beginning at 4.5 months of age in baby ruff-cut owls. Multiunit tuning to ITD and to ILD was measured using dichotic stimulation in ketamine-anesthetized owls. The tectal maps of ITD and ILD were reconstructed using visual receptive field location as a marker for recording site location in the optic tectum. 4. Adjustment of the tectal map of ITD to the altered spatial pattern of acoustic ITD was essentially complete in adults as well as in baby ruff-cut owls. This adjustment changed the magnification of ITD across the tectum, with resultant changes in ITD tuning at individual tectal sites of up to approximately 25 microseconds (approximately 5% of the physiological range) relative to normal values. 5. Adaptation of the tectal ILD map to the ruff-cut spatial pattern of acoustic ILD was substantial but clearly incomplete in both adult and baby ruff-cut owls. Although changes of up to approximately 15 dB (approximately 47% of the physiological range) relative to normal tuning were observed at certain tectal sites, the topography of the ILD map was always intermediate between normal and that predicted by the ruff-cut spatial pattern of acoustic ILD.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1992

High-order auditory filters.

The past year has seen some important advances in our understanding of central auditory function. Several central auditory neurons that differ from those in the periphery in their selectivity for various spectral and temporal parameters of complex sound have been described. Although central specializations for the processing of complex sound have been known for some time, recent findings suggest that these high-order filter properties are more widespread than previously thought. Significant progress has been made in our understanding of the neural mechanisms by which some high-order filter properties, such as delay-tuning, amplitude-tuning, and complex frequency tuning are performed by the central auditory system. New evidence has clarified the role of high-order auditory filters in auditory learning and perception, and the regions in which they are found.

Animals↗
PubMed1991

Combination-sensitive neurons in the medial geniculate body of the mustached bat: encoding of relative velocity information.

1. Orientation sounds (pulses) emitted by the mustached bat (Pteronotus parnellii) consist of up to four harmonics (H1-4); each harmonic contains a constant frequency (CF) component and a terminal frequency modulated (FM) component, so that there are eight components in total (CF1-4 and FM1-4). By referring the echo from a target to the emitted pulse, the mustached bat derives velocity information from Doppler shift and distance information from echo delay. In this study, the responses of single neurons in the medial geniculate body (MGB) to synthetic biosonar signals were investigated. Stimuli consisted of CF, FM, and CF-FM sounds. Paired CF-FM sounds were used to mimic any two harmonics of pulse-echo pairs. The dorsal and medial divisions of the MGB were found to contain combination-sensitive neurons. These neurons responded poorly to individual sounds regardless of frequency and amplitude and were facilitated by paired sounds presented at particular frequencies, amplitudes and inter-component intervals (simulated echo delay). Combination-sensitive neurons were tuned to the frequencies that characterize particular components of natural biosonar signals and were classified according to the components of pulse-echo pairs that best matched the spectral selectivity of the neuron. Two classes of combination-sensitive neurons were found, CF/CF and FM-FM. This paper focuses on CF/CF combination-sensitive neurons, which extract velocity information from paired CF components, and on CF2 and CF3 neurons, which, although not combination-sensitive, are tuned to the frequencies of the CF2 and CF3 components of biosonar signals. 2. CF2 and CF3 neurons were sharply tuned in frequency. The best frequencies of the most sharply tuned CF2 neurons were all approximately equal to 61.17 kHz (SD = 370 Hz), which closely matches the frequency at which P. parnellii stabilizes the CF2 component of an echo when compensating for Doppler shift. Thus CF2 neurons are specialized for a fine analysis of Doppler-compensated echoes. 3. Tuning curves of CF2 and CF3 neurons remained narrow regardless of stimulus level. When compared at high stimulus levels (30 and 50 dB above minimum threshold), bandwidths of tuning curves of CF2 and CF3 neurons were much smaller than those of peripheral auditory neurons turned to CF2 or CF3 frequencies but were about the same as those of cortical neurons tuned to CF2 or CF3 frequencies. Thus the sharpening of neural tuning curves by the bat's central auditory system occurs within or before the MGB.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1991

Combination-sensitive neurons in the medial geniculate body of the mustached bat: encoding of target range information.

1. Delay-tuned combination-sensitive neurons (FM-FM neurons) have been discovered in the dorsal and medial divisions of the medial geniculate body (MGB) of the mustached bat (Pteronotus parnellii). In this paper we present evidence for a thalamic origin for FM-FM neurons. Our examination of the response properties of FM-FM neurons indicates that the neural mechanism of delay-tuning depends on coincidence detection and involves an interaction between neural inhibition and excitation. 2. The biosonar pulse (P) and its echo (E) produced and heard by the mustached bat consist of four harmonics; each harmonic contains a constant frequency (CF) component and a frequency modulated (FM) component. Thus the pulse-echo pair contains eight CF components (PCF1-4, ECF1-4) and eight FM components (PFM1-4, EFM1-4). The stimuli used in this study consisted of CF, FM, and CF-FM sounds: paired CF-FM sounds were used to simulate any two harmonics of pulse-echo pairs. The responses of FM-FM neurons in the MGB were recorded extracellularly. We found that FM-FM neurons respond poorly or not at all to single sounds, respond strongly to paired sounds, and are tuned to the frequency and amplitude of each sound of the pair and to the time interval separating them (simulated echo delay). 3. All FM-FM neurons are facilitated by paired FM sounds and most are facilitated by paired CF sounds. Best facilitative frequencies measured with paired CF sounds fall outside the frequency ranges of the CF components of biosonar signals, whereas best facilitative frequencies measured with paired FM sounds fall within the frequency ranges of the FM components of biosonar signals. Thus FM-FM neurons are expected to respond selectively to combinations of FM components in biosonar signals. The FM components of pulse-echo pairs essential to facilitate FM-FM neurons are the FM component of the fundamental of the pulse (PFM1) in combination with the FM component of the second, third, or fourth harmonic of an echo (EFM2, EFM3, EFM4; collectively, EFMn). 4. The frequency combinations to which FM-FM neurons are tuned reflect small deviations from the harmonic relationship such as occurs in combinations of FM components from pulses and Doppler-shifted echoes. Compared with CF/CF neurons, however, FM-FM neurons are broadly tuned to stimulus frequency. Thus FM-FM neurons are Doppler-shift tolerant and relatively unspecialized for processing velocity information in the frequency domain.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1989

Neural maps of interaural time and intensity differences in the optic tectum of the barn owl.

This report describes the binaural basis of the auditory space map in the optic tectum of the barn owl (Tyto alba). Single units were recorded extracellularly in ketamine-anesthetized birds. Unit tuning for interaural differences in timing and intensity of wideband noise was measured using digitally synthesized sound presented through earphones. Spatial receptive fields of the same units were measured with a free field sound source. Auditory units in the optic tectum are sharply tuned for both the azimuth and the elevation of a free field sound source. To determine the binaural cues that could be responsible for this spatial tuning, we measured in the ear canals the amplitude and phase spectra produced by a free field noise source and calculated from these measurements the interaural differences in time and intensity associated with each of 178 locations throughout the frontal hemisphere. For all frequencies, interaural time differences (ITDs) varied systematically and most strongly with source azimuth. The pattern of variation of interaural intensity differences (IIDs) depended on frequency. For low frequencies (below 4 kHz) IID varied primarily with source azimuth, whereas for high frequencies (above 5 kHz) IID varied primarily with source elevation. Tectal units were tuned for interaural differences in both time and intensity of dichotic stimuli. Changing either parameter away from the best value for the unit decreased the unit's response. The tuning of units to either parameter was sharp: the width of ITD tuning curves, measured at 50% of the maximum response with IID held constant (50% tuning width), ranged from 18 to 82 microsecs. The 50% tuning widths of IID tuning curves, measured with ITD held constant, ranged from 8 to 37 dB. For most units, tuning for ITD was largely independent of IID, and vice versa. A few units exhibited systematic shifts of the best ITD with changes in IID (or shifts of the best IID with changes in ITD); for these units, a change in the value of one parameter to favor one ear shifted the best value of the other parameter in favor of the same ear, i.e., in the direction opposite to that expected from "time-intensity trading." Overall sound intensity had little or no effect on ITD tuning, but did increase the best IIDs of units tuned to nonzero IIDs. The tuning of units for ITD and IID changed systematically along different dimensions of the optic tectum to create coextensive, independent neurophysiological maps of ITD and IID.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1981

Ganglion cell distribution in the retina of the mouse.

The distribution of ganglion cells in the mouse retina was studied with the use of Nissl criteria for distinguishing cell types in the ganglion cell layer. Retrograde filling with horseradish peroxidase (HRP) from the optic fiber tract helped to validate Nissl criteria and served to identify displaced ganglion cells. We estimated a total of 117,000 nonvascular cells in the ganglion cell layer; of these, 70,000 were probably ganglion cells, and 47,000 could not be classified. The density of the presumed ganglion cells was highest-more than 8000 cells/mm2-just temporal to the optic disk, and lowest-less than 2000 cells/mm2-in the most dorsal retina. The retinal region with highest ganglion cell density was slightly elongated in a nasotemporal direction. About 2% of all HRP-filled ganglion cells had their cell bodies in the inner nuclear layer. These displaced cells differed in topographical distribution from the normally positioned ganglion cells: although occurring throughout the retina, they were more common along the retinal periphery. Measurements of ganglion cell areas showed a tendency toward larger size with eccentricity. At no retinal location did cell-size histograms reveal clearly separate size classes.

Animals↗
PubMed1980

Origins of crossed and uncrossed retinal projections in pigmented and albino mice.

The extent of the binocular cortical field in albino mice, as revealed by recording from single cells, was almost normal; although the input from the ipsilateral eye was weaker than normal, most cells were driven from both eyes. By backfilling retinal ganglion cells from one optic tract with horseradish peroxidase we examined the origins of the retinofugal projections. Filled cells ipsilateral to the injected tract were concentrated in a crescent-shaped area bordering the inferior temperal retina. In black mice this area constituted 20% of the total retinal area, in albinos 17%. In black mice we counted nearly 1,000 labeled cells in the ipsilateral retina, or 2.6% of all cells filled in both eyes. Albinos had about one-third fewer filled cells ipsilaterally than black mice. Four percent of all ipsilaterally filled cells in black mice and 8% in albinos were scattered outside of the crescent region. The density of ipsilaterally projecting cells was uniform throughout the crescent region in black mice, but decreased toward the central retina in albinos. In retinas contralateral to the injection up to 39,000 cells were filled-about two-thirds of the cells in the ganglion-cell layer whose cytoplasm contained conspicuous Nissl substance. Depending on classification of unfilled cells as ganglion cells or interneurons, we estimated a total of 48,000 to 65,000 ganglion cells to exist in the retina. The size distribution of ipsilaterally projecting ganglion cells was similar in albinos and normals. Ipsilaterally projecting ganglion cells were on average 1.8-3 times larger in volume than contralaterally projecting ones in both types of mice. Displaced ganglion cells were relatively more common in ipsilateral retinofugal projections: 21% of all ipsilateral ganglion cells were displaced versus less than 1% of all the contralateral ganglion cells in black mice. In albinos only 13% of the ganglion cells in the ipsilateral retina were displaced. The overall reduction in ipsilaterally projecting cells in albinos was reflected twice as much in displaced ganglion cells as in normally placed ones.

Animals↗