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S F Volman

Publications and source records attributed to S F Volman.

At least 19 recordsLinked to original sources
PubMed1998

Biomechanical and neurophysiological studies on audition in eared and earless harlequin frogs (Atelopus).

Tissue displacement of various body surfaces and the auditory midbrain sensitivities to sound were measured in Atelopus species with or without a tympanic middle ear ("eared" and "earless", respectively). Tissue displacement (vibration) of body regions was measured by laser Doppler vibrometer. The body wall directly overlying the lung is most dramatically displaced by sound pressure in all species tested. The otic (lateral head) region showed low displacement in earless species, but significant displacement to high-frequency sound in eared species. Peak tissue displacement of the body wall occurred within the frequency range of each species' advertisement vocalization. Peak tissue displacement of the otic region of the eared species also occurred within these frequencies. Multi-unit neurophysiological recordings of the auditory midbrain (torus semicircularis) also were obtained. Auditory sensitivity curves showed three distinct regions of sensitivity at low, middle, and high frequencies, the latter located within the frequency range of each species' advertisement vocalization. The correlation between auditory midbrain sensitivity and tissue displacement of the body wall region at advertisement vocalization frequencies, suggests that the body wall/lungs serve as the route of sound transfer to the inner ear in earless species and possibly in the eared species as well.

Animals↗
PubMed1997

Response modulation in the zebra finch neostriatum: relationship to nuclear gene regulation.

The sound of birdsong activates robust gene expression in the caudomedial neostriatum (NCM) of songbirds. To assess the function of this genomic response, we analyzed the temporal and quantitative relationships between electrophysiological activity and gene induction. Single units in zebra finch NCM showed large increases in firing in response to birdsong, whereas simple auditory tones tended to inhibit firing. Most cells showed little selectivity for individual songs based on total number of spikes produced. When a novel song stimulus was repeated, the cells rapidly modulated their firing rates so that the first response to a stimulus was markedly higher than consecutive responses. Even after many repetitions of a particular song, cells continued to fire in response to that stimulus, unlike the complete "habituation" observed previously for genomic activity. The initial modulation of the response to a particular song disappeared, however, once that song was repeated for 200 trials ( approximately 34 min). These results indicate a dissociation between gross physiological activity and "immediate early" gene expression: genomic activity occurs only during a subset of electrophysiological responses. We propose a model in which nuclear responses in NCM are modulated by pathways distinct from the primary auditory inputs to NCM. This would account for the changing selectivity of the genomic response and implies an active role for the cell nucleus as an integrating agent in the physiological operation of neural circuits.

Acoustic Stimulation↗
PubMed1997

Relative hippocampal volume in relation to food-storing behavior in four species of woodpeckers.

Previous studies have shown that those food-storing birds of the order Passeriformes that remember the locations of their caches have relatively larger hippocampal complexes than do non-storing passerines. Woodpeckers constitute a different avian order (Piciformes), which also includes some food-storing species. We compared hippocampal volume, relative to the volume of the rest of the telencephalon, across four species of woodpeckers with disparate caching behavior. Red-bellied woodpeckers (Melanerpes carolinus) are "scatter hoarders'. During the fall and winter they cache acorns or beechnuts in dispersed sites throughout a large territory. Red-headed woodpeckers (Melanerpes erythrocephalus) also store nuts but in central "larders' on their small territories which they fiercely defend. Caching is absent or much reduced in hairy woodpeckers (Picoides villosus) and downy woodpeckers (Picoides pubescens), both of which forage on a variety of foods within large winter home ranges. The relative volume of the hippocampal complex in the scatter hoarder was larger than in the larder hoarder, suggesting that red-bellied woodpeckers, like passerine scatter hoarders, rely on memory to recover their caches. Surprisingly, the relative hippocampal volumes in the two non-storing Picoides woodpeckers were most similar to the scatter hoarder of the other genus. In passerine birds, hippocampal volume and telencephalon volume are highly correlated in storing species but not in non-storers. We found that the volumes of these two brain areas were highly correlated in both Melanerpes species, uncorrelated in the hairy woodpeckers, and more weakly correlated in the downy woodpeckers. The unexpectedly large hippocampal complexes in the Picoides species suggests they may engage in some behavior, other than food-storing, that selects for this trait. Conversely, our results concerning the relationship between hippocampal and telencephalon volumes may indicate that a weak correlation is associated with a less specialized hippocampus, independent of its relative volume.

Animals↗
PubMed1996

Quantitative assessment of song-selectivity in the zebra finch "high vocal center".

1. Auditory responses in the zebra finch (Taenopygia guttata) song-system nucleus HVc were assessed at 54 recording sites by 3 different methods: discriminated action potentials; excitatory summed responses; and excitatory minus inhibitory summed responses. Four standard stimuli were presented at each site: the bird's own song; this song reversed; a conspecific song; and a noise burst. Responses were quantified by calculating a relative response index that partitoned the response, to provide a response profile, across the stimuli. 2. Regardless of analysis method, the strongest response was most often to the bird's own song (78-82%, depending on method). The predominant rank order of response strength across the remaining three stimuli was conspecific song > reversed song > noise. 3. The distribution of relative response magnitude was sensitive to analysis method. Discriminated spikes captured the heterogeneity of HVc neurons, whereas the excitatory summed responses reflected. the overall trends more consistently. When inhibition was subtracted from excitation in the summed responses, the variance of the relative responses increased, but this method presented some problems for statistical analysis. 4. A small sample of neurons in other forebrain auditory areas was used for comparative analyses. At these recording sites, the bird's own song did not consistently elicit the best response and there were generally smaller differences in the relative responses to the four stimuli. The smaller degree of stimulus selectivity among these cells resulted in less sensitivity to differences in the assessment methods.

Acoustic Stimulation↗
PubMed1995

Convergence of untutored song in group-reared zebra finches (Taeniopygia guttata).

Zebra finches develop abnormal song if they cannot interact with adult song tutors during the 1st few months after hatching. The authors investigated whether untutored juveniles would learn song from each other. The birds were isolated from adult males at 10 days of age and their songs recorded after Day 80. By the authors' measures of syllable sharing and the judgments of human listeners, the songs of untutored brothers were as similar to each other as those of birds reared together with a tutor. The songs of group untutored birds were, however, more variable, and they contained abnormal elements, as did the songs of birds reared apart from all other males. The fact that untutored brothers copied song from each other raises the possibility that juveniles might influence each other's song development, even when adult tutors are present. If this were the case, it would increase the range of social interactions that determine which songs juveniles learn.

Aging↗
PubMed1993

Development of neural selectivity for birdsong during vocal learning.

Juvenile white-crowned sparrows learn to sing by first memorizing an adult's song and then progressively matching their vocalizations to this model during plastic song. Previous studies have shown that neurons in the song-system nucleus HVC of adult sparrows respond preferentially to a bird's own song. In this study, the auditory selectivity of HVC neurons in subadult birds was examined. In young, nonsinging birds who had been song tutored, these cells responded to song stimuli, and at some recording sites had distinct preferences for one song or another. As a population, however, HVC neurons in these birds showed no preference for familiar song. They were no more likely to prefer normal tutor song to reversed tutor song or to the song of another white-crowned subspecies. By contrast, in birds producing plastic song, HVC neurons were selective for the bird's own songs, even in preference to their tutor song. Therefore, during song learning the response properties of HVC neurons appear to be dynamically modified, perhaps by auditory feedback from the bird's own vocalizations. The emergence of song selectivity during plastic song may be significant both for song learning and for song perception in adult birds.

Animals↗
PubMed1990

Neuroethological approaches to the evolution of neural systems.

Over the past two decades, neuroethologists have been unravelling the neural circuitry underlying some of the specialized capabilities animals use to obtain and process sensory information. Explicitly comparative studies of these systems can now be carried out to ask questions about the processes of evolutionary change in neural systems. In some cases, it can be seen how relatively minor modifications of neural networks may significantly expand the efficacy of sensory processing. Other comparative studies might ask whether expanding the number of steps involved in neural computation, or the area devoted to the representation of a particular sub-modality, constrains neural architecture in predictable ways.

Animals↗
PubMed1990

Comparative physiology of sound localization in four species of owls.

Bilateral ear asymmetry is found in some, but not all, species of owls. We investigated the neural basis of sound localization in symmetrical and asymmetrical species, to deduce how ear asymmetry might have evolved from the ancestral condition, by comparing the response properties of neurons in the external nucleus of the inferior colliculus (ICx) of the symmetrical burrowing owl and asymmetrical long-eared owl with previous findings in the symmetrical great horned owl and asymmetrical barn owl. In the ICx of all of these owls, the neurons had spatially restricted receptive fields, and auditory space was topographically mapped. In the symmetrical owls, ICx units were not restricted in elevation, and only azimuth was mapped in ICx. In the barn owl, the space map is two-dimensional, with elevation forming the second dimension. Receptive fields in the long-eared owl were somewhat restricted in elevation, but their tuning was not sharp enough to determine if elevation is mapped. In every species, the primary cue for azimuth was interaural time difference, although ICx units were also tuned for interaural intensity difference (IID). In the barn owl, the IIDs of sounds with frequencies between about 5 and 8 kHz vary systematically with elevation, and the IID selectivity of ICx neurons primarily encodes elevation. In the symmetrical owls, whose ICx neurons do not respond to frequencies above about 5 kHz, IID appears to be a supplementary cue for azimuth. We hypothesize that ear asymmetry can be exploited by owls that have evolved the higher-frequency hearing necessary to generate elevation cues. Thus, the IID selectivity of ICx neurons in symmetrical owls may preadapt them for asymmetry; the neural circuitry that underlies IID selectivity is already present in symmetrical owls, but because IID is not absolutely required to encode azimuth it can come to encode elevation in asymmetrical owls.

Animals↗
PubMed1989

Localization of the enhanced input to cockroach giant interneurons after partial deafferentation.

The ventral giant interneurons (GIs) in the cockroach have two distinct dendritic fields: a small one ipsilateral to the soma, and a larger, contralateral field from which the axon arises. The major input to these GIs is from the cercus on the axon side; when this cercus is ablated in the last instar before the adult stage, input from the other cercus becomes more effective within 30 days (Vardi and Camhi, 1982b). I wished to determine if the input from the intact, soma-ipsilateral cercus contacted the GIs purely ipsilaterally and if EPSPs at this site were larger in deafferented animals. Consistent with earlier anatomical findings, intracellular recordings from the GI somata showed that the majority of cercal inputs synapse on their own side of the ganglion in normal animals. This was evidenced by differences in the size and shape of the synaptic potentials evoked from the two cerci and by the presence of large EPSPs after a ganglion had been split along the midline. Unitary EPSPs produced by stimulation of single, identified cercal afferents, ipsilateral to the soma, were compared between normal and deafferented animals. Column "h" afferents were chosen because they make a large contribution to the receptive fields of GIs 1 and 2 after ablation of the contralateral cercus. In addition, the arbors of these afferents, when stained with cobalt, did not cross the ganglionic midline in normal animals. Unitary EPSPs recorded in GI 2 were significantly larger in the deafferented animals. There was, however, no significant change in the size of EPSPs in GI 1. Nevertheless, the results from GI 2 suggest that partial deafferentation in the central nervous system can increase the efficacy of synapses distant from the locus of denervation.

Action Potentials↗
PubMed1989

Spatial selectivity and binaural responses in the inferior colliculus of the great horned owl.

In this study we have investigated the processing of auditory cues for sound localization in the great horned owl (Bubo virginianus). Previous studies have shown that the barn owl, whose ears are asymmetrically oriented in the vertical plane, has a 2-dimensional, topographic representation of auditory space in the external division of the inferior colliculus (ICx). As in the barn owl, the great horned owl's ICx is anatomically distinct and projects to the optic tectum. Neurons in ICx respond over only a small range of azimuths (mean = 32 degrees), and azimuth is topographically mapped. In contrast to the barn owl, the great horned owl has bilaterally symmetrical ears and its receptive fields are not restricted in elevation. The binaural cues available for sound localization were measured both with cochlear microphonic recordings and with a microphone attached to a probe tube in the auditory canal. Interaural time disparity (ITD) varied monotonically with azimuth. Interaural intensity differences (IID) also changed with azimuth, but the largest IIDs were less than 15 dB, and the variation was not monotonic. Neither ITD nor IID varied systematically with changes in the vertical position of a sound source. We used dichotic stimulation to determine the sensitivity of ICx neurons to these binaural cues. Best ITD of ICx units was topographically mapped and strongly correlated with receptive-field azimuth. The width of ITD tuning curves, measured at 50% of the maximum response, averaged 72 microseconds. All ICx neurons responded only to binaural stimulation and had nonmonotonic IID tuning curves. Best IID was weakly, but significantly, correlated with best ITD (r = 0.39, p less than 0.05). The IID tuning curves, however, were broad (mean 50% width = 24 dB), and 67% of the units had best IIDs within 5 dB of 0 dB IID. ITD tuning was sensitive to variations in IID in the direction opposite to that expected for time-intensity trading, but the magnitude of this effect was only 1.5 microseconds/dB IID. We conclude that, in the great horned owl, the spatial selectivity of ICx neurons arises primarily from their ITD tuning. Except for the absence of elevation selectivity and the narrow range of best IIDs, ICx in the great horned owl appears to be organized much the same as in the barn owl.

Acoustic Stimulation↗
PubMed1988

The role of afferent activity in behavioral and neuronal plasticity in an insect.

Cockroaches (Periplaneta americana) have been shown to adapt behaviorally, in about 1 month, to ablation of one cercus. Additionally, those giant interneurons (GIs) that normally receive their major input from the lesioned cercus become more responsive to stimulation of the intact side (Vardi and Camhi 1982a, b). To investigate the role of afferent activity in the behavioral and neuronal plasticity, we silenced wind-evoked activity in the intact cercus by immobilizing the sensory hairs. This was carried out during the last nymphal stage which lasts for about one month. The animals were tested behaviorally and physiologically after they had molted to adults and a fresh set of mobile hairs had appeared. These animals showed no behavioral correction (Fig. 3). The responses of the GIs on the ablated side were somewhat enhanced, but they were also significantly smaller than those in animals with long-term cercal ablations and no sensory deprivation (Fig. 5). A variety of controls (Figs. 8, 9, and 10) were used to show that sensory deprivation by itself did not decrease the responsiveness of the afferents or the GIs. Thus elimination of wind-evoked activity specifically decreases enhancement of the responses in the GIs.

Afferent Pathways↗
PubMed1987

From behavior to membranes: testosterone-induced changes in action potential duration in electric organs.

The electric organ of mormyrid fishes consists of action potential-generating cells called electrocytes, which together produce a pulse-like electric organ discharge (EOD). The appearance of an EOD depends, in part, on the characteristic features of a single electrocyte's action potentials. In some species, gonadal steroid hormones induce increases in EOD duration, which mimic natural sex differences. We now show that testosterone-induced changes in EOD duration are associated with a 2- to 3-fold increase in the duration of action potentials generated by single electrocytes. Together with other anatomical and biochemical data, the results emphasize the exquisite interrelationship between steroid hormone action and the cellular machinery determining the electrical properties of single cells that underlie sexually dimorphic and seasonal behaviors.

Action Potentials↗
PubMed1976

Quantitative studies of single-cell properties in monkey striate cortex. I. Spatiotemporal organization of receptive fields.

1. The properties of single cells in striate cortex of the rhesus monkey, representing the visual field 2 degrees -5 degrees from the fovea, were examined quantitatively with stationary and moving stimuli. Three distinct classes of cells were identified: S type, CX type, and T type. 2. S-type cells were defined as those oriented cells which to the optimal direction of movement in their receptive fields exhibited one or more spatially separate subfields within each of which a response was obtained to either a light or dark edge, but not to both. Several different types of S-cells were distinguished: a) S1-type cells for which moving edges revealed a single excitatory area within which a response was elicited by either a light or a dark edge but not by both. Most of these cells were unidirectional. b) S2-type cells for which moving edges revealed two spatially separate response areas, one of which was excited by a light edge and the other by a dark edge. Both regions responded to the same direction of movement. c) S3-type cells which had two response areas, one of which was excited by a stimulus moving in one direction (at right angles to the axis of orientation) and the other, of opposite contrast, which responded in the opposite direction, d) S4-type cells which to one direction of movement showed two spatially separate regions sensitive to a light and dark edge and which in the other direction of movement had only one responsive area (either light or dark). e) Cells which had multiple spatially separate subfields (S5-7 types). 3. CX-type cells were defined as those oriented cells which in their receptive fields exhibited no spatial separation for light- and dark-edge responses; they discharged to both edges in the same direction of movement and in the same spatial area. Flashing stimuli elicited both on and off responses throughout the receptive field. CX-type cells were predominantly of two types: those which were selective for direction of stimulus movement and those which were not. 4. A third class of cells (T-type) were those which were excited by only one sign of contrast change and responded in a sustained fashion even when there was no contour within the receptive field. These cells were poorly or not at all oriented; some of them were selective to wavelength. 5. Quantitative comparisons showed the following differences between S-type and CX-type cells: a) S-type cells had smaller receptive fields than CX-type cells but the populations over-lapped considerably. Receptive-field size was smallest in layer 4c. In all other layers S-type cells had the same size fields. CX-type cells, by contrast, tended to have larger fields in layer 5-6 than 2-3. b) The spatial separation between light and dark response areas was the best criterion for distinguishing S-type and CX-type cells. The distribution of this measure disclosed two populations of cells with relatively limited overlap. c) In layers 2 and 3, both S-type and CX-type cells had low spontaneous activity...

Animals↗
PubMed1976

Quantitative studies of single-cell properties in monkey striate cortex. II. Orientation specificity and ocular dominance.

1. Quantitative analyses of orientation specificity and ocular dominance were carried out in striate cortex of the rhesus monkey. 2. Sharpness of orientation selectivity was greater for simple (S type) than for complex (CX type) cells. CX-type cells became more broadly tuned in the deeper cortical layers: S-type cells were equally well tuned throughout the cortex. 3. Sharpness of orientation selectivity for S-type cells was similar at all retinal eccentricities studied (0 degrees - 20 degrees from the fovea):in CX-type cells orientation selectivity decreased slightly with increasing eccentricity. 4. The orientation tuning of binocular cells was similar when mapped separately through each eye. 5. Orientation selectivity and direction selectivity are independent of each other, suggesting that separate neural mechanisms give rise to them. 6. More CX-type cells can be binocularly activated than S-type cells (88% versus 49%). The ocular dominance of S-type cells is similar in all cortical layers: for CX-type cells there is an increase in the number of cells in ocular-dominance category 4 in layers 5 and 6.

Animals↗
PubMed1976

Quantitative studies of single-cell properties in monkey striate cortex. III. Spatial frequency.

1. The response properties of single cells in monkey striate cortex were examined using moving bars, square-wave gratings, and sine-wave gratings. 2. The moving of cells studied were not selective for bar width or for the spatial frequency of square-wave gratings. 3. Most cells responded selectively to the spatial frequency of the sine-wave gratings. 4. The spatial frequency of the sine-wave grating eliciting the optimal response could not be predicted from the organization of the receptive field of each cell as determined by stationary or moving stimuli. 5. The sharpness of spatial-frequency selectivity is only slightly more pronounced in S-type cells than in CX-type cells. 6. S-type and CX-type cells differ significantly in the temporal modulation of their discharges to gratings. S-type cells discharge in sharp bursts to each cycle which traverses the receptive field. CX-type cells discharge in a rather continuous fashion. This measure can be used reliably to classify cells as S or CS type.

Animals↗
PubMed1976

Quantitative studies of single-cell properties in monkey striate cortex. IV. Corticotectal cells.

1. The receptive-field properties of corticotectal cells in the monkey's striate cortex were studied using stationary and moving stimuli. These cells were identified by antidromic activation from the superior colliculus. 2. Corticotectal cells form a relatively homogeneous group. They are found primarily in layers 5 and 6. These cells can usually be classified as CX-type cells but show broader orientation tuning, larger receptive fields, higher spontaneous activity, and greater binocular activation than CX-type cells do in general. A third of the corticotectal cells were direction selective. 3. These results suggest that the cortical input to the superior colliculus is not directly responsible for the receptive-field properties of collicular cells. We propose that this input has a gating function in contributing to the control of the downflow of excitation from the superficial to the deep layers of the colliculus.

Animals↗