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E R Lewis

Publications and source records attributed to E R Lewis.

At least 19 recordsLinked to original sources
PubMed1992

Seismic signal transmission between burrows of the Cape mole-rat, Georychus capensis.

Both seismic and auditory signals were tested for their propagation characteristics in a field study of the Cape mole-rat (Georychus capensis), a subterranean rodent in the family Bathyergidae. This solitary animal is entirely fossorial and apparently communicates with its conspecifics by alternately drumming its hind legs on the burrow floor. Signal production in this species is sexually dimorphic, and mate attraction is likely mediated primarily by seismic signalling between individuals in neighboring burrows. Measurements within, and at various distances away from, natural burrows suggest that seismic signals propagate at least an order of magnitude better than auditory signals. Moreover, using a mechanical thumper which could be triggered from a tape recording of the mole-rat's seismic signals, we established that the vertically-polarized surface wave (Rayleigh wave) propagates with less attenuation than either of the two horizontally-polarized waves. Thus, we tentatively hypothesize that Rayleigh waves subserve intraspecific communication in this species.

Acoustic Stimulation↗
PubMed1992

Diversity of form in the amphibian papilla of Puerto Rican frogs.

In modern frogs, the amphibian papilla exhibits a caudal extension whose shape, relative length, and proportion of hair cells vary markedly from species to species. Tuning in the caudal extension is organized tonotopically and evidently involves the tectorium. In terms of the proportion of amphibian-papillar hair cells in the caudal extension, we report more diversity among 8 species of a single genus (Eleutherodactylus) on a single island (Puerto Rico) than has been found so far among all of the (more than 50) other modern anurans examined for this feature from around the world. These 8 Puerto Rican species have overlapping habitat and conspicuous diversity in the male advertisement call. For 7 of the 8 species, we report that the call has transient spectral components in the frequency range of the amphibian papilla, and that the proportion of caudal extension hair cells and the frequency distribution of those components are correlated. Thus one might conclude that the selective pressures that led to diversity of calls among the 8 species also led to diversity in form of the amphibian papilla.

Acoustic Stimulation↗
PubMed1992

One-tone suppression in the cochlear nerve of the gerbil.

One-tone rate suppression has been reported several times for auditory nerve fibers of mammalian and non-mammalian vertebrates. Because its properties are very similar to those of two-tone rate suppression, the possibility exists that one-tone rate suppression is the result of an interaction within the inner ear of the suppressing tonal stimulus and some ongoing extraneous acoustic stimulus. For this reason, reports of one-tone rate suppression often elicit suspicions that the investigators were not sufficiently careful in controlling leaks in their acoustic barriers or in the electrical pathways to their acoustic drivers. Recent reports of one-tone rate suppression in pigeon basilar-papillar fibers and goldfish saccular fibers were accompanied by descriptions of measures taken to avoid such leaks. In this paper, we describe one-tone rate suppression in a mammal, the Mongolian gerbil; and we demonstrate that the background spike activity being suppressed is not driven by either external sounds coming from outside the acoustic isolation test chamber or by non-stimulus electrical inputs to the acoustic driver. The suppressed background spike activity evidently arises from sources within the animal. These sources may be non-acoustic, associated with spontaneous pre- or post-synaptic ion-channel activity; or they may be acoustic sources--internal sound or vibration generators.

Acoustic Stimulation↗
PubMed1992

Modulation of cochlear nerve spike rate by cardiac activity in the gerbil.

Among primary auditory axons with characteristic frequencies (CFs) below 2500 Hz, a substantial subpopulation was found in which spike activity was driven by cardiac events. The presence of cardiac-driven activity was inferred from cycle histograms triggered on the peak of the electrocardiogram (ECG). This driven activity was either like a simple onset response (often followed by a reduction of spike activity to below background level), or as a longer lasting series of peaks and troughs. In two axons with high CFs (7 kHz and 12.5 kHz), cardiac-driven suppression was observed. Recordings made by a probe microphone revealed the presence of heart-related sound in the external ear canal. The onset of that sound coincided with the onset of cardiac-driven spike activity (and suppression).

Action Potentials↗
PubMed1991

Vestibular afferent responses to microrotational stimuli.

Intracellular microelectrode recording/labelling techniques were used to investigate vestibular afferent responses in the bullfrog, to very small amplitude (less than 0.5 degree p-p) sinusoidal rotations in the vertical plane over the frequency range of 0.063-4 Hz. The axis of rotation was congruent with the axis of the anterior semicircular canal. Robust responses to peak accelerations as low as 0.031 degree/S2 were obtained from units subsequently traced to either the central portion of the anterior canal crista or the striolar region of the utricle. All of these microrotationally sensitive afferent neurons had irregular resting discharge rates and the majority had transfer ratios (relative to rotational velocity) of 1-40 spikes/s per degree/s. Individual utricular afferent velocity transfer ratios were nearly constant over the frequency range of 0.125-4 Hz. Canal units generally displayed decreasing response transfer ratios as stimulus frequencies increased. These findings indicate that although utricular striolar and central crista afferent velocity transfer ratios to microrotations were very similar, utricular striolar afferent neurons were more faithful sensors of very small amplitude rotational velocity in the vertical plane.

Acoustic Stimulation↗
PubMed1991

Seismic and auditory tuning curves from bullfrog saccular and amphibian papillar axons.

We present seismic and auditory frequency tuning curves of individual bullfrog, Rana catesbeiana, saccular and amphibian papilla axons that responded to both seismic and auditory stimuli. In this study we found: 1) most saccular axons respond well to auditory stimuli with moderate signal strength (50-70 dB SPL) as well as to seismic stimuli; 2) most amphibian papilla axons respond well to seismic stimuli as well as to auditory stimuli, and their seismic sensitivities are comparable to those of saccular axons (responding to sinusoidal stimuli with peak accelerations in the range 0.001 to 0.1 cm/S2); 3) the responses to both seismic and auditory stimuli from both saccule and amphibian papilla are tuned, i.e. the strength of the response varies with the frequency of the stimulus; and this tuning is clearly not the result of second order resonance; 4) in individual axons the tuning properties for seismic stimuli often are not the same as those for auditory stimuli, a fact that may provide clues about how the stimulus signal energy is transferred to the hair cells in each case.

Acoustic Stimulation↗
PubMed1991

Lymphoma of the lung: CT findings in 31 patients.

Lymphomatous involvement of the lungs is often a difficult clinical and radiologic diagnosis to make, yet is often critical in determining treatment. To better define the CT appearance of pulmonary lymphoma, we undertook a retrospective review of 31 patients with recurrent or secondary non-Hodgkin lymphoma or Hodgkin disease and lung parenchymal involvement on CT scans. Diagnoses were confirmed either by lung biopsy or by disease regression or progression with appropriate therapy. The CT scans were evaluated for the following findings: (1) nodules less than 1 cm, (2) a mass or masslike consolidation greater than 1 cm with or without cavitations or bronchograms, (3) alveolar or interstitial infiltrates, (4) masses of pleural origin, (5) peribronchial or perivascular thickening with or without atelectasis, (6) pleural effusions, and (7) hilar or mediastinal lymphadenopathy. The most common CT finding was a mass or masslike consolidation larger than 1 cm, seen in 21 (68%) of the 31 patients. The second most common finding was nodules less than 1 cm (19 patients). Sixty-eight percent of patients had three or more of the CT abnormalities. Lymphoma involving the lung parenchyma causes a variety of CT findings, the most common being a mass or masslike consolidation. Two-thirds of patients have more than one type of CT finding simultaneously.

Adult↗
PubMed1990

Hair cell tufts and afferent innervation of the bullfrog crista ampullaris.

Within the bullfrog semicircular canal crista, hair cell tuft types were defined and mapped with the aid of scanning electron microscopy. Intracellular recording and Lucifer Yellow labeling techniques were used to study afferent responses and arborization patterns. Dye-filled planar afferent axons had mean distal axonal diameters of 1.6-4.9 microns, highly branched arbors, and contacted 11-24 hair cells. Dye-filled isthmus afferent axons had mean distal axonal diameters of 1.8-7.9 microns, with either small or large field arbors contacting 4-9 or 25-31 hair cells. The estimated mean number of contacts per innervated hair cell was 2.2 for planar and 1.3 for isthmus afferent neurons. Data on evoked afferent responses were available only for isthmus units that were observed to respond to our microrotational stimuli (less than 3 degrees/s peak rotational velocity). Of 21 such afferent neurons, 8 were successfully dye-filled. Within this small sample, high-gain units had large field arbors and lower-gain units had small field arbors. The sensitivity of each afferent neuron was analyzed in terms of noise equivalent input (NEI), the stimulus amplitude for which the afferent response amplitude is just equivalent to the RMS deviation of the instantaneous spike rate. NEI for isthmus units varied from 0.63 to 8.2 degrees/s; the mean was 3.2 degrees/s.

Acoustic Stimulation↗
PubMed1990

Temperature effects on auditory nerve fiber response in the American bullfrog.

Single fiber recordings were made from auditory nerve fibers of the American bullfrog (Rana catesbeiana). As temperature was raised: (1) Best frequencies of fibers from the amphibian papilla (N = 15) increased. Below 600 Hz best frequency changes up to 0.06 oct/degrees C were found; above 600 Hz changes were less than 0.03 oct/degrees C. In the basilar papilla (N = 4) no significant increase of best frequency was found. (2) Spike rates in response to fixed-RMS-amplitude stimuli increased considerably: Q10 of spike rate ranged from 5 to 10. (3) Spontaneous activity, found in basilar papilla fibers, increased with average Q10 = 1.6 (+/- 0.3). (4) A conspicuous change of tuning quality factor Q10 dB was only observed in two fibers, that were taken to low temperatures (less than 16 degrees C). (5) the nearly linear frequency vs. phase relation in amphibian papilla shifts to higher frequency (along with shift of best frequency), while its average slope remains nearly unchanged.

Action Potentials↗
PubMed1989

Transient responses to tone bursts.

Investigating theoretical conditions under which linearly-operating tuned structures produce click-like transient responses to onsets and offsets of trapezoidal tone bursts, we come to the following conclusions: (1) each of the four corners of the trapezoidal tone burst is capable of eliciting such a response; (2) the amplitude of the response and its dependence on the frequency of the modulated tone both depend on the phase of the modulated sinusoid at the time a corner occurs; (3) such responses will arise in structures having sufficiently steep band edges, provided that the frequency of the modulated tone is well outside the pass band of the structure--for a corner in cosine phase, the sustained slope of the low-frequency band edge must be greater than zero and that of the high-frequency band edge must be greater than 12 dB/Oct, for a corner in sine phase the sustained slope of the low-frequency band edge must be greater than 6 dB/Oct and that of the high-frequency band edge must be greater than 18 dB/Oct; (4) they will not arise in response to tone bursts whose frequencies fall within the pass band of the structure; (5) nor will they arise in response to a trapezoidal tone burst of any frequency applied to structures (such as simple microphones or drivers) following second-order dynamics and having both spectral zeros at infinity. We present theoretically derived relationships between the amplitude of transient responses and the tone-burst frequency, not only for the corners of trapezoidal tone bursts, but also for tone bursts of more general shapes. We conclude that, owing to its extraordinarily steep high-frequency rolloff, the filter associated with each cochlear axon is well suited to extracting temporal information from onset or offset singularities in modulated tones whose frequencies are above the characteristic frequency of the filter. Applying the theory to observed onset and offset responses to high-intensity tone bursts in auditory afferents of the Mongolian gerbil, we conclude that some of the responses we observed must have been sculpted in part by cochlear nonlinearities.

Acoustic Stimulation↗
PubMed1989

Cochlear nerve responses to waveform singularities and envelope corners.

One way that discrete acoustic events may be signaled to the central nervous system is through spike synchrony over a subpopulation of cochlear axons. Each of the four corners of a trapezoidally modulated tone burst is such an event. Ordinarily, each corner comprises both an abrupt change in envelope slope and a singularity in the modulated waveform. In this study, in addition to stimuli of this sort, we employed a stimulus waveform in which a corner occurred without a waveform singularity. We obtained masker tuning curves for the CAPs corresponding to both kinds of corners and single-unit responses to both kinds of corners. The results suggest that the subpopulation of cochlear axons excited by the singularity component of a corner is distinct from that excited by the abrupt change in envelope slope.

Acoustic Stimulation↗
PubMed1989

Studies with spike initiators: linearization by noise allows continuous signal modulation in neural networks.

Engineers and neuroscientists generally believe that noise is something to be avoided in information systems. In this paper we show that noise, in fact, can be an important element in the translation of neuronal generator potentials (summed inputs) to neuronal spike trains (outputs), creating or expanding a range of amplitudes over which the spike rate is proportional to the generator potential amplitude. Noise converts the basically nonlinear operation of a spike initiator into a nearly linear modulation process. This linearization effect of noise is examined in a simple intuitive model of a static threshold and in a more realistic computer simulation of a spike initiator based on the Hodgkin-Huxley (HH) model. The results are qualitatively similar; in each case larger noise amplitude results in a larger range of nearly-linear modulation. The computer simulation of the HH model with noise shows linear and nonlinear features that we earlier had observed in spike data obtained from the VIIIth nerve of the bullfrog. This suggests that these features can be explained in terms of spike initiator properties, and it also suggests that the HH model may be useful for representing basic spike initiator properties in vertebrates.

Animals↗
PubMed1988

Tuning in the bullfrog ear.

When electrical resonances were observed in acoustic sensory cells of lower vertebrates, the hearing research community was presented with the exciting possibility that tuning in the ears of those animals might be explained directly in terms of familiar molecular devices. It is reported here that in the frog sacculus, where electrical resonances have been observed in isolated hair cells, the effects of those resonances are completely obscured in the tuning properties of the sacculus in the intact ear. This observation has important implications not only for students of the ear, but for reductionist biologists in general. All of the dynamic properties of a system of connected, bidirectional processes are consequences of all of those processes at once; in such a system, the properties of an experimentally isolated subsystem may be totally obscured in the operation of the system as a whole.

Action Potentials↗
PubMed1988

Offset AP masker tuning curve and the FFT of the stimulus.

In previous experiments, it was noted that a cochlear compound action potential (CAP) can be produced by the offset of a tone, provided that the amplitude of the tone is modulated by a trapezoid with slopes that are typically much steeper than required to produce onset responses. Subsequently, such trapezoidal tone bursts with steep slopes were used as probe stimuli in simultaneous and forward masking experiments that were designed to evaluate the tuning characteristics of these offset CAPs. Masker tuning curves (MTCs) were generated by plotting the masker frequency necessary to reduce the amplitude of the offset CAP by 50%. Simultaneous masking of the offset CAP generated a W-shaped MTC, with two sharply tuned tips and one sharply tuned peak. Forward masking generated a sharply tuned V-shaped offset MTC. By contrast, for onset CAPs, both simultaneous and forward masking generated V-shaped MTCs. The very steep stimulus slopes required to produce an offset CAP are likely to generate much more acoustic splatter than the more gradual slopes required to produce an onset CAP, and this may be related to the different shapes of the onset and offset simultaneous MTCs. To explore this possibility, the relationship of the spectral characteristics (determined by fast Fourier transform, or FFT) to the shape of the MTC was studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Speculations about noise and the evolution of vertebrate hearing.

Two of the most conspicuous and celebrated properties of human hearing--the abilities to discriminate pitch and to localize sound sources, may have been secondary derivations to which the ear was preadapted by having evolved in the inevitable presence of noise.

Adaptation, Physiological↗
PubMed1986

Correspondences between afferent innervation patterns and response dynamics in the bullfrog utricle and lagena.

Otoconial afferents in the bullfrog were characterized as gravity or vibratory sensitive by their resting activity and their responses to head tilt and vibration. The responses of gravity afferents to head tilt were tonic, phasic-tonic, or phasic. A few afferents, termed vibratory/gravity afferents, had gravity as well as vibratory sensitivity. Functionally identified otoconial afferents were injected with Lucifer Yellow and subsequently traced to their peripheral arborizations. Morphological maps, previously constructed with the scanning electron microscope, were used to identify microstructural features of the sensory maculae associated with the peripheral arborizations of dye-filled afferents. The utricular and lagenar macula each is composed of a specialized central band surrounded by a peripheral field. The central bands are composed of densely packed medial rows and more sparsely packed lateral rows of hair cells. Hair cells exhibit a variety of surface topographies which correspond with their macular location. The response dynamics of afferents in the utricle and lagena correspond with the macular locations of their peripheral arborizations. Tonic afferents were traced to hair cells in the peripheral field. Phasic-tonic and phasic afferents innervated hair cells in the lateral rows of the central band, the former innervating hair cells at the edges of the central band and the latter innervating hair cells located more medially. Afferents with vibratory sensitivity were traced to hair cells in the medial rows of the lagenar central band. The response dynamics of afferents corresponded with the surface topography of their innervated hair cells. Tonic and phasic-tonic gravity afferents innervated hair cells with stereociliary arrays markedly shorter than their kinocilium (Lewis and Li types B and C) while phasic gravity and vibratory afferents innervated hair cells with stereociliary arrays nearly equal to their kinocilium (Lewis and Li types E and F). Vibratory sensitivity was uniquely associated with hair cells possessing bulbed kinocilium (Lewis and Li type E) while afferents sensitive to both gravity and vibration innervated hair cells from both of the above groups. We argue that afferent response dynamics are determined, at least in part, at the level of the sensory hair bundle and that morphological variations of the kinocilium and the otoconial membrane are dictated by specialization of sensitivity. We propose that morphological variations of the kinocilium reflect variations in its viscoelastic properties and that these properties determine the nature of the mechanical couple between the stereociliary array and the otoconial membrane.

Acoustic Maculae↗