Stuttering induced by theophylline.

We retrospectively evaluated three fluent asthmatic children who developed speech dysfluency following administration of theophylline. The dysfluency ceased in all three, following discontinuation of the medication. The medication was re-instituted in two patients, prompting return of dysfluency. It is unknown whether the patients had characteristics of "acquired stuttering" or "developmental stuttering." We urge appropriate testing should this complication again occur. This might then provide pharmacologic information regarding stuttering.

A model of the phonatory response time of stutterers and fluent speakers to frequency-modulated tones.

Stutterers and fluent speakers tracked frequency-modulated tones by humming. The response time (RT) to the first corrective change in fundamental frequency in response to linear ramps of increasing and decreasing frequency was measured. The results demonstrate that RT is a function of the stimulus ramp velocity. A model of this dependency is provided which consists of parameters of threshold frequency and a fixed time delay. The estimated threshold frequency for the fluent speakers is 2.029 Hz with 95% confidence interval: (1.70 Hz, 2.35 Hz) whereas that of the stutterers is 3.937 Hz (3.28 Hz, 4.60 Hz). These threshold frequencies are significantly different (p < 0.0001). This implies that stutterers are slower to respond to changes in frequency than are fluent speakers. The fixed time delays for the two groups are not significantly different. This means that it is possible for the stutterers to respond as fast as the fluent speakers (i.e., their basic "reflexes" are the same); however, they spend more time in the detection of the change in a tracking signal. This supports the model of the stuttered event as being triggered by an instability in a multiloop speech motor control system.

Neurologic aspects of spasmodic dysphonia.

We discuss the etiology of 100 spasmodic dysphonia patients. Seventy-one patients had underlying essential tremor, 25 had Meige's syndrome, 12 were hypothyroid, and 27 had either a functional disturbance or focal dystonia. Six patients had intermittent breathy dysphonia. A large corpus of spasmodic dysphonia patients have organic neurolaryngeal disease.

Comments on "Two-mass models of the vocal cords for natural sounding voice synthesis".

Koizumi et al. [J. Acoust. Soc. Am. 82, 1179-1192 (1987)] have proposed a way to incorporate mucosal waves into previous two-mass mechanical models of the vocal folds. This was accomplished by allowing the mass of the masses to vary with time. The equations of motion Koizumi et al. used to mathematically describe this model neglected terms from the time rate of change of momentum of Newton's second law. In this letter, approximations of the magnitude of this term indicate that it must not be neglected.

Interval coding and band-pass filtering at oculomotor synapses in crayfish.

1. Crayfish exhibit steady-state compensatory eyestalk rotations in response to rotations of the organism or the visual surround. For stimuli in the vertical planes (pitch or roll) the visual reflexes are mediated by identified visual interneurons [sustaining fibers (SFs)], which synapse on identified oculomotor neurons (Mns) (18). 2. The optimal visual stimulus is broad-field intense illumination (simulated skylight) distributed over the dorsal half of the cornea. These stimuli are also optimal for eliciting a regular pacing discharge in SFs with dorsal receptive fields (17). Since a unique discharge pattern is associated with the reflex stimulus, we proposed that the pacing discharge interval encodes the stimulus condition and is optimal for driving the motoneuron discharge. 3. The cross-correlation of SF and Mn impulse trains exhibit large peaks (or troughs) at short latencies associated with strong excitatory (or inhibitory) interactions and "secondary effects" at longer delays associated with the periodicity of the Mn impulse train. The secondary peaks and troughs indicate delayed periods of elevated or depressed Mn excitability synchronized to the reference train (SF) events. From the structure of the cross-correlograms and the motoneuron autocorrelograms we predicted that the spike-to-spike synaptic throughput should be differentially sensitive to the various classes of SF interspike intervals. 4. The hypotheses were tested with logical-correlation functions that directly measure the relative synaptic efficacy of several classes of SF intervals during a continuous train at constant mean rate. The results indicate that the SF-to-Mn excitatory synapse is maximally driven by SF impulses separated by approximately 85 ms. These events are about 2.5 times as effective as the impulses associated with short intervals (less than 20 ms) and 1.4 times as effective as the spikes of long intervals (250 ms). The optimal interval in the various preparations is highly to correlated to the period of the Mn discharge and the SF modal interspike interval. Inhibitory synapses are also differentially sensitive to the SF interspike intervals, but they exhibit summation rather than depression in response to short interspike intervals. 5. These results are generally consistent with previously formulated relationships (39), which govern the synaptic modulation of pacemakers and may apply to any synaptic interaction in which the postsynaptic neuron exhibits a regular discharge. 6. Combinations of long and short intervals with the same mean rate as the optimal interval are not as effective in driving the SF-to-Mn synapse.(ABSTRACT TRUNCATED AT 400 WORDS)

Linear integration of convergent visual inputs in an oculomotor reflex pathway.

The functional connectivity between identified visual interneurons [sustaining fibers (SF)] and oculomotor neurons was assessed by simultaneous recording and cross-correlation analysis. A small group of SFs exhibit excitatory functional connections to an identified tonic oculomotor neuron. The excitatory interactions are found exclusively between SFs and oculomotor neurons with similar and/or overlapping excitatory receptive fields. A second group of SFs exhibit inhibitory connections to motor neurons. The excitatory receptive fields of these SFs correspond to the inhibitory receptive fields of the motor neurons. The collective action of the SFs is sufficient to produce all of the steady-state visual behavior of the motor neurons including the increment in firing rate elicited by illumination, unique features of the motor neuron receptive field, and differential sensitivity to blue light and polarized light. Pairs of SFs that converge on the same motor neuron sum their effects linearly. Thus the joint interaction of two SFs on a motor neuron is equal to the sum of the two postsynaptic effects taken separately. Coactivation of excitatory and inhibitory SF inputs to a motor neuron results in a partial cancellation of their postsynaptic effects on the motor neuron's firing rate. The antagonistic interactions protect the system from perturbations by stray light, visual adaptation, and variations in the central excited state. The ensemble information code, at the SF level of the optomotor pathway, is a set of differentially weighted mean firing rates. The weightings reflect differences in the strengths of the several SF-to- motor neuron interactions. One consequence of these differences is a selective weighting of the effects of illumination (in different regions of visual space) on the compensatory eye reflex.

Sustained, synchronous oscillations in discharge of sustaining fibers of crayfish optic nerve.

1. The regularity of the sustaining fiber (SF) steady-state discharge increases with the intensity of a uniform field of illumination. 2. In a high levels of illumination SFs exhibit a highly periodic or rhythmically bursting steady-state discharge. 3. The period of the burst cycle is independent of the light intensity and the mean firing rate. 4. Multimodal interspike-interval histograms in which successive modes decline exponentially suggest that the discharge arises from a regular input. 5. In conditions of uniform illumination, the regular input must be common to all or several SFs since the period of the burst cycle of simultaneously monitored SFs are the same and cross-correlations indicate that the SFs burst in approximate synchrony. 6. It is proposed that the common, regular input is a network of presynaptic elements exhibiting recurrent lateral inhibition. Evidence supporting this hypothesis is that following a brief light pulse to the inhibitory surround, SFs exhibit cycles of silence and bursting, phase-locked to the stimulus but with a period equal to the steady-state burst-cycle period. 7. Furthermore, lateral inhibitory influences are common to several or all SFs as indicated by the close similarity in response time course of two SFs subjected to a common inhibitory stimulus. 8. The response of the lateral pathways to sinusoidally modulated illumination is highly selective to frequencies near the burst-repetition rate. The excitatory pathways exhibit frequency modulation or entrainment over a wide range of input frequencies. 9. The intersustaining burst cycle phase is under partial visual stimulus control (position and intensity) and the possibility of phase coding in the SF ensemble is discussed.

Modeling the carotid sinus baroreceptor.

A mathematical model that describes the relationship between sinus pressure and nerve discharge frequency of the carotid sinus baroreceptor is presented. It is partly based upon the single-fiber data obtained by Clarke from the sinus nerve of a dog. The model takes into account what is currently known about the physiology of the baroreceptor. It consists of two nonlinear ordinary differential equations and eight free parameters. With one set of values for these eight parameters, the model reproduces well the experimental results reported by Clarke for positive ramp pressure inputs. Only three parameters needed to be adjusted in order to fit the dynamic data. The remaining five were obtained from static and steady-state data.