bluuebunny/crossref_metadata_2025 huggingface dataset:
Topography of binaural organization in primary auditory cortex of the cat: effects of changing interaural intensity
Authors: Reale R. A. , Kettner R. E.
Published: December 2017

Responses from neuron clusters were used to derive binaural and aural dominance maps within the 5- to 30-kHz frequency representation of the primary auditory cortical (AI) field in the barbiturate-anesthetized cat. Tone burst stimuli were presented dichotically using a calibrated and sealed acoustic delivery system to parametrically vary interaural intensity difference (IID). Neuron cluster responses were divided into three binaural interaction classes using audiovisual criteria: summation (56%), suppression (25%), and mixed (17%). Neurons in the summation and suppression classes demonstrated a single type of binaural interaction, regardless of intensity manipulations. Neurons in the mixed binaural class demonstrated summation responses when dichotic tonal intensities were near their threshold levels and the IID was small, but suppression responses when the IID was increased. The relative proportions of the three binaural interaction classes changed with distance along the dorsal-to-ventral isofrequency dimension. Nearly equal proportions of each class were observed at the ventral end of field AI, whereas quite different proportions of each class were seen at the dorsal extreme of the field. The average frequency of occurrence of the mixed binaural class increased nearly monotonically with increasing distance from the dorsal end of field AI. The majority of mapped AI loci exhibited a contralateral aural dominance (65%) with equidominance (25%), ipsilateral aural dominance (6%), and predominantly binaural (4%) classes accounting for the remainder. Average topographic distributions of aural dominance suggested that the ventral end of field AI consisted almost exclusively of the contralateral dominance class, whereas more equal proportions of the four classes were observed near the dorsal extreme of the field. The highest average proportions of ipsilateral aural dominance and predominantly binaural classes were found in the dorsal half of field AI. Single neurons, isolated at cortical loci assigned to the mixed binaural class during the mapping of neuron clusters, were shown to demonstrate both summation and suppression responses. Quantitative measurements relating either discharge rate or response latency to changes in the IID appeared to distinguish these cells from other single neurons studied. Typically, the probability of discharge was initially increased and subsequently decreased by progressive changes in IID that increased the intensity of the ipsilateral tone relative to the contralateral tone. The initial changes in IID characteristically shortened the latent period to the binaural response while subsequent increments in IID produced a more comp
Ventroposterior thalamic regions projecting to cytoarchitectonic areas 3a and 3b in the cat
Authors: Dykes R. W. , Herron P. , Lin C. S.
Published: December 2017

The adequate stimulus and body site that excited neurons in cat cortical somatosensory areas 3a and 3b were recorded using low-impedance tungsten microelectrodes. Horizontal penetrations provided a good correlation between the electrophysiological and cytoarchitectonic data. Responses best driven by cutaneous stimuli were replaced with responses driven by manipulation of deep tissue at, or very near, the border between areas 3a and 3b. Following functional identification of these areas horseradish peroxidase was injected into one of them. Injections into area 3a labeled neurons in a rostral and dorsal cap of the ventroposterior thalamus. It was suggested that this region is a distinct nucleus termed the ventroposterior oralis nucleus (VPO). Injections into the forelimb portion of area 3b labeled neurons in the ventroposterior lateral nucleus (VPL). With both vertical and horizontal microelectrode trajectories through the ventroposterior thalamic nuclei, inputs from deep structures presumed to be muscles were consistently located in the VPO nucleus and cutaneous inputs activated neurons in the VPL. The existence of several functionally-distinct subdivisions within the somatosensory nuclei of the thalamus supports the hypothesis of parallel processing and relay of somatosensory information at this level of the pathway.
Differential effects of tetanus toxin on inhibitory and excitatory synaptic transmission in mammalian spinal cord neurons in culture: a presynaptic locus of action for tetanus toxin
Authors: Bergey G. K. , Bigalke H. , Nelson P. G.
Published: December 2017

Tetanus toxin reduces monosynaptic inhibitory and excitatory synaptic transmission in mouse spinal cord neurons in culture. Inhibitory transmission is preferentially reduced by the toxin; however, excitatory transmission is also ultimately reduced and blocked by the concentrations of toxin used in these studies. Recordings from monosynaptically connected cell pairs revealed a marked diminution in amplitude of evoked monosynaptic inhibitory postsynaptic potentials coincident with the onset of convulsant action at a time when evoked monosynaptic EPSPs were relatively unaffected. Increased polysynaptic excitation occurred as a result of diminished inhibition. This supports the reduction of inhibition as an important mechanism in the convulsant action of tetanus toxin. Quantal analysis of the late effects of tetanus toxin on the monosynaptic excitatory postsynaptic potential revealed a reduction in quantal number with no reduction in quantal size, thus demonstrating a presynaptic locus of action for the toxin on spinal neurons.
Human motor-unit recruitment during isometric contractions and repeated dynamic movements
Authors: Thomas C. K. , Ross B. H. , Calancie B.
Published: December 2017

Spike-triggered averaging was used to determine the twitch tensions and contraction times of motor units in the abductor pollicis brevis muscle of two human subjects for two directions of isometric contraction: abduction and opposition of the thumb. During isometric contractions in each direction, the threshold force for motor-unit recruitment and the twitch amplitude were correlated linearly. These data suggested that an orderly pattern of recruitment, according to increasing twitch size, describes the function of the human abductor pollicis brevis muscle for each contraction direction. Rank order of motor-unit recruitment in each isometric contraction direction was correlated, but not identical. All units contributed tension in each direction of contraction, so no clear evidence was found for task-dependent motor units. In two subjects, motor-unit recruitment order during isometric contraction of the first dorsal interosseous and abductor pollicis brevis muscles was then compared with that of motor-unit pairs in both muscles during repetitive dynamic movements. Recruitment according to increasing twitch size was largely preserved during the repetitive opening and closing of scissors. The recruitment reversals that were observed were usually between pairs of units with similar thresholds.
Functional involvement of catecholamines in reward-related neuronal activity of the monkey amygdala
Authors: Nakano Y. , Lenard L. , Oomura Y. , Nishino H. , Aou S. , Yamamoto T.
Published: December 2017

Neuronal activity was studied in the behaving active monkey to elucidate the functional significance of catecholamines (CA) in the amygdala during reward-related behavior, and the effects of noradrenaline (NA), dopamine (DA), and their antagonists, electrophoretically applied, were examined using multibarreled electrode techniques. The operant food intake task had four phases: 1) cue light on to signal the start of bar pressing, 2) execution of high fixed-ratio bar pressing (FR 20), 3) short cue tone triggered by the last bar press to signal the presentation of food, and 4) ingestion, reward. More than half of the 292 cells tested (198, 68%) changed activity during the task. Most changes occurred during the bar press and/or reward periods (164/198, 83%), the former affecting neuronal activity more (127/198, 64%) than the latter (70/198, 35%). Phasic responses to the cue light and cue tone were observed in 62 cells (31%) and 19 cells (10%), respectively. The effects of NA and DA were studied in 199 and 177 cells, respectively. Of these, 90 cells (46%) responded to NA, 87 (97%) with a decrease of firing, and only 3 (3%) with an increase, whereas 40 (26%) responded to DA by increasing (28 cells, 70%) or decreasing (18 cells, 30%) activity. The inhibitory effect of NA was blocked by alpha- and/or beta-adrenoceptive antagonists. Task-related activity changes occurred significantly more often among DA sensitive cells than among DA insensitive cells. CA sensitivity and task-related neuronal activity were functionally correlated only in the reward period. Activity of NA sensitive cells decreased in this period more frequently than insensitive cells, and DA sensitive cells increased more often than insensitive cells. Application of a beta-adrenoceptive antagonist or a DA antagonist attenuated the activity changes during the reward period. Application of a alpha-adrenoceptive antagonist had no effect on the reward-related neuronal activity changes. When grouped according to recording site, centromedial cells had a significantly higher occurrence of task-related activity changes than those in the basolateral parts of the amygdala. The bar-press responsive and reward-related cells, the firing of which decreased, were found more often in the centromedial than in the basolateral division, although the numbers of cells that responded to sensory cues were not different in the two parts. Catecholaminergic involvement in the task-related activity changes was also different.(ABSTRACT TRUNCATED AT 400 WORDS)
Cat hindlimb motoneurons during locomotion. II. Normal activity patterns
Authors: Hoffer J. A. , Sugano N. , Loeb G. E. , Marks W. B. , O'Donovan M. J. , Pratt C. A.
Published: December 2017

Activity patterns were recorded from 51 motoneurons in the fifth lumbar ventral root of cats walking on a motorized treadmill at a range of speeds between 0.1 and 1.3 m/s. The muscle of destination of recorded motoneurons was identified by spike-triggered averaging of EMG recordings from each of the anterior thigh muscles. Forty-three motoneurons projected to one of the quadriceps (vastus medialis, vastus lateralis, vastus intermedius, or rectus femoris) or sartorius (anterior or medial) muscles of the anterior thigh. Anterior thigh motoneurons always discharged a single burst of action potentials per step cycle, even in multifunctional muscles (e.g., sartorius anterior) that exhibited more than one burst of EMG activity per step cycle. The instantaneous firing rates of most motoneurons were lowest upon recruitment and increased progressively during a burst, as long as the EMG was still increasing. Firing rates peaked midway through each burst and tended to decline toward the end of the burst. The initial, mean, and peak firing rates of single motoneurons typically increased for faster walking speeds. At any given walking speed, early recruited motoneurons typically reached higher firing rates than late recruited motoneurons. In contrast to decerebrated cats, initial doublets at the beginning of bursts were seen only rarely. In the 4/51 motoneurons that showed initial doublets, both the instantaneous frequency of the doublet and the probability of starting a burst with a doublet decreased for faster walking speeds. The modulations in firing rate of every motoneuron were found to be closely correlated to the smoothed electromyogram of its target muscle. For 32 identified motoneurons, the unit's instantaneous frequencygram was scaled linearly by computer to the rectified smoothed EMG recorded from each of the anterior thigh muscles. The covariance between unitary frequencygram and muscle EMG was computed for each muscle. Typically, the EMG profile of the target muscle accounted for 0.88-0.96 of the variance in unitary firing rate. The EMG profiles of the other anterior thigh muscles, when tested in the same way, usually accounted only for a significantly smaller fraction of the variance. Brief amplitude fluctuations observed in the EMG envelopes were usually also reflected in the individual motoneuron frequencygrams. To further demonstrate the relationship between unitary frequencygrams and EMG, EMG envelopes recorded during walking were used as templates to generate depolarizing currents that were applied intracellularly to lumbar motoneurons in an acute spinal preparation.(ABSTRACT TRUNCATED AT 400 WORDS)
Cat hindlimb motoneurons during locomotion. III. Functional segregation in sartorius
Authors: Hoffer J. A. , Loeb G. E. , Sugano N. , Marks W. B. , O'Donovan M. J. , Pratt C. A.
Published: December 2017

Cat sartorius has two distinct anatomical portions, anterior (SA-a) and medial (SA-m). SA-a acts to extend the knee and also to flex the hip. SA-m acts to flex both the knee and the hip. The objective of this study was to investigate how a "single motoneuron pool" is used to control at least three separate functions mediated by the two anatomical portions of one muscle. Discharge patterns of single motoneurons projecting to the sartorius muscle were recorded using floating microelectrodes implanted in the L5 ventral root of cats. The electromyographic activity generated by the anterior and medial portions of sartorius was recorded with chronically implanted electrodes. The muscle portion innervated by each motoneuron was determined by spike-triggered averaging of the EMGs during walking on a motorized treadmill. During normal locomotion, SA-a exhibited two bursts of EMG activity per step cycle, one during the stance phase and one during the late swing phase. In contrast, every recorded motoneuron projecting to SA-a discharged a single burst of action potentials per step cycle. Some SA-a motoneurons discharged only during the stance phase, whereas other motoneurons discharged only during the late swing phase. In all cases, the instantaneous frequencygram of the motoneuron was well fit by the rectified smoothed EMG envelope generated by SA-a during the appropriate phase of the step cycle. During normal locomotion, SA-m exhibited a single burst of EMG activity per step cycle, during the swing phase. The temporal characteristics of the EMG bursts recorded from SA-m differed from the swing-phase EMG bursts generated by SA-a.(ABSTRACT TRUNCATED AT 250 WORDS)
Horizontal segregation of color information in the middle layers of foveal striate cortex
Authors: Dow B. M. , Vautin R. G.
Published: December 2017

The present study examines the chromatic organization of foveal striate cortex in the awake monkey by means of a series of microelectrode penetrations made as perpendicular as possible to the layers. The study includes 79 penetrations and 261 cells, of which 218 were tested systematically for color selectivity. Detailed analyses are conducted on a subset of 41 penetrations, which included 164 color-tested cells, an average of four cells per penetration. The penetrations were divided into two major categories on the basis of orientation selectivity testing. One group of penetrations contained at least one nonoriented cell in the first 600 microns of microelectrode trajectory (upper layers), whereas the other group of penetrations contained only oriented cells in the first 600 microns of microelectrode trajectory. The two groups were called N (nonoriented) and O (oriented), respectively. Analysis of the color properties of cells in N and O penetrations revealed that middle layer cells in N penetrations showed poor responses to white light, and color preferences for endspectral wavelengths, i.e., red or blue. Middle layer cells in O penetrations, by contrast, responded well to white light and to midspectral wavelengths. There were two subgroups of N penetrations, characterized by predominantly red (NR) or blue (NB) sensitivity in the middle layers. O penetrations could likewise be divided up into three subgroups (OG, OY, OW), characterized, respectively, by predominant sensitivity to greenish wavelengths (490-540 nm), yellowish wavelengths (550–600 nm), or white (i.e., all colors). Despite the identification of five subgroups, similarities between NR and OY, between NB and OG, and between OY and OW subgroups might be consistent with a continuum. The middle layers of N penetrations contained a unique class of cells with excitatory responses restricted to the two spectral ends, endspectral double-peak cells. A model is proposed for the color organization of layer 4 in foveal striate cortex, with red and blue zones in register with alternate cytochrome oxidase “blobs” of layers 2 and 3, white zones in register with interblob centers, and yellow and green zones in between.
Motoneuron properties during motor inhibition produced by microinjection of carbachol into the pontine reticular formation of the decerebrate cat
Authors: Morales F. R. , Engelhardt J. K. , Soja P. J. , Pereda A. E. , Chase M. H.
Published: December 2017

It is well established that cholinergic agonists, when injected into the pontine reticular formation in cats, produce a generalized suppression of motor activity (1, 3, 6, 14, 18, 27, 33, 50). The responsible neuronal mechanisms were explored by measuring ventral root activity, the amplitude of the Ia-monosynaptic reflex, and the basic electrophysiological properties of hindlimb motoneurons before and after carbachol was microinjected into the pontine reticular formation of decerebrate cats. Intrapontine microinjections of carbachol (0.25-1.0 microliter, 16 mg/ml) resulted in the tonic suppression of ventral root activity and a decrease in the amplitude of the Ia-monosynaptic reflex. An analysis of intracellular records from lumbar motoneurons during the suppression of motor activity induced by carbachol revealed a considerable decrease in input resistance and membrane time constant as well as a reduction in motoneuron excitability, as evidenced by a nearly twofold increase in rheobase. Discrete inhibitory postsynaptic potentials were also observed following carbachol administration. The changes in motoneuron properties (rheobase, input resistance, and membrane time constant), as well as the development of discrete inhibitory postsynaptic potentials, indicate that spinal cord motoneurons were postsynaptically inhibited following the pontine administration of carbachol. In addition, the inhibitory processes that arose after carbachol administration in the decerebrate cat were remarkably similar to those that are present during active sleep in the chronic cat. These findings suggest that the microinjection of carbachol into the pontine reticular formation activates the same brain stem-spinal cord system that is responsible for the postsynaptic inhibition of alpha-motoneurons that occurs during active sleep.
Response properties of area 17 neurons in cats reared in stroboscopic illumination
Authors: Cremieux J. , Orban G. A. , Duysens J. , Amblard B.
Published: December 2017

The response properties of 196 area 17 cells were studied qualitatively in seven cats reared from birth in a stroboscopically illuminated environment (frequency, 2/s; duration, 200 microseconds). Quantitative testing with the multihistogram technique was carried out in 115 cells. As control population, 453 neurons recorded in area 17 of the normal adult cat and tested qualitatively (of which 301 neurons were tested quantitatively) were available. In area 17 of strobe-reared cats, a number of spatial characteristics of receptive fields investigated with hand-held stimuli were found to be abnormal. There was a strong reduction in the encounter frequency both of end-stopped cells and of binocularly driven cells in the strobe-reared cats. Central receptive fields in strobe-reared cats were wider than in normal cats, but the increase in receptive-field width with eccentricity was still observed. More cells than in normal cats showed either no selectivity or only a weak bias for stimulus orientation, but the orientation tuning of orientation-selective cells was similar in strobe-reared and normal cats. Quantitative testing revealed that the velocity preference of cells in area 17 subserving central vision was different in strobe-reared cats from that of normal cats, due to a reduction in the encounter frequency of cells showing a preference for low velocities. There was no difference in velocity preference between strobe-reared and normal cats in the parts of area 17 that subserve peripheral vision, the proportion of neurons responding to fast velocities showing a similar increase in both groups of animals. Fewer cells were direction selective in strobe-reared cats than in normal cats. Most of the remaining direction-selective cells had peripheral receptive fields and the synergism between leaving an OFF subregion and entering an ON subregion contributed to their direction selectivity. Latency of neurons in area 17 of strobe-reared cats was slightly higher than in normal cats, but the response strength of neurons was the same in the two groups. The proportion of cells failing to respond to briefly flashed stationary stimuli was significantly lower in strobe-reared than in normal animals. Qualitative and quantitative testing showed that strobe rearing has a stronger effect on the parts of area 17 that subserve central vision than on those that subserve peripheral vision. Comparing the present results with those of Kennedy and Orban (37) shows that strobe rearing has less effect on area 17 than on area 18 and that the functional differences between areas 17 and 18 in strobe-reared cats are smaller than in normal cats.
Influence of a moving textured background on direction selectivity of cat striate neurons
Authors: Orban G. A. , Gulyas B. , Vogels R.
Published: December 2017

The influence of a moving textured background on direction selectivity for a moving bar was tested in 118 striate neurons and in 19 dorsal lateral geniculate neurons of anesthetized and paralyzed cats. In the standard conditions the background was a two-dimensional noise pattern, the bar moved at optimal speed, and its contrast was adjusted to the level producing 50% of the maximum response. These experiments revealed a new typology of cortical cells based on relative direction selectivity. Six different relative-direction-selectivity types are described. Two types of cells were found to have opposite kinds of relative direction selectivity: antiphase direction-selective cells (5% of the cortical sample) preferred the direction of the bar opposite to the direction of background motion, and absolutely direction-selective cells (20% of the cortical sample) kept their direction selectivity for bar motion independently of the background motion. Three types of cortical cells were direction selective for bar motion only in restricted background motion conditions: conditionally direction-selective cells (20% of cortical sample) only expressed their direction selectivity when the bar and the background moved in antiphase, differencing direction-selective cells (5% of the cortical sample) only expressed their direction selectivity when the bar and the background differed in speed, and limited direction-selective cells (20% of the cortical sample) only expressed their direction selectivity for near zero background speeds. The sixth type, relative nondirection-selective cells (30% of the cortical sample and all of the geniculate cells) were direction selective for none of the background motion conditions. These different relative-direction-selectivity types differed in RF organization, in ocular dominance, velocity sensitivity, in laminar distribution, and in distribution in the visual field. The relative-direction-selectivity types were invariant for changes in the contrast and bar speed. The construction of these relative-direction-selectivity types from the geniculate input requires some inhibitory, but mainly facilitatory, intracortical interactions. These experimental findings suggest that area 17 in the cat has the neuronal machinery to extract depth from motion (limited direction-selective cells) and to segregate visual scenes by motion cues (antiphase, conditionally and differencing direction-selective cells).
Neural compensation for muscular fatigue: evidence for significant force regulation in man
Authors: Kirsch R. F. , Rymer W. Z.
Published: December 2017

We have investigated the role of reflex regulation of muscle force in normal human subjects by comparing changes in the stretch-evoked increments in elbow joint flexor electromyogram (EMG) and elbow joint torque before and after fatigue. Elbow flexor muscle fatigue was induced by repetitive voluntary isometric contractions. To assess the appropriateness of the EMG signal as an index of neural excitation of muscle under fatiguing conditions, we examined the time course of recovery of joint torque and EMG power spectrum following fatigue. Fatigue-related changes in the EMG power spectra recovered within 5–10 min after fatiguing exercise was terminated, yet the muscle weakness induced by the exercise lasted greater than 7 h and was substantial in magnitude. The decoupling of torque and EMG recovery allowed us to compare pre- and postfatigue EMG stretch responses without adjusting for differences in EMG spectral content. Torque and EMG responses to stretch were quantified by time-averaging over 250-ms “isometric” and “steady-state” periods, just before and just after a ramp angular stretch of the elbow joint, respectively. The torque increment elicited by stretch was lower following fatigue in seven of eight experiments. However, the average decrease of 20.13 +/- 14.42% in these seven subjects was somewhat smaller than the corresponding average shift in the slope of the isometric EMG-torque relationship of 85.84 +/- 90.29% (n = 8). Furthermore, the stretch-induced EMG increment was larger following fatigue in all eight sessions (average of 56.14 +/- 28.96%, n = 8), with six of the shifts reaching statistical significance for alpha = 0.05. Because the pattern of torque and EMG responses before and after fatigue suggested the presence of an active force regulator, we used a simple model of the neuromuscular system to estimate a loop gain value for each session. When pre- and postfatigue responses were matched by isometric background torque level, an average loop gain value of 7.9 was computed, whereas for responses matched by average prestretch EMG level, the loop gain estimates averaged 2.1. Although our assessment of force regulation was essentially static and derived from the responses to a single type of perturbation, the change in the incremental torque and EMG stretch responses indicates that meaningful neural compensation for fatigue occurred. Moreover, the loop gain estimates derived from these responses are an order of magnitude larger than those previously reported in animal models, suggesting that force regulation may be important in the control of human muscle contraction.
Eye movements induced by pontine stimulation: interaction with visually triggered saccades
Authors: Sparks D. L. , Mays L. E. , Porter J. D.
Published: December 2017

1. Rhesus monkeys were trained to look to brief visual targets presented in an otherwise darkened room. On some trials, after the visual target was extinguished but before a saccade to it could be initiated, the eyes were driven to another orbital position by microstimulation of the paramedian pontine reticular formation. If, as current models of the saccadic system suggest, a copy of the motor command is used as a feedback signal of eye position, failure to compensate for stimulation-induced movements would indicate that stimulation occurred at a site beyond the point from which the eye position signal was derived. 2. Animals compensated for perturbations of eye position induced by stimulation of most pontine sites by making saccades that directed gaze to the position of the visual target. With stimulation at other pontine sites, compensatory saccades did not occur. 3. Pontine stimulation sometimes triggered, prematurely, impending visually directed saccades. The direction and amplitude of the premature movement depended upon the location of the briefly presented visual target. The amplitude of the premature movement was also a function of the interval between the stimulation train and the impending saccade. These data suggest that input signals for the horizontal and vertical pulse/step generators develop gradually during the presaccadic interval. Saccade trigger signals need to be delayed until the formation of these signals is completed. 4. The implications of these findings for models of the saccadic system are discussed. Robinson's local feedback model of the saccadic system can explain compensation for pontine stimulation-induced changes in eye position but cannot easily account for the failure to compensate for perturbations in eye position produced by stimulation at other sites. Modified versions of Robinson's model, which assume that the input signal to the pulse/step generator is the desired displacement of the eye, can account for both compensation and the failure to compensate since two separate neural integrators are employed. However, these models ignore kinematic arguments that commands to the extraocular muscles must specify the absolute position of the eye in the orbit rather than a relative movement from a previous position.
Timing of spike initiation in cochlear afferents: dependence on site of innervation
Authors: Ruggero M. A. , Rich N. C.
Published: December 2017

1. The phase of excitation of inner hair cells (IHCs) relative to basilar membrane motion has been estimated as a function of best frequency (BF) (or, equivalently, cochlear location) by recording responses to tones (100–1,000 Hz) from chinchilla cochlear afferent axons at their central exit from the internal auditory meatus. 2. The time of IHC excitation (i.e., the time of chemical transmitter release) was derived from the neural recordings at near-threshold levels by applying a correction for the latency of synaptic processes and the propagation time of action potentials. 3. The phase of basilar membrane motion at the appropriate innervation site was estimated on the basis of previously measured basilar membrane responses at a location close to the basal end of the cochlea and estimates of mechanical travel time from the basal end to the innervation site, derived from the neural latencies to intense rarefaction clicks, as a function of BF. 4. The derived near-threshold excitation of basal IHCs leads basilar membrane displacement toward scala tympani by approximately 40-60 degrees. 5. At BFs corresponding to midcochlear locations (2–6 kHz) there is an abrupt phase transition. The derived excitation for IHCs located at more apical locations (BFs large in relation to stimulus frequency) corresponds approximately to peak velocity of the basilar membrane toward scala vestibuli. 6. Although the derived response phases of apically located IHCs are consistent with intracellular recordings from IHCs, the derived near-threshold response phases of basal IHCs may be inconsistent with intracellular IHC recordings. 7. The foregoing results, based on responses of nearly 1,000 cochlear afferents to tones 100-1,000 Hz at near-threshold stimulus levels, amply confirm our previous conclusions that were based on a smaller sample of responses to very low frequency tones (less than or equal to 100 Hz): there is a spatial transition at midcochlear regions in the mode of excitation of IHCs, which does not seem to simply reflect the macromechanics of the basilar membrane. 8. It has been proposed that both the paradoxical response phases of high-BF afferents and the spatial phase transition arise from an influence of cochlear microphonics on the transmembrane potential of IHCs. The present results, which show that the spatial phase transition occurs for frequencies at least as high as 400 Hz, would appear to make such an electrical influence of outer hair cells on IHCs less likely. An alternative explanation might be that the phase transition has a mechanical basis, perhaps localized to micromechanical events in the subtectorial regio
The inhibition of cat lateral superior olive unit excitatory responses to binaural tone bursts. I. The transient chopper response
Authors: Tsuchitani C.
Published: December 2017

1. The temporal properties of lateral superior olivary (LSO) unit discharges to binaural tone bursts were studied to determine the general time course and statistical properties of these discharges and to provide a basis for extending a point process model of LSO unit monaural discharges to describe their binaural discharges. Single-unit activity was recorded extracellularly from the LSO of the anesthetized cat. The initial transient and the gross temporal features of LSO unit discharges to binaural simultaneous tone bursts are examined in this paper. 2. The poststimulus time (PST) histograms generated by LSO unit discharges to monaural and binaural tone bursts illustrated that the ipsilaterally elicited tone-burst discharges were most strongly inhibited during the initial segment of the binaural response and that the degree of inhibition decreased (i.e., discharge rate increased) as the poststimulus onset time increased. Hence, the contralateral inhibitory effect “adapts” in a manner similar to the ipsilaterally elicited discharges. 3. When the interaural level difference was decreased, the degree of discharge inhibition increased: the period of maximal inhibition spread to shorter and longer poststimulus onset times as the contralateral latency decreased and as the contralateral response magnitude increased. The latency of the inhibitory effect could decrease sufficiently to result in the suppression of the first spike of the ipsilateral discharge. Also, when the binaural stimulus was of sufficient intensity, an increase in spike output, the OFF discharge, was often observed during the last 1-10 ms of the response. 4. It was concluded that the initial and general time course of the binaural response could serve as cues of binaural stimulus level, interaural level differences, and interaural time-of-arrival differences of high-frequency stimuli. The binaural response could be discriminated from a monaural response of similar discharge rate as the former either occurred with shorter latency or, when the first spike was suppressed, with much longer and/or more variable latency than the latter. The gross temporal differences between the monaural and binaural responses could be accounted for in terms of differences in certain gross temporal features (e.g., latency and adaptation) of the ipsilateral and contralateral responses. 5. The effect of stimulating the contralateral ear was not limited to the inhibition of discharges. The timing of a discharge to an ipsilateral stimulus could be perturbed (lengthened) by a contralateral stimulus at levels below that which suppressed the discharge.(ABSTRACT TRUNCATED AT 400 WORDS)
Gastric mill activity in the lobster. I. Spontaneous modes of chewing
Authors: Heinzel H. G.
Published: December 2017

1. The gastric central pattern generator (CPG) driving the three teeth of the gastric mill inside the lobster stomach has often been used as a model for the study of central nervous systems, but the actual functioning of the mill has never been observed directly. By using a small endoscope inserted through the esophagus a video analysis of the tooth movements was performed with restrained, but otherwise intact lobsters. 2. The teeth show spontaneous periodic chewing (cycle duration from 4 to 70 s) in two different basic modes. In the squeeze mode only the cusps of the three teeth move together simultaneously. In the cut-and-grind mode the lateral teeth close first with not only their cusps, but also their serrated edges. After this cut phase the lateral teeth grind backward along the file of the medial tooth, which simultaneously moves forward. 3. Simultaneous endoscope recordings of the teeth, filming of stomach muscles and ossicles combined with electrical stimulation of selected muscles reveal that muscle gm3c is responsible for this hitherto unknown backward grinding of the lateral teeth. 4. The complete behavioral repertoire includes the following modifications of the two basic modes. 1) The lateral teeth can perform chewing movements while the medial tooth stays still and vice versa, forms of chewing regarded even weaker than the squeeze. 2) There do not appear to be intermediates between the squeeze and cut-and-grind movements, with the latter as the strongest form of chewing. Transitions only occur as switching on a cycle-by-cycle basis. 3) A gradual change of the cut-and-grind chewing was observed as the gradual development of an additional opening over the time course of several periods. 4) After their grind phase, the lateral teeth can even move further back beyond the medial tooth. This can serve to push food into the pyloric filter apparatus. 5. Inflation of the cardiac sac can elicit single bites in a resting gastric mill. 6. The behavioral repertoire is compared with the in vivo activity of the gastric oscillator represented by simultaneous intracellular recording from 7 representative cells of the 11 CPG neurons.
Mechanical properties of muscle units in the cat diaphragm
Authors: Fournier M. , Sieck G. C.
Published: December 2017

1. Muscle units in the right sternocostal region of the cat diaphragm (DIA) were isolated in situ by dissecting filaments of the C5 ventral root. Isometric contractile and fatigue properties of DIA units were then measured. Contractile properties included: twitch contraction time (CT), peak twitch tension (Pt), maximum tetanic tension (P0), and the frequency dependence of tension production. Muscle-unit fatigue resistance was estimated using a 2-min fatigue test. 2. DIA muscle units were classified as fast (F) or slow (S) based on the presence or absence of sag in their unfused tetanic force responses. Muscle-unit fatigue indices (FI) were used to further classify DIA units as slow-twitch fatigue-resistant (S), fast-twitch fatigue-resistant (FR) fast-twitch fatigue-intermediate (FInt), or fast-twitch fatigable (FF) types. 3. Based on a total of 47 completely characterized DIA muscle units, 21% were classified as S, 4% as FR, 28% as FInt, and 47% as FF. In contrast to the distribution of unit types in other mixed appendicular muscles, the DIA was composed of a very low proportion of FR units and a relatively high proportion of FInt units. An interval of FIs between 0.50 and 0.75 separated units into fatigue-resistant and fatigable groups. The distribution of FIs for FF and most FInt units was continuous, indicating that they formed a single fatigable group. Relatively few FF units in the DIA had FIs less than 0.10. 4. A wide range of contractile properties was observed for DIA muscle units. Type S units had longer CTs and lower Pt and P0 values than type F units. The mean Pt and P0 of FF and FInt units were comparable, whereas the mean Pt and P0 of the two FR units were lower. Type S units produced a greater proportion of their P0 at lower frequencies of activation than type F units. The lower P0S produced by type F units in the DIA indicated that they were smaller than similar units in appendicular muscles. It was concluded that in meeting most normal ventilatory requirements, adequate force could be generated by the recruitment of only type S and FR units. The recruitment of the more fatigable FF and FInt units may occur only during more forceful respiratory and nonrespiratory behaviors of the DIA.
Effect of subthreshold voltage-dependent conductances on the transfer function of branched excitable cells and the conduction of synaptic potentials
Authors: Yoshii K. , Moore L. E. , Christensen B. N.
Published: December 2017

1. Impulse response functions were determined from complex point impedance and transfer functions from cultured NG-108 cells to simulate the propagation of a synaptic potential in response to the release of transmitter. In general, the flow of synaptic current has a much shorter duration than the normal membrane time constant, thereby making the use of impulse response functions useful approximations to synaptic events. 2. The resonance observed during the activation of the potassium conductance was reflected in the impulse response function as a pronounced damped oscillation. A comparison of the impulse response functions calculated from point impedance and transfer functions showed similar results for current injections in the growth cone. 3. In addition to the resonance effects of the voltage-dependent conductances on transfer and impulse response functions due principally to the activation of conductances for outward currents, transfer functions were measured during the activation of a steady-state negative conductance. Under these conditions the phase function approaches 180 degrees, indicating that the voltage response is out of phase with the current. 4. In the steady state, the effect of a negative conductance is to algebraically add to the positive conductances and generally decrease the absolute conductance unless there is a net negative current. The decreased conductance enhances the impulse response and the DC space constant, thus leading to a better propagation of slow potentials. This effect can be seen as a decrease in the electrotonic length, L, with intermediate depolarizations. At large depolarizations the steady-state activation of the K conductance generally dominates and leads to a greatly increased electrotonic length. 5. Both the net conductances and the associated kinetics play a role in shaping the potential changes during a synaptic current. This is especially critical if there is a net negative steady-state conductance. Under these conditions there is a surprising reduction in the impulse response function. 6. Thus, during a subthreshold activation of the voltage-dependent negative conductances, the observable synaptic potentials would be either large potential responses due to an apparent increase in the impedance (algebraic summation of positive and negative conductances with a net positive conductance) or a minimal response because of the phasic cancellation due to a net negative conductance. The latter condition could exist near the synaptic reversal potential due to a large synaptic drive and would appear experimentally as a form of inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)
Correlated and uncorrelated high-frequency oscillations in phrenic and recurrent laryngeal neurograms
Authors: Bruce E. N.
Published: December 2017

1. Power spectral analysis of phrenic and recurrent laryngeal (or efferent vagal) inspiratory discharge activity from anesthetized cats revealed a peak within the 60- to 110-Hz range in all spectra, plus a peak within the 40- to 60-Hz range in the laryngeal (and efferent vagal) spectra, and a peak less than 40 Hz in the phrenic spectra. 2. A 60- to 110-Hz peak was present in coherence spectra between the left and right phrenic neurograms, the left and right recurrent laryngeal (and efferent vagal) neurograms, and all combinations of phrenic-laryngeal (and phrenic-efferent vagal) pairs. It is concluded that the nearly-periodic oscillations represented by these peaks arise from a single source that projects functionally in parallel to many respiratory motor outputs. This source may be part of, or interact with, respiratory central pattern generation. 3. The 40- to 60-Hz oscillations in left and right recurrent laryngeal (and efferent vagal) neurograms were uncorrelated or occasionally were very weakly correlated. Thus it is unlikely that these oscillations arise from a common source such as a second respiratory central pattern generator. 4. The oscillations less than 40 Hz were weakly correlated between left and right phrenic neurograms. This correlation may be due substantially to spinal crossed-phrenic pathways. 5. It is proposed that both the 40- to 60-Hz oscillations in recurrent laryngeal neurograms and the oscillations below 40 Hz in phrenic neurograms originate in neural circuits associated with individual left or right recurrent laryngeal or phrenic motor outputs. 6. Our results do not support the interpretation that multiple peaks in phrenic and recurrent laryngeal power spectra are due to two respiratory central pattern generators whose outputs have parallel pathways to respiratory motoneurons.
Quantitative evaluation of the electromyographic responses to multidirectional load perturbations of the human arm
Authors: Soechting J. F. , Lacquaniti F.
Published: December 2017

1. Force perturbations consisting of a random train of pulses were applied to the forearms of human subjects, the direction of the force being varied +/- 60 degrees from vertical in the sagittal plane in different trials. 2. Both forearm and upper arm were free to move, and the perturbations resulted in angular motion and torque at both joints. By varying the direction of the force, different combinations of these variables could be obtained. 3. Average angular motion and net torque at the shoulder and elbow joints and electromyographic activity of shoulder and elbow muscles due to a single pulse of force were computed by cross-correlation methods. 4. The pattern of responses in biceps, brachio-radialis, and anterior deltoid was not related uniquely to angular motion at the shoulder or elbow joints. Furthermore, the responses appeared to consist of two distinct components, an "early" one with a latency less than 40 ms and a "late" one with a latency of approximately 80 ms. 5. The average amplitude of the early response was best correlated with the average change in angular velocities, whereas that of the late one was best correlated with average changes in torque resulting from the perturbation. The data are consistent with the hypothesis that the two components have different anatomical substrates and that they have different functional implications for the stabilization of the limb in the face of perturbations.