bluuebunny/crossref_metadata_2025 huggingface dataset:
Activity of single motor units from human forearm muscles during voluntary isometric contractions
Authors: Freund H. J. , Budingen H. J. , Dietz V.
Published: December 2017

1. Microelectrode recordings from single motor units of the first dorsal interosseus and the extensor indicis muscles of normal human subjects were studied during voluntary, isometric contractions. The conduction velocity of the nerve fiber innervating the muscle unit was used as an estimator of the size of the motoneuron. 2. During slowly increasing contractions, the units were recruited at force levels which were closely correlated to conduction velocity. The units associated with low conduction velocity were recruited first, those with high conduction velocity, last. 3. If small, stepwise force increments were used instead of slowly, continuously increasing contractions, the units were first activated during the steps and became inactive during the subsequent plateaus. If higher steady-force levels were reached, the activity was maintained also during the plateaus. This steady force, where a unit remained continuously active independent of the rate of rise of tension, represents its tonic threshold. 4. The tonic threshold is positively correlated with conduction velocity, as is the threshold force of recruitment. As a consequence, high-threshold units have a large force range below tonic threshold where they can only be transiently activated, whereas low-threshold units have a large physiological force range above tonic threshold where they operate tonically. The phasic or tonic appearance of discharge pattern reflects quantitative differences in tonic threshold between units of different size. All units examined could be activated phasically (below) and tonically (above tonic threshold). No evidence was found indicating the existence of two qualitatively different classes of units corresponding to a tonic and phasic type, although both muscles investigated consist of about equal numbers of type I and type II muscle fibers. 5. The change in firing rate per unit force was inversely related to conduction velocity: the slower conducting units showed larger changes in firing rate per unit force than faster conducting units. This corresponds to the larger excitability of the smaller units indicated by their earlier recruitment. 6. The data of this study are consistent with the hypothesis that the functional characteristics of human motoneurons are determined by the graded excitability of motoneurons according to size.
Somatotopic studies on red nucleus: spinal projection level and respective receptive fields
Authors: Eccles J. C. , Rantucci T. , Scheid P. , Taborikova H.
Published: December 2017

The somatotopic inputs into red nucleus (RN) neurons have been studied with special reference to their level of projection in the spinal cord. As inputs we employed either volleys in predominantly cutaneous nerves of forelimb and hindlimb or cutaneous mechanoreceptor discharges evoked by taps to footpads of forelimb and hindlimb. There has been physiological confirmation of the anatomical findings that RD neurons projecting to the lumbar cord are located in the ventrolateral zone of the pars magnocellularis, whereas in the dorsomedial zone are RN neurons with cervical but not lumbar projection. Somatotopically there was found to be a differentiation of input to RN neurons according as they projected to the lumbar or only to the cervical cord. This finding was presented in the form both of tables and of somatotopic maps. As expected, this discrimination was more restrictive for the more selective inputs from pad taps than for nerve inputs. Nevertheless, forelimb inputs often had a considerable excitatory and inhibitory action on lumbar-projecting RN neurons, and vice versa for cervical-projecting neurons. There were two notable somatotopic findings that suggest specificities of connectivities. First, despite the large convergence of IP neurons onto RN neurons (about 50-fold), the degree of somatotopic discrimination was about the same for interpositus and RN neurons with two testing procedures: between inputs from forelimb and hindlimb; and between inputs from pads on one foot. Second, although there was in the interpositus nucleus a considerable topographical admixture of neurons with dominant forelimb or hindlimb inputs, the axonal projections of these neurons were apparently unscrambled on the way to the target RN neurons, so as to deliver the somatotopic specificities observed for two classes of RN neurons; those projecting down the spinal cord beyond L2 level, and those projecting to C2 but not L2. Finally, there is a general discussion of motor control with reference to the pathway; pars intermedia of anterior lobe of cerebellum leads to interpositus nucleus leads to red nucleus leads to rubrospinal tract leads to spinal motoneurons.
Afferent-efferent linkages in motor cortex for single forelimb muscles
Authors: Murphy J. T. , Wong Y. C. , Kwan H. C.
Published: December 2017

1. In locally anesthetized cats, extracellular recordings were made from single neurons in the lateral cruciate gyrus of cerebral cortex. These neurons responded to natural activation of stretch receptors in single, contralateral, forelimb wrist muscles, typically with phasic excitation. Low-velocity stretches, which activate primary endings of muscle spindles, excited one set of neurons at a mean latency of 11 ms; high-velocity stretches, which principally activate Golgi tendon organs and/or secondary spindle endings, excited a second set at 18 ms. The cortical neurons showing threshold responses to low-velocity stretches were found exclusively within restricted columns, 0.5-2.0 mm in diameter, which were spatially separate for each muscle. Neurons exhibiting threshold responses to high-velocity stretches were present in high density within the same columns and were also distributed, although more sparsely, outside the columns. 2. These afferent columns were located in cytoarchitectonic area 4gamma, and were shown by intracortical microstimulation to coincide with the efferent columns for contraction of the same muscle from which in input rose. Discrete afferent columns were also found for single muscles in the peridimple region of sensory cortex (area 3a), spatially separate from the columns in motor cortex. The excitation of the columns in motor cortex by these inputs from muscle was independent of that in sensory cortex. 3. The role of the cerebellum in controlling these feedback systems to motor cortex was investigated by selective cooling of interpositus and dentate nucleus, respectively. Cooling of interpositus markedly reduced transmission in the high-threshold system; cooling of dentate had a similar effect on the low-threshold system. 4. The latency, threshold, and cooling data indicated that the low-threshold system to motor cortex utilizes extracerebellar pathways including medial lemniscus and is facilitated by dentate nucleus. The high-threshold system involves a transcerebellar pathway including interpositus nucleus. Both systems transmit velocity-related information, with each showing different and complementary sensitivity and dynamic range. 5. The results are discussed with reference to the cortical load-compensation mechanism postulated by Phillips (37-38).
Modulation of synaptic effectiveness of Ia and descending fibers in cat spinal cord
Authors: Rudomin P. , Nunez R. , Madrid J.
Published: December 2017

1. In the unanesthetized spinal cord, conditioning stimulation of low-threshold afferents (below 1.3 times threshold strength) in the biceps semitendinosus (BST) nerve often reduced the peak amplitude of the monosynaptic Ia EPSPs evoked in gastrocnemius motoneurons without affecting the monosynaptic component of the EPSPs evoked by stimulation of the ipsilateral ventral funiculus (VF) in the thoracic cord. 2. Volleys to the BST nerve comprising higher threshold afferents (usually above 1.4 times threshold strength) reduced the peak amplitude of the monosynaptic Ia and VF EPSPs and shortened their falling phase. 3. Conditioning volleys to low-threshold cutaneous afferents often increased the Ia-EPSP peak amplitude, sometimes without affecting the monosynaptic component of the VF EPSP. 4. In most cases the Ia nd VF monosynaptic EPSPs elicited in a given motoneuron summated nonlinearly. The amount of nonlinear summation between Ia and VF monosynaptic EPSPs was often reduced by low-threshold BST conditioning volleys. These observations suggest that in many instances, both species of fibers end in "electrotonically close" synaptic loci over the motoneuron surface. Therefore, amplitude changes of monosynaptic Ia EPSPs produced by conditioning afferent volleys without concomitant changes of monosynaptic VF EPSPs do not appear to result from postsynaptic remote conductance changes and may be attributed to a presynaptic mechanism. 5. At the time of occurrence of the Ia and VF monosynaptic EPSP the variance of the motoneuron membrane potential may be increased above base-line levels with a time course approximately matching the EPSP itself. Conditioning stimulation of BST afferents usually reduced Ia EPSP variance, often without affecting or even increasing the variance of the monosynaptic VF EPSPs. These observations provide additional evidence that Ia EPSP variability is introduced, at least in part, through the segmental pathways mediating primary afferent depolarization. 6. The possibility of a differential control of the information flow transmitted through two independent channels converging on a given cell ensemble is discussed.
Tendon organs of cat medial gastrocnemius: responses to active and passive forces as a function of muscle length
Authors: Stephens J. A. , Reinking R. M. , Stuart D. G.
Published: December 2017

The responses of 13 Golgi tendon organs to graded force development of 29 motor units in medial gastrocnemius of the cat have been studied in five experiments. Of the 13 tendon organs, 11 were responsive to passive stretch within the physiological range of muscle length and 5 were "spontaneously" active at very short lengths where no passive tension could be recorded. The relationship between passive force and the firing rates of the various afferents ranged from a linear one to a power relation (Y = Axb + c) with b, a widely varying exponent. Results support the general conclusion that although many Ib afferents respond to passive force within the physiological range of muscle stretch, this form of stimulus is not a particularly effective one. The statis responses of Golgi tendon organs to active force development produced by single motor units was studied at different muscle lengths. In all cases the apparent sensitivity (change in firing rate per active force developed) decreased as muscle length approached Lo. The static responses of Golgi tendon organs to force developed by single motor units were also studied during fatiguing contractions. The data suggest a sigmoid relationship between force developed at the tendon and the Ib response. The collective response of all 13 tendon organs to active and passive forces at different muscle lengths was also examined. This analysis offered further support for the viewpoint that active motor unit contractions provide themost significant excitatory input to tendon organs and that changes in passive force during muscle stretch have comparatively little effect on the collective tendon organ response. The interaction between active and passive force inputs to the Golgi tendon organs is discussed in relation to the complicated nature of the relationship between forces measured at the tendon and those acting within the receptor capsule. When these complications were taken into account it was possible to explain the differences in responsiveness of a given tendon organ to active contraction of several motor units and to passive force in terms of a single force-firing rate curve for the receptor. It is concluded that changes in the force of contraction of single motor units result in relatively small changes in Ib afferent firing and that during normal muscle contractions, changes in the number of motor units acting on a single receptor must produce far more significant changes in firing rate than changes in the amount of force developed by any single unit. Changes in dynamic Ib sensitivity to single motor unit contractions are also shown to depend on length and in a similar way to the changes in static Ib sensitivity. During fatiguing contractions, a sigmoid relation was found between the dynamic Ib response and the rate of force development by single motor units.
Electrophysiological study of formation of new synapses and collateral sprouting in red nucleus neurons after partial denervation
Authors: Tsukahara N. , Hultborn H. , Murakami F. , Fujito Y.
Published: December 2017

Intracellular recording was made from cat's red nucleus after chronic lesion of the nucleus interpositus (IP) of the cerebellum and the properties of the corticorubral EPSPs were examined. 2. It was found that the time to peak of the corticorubral ESPSs induced from cerebral peduncle (CP EPSP) of chronic cats was much faster than that of normal cats. There was no simple decay following the rapid rise and early summit; instead there was another peak as if the slow normal CP EPSPs were superimposed on the fast ones. 3. By stimulating two loci, sensorimotor cortex and the cerebral peduncle, the conduction velocities of the fibers responsible for the newly appeared fast-rising component of the corticorubral EPSPs were measured. They were almost the same as those of normal corticorubral EPSPs.
Quantitative study of cortical orientation selectivity in visually inexperienced kitten
Authors: Sherk H. , Stryker M. P.
Published: December 2017

1. Extracellular recordings were made from single units in the visual cortices of six kittens deprived of experience with pattern vision by binocular lid suture. 2. Selectivity for stimulus orientation was quantitatively assessed in 98 units; 90 responded selectively to the orientation of a moving bar stimulus, the remainder responding nonselectively or too poorly to classify. Cells in these visually inexperienced kittens were similar in their degree of selectivity for orientation to cells tested in adult cats. However, responses tended to be weaker and somewhat more erratic. 3. About half the cells in this simple responded to both directions of stimulus motion at the optimal orientation. Most of those responding to only one direction of motion were considered orientation rather than direction selective because they responded more strongly or more selectively to a moving bar than to a moving spot. 4. Cells appeared to be organized within the cortex in a pattern similar to that found in adult cats, with cells in one column selective for the same orientation, and adjacent column having similar preferred orientations. 5. It is concluded that selectivity for stimulus orientation in the cat's visual cortex is innately determined.
Reversal properties of climbing fiber potential in cat Purkinje cells: an example of a distributed synapse
Authors: Llinas R. , Nicholson C.
Published: December 2017

1. The electrophysiological properties of the EPSP generated in Purkinje cells by the activation of CFs were studies in the cat cerebellar cortex. 2. CF-EPSPs were evoked by electrical stimulation of the cerebellar white matter and recorded intracellularly from the soma of the Purkinje cells. 3. Current was injected into the Purkinje cells via the recording micropipette using a bridge amplifer in order to study the reversal properties of the EPSP. 4. The CF-EPSP reversal was biphasic with the early portion reversing first. 5. The reversed EPSP waveform was not a mirror image of the EPSP, but displayed a briefer time course. 6. A four-compartment computer stimulation showed that the reversal properities of the CF-EPSP were explicable in terms of a distributed synapse on a cable. 7. The biphasic reversal and asymmetry were shown to be due to the spatially nonuniform potential distribution created by the somatic current injection, which predominantly reversed the proximal part of the distributed synapse. Delayed rectification may also have contributed to the reversal asymmetry. 8. The advantages of a distributed synapse over a point synapse are discussed and the reversal properties of the CF-EPSP compared to those of the Ia-evoked EPSP in motoneurons.
Motor-unit activity responsible for 8- to 12-Hz component of human physiological finger tremor
Authors: Elble R. J. , Randall J. E.
Published: December 2017

Tremor of the extended third digit and bipolar surface and needle electromyograms of the extensor digitorum were recorded from six healthy volunteers for the purpose of elucidating the motor-unit activity responsible for the 8- to 12-Hz component of physiological finger tremor. Tremor was measured with a force transducer during steady voluntary contractions of approximately 200-250 g. The surface EMGs were full-wave rectified and low-pass filtered (-3 dB at 21 Hz), producing the envelope of the surface EMG (the demodulated EMG). Spectral analyses of simultaneous tremor and demodulated EMG records were performed. In four of six subjects, a pronounced 8- to 12-Hz amplitude modulation in the surface EMG was present, and coherency analysis demonstrated that this modulation was strongly correlated with the well-known 8- to 12-Hz tremor. In two subjects this amplitude modulation and tremor were barely detectable, despite the sensitive recording and analysis techniques used in this study. Spectral analysis was performed on 43 motor-unit spike trains. Twenty-two spike trains, having mean firing frequencies in the range of 10-22 spikes/s, produced statistically significant spectral peaks at 8-12 Hz, in addition to the expected spectral peaks at the mean firing frequencies. Of the 22 8- to 12-Hz-producing motor units, 12 had mean firing frequencies in the range of 17-22 spikes/s and exhibited the greatest 8- to 12-Hz activities of all motor units recorded. These motor units displayed transient sequences of double discharges in which interspike intervals (ISIS) of approximately 8-30 ms alternated with ISIS of 60-90 ms, thus producing an 8- to 12-Hz spectral peak. Adjacent ISIS of these motor units were correlated in the range of -0.5 to -0.9. Coherency analyses demonstrated that the 8- to 12-Hz activities of these motor units were correlated with the 8- to 12-Hz finger tremor and surface EMG modulation. The remaining 10 8- to 12-Hz-producing motor units had mean firing frequencies in the range of 10-17 spike/s. Although these motor units did not display the intense double-discharge firing pattern of the more rapidly firing motor units, a tendency toward action potential grouping was present and resulted in 8- to 12-Hz spectral activities which were correlated with the tremor and surface EMG modulation. .. ..
Relative strength of synaptic input from short-latency pathways to motor units of defined type in cat medial gastrocnemius
Authors: Burke R. E. , Rymer W. Z.
Published: December 2017

1. Intracellular recording and stimulation techniques were used in anesthetized cats to study the interrelations between amplitudes of PSPs produced by electrical stimulation of several short-latency pathways to MG alpha motoneurons and the mechanical properties of muscle units innervated by the same cells. Motor-unit types were identified by muscle-unit properties.2. The maximum amplitudes of monosynaptic EPSPs produced in MG motoneurons by activation of homonymous (MG) and heteronymous (LGS) group Ia afferents were clearly related to motor-unit type, being, on the average, largest in type S units, somewhat smaller in type FR and F(int) units, and smallest in type FF units. Correspondingly, group Ia EPSP amplitudes were inversely correlated with muscle-unit tension production and directly correlated with resistance to fatigue. The same input distribution was true for disynaptic IPSPs produced by group Ia afferents from antagonist ankle flexors.3. The amplitudes of monosynaptic EPSPs produced by fibers descending in the ipsilateral ventral funiculi of the low thoracic cord were not clearly related to MG motor-unit type or (therefore) to muscle-unit properties.4. A quantitative input-output model of the MG motor-unit pool, based in part on the present results, suggests that overall characteristics of MG motor units, and their relative numbers in the MG pool, reflect functional specializations determined by specific mechanical demands placed on the MG muscle by the usual motor behavior of the animal.
Habituation of a monosynaptic response in frog spinal cord: evidence for a presynaptic mechanism
Authors: Farel P. B. , Thompson R. F.
Published: December 2017

1. Using the isolated spinal cord of bullfrogs (Rana catesbeiana), intracellular correlates of habituation-like depression of the monosynaptic response elicited in motoneurons by lateral column (LC) stimulation were investigated. The following properties of the motoneuron were compared before and after response depression produced by stimulation of the LC at 0.5/s: resting membrane potential, membrane conductance, critical firing level, and rheobasic current. No alteration was found in any of these parameters. 2. To determine whether transmitter release mechanisms were changing over trials, the LC was stimulated with pairs of stimuli separated by 6 ms presented at 0.5/s. While the amplitude of the first EPSP declined (74% of initial value), the amplitude of the second EPSP increased (111% of initial value). Facilitation ratios thus increased. 3. The following conclusions can thus be drawn: 1) habituation involves a process intrinsic to the LC-motoneuron synapse; 2) habituation is not totally mediated by receptor desensitization; 3) habituation is not mediated by a mechanism extrinsic to the LC-motoneuron synapse that depolarizes terminal endings, e.g., presynaptic inhibition or accumulation of extracellular potassium; 4) habituation is not produced by transmitter depletion. Any of these possibilities has as a necessary consequence that facilitiation ratios remain unchanged. 4. Possible mechanisms that could mediate habituation are: 1) alterations in mobilization and/or release of transmitter; 2) decreased probability of invasion of terminal branches of the presynaptic fiber by the action potential.
Reflex responses of human soleus muscle to small perturbations
Authors: Stein R. B. , Bawa P.
Published: December 2017

1. A small branch of the nerve to soleus muscle in normal human subjects was stimulated intramuscularly with a needle electrode while the subjects were maintaining a steady voluntary contraction. The EMG and force fluctuations produced by these stimuli were recorded and averaged. 2. In addition to the M-wave produced directly by stimulating motoneurons and the resultant twitch contraction, one or more EMG waves were seen with a latency greater than 100 ms. These later waves produced further contractions, and when there were several later waves, the EMG and force fluctuations appeared as a damped oscillation with a frequency between 5.5 and 8 Hz. 3. By varying the angle of the ankle and hence the time course of the twitch contraction, the timing of the latter waves was shown to be closely related to the contraction time. Thus, the later waves appeared to be produced reflexly by the tension fluctuations, rather than directly by the stimulus. 4. The frequency response function between the tension fluctuations and the reflux EMG responses was computed. The gain agreed with that of primary muscle spindle afferents, but the phase data showed extra lags consistent with a time delay which was too long to be spinal in origin. This reflex probably involves supraspinal centers.
Sustained, synchronous oscillations in discharge of sustaining fibers of crayfish optic nerve
Authors: Glantz R. M. , Nudelman H. B.
Published: December 2017

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.
Retrograde invasion of lobster stretch receptor somata in control of firing rate and extra spike patterning
Authors: Calvin W. H. , Hartline D. K.
Published: December 2017

1. Extra spikes may be interleaved in the otherwise rhythmic discharge pattern of the lobster stretch receptor neuron, about 2 ms after an expected spike. A constant input to the neuron is maintained by injecting current intrasomatically. The axon recovers its excitability while the retrograde invasion of the soma and dendrites is still in progress, which provide electrotonic currents to reexcite the axon. 2. While extra spikes in the axon often arise from a prolonged somatic (dendritic?) depolarization, they may also arise from a delayed retrograde invasion of the soma. 3. Failure of retrograde invasion may cause a sudden jump in the rate of rhythmic discharge, demonstrating the role of the soma-dendritic afterhyperpolarization in the regulation of rhythmic firing rate. 4. The history of repetitive firing is often important. Because extra spikes often first appear during a decline in firing rate, turning on and then off, an additional current may sometimes activate the extra spike mode, thus doubling the resting firing rate in a metastable manner. Another mestastable state is associated with failure of retrograde invasion. 5. Extra spikes augment the high end of the frequency-current curve in some receptor neurons; in other cases, the extra spikes are seen only at low rhythmic firing rates, dropping out as current reaches intermediate values to create a paradoxical negative-sensitivity region (decline in total spikes per second with increasing current). 6. The results suggest that both the extent and the speed of active retrograde invasion of the soma and dendrites are likely candidates for pathophysiological mechanisms, since they may control whether extra spikes are generated.
Topographic organization and convergence in corticotectal projections from areas 17, 18, and 19 in the cat
Authors: McIlwain J. T.
Published: December 2017

1. Electrical stimulation in areas 17, 18 and 19 of the cat's visual cortex activated neurons in the superficial gray layer of the superior colliculus. The threshold for such excitation was lowest when the receptive fields of cells at the stimulus site lay inside the receptive field of the collicular cell under observation. 2. A substantial percentage of the recorded collicular cells received convergent excitatory input from more than one of the stimulated cortical areas. When stimuli could be applied in parts of areas 17, 18, and 19 related retinotopically to a collicular cell, over half of the units were activated from all three cortical areas by low-intensity stimulation. 3. Cells located near one another in the colliculus received excitatory cortical input from regions of areas 17, 18, and 19 which were not identical in size. This may be attributable to the disparate dimensions of collicular dendritic fields, which permit neighboring cells to sample dissimilar regions of the topographically organized cortical input. It is argued that this projection system preserves the functional unity of cortical and tectal cell groups processing information from a given retinal point.
Fast-conducting skeletofusimotor axons supplying intrafusal chain fibers in the cat peroneus tertius muscle
Authors: Harker D. W. , Jami L. , Laporte Y. , Petit J.
Published: December 2017

1. In six experiments on cat peroneus tertius muscle, from 12 to 23 motor axons with conduction velocities above 85 m/s were repetitively stimulated so as to produce glycogen depletion in the muscle fibers they innervated. 2. The whole muscle was then quick-frozen, serially cut, stained to demonstrate glycogen, and examined for intrafusal glycogen depletion. 3. Zones of glycogen depletion were found in 27 of the 99 examined spindles: they were almost invariably located on chain fibers and specifically on the longest of the chain fibers in affected spindles. 4. Since it was shown that there are no purely fusimotor fast axons in the motor supply to peroneus tertius, it is concluded that skeletofusimotor axons are present among the fastest motor axons to this muscle.
[K+]o clearance in cortex: a new analytical model
Authors: Vern B. A. , Schuette W. H. , Thibault L. E.
Published: December 2017

1. It has been suggested that passive diffusion is the principal mechanism of the clearance of locally elevated extracellular potassium, K+o, in the cerebral cortex. This concept was based on the assumption that elevated K+ could be modeled as a point source. In the present study, the functional role of passive diffusion was reevaluated in the anesthetized cat cortex following local electrical stimulation. 2. The initial spatial distribution of extracellular potassium activity, [K+]o, elevated by monopolar stimulation, could be modeled by a two-dimensional Gaussian function at and below the 500-micron cortical depth. Azimuthal symmetry around the stimulating electrode was assumed and cylindrical spatial coordinates were used. 3. The observed clearance of transiently elevated [K+]o as a function of space and time was much more rapid than that predicted by an analytical model consisting of the homogeneous diffusion equation whose initial condition was the Gaussian spatial distribution of [K+]o at the onset of the clearance process. 4. It is concluded that passive diffusion does not significantly contribute to the rapid clearance of locally elevated extracellular potassium in the cortex. Active uptake of potassium by cortical cells should be more seriously considered as being primarily responsible for the potassium clearance.
Receptive-field properties of neurons in binocular and monocular segments of striate cortex in cats raised with binocular lid suture
Authors: Watkins D. W. , Wilson J. R. , Sherman S. M.
Published: December 2017

1. We studied the receptive fields of 171 striate cortical neurons from 17 cats raised with binocular lid suture. Of these, 102 fields were within 10 degrees of the area centralis and the remaining 69 were at least 38 degrees from the vertical meridian. 2. Based on their different response properties, cells were divided into three broad groups: the mappable cells (49%) had clearly defined receptive fields, the unmappable cells (31%) were activated by visual stimuli but had diffuse fields which could not be hand plotted, and the visually inexcitable cells (20%) could not be activated by visual stimuli. Very few (less than or equal to 12% of the total sample) normal simple or complex cells could be found. 3. Orientation selectivity was assessed in these cells. Only 12% displayed orientation selectivity within normal bounds, and these were all mappable cells. None of the unmappable cells had discernible orientation selectivity. 4. Ocular dominance was assessed for 62 of the centrally located receptive fields. Among mappable cells, there was an abnormally low proportion of binocular fields, while no such abnormality was seen for unmappable cells. 5. For 47 of the neurons, average response histograms were compiled for moving stimuli of various parameters in an effort to evoke the maximum discharge or peak response. This peak response was normal for mappable cells but reduced for unmappable cells. 6. We devised a technique for studying potential inhibitory receptive-field zones in these neurons, validated the method in normal striate cortex, and used it to test 20 mappable cells in the lid-sutured cats. None showed the pattern of strong inhibitory side bands seen in normal simple cells, although six showed weak or abnormal inhibitory zones. Interestingly, six of the seven visually inexcitable cells tested by this method had purely inhibitory receptive fields. 7. The effects of binocular suture were essentially identical for the binocular and monocular segments since the cell types and their response properties did not differ between these two areas of cortex. Furthermore, the cortical monocular segments of these cats seemed qualitatively different from the deprived cortical monocular segment after monocular suture. This extends an analogous difference for these cats reported for the monocular segments of the lateral geniculate nucleus. We thus conclude that monocularly and binocularly sutured cats develop by qualitatively different mechanisms. For the former, competition between central synapses related to each eye is a prominent feature of geniculocortical development, whereas, for the latter, such specific forms of geniculocortical development may not obtain.
Neural transduction in Xenopus laevis lateral line system
Authors: Strelioff D. , Honrubia V.
Published: December 2017

1. The process of neural excitation in hair cell systems was studied in an in vitro preparation of the Xenopus laevis (African clawed toad) lateral line organ. A specially designed stimulus chamber was used to apply accurately controlled pressure, water movement, or electrical stimuli, and to record the neural responses of the two afferent fibers innervating each organ or stitch. The objective of the study was to determine the characteristics of the neural responses to these stimuli, and thus gain insight into the transduction process. 2. A sustained deflection of the hair cell cilia due to a constant flow of water past the capula resulted in a maintained change in the mean firing rate (MFR) of the afferent fibers. The data also demonstrated that the neural response was proportional to the velocity of the water flow and indicated that both deflection and movement of the cilia were the effective physiological stimuli for this hair cell system. 3. The preparations responded to sinusoidal water movements (past the capula) over the entire frequency range of the stimulus chamber, 0.1-130 Hz, and were most sensitive between 10 and 40 Hz. The variation of the MFR and the percent modulation indicated that the average dynamic range of each organ was 23.5 dB. 4. The thresholds, if any, for sustained pressure changes and for sinusoidal pressure variations in the absence of water movements were very high. Due to the limitations of the stimulus chamber it was not possible to generate pressure stimuli of sufficient magnitude to elicit a neural response without also generating suprathreshold water-movement stimuli. Sustained pressures had no detectable effect on the neural response to water-movement stimuli. 5. The preparations were very sensitive to electrical potentials applied across the toad skin on which the hair cells were located. Potentials which made the ciliated surfaces of the hair cells positive with respect to their bases increased the MFR of the fibers, whereas negative potentials decreased it. The responses to sinusoidal electrical stimuli were similar to responses to water-movement stimuli with respect to frequency and dynamic ranges. Thresholds as low as 100 muV peak to peak (p-p) for 16-Hz stimuli were found. 6. The characteristics of the neural responses to electrical stimulation as well as supporting data obtained from the studies of the effects of anoxia on the evoked responses indicate that the electrical stimulus acts on the hair cells or on the synapses, rather than directly on the nerve fibers. This finding suggests that receptor potentials or their associated currents play an important role in the process of neural excitation in hair cell systems.
Neural correlates of auditory fatigue: frequency-dependent changes in activity of single cochlear nerve fibers
Authors: Lonsbury-Martin B. L. , Meikle M. B.
Published: December 2017

1. These experiments were designed to test whether intense pure tones produced greater depression of cochlear nerve fibers tuned to the exposure frequency or of those tuned to frequencies above the exposure frequency. Spike discharges of single fibers were studied in anesthetized cats before, during, and after exposures lasting 1 min. Exposure frequency was varied relative to each fiber's characteristic frequency (CF), and was either at the CF or 1/2 octave above (+1/2 oct) or 1/2 octave below (-1/2 oct) the CF. Exposure levels were 85 or 90 dB SPL. Effects of the various exposures on driven discharge rates were evaluated using standard test stimuli at each fiber's CF. In addition, nonevoked discharges were measured during the brief quiet intervals between test stimuli ("interstimulus activity") as well as during extended quiet periods ("resting activity"). Major results were as follows: 2. All the exposures resulted in depression of the driven discharge rates; however, these effects were strongly dependent on the exposure frequency. The depression was greatest and endured the longest following -1/2 oct exposures at 90 dB. The CF exposures at 85 and 90 dB were much less depressant, as were exposures at -1/2 oct at 85 dB; these three exposures resulted in very similar recovery functions. The +1/2 oct exposures produced little or no depression, whether at 85 or 90 dB. 3. Interstimulus activity was depressed immediately following all exposures, but recovered to normal quickly than did driven discharge rates. Following exposures at -1/2 oct at 90 dB, recovery was non-monotonic in that an extended period of supernormality preceded the return to normal rates. During this period of elevated activity, the interstimulus activity approached but never exceeded the resting rate of the same fiber. 4. Resting activity recovered even more rapidly than interstimulus activity, being completely normal by 1 min following all exposures. 5. These results constitute the first demonstration that the CF is not necessarily the most depressant exposure frequency for a given cochlear nerve fiber. Further, the results imply that the half-octave (or greater) shifts of the point of maximum hearing loss, so characteristic of auditory fatigue, may be accounted for by frequency-dependent alterations in the responsiveness of cochlear nerve fibers.
Development of functional motor innervation in supernumerary hindlimbs of the chick embryo
Authors: Morris D. G.
Published: December 2017

1. The development of functional motor innervation in supernumerary chick hindlimbs transplated to host embryos at stages 16--18, was studied throughout the embryonic period from stage 27 when peripheral synapses were first formed. 2. The innervation pattern, defined as the number and sequential order of spinal nerves innervating individual muscles, were determined for supernumerary hindlimbs innervated by thoracic, lumbosacral-thoracic, or wholly lumbosacral spinal cord segments. Spinal nerves were electrically stimulated and muscle contraction was scored visually or by tension measurement and compound action-potential recordings were made from muscle nerves. 3. There was no tendency for spinal nerves to grow to or to synapse with the muscles which they normally innervate. Rather, they formed functional connections with inappropriate muscles, which were maintained throughout the developmental period studied. The localization of the motoneuron cell bodies was confirmed with retrograde transport of horseradish peroxidase (HRP) and shown to be adjacent to the spinal nerves through which their axons exited. Motoneurons innervating specific muscles occupied a similar medial-to-lateral position in the cord in both control and supernumerary limbs. 4. In all supernumerary limbs a definite peripheral innervation pattern was formed, which approximated the normal pattern. Specifically, the relative craniocaudal position of motor columns innervating individual muscles was conserved, even though the actual spinal nerves innervating the transplant were different from animal to animal. In limbs reversed along the anterior-posterior axis, the innervation pattern was also reversed. 5. The results suggest that motoneurons have not been rigidly specified to innervate certain muscles at the time when the limb buds were transplanted. Further, the limb itself can apparently influence the innervation pattern in an important manner, possibly by specifying motoneurons or by subsequently directing axon outgrowth and synapse formation.
Proprioceptive fields of crayfish claw motor neurons
Authors: Lindsey B. G.
Published: December 2017

1. Action potentials of crayfish claw motor neurons were recorded during both imposed constant-velocity displacements and imposed alternating sequences of opening and closing step movements of the dactyl. 2. Peristimulus time (PST) histograms show that the firing probabilities of two neurons, the opener inhibitor (OI) and the slow closer excitor (CE) consistently increased during opening ramp movements and declined during closing ramp movements. Hyperpolarizing synaptic potentials were observed in both cells during closing movements. 3. The proprioceptive field organizations of OI and CE were analyzed with response planes and contour planes. Each PST histogram in a plane displays the firing probability of the neuron as a function of time following step displacements at a given position. A relatively uniform early primary response followed each successive opening step. The probability of occurrence of later activity, when present, usually became more pronounced as the joint angle increased. Often both cells were silent during closing steps; when the cells were active, their firing probabilities were highest at the more open joint angles. 4. When both OI and CE were active, their spike trains were usually temporally correlated. 5. The other claw efferents did not respond to imposed movements in a consistent manner. When CE was active it was most likely to respond to closing movements near the closed position. 6. It is concluded that OI and CE are strongly and similarly influenced by proprioceptive reflexes. The responses of the two cells to imposed dactyl movements change as a function of joint angle, time after movement, and direction of movement.
Identifiable neurons controlling penile eversion in the leech
Authors: Zipser B.
Published: December 2017

1. This paper describes the neuroanatomy and electrophysiology of motor neurons causing penile eversion in the leech. 2. The male organ is innervated by ganglia 5 and 6 of the 34 ganglia in the leech brain through special sex nerves deriving from anterior roots. These sex ganglia have at least 200 more neurons than the other midbody ganglia. Many of the extra neurons are involved in reproductive behavior. 3. Two pairs of motor neurons on the ventral side of ganglion 6, named rostral and lateral neurons, are the only ones that elicit full penile eversion. Evidence that the lateral and rostral neurons are, in fact, motor neurons comes from HRP and electrophysiological studies. HRP injections reveal that each neuron's single primary axon grows into the sex nerve. Electrophysiological evidence is twofold: a) action potentials of lateral and rostral cells can still contract the genitalia after the neurons are deafferented from chemical synaptic input in the ganglion by high Mg2+, b) their action potentials are followed by junction potentials in male organ muscle fibers.
Cross-correlation analysis of connectivities among cat lumbosacral dorsal horn cells
Authors: Brown P. B. , Koerber H. R. , Yezierski R. P.
Published: December 2017

1. Eighty-three cell pairs were recorded in dorsal horns of 19 cats. Cross-correlograms were flat in 65 cell pairs; of the remaining 18 pairs, cross-correlograms had broad peaks or troughs suggestive of nonmonosynaptic causal relations in their discharges; one cell pair had a biphasic deviation from base line. 2. No cross-correlograms indicative of monosynaptic interactions were observed. 3. All cell pairs with nonflat cross-correlograms had overlapping receptive fields. 4. It is concluded that monosynaptically connected cell pairs are rare at the interelectrode distances used in this experiment because such cell pairs must lie close together on the somatotopic map or because our recording methods bias against monosynaptically linked cell pairs.
Responses of primate spinothalamic neurons to graded and to repeated noxious heat stimuli
Authors: Kenshalo D. R. , Leonard R. B. , Chung J. M. , Willis W. D.
Published: December 2017

1. The responses of primate spinothalamic tract cells innervating the glabrous skin of the foot to noxious thermal stimuli have been examined. 2. Of the 41 cells studied, 98% responded to noxious thermal stimuli. Heating the cutaneous receptive field with a series of stimuli from 35 to 43, 47, and 50 degrees C produced a graded increase in discharge rate. The responses were characterized by an onset, which occurred after the temperature change had either slowed or stopped, an acceleration in the discharge up to a peak, and then an adaptation to a new base-line level. The time constants of adaptation were faster than those reported for C polymodal nociceptors. 3. No systematic differences were found in the responses to noxious thermal stimuli of cells with wide dynamic range receptive fields and of cells with narrow dynamic range, high-threshold receptive fields. There were also no differences in the responses of cells located in the marginal zone and of cells located in the neck of the dorsal horn. 4. The relationship between peak frequency and final skin temperature with a 30 s stimulus duration can best be described by a power function with an exponent of 2.1. An increase in the stimulus duration to 120 s resulted in an increase in the exponent of the power function to 3.2. 5. Repetition of the series of 30-s heat stimuli resulted in an increase in peak frequency, total impulse count, and background activity. Repetition of stimuli having a duration of 120 s produced an increase in the peak frequency at 43 and 45 degrees C, a smaller increase at 47 degrees C, and a decrease at 50 degrees C. Background activity was increased by the lower temperature stimuli, but was decreased following higher temperature stimuli. 6. In six additional cells, the skin was heated with three consecutive presentations at each temperature level (43, 45, 47, and 50 degrees C) for 30 s. No change was observed in the peak frequencies of the responses to successive stimuli of the same intensity. However, the exponent of the power function relating the average peak frequency for the six cells to changes in skin temperature was 3.9. This exponent was larger than that seen when two series of graded heat stimuli of 120 s duration were used, indicating more sensitization despite the fact the total time of exposure to noxious heat was less. 7. A role for both high-threshold and wide dynamic range spinothalamic cells in transmitting nociceptive information to the diencephalon is postulated.