bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of sequential movements: evidence for generalized motor programs
Authors: Carter M. C. , Shapiro D. C.
Published: December 2017

The neuromotor processes underlying the control of rapid sequential limb movements were investigated. Subjects learned to pronate and supinate their forearms rapidly to four target locations in a specific spatio-temporal pattern under two movement-time conditions. The response sequence was first performed in a total movement time of 600 ms. Subjects were then told to produce the movement as quickly as possible while ignoring any timing pattern that they had previously learned. Electromyographic (EMG) signals were recorded from the biceps brachii and pronator teres muscles. Kinematic and EMG analyses were performed to investigate the temporal characteristics underlying the two movement-time conditions. When subjects produced the response as quickly as possible, average movement time to perform each reversal movement decreased while average peak velocity increased. Average total movement time was reduced by approximately 100 ms. Although movement time decreased, the proportion of total time to perform each movement of the sequence remained essentially invariant between movement-time conditions. Similar results were obtained for velocity. The time at which peak velocity was achieved occurred earlier in absolute time, although when normalized to the proportion of total movement time, the time to reach peak velocity was also invariant. Thus subjects proportionally compressed the entire movement sequence in time. The EMG analysis demonstrated that total EMG time decreased 89 ms on the average when subjects sped up the movement sequence. Thus average burst durations for both the biceps and pronator teres muscles decreased when movement speed increased. When burst durations were normalized to a proportion of total EMG time, the average proportion of time each muscle was active remained invariant. Therefore, the temporal pattern of activity for the biceps and pronator teres muscles were also proportionally compressed. The present experiment provided additional evidence for the structure of generalized motor programs consisting of invariant and variant features. Movement speed was considered a variant feature, which is specified each time the program is executed. Relative timing, the proportion of total time to produce each segment of the response, was considered to be an invariant feature and inherent in the structure of the motor program. Support for the invariance of relative timing was observed at both the kinematic and neuromuscular levels of analyses. Alternative models (9-11, 24) were found inadequate to account for the invariance of relative timing with the variation in movement time observed in the present experiment.
Cat medial interlaminar nucleus: retinotopy, relation to tapetum and implications for scotopic vision
Authors: Lee C. , Malpeli J. G. , Schwark H. D. , Weyand T. G.
Published: December 2017

The medial interlaminar nucleus (MIN) of the cat was electrophysiologically mapped in sufficient detail to resolve individual laminae and to allow reconstruction of isoazimuth and isoelevation lines in coronal, sagittal, and horizontal planes. The electrophysiologically defined laminar pattern was in agreement with that revealed anatomically in the same animal, as well as with the general pattern revealed by anatomical methods in several unmapped nuclei. The MIN is made up of three distinct layers, each receiving inputs from one hemi-retina but none representing an entire hemifield. We confirm the findings of Guillery et al. (19) that the contralateral hemifield is represented in layers 1 and 2 through the contralateral and ipsilateral eyes, respectively, and that layer 3 represents the ipsilateral hemifield through the contralateral eye. Elevation and absolute value of azimuth are represented continuously through the MIN. When an isoazimuth line crosses the border between layer 3 and either layer 1 or 2, the absolute value of azimuth is maintained but the sign of the azimuth changes. Adjacent points on either side of this border represent mirror symmetrical visual directions on opposite sides of the vertical meridian. This indicates that the distance from the vertical meridian is an independently coded parameter within the geniculate complex. There is virtually no nasotemporal overlap in any layer of the MIN. The function relating magnification (mm3 per steradian) to eccentricity is strikingly similar to the function relating retinal ganglion cell density to eccentricity, suggesting that a constant fraction of retinal ganglion cells project to the MIN at all eccentricities. Most of the volume of each MIN layer is devoted to lower visual fields. Analysis of the geniculate retinotopic maps of Sanderson (46) reveals no equivalent bias toward lower visual fields in the dorsal lateral geniculate nucleus. The MIN represents a region of retina roughly coincident with the tapetum, suggesting a role of the MIN in dim-light vision.
Physiological identification of midbrain neurons related to lens accommodation in cats
Authors: Bando T. , Tsukuda K. , Yamamoto N. , Maeda J. , Tsukahara N.
Published: December 2017

Single units were sought in the medial midbrain, whereas lens accommodation of the eye was monitored by using an infrared high-speed optometer. Nineteen of 135 units isolated were identified as accommodation-related units by two criteria: 1) they discharged in synchrony with spontaneously occurring accommodation, and b) the units were driven by stimulating the interpositus nucleus of the cerebellum. In eight other experiments, units were sought that were antidromically activated by stimulating parasympathetic preganglionic fibers to the ciliary ganglion. Eleven of 46 antidromically activated units were identified as accommodation-related units (accommodation-related oculomotor units). Accommodation-related oculomotor units were found in the medial midbrain within 1 mm of the midline. The majority of them were located lateral and dorsal to the Edinger-Westphal nucleus.
Cortical neurons related to lens accommodation in posterior lateral suprasylvian area in cats
Authors: Bando T. , Yamamoto N. , Tsukahara N.
Published: December 2017

Cortical units were sought that discharged in temporal correlation with spontaneously occurring lens accommodation in the area surrounding the middle suprasylvian sulcus, between the stereotaxic coordinates A8.0 and P1.0, while monitoring lens accommodation by using an infrared optometer. Units were tentatively identified as accommodation related if their discharges were modulated before the onset times of lens accommodation. Forty-eight accommodation-related units were found. Modulation of discharges preceded the onset times of accommodation by 360 ms on the average. Most (95%) of these units were related to the increase in the refractive power of the lens. Antidromic activation from the dorsal midbrain was tested in 26 of 48 accommodation-related units. Fourteen (67%) units were antidromically activated from the superior colliculus and/or the pretectum. Nine (64%) of them were also activated antidromically from the lateral posterior nucleus of the thalamus. The location of these units were confirmed by histological reconstruction. They were found in the posterior medial and posterior lateral lateral suprasylvian (PMLS and PLLS) areas and in the transitional zone of PMLS to the suprasylvian gyrus, between stereotaxic coordinates A7.0 and A1.5.
Response properties and functional organization of neurons in midline region of medullary reticular formation of cats
Authors: Yen C. T. , Blum P. S.
Published: December 2017

Extracellular single-unit recordings were made in the anesthetized cat from neurons within the medullary raphe nuclei and nearby reticular formation. The descending axons from some of these neurons were characterized in terms of length, conduction velocity, and location within the white matter of the spinal cord. The sensory properties were characterized following somatic, baroreceptor, visual, and auditory stimuli. The mean conduction velocities of the descending axons from neurons in the medullary raphe nuclei and in the magnocellular tegmental field (26 m/s) were significantly slower than the mean conduction velocities of units in the regions immediately dorsal to them (50 m/s). Action potentials in neurons in the medullary raphe nuclei and in the magnocellular tegmental field were evoked by anti-dromic stimulation from the dorsolateral portion of the spinal cord (30 of 43, 70%), whereas neurons located in more dorsal regions along the midline and in the reticular formation projected into the ventral columns (18 of 25, 72%). Neurons were most easily activated by a tap stimulus to the body surface. This stimulus activated 84% of the neurons tested. The receptive fields were large, often including the four limbs, back, and head. Tap-sensitive neurons were found throughout the regions investigated. Stimulation of hair receptors activated 37% of neurons tested, whereas 19% responded to a high-intensity cutaneous stimulus (pinch), 35% responded to baroreceptor stimuli, 32% responded to visual stimuli, and 33% responded to auditory stimuli. Neurons responsive to pinch were likely to respond to baroreceptor stimuli and unlikely to respond to visual stimuli. Neurons responsive to visual stimuli were likely to respond to auditory stimuli.
Saccade-related neurons in cat superior colliculus: pandirectional movement cells with postsaccadic responses
Authors: Peck C. K.
Published: December 2017

The superior colliculus is known to contain cells discharging before saccadic eye movements as well as cells responding to sensory stimuli. In this study extracellular single unit recordings were made in the alert trained cat with the head fixed. A novel type of eye movement-related response was found in 9% (32/344) of the cells recorded. These cells differ from previously reported eye movement-related neurons in the timing of their discharge, which accompanies but does not precede saccades. The timing of discharge varies across units from less than 10 ms after the onset of eye movement to as much as 80 ms. Comparable latencies were found regardless of whether saccades were directed contralateral or ipsilateral to the recording site. Most units have an abrupt onset of discharge, but some show a very gradual increase in discharge rate. Most cells (69% or 22/32) discharged with equal vigor for all saccades, regardless of direction. The remainder tended to show higher-frequency bursts when saccades were directed contralaterally, but even these units were not encoding saccade direction by their pattern of discharge. Thus the discharge pattern could be summarized as an omnidirectional burst. For the vast majority of cells (81% or 26/32) the duration of discharge did not correlate with the duration of eye movement. The same pattern of firing was seen with saccades in light and in complete darkness. Thus the saccade-related discharge was not due to changes in visual stimulation during saccades. A minority of the units (15% or 5 of 32) that discharged with but not before saccades also responded to visual stimuli in the absence of eye movements. Saccade-related activity was dependent on alertness of the cat, as measured by behavioral performance and EEG. The close temporal association between saccades and unit discharge disappeared during drowsiness. These units could be reflecting either proprioceptive or corollary discharge signals to the superior colliculus. However, their response properties differ somewhat from those found in previous studies of proprioceptive inputs to the colliculus. Such differences could be due to the effects of the anesthetics that were used in studies of proprioceptive responses. Alternatively, the cells reported here could be conveying a corollary discharge signal. These cells occurred in patches or clusters. This is consistent with a wealth of anatomic data indicating a modular organization of the colliculus.
Swallow-evoked action potentials in vagal preganglionic efferents
Authors: Gidda J. S. , Goyal R. K.
Published: December 2017

Swallow<evoked potentials in the preganglionic vagal fibers were studied using the single<fiber recording technique in anesthetized opossums. Swallows were evoked by tactile pharyngeal stimulation or electrical stimulation of the cut central end of the superior laryngeal nerve (SLN). Swallowing activity was recorded by the mylohyoid electromyogram and esophageal motility. Sixty<six fibers were studied in which swallowing evoked action potentials. The latencies (from the onset of mylohyoid activity) of evoked responses in different fibers varied from 100 ms to 5 s. The discharge rate of the evoked response was 3<8 action potentials per burst. Each burst lasted 1.1 +/- 0.02 (SE)s. The latencies of evoked spike bursts showed a bimodal distribution. In 34 fibers the latencies were less than 1 s, and in 32 fibers the latencies ranged between 1 and 5 s; these are the short- and long-latency fibers, respectively. Short-latency fibers could easily be distinguished from long-latency fibers based on the influence of SLN-stimulus frequency. Short-latency discharges had low thresholds of activation and were sensitive to changes in the frequency of SLN stimulation, since their latencies decreased and their discharge rate increased with increasing SLN-stimulus frequency. On the other hand, the latencies and discharge rates of long-latency discharges were not modified with changing SLN stimulus frequencies. The conduction velocities of 6 short- and 9 long-latency fibers were 5.64 +/- 0.12 and 5.78 +/- 0.12 (SE) m/s, respectively (P greater than 0.05). The relationship between the latencies of swallow-evoked discharges in the short- and long-latency fibers and the esophageal smooth muscle responses suggested that the short-latency discharges may correlate with the latency of initial inhibition, and the long-latency fibers may correlate with latencies of peristaltic contractions. Based on these temporal relationships, we speculate that vagal efferent fibers showing swallow-evoked, short-latency discharges make contact with intramural inhibitory neurons. They may mediate deglutitive inhibition in the body of the esophagus, relaxation of the lower esophageal sphincter, and receptive relaxation of the fundus of the stomach. The fibers showing late discharges make contact with intramural excitatory neurons and participate in their sequential activation. This dual pathway of activation may be responsible for physiological esophageal peristalsis.
Effects of medial geniculate lesions on sound localization by the rat
Authors: Kelly J. B. , Judge P. W.
Published: December 2017

Rats with bilateral lesions of the medial geniculate body were tested on a two-choice sound-localization task that required a directional response to a distant sound source. Stimuli included both broadband and filtered noise bursts presented singly or in repetitive trains. Separate tests were conducted with loudspeakers 180 and 60 degrees apart, centered around 0 degree azimuth. With complete bilateral destruction of the medial geniculate, rats could localize both trains and single bursts of noise and were capable of high levels of performance even at small angles of speaker separation. Some evidence of impaired performance was noted with high-frequency noise bursts, but generally the deficits were not severe. Animals with lesions that extended caudally into the brachium of the inferior colliculus and lateral tegmentum were severely impaired in their ability to localize sounds even at large angles of speaker separation. Three of the four animals in this group were incapable of localizing single bursts even with loudspeakers separated by 180 degrees, and the fourth was unable to perform above chance at 60 degrees. The effects of medial geniculate lesions were very similar to those reported previously for rats with lesions of the auditory cortex, but contrasted with reports of severe impairments in sound localization following damage to the auditory cortex in other mammalian species.
Use-dependent depression of IPSPs in rat hippocampal pyramidal cells in vitro
Authors: McCarren M. , Alger B. E.
Published: December 2017

We have used intracellular recording techniques to study the use-dependence of evoked inhibitory postsynaptic potentials (IPSPs) in rat CA1 hippocampal pyramidal cells. We determined reversal potentials and conductance changes associated with IPSPs and responses to directly applied gamma-aminobutyric acid (GABA). The IPSP depression could be seen after a single conditioning stimulus. This depression appeared to be due primarily to a 50% decrease in IPSP conductance (gIPSP). Trains of stimulating pulses (50 pulses at 5 or 10 Hz) produced more pronounced effects than a single conditioning pulse. Suprathreshold repetitive stimulation of stratum radiatum (SR) produced epileptiform burst firing and greater depression of IPSPs than did alvear (ALV) or subthreshold SR stimulation. During suprathreshold SR stimulation the IPSP was nearly abolished and the membrane potential could become less negative than the resting potential. A masking effect of facilitated depolarizing potentials on IPSPs was unlikely since IPSPs accompanied by little or no depolarizing potential were also depressed by SR trains. The 75% reduction in IPSP conductance found after repetitive stimulation confirmed that an overlapping conductance was not responsible for the depression of the IPSP. The GABA-induced conductance increase was not depressed by identical trains. Trains of stimulation induced depolarizing shifts in equilibrium potentials for the IPSP (EIPSP) and GABA (EGABA) of approximately 10 mV. These shifts were always greater after SR trains than after ALV trains. Simultaneous recordings of membrane potential and extracellular potassium concentration ([K+]o) with K+-sensitive microelectrodes revealed a direct correlation between the two during a stimulus train. Membrane potential depolarized as much as 18 mV from the peak of the IPSP and [K+]o could increase to a maximum of 10 mM during some trains. A depressant effect (of approximately 50%) of K+ on IPSPs was demonstrated by brief pressure ejection of K+ near the soma. We conclude that repetitive stimulation depresses gIPSP and shifts EIPSP in the depolarizing direction. Whereas gIPSP began to decline after a single conditioning pulse, the additional depression of IPSPs produced by stimulus trains was due in large part to shifts in EIPSP. Depression of gIPSP was not due to desensitization or block of ionic conductances, since gGABA was not reduced. The EIPSP may change as a result of increases in [K+]o.
Analysis of decreased conductance serotonergic response in Aplysia ink motor neurons
Authors: Walsh J. P. , Byrne J. H.
Published: December 2017

Micropressure ejection of serotonin (5-hydroxytryptamine, 5-HT) produced excitatory responses in the L14 ink motor neurons of Aplysia that depended on the site of application. Ejection of 5-HT onto the cell body produced a slow response that showed variability in voltage sensitivity between preparations. In contrast, ejection of 5-HT onto the neuropil underneath the cell body produced a response whose amplitude was consistently a linear function of the holding potential, reversing near the predicted potassium equilibrium potential. Subsequent analyses focused on this second response. The neuropil response induced by 5-HT had a linear current-voltage relationship (reversing at ca. -80 mV), was associated with a decrease in input conductance, and was sensitive to changes in the concentration of extracellular K+. Serotonin application in artificial seawater (ASW) containing 30 mM K+ produced a response that reversed close to the altered Nernst potential for K+. The 5-HT response did not appear to be due to secondary activation of interneurons or to depend primarily on extracellular Ca2+, since ejection of 5-HT onto cells bathed in ASW containing 30 mM Co2+ produced responses comparable to, although somewhat attenuated from, those observed in ASW. Serotonin responses similar to those produced in ASW were obtained after perfusing the ganglion with ASW containing Co2+, 4-aminopyridine (4-AP), and tetraethylammonium (TEA). This suggests that the 5-HT-sensitive current is separate from the Ca2+-activated, fast, and delayed rectifying K+ currents. The 5-HT response appeared to be mediated by changes in levels of cAMP. Bath application of the phosphodiesterase inhibitors IBMX (3-isobutyl-1-methylxanthine) or Ro 20-1724, or the adenylate cyclase activator forskolin mimicked the 5-HT response by producing a slow inward current associated with a decrease in membrane conductance. Alteration of cellular cAMP metabolism modulated the response to 5-HT. Exposure of the ganglion to low concentrations of either Ro 20-1724 or forskolin potentiated the 5-HT response. Higher concentrations of these agents largely blocked the response to subsequent 5-HT applications. Bath application of the 8-bromo derivative of either cAMP or cGMP produced a slow inward current associated with a decrease in membrane conductance in cells voltage clamped at the resting potential. Responses to 5-HT were blocked, however, after exposure to 8-bromo-cAMP, but not to 8-bromo-cGMP. These results suggest that 5-HT produces a voltage-independent decrease in a steady-state potassium conductance that may be mediated by cAMP.(ABSTRACT TRUNCATED AT 400 WORDS)
White noise analysis of cable properties of neuroblastoma cells and lamprey central neurons
Authors: Moore L. E. , Christensen B. N.
Published: December 2017

The integrative properties of two kinds of excitable cells, a cultured neuroblastoma cell and the lamprey giant interneuron, are described using a white-noise impedance method. The impedance functions were fitted with a neuron model consisting of an isopotential soma plus a single equivalent dendritic process, which contained up to 16 equal elements. The frequency-domain characteristics of both the passive and active conductances were used to estimate the dendritic-to-soma areas, the electrotonic length of an equivalent dendrite, the membrane time constant, and the relaxation time constants associated with the voltage-dependent conductances. The effect of differing degrees of synaptic input was simulated by localizing the synaptically activated conductances to the soma, a point at the end of the dendrite, or the entire dendritic membrane.
Patterns of facilitation and suppression of antagonist forelimb muscles from motor cortex sites in the awake monkey
Authors: Cheney P. D. , Fetz E. E. , Palmer S. S.
Published: December 2017

Patterns of excitatory and inhibitory effects were produced in antagonistic forelimb muscles by single intracortical microstimuli (S-ICMS) applied to motor cortex sites in macaque monkeys performing ramp-and-hold wrist movements. Stimulus-triggered averages (stimulus-TAs) of rectified electromyographic (EMG) activity revealed poststimulus facilitation and/or suppression in identified flexor and extensor muscles of the wrist and fingers. At 22 cortical sites the action potentials of single cells were also recorded and used to compute spike-triggered averages (spike-TAs) of covarying muscles. The set of muscles activated during the movement in which the cell was active are referred to here as "agonists"; those muscles active during wrist movement in the opposite direction are called "antagonists." (At sites where cells were not isolated the muscles showing poststimulus facilitation were called agonists.) Poststimulus effects in agonist muscles typically consisted of facilitation in a subset of the agonists. For 48 sites from which poststimulus effects were tested on both flexors and extensors, the following combinations of effects were observed: 1) pure facilitation of agonist muscles with no effect on antagonists; 2) facilitation of both agonists and antagonists; 3) facilitation of agonist muscles with reciprocal suppression of antagonists; 4) "mixed" facilitation and suppression of synergist muscles; and 5) pure suppression of some muscles with no effect on their antagonists. The suppression effects appeared most commonly in flexor muscles; conversely, facilitation was generally stronger in extensors. Cortical sites eliciting pure suppression of flexor muscles with no facilitation of extensor muscles were found in two monkeys. These purely suppressive effects were observed not only in stimulus-TAs but also in spike-TAs computed from single cells at these sites. Some of these cells increased their activity during wrist extension (but had no detectable effect on the extensor muscles); others discharged during flexion. Several observations suggest that the cortically evoked suppression is mediated by polysynaptic relays. The mean onset latency of the postspike suppression (7.4 ms) produced by inhibitory cells was longer than the mean onset latency of postspike facilitation (6.7 ms) produced by CM cells. Similarly, the mean onset latency of poststimulus suppression (8.9 ms) was longer than that of poststimulus facilitation (8.0 ms). Moreover, suppression was usually weaker than facilitation in the spike-TAs, as well as in stimulus-TAs compiled for the same stimulus intensity.(ABSTRACT TRUNCATED AT 400 WORDS)
Transient voltage and calcium-dependent outward currents in hippocampal CA3 pyramidal neurons
Authors: Zbicz K. L. , Weight F. F.
Published: December 2017

Membrane currents activated by step changes in membrane potential were studied in hippocampal pyramidal neurons of region CA3 using the single microelectrode voltage-clamp technique. The transient outward current activated by depolarizing steps appeared to be composed of two transient currents that could be distinguished by differences in voltage sensitivity, time course, and pharmacological sensitivity. The more slowly decaying current was activated by voltage steps positive to -60 mV and declined exponentially with a time constant between 200 and 400 ms. This current inactivated as the holding potential was made more positive over the range of -75 to -45 mV and was 50% inactivated near -60 mV. The more slowly decaying transient current was selectively blocked by 0.5 mM 4-aminopyridine (4-AP) but not by 5-10 mM tetraethylammonium (TEA) or 2-5 mM Mn2+. The second transient current had a much faster time course than the 4-AP-sensitive current, having a duration of 5-20 ms. This very fast transient current was observed during potential steps positive to -45 mV. The fast transient current was inactivated when the holding potential was made positive to -45 mV. The amplitude of the fast transient current was greatly reduced by the application of 4 mM Mn2+ or Ca2+-free artificial cerebrospinal fluid (CSF). The fast transient current appeared to be unaffected by 0.5 mM 4-AP but was greatly reduced by 10 mM TEA. These results suggest that the transient outward current observed during depolarizing steps is composed of at least two distinct transient currents. The more slowly decaying current resembles the A-current originally described in molluscan neurons (9, 32, 42) in voltage sensitivity, time course, and pharmacological sensitivity. The faster transient current resembles a fast, Ca2+-dependent transient current previously observed in bull-frog sympathetic neurons (5, 27).
Inhibition and level-tolerant frequency tuning in the auditory cortex of the mustached bat
Authors: Suga N. , Tsuzuki K.
Published: December 2017

For echolocation the mustached bat, Pteronotus parnellii, emits complex orientation sounds (pulses), each consisting of four harmonics with long constant-frequency components (CF1-4) followed by short frequency-modulated components (FM1-4). The CF signals are best suited for target detection and measurement of target velocity. The CF/CF area of the auditory cortex of this species contains neurons sensitive to pulse-echo pairs. These CF/CF combination-sensitive neurons extract velocity information from Doppler-shifted echoes. In this study we electrophysiologically investigated the frequency tuning of CF/CF neurons for excitation, facilitation, and inhibition. CF1/CF2 and CF1/CF3 combination-sensitive neurons responded poorly to individual signal elements in pulse-echo pairs but showed strong facilitation of responses to pulse-echo pairs. The essential components in the pairs were CF1 of the pulse and CF2 or CF3 of the echo. In 68% of CF/CF neurons, the frequency-tuning curves for facilitation were extremely sharp for CF2 or CF3 and were "level-tolerant" so that the bandwidths of the tuning curves were less than 5.0% of best frequencies even at high stimulus levels. Facilitative tuning curves for CF1 were level tolerant only in 6% of the neurons studied. CF/CF neurons were specialized for fine analysis of the frequency relationship between two CF sounds regardless of sound pressure levels. Some CF/CF neurons responded to single-tone stimuli. Frequency-tuning curves for excitation (responses to single-tone stimuli) were extremely sharp and level tolerant for CF2 or CF3 in 59% of CF1/CF2 neurons and 70% of CF1/CF3 neurons. Tuning to CF1 was level tolerant in only 9% of these neurons. Sharp level-tolerant tuning may be the neural basis for small difference limens in frequency at high stimulus levels. Sharp level-tolerant tuning curves were sandwiched between broad inhibitory areas. Best frequencies for inhibition were slightly higher or lower than the best frequencies for facilitation and excitation. We thus conclude that sharp level-tolerant tuning curves are produced by inhibition. The extent to which neural sharpening occurred differed among groups of neurons tuned to different frequencies. The more important the frequency analysis of a particular component in biosonar signals, the more pronounced the neural sharpening. This was in addition to the peripheral specialization for fine frequency analysis of that component. The difference in bandwidth or quality factor between the excitatory tuning curves of peripheral neurons and the facilitative and excitatory tuning curves of CF/CF neurons was larger at higher stimulus levels.(ABSTRACT TRUNCATED AT 400 WORDS)
Voluntary and reflexive recruitment of flexor carpi radialis motor units in humans
Authors: Calancie B. , Bawa P.
Published: December 2017

The order of recruitment of flexor carpi radialis (FCR) motor units was studied during voluntary and reflexive activation of the motoneuron pool for two adult subjects. During slow "voluntary" activation, the recruitment threshold for tonic motoneuron firing was determined, and then the twitch profile of the motor unit was computed by the spike-triggered averaging technique. A positive correlation (r = 0.79 and 0.68 for the two subjects, respectively) between recruitment threshold and twitch amplitude implies that recruitment of FCR motoneurons during slow ramp isometric contractions proceeds in order of increasing size. The accompanying paper describes the behavior of single motor units during the short- and long-latency periods of the stretch reflex. When the effects of sufficient voluntary facilitation (preload) combined with a sufficiently large torque step were just adequate to cause a motor unit to fire during the stretch reflex, its response was virtually always confined to the long-latency period. In addition, the first unit to begin responding to muscle stretch always had the lowest voluntary recruitment threshold relative to other units "visible" at that recording site. By making this unit tonic, the reflex response to the same load increased substantially during the short-latency reflex period, while a second unit increased its reflex response probability during the long-latency period. Thus the voluntary recruitment order of two or more motor units is preserved during the stretch reflex, and is in fact maintained within first the long-latency and then short-latency components of this reflex.
A complex-cell receptive-field model
Authors: Spitzer H. , Hochstein S.
Published: December 2017

The time course of the response of a single cortical neuron to counterphase-grating stimulation may vary as a function of stimulation parameters, as shown in the preceding paper (19). The poststimulus-time histograms of the response amplitudes against time are single or double peaked, and where double peaked, the two peaks are of equal or unequal amplitudes. Furthermore, the spatial-phase dependence of cortical complex-cell responses may be a function of spatial frequency, so that the receptive field appears to have linear spatial summation at some spatial frequencies and nonlinear spatial summation at others (19). In the first part of this paper, we analyze a model receptive field that displays this behavior, and in the second part experimental data are presented and analyzed with regard to the model. The model cortical receptive field in its simplest form contains (two rows) of geniculate X-cell-like, DOG (difference-of-Gaussians)-shaped, center-surround antagonistic, circular-input subunits. We propose nonlinear summation between these two subunits, by introducing a half-wave rectification stage before pooling. The model is tested for the responses it predicts for the application of counterphase-grating stimulation. This simple model predicts the appearance of three response forms as a function of counterphase-stimulation parameters. At periodic spatial frequencies the expected-response histogram has a single peak, whose amplitude has a sinusoidal dependence on spatial phase. At spatial frequencies halfway between these, the expected-response histogram has two equal peaks whose amplitudes have a full-wave rectified sinusoidal dependence on spatial phase. At all intermediate spatial frequencies the expected-response histogram has a "mixed" form; the histogram appears sometimes with one peak, sometimes with two equal peaks, and generally with two peaks of unequal amplitude, as a function of spatial phase. Null responses are expected to appear at specific spatial phases only for the periodic spatial frequencies that give "pure" response time courses as in paragraph 5 above, and not in the more common mixed response case of paragraph 6. The analysis procedure described in the preceding paper (19) is used, separating the odd and even Fourier components of the response histograms reflecting the receptive-field intrasubunit linear summation and intersubunit nonlinear summation, respectively. We propose that this model may be used as a working hypothesis for the analysis of these aspects of the various cortical receptive-field types. Experimental data are described and discussed in terms of the model.(ABSTRACT TRUNCATED AT 400 WORDS)
Relationship among recruitment order, axonal conduction velocity, and muscle-unit properties of type-identified motor units in cat plantaris muscle
Authors: Zajac F. E. , Faden J. S.
Published: December 2017

A strict interpretation of the size-principle hypothesis (37, 39-41) is that a muscle's motor units should be recruited in an ascending order according to both the size of their motoneurons and the size of their innervated muscle units (for reviews see Refs. 9, 39, 73). Studies of large mixed muscles in the cat hindlimb, however, have shown that motor axonal conduction velocity and tetanic tension, which are frequently considered indices of motoneuron and muscle-unit size, respectively, are uncorrelated in the fast-twitch (type F) motor-unit subpopulation (12, 13, 23, 24, 30, 32, 63, 71, 79). Attempting to focus on type F units, we compared the recruitment order of 42 pairs of cat plantaris (PL) motor units with both axonal conduction velocity and tetanic tension as well as with other muscle-unit properties. Single PL alpha-motor axons were functionally isolated in intact L7 ventral root filaments of decerebrate cats. Tension responses produced by stimulating each isolated motor axon were used to find the tetanic tension of the muscle unit and to classify the unit (12) as either type S (slow twitch, fatigue resistant), type FR (fast twitch, fatigue resistant), type FI (fast twitch, intermediate fatigability), or type FF (fast twitch, highly fatigable). Conduction velocity of each isolated axon was computed from measurements of axonal conduction time and length. The axon's reflex discharges were recorded from the proximal end of the cut filament and compared with the discharges of another PL axon residing in a different, previously cut filament of the same cat. The recruitment order of each motor-unit pair studied was found during reflexes elicited by homonymous muscle stretch, tendon taps, or single shocks at group I intensity to the PL nerve. If either axon of the pair failed to discharge, as often was the case with the high-threshold type F units, the monosynaptic reflex was facilitated by a 500-pps conditioning train applied proximal to a complete reversible cooling block of the PL nerve. In all 42 pairs studied, the weaker motor unit had the lower functional threshold for recruitment. Recruitment also invariably followed the order S greater than FR greater than FI greater than FF units. The motor unit of a pair with the higher resistance to fatigue thus always had the lower functional threshold. In 21 of the 22 pairs containing at least one type S motor unit, the unit with the slower-conducting motor axon had the lower functional threshold for recruitment.(ABSTRACT TRUNCATED AT 400 WORDS)
Somatotopic distribution of trigeminal nociceptive neurons in ventrobasal complex of cat thalamus
Authors: Yokota T. , Koyama N. , Matsumoto N.
Published: December 2017

Recordings were made from single thalamic units in the urethan-chloralose anesthetized cat. Altogether 2,905 trigeminal single units having a receptive field in the contralateral trigeminal integument were isolated from the somatosensory part of nucleus ventralis posteromedialis, or VPM proper. Each isolated unit was tested for responses to a series of mechanical stimuli. The stimuli included brushing the skin, touch, pressure, noxious pinch, and pinpricks. The majority of VPM proper units responded with the greatest discharge frequency to gentle mechanical stimulation: either hair movement or light pressure to the trigeminal integument, but 341 units were identified as trigeminal nociceptive units. They were partitioned into two functionally defined subclasses, nociceptive specific (NS) and wide dynamic range (WDR) units, but not intermingled with low-threshold mechanoreceptive (LTM) units. Both NS and WDR units were found at or near the margin of the VPM proper but not outside this nucleus. This marginal area was referred to as the shell region of the VPM proper. A total of 248 NS units was found within the shell region of the caudal third of the VPM proper. This part was called the NS zone. These units were somatotopically organized. In the rostral part of the NS zone, ophthalmic NS units having a receptive field in the contralateral ophthalmic division were located dorsolaterally, maxillary NS units occurred dorsomedially, and mandibular NS units were found ventromedially. In the caudal part of the NS zone, maxillary NS units were encountered in the dorsal shell region, whereas mandibular NS units were found in the ventromedial shell region. Ophthalmic NS units were not found in this part of the NS zone. Altogether 93 WDR units were encountered in the shell region of the VPM proper. They were confined to a narrow band approximately 300 micron wide just rostral to the NS zone. These units were somatotopically organized. Ophthalmic WDR units having a low-threshold center of the receptive field in the contralateral ophthalmic division were located dorsolaterally, maxillary WDR units were located dorsomedially, and mandibular WDR units were located ventromedially. The majority of maxillary as well as mandibular WDR units were activated by electrical stimulation of the contralateral maxillary and/or mandibular canine tooth pulp afferents. Both NS and WDR zones of the VPM proper extended into the shell region of the nucleus ventralis posterolateralis (VPL).(ABSTRACT TRUNCATED AT 400 WORDS)
Development of locomotor mechanisms in the frog
Authors: Stehouwer D. J. , Farel P. B.
Published: December 2017

Tadpoles swim by undulations of the body and tail, whereas frogs locomote by alternate (stepping) and synchronous (frog-kick) movements of the hindlimbs. The development of interlimb coordination was studied by recording the activity of hindlimb motoneurons from the left and right ninth ventral roots of the isolated central nervous system (CNS). Results showed that mechanisms responsible for interlimb coordination of stepping are functional when the hindlimb is still composed of undifferentiated mesenchyme and before the lateral motor column has stabilized (stage III). The early appearance of coordinated activation of hindlimb motoneurons suggests that innervation of appropriate target muscles is not a prerequisite for normal development of circuits that mediate interlimb coordination of stepping. Synchronous activation of left and right hindlimb motoneurons (fictive frog kicks) appeared later in development (stage XIV). Throughout larval development 1:1 frequency coupling between both alternating and synchronous bursts of hindlimb motoneurons and bursts of primary motoneurons (those innervating axial muscles) was found. Recordings of peripheral nerve activity showed that motoneurons innervating antagonistic muscles of the thigh burst in antiphase. This intralimb coordination was present at stage X, a foot paddle stage that was the earliest stage in which the peripheral nerves were successfully dissected. That the neural activity of the isolated nervous system described above indeed underlies coordinated locomotor movements of the hindlimbs was shown by single-frame videotape analysis of hindlimb movements produced by the otherwise isolated CNS. The stepping movements displayed by those preparations were consistent with patterns of electrophysiological burst activity recorded from the ventral roots and peripheral nerves. The ontogenetic sequence in which the different patterns of electrophysiological activity emerged is the same as that of the corresponding behaviors in the intact tadpole. Although there were developmental changes in the reliability with which coordinated activity in the ventral roots and peripheral nerves was observed, each mode of coordination remained qualitatively unchanged from its earliest appearance through metamorphosis. These results show that mechanisms underlying locomotor coordination of the hindlimbs develop very early in larval ontogeny of the frog and can function when isolated from the periphery.
Three forms of the scratch reflex in the spinal turtle: movement analyses
Authors: Mortin L. I. , Keifer J. , Stein P. S.
Published: December 2017

The scratch reflex is a motor task exhibited by the hindlimb of a turtle after complete transection of the spinal cord just posterior to the forelimb enlargement. The scratch is elicited by applying gentle tactile stimulation to a site innervated by spinal segments caudal to the level of the transection. During the scratch response, the ipsilateral hindlimb reaches toward and rubs against the stimulated site. Each scratch response consists of either a single rub or a rhythmic series of rubs. There are three types or “forms” of the scratch reflex in the spinal turtle: rostral scratch (previously termed the scratch reflex in Refs. 5, 43, 45), pocket scratch, and caudal scratch. We have characterized each scratch form according to which portion of the hindlimb is used to rub against the stimulated site. During a rostral scratch, the dorsum of the foot and/or toes is used to rub against the stimulated site. During a pocket scratch, the side of the thigh, knee, and/or calf is used to rub. During a caudal scratch, the heel or side of the foot is used to rub. Each scratch form has a distinct receptive field on the turtle shell and skin. A rhythmic scratch response to maintained tactile stimulation consists of as many as 10-25 cycles. We have divided each cycle of movement into a prerub, rub, and postrub phase. Extension of the knee joint occurs during the rub phase of each scratch cycle for all scratch forms. The timing of the extension phase of the knee joint movement within the protraction-retraction (flexion-extension) cycle of the hip joint is different for each form of the scratch. During a rostral scratch, extension of the knee joint occurs when the hip is protracted. During a pocket scratch, knee extension occurs when the hip is retracting. During a caudal scratch, knee extension occurs when the hip is retracted. The spinal turtle therefore shifts the timing of movements of a distal joint (knee) with respect to the timing of movements of a proximal joint (hip) to obtain appropriate scratching movements to different regions of the body. A narrow transition zone exists between the receptive field for one form of the scratch and the nearby receptive field for another form of the scratch. There is a rostral-pocket transition zone and caudal-pocket transition zone in the spinal turtle.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of pattern deprivation on visual cortical cells in the rabbit: a reevaluation
Authors: Murphy E. H.
Published: December 2017

The response properties of 217 cells recorded from the monocular segment of primary visual cortex in rabbits reared with lid suture of the contralateral eye (monocular deprivation, MD) were studied. These data were compared with 280 cells recorded from normal rabbits. There was no change in the percentage of orientation-selective cells, nonorientation-selective cells, or unmappable/unresponsive cells in MD animals compared with normals. Among orientation selective cells the orientation-tuning range of cells in MD animals was normal, and the predominance of cells with horizontal preferred orientation was maintained. However, some abnormalities were seen in orientation-selective cells of MD animals. These included an increased frequency of SI cells; a change in the distribution of preferred orientations; a disruption of the clustered organization of the cortex; a decrease in direction selectivity; an increase in the percentage of cells preferring slow stimulus movements and having low spontaneous activity; an increase in receptive-field size in all cell classes except SI. Among nonorientation-selective cells there was an increase in the percentage of movement sensitive cells and an increase in receptive-field size in MD animals. It is concluded that the effects of MD are much less severe in rabbit than in cat. In MD rabbits, many cells develop normally. In cells that do not develop normally, many of the changes observed can be interpreted as reflecting deficits in inhibitory functions.
Convergence of hepatic osmoreceptive inputs on sodium-responsive units within the nucleus of the solitary tract of the rat
Authors: Kobashi M. , Adachi A.
Published: December 2017

Single-shock electrical stimulation of the hepatic branch of the vagus induced both facilitation and suppression in units within the nucleus of the solitary tract (NTS). Some units that were facilitated by electrical stimulation also increased their discharge rates during topical iontophoretic application of Na+, as well as portal infusion of hypertonic saline. Other facilitatory units produced opposite responses; their discharge rates decreased during topical iontophoretic application of Na+ and portal infusion of hypertonic saline. Some units that were suppressed by electrical stimulation also responded to the topical application of Na+ and portal infusion of hypertonic saline. The responses to these two different stimuli were positively correlated in some units but not in others. The evidence suggests that the units within the NTS that are responsive to hepatic osmosensitive primary afferents may serve a Na+-responsive function and may be important in integration within the NTS for isosmotic or isovolemic homeostasis.