bluuebunny/crossref_metadata_2025 huggingface dataset:
Forms of Forward Quadrupedal Locomotion. II. A Comparison of Posture, Hindlimb Kinematics, and Motor Patterns for Upslope and Level Walking
Authors: Carlson-Kuhta Patricia , Trank Tamara V. , Smith Judith L.
Published: December 2017

Carlson-Kuhta, Patricia, Tamara V. Trank, and Judith L. Smith. Forms of forward quadrupedal locomotion. II. A comparison of posture, hindlimb kinematics, and motor patterns for upslope and level walking. J. Neurophysiol. 79: 1687–1701, 1998. To gain insight into the neural mechanisms controlling different forms of quadrupedal walking of normal cats, data on postural orientation, hindlimb kinematics, and motor patterns of selected hindlimb muscles were assessed for four grades of upslope walking, from 25 to 100% (45° incline), and compared with similar data for level treadmill walking (0.6 m/s). Kinematic data for the hip, knee, ankle, and metatarsophalangeal joints were obtained from digitizing ciné film that was synchronized with electromyographic (EMG) records from 13 different hindlimb muscles. Cycle periods, the structure of the step cycle, and paw-contact sequences were similar at all grades and typical of lateral-sequence walking. Also, a few half-bound and transverse gallop steps were assessed from trials at the 100% grade; these steps had shorter cycle periods than the walking steps and less of the cycle (68 vs. 56%) was devoted to stance. Each cat assumed a crouched posture at the steeper grades of upslope walking and stride length decreased, whereas the overall position of the stride shifted caudally with respect to the hip joint. At the steeper grades, the range and duration of swing-related flexion increased at all joints, the stance-phase yield was absent at the knee and ankle joints, and the range of stance-phase extension at knee and ankle joints increased. Patterns of muscle activity for upslope and level walking were similar with some notable exceptions. At the steeper grades, the EMG activity of muscles with swing-related activity, such as the digit flexor muscle, the flexor digitorum longus (FDL), and the knee flexor muscle, the semitendinosus (ST), was prolonged and continued well into midswing. The EMG activity of stance-related muscles also increased in amplitude with grade, and three muscles not active during the stance phase of level walking had stance activity that increased in amplitude and duration at the steepest grades; these muscles were the ST, FDL, and extensor digitorum brevis. Overall the changes in posture, hindlimb kinematics, and the activity patterns of hindlimb muscles during upslope walking reflected the need to continually move the body mass forward and upward during stance and to ensure that the paw cleared the inclined slope during swing. The implications of these changes for the neural control of walking and expected changes in hindlimb kinetics for slope walking are discussed.
Complex Blockade of TTX-Resistant Na+Currents by Lidocaine and Bupivacaine Reduce Firing Frequency in DRG Neurons
Authors: Scholz Andreas , Kuboyama Noboru , Hempelmann Gunter , Vogel Werner
Published: December 2017

Scholz, Andreas, Noboru Kuboyama, Gunter Hempelmann, and Werner Vogel. Complex blockade of TTX-resistant Na+currents by lidocaine and bupivacaine reduce firing frequency in DRG neurons. J. Neurophysiol. 79: 1746–1754, 1998. Mechanisms of blockade of tetrodotoxin-resistant (TTXr) Na+channels by local anesthetics in comparison with the sensitivity of tetrodotoxin-sensitive (TTXs) Na+channels were studied by means of the patch-clamp technique in neurons of dorsal root ganglions (DRG) of rat. Half-maximum inhibitory concentration (IC50) for the tonic block of TTXr Na+currents by lidocaine was 210 μmol/l, whereas TTXs Na+currents showed five times lower IC50of 42 μmol/l. Bupivacaine blocked TTXr and TTXs Na+currents more potently with IC50of 32 and 13 μmol/l, respectively. In the inactivated state, TTXr Na+channel block by lidocaine showed higher sensitivities (IC50= 60 μmol/l) than in the resting state underlying tonic blockade. The time constant τ1of recovery of TTXr Na+channels from inactivation at −80 mV was slowed from 2 to 5 ms after addition of 10 μmol/l bupivacaine, whereas the τ2value of ∼500 ms remained unchanged. The use-dependent block of TTXr Na+channels led to a progressive reduction of current amplitudes with increasing frequency of stimulation, which was ≤53% block at 20 Hz in 10 μmol/l bupivacaine and 81% in 100 μmol lidocaine. The functional importance of the use-dependent block was confirmed in current-clamp experiments where 30 μmol/l of lidocaine or bupivacaine did not suppress the single action potential but clearly reduced the firing frequency of action potentials again with stronger potency of bupivacaine. Because it was found that TTXr Na+channels predominantly occur in smaller sensory neurons, their blockade might underlie the suppression of the sensation of pain. Different sensitivities and varying proportions of TTXr and TTXs Na+channels could explain the known differential block in spinal anesthesia. We suggest that the frequency reduction at low local anesthetic concentrations may explain the phenomenon of paresthesia where sensory information are suppressed gradually during spinal anesthesia.
Vowel Representations in the Ventral Cochlear Nucleus of the Cat: Effects of Level, Background Noise, and Behavioral State
Authors: May Bradford J. , Prell Glenn S. Le , Sachs Murray B.
Published: December 2017

May, Bradford J., Glenn S. Le Prell, and Murray B. Sachs. Vowel representations in the ventral cochlear nucleus of the cat: effects of level, background noise, and behavioral state. J. Neurophysiol. 79: 1755–1767, 1998. Single-unit responses were studied in the ventral cochlear nucleus (VCN) of cats as formant and trough features of the vowel /ε/ were shifted in the frequency domain to each unit's best frequency (BF; the frequency of greatest sensitivity). Discharge rates sampled with this spectrum manipulation procedure (SMP) were used to estimate vowel representations provided by populations of VCN neurons. In traditional population measures, a good representation of a vowel's formant structure is based on relatively high discharge rates among units with BFs near high-energy formant features and low rates for units with BFs near low-energy spectral troughs. At most vowel levels and in the presence of background noise, chopper units exhibited formant-to-trough rate differences that were larger than VCN primary-like units and auditory-nerve fibers. By contrast, vowel encoding by primary-like units resembled auditory nerve representations for most stimulus conditions. As is seen in the auditory nerve, primary-like units with low spontaneous rates (SR <18 spikes/s) produced better representations than high SR primary-like units at all but the lowest vowel levels. Awake cats exhibited the same general response properties as anesthetized cats but larger between-subject differences in vowel driven rates. The vowel encoding properties of VCN chopper units support previous interpretations that patterns of auditory nerve convergence on cochlear nucleus neurons compensate for limitations in the dynamic range of peripheral neurons.
Temporal and Amplitude Generalization in Motor Learning
Authors: Goodbody Susan J. , Wolpert Daniel M.
Published: December 2017

Goodbody, Susan J. and Daniel M. Wolpert. Temporal and amplitude generalization in motor learning. J. Neurophysiol. 79: 1825–1838, 1998. A fundamental feature of human motor control is the ability to vary effortlessly over a substantial range, both the duration and amplitude of our movements. We used a three-dimensional robotic interface, which generated novel velocity dependent forces on the hand, to investigate how adaptation to these altered dynamics experienced only for movements at one temporal rate and amplitude generalizes to movements made at a different rate or amplitude. After subjects had learned to make a single point-to-point movement in a novel velocity-dependent force field, we examined the generalization of this learning to movements of both half the duration or twice the amplitude. Such movements explore a state-space not experienced during learning—any changes in behavior are due to generalization of the learning, the form of which was used to probe the intrinsic constraints on the motor control process. The generalization was assessed by determining the force field in which subjects produced kinematically normal movements. We found substantial generalization of the motor learning to the new movements supporting a nonlocal representation of the control process. Of the fields tested, the form of the generalization was best characterized by linear extrapolation in a state-space representation of the controller. Such an intrinsic constraint on the motor control process can facilitate the scaling of natural movements.
Synchronous Period-Doubling in Flicker Vision of Salamander and Man
Authors: Crevier Daniel W. , Meister Markus
Published: December 2017

Crevier, Daniel W. and Markus Meister. Synchronous period-doubling in flicker vision of salamander and man. J. Neurophysiol. 79: 1869–1878, 1998. Periodic flashes of light have long served to probe the temporal properties of the visual system. Here we show that during rapid flicker of high contrast and intensity the eye reports to the brain only every other flash of light. In this regime, retinal ganglion cells of the salamander fire spikes on alternating flashes. Neurons across the entire retina are locked to the same flashes. The effect depends sharply on contrast and flash frequency. It results from a period-doubling bifurcation in retinal processing, and a simple model of nonlinear feedback reproduces the phenomenon. Pharmacological studies indicate that the critical feedback interactions require only cone photoreceptors and bipolar cells. Analogous period-doubling is observed in the human visual system. Under bright full-field flicker, the electroretinogram (ERG) shows a regime of period-doubling between 30 and 70 Hz. In visual evoked potentials from the occiput, the subharmonic component is even stronger. By analyzing the accompanying perceptual effects, we find that retinal period-doubling begins in the periphery of the visual field, and that it is the cause of a long mysterious illusory flicker pattern.
Dendritic Structure and Receptive-Field Organization of Optic Flow Processing Interneurons in the Fly
Authors: Krapp Holger G. , Hengstenberg Bärbel , Hengstenberg Roland
Published: December 2017

Krapp, Holger G., Bärbel Hengstenberg, and Roland Hengstenberg. Dendritic structure and receptive-field organization of optic flow processing interneurons in the fly. J. Neurophysiol. 79: 1902–1917, 1998. The third visual neuropil (lobula plate) of the blowfly Calliphora erythrocephala is a center for processing motion information. It contains, among others, 10 individually identifiable “vertical system” (VS) neurons responding to visual wide-field motions of arbitrary patterns. We demonstrate that each VS neuron is tuned to sense a particular aspect of optic flow that is generated during self-motion. Thus the VS neurons in the fly supply visual information for the control of head orientation, body posture, and flight steering. To reveal the functional organization of the receptive fields of the 10 VS neurons, we determined with a new method the distributions of local motion sensitivities and local preferred directions at 52 positions in the fly's visual field. Each neuron was identified by intracellular staining with Lucifer yellow and three-dimensional reconstructions from 10-μm serial sections. Thereby the receptive-field organization of each recorded neuron could be correlated with the location and extent of its dendritic arborization in the retinotopically organized neuropil of the lobula plate. The response fields of the VS neurons, i.e., the distributions of local preferred directions and local motion sensitivities, are not uniform but resemble rotatory optic flow fields that would be induced by the fly during rotations around various horizontal axes. Theoretical considerations and quantitative analyses of the data, which will be presented in a subsequent paper, show that VS neurons are highly specialized neural filters for optic flow processing and thus for the visual sensation of self-motions in the fly.
Dynamics of Excitatory Transmitter Release: Analysis of Synaptic Responses in CA3 Hippocampal Neurons After Repetitive Stimulation of Afferent Fibers
Authors: Canepari Marco , Cherubini Enrico
Published: December 2017

Canepari, Marco and Enrico Cherubini. Dynamics of excitatory transmitter release: analysis of synaptic responses in CA3 hippocampal neurons after repetitive stimulation of afferent fibers. J. Neurophysiol. 79: 1977–1988, 1998. The patch-clamp technique (whole cell configuration) was used to record excitatory postsynaptic currents (EPSCs) evoked by repetitive stimulation (4 pulses at 50-ms intervals) of afferent fibers in the stratum lucidum-radiatum. Different synaptic behaviors (EPSC patterns) were classified in terms of facilitation or depression of the mean amplitude of the second, third, and fourth EPSC with respect to the previous one. A large variety of EPSC patterns was observed by stimulating different afferent fibers. Experiments with the mGluR2/mGluR3 agonist 2-(2,3-dicarboxycyclopropyl)glycine (DCG-IV) (1 μM), a compound that reduces release at mossy but not at associative commissural fibers and therefore allows to identify the origin of synaptic responses, showed that particular EPSC patterns could not be associated to the activation of a specific type of synaptic input. To investigate the role of the probability of release in the dynamics of synaptic activity, the extracellular calcium concentration was varied from 0.8 to 4 mM in several experiments. EPSC patterns dominated by depression, characteristics of high release probability conditions, could be observed in the majority of the cases in the presence of higher calcium concentrations. A quantitative model for dynamics of transmitter release has been developed. Experimental results were compared with data computed with the model taking into account the probability of release and the time course of reavailability. This work indicates that short-term changes of presynaptic conditions occurring during a train of action potentials can account for the high variability of EPSC responses. The model that is proposed also suggests a general method of experimental data analysis to investigate the possible presynaptic mechanisms underlying long-lasting changes in synaptic efficacy.
Biophysical Characterization and Functional Consequences of a Slowly Inactivating Potassium Current in Neostriatal Neurons
Authors: Gabel Lisa A. , Nisenbaum Eric S.
Published: December 2017

Gabel, Lisa A. and Eric S. Nisenbaum. Biophysical characterization and functional consequences of a slowly inactivating potassium current in neostriatal neurons. J. Neurophysiol. 79: 1989–2002, 1998. Neostriatal spiny projection neurons can display a pronounced delay in their transition to action potential discharge that is mediated by a slowly developing ramp depolarization. The possible contribution of a slowly inactivating A-type K+ current ( I As) to this delayed excitation was investigated by studying the biophysical and functional properties of I As using whole cell voltage- and current-clamp recording from acutely isolated neostriatal neurons. Isolation of I As from other voltage-gated, calcium-independent K+ currents was achieved through selective blockade of I As with low concentrations (10 μM) of the benzazepine derivative,6 - chloro - 7 , 8 - dihydroxy - 3 - allyl - 1 - phenyl - 2 , 3 , 4 , 5 - tetra - hydro1H-3-benzazepine (APB; SKF82958) and subsequent current subtraction. Examination of the voltage dependence of activation showed that I As began to flow at approximately −60 mV in response to depolarization. The voltage dependence of inactivation revealed that ∼50% of I As channels were available at the normal resting potential (−80 mV) of these cells, but that only 20% of the channels were available at membrane potentials corresponding to spike threshold (about −40 mV). At these depolarized membrane potentials, the rate of activation was moderately rapid (τ ∼ 60 ms), whereas the rate of inactivation was slow (τ ∼ 1.5 s). The time course of removal of inactivation of I As at −80 mV also was relatively slow (τ ∼ 1.0 s). The subthreshold availability of I As combined with its rapid activation and slow inactivation rates suggested that this current should be capable of dampening the onset of prolonged depolarizing responses, but over time its efficacy should diminish, slowly permitting the membrane to depolarize toward spike threshold. Voltage recording experiments confirmed this hypothesis by demonstrating that application of APB at a concentration (10 μM) that selectively blocks I As substantially decreased the latency to discharge and increased the frequency of firing of neostriatal neurons. The properties of I As suggest that it should play a critical role in placing the voltage limits on the recurring episodes of subthreshold depolarization which are characteristic of spiny neurons recorded in vivo. However, the voltage dependence and recovery kinetics of inactivation of I As predict that its effectiveness will vary exponentially with the level and duration of hyperpolarization which precedes depolarizing episodes. Thus long periods of hyperpolarization should increase the availability of I As and dampen succeeding depolarizations; whereas brief epochs of hyperpolarization should not sufficiently remove inactivation of I As, thereby reducing its ability to limit subsequent depolarizing responses.
Auditory Motion Induces Directionally Dependent Receptive Field Shifts in Inferior Colliculus Neurons
Authors: Wilson Willard W. , O'Neill William E.
Published: December 2017

Wilson, Willard W. and William E. O'Neill. Auditory motion induces directionally dependent receptive field shifts in inferior colliculus neurons. J. Neurophysiol. 79: 2040–2062, 1998. This research focused on the response of neurons in the inferior colliculus of the unanesthetized mustached bat, Pteronotus parnelli, to apparent auditory motion. We produced the apparent motion stimulus by broadcasting pure-tone bursts sequentially from an array of loudspeakers along horizontal, vertical, or oblique trajectories in the frontal hemifield. Motion direction had an effect on the response of 65% of the units sampled. In these cells, motion in opposite directions produced shifts in receptive field locations, differences in response magnitude, or a combination of the two effects. Receptive fields typically were shifted opposite the direction of motion (i.e., units showed a greater response to moving sounds entering the receptive field than exiting) and shifts were obtained to horizontal, vertical, and oblique motion orientations. Response latency also shifted as a function of motion direction, and stimulus locations eliciting greater spike counts also exhibited the shortest neural latency. Motion crossing the receptive field boundaries appeared to be both necessary and sufficient to produce receptive field shifts. Decreasing the silent interval between successive stimuli in the apparent motion sequence increased both the probability of obtaining a directional effect and the magnitude of receptive field shifts. We suggest that the observed directional effects might be explained by “spatial masking,” where the response of auditory neurons after stimulation from particularly effective locations in space would be diminished. The shift in auditory receptive fields would be expected to shift the perceived location of a moving sound and may explain shifts in localization of moving sources observed in psychophysical studies. Shifts in perceived target location caused by auditory motion might be exploited by auditory predators such as Pteronotus in a predictive tracking strategy to capture moving insect prey.
Dopamine Modulates Graded and Spike-Evoked Synaptic Inhibition Independently at Single Synapses in Pyloric Network of Lobster
Authors: Ayali Amir , Johnson Bruce R. , Harris-Warrick Ronald M.
Published: December 2017

Ayali, Amir, Bruce R. Johnson, and Ronald M. Harris-Warrick. Dopamine modulates graded and spike-evoked synaptic inhibition independently at single synapses in pyloric network of lobster. J. Neurophysiol. 79: 2063–2069, 1998. Bath application of dopamine (DA) modifies the rhythmic motor pattern generated by the pyloric network in the stomatogastric ganglion of the spiny lobster, Panulirus interruptus. Synaptic transmission between network members is an important target of DA action. All pyloric neurons employ both graded transmitter release and action-potential–mediated synaptic inhibition. DA was previously shown to alter the graded synaptic strength of every pyloric synapse. In this study, we compared DA's effects on action-potential–mediated and graded synaptic inhibition at output synapses of the lateral pyloric (LP) neuron. At each synapse the postsynaptic cell tested was isolated from other descending and pyloric synaptic inputs. DA caused a reduction in the size of the LP spike-evoked inhibitory postsynaptic potentials (IPSPs) in the pyloric dilator (PD) neuron. The change in IPSP size was significantly and linearly correlated with DA-induced reduction in the input resistance of the postsynaptic PD neuron. In contrast, graded inhibition, tested in the same preparations after superfusing the stomatogastric ganglion (STG) with tetrodotoxin (TTX), was consistently enhanced by DA. DA shifted the amplitude of spike-evoked IPSPs in the same direction as the alteration of the postsynaptic cell input resistance at two additional synapses tested: DA weakened the LP spike-mediated inhibition of the ventricular dilator (VD) and reduced the VD input resistance, while strengthening the LP → pyloric constrictor (PY) synapse and increasing PY input resistance. As previously reported, graded inhibition was enhanced at these two LP output synapses. We conclude that DA can differentially modulate the spike-evoked and graded components of synapses between members of a central pattern generator network. At the synapses we studied, actions on the presynaptic cell predominate in the modulation of graded transmission, whereas effects on postsynaptic cells predominate in the regulation of spike-evoked IPSPs.
Pharmacologically and Functionally Distinct Calcium Currents of Stomatogastric Neurons
Authors: Hurley Laura M. , Graubard Katherine
Published: December 2017

Hurley, Laura M. and Katherine Graubard. Pharmacologically and functionally distinct calcium currents of stomatogastric neurons. J. Neurophysiol. 79: 2070–2081, 1998. Previous studies have suggested the presence of different types of calcium channels in different regions of stomatogastric neurons. We sought to pharmacologically separate these calcium channel types. We used two different preparations from different regions of stomatogastric neurons to screen a range of selective calcium channel blockers. The two preparations were isolated cell bodies in culture, in which calcium current was measured directly, and isolated neuromuscular junction, in which synaptic transmission was the indirect assay for presynaptic calcium influx. The selective blockers were two different dihydropyridines, ω-Agatoxin IVA, and ω-Conotoxin GVIA. Cultured cell bodies possessed both high-threshold calcium current and calcium-activated outward current, similar to intact neurons. The calcium current had transient and maintained components, but both components had the same voltage dependence of activation and inactivation. Dihydropyridines at ≥10 μM blocked both high-threshold calcium current and calcium-activated outward current. Nanomolar doses of ω-Agatoxin IVA did not block calcium current, but micromolar doses did. ω-Conotoxin GVIA did not block either current. In contrast, at the neuromuscular junction, dihydropyridines reduced the amplitude of postsynaptic potentials by only a modest amount, whereas ω-Agatoxin IVA at doses as low as 64 nM reduced the amplitude of postsynaptic potentials almost entirely. These effects were presynaptic. ω-Conotoxin GVIA did not change the amplitude of postsynaptic potentials. The different pharmacological profiles of the two isolated preparations suggest that there are at least two different types of calcium channel in stomatogastric neurons and that ω-Agatoxin IVA and dihydropridines can be used to pharmacologically distinguish them.
Reversible Inactivation of Monkey Superior Colliculus. I. Curvature of Saccadic Trajectory
Authors: Aizawa Hiroshi , Wurtz Robert H.
Published: December 2017

Aizawa, Hiroshi and Robert H. Wurtz. Reversible inactivation of monkey superior colliculus. I. Curvature of saccadic trajectory. J. Neurophysiol. 79: 2082–2096, 1998. The neurons in the intermediate layers of the monkey superior colliculus (SC) that discharge before saccadic eye movements can be divided into at least two types, burst and buildup neurons, and the differences in their characteristics are compatible with different functional contributions of the two cell types. It has been suggested that a spread of activity across the population of the buildup neurons during saccade generation may contribute to the control of saccadic eye movements. The influence of any such spread should be on both the horizontal and vertical components of the saccade because the map of the movement fields on the SC is a two-dimensional one; it should affect the trajectory of saccade. The present experiments used muscimol injections to inactivate areas within the SC to determine the functional contribution of such a spread of activity on the trajectory of the saccades. The analysis concentrated on saccades made to areas of the visual field that should be affected primarily by alteration of buildup neuron activity. Muscimol injections produced saccades with altered trajectories; they became consistently curved after the injection, and successive saccades to the same targets had similar curvatures. The curved saccades showed changes in their direction and speed at the very beginning of the saccade, and for those saccades that reached the target, the direction of the saccade was altered near the end to compensate for the initially incorrect direction. Postinjection saccades had lower peak speeds, longer durations, and longer latencies for initiation. The changes in saccadic trajectories resulting from muscimol injections, along with the previous observations on changes in speed of saccades with such injections, indicate that the SC is involved in influencing the eye position during the saccade as well as at the end of the saccade. The changes in trajectory when injections were made more rostral in the SC than the most active burst neurons also are consistent with a contribution of the buildup neurons to the control of the eye trajectory. The results do not, however, support the hypothesis that the buildup neurons in the SC act as a spatial integrator.
Reversible Inactivation of Monkey Superior Colliculus. II. Maps of Saccadic Deficits
Authors: Quaia Christian , Aizawa Hiroshi , Optican Lance M. , Wurtz Robert H.
Published: December 2017

Quaia, Christian, Hiroshi Aizawa, Lance M. Optican, and Robert H. Wurtz. Reversible inactivation of monkey superior colliculus. II. Maps of saccadic deficits. J. Neurophysiol. 79: 2097–2110, 1998. Neurons in the superior colliculus (SC) are organized as maps of visual and motor space. The companion paper showed that muscimol injections into intermediate layers of the SC alter the trajectory of the movement and confirmed previously reported effects on latency, amplitude, and speed of saccades. In this paper we analyze the pattern of these deficits across the visual field by systematically comparing the magnitude of each deficit throughout a grid of targets covering a large fraction of the visual field. We also translate these deficits onto the SC map of the visual/movement fields to obtain a qualitative estimate of the extent of the deficit in the SC. We found a consistent pattern of substantially increased saccadic latency to targets in the contralateral visual hemifield, accompanied by slight and inconsistent increases and decreases for saccades to the ipsilateral hemifield. The initial and peak speed of saccades was reduced after the injection. The postinjection amplitude of the saccades were either hypometric or normometric, but rarely hypermetric. Although errors in the initial direction of the postinjection saccades were small, they consistently formed a simple pattern: an initial direction with minimal errors (a null direction) separating regions with clockwise and counterclockwise rotations of the initial direction. However, the null direction did not go through the center of the inactivated zone, as would be expected if the SC alone were determining saccade direction, e.g., with a population code. One hypothesis that can explain the misalignment of the null direction with the lesion site is that another system, acting in parallel with the SC, contributes to the determination of saccadic trajectory.
Kinematic Coordination in Human Gait: Relation to Mechanical Energy Cost
Authors: Bianchi L. , Angelini D. , Orani G. P. , Lacquaniti F.
Published: December 2017

Bianchi, L., D. Angelini, G. P. Orani, and F. Lacquaniti. Kinematic coordination in human gait: relation to mechanical energy cost. J. Neurophysiol. 79: 2155–2170, 1998. Twenty-four subjects walked at different, freely chosen speeds ( V) ranging from 0.4 to 2.6 m s−1, while the motion and the ground reaction forces were recorded in three-dimensional space. We considered the time course of the changes of the angles of elevation of the trunk, pelvis, thigh, shank, and foot in the sagittal plane. These angles specify the orientation of each segment with respect to the vertical and to the direction of forward progression. The changes of the trunk and pelvis angles are of limited amplitude and reflect the dynamics of both right and left lower limbs. The changes of the thigh, shank, and foot elevation are ample, and they are coupled tightly among each other. When these angles are plotted one versus the others, they describe regular loops constrained on a plane. The plane of angular covariation rotates, slightly but systematically, along the long axis of the gait loop with increasing V. The rotation, quantified by the change of the direction cosine of the normal to the plane with the thigh axis ( u3 t), is related to a progressive phase shift between the foot elevation and the shank elevation with increasing V. As a next step in the analysis, we computed the mass-specific mean absolute power ( Pu) to obtain a global estimate of the rate at which mechanical work is performed during the gait cycle. When plotted on logarithmic coordinates, Puincreases linearly with V. The slope of this relationship varies considerably across subjects, spanning a threefold range. We found that, at any given V > 1 m s−1, the value of the plane orientation ( u3 t) is correlated with the corresponding value of the net mechanical power ( Pu). On the average, the progressive rotation of the plane with increasing V is associated with a reduction of the increment of Puthat would occur if u3 tremained constant at the value characteristic of low V. The specific orientation of the plane at any given speed is not the same in all subjects, but there is an orderly shift of the plane orientation that correlates with the net power expended by each subject. In general, smaller values of u3 ttend to be associated with smaller values of Puand vice versa. We conclude that the parametric tuning of the plane of angular covariation is a reliable predictor of the mechanical energy expenditure of each subject and could be used by the nervous system for limiting the overall energy expenditure.
Temporal Contrast Enhancement via GABAC Feedback at Bipolar Terminals in the Tiger Salamander Retina
Authors: Dong Cun-Jian , Werblin Frank S.
Published: December 2017

Dong, Cun-Jian and Frank S. Werblin. Temporal contrast enhancement via GABAC feedback at bipolar terminals in the tiger salamander retina. J. Neurophysiol. 79: 2171–2180, 1998. Most retinal amacrine (ACs) and ganglion cells (GCs) express temporal contrast by generating action potentials at only the onset and offset of the light stimulus. This study investigated the neural mechanisms that underlie this temporal contrast enhancement. Whole cell patch recordings were made from bipolar cells (BCs), ACs, and GCs in the retinal slice preparation. The cells were identified by the locations of their somas in the inner nuclear layer and ganglion cell layers, their characteristic light responses, and morphology revealed by Lucifer yellow staining. Depolarizing a single BC with a brief voltage pulse elicited a Cl− tail current that was completely abolished when Ca2+ entry to bipolar terminals was prevented, by either removing Ca2+ from the Ringer solution or blocking Ca2+ channels with Co2+. This suggests that the Cl− current is Ca2+-dependent. In those bipolar cells whose axon terminals were cutoff during slicing no Cl− current was observed, indicating that this current is generated at the synaptic terminals. The Cl− current consists of a predominant synaptic component that can be blocked by the non- N-methyl-d-aspartate (NMDA) glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) or by the γ-aminobutyric acid-C (GABAC) receptor antagonist picrotoxin. There also exists a relatively small nonsynaptic component. Thus both glutamatergic and GABAergic transmission were involved in the generation of this Cl− current, suggesting that it is mediated by a recurrent feedback to bipolar cells. Picrotoxin, which blocks both GABAC receptors at BC terminals and GABAA receptors on the dendrites of ACs and GCs, converted the light-elicited voltage response in most on-off ACs and GCs from transient to sustained. Bicuculline, which blocks only the GABAA receptors, did not prolong the transient response in on-off ACs and GCs. This suggests that a negative feedback mediated by the GABAC receptor on the bipolar terminals is responsible for making these responses transient. After the GABAergic feedback was blocked with picrotoxin the light-elicited voltage responses (recorded under current clamp) were more sustained than the current responses (recorded under voltage clamp) to the same light stimuli. This suggests that a voltage-dependent conductance converts the relatively transient current responses to more sustained voltage responses. Our results imply a synaptically driven local GABAergic feedback at bipolar terminals, mediated by GABAC receptors. This feedback appears to be a significant component of the mechanism underlying temporal contrast enhancement in on-off ACs and GCs.
L-Type Calcium Channels Are Required for One Form of Hippocampal Mossy Fiber LTP
Authors: Kapur Ajay , Yeckel Mark F. , Gray Richard , Johnston Daniel
Published: December 2017

Kapur, Ajay, Mark F. Yeckel, Richard Gray, and Daniel Johnston. L-type calcium channels are required for one form of hippocampal mossy fiber LTP. J. Neurophysiol. 79: 2181–2190, 1998. The requirement of postsynaptic calcium influx via L-type channels for the induction of long-term potentiation (LTP) of mossy fiber input to CA3 pyramidal neurons was tested for two different patterns of stimulation. Two types of LTP-inducing stimuli were used based on the suggestion that one of them, brief high-frequency stimulation (B-HFS), induces LTP postsynaptically, whereas the other pattern, long high-frequency stimulation (L-HFS), induces mossy fiber LTP presynaptically. To test whether or not calcium influx into CA3 pyramidal neurons is necessary for LTP induced by either pattern of stimulation, nimodipine, a L-type calcium channel antagonist, was added during stimulation. In these experiments nimodipine blocked the induction of mossy fiber LTP when B-HFS was given [34 ± 5% (mean ± SE) increase in control versus 7 ± 4% in nimodipine, P < 0.003]; in contrast, nimodipine did not block the induction of LTP with L-HFS (107 ± 10% in control vs. 80 ± 9% in nimodipine, P > 0.05). Administration of nimodipine after the induction of LTP had no effect on the expression of LTP. In addition, B- and L-HFS delivered directly to commissural/associational fibers in stratum radiatum failed to induce a N-methyl-d-aspartate-independent form of LTP, obviating the possibility that the presumed mossy fiber LTP resulted from potentiation of other synapses. Nimodipine had no effect on calcium transients recorded from mossy fiber presynaptic terminals evoked with the B-HFS paradigm but reduced postsynaptic calcium transients. Our results support the hypothesis that induction of mossy fiber LTP by B-HFS is mediated postsynaptically and requires entry of calcium through L-type channels into CA3 neurons.
Effect of Luminance Contrast on BOLD fMRI Response in Human Primary Visual Areas
Authors: Goodyear Bradley G. , Menon Ravi S.
Published: December 2017

Goodyear, Bradley G. and Ravi S. Menon. Effect of luminance contrast on BOLD fMRI response in human primary visual areas. J. Neurophysiol. 79: 2204–2207, 1998. In this study, we examined the effect of stimulus luminance contrast on blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging within human visual cortex (V1 and extrastriate). Between experiments, the calibrated luminance of a single red LED covering 2° of the subject's visual field was changed relative to a constant background luminance. This stimulus provided a different foveal luminance contrast for each experiment. We used an echo planar imaging sequence to collect blood-oxygenation-sensitive images during and in the absence of the presented stimulus. Our results showed that within V1 there was an increase in the spatial extent of activation with increasing stimulus contrast, but no trend was seen within extrastriate. In both V1 and extrastriate, the local mean activation level for all activated image pixels remained constant with increasing luminance contrast. However, when we investigated activated pixels common to all luminance contrast levels, we found that there was an increase in the mean activation level within V1, but not within extrastriate. These results suggest that there is an increase in the activity of cells in V1 with increasing luminance contrast.
Neurons in the Human Thalamic Somatosensory Nucleus (Ventralis Caudalis) Respond to Innocuous Cool and Mechanical Stimuli
Authors: Lenz F. A. , Dougherty P. M.
Published: December 2017

Lenz, F. A. and P. M. Dougherty. Neurons in the human thalamic somatosensory nucleus (ventralis caudalis) respond to innocuous cool and mechanical stimuli. J. Neurophysiol. 79: 2227–2230, 1998. A population of neurons in the principal somatosensory nucleus of human thalamus (ventralis caudalis, Vc) had a significant tonic, graded response to cool stimuli and also responded to innocuous mechanical stimuli (mechanical-cool neurons). These neurons were clustered at the dorsal aspect of medial Vc. Stimulation at the sites where these neurons were recorded evoked tingling sensations in the part of the body including or adjacent to the receptive field of these neurons. These neurons may contribute to the mechanism that mediates the perception of cold in man.
Ionic Currents and Electromotility in Inner Ear Hair Cells From Humans
Authors: Oghalai John S. , Holt Jeffrey R. , Nakagawa Takashi , Jung Thomas M. , Coker Newton J. , Jenkins Herman A. , Eatock Ruth Anne , Brownell William E.
Published: December 2017

Oghalai, John S., Jeffrey R. Holt, Takashi Nakagawa, Thomas M. Jung, Newton J. Coker, Herman A. Jenkins, Ruth Anne Eatock, and William E. Brownell. Ionic currents and electromotility in inner ear hair cells from humans. J. Neurophysiol. 79: 2235–2239, 1998. The upright posture and rich vocalizations of primates place demands on their senses of balance and hearing that differ from those of other animals. There is a wealth of behavioral, psychophysical, and CNS measures characterizing these senses in primates, but no prior recordings from their inner ear sensory receptor cells. We harvested human hair cells from patients undergoing surgical removal of life-threatening brain stem tumors and measured their ionic currents and electromotile responses. The hair cells were either isolated or left in situ in their sensory epithelium and investigated using the tight-seal, whole cell technique. We recorded from both type I and type II vestibular hair cells under voltage clamp and found four voltage-dependent currents, each of which has been reported in hair cells of other animals. Cochlear outer hair cells demonstrated electromotility in response to voltage steps like that seen in rodent animal models. Our results reveal many qualitative similarities to hair cells obtained from other animals and justify continued investigations to explore quantitative differences that may be associated with normal or pathological human sensation.
Intracortical Microstimulation of Bilateral Frontal Eye Field
Authors: Fujii Naotaka , Mushiake Hajime , Tanji Jun
Published: December 2017

Fujii, Naotaka, Hajime Mushiake, and Jun Tanji. Intracortical microstimulation of bilateral frontal eye field. J. Neurophysiol. 79: 2240–2244, 1998. We trained two monkeys to perform a fixation task. Intracortical microstimulation (ICMS) was applied to the monkey frontal eye field (FEF) while monkeys were fixating on one of five fixation LEDs. The ICMS was applied in two different manners. Under the single stimulation condition, ICMS was delivered to either right or left FEF. Under the paired stimulation condition, bilateral FEF were successively stimulated with an interval of 30–250 ms. The single stimulation elicited contraversive saccades. As reported previously, these saccades were not much affected by initial eye positions, maintaining the same vector. In contrast, the paired stimulation elicited double-step saccades. The first of the paired stimulation elicited constant vector saccades, but the second of the paired stimulation evoked saccades whose vector varied greatly depending on the eye position at the start of individual saccades. The second saccades, starting from various initial positions, were directed to the endpoint of saccades that were elicited from the same FEF site under the single stimulation condition. Endpoints of second saccades varied little despite variations of intervals of the stimulation pairs, ranging from 60 to 150 ms. On the basis of these observations, we propose a novel view that the FEF is involved in directing saccades to an internally referenced visual target.
Representation of Wrist Joint Kinematics by the Ensemble of Muscle Spindles From Synergistic Muscles
Authors: Verschueren Sabine M. P. , Cordo Paul J. , Swinnen Stephan P.
Published: December 2017

Verschueren, Sabine M. P., Paul J. Cordo, and Stephan P. Swinnen. Representation of wrist joint kinematics by the ensemble of muscle spindles from synergistic muscles. J. Neurophysiol. 79: 2265–2276, 1998. Proprioceptive information about movement is transmitted to the central nervous system by a variety of receptor types, which are widely distributed among the muscles, joints, and skin. Muscle spindles are known to be an important and reliable source of information for the perception of movement kinematics. Previous studies that focused on the characteristics of single muscle spindle firing patterns have left the impression that each receptor fires in relation to a number of kinematic variables, leaving the following question unanswered: what role is played by the ensemble of muscle spindles within the same muscle or within synergistic muscles? The study described in this paper addressed whether the perception of joint position and velocity is based on the net input of muscle spindles residing in all synergistic muscles crossing a joint. Normal human adults performed a motor coordination task that required perception of joint velocity and dynamic position at the wrist. The task was to open the left hand briskly as the right wrist was passively rotated in the flexion direction through a prescribed target angle. In randomly occurring trials, the tendons to three muscles [extensor carpi radialis (ECR), extensor carpi ulnaris (ECU), and extensor digitorum (ED)] were vibrated either individually or in different combinations during the performance of the motor task. Tendon vibration is known to distort muscle spindle firing patterns, and consequently, kinesthesia. By comparing performance errors with and without tendon vibration, the relative influences of muscle spindles residing in ECR, ECU, and ED were quantified. Vibration of the individual ECR, ECU, or ED tendons produced systematic undershoot errors in performance, consistent with the misperception of wrist velocity and dynamic position. Performance errors were larger when combinations of, rather than individual, muscle tendons were vibrated. The error resulting from simultaneous vibration of ECR and ECU was roughly equal to the sum of the errors produced by vibration of the individual tendons. These effects of vibrating synergistic tendons at the wrist suggest that kinesthesia is derived from the integrated input of muscle spindles from all synergistic muscles.
Roles of Ascending Inhibition During Two Rhythmic Motor Patterns inXenopusTadpoles
Authors: Green C. S. , Soffe S. R.
Published: December 2017

Green, C. S. and S. R. Soffe. Roles of ascending inhibition during two rhythmic motor patterns in Xenopus tadpoles. J. Neurophysiol. 79: 2316–2328, 1998. We have investigated the effects of ascending inhibitory pathways on two centrally generated rhythmic motor patterns in a simple vertebrate model, the young Xenopus tadpole. Tadpoles swim when touched, but when grasped respond with slower, stronger struggling movements during which the longitudinal pattern of motor activity is reversed. Surgical spinal cord transection to remove all ascending connections originating caudal to the transection (in tadpoles immobilized in α-bungarotoxin) did not affect “fictive” swimming generated more rostrally. In contrast, cycle period and burst duration both significantly increased during fictive struggling. Increases were progressively larger with more rostral transection. Blocking caudal activity with the anesthetic MS222 (pharmacological transection) produced equivalent but reversible effects. Reducing crossed-ascending inhibition selectively, either by midsagittal spinal cord division or rostral cord hemisection (1-sided transection) mimicked the effects of transection. Like transection, both operations increased cycle period and burst duration during struggling but did not affect swimming. The changes during struggling were larger with more rostral hemisection. Reducing crossed-ascending inhibition by spinal hemisection also increased the rostrocaudal longitudinal delay during swimming, and the caudorostral delay during struggling. Weakening inhibition globally with low concentrations of the glycine antagonist strychnine (10–100 nM) did not alter swimming cycle period, burst duration, or longitudinal delay. However, strychnine at 10–60 nM decreased cycle period during struggling. It also increased burst duration in some cases, although burst duration increased as a proportion of cycle period in all cases. Strychnine reduced longitudinal delay during struggling, making rostral and caudal activity more synchronous. At 100 nM, struggling was totally disrupted. By combining our results with a detailed knowledge of tadpole spinal cord anatomy, we conclude that inhibition mediated by the crossed-ascending axons of characterized, glycinergic, commissural interneurons has a major influence on the struggling motor pattern compared with swimming. We suggest that this difference is a consequence of the larger, reversed longitudinal delay and the extended burst duration during struggling compared with swimming.