bluuebunny/crossref_metadata_2025 huggingface dataset:
Depolarization-Induced Facilitation of a Plateau-Generating Current in Ventral Horn Neurons in the Turtle Spinal Cord
Authors: Svirskis Gytis , Hounsgaard Jørn
Published: December 2017

Svirskis, Gytis and Jørn Hounsgaard. Depolarization-induced facilitation of a plateau-generating current in ventral horn neurons in the turtle spinal cord. J. Neurophysiol. 78: 1740–1742, 1997. Plasticity at the neuronal level commonly involves use-dependent changes in strength of particular synaptic pathways or regulation of postsynaptic properties by modulatory transmitters. Here we analyze a novel form of short-term plasticity mediated by use- dependent facilitation of postsynaptic responsiveness. Using current- and voltage-clamp recordings, we found that all spinal ventral horn neurons able to generate plateau potentials showed depolarization-induced facilitation of the underlying inward current. Facilitation was noticeable when the neurons were depolarized to more than −50 mV at intervals <4 s. When stimulation with fast triangular voltage ramps was used, the inward current activated at a less depolarized potential during the second ramp. The inward current and facilitation was eliminated by nifedipine, a selective antagonist of L-type calcium channels. Depolarization-induced facilitation of low-voltage-activated L-type calcium channels is suggested to be the underlying mechanism. It is noted that facilitation occurs on a time scale compatible with a role in phasic motor activity.
Prolonged Firing in Motor Units: Evidence of Plateau Potentials in Human Motoneurons?
Authors: Kiehn Ole , Eken Torsten
Published: December 2017

Kiehn, O. and T. Eken. Prolonged firing in motor units: evidence of plateau potentials in human motoneurons? J. Neurophysiol. 78: 3061–3068, 1997. Serotonin (5-HT) and norepinephrine-dependent plateau potentials are found in spinal motoneurons in reduced turtle and cat preparations. Triggering the plateau potential by short-lasting synaptic excitation causes a prolonged self-sustained firing, which can be terminated by short-lasting synaptic inhibition. The presence of plateau potentials can also allow neurons to fire in a bistable manner, i.e., shifting between stable low and high firing frequencies. Such a bistable firing behavior has been found in soleus motor units in unrestrained rats. In the present study single motor-unit activity was recorded from low-threshold units in human soleus and tibialis anterior muscles to evaluate whether a bistable firing behavior and/or prolonged firing could be evoked. Vibration of the homonymous muscle tendon (30–100 Hz, 2–10 s) was used as excitatory input to the motoneuron pool. Brief excitation while the muscle was electrically silent induced firing during the vibration and sometimes recruited units into prolonged stable firing outlasting the vibratory stimulus. However, a bistable firing behavior, i.e., vibration-induced maintained shifts between two stable levels of firing, could not be convincingly demonstrated. The reason for this was twofold. First, low-threshold human motor units tended to jump to a “preferred firing range” shortly after voluntary recruitment. This firing range was the same as when units were recruited from silence into prolonged firing by vibration. Below the preferred firing range, maintained firing was unstable and usually only possible when subjects were listening to the spike potentials or had visual force-feedback. Second, vibration when units were firing in the preferred firing range caused a transient increase in firing frequency but no maintained frequency shifts. Recordings from pairs of motor units showed that short-lasting vibration could recruit one unit into prolonged firing, while a second unit, which already fired in its preferred firing range, only transiently increased its firing rate during the vibration. This suggests that the prolonged firing was not the result of an increase in the common synaptic drive to the motoneuron pool. We conclude that a bistable firing behavior as seen in intact rats is probably absent in human low-threshold motor units, but that prolonged firing could be seen in response to short-lasting excitation. This latter phenomenon is compatible with the existence of plateau potentials, which have to have a threshold close to the threshold for sodium spike generation.
EPSP Amplitude Modulation at the Rat Ia-Alpha Motoneuron Synapse: Effects of GABAB Receptor Agonists and Antagonists
Authors: Peshori Kavita R. , Collins William F. , Mendell Lorne M.
Published: December 2017

Peshori, Kavita R., William F. Collins III, and Lorne M. Mendell. EPSP amplitude modulation at the rat Ia-alpha motoneuron synapse: effects of GABAB receptor agonists and antagonists. J. Neurophysiol. 79: 181–189, 1998. The object of this study was to examine the relationship between excitatory postsynaptic potential (EPSP) amplitude, posttetanic potentiation, and EPSP amplitude modulation at synapses made by group Ia afferents on motoneurons in the rat. These relationships were evaluated in cells in untreated rats and in cells in rats treated with the γ-aminobutyric acid-B (GABAB) receptor agonist baclofen and antagonist CGP-35348, which were used to manipulate Ca2+ entry into presynaptic terminals and consequently probability of transmitter release from them. There was no evidence for postsynaptic action of these drugs from measurement of their effects on motoneuron properties. During high-frequency stimulation (32 shock bursts at 167 Hz), EPSP amplitude either decreased (negative modulation) or increased (positive modulation) in response to successive stimuli at different connections. In untreated rats this frequency-dependent amplitude modulation behavior was inversely but weakly correlated with EPSP amplitude measured at low frequency. Intravenous (iv) administration of the GABAB agonist, baclofen, produced a marked and progressive decrease in EPSP amplitude measured at low frequency coincident with a change in frequency-dependent EPSP amplitude modulation toward more positive values (synaptic facilitation). In contrast, an increase in EPSP amplitude occurred after iv administration of the GABAB antagonist CGP-35348 that was accompanied by a negative shift in EPSP amplitude modulation during high-frequency stimulation. The negative shift in EPSP amplitude modulation (synaptic depression) after CGP-35348 application was much smaller than the positive shift induced by baclofen when normalized to the change in EPSP amplitude. Posttetanic potentiation decreased after baclofen but did not increase after CGP-35348. The relationship between modulation and EPSP amplitude was much steeper after GABAB receptor manipulation in either direction than that observed in the population of motoneurons in untreated preparations. This suggests that in the rat differences in probability of release play at most a small role in determining EPSP amplitude across the motoneuron pool.
Tetanic Stimulation Induces Short-Term Potentiation of Inhibitory Synaptic Activity in the Rostral Nucleus of the Solitary Tract
Authors: Grabauskas Gintautas , Bradley Robert M.
Published: December 2017

Grabauskas, Gintautas and Robert M. Bradley. Tetanic stimulation induces short-term potentiation of inhibitory synaptic activity in the rostral nucleus of the solitary tract. J. Neurophysiol. 79: 595–604, 1998. Whole cell recordings from neurons in the rostral nucleus of the solitary tract (rNST) were made to explore the effect of high-frequency tetanic stimulation on inhibitory postsynaptic potentials (IPSPs). IPSPs were elicited in the rNST by local electrical stimulation after pharmacological blockade of excitatory synaptic transmission. Tetanic stimulation at frequencies of 10–30 Hz resulted in sustained hyperpolarizing IPSPs that had a mean amplitude of −68 mV. The hyperpolarization resulted in a decrease in neuronal input resistance and was blocked by the γ-aminobutyric acid-A (GABAA) antagonist bicuculline. For most of the neurons ( n = 87/102), tetanic stimulation resulted in a maximum hyperpolarization immediately after initiation of the tetanic stimulation, but for some neurons the maximum was achieved after three or more consecutive shock stimuli in the tetanic train of stimuli. When the extracellular Ca2+ concentration was reduced, the maximum IPSP amplitude was reached after several consecutive shock stimuli in the tetanic train for all neurons. Tetanic stimulation at frequencies of 30 Hz and higher resulted in IPSPs that were not sustained but decayed to a more positive level of hyperpolarization. In some neurons the decay was sufficient to become depolarizing and resulted in a biphasic IPSP. It was possible to evoke this biphasic IPSP in all the neurons tested if the cells were hyperpolarized to −75 to −85 mV. The ionic mechanism of the depolarizing IPSPs was examined and was found to be due to an elevation of the extracellular K+ concentration and accumulation of intracellular Cl−. Tetanic stimulation increased the mean 80-ms decay time constant of a single shock–evoked IPSP up to 8 s. The length of the IPSP decay time constant was dependent on the duration and frequency of the tetanic stimulation as well as the extracellular Ca2+ concentration. Afferent sensory input to the rNST consists of trains of relatively high-frequency spike discharges similar to the tetanic stimulation frequencies used to elicit the IPSPs in the brain slices. Thus the short-term changes in inhibitory synaptic activity in the slice preparation probably occur in vivo and may play a key role in taste processing by facilitating synaptic integration.
Inflammatory Mediators at Acidic pH Activate Capsaicin Receptors in Cultured Sensory Neurons From Newborn Rats
Authors: Vyklický Ladislav , Knotková-Urbancová Helena , Vitásková Zdeňka , Vlachová VIKTORIE , Kress Michaela , Reeh Peter W.
Published: December 2017

Vyklický, Ladislav, Helena Knotková-Urbancová, Zdeňka Vitásková, Viktorie Vlachová, Michaela Kress, and Peter W. Reeh. Inflammatory mediators at acidic pH activate capsaicin receptors in cultured sensory neurons from newborn rats. J. Neurophysiol. 79: 670–676, 1998. Whole cell membrane currentsinduced by the inflammatory mediators, bradykinin, 5-hydroxytryptamine (5-HT) and prostaglandin E2, were investigated in capsaicin-sensitive dorsal root ganglion (DRG) neurons from newborn rats grown on a monolayer of hippocampal glia without nerve growth factor (NGF). When firmly attached to an underlying cell, the neurons survived >14 days without growing extensive processes. A majority of the small diameter neurons (∼80%) exhibited sensitivity to capsaicin (3–6 μM) and this was enhanced in solution of low pH. In acidic extracellular solution (pH 6.1), the combination of bradykinin (10 μM), 5-HT (10 μM) and prostaglandin E2 (1 μM) induced an inward membrane current in all capsaicin-sensitive DRG neurons ( n = 43). The current exceeded the sustained, low pH-induced membrane current by 205 ± 53 (SE) pA. The combination of acidic inflammatory mediators was ineffective in cells that were insensitive to capsaicin. In capsaicin-sensitive neurons, the inflammatory mediators when applied singly or in any combination of two, induced no membrane currents or small current at pH 7.3 and 6.1. Capsazepine (10 μM), the capsaicin antagonist, completely inhibited the facilitatory action of inflammatory mediator combination but not the sustained inward current induced by acidic extracellular solution (pH 6.1 or 5.5). It is suggested that the inflammatory mediators, bradykinin,5-HT, and prostaglandin E2 together act as endogenous mediators at capsaicin receptors to generate an inward current when the ion channel is protonized.
Somatostatin Increases a Voltage-Insensitive K+Conductance in Rat CA1 Hippocampal Neurons
Authors: Schweitzer Paul , Madamba Samuel G. , Siggins George R.
Published: December 2017

Schweitzer, Paul, Samuel G. Madamba, and George R. Siggins. Somatostatin increases a voltage-insensitive K+conductance in rat CA1 hippocampal neurons. J. Neurophysiol. 79: 1230–1238, 1998. Somatostatin (SST) is a neuropeptide involved in several central processes. In hippocampus, SST hyperpolarizes CA1 pyramidal neurons and augments the K+M current ( IM). However, the limited involvement of IMat resting potential in these cells suggests that the peptide also may modulate another channel to hyperpolarize hippocampal pyramidal neurons (HPNs). We studied the effect of SST on noninactivating conductances of rat CA1 HPNs in a slice preparation. Using MK886, a specific inhibitor of the enzymatic pathway that leads to the augmentation of IMby SST, we have uncovered and characterized a second conductance activated by the peptide. SST did not affect IMwhen applied with MK886 or the amplitudes of the slow Ca2+-dependent K+afterhyperpolarization-current and the cationic Q current but still caused an outward current, indicating that SST acts upon another conductance. In the presence of MK886, SST elicited an outward current that reversed around −100 mV and that displayed a linear current-voltage relationship. Reversal potentials obtained in different external K+concentrations are consistent with a conductance carried solely by K+ions. The slope of the current-voltage relationship increased proportionately with the extracellular K+concentration and remained linear. This suggests that SST opens a voltage-insensitive leak current ( IK(L)) in HPNs not an inwardly rectifying K+current as reported in other neuron types. A low concentration of extracellular Ba2+(150 μM) only slightly decreased the SST-induced effect in a voltage-independent manner, whereas a high concentration of Ba2+(2 mM) completely blocked it. Extracellular Cs+(2 mM) did not affect the outward SST current but inhibited the inward component. We conclude that SST inhibits HPNs by activating two different K+conductances: the voltage-insensitive IK(L)and the voltage-dependent IM. The hyperpolarizing effect of SST at resting membrane potential appears to be mainly carried by IK(L), whereas IMdominates at slightly depolarized potentials.
Covert Visual Attention Modulates Face-Specific Activity in the Human Fusiform Gyrus: fMRI Study
Authors: Wojciulik Ewa , Kanwisher Nancy , Driver Jon
Published: December 2017

Wojciulik, Ewa, Nancy Kanwisher, and Jon Driver. Covert visual attention modulates face-specific activity in the human fusiform gyrus: an fMRI study. J. Neurophysiol. 79: 1574–1578, 1998. Several lines of evidence demonstrate that faces undergo specialized processing within the primate visual system. It has been claimed that dedicated modules for such biologically significant stimuli operate in a mandatory fashion whenever their triggering input is presented. However, the possible role of covert attention to the activating stimulus has never been examined for such cases. We used functional magnetic resonance imaging to test whether face-specific activity in the human fusiform face area (FFA) is modulated by covert attention. The FFA was first identified individually in each subject as the ventral occipitotemporal region that responded more strongly to visually presented faces than to other visual objects under passive central viewing. This then served as the region of interest within which attentional modulation was tested independently, using active tasks and a very different stimulus set. Subjects viewed brief displays each comprising two peripheral faces and two peripheral houses (all presented simultaneously). They performed a matching task on either the two faces or the two houses, while maintaining central fixation to equate retinal stimulation across tasks. Signal intensity was reliably stronger during face-matching than house matching in both right- and left-hemisphere predefined FFAs. These results show that face-specific fusiform activity is reduced when stimuli appear outside (vs. inside) the focus of attention. Despite the modular nature of the FFA (i.e., its functional specificity and anatomic localization), face processing in this region nonetheless depends on voluntary attention.
Forms of Forward Quadrupedal Locomotion. III. A Comparison of Posture, Hindlimb Kinematics, and Motor Patterns for Downslope and Level Walking
Authors: Smith Judith L. , Carlson-Kuhta Patricia , Trank Tamara V.
Published: December 2017

Smith, Judith L., Patricia Carlson-Kuhta, and Tamara V. Trank. Forms of forward quadrupedal locomotion. III. A comparison of posture, hindlimb kinematics, and motor patterns for downslope and level walking. J. Neurophysiol. 79: 1702–1716, 1998. To gain further insight into the neural mechanisms for different forms of quadrupedal walking, data on postural orientation, hindlimb kinematics, and motor patterns were assessed for four grades of downslope walking, from 25% (14° slope) to 100% (45°), and compared with data from level and downslope walking at five grades (5–25%) on the treadmill (0.6 m/s). Kinematic data were obtained by digitizing ciné film, and electromyograms (EMGs) synchronized with kinematic records were taken from 13 different hindlimb muscles. At grades from 25 to 75%, cycle periods were similar, but at the steepest grade the cycle was shorter because of a reduced stance phase. Paw-contact sequences at all grades were consistent with lateral-sequence walking, but pace walking often occurred at the steepest grades. The cats crouched at the steeper grades, and crouching was associated with changes in fore- and hindlimb orientation that were consistent with increasing braking forces and decreasing propulsive forces during stance. The average ranges of motion at the hindlimb joints, except at the hip, were often different at the two steepest slopes. During swing, the range of knee- and ankle-joint flexion decreased, and the range and duration of extension increased at the ankle joint to lower the paw downward for contact. During stance the range of flexion during yield increased at the ankle joint, and the range of extension decreased at the knee and metatarsophalangeal joints. Downslope walking was also associated with EMG changes for several muscles. The hip extensors were not active during stance; instead, hip flexors were active, presumably to slow the rate of hip extension. Although ankle extensors were active during stance, their burst durations were truncated and centered around paw contact. Ankle flexors were active after midstance at the steeper slopes before the need to initiate swing, whereas flexor and extensor digit muscles were coactive throughout stance. Overall the changes in posture, hindlimb kinematics, and activity patterns of hindlimb muscles during stance reflected a need to counteract external forces that would accelerate angular displacements at some joints. Implications of these changes are discussed by using current models for the neural control of walking.
Information About Spatial View in an Ensemble of Primate Hippocampal Cells
Authors: Rolls Edmund T. , Treves Alessandro , Robertson Robert G. , Georges-François Pierre , Panzeri Stefano
Published: December 2017

Rolls, Edmund T., Alessandro Treves, Robert G. Robertson, Pierre Georges-François, and Stefano Panzeri. Information about spatial view in an ensemble of primate hippocampal cells. J. Neurophysiol. 79: 1797–1813, 1998. Hippocampal function was analyzed by making recordings from hippocampal neurons in monkeys actively walking in the laboratory. “Spatial view” cells, which respond when the monkey looks at a part of the environment, were analyzed. To assess quantitatively the information about the spatial environment represented by these cells, we applied information theoretic techniques to their responses. The average information provided by these cells about which location the monkey was looking at was 0.32 bits, and the mean across cells of the maximum information conveyed about which location was being looked at was 1.19 bits, measured in a period of 0.5 s. There were 16 locations for this analysis, each being one-quarter of one of the walls of the room. It also was shown that the mean spontaneous rate of firing of the neurons was 0.1 spikes/s, that the mean firing rate in the center of the spatial field of the neurons was 13.2 spikes/s, and that the mean sparseness of the representation measured in a 25-ms period was 0.04 and in a 500-ms time period was 0.19. (The sparseness is approximately equivalent to the proportion of the 25- or 500-ms periods in which the neurons showed one or more spikes.) Next it was shown that the mean size of the view fields of the neurons was 0.9 of a wall. In an approach to the issue of how an ensemble of neurons might together provide more precise information about spatial location than a single neuron, it was shown that in general the neurons had different centers for their view fields. It then was shown that the information from an ensemble of these cells about where in space is being looked at increases approximately linearly with the number of cells in the ensemble. This indicates that the number of places that can be represented increases approximately exponentially with the number of cells in the population. It is concluded that there is an accurate representation of space “out there” in the primate hippocampus. This representation of space out there would be an appropriate part of a primate memory system involved in memories of where in an environment an object was seen, and more generally in the memory of particular events or episodes, for which a spatial component normally provides part of the context.
Transient Disturbances to One Limb Produce Coordinated, Bilateral Responses During Infant Stepping
Authors: Yang Jaynie F. , Stephens Marilee J. , Vishram Rosie
Published: December 2017

Yang, Jaynie F., Marilee J. Stephens, and Rosie Vishram. Transient disturbances to one limb produce coordinated, bilateral responses during infant stepping. J. Neurophysiol. 79: 2329–2337, 1998. Transient disturbances were applied to the lower limbs of infants (3–10 mo of age) while they were supported to stepped on a treadmill. The aim was to determine how stepping infants respond to novel disturbances that would disrupt equilibrium during independent walking. Their responses were also compared with those from lower mammals and adult humans. In the first series of experiments, the motion of the limb in the swing phase was transiently stopped by the experimenter grasping the limb for a short time (0.1–1.7 s). During such disturbances, the stance phase was prolonged in the contralateral limb, and the onset of the swing phase was delayed. The degree to which the stepping was modified in the contralateral limb depended on the amount of load experienced by that limb. If the contralateral limb was bearing very little weight at the time of the disturbance, its rhythm did not change appreciably. In the second series of experiments, load was added to the infant by pushing down on the pelvis during the stance phase. This greatly prolonged the stance phase and delayed the swing phase. It did not increase the amplitude of the extensor electromyogram (EMG) of the loaded limb. In conclusion, the neural circuitry controlling stepping in the infants responds to disturbances in an organized fashion that is conducive to maintaining equilibrium and forward progression.
Matching Patterns of Activity in Primate Prefrontal Area 8a and Parietal Area 7ip Neurons During a Spatial Working MemoryTask
Authors: Chafee Matthew V. , Goldman-Rakic Patricia S.
Published: December 2017

Chafee, Matthew V. and Patricia S. Goldman-Rakic. Matching patterns of activity in primate prefrontal area 8a and parietal area 7ip neurons during a spatial working memory task. J. Neurophysiol. 79: 2919–2940, 1998. Single-unit recording studies of posterior parietal neurons have indicated a similarity of neuronal activation to that observed in the dorsolateral prefrontal cortex in relation to performance of delayed saccade tasks. A key issue addressed in the present study is whether the different classes of neuronal activity observed in these tasks are encountered more frequently in one or the other area or otherwise exhibit region-specific properties. The present study is the first to directly compare these patterns of neuronal activity by alternately recording from parietal area 7ip and prefrontal area 8a, under the identical behavioral conditions, within the same hemisphere of two monkeys performing an oculomotor delayed response task. The firing rate of 222 posterior parietal and 235 prefrontal neurons significantly changed during the cue, delay, and/or saccade periods of the task. Neuronal responses in the two areas could be distinguished only by subtle differences in their incidence and timing. Thus neurons responding to the cue appeared earliest and were more frequent among the task-related neurons within parietal cortex, whereas neurons exhibiting delay-period activity accounted for a larger proportion of task-related neurons in prefrontal cortex. Otherwise, the task-related neuronal activities were remarkably similar. Cue period activity in prefrontal and parietal cortex exhibited comparable spatial tuning and temporal duration characteristics, taking the form of phasic, tonic, or combined phasic/tonic excitation in both cortical populations. Neurons in both cortical areas exhibited sustained activity during the delay period with nearly identical spatial tuning. The various patterns of delay-period activity—tonic, increasing or decreasing, alone or in combination with greater activation during cue and/or saccade periods—likewise were distributed to both cortical areas. Finally, similarities in the two populations extended to the proportion and spatial tuning of presaccadic and postsaccadic neuronal activity occurring in relation to the memory-guided saccade. The present findings support and extend evidence for a faithful duplication of receptive field properties and virtually every other dimension of task-related activity observed when parietal and prefrontal cortex are recruited to a common task. This striking similarity attests to the principal that information shared by a prefrontal region and a sensory association area with which it is connected is domain specific and not subject to hierarchical elaboration, as is evident at earlier stages of visuospatial processing.
Increased Calcium Buffering in Basal Forebrain Neurons During Aging
Authors: Murchison David , Griffith William H.
Published: December 2017

Murchison, David and William H. Griffith. Increased calcium buffering in basal forebrain neurons during aging. J. Neurophysiol. 80: 350–364, 1998. Alterations of neuronal calcium (Ca2+) homeostasis are thought to underlie many age-related changes in the nervous system. Basal forebrain neurons are susceptible to changes associated with aging and to related dysfunctions such as Alzheimer's disease. It recently was shown that neurons from the medial septum and nucleus of the diagonal band (MS/nDB) of aged (24–27 mo) F344 rats have an increased current influx through voltage-gated Ca2+channels (VGCCs) relative to those of young (1–4.5 mo) rats. Possible age-related changes in Ca2+buffering in these neurons have been investigated using conventional whole cell and perforated-patch voltage clamp combined with fura-2 microfluorimetric techniques. Basal intracellular Ca2+concentrations ([Ca2+]i), Ca2+influx, Ca2+transients (Δ[Ca2+]i), and time course of Δ[Ca2+]iwere quantitated, and rapid Ca2+buffering values were calculated in MS/nDB neurons from young and aged rats. The involvement of the smooth endoplasmic reticulum (SER) was examined with the SER Ca2+uptake blocker, thapsigargin. An age-related increase in rapid Ca2+buffering and Δ[Ca2+]itime course was observed, although basal [Ca2+]iwas unchanged with age. The SER and endogenous diffusible buffering mechanisms were found to have roles in Ca2+buffering, but they did not mediate the age-related changes. These findings suggest a model in which some aging central neurons could compensate for increased Ca2+influx with greater Ca2+buffering.
Corticoreticular Pathways in the Cat. I. Projection Patterns and Collaterization
Authors: Kably Bouchra , Drew Trevor
Published: December 2017

Kably, Bouchra and Trevor Drew. Corticoreticular pathways in the cat. I. Projection patterns and collaterization. J. Neurophysiol. 80: 389–405, 1998. This paper summarizes and compares the projection patterns and the receptive fields of cortical neurons in areas 4 and 6 that project to the pontomedullary reticular formation (PMRF). A total of 326 neurons were recorded in area 4 and 129 in area 6 in four awake, unrestrained cats that were chronically implanted with arrays of electrodes in the PMRF and the pyramidal tract (PT). In area 4, 47% of the neurons projected to the caudal PT but not to the PMRF (PTNs); 19% were activated only from the PMRF [corticoreticular neurons (CRNs)], whereas 27% were activated from both the PT and the PMRF (PTN/CRNs). More PTN/CRNs conducted at velocities >20 m/s (82%) than did CRNs (23%). In area 6, only 19% of the neurons were identified as PTNs, 12% were PTN/CRNs and 31% were CRNs; a further 38% could not be activated from either structure. Collateral branches within the PMRF conducted at maximum velocities of 20 m/s (average = 6.5 m/s). No significant differences in the conduction velocities of the collateral branches were found either between fast and slow PTNs or between area 4 and area 6 neurons. A large proportion of neurons in area 4 (85/173, 49%) were activated by passive manipulation of the more distal, contralateral forelimb, with approximately equal numbers being classed as PTNs, PTN/CRNs and CRNs. Most neurons in area 6 for which a receptive field could be found were excited by lightly touching or tapping the face and neck; a receptive field could not be determined for 39% of the area 6 neurons compared with only 5% of those in area 4. Finally, there was evidence that neurons in quite widespread areas of the pericruciate cortex, including both areas 4 and 6 projected onto similar, restricted regions of the PMRF. The fact that the cortical projection from area 4 to the PMRF includes a high percentage of fast PTNs with a receptive field on the distal forelimb is consistent with the view that this projection may serve to integrate movement and the dynamic postural adjustments that accompany them. The fact that the cortical projection from area 6 to the PMRF is primarily from slow PTNs with receptive fields on the face, neck and back is consistent with a role for this cortical area in adjusting the general posture of the animal on which movements are superimposed.
Interactions Between Idiothetic Cues and External Landmarks in the Control of Place Cells and Head Direction Cells
Authors: Knierim James J. , Kudrimoti Hemant S. , McNaughton Bruce L.
Published: December 2017

Knierim, James J., Hemant S. Kudrimoti, and Bruce L. McNaughton. Interactions between idiothetic cues and external landmarks in the control of place cells and head direction cells. J. Neurophysiol. 80: 425–446, 1998. Two types of neurons in the rat brain have been proposed to participate in spatial learning and navigation: place cells, which fire selectively in specific locations of an environment and which may constitute key elements of cognitive maps, and head direction cells, which fire selectively when the rat's head is pointed in a specific direction and which may serve as an internal compass to orient the cognitive map. The spatially and directionally selective properties of these cells arise from a complex interaction between input from external landmarks and from idiothetic cues; however, the exact nature of this interaction is poorly understood. To address this issue, directional information from visual landmarks was placed in direct conflict with directional information from idiothetic cues. When the mismatch between the two sources of information was small (45°), the visual landmarks had robust control over the firing properties of place cells; when the mismatch was larger, however, the firing fields of the place cells were altered radically, and the hippocampus formed a new representation of the environment. Similarly, the visual cues had control over the firing properties of head direction cells when the mismatch was small (45°), but the idiothetic input usually predominated over the visual landmarks when the mismatch was larger. Under some conditions, when the visual landmarks predominated after a large mismatch, there was always a delay before the visual cues exerted their control over head direction cells. These results support recent models proposing that prewired intrinsic connections enable idiothetic cues to serve as the primary drive on place cells and head direction cells, whereas modifiable extrinsic connections mediate a learned, secondary influence of visual landmarks.
Deficits in Smooth-Pursuit Eye Movements After Muscimol Inactivation Within the Primate's Frontal Eye Field
Authors: Shi Dexiu , Friedman Harriet R. , Bruce Charles J.
Published: December 2017

Shi, Dexiu, Harriet R. Friedman, and Charles J. Bruce. Deficits in smooth-pursuit eye movements after muscimol inactivation within the primate's frontal eye field. J. Neurophysiol. 80: 458–464, 1998. To evaluate smooth-pursuit (SP) function in the primate frontal eye field (FEF), microinjections of muscimol, a γ-aminobutyric acid (GABA) agonist, were used to reversibly deactivate physiologically characterized sites in FEF. SP was severely impaired by deactivation at sites in the FEF's smooth eye movement region (FEFsem) located in the fundus and posterior bank of the macaque monkey's arcuate sulcus. These SP deficits were apparent immediately after the muscimol injection and persisted for several hours but recovered by the next day. SP was most drastically and consistently impaired for directions similar to the injected site's elicited smooth eye movement direction or to the optimal SP direction for its neuronal responses. Targets moving in these directions, usually ipsilateral to the injected hemisphere, were tracked primarily with saccades after the muscimol injection, the peak SP velocity being only 10–30% of preinjection velocity. SP in other directions, including contralateral, was less strongly affected. Initial SP acceleration in response to target motion onset was also significantly diminished, generally by approximately the same proportion as peak SP velocity. In contrast, saccades were largely unaffected by muscimol injections in FEFsem; nor was there an immediate effect on SP when control sites in the saccadic region of FEF (FEFsac) were deactivated, although a SP deficit often appeared 30–60 min after FEFsac injections, possibly reflecting diffusion of muscimol into neighboring FEFsem. These reversible SP deficits produced by muscimol inactivation within FEFsem are similar to permanent deficits caused by large aspiration lesions of FEF and indicate that inclusion of FEFsem is the critical factor determining whether FEF lesions impair SP. The severity of the reversible deficits found here indicates how extremely critical FEFsem is for normal highgain SP.
Resting Membrane Properties of Locust Muscle and Their Modulation II. Actions of the Biogenic Amine Octopamine
Authors: Walther Christian , Zittlau Klaus E.
Published: December 2017

Walther, Christian and Klaus E. Zittlau. Resting membrane properties of locust muscle and their modulation. II. Actions of the biogenic amine octopamine. J. Neurophysiol. 80: 785–797, 1998. Ionic currents in the resting membrane of locust jumping muscle and their modulation by the biogenic amine octopamine were investigated using the two-electrode voltage clamp. A Cl−conductance, GCl,H, which slowly activates on hyperpolarization, can be induced by raising the intracellular Cl−concentration via diffusion of Cl−ions from the recording electrode. The instantaneous I-V characteristic of the current, ICl,H, is linear and reverses at the same potential as the γ-aminobutyric acid (GABA)-mediated Cl−current. Elevation of [Cl−]iincreases the maximal steady state GCl,H( Gmax) and shifts the activation curve of GCl,Hto more positive potentials. Octopamine enhances GCl,H, mainly by increasing Gmax. Octopamine also lowers the resting K+conductance ( GK,r). It reduces a hyperpolarization-activated component ( GK,H) of GK,r, mainly by decreasing Gmax. Octopamine also transiently stimulates the Na+/K+pump although this effect was not always seen. The effects of octopamine on the Cl−and K+conductances are mimicked by membrane permeant cyclic nucleotides. The modulation of GK,r, but not that of GCl,H, seems to be mediated by protein kinase A (PKA). PKA seems to be constitutively activated as indicated by the pronounced increase in GK,rinduced by a PKA inhibitor, H89. The properties of GCl,Hand related Cl−conductances in invertebrate and vertebrate neurons are compared. GCl,Hprobably supports efflux of Cl−ions accumulating in the fibers during synaptic inhibition. Octopamine's multiple modulation at the level of the muscle cell membrane, in conjunction with previously established effects on synaptic transmission and excitation-contraction coupling, are suited to support strong and rapid muscle contractions.
Functional and Ionic Properties of a Slow Afterhyperpolarization in Ferret Perigeniculate Neurons In Vitro
Authors: Kim Uhnoh , Mccormick David A.
Published: December 2017

Kim, Uhnoh and David A. McCormick. Functional and ionic properties of a slow afterhyperpolarization in ferret perigeniculate neurons in vitro. J. Neurophysiol. 80: 1222–1235, 1998. Intracellular recordings from spontaneously spindling GABAergic neurons of the ferret perigeniculate nucleus in vitro revealed a fast afterhyperpolarization after each action potential, a medium-duration afterhyperpolarization after each low-threshold Ca2+ spike, and a slow afterhyperpolarization after the cessation of spindle waves. The slow afterhyperpolarization was associated with an increase in membrane conductance, and the reversal potential was sensitive to extracellular [K+]o, indicating that it is mediated at least in part by the activation of a K+ conductance. However, the block of Ca2+ channels did not block the slow afterhyperpolarization, whereas the block of Na+ channels did block this event, even after the generation of repetitive Ca2+ spikes, indicating that it is mediated by a Na+-activated K+ current. Application of apamin reduced the afterhyperpolarization and enhanced a plateau potential after each low-threshold Ca2+ spike. This plateau potential could result in a prolonged depolarization of perigeniculate neurons, even before the application of apamin, resulting in the generation of tonic discharge. The plateau potential was blocked by the local application of tetrodotoxin, indicating that it is mediated by a persistent Na+ current. The activation and interaction of these slowly developing and persistent currents contributes significantly to low-frequency components of spindle wave generation. In particular, we suggest that the activation of the slow afterhyperpolarization may contribute to the generation of the spindle wave refractory period in vitro.
Intermittency in Preplanned Elbow Movements Persists in the Absence of Visual Feedback
Authors: Doeringer Joseph A. , Hogan Neville
Published: December 2017

Doeringer, Joseph A. and Neville Hogan. Intermittency in preplanned elbow movements persists in the absence of visual feedback. J. Neurophysiol. 80: 1787–1799, 1998. It has been observed for nearly 100 years that visually guided human movements appear to be composed of submovements, intermittently executed overlapping segments. This paper presents experiments to investigate the pervasiveness of movement intermittency and, in particular, whether it is exclusively due to visual feedback. With and without visual feedback, human subjects were asked to 1) move with constant velocity and 2) draw elliptical figures on a phase-plane display (showing velocity vs. position) that required cyclic movements at different frequencies. In both tasks, we found that removal of visual feedback did not significantly change movement intermittency. Subjects were unable to generate movements at constant speed. In addition, subjects moved less smoothly when drawing slower phase-plane ellipses. Furthermore, elliptical phase-plane figures were not always drawn at the frequency suggested by the center of the display. Instead, subjects moved more slowly than the tall (fast) ellipse displays suggested, and faster than the wide (slow) displays suggested. These results show that 1) movement intermittency is not exclusively due to visual feedback and 2) may in fact be a fundamental feature of movement behavior.
Azimuth Coding in Primary Auditory Cortex of the Cat. II. Relative Latency and Interspike Interval Representation
Authors: Eggermont Jos J.
Published: December 2017

Eggermont, Jos J. Azimuth coding in primary auditory cortex of the cat. II. Relative latency and interspike interval representation. J. Neurophysiol. 80: 2151–2161, 1998. This study was designed to explore a potential representation of sound azimuth in the primary auditory cortex (AI) of the cat by the relative latencies of a population of neurons. An analysis of interspike intervals (ISI) was done to asses azimuth information in the firings of the neurons after the first spike. Thus latencies of simultaneously recorded single-unit (SU) spikes and local field potentials (LFP) in AI of cats were evaluated for sound presented from nine speakers arranged horizontally in the frontal half field in a semicircular array with a radius of 55 cm and the cat's head in the center. SU poststimulus time histograms (PSTH) were made for each speaker location for a 100-ms window after noise-burst onset using 1-ms bins. PSTH peak response latencies for SUs and LFPs decreased monotonically with intensity, and most of the change occurred within 15 dB of the threshold at that particular azimuth. After correction for threshold differences, all latency-intensity functions had roughly the same shape, independent of sound azimuth. Differences with the minimum spike latency observed in an animal at each intensity were calculated for all azimuth-intensity combinations. This relative latency showed a weakly sigmoidal dependence on azimuth that was independent of intensity level >40 dB SPL. SU latency differences also were measured with respect to the latencies of the LFP triggers, simultaneously recorded on the same electrode. This difference was independent of stimulus intensity and showed a nearly linear dependence on sound azimuth. The mean differences across animals for both measures, however, were only significant between contralateral azimuths on one hand and frontal and ipsilateral azimuths on the other hand. Mean unit-LFP latency differences showed a monotonic dependence on azimuth with nearly constant variance and may provide the potential for an unbiased conversion of azimuth into neural firing times. The general trend for the modal ISI was the same as for relative spike latency: the shortest ISIs were found for contralateral azimuths (ISI usually 3 ms) and the longer ones for ipsilateral azimuths (the most frequent ISI was 4 ms, occasionally 5 ms was found). This trend was also independent of intensity level. This suggests that there is little extra information in the timing of extra spikes in addition to that found in the peak PSTH latency.
Spinal Cord Modular Organization and Rhythm Generation: An NMDA Iontophoretic Study in the Frog
Authors: Saltiel Philippe , Tresch Matthew C. , Bizzi Emilio
Published: December 2017

Saltiel, Philippe, Matthew C. Tresch, and Emilio Bizzi. Spinal cord modular organization and rhythm generation: a NMDA iontophoretic study in the frog. J. Neurophysiol. 80: 2323–2339, 1998. Previous work using electrical microstimulation has suggested the existence of modules subserving limb posture in the spinal cord. In this study, the question of modular organization was reinvestigated with the more selective method of chemical microstimulation. N-methyl-d-aspartate (NMDA) iontophoresis was applied to 229 sites of the lumbar spinal cord gray while monitoring the isometric force output of the ipsilateral hindlimb at the ankle. A force response was elicited from 69 sites. At 18 of these sites, tonic forces were generated and rhythmic forces at 44. In the case of tonic forces, their directions clustered along four orientations: lateral extension, rostral flexion, adduction, and caudal extension. For the entire set of forces (tonic and rhythmic), the same clusters of orientations were found with the addition of a cluster directed as a flexion toward the body. This distribution of force orientations was quite comparable to that obtained with electrical stimulation at the same sites. The map of tonic responses revealed a topographic organization; each type of force orientation was elicited from sites that grouped together in zones at distinct rostrocaudal and depth locations. In the case of rhythmic sequences of force orientations, some were distinctly more common, whereas others were rarely elicited by NMDA. Mapping of the most common rhythms showed that each was elicited from two or three regions of the cord. These regions were close in location to the tonic regions that produced those forces that represented components specific to that rhythm. There was an additional caudal region from which the different rhythms also could be elicited. Taken together, these results support the concept of a modular organization of the motor system in the frog's spinal cord and delineate the topography of these modules. They also suggest that these modules are used by the circuitry underlying rhythmic pattern generation by the spinal cord.
Activity of Spinal Interneurons and Their Effects on Forearm Muscles During Voluntary Wrist Movements in the Monkey
Authors: Perlmutter Steve I. , Maier Marc A. , Fetz Eberhard E.
Published: December 2017

Perlmutter, Steve I., Marc A. Maier, and Eberhard E. Fetz. Activity of spinal interneurons and their effects on forearm muscles during voluntary wrist movements in the monkey. J. Neurophysiol. 80: 2475–2494, 1998. We studied the activity of 577 neurons in the C6–T1 spinal cord of three awake macaque monkeys while they generated visually guided, isometric flexion/extension torques about the wrist. Spike-triggered averaging of electromyographic activity (EMG) identified the units' correlational linkages with ≤12 forearm muscles. One hundred interneurons produced changes in the level of average postspike EMG with onset latencies consistent with mono- or oligosynaptic connections to motoneurons; these were classified as premotor interneurons (PreM-INs). Most PreM-INs (82%) produced postspike facilitations in forearm muscles. Earlier spike-related features, often beginning before the trigger spike, were seen in spike-triggered averages from 72 neurons. Postspike effects were present in one muscle for 64% of the PreM-INs. Neurons with divergent linkages to larger “muscle fields” usually generated postspike effects in synergistic muscles. Fifty-eight percent of the PreM-INs had postspike effects in flexor muscles only and 29% in extensor muscles only. Postspike effects were distributed relatively evenly among the primary flexor and extensor muscles studied. The mean percent change in EMG level from baseline and the mean onset latencies for postspike facilitations and postspike suppressions were similar. PreM-INs exhibited a variety of response patterns during the generation of isometric wrist torque. The response patterns and output effects of 24% of the PreM-INs were consistent with a strict reciprocal organization of flexor and extensor muscle control. For another 60% of the PreM-INs, there was a congruent relation between activity and output effects for only one direction of torque production. These neurons were active for both flexion and extension torques, including 37 neurons that exhibited bidirectional increases in discharge rate. The relatively small number of postspike suppressions observed suggests that inhibitory interneurons were silent when their target muscles were recruited. Compared with premotor neurons in the motor cortex, the red nucleus and the C8–T1 dorsal root ganglia, spinal PreM-INs affected flexor muscles in greater proportions and had smaller muscle fields. The magnitudes of postspike facilitations were similar in all premotor populations. Bidirectional activity, common for PreM-INs, was rare for corticomotoneuronal and premotor dorsal root ganglion cells, which discharge only for torques in their preferred direction.