Showing papers in "Journal of Neurophysiology in 1980"

Supplementary motor area and other cortical areas in organization of voluntary movements in man

Abstract: 1. Previous studies in man have revealed a coupling between the regional cerebral blood flow (rCBF) and the regional cerebral metabolic rate for oxygen. In normal man, increases in the regional cerebral metabolic rate for oxygen leads to proportional increases in the rCBF(34). We have measured the rCBF as an expression of the level of cortical activity simultaneously from 254 cortical regions in 28 patients with no major neurological defects, during rest and during planning and execution of a few types of learned voluntary movements with the hand. 2. We found that the rCBF increases exclusively in the supplementary motor area while subjects were programming a sequence of fast isolated movements of individual fingers, without actually executing it. 3. During execution of the same motor sequence, there were equivalent increases of the rCBF in both supplementary motor areas, but only in the contralateral primary motor area. In addition, there were more modest rCBF increases in the contralateral sensory hand area, the convexity part of the premotor area, and bilaterally in the inferior frontal region. 4. Repetitive fast flexions of the same finger or a sustained isometric muscular contraction raise the blood flow in the contralateral primary motor and sensory hand area. 5. A pure somatosensory discrimination of the shapes of objects, without any concomitant voluntary movements, also leaves the supplementary motor areas silent. 6. We conclude that the primary motor area and the part of the motor system it projects to by itself can control ongoing simple ballistic movements with the self-same body part. A sequence of different isolated finger movements requires programming in the supplementary motor areas. We suggest that the supplementary motor areas are programming areas for motor subroutines and that these areas form a queue of time-ordered motor commands before voluntary movement are executed by way of the primary motor area.

Functional classes of primate corticomotoneuronal cells and their relation to active force

Abstract: I. The activity of corticomotoneuronal (CM) cells, identified by clear postspike facilitation (PSF) of rectified EMG activity in spike-triggered averages, was recorded in precentral cortex of monkeys making two types of ramp-and-hold wrist responses. “Auxotonic” wrist movements against elastic loads required active torque proportional to wrist displacement, and isometric responses involved ramp-and-hold torque trajectories with no wrist displacement. 2. On the basis of their firing pattern during the ramp-and-hold responses, all CM cells (ut = 135) could be classified into four types: phasic-tonic (59%), tonic (28%), phasic-ramp (8%), or ramp (5%). All CM cells (as defined by PSF) were active during the static hold period; “tonic” cells discharged at a constant rate, while “ramp” cells showed steadily increasing discharge during the hold period. During the dynamic phase of the response, i.e., during the torque ramp, the “phasic” cells exhibited an additional peak of activity exceeding the final tonic level associated with the hold period. Single CM cells exhibited the same response pattern in association with both isometric and auxotonic responses; thus, the torque trajectory rather than displacement or velocity seems to be the primary determinant of the CM cell’s response pattern. Other precentral cells, which discharged phasically at onset of movement but exhibited no tonic discharge during the hold period, did not produce PSF. The four types of CM cells did not differ significantly in the size of their muscle field, their response to passive movements, or their location in the cortex. 3. From response averages we measured the onset time of CM cell activity relative to the onset of EMG activity in its facilitated target muscle(s). The phasic-tonic and phasic-ramp cells began firing significantly earlier with respect to their target muscles (mean onset latencies: -71 and -63 ms, respectively) than the tonic and the ramp cells (+5 and + 101 ms, respectively). Since the peak PSF occurred about 10 ms after the spike, the initial discharges in many CM cells would contribute to subthreshold facilitation of their target motoneurons. 4. To investigate the relation between firing rate of CM cells and active torque, monkeys were required to exert different levels of active torque for the same displacement. During the hold period the tonic activity of each cell was a linearly increasing function of static torque over all or much of the range examined. The ratetorque slope of CM cells-i.e., the increase in firing rate per increase in static torque in the linear range-was similar for auxotonic responses (constant displacement) and isometric responses (zero displacement). The mean rate-torque slope of all extension CM cells (4.8 impulses l s-l/lo5 dyn cm) was about twice that of flexion-related cells (2.5 impulses . s-l/ lo5 dyn l cm). This difference may reflect different degrees of cortical influence on wrist flexor and extensor muscles, although mechanical factors cannot be entirely excluded. 5. Over the range of torque studied, only a few CM cells had appreciable nonzero torque thresholds for tonic firing. Most

Postspike facilitation of forelimb muscle activity by primate corticomotoneuronal cells.

Abstract: 2. In macaque monkeys making rampand-hold wrist movements against elastic loads we recorded activity of task-related motor cortex cells and specific wrist and finger muscles. EMG electrode pairs were implanted in six flexor and six extensor muscles identified by their anatomical location in the forelimb and by characteristic movements evoked by intramuscular stimulation. For precentral cortex cells that discharged during the wrist movements we compiled spike-triggered averages (STAs) of full-wave rectified EMG activity of five to six coactivated muscles. 2. Eighteen percent of the STAs compiled from selected cells showed evidence of postspike facilitation (PSF) of average EMG activity. Such PSF began after the cortical spike (mean onset latency, 6.7 ms), reached a peak (mean peak latency, 10.2 ms), and declined again to prespike baseline levels (mean decay time, 7.0 ms). Seventy-eight percent of the STAs showed no spike-related features, and 4% exhibited complex features. 3. The strength of the PSF was qualitatively rated as strong, moderate, or weak on the basis of clarity relative to base-line fluctuations. When quantified, strong PSF had the largest peak amplitudes relative to mean base-line levels and relative to maximal base-line fluctations. Strong PSF had slightly shorter onset latency and longer duration than moderate or weak PSF. 4. In some monkeys the cells’ projection into the pyramidal tract was tested by the collision technique. Fast pyramidal tract neurons (PTNs) produced mainly PSF with the shortest onset latencies, but also gave rise to PSF with longer latencies; slow PTNs produced PSF with longer latencies. 5. Pairs of spikes with brief interspike intervals were found to be particularly effective in generating PSF. STAs triggered from two action potentials separated by very short interspike intervals showed a net facilitation exceeding the linear sum of the PSF of isolated action potentials. 6. Most cells produced PSF in more than one of the coactivated forelimb muscles. To eliminate any possibility of redundant recording of the same facilitated motor units through different electrodes, EMG activity was cross-correlated and those records with evidence of significant cross talk were excluded from the data base. Of 370 taskrelated neurons recorded with five to six independent muscles, 27% produced strong or moderate PSF in at least one muscle. Half of these produced clear PSF in more than one muscle. The cell’s muscle field, i.e., the set of facilitated muscles, typically comprised a subset of the coactivated synergist muscles. The mean number of facilitated muscles was 2.5 for extensor cells and 2.1 for flexor cells. 7. The excitatory effects on forelimb extensor muscles tended to be stronger and more widespread than on flexor muscles. The proportion of task-related cells showing clear PSF was larger for extensor cells (37%) than flexor cells (22%). Moreover, the ratio of strong to weak PSF was twice as great for extensor cells ( 1.2) as for flexor cells (0.6). Finger extensor muscles were more strongly facilitated than wrist extensor muscles or flexor muscles.

Cerebellar-dependent adaptive control of primate saccadic system

Abstract: 1. The ability of the central nervous system to compensate for saccadic dysmetria was demonstrated in rhesus monkeys. The behavior of this adaptive mechanism after cerebellar ablations was examined...

Dissociation of visual and saccade-related responses in superior colliculus neurons.

Abstract: 1. Single-unit activity was recorded from the superior colliculus (SC) of monkeys trained to look to visual targets presented on an oscilloscope screen. On one task, target localization required that information concerning the retinal position of the target be combined with information concerning current or future eye position. This task also permitted a dissociation between the site of retinal stimulation and the metrics of the saccade triggered by the stimulation. 2. Vigorous visual responses of superficial SC neurons may occur that do not result in the activation of underlying saccade-related cells. The activity of these neurons signals the occurrence of a visual stimulus, whether or not the stimulus is selected for foveal viewing. 3. Saccade-related (SR) discharges of most intermediate and deep-layer SC neurons precede saccades with particular vectors, regardless of the region of retinal activation initiating the saccade. The discharge of these neurons is tightly coupled to saccade onset, even if changes in eye position have occurred since target appearance. Thus, the discharge of these SR neurons must occur after retinal error and eye-position signals have been combined to compute the necessary saccade vector. For most SR neurons, direct retinal activation of overlying visual neurons had no effect on either the vigor or probability of a SR discharge. The discharge of overlying visual cells is neither necessary nor sufficient to activate most SR cells. 4. The discharge of some SR cells is dependent on prior activation of overlying visual cells. Of 53 SR cells, only 3 were completely dependent on visual stimulation, while another 8 discharged less vigorously if corresponding visual activation failed to occur. 5. About one-quarter of the SR cells showed long-lead preburst activity. This activation was characterized by a low level of firing, which began after the saccade signal and continued until a saccade-linked burst occurred. 6. Cells were isolated that were visually responsive yet discharged prior to saccades in the absence of appropriate retinal stimulation. No component of the discharge of these quasi-visual (QV) cells appeared to be motor in the usual sense. The activity of these neurons appears to reflect eye-position error (the difference between actual and desired eye position) and to hold this information in spatial register until a saccade occurs or is cancelled. 7. It is concluded that the presumed linkage, implied in earlier versions of the foveation hypothesis, between the superficial layers (receiving direct retinal inputs) and the deeper layers of the SC is not necessary for the activation of SR neurons. Results suggest that the SC must generate or receive a signal that combines retinal error and eye-position information. These findings are discussed in terms of current models of the saccadic-control system.

Deficits in eye movements following frontal eye-field and superior colliculus ablations

Abstract: 1. This study investigated the effects of frontal eye-field and superior colliculus ablations on fixation patterns and saccadic eye movements. Monkeys were trained to pick apple pieces out of a multiple-slotted apple board while their heads were fixed. Eye movement records were obtained using predominantly the implanted search-coil method. 2. Both unilateral and bilateral frontal eye-field lesions produced only temporary deficits in eye movements. Following surgery monkeys tended to neglect the contralateral peripheral visual field and made fewer saccades to peripheral targets. Recovery was virtually completed in 2-4 wk. 3. Superior colliculus ablation reduced fixation accuracy, saccade frequency, and saccade velocity. These deficits showed little recovery with time. 4. Paired frontal eye-field and superior colliculus lesions produced dramatic deficits in visually triggered eye movements. Animals could no longer fixate their eyes on visual targets with any degree of accuracy. The range of eye movements was greatly reduced, as was the frequency and velocity of saccades. These deficits showed little recovery with time. 5. These results suggest that visually triggered saccadic eye movements are controlled by two parallel channels, one involving the superior colliculus and the other the frontal eye field.

A calcium-activated hyperpolarization follows repetitive firing in hippocampal neurons.

Abstract: 1. A long-lasting afterhyperpolarization (AHP) follows current-induced repetitive firing in hippocampal CA1 neurons studied in vitro. A 10-25% increase in membrane slope conductance occurs during the AHP, suggesting that it may be mediated by an increased conductance to either K+ or Cl-. 2. Intracellular Cl- iontophoresis does not alter the AHP but does attenuate the IPSP. In contrast Ba2+, a cation that can decrease K+ conductance, eliminates the AHP but not the IPSP. These findings suggest the AHP is produced by a long-lasting increased conductance to K+, and is distinct from the IPSP. 3. Mn2+, a Ca2+-channel blocker, eliminates the AHP. In comparison, the AHP persists in the presence of the Na+-channel blocker, tetrodotoxin (TTX), and appears to be temporally associated with TTX-resistant "Ca2+ spikes." It is concluded that AHP is probably activated by Ca2+ influx. 4. These observations indicate that the AHP may be produced by a Ca2+ activated K+ current. A balance between cellular depolarization produced by Ca2+ entry and repolarization generated by a Ca2+-activated K+ current appears to operate to control excitability in some mammalian cortical neurons as it does in molluscan neurons. Disruption of this balance by Ba2+ produces spontaneous membrane-potential oscillations and recurrent burst firing in hippocampal neurons. Increases in the magnitude and duration of Ca2+ depolarization and/or decreases in the Ca2+-activated, K+-mediated repolarization may be mechanisms that lead to spontaneous, epileptiform bursting in mammalian cortical neurons.

Long-term adaptive changes in primate vestibuloocular reflex. III. Electrophysiological observations in flocculus of normal monkeys.

Abstract: 1. The discharge characteristics of 1,239 single units recorded in the flocculus of alert monkeys were studied in relation to visual, vestibular, and oculomotor events in a variety of paradigms. Animals were trained to fixate small target lights and were required to perform various tracking tasks designed to facilitate the quantitative analysis of associated unit discharges. Units were subdivided into three major groups: granular layer input elements (GLIEs, 77 1 units), interneurons (tentatively classified as Golgi cells, 122 units), and Purkinje output cells (P-cells, 346 units). 2. The discharges of 94.2% of the GLIEs modulated in one or more of the paradigms and two major classes were defined: a) eye movement-only GLIEs (53.6%) modulated their discharge solely in relation to eye movements. Some altered their discharge only in relation to saccadic eye movements (saccadeonly units, y1 = 65), the majority of these being silent during fixation and discharging at high rates just before and during saccades in one or more directions. The remainder of the units in this class exhibited maintained discharges, which were influenced by steady eye positionthe rate increasing progressively as fixation shifted in the socalled on-directionand also showed additional modulation related to eye velocity during pursuit and/or vestibular stimulation (phasic-tonic units, y1 = 348); saccade-related discharges were various, but the most common pattern was the so-called burst-tonic. b) vestibular GLIEs (27.8%) modulated their discharge in relation to head velocity during horizontal chair oscillations as if receiving a vestibular input. The modulation of some of these units was solely determined by the chair movement (vestibular-only units, yt = 47), while others also altered their discharge in relation to saccadic eye movements, mostly by pausing (vestibularplus-saccade units, y2 = 70); yet others were further influenced by steady eye position and, in addition, by eye velocity during pursuit and/or vestibular stimulation (vestibular-plus-position units, y2 = 97). Other GLIEs discharged in relation to vergence/ accommodation (3.9%), visual inputs (2.7%), attempted head movements (5.2%), and blinks (1%). 3. Discharges of putative Golgi cells had unusually regular interspike intervals. Seventy-one of the 122 such cells modulated in one or more of the paradigms, most discharging in relation to eye movements but less clearly and vigorously than the corresponding GLIEs. Some produced only weak saccade-related bursts (~1 = 12), while others discharged tonically in relation to steady eye position (yt = 24) but only weakly and frequently exhibited nonlinear rate-position relationships. One-quarter of the cells (~2 = 32) discharged tonically in relation to eye movements, but showed marked decays in firing during prolonged eccentric fixation and displayed very distorted, though consistent, discharge frequency profiles during sinusoidal and triangle-waveform pursuit. 4. P-cell simple spike discharges often had unusually irregular interspike intervals; 93% modulated in one or more of the para-

Brief bursts of high-frequency stimulation produce two types of structural change in rat hippocampus.

Abstract: 1. Electrophysiological and electron-microscopic techniques were used to investigate possible structural modifications associated with the induction of long-term synaptic potentiation in the hippocampal formation. Stimulation and recording were carried out using the Schaffer collateral-commissural projections from field CA3 to field CA1 of the rostra1 hippocampus of anesthetized rats. 2. In one group of animals repetitive stimulation was administered at a frequency of 100 s-l for 1 s (potentiated), while another group was stimulated at 0.2 s-l for 3 min (control). The first paradigm produced a marked increase in the strength of the postsynaptic potentials, which persisted without decrement for the 15-min periods of control testing, while the repetitive low-frequency activation had no detectable effects on synaptic transmission. 3. Following testing, the rats were perfused and prepared for electron microscopy. The dendritic zone adjacent to the recording microelectrode tip was found and measurements made of the numbers of synapses as well as of the area and length of various constituents of the neuropil. 4. The number of synaptic contacts on dendritic spines was not different between the two groups, but the incidence of synapses onto dendritic shafts was 33% higher in the animals that received high-frequency stimulation (potentiated group). 5. No statistically significant changes were observed in the mean size of any of the following measures: 1) area of synaptic boutons contacting dendritic spines, 2) area of dendritic spines, 3) width of dendritic spine stalks, 4) length of postsynaptic densities (PSDs) on dendritic spines, 5) area of synaptic boutons contacting dendritic shafts, 6) length of PSDs on dendritic shafts. 6. However, there were distinct changes in the within-animal variance and distribution of the dendritic spine measures. Specifically, in the potentiated group there was a reduction in the coefficient of variation in 1) the area of dendritic spines, 2) the length of PSDs on dendritic spines, and3) the width of spine stalks. The extent to which the within-animal distributions of each of these measures were positively skewed was also reduced in the potentiated group. 7. It appears then that brief bursts of highfrequency stimulation produce two very different types of structural change: 1) an apparent increase in the number of shaft synapses, and 2) a decrease in the variability of the dendritic spines. The possible relationship of these morphological effects to long-term potentiation of synaptic responses is discussed.

Rapid ankle extension during paw shakes: Selective recruitment of fast ankle extensors

Abstract: 1. Electromyographic (EMG) signals from slow (soleus) and fast (lateral gastrocnemius) ankle extensors of six cats were recorded during rapid and alternate flexion-extension of the hindlimb elicited by placing the paw in water or by sticking tape to the plantar pads. High-speed 16-mm film, taken at 100 or 200 frames/s, was analyzed to determine the knee and ankle joint kinematics. 2. During 77 typical records, which averaged eight paw shakes each, a single extension-flexion cycle measured by the paw shake interval (PSI) of the electromyogram record, averaged 88 ms and ranged from 55 to 110 ms. LG EMG bursts of 10 ms in duration were synchronized with the peak displacement of ankle flexion. The SOL was inactive throughout these typical records. 3. During four atypical records from one cat, the average OSI was 141 ms, and both lateral gastrocnemius (LG and soleus (SOL) were active simultaneously. At a range of 6--8 cycles/s, these slower shakes are comparable to rhythmic actions of scratching )12) and locomotion (27); cyclic movements that typically include the recruitment of soleus. 4. It is suggested that paw shaking is an automatic movement triggered primarily by large, low-threshold afferents innervating the central plantar pads, which may selectively recruit the fast extensors while inhibiting the slow extensor. This is the only movement of the hindlimb recorded to date in our laboratory in which the tlg was active without the SOL. This unique dissociation of recruitment of slow and fast ankle extensors may be dictated by the time constraints imposed by the rapid cyclic movements of paw shaking.

Different cortical areas in man in organization of voluntary movements in extrapersonal space

Abstract: 1. This paper reports regional cerebral blood flow (rCBF) measurements in 254 cortical regions with 133Xe injected into the internal carotid artery in 19 patients, none of whom had any major neurological defect. The purpose was to demonstrate the pattern of cortical activity, as revealed by rCBF increases, during two types of unilateral voluntary movement in extrapersonal space: a) the maze test, series of fast isolated movements in various directions in a frame, executed under verbal command; and b) the drawing of a spiral in the air. 2. Both types of movements were associated with increases of rCBF in the supplementary motor area (bilaterally), the convexity part of the premotor area (bilaterally), the primary sensorimotor hand and arm area (contralaterally), and in the superior and inferior parietal region (bilaterally). 3. During the maze test there were, in addition, bilateral focal increases of the blood flow in the auditory areas, the inferior frontal regions, and the frontal eye fields. 4. It is concluded that the supplementary motor areas, which are also active during programming and execution of movement sequences in intrapersonal space (33), elaborate programs for motor subroutines necessary in skilled voluntary motion. The convexity parts of the premotor areas are activated when a new motor program is established or a previously learned motor program is modulated. The primary motor area is the exclusive executive locus for voluntary movements of the hand and arm. 5. Voluntary movements in extrapersonal space only are associated with activation of the parietal regions. These areas are assumed to provide information to the motor programming neurons about the demanded direction of motion in extrapersonal space in relation to proprioceptive reference systems. 6. The increase of rCBF in the auditory areas, the inferior frontal regions, and the frontal eye fields during the maze test were ascribed to the processing of auditory information. 7. Both tests are accompanied by a diffuse increase of the hemispheric blood flow (approximately 10%), which is assumed to be a parallel to the commonly known desynchronization of the EEG during mental work.

Muscle architecture and force-velocity characteristics of cat soleus and medial gastrocnemius: implications for motor control

Abstract: 1. Isometric and isotonic contractile parameters of the soleus (SOL) and medial gastrocnemius (MG) muscles of seven adult cats were studied. In addition, architectural characteristics of six contralateral pairs of these ankle extensors were determined. 2. The in situ peak isometric tetanic tension developed by the MG at the Achilles tendon is nearly 5 times (9,846 vs 2,125 g) that of the SOL muscle. However, when differences between the MG and SOL in fiber length (2.01 vs 3.66 cm), muscle mass (9.80 vs. 3.31 g), and angle of pinnation (21.4 vs. 6.4 degrees) are considered, the specific tensions of these muscles are similar (approximately 2.3 kg x cm-2). 3. When the effects of muscle architecture are eliminated, the nearly threefold greater maximum isotonic shortening velocity (Vmax) of sarcomeres of the MG (38.2 micron/s) relative to the SOL (13.4 micron/s) is presumably due to intrinsic differences in the biochemical properties of these muscle. However, the Vmax developed by the MG at the Achilles tendon (258.6 mm/s) during a shortening contraction is only 1.5 times that of the SOL (176.3 mm/s) due to the influence of these muscles' specific architectures. 4. Variations in geometrical characteristics of the SOL and MG are consonant with the relative amounts of participation of these muscles during posture, locomotion, and jumping. Posture requires the development of low forces for prolonged periods for which the SOL seems best suited both architecturally and physiologically. The MG, relatively inactive during quiet standing, becomes responsible for a greater percentage of tension and shortening speed during plantar flexion (E3) as gait speeds increase, which is consistent with this muscle's greater tension- and velocity-generating capacity. 5. At high speeds of locomotion (3.0 m/s) and jumping, the shortening velocities developed at the end of E3 (approximately 20-40 ms before paw off) exceed Vmax of the SOL. Consequently, the SOL, although electrically active, cannot contribute to the tensions required to generate the shortening velocities dictated by these movements. 6. These data demonstrate the influence of the differing geometries of the SOL and MG on the roles of these muscles in generating forces at varying velocities, as demanded by the dynamics of the movement.

Spatial properties of visual fixation neurons in posterior parietal association cortex of the monkey

Abstract: 1. A systematic study of the positional selectivity of visual fixation (VF) neurons of the posterior parietal association cortex (area 7a or PG) was made in seven hemispheres of four alert behaving...

Exploring a vibratory systems analysis of human movement production.

Abstract: the most desirable attributes of the human motor system are that of the limbs accurately in space using a variety of movement trajectories and that localization be accomplished relatively independent of changes in the initial conditions of the limbs c Al though it is well-documented that these features are characteristic of the behavioral of both animal s and humans, less clear is the nature of the control mechanism(s) e Neither of the currentl y popular closed-feedback (Adams, 1977) or programming accounts (Schmid t, seem completely ad For , al though a closed-loop model accommodate the fact that achievement of final position is possible in of (a) in limb position prior to movement (Stelmach, Kelso, & Wallace, 1975) or (b) the introduction of abrupt changes in load during movement execution (Houk, 1978; Polit & Bizzi, 1978), it is at a loss when the same finding s can be demonstrated under deafferentation conditions (Bi zzi &0 Similarly, central motor programs that do not ongoing feedback moni toring may handle deafferentation findings, but go awry when confronted with unforeseen changes in the movement contexte Indeed, even a hybrid model that incorporates internal, central feedback loops (Evarts, 1971; Kelso & Stelmach, 1976) has great difficulty with the finding that normal accuracy may result when monkeys are deafferented and consequently subjected to unpredictable movement perturbations (Polit & Bizzi, 1978)0 An al ternative approach to of localization-stemming from Bern-stein's orig inal work (1947) 1, proposes that where muscles at a joint are constrained to act as a unit, the linkage is describable as a class of vibratory system with the physical and behavioral characteristics of a mass-There are several properties of a mass-spring that are advantageous in explaining the style of control observed in localization experiments. Perhaps its major characteristic for our purposes is that it is intrinsically self-equil ibrating; once set in motion the spr ing will al ways come to rest at the same resting length (equilibrium point)\" Neither an increase in initial deflection of the spring from its resting length nor temporary perturbations will prevent the achievement of the equil ibrium point, a property known as AcknOWledgment: We thank James Pruitt for his assistance and two anonymous rev iewers for their helpful remarks.

Long-term adaptive changes in primate vestibuloocular reflex. I. Behavioral observations.

Abstract: 1. Experiments were concerned with the long-term adaptive changes that occur in the primate vestibuloocular reflex (VOR) when the visual input associated with head movements is disturbed by various optical devices, including telescopic spectacles (magnification 2.0 and OS), fixed-field spectacles (field of view fixed with respect to the head; hence, equivalent here to “zero power” lenses), and dove prism spectacles (providing left-right reversal of vision). 2. Assessed with sinusoidal oscillations (0. l- 1.0 Hz), the VOR of the normal rhesus monkey measured in the dark was close to ‘ ‘ideal’ ’ for maintaining ocular stability during had turns: 180’ out of phase with the head and gain (slow-phase eye velocity/head velocity) close to one. 3. Telescopic and fixed-field spectacles induced adaptive changes in the gain of the reflex, which proceeded roughly exponentially, eventually achieving up to 75% compensation. No phase changes were observed. Caloric responses in the high-gain state were elevated above normal by an amount corresponding to the increase in VOR gain indicated by passive oscillation. The compensatory eye movements coupled to voluntary head turns in the dark were only slightly greater than would have been predicted solely from the passively assessed VOR gain in both normal and highgain animals; nonvestibular factors continued to play, at best, a minor role in the stabilization of retinal images during head turns in the adapted animals. Recovery after removal of the spectacles also followed a

Properties of a persistent inward current in normal and TEA-injected motoneurons.

Abstract: 1. Membrane currents of normal and TEA-injected cat lumbar motoneurons were investigated using the technique of somatic voltage clamp. 2. The current-voltage (I-V) relation of healthy motoneurons contains a region of negative slope conductance caused by a persistent inward current component (Ii). In the most striking examples, Ii is net inward at some potentials between 10 and 30 mV positive to resting potential. 3. Near its activation threshold (greater than or equal to 10 mV positive to rest), Ii does not decrement during prolonged voltage steps and, in most cells, activates very slowly. Ii amplitude increases and time to peak Ii decreases with further small increments of depolarization, and Ii decrements during sustained voltage steps. Maximum Ii amplitude occurs 20--30 mV positive to rest in most cells. Ii is not visible at sufficiently large depolarizations. 4. Ii appears to be mixed with potassium current components at nearly every potential where it is visible. These include a slow outward current first activated near Ii activation threshold, a fast outward current additonally activated at larger depolarizing potentials, and a fast, transient outward current that obscures the true onset of Ii at nearly every potential. 5. Ii is not carried by sodium entering via the fast, transient channels and is present after pharmacological blockage of sodium currents. It is proposed that Ii is predominantly carried by calcium ions. 6. The presence of inward tail currents after repolarization from potentials that activate a steady outward current suggest that Ii remains present but hidden at large depolarizations. Ii inactivation was further investigated in TEA-injected motoneurons since Ii and the tail currents are more prominent in these cells. 7. Conventional recordings from TEA-injected motoneurons suggest that a prolonged, postspike plateau potential is maintained by a persistent inward current. Voltage-clamp data can account for the principal features of the plateau potential. 8. Voltage-clamp results in TEA-injected motoneurons suggest that Ii is subject to little or no inactivation at potentials less than or equal to 30 mV positive to rest and to partial inactivation, at most, at higher potentials during steps lasting less than or equal to 100 ms. The apparent decay of Ii during sustained depolarization is caused by the development of a larger outward current. 9. Ii is similar in several ways to a persistent calcium current observed in some molluscan neurons. Theoretical and experimental results suggest that Ii is generated predominantly in a local region under voltage control and that the observed membrane currents govern somatic membrane potential and cell behavior.

Supplementary motor area: neuronal response to motor instructions

Abstract: 1. Single-unit recordings were obtained from the supplementary motor area of the cerebral cortex of two monkeys during execution of learned movements 2. Monkeys were required to push or pull a cast attached to the right forelimb in response to a sudden perturbation delivered via the cast. An instruction as to the direction of the monkey's movement was delivered 2.5--5 s prior to the occurrence of the perturbation and correct performance, therefore, required the animal to develop a preparatory state prior to the perturbation. 3. Of many hundreds of neurons recorded, 201 exhibited instruction-induced changes of activity during the period intervening between the instruction and the perturbation-triggered movement. 4. In 94 neurons, effects of the instruction were differential depending on which of the two instructions was given, whereas in 107 neurons, effects were nondifferential. The latencies of the differential responses appeared to be shorter (starting as early as 140 ms after the instruction). 5. The magnitude of the instruction effects varied in parallel with development of enhanced motor skill as the monkeys gained more experience in responding to the triggering stimulus. 6. These observations substantiate the hypothesis that the supplementary motor area plays a part in modifying a sensory-triggered motor output.

Sensory and motor responses of precentral cortex cells during comparable passive and active joint movements

Abstract: Seventy-five percent of the cells in leg and arm areas responded only to passive joint movement, 8% were activated by cutaneous stimulation, and 17% did not respond to the somatic stimuli tested. Half of the units with cutaneous input could also be activated by passive joint rotation. A small number of precentral neurons responded to complex visual stimuli, such as approaching objects or appearance of novel objects. 2. Of the precentral cells responsive to passive joint movement, over three-fourths responded only phasically during joint rotation and exhibited no tonic discharge related to joint angle. Two-thirds responded to movement of only a single joint. For most arm and leg joints, the numbers of neurons responding to flexion and to extension were approximately equal; some cells were activated by both flexion and extension of the same joint. 3. In exploring specific precentral regions, we found cells with input from different parts of a limb to be extensively intermingled. On the cellular level, we did not find somatotopic organization to be sufficiently precise and detailed to predict the response properties encountered in adjacent tracks, except in probabilistic terms. Nevertheless, successive neurons in vertical penetrations tended to respond to passive movements of the same joints. 4. The response patterns of precentral neurons, identified by anatomical location, adequate natural stimulus , and pyramidal tract projection, were documented during comparable active and passive elbow movements, with the forearm held in a cast. Response averages for each of the four ramp-and-hold movements indicated that the strongest neural activity occurred with active phasic movements. In these selfpaced movements, changes in precentral cell activity preceded agonist muscle activity by an average of 159 ms and preceded the mean onset of postcentral cells (47). 5. Responses to controlled passive elbow movements with the arm restrained were usually consistent with the cells’ adequate stimulus. Precentral neurons responding to passive elbow movement in one direction were about equally divided into those firing with active elbow movements in the same direction, the opposite direction, and both directions. Thus, we found no predominant relationship between the cells’ peripheral input, as determined by their passive response, and their central input, as evidenced by early changes in activity before active movements. (However, recent evidence indicates that certain precentral output neurons, namely, reciprocally related pyramidal tract neurons (PTNs) (8, 15, 52), and cells that facilitate forelimb muscle activity (7, 18, 19) tend to respond to passive joint movements that stretch their coactivated muscles.) 6. Some precentral neurons responded to active and passive elbow movements in both directions. Most of these had adequate

Responses of neurons in primate ventral posterior lateral nucleus to noxious stimuli

Abstract: 1. Recordings were made from the caudal part of the ventral posterior lateral (VPLc) nucleus of the thalamus in anesthetized macaque monkeys. In additon to many neurons that responded only to weak mechanical stimuli, scattered neurons were found that responded to both innocuous and noxious stimulation or just to noxious stimulation of the skin. A total of 73 such neurons were examined in 26 animals. 2. Noxious stimuli included strong mechanical stimuli (pressure, pinch, and squeezing with forceps) and graded noxious heat (from 35 degrees C adapting temperature to 43, 45, 47, and 50 degrees C). The responses of the VPLc neurons increased progressively with greater intensities of noxious stimulation. The stimulus-response function when noxious heat stimuli were used was a power function with an exponent greater than one. 3. Repetition of the noxious heat stimuli revealed sensitization of the responses of the thalamic neurons to such stimuli. The threshold for a response to noxious heat was lowered, and the responses to supra-threshold noxious heat stimuli were enhanced. 4. The responses of VPLc neurons to noxious heat stimuli adapted after reaching a peak discharge frequency. The rate of adaptation was slower for a stimulus of 50 degrees C than for one of 47 degrees C. 5. For the six neurons tested, responses to noxious heat were dependent on pathways ascending in the ventral part of the lateral funiculus contralateral to the receptive field (ipsilateral to the thalamic neuron). In two cases, the input to the thalamic neurons from axons of the dorsal column was also conveyed by way of a crossed pathway in the opposite ventral quadrant. In another case, access to the thalamic neuron by way of ascending dorsal column fibers was demonstrated. 6. The thalamic neurons had restricted contralateral receptive fields that were somatotopically organized. Neurons with receptive fields on the hindlimb were in the lateral part of the VPLc nucleus, whereas neurons with receptive fields on the forelimb were in medial VPLc. 7. Ninety percent of the VPLc neurons tested that responded to noxious stimuli could be activated antidromically by stimulation of the surface of SI sensory cortex. It was possible to confirm that many of these cells project to the SI sensory cortex by using microstimulation. Successful microstimulation points were either within the SI cortex or in the white matter just beneath the cortex. 8. We conclude that some neurons in the VPLc nucleus are capable of signaling noiceptive stimuli. The nociceptive information appears to reach these cells through the ventral part of the lateral funiculus on the side contralateral to the receptive field, presumably by way of the spinothalamic tract. The VPLc cells are somatotopically organized, and they are thalamocortical neurons that project to the VPLc nucleus and SI cortex play a role in nociception.

Magnification, receptive-field area, and "hypercolumn" size in areas 3b and 1 of somatosensory cortex in owl monkeys.

Abstract: 1. Several features of the two complete and separate representations of the contralateral body surface in cortical areas 3b and 1 of somatosensory cortex in owl monkeys were quantitatively studied. 2. Area1 magnification factors for different body regions in the two representations were obtained. The glabrous hand and foot regions were found to occupy nearly 100 times more cortical tissue per unit body-surface area than the trunk or upper arm. 3. In the representations of the hand digits, inverse magnification was linearly related to distance from the digit tips. 4. Receptive-field size was found to be proportional to inverse magnification over the entire body-surface representation as well as over the local region of the glabrous hand digits. The relation between receptive-field size and inverse magnification appears to be linear; specification of one would specify the other over the representation in one area. 5. By relating receptive-field overlap to distance separating recording sites, the area of cortex presumed to receive all fibers from any given receptive field was obtained and found to be independent of the body surface represented. Such an area of somatosensory cortex, about l1.5 mm in diameter, may be akin to the “hypercolumn” proposed for primary visual cortex (6).

Mechanisms underlying pattern generation in lobster stomatogastric ganglion as determined by selective inactivation of identified neurons. I. Pyloric system

Abstract: 1. Four factors contribute to pattern generation in the pyloric network of the lobster stomatogastric ganglion. These are: a) endogenously oscillating neurons; b) synaptic network properties; c) nonlinear cellular properties, including the generation of plateau potentials; and d) excitatory input from the commissural ganglia. The roles and relative importance of these factors were investigated with a new technique for inactivating single specific identified neurons. 2. In stomatogastric ganglia in which the excitatory input is left intact, a) pattern generation continues when any cell or pair of cells other than the endogenous bursters are inactivated, b) pattern generation also continues when the endogenous bursters are inactivated, c) pattern generation ceases when the endogenous bursters plus one other particular cell are inactivated. This cell, although not an endogenous burster, displays a strong tendency to generate plateau potentials. 3. In stomatogastric ganglia that have been isolated from excitatory input, a) pattern generation continues when any cell or pair of cells other than the endogenous bursters are inactivated, b) pattern generation ceases when the endogenous bursters are inactivated. 4. Some of the inputs to the stomatogastric ganglion normally fire in bursts. However, their potentiation and acceleration of the output pattern are also produced by tonic stimulation of the nerve. The effect of one of those inputs is mimicked by bath application of dopamine to the stomatogastric ganglion. 5. The roles and importance of the three most important factors were qualitatively summarized in a chart specifying the activity of the network as a function of its intactness.

Modulation of ipsi- and contralateral reflex responses in unrestrained walking cats

Abstract: 1. The modulation of reflex responses in up to 10 simultaneously recorded hindlimb muscles was studied in unrestrained cats walking on a treadmill. Single electrical shocks of various strengths were applied to different skin areas of teh hindlimb at different times of the step cycle while the resulting EMG responses were sampled and analyzed. 2. Two excitatory response peaks (P1 and P2) at a latency of about 10 and 25 ms, respectively, were seen in all flexors examined (sartorius, semitendinosus, tibialis anterior, extensor digitorum longus). Stimulation of most skin areas was effective but responses were most easily obtained from stimuli applied to the foot or ankle. During the step cycle there was a marked modulation of the amplitudes of the responses, especially the P2 responses, which grew larger toward the end of stance when a maximum was reached, followed by a steady decline throughout swing. This pattern was very similar for various flexors, although these muscles differed considerably in their normal EMG activity pattern during walking. 3. Flexor responses were absent when the same stimuli were applied during the early stance phase. Instead, inhibition of the ongoing EMG activity was seen at a latency of 10 ms or less in all extensors examined (semimembranosus, quadriceps, soleus, gastrocnemius medialis, flexor digitorum longus). The inhibition was followed by a late excitatory peak (P3) at about 35-ms latency in all extensors except soleus. 4. Certain stimulation sites yielded exceptions to the above patterns. Stimulation of the skin area innervated by the sural nerve yielded larger and earlier MG excitatory responses as compared to stimulation of other skin areas. Activation of the plantar surface of the foot often failed to elicit P2 responses in the hip flexor sartorius, which showed inhibition instead. 5. In the hindlimb contralateral to the stimulus, excitatory responses occurred both in flexors and extensors at a latency of 20-25 ms. The pattern of modulation of these responses was similar to the ipsilateral modulation of P2 flexor and P3 extensor responses. Soleus failed to show a crossed response. 6. The data indicate that flexor and extensor responses differ both with respect to their latency and to their correlation with the ongoing EMG reactivity. It is concluded that these stimuli do not demonstrate reflex reversal in the strict sense in the normal walking cat but that there is modulation of transmission in a flexor excitatory and extensor inhibitory pathway, possibly by the flexor part of the spinal locomotor oscillator. In addition, there are some specialized flexor inhibitory and extensor excitatory pathways. The slow soleus muscle does not seem to be excited through these pathways.

Location and properties of dorsal horn neurons at origin of spinoreticular tract in lumbar enlargement of the rat

Abstract: 1. Spinoreticular tract neurons at the rat lumbar cord level were identified by antidromic activation following stimulation at mainly pontine and mesencephalic levels. These units, which were found in the dorsal half of the cord, could be separated into two groups according to their spinal location, electrophysiological properties, and their central projections. 2. Units in the dorsolateral funiculus nucleus projected mainly to the cuneiformis area and adjacent structures with frequent bilateral projections. They had the slowest conduction velocities, sometimes in the unmyelinated range. Generally, they were driven only by stimulation of subcutaneous and/or deep structures. 3. Neurons located in the dorsal horn mainly projected contralaterally to pontine and mesencephalic levels. their conduction velocities and the electrophysiological properties were identical to those observed for the rat spinothalamic tract (22). Almost all (86%) had clear cutaneous sensitivity and generally large receptive fields: 40% responded to nonnoxious and noxious mechanical cutaneous stimuli and frequently to noxious radiant heat, 26% were exclusively excited by light tactile stimuli, and 20% required noxious cutaneous mechanical stimulation for activation. There was a good correlation between responses to natural and transcutaneous electrical stimulation: units driven by noxious mechanical stimuli received A-delta- and/or C-fiber inputs. The remaining units (14%) had more complex receptive fields associated with both excitatory and inhibitory inputs originating from a single peripheral area. 4. The functional heterogeneity of the rat spinoreticular tract is reminiscent of that demonstrated for the rat and monkey spinothalamic tracts. Similarly, the rat spinoreticular neurons are under the influence of descending inhibitory controls originating from the nucleus raphe magnus and bulbar reticular formation. 5. Responses of the rat spinoreticular tract neurons are consistent with the involvement of this pathway in the transmission of messages of both innocuous and noxious origins.