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E E Fetz

Publications and source records attributed to E E Fetz.

At least 19 recordsLinked to original sources
PubMed1999

Increased gamma-range activity in human sensorimotor cortex during performance of visuomotor tasks.

OBJECTIVE: We documented changes in spectral power of human electrocorticograms (ECoG) during performance of sensorimotor tasks. METHODS: In 6 human subjects, ECoGs were recorded simultaneously from 14 subdural cortical sites in forearm sensorimotor cortex. The subjects performed 3 visuomotor tasks: tracking a moving visual target with a joystick-controlled cursor, threading pieces of tubing, and pinching the fingers sequentially against the thumb. Control conditions consisted of passive resting and active extension of the wrist. For each site the spectral power of the ECoG during these behaviors was computed for 5 10 Hz ranges between 10 and 60 Hz. RESULTS: All subjects showed power decreases in the range of 11-20 Hz and power increases in the 31-60 Hz range during performance of the visuomotor tasks, at sites in forearm sensorimotor cortex and adjacent areas. Simple wrist movements often produced little change in power. Three subjects showed episodes of explicit gamma oscillations during the visuomotor tasks. Different sites showed increases in gamma-range power for different tasks, indicating that the spatial distribution of the gamma activity is specific to the tasks. Cross-spectra showed that gamma activity could become synchronized between separate sites during particular tasks. CONCLUSIONS: Synchronized gamma-range activity in human sensorimotor cortex increases with performance of manipulative visuomotor tasks, supporting the hypothesis that coherent gamma oscillations may play a role in sensorimotor integration or attention.

Adolescent↗
PubMed1998

Activity of spinal interneurons and their effects on forearm muscles during voluntary wrist movements in the monkey.

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.

Action Potentials↗
PubMed1998

Response patterns and force relations of monkey spinal interneurons during active wrist movement.

The activity of C6-T1 spinal cord neurons was recorded in three macaques while they generated isometric wrist flexion and extension torques in visually guided step-tracking tasks. Electromyographic activity (EMG) was recorded in </=12 independent forearm muscles. Spike-triggered averages (STAs) of rectified and unrectified EMG were used to classify neurons into four groups. Motoneurons (MNs) had a clear postspike motor unit signature in the unrectified STA of one muscle. Premotor interneurons (PreM-INs) had postspike effects in at least one muscle, with onset latencies of >/=3.5 ms from the trigger. Synchrony interneurons (Sy-INs) were non-PreM-Ins that had spike-related features with latencies <3.5 ms in at least one muscle. Unidentified interneurons (U-INs) showed no features in any of the STAs. A total of 572 task-related spinal neurons were studied; 29 cells were MNs, 97 PreM-INs, 32 Sy-INs, and 414 U-INs. MNs were activated predominantly in a tonic fashion during the ramp-and-hold torques and were active in one direction only. The most common response pattern for interneurons, irrespective of their class, was phasic-tonic activity, followed by purely tonic and purely phasic activity. Most interneurons (77%) were bidirectionally active in both flexion and extension. For all classes of interneurons, units with phasic response components tended to be activated first, before torque onset, followed by tonic units. The onset times of PreM-INs relative to onsets of their target muscles were distributed broadly, with a mean of -25 +/- 128 (SD) ms. For most neurons with tonic response components (all MNs, 71% of PreM-INs, 67% of Sy-INs, and 84% of U-INs), activity during the hold period was correlated significantly with the magnitude of static torque exerted by the monkey. The rate-torque regressions generally had positive slopes with higher mean slopes for extension than for flexion. The phasic response components were correlated significantly with rate of change of torque for a smaller percentage of tested PreM-Ins (50%), Sy-INs (83%), and U-INs (77%). In contrast to other premotor neurons [corticomotoneuronal (CM), rubromotoneuronal (RM), and dorsal root ganglion (DRG) afferents] previously characterized under similar conditions, a larger proportion of the spinal PreM-INs were activated after onset of their target muscles, probably reflecting a larger proportion of PreM-INs driven by peripheral input. The rate-torque slopes of PreM-INs tended to be less steep than those of CM and RM cells. Unlike the CM and DRG PreM afferents, which were activated unidirectionally, most spinal PreM-INs showed bidirectional activity, like RM cells.

Action Potentials↗
PubMed1996

Synaptic interactions between primate precentral cortex neurons revealed by spike-triggered averaging of intracellular membrane potentials in vivo.

To document synaptic interactions between neurons in the precentral cortex of macaque monkeys, we recorded in vivo the intracellular (IC) membrane potentials of cortical neurons simultaneously with extracellular (EC) action potentials of neighboring cells. The synaptic potentials correlated with EC spikes were obtained by spike-triggered averages (STA) of the IC membrane potentials for 373 cell pairs recorded in anesthetized and awake behaving monkeys. Sixty-three STAs (17%) showed excitatory postsynaptic potentials (EPSPs), beginning after the trigger spike. Pure EPSPs had onset latencies of 0.9 +/- 0.7 msec (mean +/- SD) and amplitudes of 226 +/- 130 microV. Sixteen STAs (4%) showed postspike inhibitory postsynaptic potentials (IPSPs), with onset latencies of 0.4 +/- 0.4 msec and amplitudes of -274 +/- 188 microV. The most common waveform, observed in 82% of the STAs with features, was a broad depolarization straddling the trigger spikes, reflecting synchronized synaptic input to both IC and EC neurons. These average synchronous excitation potentials (ASEPs) began 14.3 +/- 6.6 msec before the trigger spike and had amplitudes of 1064 +/- 867 microV. Twenty-three STAs (6%) showed an average synchronous inhibitory potential (ASIP): a hyperpolarization beginning before the trigger spike and reflecting IPSPs produced by a group of local inhibitory cells synchronized with the trigger cell. ASIPs had an onset latency of -5.5 +/- 2.7 msec and amplitude of -589 +/- 502 microV. Combinations of synchronous and postspike potentials were also observed. Successive recordings provided examples of convergent and divergent connections between EC and IC cells. Neuron pairs with depolarizing postsynaptic potentials (PSPs) in the STA yielded peaks in the cross-correlograms of the IC and EC action potentials; the peak area was proportional to the amplitude of the PSP. These data suggest that a significantly larger proportion of cortical neurons interact through synchronous activity than through simple serial interactions; moreover, synchronous excitation affected more widely separated cell pairs than EPSPs and IPSPs, which were seen most often among the closest cells.

Action Potentials↗
PubMed1996

Oscillatory activity in sensorimotor cortex of awake monkeys: synchronization of local field potentials and relation to behavior.

1. Oscillations of 20-40 Hz were observed in local field potentials (LFPs) and unit activity in sensorimotor cortices of three awake monkeys while the monkeys performed trained wrist movements and untrained exploratory arm movements. The mean frequency of LFP oscillations was 25.9 +/- 1.4 (SD) Hz and the number of cycles of oscillations per episode was variable, with a mean of 4.2 +/- 0.5 (mean +/- SE). 2. Oscillatory episodes occurred most often when the monkeys retrieved raisins from a Klüver board (0.59 +/- 0.23 episodes per s, mean +/- SD) or from unseen locations with the use of somatosensory feedback (0.62 +/- 0.12 episodes per s); they occurred less often when the monkeys performed repetitive wrist flexion and extension movements (0.22 +/- 0.04 episodes per s) or sat quietly at rest (0.23 +/- 0.17 episodes per s). 3. The amplitude of LFP oscillations increased with depth in cortex, reaching a maximum between 1 and 2 mm. LFP oscillations at the surface of the cortex were 180 degrees out of phase with oscillations in the deep cortical layers. The phase shift (with respect to the deep layers) decreased with depth in the cortex and disappeared at depths of > 1 mm. 4. LFPs were recorded simultaneously at multiple sites in the sensorimotor cortex when monkeys retrieved raisins from a Klüver board or from unseen locations. Cross-correlation of LFPs recorded at different sites indicated that oscillations in the 20- to 40-Hz range could become synchronized at sites separated by up to > or = 14 mm in the precentral cortex. 5. The probability of occurrence of significant correlations between LFP oscillations at paired sites and the average correlation amplitude decreased with increasing horizontal separation of sites in precentral cortex. The phase shift between LFP oscillations recorded at paired sites did not change significantly with increasing horizontal separation. 6. For paired sites in precentral cortex, the average strength of correlations and the proportion of oscillations that were significantly correlated were greater during exploratory behaviors such as retrieving raisins from slots of the Klüver board than during periods of rest or overtrained wrist movements. 7. Oscillations could become synchronized with small phase shifts (0.5 +/- 1.6 ms) between pre- and postcentral cortical sites. Average strength and probability of occurrence of significant correlations between pre- and postcentral LFPs increased during exploratory behaviors. 8. Oscillations occurred simultaneously in the left and right motor cortex and could become synchronized with negligible phase shifts when the monkey performed bimanual manipulations. However, synchronization occurred as often and as strongly for unimanual as for bimanual manipulations. 9. These results indicate that episodes of 20- to 40-Hz oscillations occur often and become synchronized over a large cortical area during exploratory forelimb movements. However, they have no reliable relation to particular components of the movement and therefore seem unlikely to be involved directly in movement execution; instead, they may represent a neural correlate of attention during demanding sensorimotor behaviors.

Animals↗
PubMed1996

Synchronization of neurons during local field potential oscillations in sensorimotor cortex of awake monkeys.

1. The neural activity associated with 20- to 40-Hz oscillations in sensorimotor cortex of awake monkeys was investigated by recording action potentials of single and multiple units. At a given site, activity of many units became synchronized with local field potential (LFP) oscillations. Cycle-triggered histograms (CTHs) of unit spikes aligned on cycles of LFP oscillations indicated that about two thirds of the recorded units (n = 268) were entrained with LFP oscillations. On average, units had the highest probability of spiking 2.7 ms before peak LFP negativity, corresponding to a -27.6 degrees phase shift relative to the negative peak of the LFP. 2. The average relative modulation amplitude (RMA), defined as the ratio of amplitude of oscillatory component of CTH and the baseline multiplied by 100, was 45 +/- 27% (mean +/- SD). The RMAs of single units did not differ significantly from those of multiple units. 3. Phase shifts and RMAs did not vary systematically with the cortical depth of recorded units. 4. Autocorrelation histograms (ACHs) of entrained units exhibited clear 20- to 40-Hz periodicity if they were compiled with spikes that occurred during oscillatory episodes in LFPs. ACHs of spikes outside oscillatory episodes usually did not show periodicity. Global ACHs of all spikes typically showed weak or no evidence of periodic activity. 5. Cross-correlation histograms (CCHs) between pairs of units complied with all spikes, whether they occurred during or outside LFP oscillations, seldom revealed significant features (19 of 134 pairs or 14%). However, CCHs compiled with spikes that occurred during oscillatory episodes (OS-CCHs) had significant features in 67 of 134 pairs recorded ipsilaterally; in these 67 cases, units at both sites showed modulation in CTHs. 6. The latencies of the OS-CCH peaks (taking the medial unit as reference) were normally distributed about a mean of -0.5 +/- 13 ms. Normalized peak height of CCHs (peak/baseline x 100) was, on average, 14.3 +/- 11.2%. Peak latency and normalized peak amplitude did not change significantly with horizontal separation of recorded precentral pairs up to 14 mm. 7. Units in the left and right hemispheres could become synchronized during oscillations. Significant features in OS-CCH were detected in 22 of 42 pairs of units recorded bilaterally. The average peak latency was 0.2 +/- 8.0 ms and the average normalized peak amplitude was 10 +/- 8%. These parameters did not differ significantly from those for ipsilateral OS-CCHs. 8. Oscillations tended to affect both the temporal structure and net rate of unit firing. For each unit, the firing rate was clamped to a narrow range of frequencies during oscillatory episodes. The coefficient of variation (SD/mean) of firing rates was significantly reduced during oscillatory episodes compared with prior rates (P < 0.001, paired t-test). However, the overall mean firing rate of each unit during all oscillatory episodes did not differ from its average rate immediately before the episodes. Thus oscillatory episodes tended to clamp mean firing rates to the cells' average rates outside episodes. 9. The strength of synchronization between units during oscillatory episodes was unrelated to their involvement in the task. For pairs of precentral units recorded ipsilaterally, the probability of occurrence of significant features in the OS-CCH was slightly larger when both units of the pair were task related (33 of 56 pairs or 59%) than when only one unit was task related (20 of 39 pairs or 51%) or neither unit was task related (7 of 16 or 44%). However, these differences were not statistically significant. The magnitude of the correlation peak and the latency to peak were also not significantly different for the three cases. 10. These results suggest that units across wide regions can become transiently synchronized specifically during LFP oscillations, even if their spikes are uncorrelated during nonoscillatory periods.

Action Potentials↗
PubMed1996

Response patterns and postspike effects of premotor neurons in cervical spinal cord of behaving monkeys.

Most of our information about spinal neurons has been derived from experiments with anesthetized or surgically. reduced preparations. To investigate these neurons under normal behavioral conditions, we recorded the activity of single afferent units in cervical dorsal root ganglia and of single interneurons in the cervical spinal cord of macaque monkeys, as they generated alternating flexion and extension torques about the wrist. Spike-triggered averages of rectified electromyographic activity were used to identify "premotor" (PreM) units associated with correlated postspike effects in active muscles. In addition to postspike effects, some spike-triggered averages showed early increases in average muscle activity, which were attributed to synchronous discharges in other PreM units. In recordings of peripheral afferents, 49% of the task-related dorsal root ganglia units produced postspike facilitation (PSF) of at least one forearm muscle, with a mean PSF latency of 5.8 +/- 0.3 ms (SE). The PSF amplitude was measured as the mean percent increase (MPI): the average increase of the PSF as a percentage of the prespike baseline mean. PreM afferent units produced PSF with an average MPI of 4.6 +/- 0.3%. In a study of cervical interneurons, about 13% (72/562) of the task-related cells showed postspike effects. These PreM interneurons had a mean PSF latency of 7.2 +/- 0.3 ms and a mean MPI of 4.6 +/- 0.2%. The MPI values for spinal neurons were similar to the MPIs reported for rubromotoneuronal and corticomotoneuronal cells. PreM neurons usually facilitated a subset of the coactivated muscles called the unit's "muscle field." The PreM afferents facilitated an average of 46% of the synergistically coactivated muscles, while PreM interneurons facilitated an average of 37%. These are comparable with the percentage of muscles facilitated by corticomotoneuronal (40%) and rubromotoneuronal (50%) cells. During the step-tracking task the monkeys generated ramp-and-hold torques about the wrist. The PreM afferents typically became active during either flexion or extension of the wrist, although a few were bidirectionally active. The most common response pattern in PreM afferents was a tonic discharge, followed by phasic and phasic-tonic discharge. The most common patterns exhibited by PreM interneurons were tonic and phasic-tonic responses. PreM afferent units began to discharge on average 51 +/- 13 ms before activation of their target muscle. This early onset supports our hypothesis that these PreM afferents arose from muscle spindles, which is also consistent with their short-latency PSF and their responses to perturbations that stretched their target muscles. The results reveal some salient differences between the discharge properties of dorsal root ganglia neurons, spinal interneurons, and supraspinal PreM cells in the motor cortex and red nucleus. All four PreM populations include tonic, phasic-tonic, and phasic cells, but in significantly different proportions. Most PreM afferents resembled corticomotoneuronal cells in being active only with their target muscles, unlike rubromotoneuronal cells and spinal PreM interneurons, which tended to exhibit more bidirectional discharges.

Afferent Pathways↗
PubMed1993

Short-term synchronization of motor units in human extensor digitorum communis muscle: relation to contractile properties and voluntary control.

Synchronous activity was studied in relation to the contractile properties of pairs of motor units (MUs) recorded with independent microelectrodes in the right extensor digitorum communis muscle (EDC) of human subjects during isometric finger extension. MU contractile properties were characterized in terms of the rise time and amplitude of twitch tensions extracted by spike-triggered averages of the extension force. Synchronization of MU discharges appeared in the form of narrow central peaks in the cross-correlograms of 35 of 50 pairs of MUs, suggesting the contribution of common last-order neurons. Synchronization peaks tended to be briefer and higher among pairs of MUs with slower and smaller twitches than among pairs of MUs with faster and larger twitches. The higher peaks of slow-contracting MUs suggest a greater effectiveness of the common synaptic inputs. The broader peaks of fast-contracting MUs might reflect an additional synchronization of the inputs to fast MUs at high force levels. The areas of the cross-correlogram peaks were similar for both groups and suggest that under our conditions, about three motoneurons would discharge synchronously for a given motoneuron spike. To test whether the amount of MU synchronization could be altered voluntarily, four subjects attempted to increase or decrease synchrony, using as feedback clicks triggered by coincident firings of the recorded MUs. In nine of 15 conditioning sessions, the magnitudes of the synchronization peaks showed significant changes in the intended direction. These results imply that supraspinal centers can control the relative amount of inputs that contribute to the synchronization of motoneuron discharges during voluntary contraction of EDC.

Acoustic Stimulation↗
PubMed1993

Cortical mechanisms controlling limb movement.

Significant advances have been made this past year toward understanding the anatomy and physiology of motor cortical regions. New anatomical tracing techniques have elucidated intrinsic cortical connections as well as inter-areal connectivity. Magnetic stimulation of human cortex has provided new insights about the pathways mediating movements in humans. Neural recording studies in animals have further explored the behavioral variables that may be coded in activity of single units and populations. Recent approaches to neural network modeling offer some hope of synthesizing this wealth of detail into working simulations of networks that mediate motor behavior.

Animals↗
PubMed1993

Two modes of interspike interval shortening by brief transient depolarizations in cat neocortical neurons.

1. The effects of small, brief depolarizing pulses and excitatory postsynaptic potentials (EPSPs) on neuronal firing were examined in layer V neurons in slices of cat sensorimotor cortex. During intracellular recording, brief depolarizing current pulses (duration, 0.5-2.0 ms; amplitude, 0.1-4.0 nA) were injected in neurons to produce pulse potentials (PPs) with a near-linear rise to a peak (0.08-3.6 mV; rise time = pulse duration) followed by an exponential decay. These PPs resembled EPSPs evoked by electrical stimulation of adjacent sites. When injected in neurons that were induced to discharge tonically, the PPs shortened the interspike intervals (ISIs) in two ways, depending on their time of arrival in the ISI. 2. Toward the end of the ISI, the PPs crossed a time-varying firing level, thereby directly evoking action potentials and shortening the ISIs. These directly evoked spikes occurred during the rise or peak of the PPs. The absolute firing level increased with the membrane trajectory during the latter part of the ISI. 3. PPs that appeared earlier in the ISI did not cross firing level directly but could nevertheless shorten the ISI by a slow regenerative process. The indirectly evoked spikes occurred after the peak of the PPs, at latencies whose magnitude and variability increased as the PPs appeared at successively earlier times in the ISI. PPs that occurred during the initial portion (approximately the 1st 3rd) of the ISI did not affect ISI duration. 4. Stimulus-evoked EPSPs shortened the ISIs in a manner similar to that of PPs. Like PPs, EPSPs caused direct crossings late in the ISI and indirect crossings earlier. Comparison of the mean and maximum ISI shortenings and the range of delays in which the PPs and EPSPs consistently produced ISI shortenings revealed no systematic differences. These similarities suggest that PPs may be used to simulate the ISI shortenings caused by EPSPs. 5. To characterize possible mechanisms underlying the ISI shortening, we examined the PP shapes at different times in the ISI. PPs immediately following a spike were smaller and decayed more rapidly than those evoked by the same current at rest. Late in the ISI, when the membrane potential was > 5 mV above rest, the PP height exceeded that of the PP at rest. This amplitude increase may be due to activation of the persistent sodium current.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Effects of transient depolarizing potentials on the firing rate of cat neocortical neurons.

1. The effects of excitatory postsynaptic potentials (EPSPs) on interspike intervals (ISIs) of neocortical neurons can be mimicked by pulse potentials (PPs) produced by current injection. The present report documents the dependence of the ISI shortening on the amplitudes of PPs and EPSPs and on the firing rate of the affected neuron. 2. In rhythmically firing necortical neurons, the ISI shortenings caused by PPs arriving at specific times in the ISI can be described by a shortening-delay (S-D) curve. The S-D curve yields three measures of the PPs' ability to shorten the ISI: 1) the mean ISI shortening, S; 2) the maximum shortening, Smax; and 3) the effective interval, defined as the portion of the ISI in which the PP consistently shortens the ISI. For PPs ranging between 80 microV and 3.6 mV (and cells firing at 25 imp/s), the mean shortening increased with amplitude h as S (ms) = 1.2*h (mV)1.24 (r = 0.94; P < 0.01). Smax increased linearly with amplitude as 4.9 ms/mV (r = 0.86, P < 0.01). The effective interval (as a percentage of the ISI) increased slightly with PP amplitude and had a mean value of 65 +/- 21% (mean +/- SD). 3. S-D curves obtained with stimulus-evoked EPSPs varied with EPSP amplitude in a manner similar to those of PPs. The relations obtained for stimulus-evoked EPSPs were not statistically different from those obtained for PPs in the same cells. 4. To determine the effect of firing rate. PPs were applied while neurons fired at frequencies ranging from 8 to 71 imp/s. Both S and Smax were approximately inversely proportional to the baseline firing rate (fo) and could be described as: S or Smax = kfo-m. The mean value of the exponent m (+/- SD) was 0.96 +/- 0.25 for S and 1.2 +/- 0.4 for Smax. These values were not statistically different from a value of 1 (1 group, 2-tailed t test). The effective interval did not vary significantly with firing rate. 5. The dependence of S on PP amplitude and baseline firing rate was incorporated into an expression for the average change in firing rate (delta f) produced by PPs occurring at rate fs: delta f = 0.03 h1.24 fs. The delta f increased with PP amplitude but did not vary significantly with the baseline firing rate. The values of delta f calculated from the S-D curves matched the values that were computed directly from the spike trains.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Coherent 25- to 35-Hz oscillations in the sensorimotor cortex of awake behaving monkeys.

Synchronous 25- to 35-Hz oscillations were observed in local field potentials and unit activity in sensorimotor cortex of awake rhesus monkeys. The oscillatory episodes occurred often when the monkeys retrieved raisins from a Klüver board or from unseen locations using somatosensory feedback; they occurred less often during performance of repetitive wrist flexion and extension movements. The amplitude, duration, and frequency of oscillations were not directly related to movement parameters in behaviors studied so far. The occurrence of the oscillations was not consistently related to bursts of activity in forearm muscles, but cycle-triggered averages of electromyograms revealed synchronous modulation in flexor and extensor muscles. The phase of the oscillations changed continuously from the surface to the deeper layers of the cortex, reversing their polarity completely at depths exceeding 800 microns. The oscillations could become synchronized over a distance of 14 mm mediolaterally in precentral cortex. Coherent oscillations could also occur at pre- and postcentral sites separated by an estimated tangential intracortical distance of 20 mm. Activity of single units was commonly seen to burst in synchrony with field potential oscillations. These findings suggest that such oscillations may facilitate interactions between cells during exploratory and manipulative movements, requiring attention to sensorimotor integration.

Animals↗
PubMed1992

A general diffusion model for analyzing the efficacy of synaptic input to threshold neurons.

We describe a general diffusion model for analyzing the efficacy of individual synaptic inputs to threshold neurons. A formal expression is obtained for the system propagator which, when given an arbitrary initial state for the cell, yields the conditional probability distribution for the state at all later times. The propagator for a cell with a finite threshold is written as a series expansion, such that each term in the series depends only on the infinite threshold propagator, which in the diffusion limit reduces to a Gaussian form. This procedure admits a graphical representation in terms of an infinite sequence of diagrams. To connect the theory to experiment, we construct an analytical expression for the primary correlation kernel (PCK) which profiles the change in the instantaneous firing rate produced by a single postsynaptic potential (PSP). Explicit solutions are obtained in the diffusion limit to first order in perturbation theory. Our approximate expression resembles the PCK obtained by computer simulation, with the accuracy depending strongly on the mode of firing. The theory is most accurate when the synaptic input drives the membrane potential to a mean level more than one standard deviation below the firing threshold, making such cells highly sensitive to synchronous synaptic input.

Computer Simulation↗
PubMed1992

Response patterns and postspike effects of peripheral afferents in dorsal root ganglia of behaving monkeys.

1. The activity of single afferent units was recorded in cervical dorsal root ganglia (DRG) in two macaque monkeys as they generated alternating flexion and extension torques about the wrist during a step-tracking task. During these isometric and auxotonic muscle contractions, electromyographic (EMG) activity was recorded with electrode pairs in up to 12 independent forearm muscles. Spike-triggered averages (STAs) of rectified EMG activity were used to identify afferents that were associated with correlated facilitation of active muscles. 2. Our aim was to find peripheral afferents producing postspike effects in muscles and to compare their properties with those of corticomotoneuronal (CM) and rubromotoneuronal (RM) cells previously obtained under identical behavioral conditions. We documented the timing, magnitude and distribution of their postspike facilitation (PSF) of forearm muscles and investigated the response properties of task-related units. 3. Of 125 afferent units tested with STAs, 68 showed PSF of EMG activity in at least one muscle. Fifty-nine DRG units provided sufficiently long recordings to generate averages with greater than or equal to 2,000 triggers, the minimum number considered to demonstrate reliable effects. Of these 59 units, 29 (49%) were associated with facilitation of forearm muscle activity. 4. Many STAs showed a gradual increase in EMG activity starting before or near the afferent trigger spike; often superimposed on this broad facilitation was a sharply rising PSF starting at a longer latency. The earliest poststimulus facilitation evoked by single microstimuli delivered in DRG occurred in stimulus-triggered averages at a latency of 3.5 ms. In STAs the broad facilitation beginning at latencies shorter than the responses to electrical stimulation was attributed to synchronous discharges in other afferent units. The sharper postspike EMG increases occurring with latencies of greater than or equal to 3.5 ms were identified as PSF produced by the afferent. The PSF parameters documented in this study were measured after subtracting the effects of synchrony facilitation. 5. PSF of EMG activity began at a mean latency of 5.8 +/- 0.3 (SE) ms and peaked at a mean latency of 7.5 +/- 0.3 (SE) ms. In previous studies, the PSFs from CM and RM cells had mean onset latencies of 6.3 and 5.6 ms, respectively, and mean peak latencies of 10.2 and 9.1 ms. 6. A measure of the PSF amplitude is the mean percent increase (MPI), defined as the increase of the PSF above its base measured as a percentage of the prespike baseline mean.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗