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P D Cheney

Publications and source records attributed to P D Cheney.

At least 19 recordsLinked to original sources
PubMed1998

A low-cost, multi-channel, EMG signal processing amplifier.

There is a growing need in studies of movement control to expand the number of muscles from which EMG activity is recorded during performance of motor tasks. Optimal viewing and analysis of this EMG activity requires signal processing which provides adjustable gain and baseline offset as wells as selectable AC coupling, rectification and filtering. This paper presents a low-cost circuit that combines two channels of EMG signal processing capability in one module.

Animals↗
PubMed1998

Fractionator analysis shows loss of neurons in the lateral geniculate nucleus of macaques infected with neurovirulent simian immunodeficiency virus.

Infection of macaques with neurovirulent strains of simian immunodeficiency virus (SIVmac) is an experimental model for the neurological manifestations of AIDS. Loss of neurons has been reported in the cerebral cortex following immunodeficiency viral infection, but thalamic structures which may contribute to electrophysiological changes and neurological deficits have not been examined. In this study, the lateral geniculate nucleus (LGN) of macaques inoculated with macrophage-tropic, neurovirulent virus SIVmac239 (R71 and 17E) was examined for neuron loss using the optical fractionator method. Estimates of the number of neurons in the P layers of the lateral geniculate nucleus of age-matched control macaques ranged from 1.0 to 1.3 x 10(6), while the number of neurons in SIV infected macaques ranged from 0.8 to 1.1 x 10(6), reflecting neuron loss of up to 28%. Neuron loss was not observed in the magnocellular layer. The total number of glia and glial density were unchanged. Loss of neurons in the lateral geniculate nucleus was correlated with the pattern of neuropathological changes. Neuron loss was most severe in animals with encephalitis concentrated in the brain stem and subcortical white matter and was less apparent in animals with diffuse encephalitis. Neuron loss in the lateral geniculate nucleus did not explain changes observed in the visual evoked potential, which was severely affected in two animals which showed a loss of 24 and 26%, while it was normal in a third animal which showed neuron loss of 28%.

Animals↗
PubMed1998

Distribution and characteristics of poststimulus effects in proximal and distal forelimb muscles from red nucleus in the monkey.

We used stimulus-triggered averaging (StTA) of electromyographic (EMG) activity to investigate two major questions concerning the functional organization of the magnocellular red nucleus (RNm) for reaching movements in the macaque monkey. The first is whether the clear preference toward facilitation of extensor muscles we have reported in previous studies for distal (wrist and digit) forelimb muscles also exists for proximal muscles (shoulder and elbow). The second question is whether distal and proximal muscles may be cofacilitated from RNm suggesting the representation of functional muscle synergies for coordinated reaching movements. Two monkeys were trained to perform a prehension task requiring multijoint coordination of the forelimb. EMG activity was recorded from 24 forelimb muscles including 5 shoulder, 7 elbow, 5 wrist, 5 digit, and 2 intrinsic hand muscles. Microstimulation (20 microA at 20 Hz) was delivered throughout the movement task. From 137 microstimulation sites in the RNm, a total of 977 poststimulus effects was obtained including 733 poststimulus facilitation effects (PStF) and 244 poststimulus suppression effects (PStS). Of the PStF effects, 58% were obtained from distal muscles; 42% from proximal muscles. Digit muscles were more frequently facilitated (35%) than the wrist, elbow, or shoulder muscles (20, 24, and 18%, respectively). The intrinsic hand muscles were infrequently facilitated (3%). At all joints tested, PStF was more common in extensor muscles than flexor muscles. This extensor preference was very strong for shoulder (85%), wrist (85%), and digit muscles (94%) and weaker for elbow muscles (60%). Of the PStS effects, 65% were in distal muscles and 35% in proximal muscles. Interestingly, the flexor muscles were more frequently inhibited from RNm than extensor muscles. At 72% of stimulation sites, at least two muscles were facilitated. The majority of these sites (61%) cofacilitated both proximal and distal muscles. At the remaining sites (39%), PStF was observed in either the proximal (17%) or distal muscles (22%). Facilitation most often involved combinations of shoulder, elbow, and distal muscles (30%) or shoulder and distal muscles (26%). Only rarely were intrinsic hand muscles part of the total muscle synergy. Our results show that the RNm 1) controls both proximal and distal muscles but the strength of influence is biased toward distal muscles, 2) preferentially controls extensor muscles not only at distal forelimb joints but also at proximal joints, and 3) output zones cofacilitate synergies of proximal and distal muscles involved in the control of forelimb reaching movements.

Animals↗
PubMed1997

Texture analysis of cerebral white matter in SIV-infected macaque monkeys.

Image texture analysis is used in a wide variety of applications in medical research. Neurovirulent simian immunodeficiency virus (SIV) infection in monkeys is considered a good model for HIV-1 infection in humans and causes neuropathological changes in white matter which can include diffuse myelin pallor, subtle white matter astrocytosis, perivascular macrophage infiltrates, and microglial nodules with multinucleated giant cells. The ability of image texture analysis to quantify these changes was evaluated. Sections of thionin-stained brain tissue from eight male rhesus macaques ranging in age from 42-59 months were used. Four animals served as controls and four animals were infected with neurovirulent SIVmac239/17E-R71 by bone marrow inoculation. Images of cerebral white matter were captured and analyzed by calculating 13 textural features based on statistical analysis of spatial co-occurrence matrices. Statistical analysis of the results included multiple comparisons using the Newman-Keuls multiple range test. The effect of variation in background illumination used at image acquisition was also evaluated. Ten of the 13 textural features used in this study successfully discriminated between tissue from control and SIV-infected animals and were consistent with independent neuropathological assessment. Three textural features were highly sensitive to variation in background illumination and found not useful in this application.

Acquired Immunodeficiency Syndrome↗
PubMed1997

Effects on muscle activity from microstimuli applied to somatosensory and motor cortex during voluntary movement in the monkey.

It is well known that electrical stimulation of primary somatosensory cortex (SI) evokes movements that resemble those evoked from primary motor cortex. These findings have led to the concept that SI may possess motor capabilities paralleling those of motor cortex and speculation that SI could function as a robust relay mediating motor responses from central and peripheral inputs. The purpose of this study was to rigorously examine the motor output capabilities of SI areas with the use of the techniques of spike- and stimulus-triggered averaging of electromyographic (EMG) activity in awake monkeys. Unit recordings were obtained from primary motor cortex and SI areas 3a, 3b, 1, and 2 in three rhesus monkeys. Spike-triggered averaging was used to assess the output linkage between individual cells and motoneurons of the recorded muscles. Cells in motor cortex producing postspike facilitation (PSpF) in spike-triggered averages of rectified EMG activity were designated corticomotoneuronal (CM) cells. Motor output efficacy was also assessed by applying stimuli through the microelectrode and computing stimulus-triggered averages of rectified EMG activity. One hundred seventy-one sites in motor cortex and 68 sites in SI were characterized functionally and tested for motor output effects on muscle activity. The incidence, character, and magnitude of motor output effects from SI areas were in sharp contrast to effects from CM cell sites in primary motor cortex. Of 68 SI cells tested with spike-triggered averaging, only one area 3a cell produced significant PSpF in spike-triggered averages of EMG activity. In comparison, 20 of 171 (12%) motor cortex cells tested produced significant postspike effects. Single-pulse intracortical microstimulation produced effects at all CM cell sites in motor cortex but at only 14% of SI sites. The large fraction of SI effects that was inhibitory represented yet another marked difference between CM cell sites in motor cortex and SI sites (25% vs 93%). The fact that motor output effects from SI were frequently absent or very weak and predominantly inhibitory emphasizes the differing motor capabilities of SI compared with primary motor cortex.

Animals↗
PubMed1994

Primate rubromotoneuronal cells: parametric relations and contribution to wrist movement.

1. Fifty-nine rubromotoneuronal (RM) cells were identified in two rhesus monkeys on the basis of their postspike facilitation (PSpF) of rectified electromyographic (EMG) activity. These cells were studied in relation to a step tracking task requiring wrist movements between fixed target zones in flexion and extension. Movement away from a 0 position was opposed by spring-like loads (auxotonic). Additionally, nine cells were evaluated using an isometric task. Neuronal discharge could be divided into three basic components: background discharge in the absence of movement, phasic modulation during movement, and tonic modulation during sustained holding against external loads. 2. Four basic patterns of RM cell activity were observed in relation to ramp-and-hold wrist movements: phasic-tonic (44%), pure phasic (22%), pure tonic (2%), and unmodulated (24%). The discharge of unmodulated cells did not covary with movement parameters but, as with other RM cells, background discharge did increase in association with task performance. 3. The phasic discharge of RM cells led to the onset of target muscle EMG activity by an average of 89 +/- 82 ms (mean +/- SD, n = 104) in extensors and 88 +/- 74 ms (n = 30) in flexors. Target muscles are defined as ones showing PSpF of EMG activity. It was found that 94% of extensor and 87% of flexor RM cells discharged before or synchronous with the onset of target muscle EMG activity. 4. Thirty-one RM cells (53%) showed a tonic increase in cell activity during the static hold phase of the task. Twenty-three of these were tested for relations to static torque. Fifteen extension related cells and one flexion cell had significant, positive regression slopes for the relation between tonic discharge rate and static torque. The mean rate-torque slope for extension related cells was 160 Hz/Nm and 103 Hz/Nm for flexion related cells. These mean slopes are about one-third those of corticomotoneuronal (CM) cells. 5. Cell discharge rate was correlated with velocity and rate of change of torque (dT/dt) for 32 RM cells with a phasic component of discharge during movement. The peak increase in phasic discharge above tonic firing rate (PDI, peak dynamic index) was significantly correlated only with velocity in eight cells and only with dT/dt in five cells. The phasic discharge of four additional cells was correlated with both velocity and dT/dt, but for three of these cells, the correlation was stronger for velocity. The mean slope for the relation between velocity and PDI was 0.31 Hz.deg-1.s-1.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Facilitation and suppression of wrist and digit muscles from single rubromotoneuronal cells in the awake monkey.

1. The output effects of 214 cells in the magnocellular red nuclei of two rhesus monkeys (Macaca mulatta) were tested with spike-triggered averaging of electromyogram (EMG) activity from six forearm extensor and six flexor muscles. The monkeys performed an alternating wrist movement task (auxotonic paradigm) or generated wrist torque trajectories alternating between flexion and extension (isometric paradigm). 2. Sixty-five cells (30%) were identified as rubromotoneuronal (RM) cells on the basis of their postpike effects on forearm flexor and extensor muscles. Three major types of RM cell output organization were identified: 1) pure facilitation (28 cells), 2) reciprocal (18 cells), and 3) cofacilitation (16 cells). 3. RM cell output showed a strong preference for facilitation of extensor forearm muscles. This preference was reflected in the fact that 69% (43 of 62) of RM cells facilitated extensors exclusively or most strongly; 27% facilitated flexors exclusively or most strongly; and 5% facilitated flexors and extensors equally. Postspike facilitation (PSpF) was observed in 45% of the extensor muscles and 20% of the flexors tested. In contrast, postpike suppression (PSpS) was observed in 3% of the extensors and 7% of the flexors. 4. The mean number of extensors facilitated per RM cell was 3.1 (53% of tested) compared with 2.8 (51% of tested) flexors facilitated per cell. The extensor and flexor PSpS muscle field sizes were both 2.0 (35% of extensors and 36% of flexors tested). The mean number of muscles facilitated by cofacilitation cells was 5.8 (48%) per cell. No clear preference was found for facilitation of particular combinations of synergist muscles. 5. PSpF magnitude was assessed by measuring both the percent change of facilitation or suppression from baseline and the signal-to-noise ratio of effects. The overall average magnitudes of RM PSpF and PSpS were 4.1 +/- 2.0 and 4.0 +/- 2.3% change from baseline, respectively. The average magnitude of PSpF in flexors was not significantly different from that of extensors; neither was there a difference in the average magnitude of PSpS in flexors and extensors. 6. The mean onset latency of RM cell PSpS was greater than PSpF (9.2 +/- 3.0 vs. 5.7 +/- 1.8 ms; P less than or equal to 0.05). This can be attributed to an underlying minimal disynaptic linkage to motoneurons for suppression effects, whereas most PSpFs are probably mediated by underlying monosynaptic connections. The mean onset latency of flexor PSpFs was greater than that of extensors (6.4 +/- 2.3 vs. 5.4 +/- 1.5 ms; P less than or equal to 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Effects on wrist and digit muscle activity from microstimuli applied at the sites of rubromotoneuronal cells in primates.

1. The purpose of this study was to use the techniques of spike- and stimulus-triggered averaging (SpTA and StTA, respectively) to examine the output organization of individual rubromotoneuronal (RM) cells in relation to clusters of neighboring cells. SpTA of electromyographic (EMG) activity in awake monkeys reveals the target muscles of an individual recorded neuron, whereas StTA reveals the target muscles of the neuronal aggregate activated by the stimulus. 2. Three questions were of particular interest. First, does the pattern of poststimulus facilitation (PStF) across forearm muscles match the pattern of postspike facilitation (PSpF)? Second, does the output of RM cell aggregates tested with StTA favor forearm extensor muscles, as reported for individual RM cells in the companion paper? Third, how do RM poststimulus effects compare with corticomotoneuronal (CM) poststimulus effects? 3. Microstimuli were applied at the sites of 37 RM cells, identified by SpTA of EMG activity in awake monkeys performing an alternating wrist movement task. 4. The magnitudes of PStF at 5, 10, and 20 microA were, respectively, 4.3, 10.1, and 13.7 times greater than PSpF of the same muscles, reflecting activation, by the stimulus, of multiple RM cells. RM cell PStF was weaker than CM PStF. 5. The onset latency of poststimulus suppression (PStS) exceeded that of PStF. For example, at 20 microA the difference was 2.6 ms, comparable with the difference between PSpF and postspike suppression (PSpS). 6. The patterns of poststimulus effects on forearm flexor and extensor muscles were categorized in the same manner as postspike effects. Three major patterns were observed: 1) pure facilitation, 2) reciprocal suppression, and 3) cofacilitation of extensors and flexors. 7. The profile of PStF across synergist muscles was broadly similar to that of PSpF. At 83% of sites, the muscle with the greatest PSpF was also the muscle with the greatest PStF. At 30% of sites (11 of 37), the set of muscles with PStF (muscle field) exactly matched the set with PSpF. Overall, the level of discrepancies in SpTAs versus StTAs computed at the same RM cell sites was 27%. Most of these discrepancies could be attributed to muscles with the weakest effects. 8. The fact that the poststimulus muscle fields at many RM cell sites matched the postspike fields at the same sites, even though the poststimulus effects were greater in magnitude and were mediated by more cells, suggests clustering of RM cells with similar target motoneuron pools.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Control of forelimb muscle activity by populations of corticomotoneuronal and rubromotoneuronal cells.

We review and synthesize evidence on the activity of corticomotoneuronal (CM) and rubromotoneuronal (RM) cells and single motor units in forearm muscles in monkeys performing alternating wrist movements. The CM and RM cells were identified by post-spike facilitation of rectified forelimb EMG activity. RM cells facilitated more muscles per cell (mean: 3.0 of 6 synergist muscles) than CM cells (2.4/6). Both groups had "reciprocal" cells which also suppressed antagonists of their facilitated target muscles. Unlike CM cells, some RM cells cofacilitated flexor and extensor muscles (5.8 or 12 muscles). During performance of a standard ramp-and-hold force tracking task the firing patterns of CM and RM cells, as well as single motor units, fell into distinct response types. Each population had phasic-tonic and tonic cells. Unique to the CM population were cells whose discharge increased during the static hold period; unique to RM cells were bidirectionally responsive and unmodulated neurons. Many motor units showed decrementing discharge. To estimate the ensemble activities of these populations the response histograms of different cells were summed (with force ramps aligned) in proportion to the relative frequency of each cell type. The population response histogram of CM cells was phasic-tonic, consistent with the predominant response type. The population response of RM cells was also phasic-tonic, but showed a shallower phasic modulation relative to discharge that was sustained during both directions of movement. The population histogram of motor units of a muscle was proportional to the average of rectified multiunit EMG, and typically exhibited decrementing activity during the static hold. The effects of excitatory postsynaptic potentials (EPSPs) on firing probability of motoneurons previously documented in intracellular studies are combined with the mean firing rates in the population histograms and the known amplitudes of CM-EPSPs and RM-EPSPs to infer the relative contributions of the supraspinal cells to tonic discharge of active motoneurons. This analysis suggests that for intermediate levels of force, the CM cells would increment motoneuron discharge by about 9 impulses/second (i.p.s.) and RM cells by about 2.4 i.p.s. The analysis also reveals differences in the population activity of CM and RM cells compared to their target motoneurons, which may be due to other input cells and to recruitment properties of motoneurons.

Animals↗
PubMed1989

Corticomotoneuronal postspike effects in averages of unrectified EMG activity.

1. Spike-triggered averaging (SpTA) of rectified electromyograms (EMGs) in awake monkeys is recognized as an effective means of establishing causal relations between cortical/cell discharge and muscle activity. The appearance of postspike facilitation (PSF) in averages of rectified EMG activity is interpreted as evidence of an underlying excitatory synaptic linkage between the trigger cell and motoneurons. Cells producing PSF are referred to as corticomotoneuronal (CM) cells. Similarly, postspike suppression (PSS) is interpreted as evidence of underlying inhibitory synaptic linkages. Studies to date have focused almost exclusively on averages of full-wave rectified EMG activity. Because the potential utility of SpTA of unrectified EMG activity has not been systematically examined, we compared postspike effects in SpTAs of rectified and unrectified EMGs for 44 cortical cells yielding 293 cell-target muscle pairs (CMPs). 2. Clear PSF was found in 110 of 293 averages of rectified EMG activity from 28 known CM cells. Forty-nine of these 110 CMPs (45%) also showed clear postspike effects (PSE) in the corresponding averages of unrectified EMGs activity. Loss of effects in averages of unrectified EMGs can be attributed to cancellation of the negative and positive phases of motor unit potentials. Mean onset latencies were similar for effects in rectified and unrectified EMGs [6.9 +/- 1.8 (SD) ms vs. 6.6 +/- 1.2 (SD) ms]. Overall, the magnitudes of effects measured as peak-to-noise ratios were also similar for effects in the two groups (8.8 vs. 8.7). The 61 CMPs that showed clear PSF in rectified EMGs but no effects in corresponding unrectified EMGs had, as a group, longer and more dispersed onset latencies and were weaker in magnitude than those that showed effects in both rectified and unrectified EMGs. Moreover, the occurrence of clear effects in averages of unrectified EMGs was correlated with the strength of PSF (75% of strong but only 29% of weak PSFs showed clear PSEs in averages of unrectified EMG activity). 3. Clear PSS was observed in 24 (8%) averages of rectified EMGs derived from nine cells. Remarkably, clear PSEs were found in 12 of the corresponding averages of unrectified EMG activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1987

Functional relations between primate motor cortex cells and muscles: fixed and flexible.

In behaving monkeys the effects of motor cortex cells on muscles are inferred from two quite different types of 'correlational' evidence: their coactivation and cross-correlation. Many precentral cells are coactivated with limb muscles, suggesting that they make a proportional contribution to muscle activity; however, such coactivation is typically quite flexible, and can be changed by operantly conditioning the dissociation of cell and muscle activity. Cross-correlating cells and muscles by spike-triggered averaging of the electromyogram (EMG) shows that certain cells produce short-latency post-spike facilitation of EMG; this correlational linkage is relatively fixed under different behavioural conditions and its time course suggests it is mediated by a corticomotoneuronal (CM) synaptic connection. CM cells typically facilitate a set of coactivated agonist muscles, and some also inhibit their antagonists. The firing patterns of CM cells can differ significantly from those of their target muscles. During ramp-and-hold wrist responses most CM cells discharge a phasic burst that precedes target muscle onset and that contributes to changes in muscle activity. At low force levels many CM cells are activated without their target motor units. Conversely, many CM cells are paradoxically inactive during rapid forceful movements that vigorously activate their target muscles; they appear to be preferentially active during finely controlled movements. Thus CM cells, with a fixed correlational linkage to their target muscles, may be recruited without their target muscles, and vice versa.

Animals↗
PubMed1987

Effects of DFP on unit activity in rat superior colliculus.

The effect of systemically administered diisopropylfluorophosphate (DFP) on the spontaneous firing rate and light-evoked responses of rat superior colliculus neurons was determined from average histograms of single unit and multiunit activity. DFP produced a dose-dependent increase in superior colliculus spontaneous activity, and a decrease in light evoked activity. In many experiments, light evoked responses were completely abolished. The changes in spontaneous activity were reversible over a period of about 5 hours following DFP injection. These results establish the retino-tectal pathway as a major target of DFP toxicity.

Action Potentials↗
PubMed1987

DFP action on rat superior colliculus: localization and role of cholinergic receptors.

DFP, an irreversible acetylcholinesterase inhibitor, markedly increases spontaneous unit activity and reduces light-evoked responses in the superficial layers of the rat superior colliculus (Cheney et al., 1987). The purpose of this study was to investigate: (1) the sites of DFP action within the retino-tectal pathway (retinal, central or both), and (2) the types of cholinergic receptors (muscarinic, nicotinic, or both) involved. DFP increased SGS unit activity when injected intraocularly, confining its action to the retina, or when given systemically in bilateral enucleate rats. Thus, DFP acts at both retinal and central sites to increase unit activity in the SGS. Pretreating with muscarinic receptor antagonists such as atropine or scopolamine blocked DFP's effects at both sites whereas the nicotinic receptor antagonist mecamylamine was ineffective. Moreover, DFP's actions were mimicked by injections of the muscarinic receptor agonist, oxotremorine. The oxotremorine effects were also blocked or reversed by treatment with atropine or scopolamine. We conclude that DFP acts at both retinal and central sites to influence SGS unit activity and, at both sites, muscarinic receptors mediate DFP's effects.

Animals↗
PubMed1985

Implementation of a movement paradigm using the Commodore 64 microcomputer.

Implementation of an alternating movement paradigm for monkeys was achieved using an inexpensive but versatile microcomputer, the Commodore 64. During task performance, the computer monitors one of three user selectable input signals (e.g. joint position) and continuously displays this signal as a moving cursor on a video monitor along with a user positioned target box. Other user defined parameters include in-target holding time and reinforcement ratio. The system also provides two sound cues to signal entry of the cursor into the target box and successful completion of a trial. Extensive use is made of the computer's intrinsic hardware features for implementation of movement paradigm functions. Use of external components is limited to digitizing and interface hardware. A two part software package consisting of a BASIC and a machine language program performs all task and hardware related functions. Acquisition and display of analog input signals, display of target positions, and delivery of auditory cues and applesauce rewards are all controlled by the machine language program. All user defined parameters are specified from the BASIC menu program. The specific programs described in this paper should be applicable to the control of tasks requiring alternation of a behavioral parameter between two target zones.

Animals↗
PubMed1985

Role of cerebral cortex in voluntary movements. A review.

Findings from studies using electrical stimulation of cortex, recording from single neurons in awake animals, and measuring regional cerebral blood flow in humans have revealed some specific motor functions for several cerebral cortical areas. These areas include primary motor cortex, supplementary motor area, premotor area, parietal areas 5 and 7, and prefrontal area. Execution of movement is a function of the primary motor cortex, which translates program instructions for movement from other parts of the brain into signals. These signals encode variables of movement, such as the muscles to contract and the force and timing of their contraction. Long-latency reflex responses of muscles to stretch and cutaneous stimulation are also mediated by the motor cortex; other motor areas seem to perform higher order motor functions. The supplementary motor area controls input-output coupling in motor cortex and the programming of complex sequences of rapidly occurring discrete movements, such as playing the piano. The premotor area participates in the assembly of new motor programs. The parietal areas 5 and 7 are involved in directing attention to objects of interest in visual space and issuing commands for arm movements and eye movements to these objects. The prefrontal cortex performs cognitive functions, such as short-term memory of correct motor responses in delayed response tests.

Animals↗
PubMed1985

Comparable patterns of muscle facilitation evoked by individual corticomotoneuronal (CM) cells and by single intracortical microstimuli in primates: evidence for functional groups of CM cells.

We compared the averaged responses of forelimb muscles to action potentials of single motor cortex cells and to single intracortical microstimuli (S-ICMS). Activity of precentral neurons and 12 identified forelimb muscles (6 flexors and 6 extensors of wrist and fingers) was recorded in macaques while they performed alternating ramp-and-hold wrist movements. Action potentials of cells that covaried reliably with wrist flexion or extension were used to compile spike-triggered averages (spike-TAs) of rectified electromyographic (EMG) activity of six synergistically coactivated muscles. Cells whose spikes were followed by a clear postspike facilitation (PSF) of rectified muscle activity were designated corticomotoneuronal (CM) cells. CM cells typically facilitated a subset of the coactivated muscles called the cell's target muscles. The relative strength of the PSF in different target muscles ranged from clear increases above base-line fluctuations to weak but significant effects. For each CM cell we characterized the "PSF profile" of facilitation across different muscles, defined as the relative strength of PSF in each of the coactivated agonist muscles. After identifying the CM cell's target muscles, we delivered S-ICMS through the microelectrode at the same site. Biphasic stimuli were delivered during the same wrist movements in which the recorded CM cell had been active. Stimulus intensities were too weak (typically 5-10 microA) and their repetition rate too slow (5-15 Hz) to evoke muscle excitation evident in the raw EMG record. However, stimulus-triggered averages (stimulus-TAs) of the rectified EMGs of coactivated muscles revealed consistent patterns of poststimulus facilitation (PStimF). In most cases the muscles facilitated by the CM cell in spike-TAs (n = 60) were also facilitated by S-ICMS in stimulus-TAs. At sites of CM cells the threshold stimulus intensities for evoking a statistically significant effect were between 0.5 and 2 microA. S-ICMS of 5 microA evoked PStimF that was, on the average, six times stronger than the PSF of the CM cell. The height of the facilitation peak relative to base-line fluctuations was 5-60 times greater for the stimuli than the spikes of the CM cell. The average onset latency of PStimF (8.0 +/- 1.2 ms) was 1.3 ms longer than the mean latency of PSF (6.7 +/- 1.4 ms). At two-thirds of the cortical sites where both spike- and stimulus-TAs were computed (n = 30), the PStimF profile exactly matched the PSF profile.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗