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Biomedical subjects

E E Fetz

Publications and source records attributed to E E Fetz.

At least 55 records · Page 3Linked to original sources
PubMed1985

Patterns of facilitation and suppression of antagonist forelimb muscles from motor cortex sites in the awake monkey.

Patterns of excitatory and inhibitory effects were produced in antagonistic forelimb muscles by single intracortical microstimuli (S-ICMS) applied to motor cortex sites in macaque monkeys performing ramp-and-hold wrist movements. Stimulus-triggered averages (stimulus-TAs) of rectified electromyographic (EMG) activity revealed poststimulus facilitation and/or suppression in identified flexor and extensor muscles of the wrist and fingers. At 22 cortical sites the action potentials of single cells were also recorded and used to compute spike-triggered averages (spike-TAs) of covarying muscles. The set of muscles activated during the movement in which the cell was active are referred to here as "agonists"; those muscles active during wrist movement in the opposite direction are called "antagonists." (At sites where cells were not isolated the muscles showing poststimulus facilitation were called agonists.) Poststimulus effects in agonist muscles typically consisted of facilitation in a subset of the agonists. For 48 sites from which poststimulus effects were tested on both flexors and extensors, the following combinations of effects were observed: 1) pure facilitation of agonist muscles with no effect on antagonists; 2) facilitation of both agonists and antagonists; 3) facilitation of agonist muscles with reciprocal suppression of antagonists; 4) "mixed" facilitation and suppression of synergist muscles; and 5) pure suppression of some muscles with no effect on their antagonists. The suppression effects appeared most commonly in flexor muscles; conversely, facilitation was generally stronger in extensors. Cortical sites eliciting pure suppression of flexor muscles with no facilitation of extensor muscles were found in two monkeys. These purely suppressive effects were observed not only in stimulus-TAs but also in spike-TAs computed from single cells at these sites. Some of these cells increased their activity during wrist extension (but had no detectable effect on the extensor muscles); others discharged during flexion. Several observations suggest that the cortically evoked suppression is mediated by polysynaptic relays. The mean onset latency of the postspike suppression (7.4 ms) produced by inhibitory cells was longer than the mean onset latency of postspike facilitation (6.7 ms) produced by CM cells. Similarly, the mean onset latency of poststimulus suppression (8.9 ms) was longer than that of poststimulus facilitation (8.0 ms). Moreover, suppression was usually weaker than facilitation in the spike-TAs, as well as in stimulus-TAs compiled for the same stimulus intensity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Discharge properties of primate forearm motor units during isometric muscle activity.

Activity of single motor units (MUs) was recorded in forelimb muscles of rhesus macaques while they generated isometric ramp-and-hold torques about the wrist. Multiunit electromyographic (EMG) activity was recorded from 10-12 identified flexor and extensor muscles of the wrist and digits with implanted EMG wire electrodes. Single MUs from these muscles were recorded with a remotely controlled tripolar microelectrode array. The parent muscle of each MU was determined by compiling MU-triggered averages of multiunit EMGs. The MU firing patterns during the isometric task were determined from response histograms aligned with change in torque. At moderate torque levels, MUs (n = 86) exhibited four types of discharge patterns during the ramp-and-hold trajectory: phasic-tonic (23%), tonic (33%), decrementing (39%), and phasic (5%). Phasic-tonic MUs exhibited a phasic burst of activity during the torque ramp which exceeded the firing rate during the static hold period. Both phasic-tonic and tonic MUs exhibited a constant mean firing rate during the hold period; the discharge of decrementing MUs gradually decreased during the static hold. Phasic MUs fired only during the change in force. The relation between MU firing rate and torque was investigated as the monkeys generated responses of different levels of static torque during the hold period. Mean firing rate during the hold was found to be proportional to static torque up to moderate torque levels, where it reached a maximum. In the linear range, the mean rate-torque slope was 3.4 +/- 1.9 imp/s per 10(5) dyn . cm (n = 9).

Animals↗
PubMed1985

Effects of single intracortical microstimuli in motor cortex on activity of identified forearm motor units in behaving monkeys.

We examined the magnitude and extent of output effects elicited from focal cortical sites on the activity of individual motor units (MUs) by delivering single-pulse intracortical microstimuli (S-ICMS) (5-15 microA) during isometric wrist activity. Stimulation sites in the precentral gyrus (area 4) were chosen for study if stimulus-triggered averages (stimulus-TAs) of multiunit electromyograms (EMGs) revealed poststimulus facilitation (PStimF) of EMG activity in any of the coactivated wrist muscles. Single MUs were then isolated in the facilitated muscles with a remotely controlled tripolar microelectrode. MUs were identified by their signatures in their parent muscles (from MU-triggered averages of EMGs) and by their firing pattern during ramp-and-hold wrist responses. One objective was to quantify the magnitude and time course of the effects on single MUs by compiling peristimulus histograms of MU firing. The cross-correlation histograms between S-ICMS and MU action potentials showed peaks with onset latencies of 8.8 +/- 1.7 ms (mean +/- SD, n = 64) and durations of 1.8 +/- 1.2 ms (n = 104). The cumulative sums of the correlogram peaks resembled the rising phase of corticomotoneuronal excitatory postsynaptic potentials previously recorded in forelimb motoneurons. Comparison of correlogram peaks with stimulus-TAs of MU potentials suggests that the duration of PStimF of multiunit EMG can be accounted for, in approximately equal proportions, by l) the variation in firing time of single MUs (i.e., the width of the MU correlogram peaks), 2) the width of single MU potentials, and 3) the contribution of different MUs at different latencies. The sizes of the correlogram peaks relative to base line were larger than the PStimF of multiunit EMGs, and increased more rapidly with stimulus intensity, indicating appreciable cancellation in the multiunit records. A second objective was to determine whether S-ICMS affected all the MUs of a facilitated muscle, or only a particular subset. Of 104 MUs sampled in facilitated muscles, 99 (95%) were found to be individually facilitated (P less than 0.05). MU firing patterns during isometric ramp-and-hold torque responses were characterized as phasic, phasic-tonic, tonic, or decrementing; stimulation at a given cortical site was found to facilitate all four types of MUs. When more than one muscle showed PStimF from a site, MUs belonging to each of the facilitated muscles were facilitated individually by S-ICMS at that site.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1984

Corticomotoneuronal cells contribute to long-latency stretch reflexes in the rhesus monkey.

To test the hypothesis that a transcortical reflex contributes to the stretch-evoked long-latency electromyographic (e.m.g.) response we documented the responses of identified corticomotoneuronal (c.m.) cells and their target muscles to perturbations of active wrist movements. Macaque monkeys performed ramp-and-hold wrist movements against elastic loads, alternating between flexion and extension zones; brief (25 ms) torque pulses were intermittently applied during the hold period. C.m. cells were identified by a clear post-spike facilitation in spike-triggered averages of forelimb muscle e.m.g. activity. Activity of c.m. cells and twelve wrist and digit flexor and extensor muscles was recorded during: (a) active ramp-and-hold wrist movements, (b) passive ramp-and-hold wrist movements, and (c) torque perturbations applied during the hold phase of active flexion and extension which either lengthened or shortened the c.m. cell's target muscles. Muscle-lengthening perturbations evoked a reproducible pattern of average e.m.g. activity in the stretched muscles, consisting of two peaks: the first response (M1) had an onset latency of 11.2 +/- 2.1 ms (mean +/- S.D.), and the second (M2) began at 27.9 +/- 5.1 ms. Torque perturbations which shortened the active muscles also evoked a characteristic e.m.g. response consisting of an initial cessation of activity at 13.5 +/- 3.4 ms followed by a peak beginning at 33.9 +/- 3.0 ms. The responses of twenty-one c.m. cells which facilitated wrist muscles were documented with torque pulse perturbations applied during active muscle contraction. Twenty of twenty-one c.m. cells responded at short latency (23.4 +/- 8.8 ms) to torque perturbations which stretched their target muscles. For each c.m. cell-target muscle pair, transcortical loop time was calculated as the sum of the onset latency of the c.m. cell's response to lengthening perturbations (afferent time) and the onset latency of post-spike facilitation (efferent time). The mean transcortical loop time was 30.4 +/- 10.2 ms, comparable to the mean onset latency of the M2 peak (27.9 +/- 5.1). The duration of a c.m. cell's response to torque perturbations provides a further measure of the extent of its potential contribution to the M2 muscle response. In all cases but two, the c.m. cell response, delayed by the latency of the post-spike facilitation, overlapped the M2 e.m.g. peak.

Action Potentials↗
PubMed1983

Relation between shapes of post-synaptic potentials and changes in firing probability of cat motoneurones.

1. The shapes of post-synaptic potentials (p.s.p.s) in cat motoneurones were compared with the time course of changes in firing probability during repetitive firing. Excitatory and inhibitory post-synaptic potentials (e.p.s.p.s and i.p.s.p.s) were evoked by electrical stimulation of peripheral nerve filaments. With the motoneurone quiescent, the shape of each p.s.p. was obtained by compiling post-stimulus averages of the membrane potential. Depolarizing current was then injected to evoke repetitive firing, and the post-stimulus time histogram of motoneurone spikes was obtained; this histogram reveals the primary features (peak and/or trough) of the cross-correlogram between stimulus and spike trains. The time course of the correlogram features produced by each p.s.p. was compared with the p.s.p. shape and its temporal derivative.2. E.p.s.p.s of different sizes (0.15-3.1 mV, mean 0.75 mV) and shapes were investigated. The primary correlogram peak began, on the average, 0.48 msec after onset of the e.p.s.p., and reached a maximum 0.29 msec before the summit of the e.p.s.p; in many cases the correlogram peak was followed by a trough, in which firing rate fell below base-line rate. The height of the correlogram peak with respect to base-line firing rate increased in proportion to both the amplitude of the e.p.s.p.s and the magnitude of their rising slope (in these data, amplitude and rising slope also covaried).3. The mean half-width of the correlogram peaks (0.65+/-0.28 msec (S.D.)) agreed better with the average half-width of the e.p.s.p. derivatives (0.55+/-0.33 msec) than with the half-width of the e.p.s.p.s (4.31+/-1.50 msec). The shape of the primary correlogram peak produced by simple e.p.s.p.s often resembled the temporal derivative of the e.p.s.p. rise. For larger e.p.s.p.s, the shape of the correlogram peak closely matched the e.p.s.p. derivative, while smaller e.p.s.p.s in appreciable synaptic noise often generated correlogram peaks somewhat wider than their derivatives. On the other hand, the match between the correlogram trough that followed the peak and the negative slope of the e.p.s.p. was better for the small e.p.s.p.s than for the large e.p.s.p.s; for large e.p.s.p.s the drop in firing rate during the trough was typically limited at zero. These relations were tested further by comparing the integral of the correlogram with the time course of the e.p.s.p. For large e.p.s.p.s, the correlogram integral matched the rising phase of the e.p.s.p. quite well, although it underestimated the rate of decline of the e.p.s.p.4. Complex e.p.s.p.s with distinct components during their rising phase often produced correlogram peaks that did not accurately reflect the features in their temporal derivative. Temporal summation of large e.p.s.p.s and summation of their derivatives was linear, but the resulting correlogram peaks did not add linearly; the second correlogram peak was often smaller than the first. However, when small e.p.s.p.s were summed, the correlogram peaks more closely matched the e.p.s.p. derivatives.5. Compound i.p.s.p.s produced primary correlogram troughs followed by a shallow compensatory peak. The width of the trough extended through the peak of the i.p.s.p., well into the falling phase of the i.p.s.p. During the trough the firing rate usually dropped to zero. Thus, the primary correlogram features produced by large i.p.s.p.s did not resemble any linear combination of the shape of the i.p.s.p. and/or its temporal derivative. Moreover, the integral of the correlogram did not resemble the i.p.s.p.6. The major observations are consistent with a motoneurone model in which a membrane potential ramp approaches a voltage threshold for spike initiation. Near threshold, e.p.s.p.s superimposed on the ramp advance the occurrence of spikes to their rising phase, producing a correlogram peak resembling their temporal derivative. Synaptic noise would increase the probability of sampling the peak of the e.p.s.p., leading to wider correlogram peaks. I.p.s.p.s would delay the occurrence of spikes to their falling phase.

Action Potentials↗
PubMed1981

Language-related potentials specific to human language cortex.

Event-related potentials following silently named object pictures were recorded directly from the exposed left hemisphere of the human cortex at sites whose relation to naming was subsequently established by electrical stimulation mapping. Two simultaneous potential changes are specific to sites where stimulation disrupts naming: slow potentials as premotor sites and focal desynchronization at posterior sites surrounding the Sylvian fissure. These anatomically specific changes are also specific to the task--present with silent naming and absent in a spatial task with the same visual input. Overt speech is also preceded by slow potentials with earliest onset at premotor sites.

Adult↗
PubMed1979

Autogenetic inhibition of motoneurones by impulses in group Ia muscle spindle afferents.

1. Inhibitory post-synaptic potentials evoked by adequate stimulation of group Ia muscle spindle afferents of homonymous and synergistic muscles and by selective electrical stimulation of tendon organ afferents were analysed in motoneurones of triceps surae and plantaris. 2. Selective activation of Ia afferents was verified to occur with brief stretches of triceps surae and plantaris 35 micrometer or less in amplitude with an initial muscle tension of 5 N; stretches of 30--35 micrometer were estimated to activate 80--90% of Ia afferents in these muscles. Under the same conditions the lowest thresholds for group Ib tendon organ afferents were about 40 micrometer. 3. Stretches less than or equal to 30 micrometer evoked i.p.s.p.s in 80% of triceps surae and plantaris motoneurones; lowest thresholds for evoking i.p.s.p.s wef triceps surae and plantaris motoneurones; lowest thresholds for evoking i.p.s.p.s were 10 micrometer or less. However, such low thresholds for stretch-evoked i.p.s.p.s, lower than the thresholds for activation of Ib afferents, were found mainly in spinalized, unanaesthetized (after decerebration) or lightly anaesthetized animals. The latencies of these i.p.s.p.s indicated disynaptic and trisynaptic coupling between Ia afferents and motoneurones. The i.p.s.p.s were evoked (i) from the homonymous and synergistic muscles stretched together, (ii) from the homonymous muscles alone and (iii) from the synergistic muscles alone. 4. Control experiments showed that i.p.s.p.s could be evoked by stretches sub-threshold for discharging motoneurones, thus showing that those i.p.s.p.s were not mediated by Renshaw cells. The stretch-evoked i.p.s.p.s disappeared after sectioning the nerves from the corresponding muscles, further excluding their mediation by afferents other than group Ia afferents from thf stretched muscle. 5. In order to selectively activate tendon organ afferents, thresholds for excitation of Ia afferents by electrical stimuli were increased to a level above the threshold for Ib afferents by prolonged muscle vibration (Coppin, Jack & MacLennan, 1970). I.p.s.p.s evoked by stimuli near threshold for Ib afferents appeared with latencies indicating disynaptic coupling. Later (trisynaptic) components of Ib i.p.s.p.s required somewhat stronger stimuli. 6. Amplitudes of Ia i.p.s.p.s evoked by muscle stretches activating about 80% of muscle spindle afferents were compared with amplitudes of Ib i.p.s.p.s due to less than 50% of tendon organ afferents of the same muscles. The Ia i.p.s.p.s were much smaller (16--35%) than the Ib i.p.s.p.s. The amplitudes of such Ia and Ib i.p.s.p.s constituted about 10 and 25--66%, respectively, of the maximal i.p.s.p.s evoked by electrical stimulation of all group I afferents. 7. We conclude that inhibition of motoneurones may be evoked from Ia muscle spindle afferents from homonymous and synergistic muscles as well as from Ib tendon organ afferents...

Animals↗
PubMed1976

Responses of primate locus coeruleus and subcoeruleus neurons to stimulation at reinforcing brain sites and to natural reinforcers.

In alert rhesus monkeys the activity of 64-neurons was recorded in the locus coeruleus and subcoeruleus region, collectively referred to as coeruleus (C) neurons. C neurons were identified physiologically by antidromic activation from electrodes in the medial forebrain bundle (MFB) and medial septal nucleus which sustained intracranial self-stimulation (ICSS) behavior, and/or anatomically by their proximity to microlesions at unit recording sites. The following results were obtained: (1) the current intensity that supported the highest rate of MFB and septal ICSS was similar to the current intensity for evoking antidromic responses in C neurons; (2) stimulation in the vicinity of the dopaminergic neurons of nucleus A10 did not activate C neurons; (3) C neurons were antidromically activated by ipsilateral and contralateral MFB shocks; (4) the C axons had slow estimated conduction velocities (1-5 m/sec), and a mean neural refractory period of 0.8 msec; (5) the behaviorally determined refractory period for MFB ICSS was also approximately 0.8 msec; and (6) mean firing rates while the monkey sat quietly were 15 +/- 2 Hz (S.D.) for subcoeruleus cells and 5 +/- 3 Hz for locus coeruleus cells, and activity of most cells changed negligibly during operant responding for apple-sauce reinforcement. These results suggest that the reinforcing effects of ICSS may be mediated by activation of coeruleus cells, but that these cells do not appear to be strongly involved in operant responding for natural reinforcers.

Animals↗
PubMed1975

Correlations between activity of motor cortex cells and arm muscles during operantly conditioned response patterns.

Monkey motor cortex cells were recorded during isolated, isometric contractions of each of four representative arm muscles -- a flexor and extensor of wrist and elbow -- and comparable response averages computed. Most cells were coactivated with several of the muscles; some fired the same way with all four and others with none. Results suggest that many precentral cells have a higher order relation to muscles than motoneurons. Operantly reinforced bursts of cell activity were associated with coactivation of specific muscles, called the cell's "motor field"; the most strongly coactivated muscle was usually the one whose isolated contraction had evoked the most intense unit activity. During active elbow movements most cells fired in a manner consistent with their isometric patterns, but clear exceptions were noted. Differential reinforcement of unit activity and muscle suppression was invariably successful in dissociating correlations. The strength of each unit-muscle correlation was assessed by the relative intensity of their coactivation and its consistency under different response conditions. Several cells exhibited the most intense coactivation with the same muscle during all conditions. Thus, intensity and consistency criteria usually agreed, suggesting that strong correlations so determined may operationally define a "functional relation". However, correlations in the sense of covariation are neither necessary nor sufficient evidence to establish anatomical connections. To test the possibility of direct excitatory connections we stimulated the cortex, but found lowest threshold responses in distal muscles, even from points where most cells had been strongly correlated with proximal muscles. Post-spike averages of rectified EMG activity provided scant evidence for cell-related fluctuations in firing probabilities of any muscles.

Animals↗