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    • Abstract: stimulus-triggered averaging effects evoked from the monkey PMRF ... trains in the cat PMRF; both response patterns are consistent with the. PMRF contributing to the control of arm reaching movements. ...

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Spike-Triggered Average Effects in Arm and Shoulder Muscles
from Monkey Pontomedullary Reticular Formation Neurons
Adam G. Davidson1, John A. Buford3, and Marc H. Schieber1,2. 1 Neurobiology and Anatomy, 2 Neurology, University of Rochester,
Rochester, NY; 3 School of Allied Medical Professions, The Ohio State University, Columbus, OH. 57.16
1. Abstract
Previous studies using stimulus-triggered averaging in the monkey 3. Single PMRF neurons produce SpikeTA Effects in 6. PMRF SpikeTA effects are similar to StimulusTA effects 7. Similar spatial location of PMRF neurons
pontomedullary reticular formation (PMRF) have revealed extensive
bilateral reticulospinal outputs to arm and shoulder muscles. Forelimb
stimulus-triggered averaging effects evoked from the monkey PMRF
muscles bilaterally •Stimulus triggered averaging was attempted at 13 producing SpikeTA effects
are similar to forelimb EMG response patterns evoked with stimulus of the 14 sites where PMRF neurons produced
trains in the cat PMRF; both response patterns are consistent with the
PMRF contributing to the control of arm reaching movements.
•309 neurons were recorded throughout PMRF; 292 analyzed with SpikeTA, SpikeTA effects
Anatomical and electrophysiological studies in the cat show 3,968 neuron-muscles pairs
reticulospinal neurons have monosynaptic projections to hind limb and •These 13 PMRF neurons produced SpikeTA effects
forelimb motoneurons; however, there is little evidence for
monosynaptic reticulospinal projections to monkey forelimb •14 PMRF neurons produced 42 SpikeTA effects: 23 facilitation, 19 suppression in a total of 39 neuron-muscle pairs.
motoneurons. Here, we report spike-triggered averaging effects from
PMRF neurons in arm, shoulder, and back muscles in monkeys •27 of 39 (69%) SpikeTA effects had matching
performing a bilateral arm reaching task. Spike-triggered averaging
effects were seen throughout the arm, including two wrist muscles,
•On average, PMRF neurons StimulusTA effects; 8 (21%) had no matching
and were sometimes organized in reciprocal patterns between flexors produced a SpikeTA effect in 25% of StimulusTA effect
and extensors. Some PMRF neurons produced spike-triggered
averaging effects bilaterally. The onset latency and peak width at half- the simultaneously recorded muscles
maximum of spike-triggered averaging effects from PMRF neurons •4 of 39 (10%) SpikeTA effects were opposite in
covered a range indicating both pure and synchrony effects. These
observations suggest that some monkey PMRF neurons may make
sign to the StimulusTA effect: all of which were Recording sites plotted for
monosynaptic connections to forelimb motoneurons.
•9 of the 14 neurons produced SpikeTA effects in the upper trapezius (UTr) monkeys I and G; neurons
SpikeTA effects bilaterally: 28 with SpikeTA effects plotted
2. Methods ipsilateral, 14 contralateral
for all 4 monkeys
Four male Macaca fascicularis monkeys performed an
instructed-delay arm reaching task as single neural-unit activity
was recorded from the PMRF simultaneously with EMG activity in •Oscillations were present in the
arm and shoulder muscles. Monkeys I and G reached with either SpikeTAs of 5 PMRF neurons •We recorded neurons and performed StimulusTA
the left or right arm to targets presented on a touch screen throughout the PMRF (Davidson and Buford 2004; Davidson
monitor; monkeys C and D performed a center-out planar
reaching task with the right arm. Recording sites were ventral to
and Buford 2006)
the abducens nucleus, dorsal to the inferior olive and/or medullary
pyramids, and medial to the facial nucleus (~ 4 mm lateral to the
•15 neurons producing SpikeTA effects or spike-locked
midline) and were confirmed with post-mortem anatomical oscillations were recorded in a rostral-dorsal region (ventral
reconstructions. For monkeys and I and G, EMG electrodes were to the abducens nucleus); 4 neurons recorded in a caudal-
implanted bilaterally in Flexor Carpi Radialis (FCR), Extensor
carpi radialis (ECU), Brachioradialis (Brac), Biceps (Bic), Triceps
ventral region
(Tri), deltoids (anterior- ADlt; posterior- PDlt), Pectoralis Major
(PMj), Lats (Lat), and the upper and middle trapezius (MTr, UTr).
•In rostral-dorsal region, low threshold stimulation often
For monkeys C and D, Bic, Tri, PDlt, and Adlt were implanted evoked large StimulusTA effects and single pulses of > 10
ipsialterally; the UTr and MTr were implanted bilatteraly. In total, uA evoked visible twitches in shoulder muscles (Davidson
EMG data from 43 arm and shoulder muscles were analyzed with 4. Temporal and amplitude characteristics of SpikeTA 5. PMRF neurons produce reciprocal SpikeTA effects in the
SpikeTA; 20 were ipsilateral, 23 were contralateral. Spike- and Buford 2006). This region appears to lie close to the site
triggered averages (SpikeTAs) were compiled off-line for each effects from the PMRF flexors and extensors of the arm and shoulder from which head movement can be elicited (Quessay and
neuron-muscle pair. EMG was rectified and averaged over an 80 Freedman 2004; Cowie and Robinson 1984)
ms interval beginning 30 ms before the spike and ending 50 ms •The onset latency and peak width at half-maximum of SpikeTA effects from •In general PMRF SpikeTA effects facilitated ipsilateral flexors and contralateral extensors;
following the spike, smoothed with a five-point flat filter, and PMRF neurons covered a range suggestive of both pure and synchrony effects
baseline ramps were removed by subtracting their slope from the
but suppressed ipsilateral extensors and contralateral flexors 8. Conclusions
final average. SpikeTAs were analyzed with multi-fragment •Mean onset latency was earlier for suppression (3.1 ms) than for facilitation •Only exception was iPdlt: 2 of 3 SpikeTA effects were facilitation 1. PMRF neurons produce SpikeTA effects bilaterally.
statistical analysis (MFSA) (Poliakov and Schieber 1999), where
the spike train was divided into smaller fragments to compile
(6.7 ms) (p

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