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Motor Outputs From the Primate Reticular Formation to Shoulder Muscles as Revealed by Stimulus-Triggered Averaging 1Neuroscience Graduate Studies Program and 2Division
of Physical Therapy, School of Allied Medical Professions, The Ohio
State University, Columbus, Ohio 43210 Submitted 29 January 2004; accepted in final form 4 March 2004 The subjects were 2 male Macaca fascicularis monkeys
(C and D) trained for a separate study. In the
context of an instructed delay task, the subjects
performed planar reaching movements (5.08-cm
displacement) from a central position to one of 4 peripheral
targets (45, 135, 225, and 315° in Cartesian coordinates).
A sip of flavored applesauce was the reward for each
correct trial. The head was restrained for recording
and stimulation to help maintain stable electrode
positioning. Experimental procedures were approved by
the ILACUC of The Ohio State University, and subject
care was according to the National Institutes of
Health Guide for the Care and Use of Laboratory Animals.
After training, a stainless steel recording chamber was
implanted over a craniotomy in the left parietal
bone. The chamber's axis was in the frontal plane,
angled 10° to the left from the parasagittal plane to
allow access to the right mPMRF, and aimed for
stereotaxic coordinates AP0, ML0, DV-12 (Horsley–Clark
stereotaxic coordinates, Szabo and Cowan 1984 EMG implants Electromyographic data were collected with acute percutaneous
(first 6 averages from subject D) and chronically
implanted pairs of Teflon-coated stainless steel
wires. Wire pairs were separated by approximately 5
mm and inserted into the muscle by a hypodermic
needle (Betts et al. 1976 For both subjects, electrodes were located in the
contralateral and ipsilateral upper trapezius (cUTr,
iUTr) and ipsilateral posterior deltoid (iPDlt). Additional
implants in subject C were located on the ipsilateral side
in latissimus dorsi (iLat), long head of triceps (iTri),
long head of biceps (iBic), and in contralateral
middle trapezius (cMTr). For subject D, additional implants were located in the
ipsilateral anterior deltoid (iADlt) and ipsilateral
middle trapezius (iMTr). EMG data for ipsilateral
iBic and iTri were available from subject D for the 6
experiments conducted with percutaneous EMG. Over the
8 mo of study most EMG implants remained stable, except
for iADlt in subject D, which failed in the last month. The present investigations are designed to reveal the
function of reticulospinal outputs originating in the
pontomedullary reticular formation (PMRF), in nucleus
reticularis gigantocellularis and nucleus reticularis pontis
caudalis. Experiments for Aim 1 are designed to measure
reticulospinal outputs to muscles of the arm and shoulder
girdle bilaterally (24 muscles). Understanding how arm muscles are controlled bilaterally
by the reticulospinal system will permit understanding of
this systems capacity for contribution to functional
recovery after stroke. Experiments for Aims 2-3 explore
mechanisms for corticospinal and reticulospinal interaction
in the control of movement. Aim 2 uses physiological methods
to study corticoreticular coordination through paired
stimulus-triggered averaging studies in the cortical motor
areas (Ml, SMA, and PMd) and the PMRF. Experiments for Aim 3 will use neuroanatomical methods to
reveal the sources of corticospinal cells with collaterals
to reticulospinal cells and to determine the strengths of
projections from SMA, PM, and Ml to the reticulospinal
system. Combined, Aims 2 and 3 examine substrates for
coordination of corticospinal and reticulospinal control of
movement. Experiments for Aim 4 will test for kinematic and kinetic
coding in the activity of PMRF neurons, testing for
directional tuning and coding of force. Together, these
experiments will measure the outputs and functions of the
reticulospinal system along with the relevant sources of
input from cortical projections for the preparation and
performance of reaching. Much of the focus will be on coordination of bilateral
arm movements, which is proposed to be a key function of the
reticulospinal system. Bilateral coordination of arm
movements is important for functional activities, such as
wheelchair mobility, walking with assistive devices, and bed
mobility, which are central to neurological rehabilitation
after stroke. Thus, the proposed studies will significantly extend our
understanding of a critical but poorly understood part of
the motor control system of the brain.
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