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Articles and Reports

Motor Outputs From the Primate Reticular Formation to Shoulder Muscles as Revealed by Stimulus-Triggered Averaging

Adam G. Davidson1 and John A. Buford1,2

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

Subjects, task, and surgery

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 1984Go). Surgery was performed under isoflorane inhalation anesthesia with ketamine HCl as a preanesthetic. Analgesics (buprenorphine, ibuprofen) and a long-acting antibiotic (Baytril) were given after surgery.

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. 1976Go; Park et al. 2000Go). For the chronic implants, the wires were led subcutaneously to a 17-pin plug (WPI #223-1617) mounted in the dental acrylic of the cranial implant. The integrity of EMG implants was verified by stimulating through the EMG wires, and by periodic testing of electrode impedances. Because recordings were made from the right reticular formation, ipsilateral muscles were located on the right side.

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.

Grant Number: 5R01NS037822-08
PI Information: Name Email Title
  BUFORD, JOHN A. [email protected]  

DESCRIPTION (provided by applicant): The reticulospinal tracts are a major descending system, but their role in motor control has received limited study. Understanding reticulospinal function is important because when brain injuries affect cortex, extrapyramidal systems like the reticulospinal system may be critical for functional recovery.

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.

Thesaurus Terms:
limb movement, neuromuscular function, neurophysiology, neuroregulation, reticular formation, reticulospinal tract
brain electrical activity, brain injury, cerebral cortex, cerebral dominance, electrophysiology, evoked potential, motor cortex, neural information processing
Macaca fascicularis, brain mapping, electrode, electromyography, electrostimulus, microinjection
  COLUMBUS, OH 43210
Fiscal Year: 2008
Project Start: 30-JUL-1999
Project End: 31-JAN-2009

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