Neurons in the Pontomedullary Reticular Formation Signal Posture and Movement Both as an Integrated Behavior and Independently

Schepens, Bénédicte; Stapley, Paul J.; Drew, Trevor

doi:10.1152/jn.01381.2007

Cited by 100 publications

(102 citation statements)

References 40 publications

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“…The ipsilateral reticulospinal motor system has been previously implicated in the abnormal coactivation of shoulder abductors with distal limb flexors (flexion synergy) and the resultant loss of independent joint control in individuals with stroke (Dewald et al 1995(Dewald et al , 2001Ellis et al 2007;Schwerin et al 2008Schwerin et al , 2011Sukal et al 2007). Furthermore, animal evidence has demonstrated the involvement of reticular formation neurons in general during reaching (Buford and Davidson 2004;Drew 2006, 2004;Schepens et al 2008). The means by which selective increased reliance on ipsilateral reticular formation occurs is unclear since corticoreticular projections are bilateral in both the cat and monkey Kuypers 1984, 1989).…”

Section: Brain Stem Projections and Implications Of Current Resultsmentioning

confidence: 99%

Neck rotation modulates flexion synergy torques, indicating an ipsilateral reticulospinal source for impairment in stroke

Ellis

Drogos

Carmona

et al. 2012

Journal of Neurophysiology

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Ellis MD, Drogos J, Carmona C, Keller T, Dewald JP. Neck rotation modulates flexion synergy torques, indicating an ipsilateral reticulospinal source for impairment in stroke. J Neurophysiol 108: 3096 -3104, 2012. First published September 5, 2012 doi:10.1152/jn.01030.2011.-The effect of reticular formation excitability on maximum voluntary torque (MVT) generation and associated muscle activation at the shoulder and elbow was investigated through natural elicitation (active head rotation) of the asymmetric tonic neck reflex (ATNR) in 26 individuals with stroke and 9 agerange-matched controls. Isometric MVT generation at the shoulder and elbow was quantified with the head rotated (face pointing) contralateral and ipsilateral to the paretic (stroke) and dominant (control) arm. Given the dominance of abnormal torque coupling of elbow flexion with shoulder abduction (flexion synergy) in stroke and welldeveloped animal models demonstrating a linkage between reticular formation and ipsilateral elbow flexors and shoulder abductors, we hypothesized that constituent torques of flexion synergy, specifically elbow flexion and shoulder abduction, would increase with contralateral head rotation. The findings of this investigation support this hypothesis. Increases in MVT for three of four flexion synergy constituents (elbow flexion, shoulder abduction, and shoulder external rotation) were observed during contralateral head rotation only in individuals with stroke. Electromyographic data of the associated muscle coactivations were nonsignificant but are presented for consideration in light of a likely underpowered statistical design for this specific variable. This study not only provides evidence for the reemergence of ATNR following stroke but also indicates a common neuroanatomical link, namely, an increased reliance on ipsilateral reticulospinal pathways, as the likely mechanism underlying the expression of both ATNR and flexion synergy that results in the loss of independent joint control. flexion synergy; strength; tonic neck reflex; asymmetric tonic neck reflex REACHING FUNCTION FOLLOWING STROKE can be profoundly impaired and has been historically described as being constrained, at least in part, to stereotypic multijoint movement patterns or synergies (Brunnstrom 1970;Foerster 1936;Twitchell 1951). Initial quantitative investigations thoroughly described the phenomena under isometric conditions highlighting the abnormal coactivation of brachialis, biceps brachii, and brachioradialis with deltoid (Dewald et al. 1995). The coactivation manifests as a "flexion synergy" and is significant for abnormal joint torque coupling of elbow flexion during shoulder abduc-

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Section: Brain Stem Projections and Implications Of Current Resultsmentioning

confidence: 99%

Neck rotation modulates flexion synergy torques, indicating an ipsilateral reticulospinal source for impairment in stroke

Ellis

Drogos

Carmona

et al. 2012

Journal of Neurophysiology

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show abstract

“…Various descending pathways can then modulate the spinal cord for greater flexibility of basic reflexes. For instance, recent data recorded in cat showed that neurons in pontomedullary reticular formation can both ensure integrated or independent control of posture and reaching (Schepens and Drew, 2004;Schepens et al, 2008). Together, one can speculate that the basic coordinative structure could first emerge at the level of M1 depending on task demands.…”

Section: Discussionmentioning

confidence: 99%

Modular Control of Pointing beyond Arm's Length

Berret¹,

Bonnetblanc²,

Papaxanthis³

et al. 2009

J. Neurosci.

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Hand reaching and bipedal equilibrium are two important functions of the human motor behavior. However, how the brain plans goal-oriented actions combining target reaching with equilibrium regulation is not yet clearly understood. An important question is whether postural control and reaching are integrated in one single module or controlled separately. Here, we show that postural control and reaching motor commands are processed by means of a modular and flexible organization. Principal component and correlation analyses between pairs of angles were used to extract global and local coupling during a whole-body pointing beyond arm's length. A low-dimensional organization of the redundant kinematic chain allowing simultaneous target reaching and regulation of the center of mass (CoM) displacement in extrinsic space emerged from the first analysis. In follow-up experiments, both the CoM and finger trajectories were constrained by asking participants to reach from a reduced base of support with or without knee flexion, or by moving the endpoint along a predefined trajectory (straight or semicircular trajectories). Whereas joint covaried during free conditions and under equilibrium restrictions, it was decomposed in two task-dependent and task-independent modules, corresponding to a dissociation of arm versus legs, trunk, and head coordination, respectively, under imposed finger path conditions. A numerical simulation supported the idea that both postural and focal subtasks are basically integrated into the same motor command and that the CNS is able to combine or to separate the movement into autonomous functional synergies according to the task requirements.

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“…Stimulation in the pontomedullary reticular formation (PMRF) evokes ipsilateral limb flexor and contralateral limb extensor muscle excitation sometimes accompanied by a reciprocal suppression of the antagonistic muscles. The PMRF is therefore not only involved in the control of locomotion (Matsuyama et al, 2004) and postural support during reaching movements (Schepens et al, 2008), but also in voluntary reaching (Buford and Davidson, 2004), and is thus in a position to relay reach related tectal output to arm muscles (Davidson and Buford, 2004). These findings and the short latencies presented in the present study could explain the presence of rapid arm muscle activity (Ͻ100 ms latency) that was time locked to the target appearance but not movement onset (Pruszynski et al, 2010).…”

Section: Discussionmentioning

confidence: 99%

Arm Movements Induced by Electrical Microstimulation in the Superior Colliculus of the Macaque Monkey

Philipp

Hoffmann

2014

J. Neurosci.

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Neuronal activity in the deep layers of the macaque (Macaca mulatta) superior colliculus (SC) and the underlying reticular formation is correlated with the initiation and execution of arm movements (Werner, 1993). Although the correlation of this activity with EMGs of proximal arm muscles is as strong as in motor cortex (Werner et al., 1997a; Stuphorn et al., 1999), little is known about the influence of electrical microstimulation in the SC on the initiation and trajectories of arm movements. Our experiments on three macaque monkeys clearly show that arm movements can be elicited by electrical microstimulation in the deep layers of the lateral SC and underlying reticular formation. The most extensively trained monkey, M1, extended his arm toward the screen in front of him more or less stereotypically upon electrical SC stimulation. In two other monkeys, M2 and M3, a larger repertoire of arm movements were elicited, categorized into three movement types, and compared before (M3) and after (M2 and M3) training: twitch (56% vs 62%), lift (6% vs 5%), and extend (37% vs 32%), respectively. Therefore, arm movements induced by electrical stimulation in the monkey SC represent a further component of the functional repertoire of the SC using its impact on motoneurons in the spinal cord, probably via premotor neurons in the brainstem, as well as on structures involved in executing more complex movements such as target-directed reaching. Therefore, the macaque SC could be involved directly in the initiation, execution, and amendment of arm and hand movements.

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Neurons in the Pontomedullary Reticular Formation Signal Posture and Movement Both as an Integrated Behavior and Independently

Cited by 100 publications

References 40 publications

Neck rotation modulates flexion synergy torques, indicating an ipsilateral reticulospinal source for impairment in stroke

Neck rotation modulates flexion synergy torques, indicating an ipsilateral reticulospinal source for impairment in stroke

Modular Control of Pointing beyond Arm's Length

Arm Movements Induced by Electrical Microstimulation in the Superior Colliculus of the Macaque Monkey

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