Motor and Premotor Cortices in Subcortical Stroke: Proton Magnetic Resonance Spectroscopy Measures and Arm Motor Impairment

Something might be important in here but with all the big words I got nothing out of it.

Motor and Premotor Cortices in Subcortical Stroke: Proton Magnetic Resonance Spectroscopy Measures and Arm Motor Impairment 

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Sorin C. Craciunas, MD, PhD, William M. Brooks, PhD, Randolph J. Nudo, PhD,

First Published January 8, 2013 Research Article Find in PubMed 

https://doi.org/10.1177/1545968312469835

Article information

Abstract

Background. 

Although functional imaging and neurophysiological approaches reveal alterations in motor and premotor areas after stroke, insights into neurobiological events underlying these alterations are limited in human studies.  

Objective. 

We tested whether cerebral metabolites related to neuronal and glial compartments are altered in the hand representation in bilateral motor and premotor areas and correlated with distal and proximal arm motor impairment in hemiparetic persons.  

Methods. 

In 20 participants at >6 months postonset of a subcortical ischemic stroke and 16 age- and sex-matched healthy controls, the concentrations of N-acetylaspartate and myo-inositol were quantified by proton magnetic resonance spectroscopy. Regions of interest identified by functional magnetic resonance imaging included primary (M1), dorsal premotor (PMd), and supplementary (SMA) motor areas. Relationships between metabolite concentrations and distal (hand) and proximal (shoulder/elbow) motor impairment using Fugl-Meyer Upper Extremity (FMUE) subscores were explored.  

Results. 

N-Acetylaspartate was lower in M1 (P = .04) and SMA (P = .004) and myo-inositol was higher in M1 (P = .003) and PMd (P = .03) in the injured (ipsilesional) hemisphere after stroke compared with the left hemisphere in controls. N-Acetylaspartate in ipsilesional M1 was positively correlated with hand FMUE subscores (P = .04). Significant positive correlations were also found between N-acetylaspartate in ipsilesional M1, PMd, and SMA and in contralesional M1 and shoulder/elbow FMUE subscores (P = .02, .01, .02, and .02, respectively).  

Conclusions. 

 Our preliminary results demonstrated that proton magnetic resonance spectroscopy is a sensitive method to quantify relevant neuronal changes in spared motor cortex after stroke and consequently increase our knowledge of the factors leading from these changes to arm motor impairment.

Keywords subcortical stroke, motor and premotor cortices, proton magnetic resonance spectroscopy, distal and proximal arm motor impairment

Introduction

Human imaging studies have revealed that early after subcortical stroke, restoration of paretic arm function is associated with a greater involvement of radiologically normal-appearing (or spared) motor (primary motor cortex or M1) and premotor (dorsal premotor cortex or PMd, supplementary motor area or SMA) areas in both injured (ipsilesional) and uninjured (contralesional) hemispheres.^1-3 Later, successful recovery occurs in stroke survivors who exhibit relatively normal patterns of ipsilesional activation and less contralesional motor activation, whereas patients, who often show bilateral cortical activation, typically have less complete recovery.^4-6 These results should be viewed in the context of the anatomic structures and pathways of these areas. Although M1 motor pathways are critical, the premotor areas also contribute to motor control and might be recruited during motor recovery after stroke. The parallel nature of the direct (corticospinal) pathways from premotor areas and M1 emphasizes that PMd and SMA are, in some respects, at a similar level of hierarchical organization as M1,⁷ although these projections to spinal cord motor neurons are less numerous and less efficient than those from M1.^8-10 Another possibility is the indirect (corticoreticulospinal) projections to cervical propriospinal premotoneurons, which have divergent projections to muscle groups operating at multiple joints.^11,12 Finally, corticocortical connections between these areas might also play an important role in poststroke recovery.^7,13-15 Thus, understanding the neural events associated with the functional changes in these areas could provide critical insight into successful treatments of patient’s impairment.

Proton magnetic resonance spectroscopy (¹H-MRS) provides a noninvasive means to measure concentrations of certain metabolites associated with a specific cell type¹⁶ after stroke.¹⁷ Most clinical stroke studies report lower levels of N-acetylaspartate (NAA, putative marker of neuronal integrity) in spared ipsilesional M1 and PMd.^18-21 In some instances, the NAA levels were related to clinical severity. In a series of studies of stroke survivors, we also found higher myo-inositol (mI, putative marker of glial cells) in ipsilesional and contralesional M1.²¹ However, none of these studies addressed the changes in key metabolites related to neuronal and glial compartments, that is, NAA and mI, in motor and premotor areas in stroke.

The first aim of the current study was to quantify NAA and mI concentrations in ipsilesional and contralesional motor and premotor areas in chronic subcortical stroke. Since neuronal integrity might be compromised in these remote areas,^21,22 we expected NAA to be lower, especially in the ipsilesional areas. Given the role of glia in plastic brain changes,^23-25 we also expected mI to be higher. The second aim was to explore correlations between metabolite concentrations and arm motor impairment. Since the premotor projections are significantly stronger on the proximal muscles than distal muscles compared with M1^8,9, we predicted that metabolite measures in ipsilesional PMd and SMA would be correlated with proximal (shoulder/elbow) motor impairment whereas those in M1 would be correlated with both proximal and distal (hand) impairments. Since both direct and indirect pathways from the contralesional M1 project to axial and proximal muscles rather than hand muscles,^26,27 relationships between contralesional M1 metabolites and proximal impairment were also expected.

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