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Motor cortical excitability and pre-supplementary motor area neurochemistry in healthy adults with substantia nigra hyperechogenicity |
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| Authors: | Gabrielle Todd Caroline D. Rae Janet L. Taylor Nigel C. Rogasch Jane E. Butler Michael Hayes Robert A. Wilcox Simon C. Gandevia Karl Aoun Adrian Esterman Simon J. G. Lewis Julie M. Hall Elie Matar Jana Godau Daniela Berg Christian Plewnia Anna-Katharina von Thaler Clarence Chiang Kay L. Double |
| Affiliation: | 1. UniSA Clinical & Health Sciences and Alliance for Research in Exercise, Nutrition and Activity (ARENA), University of South Australia, Adelaide, South Australia, Australia;2. Neuroscience Research Australia, Randwick, New South Wales, Australia Faculty of Medicine, University of New South Wales, Kensington, New South Wales, Australia;3. Neuroscience Research Australia, Randwick, New South Wales, Australia Faculty of Medicine, University of New South Wales, Kensington, New South Wales, Australia School of Medical and Health Sciences, Edith Cowan University, Joondalup, Western Australia, Australia;4. Hopwood Centre for Neurobiology, South Australian Health and Medical Research Institute, Adelaide, South Australia, Australia Faculty of Health and Medical Sciences, The University of Adelaide, Adelaide, South Australia, Australia School of Psychological Sciences and Turner Institute for Brain and Mental Health, Monash University, Melbourne, Victoria, Australia;5. Department of Neurology, Concord Repatriation General Hospital, Concord, New South Wales, Australia;6. UniSA Clinical & Health Sciences and Alliance for Research in Exercise, Nutrition and Activity (ARENA), University of South Australia, Adelaide, South Australia, Australia Department of Neurology, Flinders Medical Centre, Bedford Park, South Australia, Australia College of Medicine and Public Health, Flinders University, Bedford Park, South Australia, Australia;7. Brain and Mind Centre and School of Medical Sciences (Neuroscience), The University of Sydney, Sydney, New South Wales, Australia;8. ForeFront Parkinson's Disease Research Clinic, Brain and Mind Centre, Faculty of Medicine and Health, The University of Sydney, Camperdown, New South Wales, Australia;9. Department of Experimental Psychology, Ghent University, Ghent, Belgium;10. Department of Neurology, Klinikum Kassel GmbH, Kassel, Germany;11. Department of Neurology, UKSH, Campus Kiel, Christian-Albrechts-University, Kiel, Germany;12. Department of Psychiatry and Psychotherapy, Neurophysiology & Interventional Neuropsychiatry, University of Tübingen, Tübingen, Germany;13. Zentrum für Neurologie, Abteilung Neurodegeneration, Universitätsklinikum Tübingen, Tübingen, Germany;14. Neuroscience Research Australia, Randwick, New South Wales, Australia Brain and Mind Centre and School of Medical Sciences (Neuroscience), The University of Sydney, Sydney, New South Wales, Australia |
| Abstract: | Substantia nigra (SN) hyperechogenicity, viewed with transcranial ultrasound, is a risk marker for Parkinson's disease. We hypothesized that SN hyperechogenicity in healthy adults aged 50–70 years is associated with reduced short-interval intracortical inhibition in primary motor cortex, and that the reduced intracortical inhibition is associated with neurochemical markers of activity in the pre-supplementary motor area (pre-SMA). Short-interval intracortical inhibition and intracortical facilitation in primary motor cortex was assessed with paired-pulse transcranial magnetic stimulation in 23 healthy adults with normal (n = 14; 61 ± 7 yrs) or abnormally enlarged (hyperechogenic; n = 9; 60 ± 6 yrs) area of SN echogenicity. Thirteen of these participants (7 SN− and 6 SN+) also underwent brain magnetic resonance spectroscopy to investigate pre-SMA neurochemistry. There was no relationship between area of SN echogenicity and short-interval intracortical inhibition in the ipsilateral primary motor cortex. There was a significant positive relationship, however, between area of echogenicity in the right SN and the magnitude of intracortical facilitation in the right (ipsilateral) primary motor cortex (p = .005; multivariate regression), evidenced by the amplitude of the conditioned motor evoked potential (MEP) at the 10–12 ms interstimulus interval. This relationship was not present on the left side. Pre-SMA glutamate did not predict primary motor cortex inhibition or facilitation. The results suggest that SN hyperechogenicity in healthy older adults may be associated with changes in excitability of motor cortical circuitry. The results advance understanding of brain changes in healthy older adults at risk of Parkinson's disease. |
| Keywords: | motor cortex pre-supplementary motor area substantia nigra transcranial magnetic stimulation |