Cortical Excitability Measured with nTMS and MEG during Stroke Recovery.
OBJECTIVE
Stroke alters cortical excitability both in the lesioned and in the nonlesioned hemisphere. Stroke recovery has been studied using transcranial magnetic stimulation (TMS). Spontaneous brain oscillations and somatosensory evoked fields (SEFs) measured by magnetoencephalography (MEG) are modified in stroke patients during recovery.


METHODS
We recorded SEFs and spontaneous MEG activity and motor threshold (MT) short intracortical inhibition (SICI) and intracortical facilitation (ICF) with navigated TMS (nTMS) at one and three months after first-ever hemispheric ischemic strokes. Changes of MEG and nTMS parameters attributed to gamma-aminobutyrate and glutamate transmission were compared.


RESULTS
ICF correlated with the strength and extent of SEF source areas depicted by MEG at three months. The nTMS MT and event-related desynchronization (ERD) of beta-band MEG activity and SICI and the beta-band MEG event-related synchronization (ERS) were correlated, but less strongly.


CONCLUSIONS
This first report using sequential nTMS and MEG in stroke recovery found intra- and interhemispheric correlations of nTMS and MEG estimates of cortical excitability. ICF and SEF parameters, MT and the ERD of the lesioned hemisphere, and SICI and ERS of the nonlesioned hemisphere were correlated. Covarying excitability in the lesioned and nonlesioned hemispheres emphasizes the importance of the hemispheric balance of the excitability of the sensorimotor system.
BioMag Laboratory, HUS Medical Imaging Center, Helsinki University Hospital and University of Helsinki, 00029 Helsinki, Finland.
Jyrki P
JP
Mäkelä
BioMag Laboratory, HUS Medical Imaging Center, Helsinki University Hospital and University of Helsinki, 00029 Helsinki, Finland ; Neuroscience Center, University of Helsinki, 00014 Helsinki, Finland.
Pantelis
P
Lioumis
Department of Neurology, Helsinki University Hospital and University of Helsinki, 00029 Helsinki, Finland ; Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, P.O. Box 15100, 00076 Espoo, Finland.
Kristina
K
Laaksonen
Department of Neurology, Helsinki University Hospital and University of Helsinki, 00029 Helsinki, Finland ; Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, P.O. Box 15100, 00076 Espoo, Finland.
Nina
N
Forss
Department of Neurology, Helsinki University Hospital and University of Helsinki, 00029 Helsinki, Finland ; Institute of Neuroscience and Physiology, Sahlgrenska Academy, University of Gothenburg, 41345 Gothenburg, Sweden ; Department of Neurology, Sahlgrenska University Hospital, 41345 Gothenburg, Sweden.
Turgut
T
Tatlisumak
Department of Neurology, Helsinki University Hospital and University of Helsinki, 00029 Helsinki, Finland.
Markku
M
Kaste
Department of Neurology, Helsinki University Hospital and University of Helsinki, 00029 Helsinki, Finland.
Satu
S
Mustanoja
D000368:Aged; D000369:Aged, 80 and over; D001611:Beta Rhythm; D002540:Cerebral Cortex / Q000503:physiopathology*; D003344:Cortical Synchronization; D005073:Evoked Potentials, Somatosensory; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D018698:Glutamic Acid; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods*; D008297:Male; D008875:Middle Aged; D020127:Recovery of Function; D020521:Stroke / Q000503:physiopathology*; D009435:Synaptic Transmission; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D005680:gamma-Aminobutyric Acid
D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid