Human brain connectivity during single and paired pulse transcranial magnetic stimulation.
OBJECTIVE
Intracortical inhibition (SICI) and facilitation (ICF) in the human motor cortex can be measured using a paired pulse transcranial magnetic stimulation (ppTMS) protocol. Recently, a technical device has been introduced, which allows recording electroencephalographic (EEG) responses to TMS of a given scalp site. The latency, amplitude and scalp topography of such responses are considered a reflection of cortico-cortical connectivity and functional state. The aim of the present study is to better characterize the neuronal circuits underlying motor cortex connectivity as well as the mechanisms regulating its balance between inhibition and facilitation by means of EEG navigated-ppTMS coregistration.


METHODS
Sub-threshold and supra-threshold single and ppTMS of the left primary motor cortex were carried out during a multi-channel EEG recording on 8 healthy volunteers; the between-pulse intervals used in the paired pulse trials were 3 (for SICI) and 11 ms (for ICF). Motor evoked potentials (MEPs) from the opposite hand were simultaneously recorded.


RESULTS
Single and ppTMS induced EEG responses characterized by a sequence of negative deflections peaking at approximately 7, 18, 44, 100 and 280 ms alternated with positive peaks at approximately 13, 30, 60 and 190 ms post-TMS. Moreover, ppTMS modulated both EEG evoked activity and MEPs. Amplitude variability of EEG responses was correlated with - and therefore might partially explain - amplitude variability of MEPs.


CONCLUSIONS
EEG-ppTMS is a promising tool to better characterize the neuronal circuits underlying cortical effective connectivity as well as the mechanisms regulating the balance between inhibition and facilitation within the human cortices and the corticospinal pathway.
Ferreri
Florinda
F
Department of Neurology, University Campus Biomedico, Rome, Italy.
Pasqualetti
Patrizio
P
Määttä
Sara
S
Ponzo
David
D
Ferrarelli
Fabio
F
Tononi
Giulio
G
Mervaala
Esa
E
Miniussi
Carlo
C
Rossini
Paolo Maria
PM
D000293:Adolescent; D000328:Adult; D001921:Brain / Q000033:anatomy & histology* / Q000502:physiology*; D004558:Electric Stimulation / Q000379:methods; D004566:Electrodes; D004569:Electroencephalography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008183:Luteal Phase / Q000502:physiology; D009044:Motor Cortex / Q000033:anatomy & histology / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D011930:Reaction Time; D012535:Scalp / Q000294:innervation; D011795:Surveys and Questionnaires; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult