ABC Seminar: Re-wiring the human brain - Modulating interregional effective connectivity with TMS-EEG
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Welcome to our ABC Seminars! This seminar series is open for everyone. The talk will take place in . After the talks, coffee and pulla will be served.
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Title:
Re-wiring the human brain: Modulating interregional effective connectivity with TMS-EEG
Abstract:
Controlled and selective modulation of connectivity strengths between specific brain areas would be useful for therapeutic and research purposes. Here, we describe TMS-EEG experiments designed to induce synaptic changes based on spike-timing dependent plasticity (STDP) that reflect long-term potentiation and -depression (LTP/LTD) and lead to increased or decreased effective connectivity. We employed cortico-cortical paired associative stimulation (ccPAS) protocols in which two areas were repeatedly stimulated with 2-channel TMS at a millisecond-level asynchrony. Specifically, ccPAS was delivered to the left primary motor cortex (M1) → right M1 with three different asynchronies (5 milliseconds shorter, equal to, or 5 milliseconds longer than the 9-millisecond transcallosal conduction delay) in separate sessions. To observe the neurophysiological effects, single-pulse TMS was delivered to the left M1 before and after ccPAS while cortico-cortical evoked responses were extracted from the contralateral M1 using source-resolved EEG. Consistent with STDP mechanisms, the effects on synaptic strengths flipped depending on the asynchrony. Further implicating STDP, control experiments suggested that the effects were unidirectional and selective to the targeted connection. The results support the idea that ccPAS induces STDP and may selectively up- or downregulate effective connectivity between targeted regions in the human brain.
Bio:
Tommi Raij, MD, PhD. Dr. Raij received his MD in 1994 from University of Helsinki, followed by PhD in 2000 from Brain Research Unit at the Low Temperature Laboratory, Helsinki University of Technology (now Aalto University), where he studied network-level functions of the human brain using magnetoencephalography (MEG). In 2002, Dr. Raij moved to MGH Martinos Center for Biomedical Imaging, Boston, MA, USA, for post-doctoral studies, and was promoted to Harvard Medical School faculty at the Department of Radiology in 2008 when he also became the founding director of the transcranial magnetic stimulation (TMS) core at Martinos Center. In 2014 - 2019 he served as the Director of the Center for Brain Stimulation at Rehabilitation Institute of Chicago and Northwestern University, Chicago, IL, USA, and then returned to Martinos Center where he currently leads TMS Clinical Research.