Enhancement of long‐range EEG coherence by synchronous bifocal transcranial magnetic stimulation

Abstract

Interregional coupling of distant brain regions can be measured by electroencephalographic (EEG) coherence reflecting the spatial-temporal correlation between two oscillatory signals. It has been suggested that this coherence in activity is a signature of functional integration of multimodal neuronal networks. Repetitive transcranial magnetic stimulation (rTMS) is a well-established technique for non-invasive cortical stimulation. Its modulating effects outlast the train of stimulation and affect behavior. In the present study, we tested the hypothesis that cortico-cortical coherence between distant brain areas can be selectively enhanced by synchronous bifocal rTMS. Cortico-cortical coherence was assessed in 16 healthy human subjects before and after three trains of synchronous high-frequency (10 Hz) rTMS to the left primary motor cortex and the visual cortex at the occipital pole simultaneously. Stimulation of the left M1 alone served as the control condition. Coherence and spectral power were measured between these areas on the stimulated and the homologue contralateral side. Synchronous bifocal rTMS induced an increase of interregional coupling in the alpha and lower beta band on the stimulated side without effects on spectral power. These data indicate that synchronous bifocal rTMS is a feasible technique for selective modulation of interregional EEG coherence. Furthermore, they raise the hypothesis that interventional enhancement of long-range coherence may effectively modulate interregional integration with behavioral consequences.

Paired Associative Stimulation Enforces the Communication between Interconnected Areas

“…When looking at TEPs at baseline, TMS pulse elicited several responses with latency and scalp distributions matching those already described (Komssi et al, 2002;Bonato et al, 2006;Litvak et al, 2007). However, the activity evoked by PPC stimulation was smaller in amplitude than TEPs evoked by M1 stimulation.…”

“…In particular, when PAS increased corticospinal excitability (PPC-M1 PA PASϪ5ms, PPC-M1 AP PASϩ 5ms), the activity evoked within 18 ms after the pulse decreased in amplitude, whereas an increased cortical response (PPC-M1 PA PASϪ5ms) was associated with a decrease of MEP amplitude. Given the topographical distribution and source reconstruction performed in previous studies (Litvak et al, 2007), we hypothesize that this activity could represent an inhibitory process initiated by the stimulated motor areas. However, the relationship between TEP and MEP amplitude is far from being understood.…”

“…However, the relationship between TEP and MEP amplitude is far from being understood. Previous studies found a direct correlation between MEP and TEP amplitude (Esser et al, 2006;Mäki and Ilmoniemi, 2010). As an example, Esser et al (2006) found that high-frequency repetitive TMS, which induces LTP-like phenomena, concurrently generates MEP and TEP amplitude increase.…”

“…LTP-and LTDlike effects can be induced in the primary motor cortex (M1) following the repeated application of paired pulses over interconnected areas such as contralateral M1 (Rizzo et al, 2009), ventral premotor cortex (Buch et al, 2011, or supplementary motor area (Arai et al, 2011). Recently, by targeting the posterior parietal cortex (PPC) and M1, we provided evidence suggesting the existence of both hebbian and anti-hebbian phenomena in humans (Koch et al, 2013).…”

13 Chronic Disorders of Consciousness

“…CS can force into resynchronization -"rebind"-(Slewa-Younan et al 2002) and rebalance activity across wide swaths of damaged hemispheres bilaterally (see Chapter 10), by altering thalamocortical transmission ipsilaterally and contralaterally via the corpus callosum and other deep structures. Cortico-cortical coherence between distant brain areas has been selectively enhanced by simultaneous bifocal 10Hz rTMS (Plewnia et al 2008). CS may also compensate for a loss of arousal regulation that is normally controlled by the frontal lobe in the intact brain.…”