Simultaneous TMS-fMRI of the Visual Cortex Reveals Functional Network, Even in Absence of Phosphene Sensation
E.C. Caparelli1, 6, *, W. Backus2, F. Telang5, G-J Wang1, T. Maloney1, R.Z. Goldstein1, D. Anschel3, 4, F. Henn1
Identifiers and Pagination:Year: 2010
First Page: 100
Last Page: 110
Publisher ID: TONIJ-4-100
Article History:Received Date: 8/7/2009
Revision Received Date: 25/11/2009
Acceptance Date: 23/4/2010
Electronic publication date: 12/8/2010
Collection year: 2010
open-access license: This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.
Phosphene sensation is commonly used to measure cortical excitability during transcranial magnetic stimulation (TMS) of the occipital cortex. However, some individuals lack this perception, and the reason for it is still unknown. In this work, we used functional magnetic resonance imaging (fMRI) to detect brain activation during local TMS of the occipital cortex in twelve healthy subjects. We found that TMS modulated brain activity in areas connected to the stimulation site, even in people unable to see phosphene. However, we observed a trend for a lower blood-oxygenation-level dependent (BOLD) signal, and smaller brain-activation clusters near the stimulated site than in the interconnected brain areas, suggesting that TMS pulse is more effective downstream than at its application site. Furthermore, we noted prominent differences in brain activation/deactivation patterns between subjects who perceived phosphene and those who did not, implying a functional distinction in their neuronal networks that might explain the origin of differences in phosphene generation.