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Free keywords:
MEG, Cortical oscillatory activity, Evoked response, Beamforming, Picture naming
Abstract:
Phase-locked evoked responses and event-related modulations of spontaneous rhythmic activity are the two
main approaches used to quantify stimulus- or task-related changes in electrophysiological measures. The relationship
between the two has beenwidely theorized upon but empirical research has been limited to the primary
visual and sensorimotor cortex. However, both evoked responses and rhythms have been used as markers of
neural activity in paradigms ranging from simple sensory to complex cognitive tasks.While some spatial agreement
between the two phenomena has been observed, typically only one of the measures has been used in any
given study, thus disallowing a direct evaluation of their exact spatiotemporal relationship. In this study, we
sought to systematically clarify the connection between evoked responses and rhythmic activity. Using both
measures, we identified the spatiotemporal patterns of task effects in three magnetoencephalography (MEG)
data sets, all variants of a picture naming task. Evoked responses and rhythmic modulation yielded largely separate
networks, with spatial overlap mainly in the sensorimotor and primary visual areas.Moreover, in the cortical
regions thatwere identified with both measures the experimental effects they conveyed differed in terms of
timing and function. Our results suggest that the two phenomena are largely detached and that both measures
are needed for an accurate portrayal of brain activity.
