In this proposal we will develop a novel method to study the neural bases of higher-order cognitive processing using magnetoencephalography (MEG). The spatial and temporal abilities of MEG should make it the ideal tool for describing the patterns of activity among structures comprising neural networks activated by the performance of cognitive tasks. However, MEG analyses are very difficult when an unknown and large number of sources with similar temporal, spatial, and frequency characteristics contribute to the evoked response. This superimposition makes large amplitude sensory sources dominate source analyses and limits the utility of MEG by masking lower amplitude sources, in higher-order cortices. We propose a modification to the stimulus presentation in an evoked response paradigm to make the source characteristics in sensory and higher-order cortices distinct. Presenting stimuli as a series of minimally different frames in rapid succession causes the smooth transition from one discreet stimulus to another; as in a movie. We hypothesize that this method will cause low-amplitude activation of the sensory cortices while preserving activity time-locked to cognitive requirements of the task in higher-order cortices. We compared this method to traditional stimulus presentation with rapid onsets in a visual delayed match-to-sample working memory task. With rapid onsets nearly half of all source localizations were to primary visual cortex and only one subject showed frontal activation. In contrast, smooth transitions dramatically reduced visual cortex sources and frontal activations were observed in all subjects. Our preliminary data show that our novel method makes higher-order cortices involved in cognitive processing significantly more amenable to efficient, informative, and subtle, systematic analyses. The development of this method will become especially important in disorders like schizophrenia where there are typically no discreet lesions and the core of the disorder may lie in the functional status of or functional connections between higher-orders of brain. ? ?
| Plis, Sergey M; Weisend, Michael P; Damaraju, Eswar et al. (2011) Effective connectivity analysis of fMRI and MEG data collected under identical paradigms. Comput Biol Med 41:1156-65 |
