Dissociated mean and functional connectivity BOLD signals in visual cortex during eyes closed 1 and fixation 2

24 We investigated the effects of resting state type on the blood oxygen level-dependent (BOLD) signal and 25 functional connectivity in two paradigms: participants either alternated between fixation and eyes closed or 26 maintained fixation or eyes closed throughout each scan. The BOLD signal and functional connectivity of lower 27 and higher tiers of the visual cortical hierarchy were found to be differentially modulated during eyes closed 28 versus fixation. Fixation was associated with greater mean BOLD signals in primary visual cortex and lower 29 mean BOLD signals in extrastriate visual areas than periods of eyes closed. In addition, analysis of 30 thalamocortical functional connectivity during scans in which participants maintained fixation showed 31 synchronized BOLD fluctuations between those thalamic nuclei whose mean BOLD signal was systematically 32 modulated during alternating epochs of eyes closed and fixation, primary visual cortex and the attention 33 network, while during eyes closed negatively correlated fluctuations were seen between the same thalamic 34 nuclei and extrastriate visual areas. Finally, in all visual areas the amplitude of spontaneous BOLD fluctuations 35 was greater during eyes closed than fixation. The dissociation between early and late tiers of visual cortex, 36 which characterizes both mean and functionally connected components of the BOLD signal, may depend on the 37 reorganization of thalamocortical networks. Since dissociated changes in local blood flow also characterize 38 transitions between different stages of sleep and wakefulness (Braun et al. 1998), our results suggest that 39 dissociated endogenous neural activity in primary and extrastriate cortex may represent a general aspect of 40 brain function. 41 42