Society for Neuroscience Annual Meeting edition:39 location:Chicago, USA date:17-21 October 2009
Functional connectivity magnetic resonance imaging (fcMRI) studies of the primate brain have shown a finite set of large-scale networks of coherent hemodynamic fluctuations. It is suggested that such fluctuations have a neuronal origin as they consistently correlate with fluctuations in band-limited neuronal power. In this fcMRI study we characterized changes in large-scale spatio-temporal properties of the fMRI signal acquired (at 3 T) in awake behaving monkeys (N = 4) in different behavioral conditions. Experimental procedures were approved by and conducted at the K.U.Leuven. In 3 experiments, animals were rewarded for: 1) fixating on a red spot in an otherwise empty field; 2) fixating while watching and listening to clips of a movie; 3) watching and listening to the same movie clips without eye-movement restrictions. Eye-positions were collected at 120Hz throughout the scans. The fMRI data were analyzed using an independent component analysis (ICA) method to retrieve spatio-temporal patterns of coherent brain activity. We used an hierarchical cluster analysis based on spatial correlation to match the corresponding patterns from different datasets. The criteria for the selection of the large-scale networks were: 1) consistency across animals, and 2) the statistical difference between intra- and extra-cluster spatial correlation (Mann-Whitney test, p<0.001 corrected). After fixed-effect group analysis, the network maps were thresholded at |z|>2.33 and represented on flattened 2D reconstructions of the cortex. We could identify 8 consistent bilateral networks in monkeys during resting state. On the basis of topographic maps from previous studies, they can be tentatively characterized as: default-mode, attention, oculomotor, auditory, face and body somato-motor, foveal and peripheral visual networks. When presenting the movie, the number of networks and the lateralization of individual networks increased considerably. Somato-motor and auditory networks were minimally altered, whereas default-mode and visual networks were split into multiple sub-networks. Surprisingly, multiple retinotopic-specific early visual networks emerged when the subjects fixated to or watched the movie. The latter condition revealed also additional frontal and higher-order visual areas. A reverse correlation analysis approach showed a correlation between viewing hand movements and higher fMRI activity in the somato-motor network. Our description of large-scale functional networks in monkeys across different behavioral conditions can provide an important framework through which evolutionary differences of functional brain architecture can be evaluated in a task-independent manner.