Functional neuroimaging of resting-state and stimulus-driven networks in the macaque brain

Abstract

The brain is dynamic. Spontaneous neuronal activity can be observed in cortical and subcortical regions even in the absence of external inputs. At a large scale, long-range coherent spontaneous fluctuations are thought to produce spatially-structured temporal correlations in hemodynamic activity. The set of functional networks observed in the brain during periods of rest, the resting-state networks, constitute what is believed to reflect brain’s intrinsic functional architecture. On the other hand, the brain is constantly stimulated by extraneous information. As a consequence, stimulus-driven neuronal activity contributes to shape an extended functional framework, with extrinsic functional topology on top of the intrinsic. How intrinsic and extrinsic network topologies dynamically operate is still unknown. In this thesis, we shed light in this issue after investigating different operational aspects of resting-state and stimulus-driven networks in the macaque brain. We took advantage of the broad coverage at high spatial resolution provided by modern functional neuroimaging to have a global view of brain’s functional organization, be it during rest or during sensory stimulation. We started by assessing the topographic relationship of intrinsic and extrinsic functional topologies under different conditions of visual stimulation. Our findings suggest that extrinsic architectures contain an intrinsic component, topographically equivalent to the resting-state architecture, in addition to a stimulus-driven counterpart. Next, we continued our investigation by focusing on the interactions of functional networks evoked by multiple sensory modalities. Specifically, we were interested in the modulatory influences of vision and audition, primate’s dominant senses, at early stages of cortical processing. Since no general framework existed concerning auditory influences in early visual cortices, we filled this gap by proposing a novel model for auditory interactions in primary visual cortex, based on recent evidences. Finally, we went beyond early cortical processing and provided evidence supporting the hypothesis of “what” and “where” streams in the auditory cortex specialized in object recognition and spatial representations, respectively. However, we also showed that the analogy between visual and auditory dual streams isn’t complete.