Looming and receding visual networks in awake marmosets investigated with fMRI

© 2020 The Author(s) An object that is looming toward a subject or receding away contains important information for determining if this object is dangerous, beneficial or harmless. This information (motion, direction, identity, time-to-collision, size, velocity) is analyzed by the brain in order to execute the appropriate behavioral responses depending on the context: fleeing, freezing, grasping, eating, exploring. In the current study, we performed ultra-high-field functional MRI (fMRI) at 9.4T in awake marmosets to explore the patterns of brain activation elicited by visual stimuli looming toward or receding away from the monkey. We found that looming and receding visual stimuli activated a large cortical network in frontal, parietal, temporal and occipital cortex in areas involved in the analysis of motion, shape, identity and features of the objects. Looming stimuli strongly activated a network composed of portions of the pulvinar, superior colliculus, putamen, parietal, prefrontal and temporal cortical areas. These activations suggest the existence of a network that processes visual stimuli looming toward peripersonal space to predict the consequence of these stimuli. Together with previous studies in macaque monkeys, these findings indicate that this network is preserved across Old and New World primates

Cortico-subcortical functional connectivity profiles of resting-state networks in marmosets and humans

Copyright © 2020 the authors Understanding the similarity of cortico-subcortical networks topologies between humans and nonhuman primate species is critical to study the origin of network alternations underlying human neurologic and neuropsychiatric diseases. The New World common marmoset (Callithrix jacchus) has become popular as a nonhuman primate model for human brain function. Most marmoset connectomic research, however, has exclusively focused on cortical areas, with connectivity to subcortical networks less extensively explored. Here, we aimed to first isolate patterns of subcortical connectivity with cortical resting-state networks in awake marmosets using resting-state fMRI, then to compare these networks with those in humans using connectivity fingerprinting. In this study, we used 5 marmosets (4 males, 1 female). While we could match several marmoset and human resting-state networks based on their functional fingerprints, we also found a few striking differences, for example, strong functional connectivity of the default mode network with the superior colliculus in marmosets that was much weaker in humans. Together, these findings demonstrate that many of the core cortico-subcortical networks in humans are also present in marmosets, but that small, potentially functionally relevant differences exist

FUNCTIONAL NEUROIMAGING OF VENTRAL AND DORSAL STREAM PATHWAYS IN THE MACAQUE AUDITORY SYSTEM

One fundamental goal of the brain is to predict sensory events in the environment in order to spatially direct actions. In vision, the ability to identify and locate objects depends on two cortical pathways: a ventral “what” stream supporting object recognition and a dorsal “where” stream supporting object localization. While this hierarchical model received strong support in vision, in audition the analogues functional roles have remained rather elusive, particularly for the dorsal “where” stream. Thus, the objective of this thesis was to explore the functional roles of auditory ventral and dorsal stream pathways in the macaque brain. We first explored the representational structure of natural sounds in early regions of the ventral pathway utilizing single-unit electrophysiology. We then used functional magnetic resonance imaging (fMRI) to map the representation of natural sounds along the ventral pathway including regions outside auditory cortex. Finally, using high-field fMRI we examined the functional representation of acoustic space in auditory cortical regions. Overall, our work confirms the role of the ventral stream in decoding sound identity and extends the evidence suggesting that vocalizations carry information that is represented outside auditory cortex. Moreover, our work in the dorsal stream also confirms the role of a posterior dorsal cortical region specialized in processing spatial information and reconciles competitive theories of spatial coding in auditory cortex. However, our space work also indicates a fundamental difference in the representation format for acoustic space in auditory cortex as compared to visual cortex. Taken together, our work confirms the functional roles of the ventral and dorsal streams and suggests incorporating subcortical level processes in the cortical model for a more integrated framework of acoustic processing in the primate brain

A right hemisphere advantage for processing blurred faces

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