Top-down attention: neural pathways in the human and non-human primate examined by electrophysiology, optogenetics and psychophysics

We are constantly exposed to an abundance of visual information in our environment. Selective visual attention allows us to behave in a goal-directed and flexible manner in this crowded environment. However, we still do not understand the complex neuronal networks underlying the ability to attend and filter out selected information. This thesis contains four studies investigating the networks of selective visual attention in the human and non-human primate. The prefrontal area FEF has been suggested to play a fundamental role in guiding attentional modulation in visual areas. However, the methods used until now were unable to distinguish between direct and indirect effects of the FEF on visual areas. We provide histological evidence that the method of optogenetics can be used to target the fronto-visual and fronto-parietal network and its long-range axonal projections. Based on these results, we inhibited the direct connection of the FEF to visual area MT in one monkey performing a visual spatial attention task. By using optogenetics, we show that the modulation that the FEF exerts on visual area MT during attention results at least partly from a direct input from the FEF. In two psychophysics projects, we investigated the phenomenon of the attentional blink for stimuli processed in the dorsal visual pathway. The attentional blink has so far primarily been studied for stimuli processed in the ventral visual pathway. The results of our first study suggest that an attentional blink affects the whole visual processing system and speak for the existence of a unified attentional system operating comprehensively within the visual system. In the second study, we measured pupil size as a measure for internal cognitive processes in addition to behavioral performance. We show that pupil size can reflect different parameters of the task and could be related to the activity of the locus coeruleus.