Imposing structure and interpretation on the multitude of sensory input we collect constantly through our senses is a primordial aspect of brain functioning. When scanning our surroundings we automatically segregate the visual scene into objects versus background. Although seemingly happening without any effort, the underlying computations performed by the brain are massive. Perceiving ambiguous figures exemplifies this complexity clearly. In case of the famous Rubin Face-Vase illusion we can perceive either faces or vases as figures against a background. Moreover we are able to consciously switch between percepts.
Previous studies in the non-human primate have shown that already at the very early stages of visual processing neurons respond differently when stimulated by part of the visual scene belonging to an object than to the background. It is proposed that feedback connections from higher visual areas drive this figure-background modulation, but currently no technologies exist to examine this hypothesis adequately in the primate brain.
Recently, Heimel (NIN) discovered the same figure-background effect in the visual cortex of the mouse. The possibility to easily manipulate neuronal activity in mice by illuminating the cortex will enable me to examine the function of feedback connections during figure-background modulation, a process also important for conscious vision.
After thorough mapping of single and laminar response properties of V1 neurons in a figure-ground modulation paradigm, I will chart its network, i.e. characterize the information flow from V1 to higher areas, in real-time and with single cell resolution by means of two-photon calcium imaging. Both protocols are available and ready-to-use at the NIN. Finally, while recording single/laminar neural activity in V1, I will turn to transgenic mouse lines expressing channelrhodopsin-2 (ChR2) and individual viral injections of archaerhodopsin-3 (Arch), to modulate/prevent feedback activity into V1.
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