A LIGHT ON VISION

Controlling conscious visual perception with light

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 Obiettivo del progetto (Objective)

'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.'

Introduzione (Teaser)

The brain is a complex organ that processes visual stimuli through combinations of neural activation and inhibition. Optical illusions occur as a result of contextual modulations during neural processing and surround suppression is one such mechanism.

Descrizione progetto (Article)

Studying neuronal circuitry in depth to understand contextual modulations has not been possible until recently due to limited spatial and temporal resolution. The recent discovery of optogenetics has enabled unprecedented cell specificity and spatiotemporal control of neural activity.

EU-funded scientists of the project 'Controlling conscious visual perception with light.' (A LIGHT ON VISION) employed optogenetics along with electrophysiological recordings of neural circuitry in the primary visual cortex (V1) of the brain. Researchers focused on elucidating contextual modulation and surround suppression in particular. Surround suppression is mostly seen in V1 where the neurons produce a smaller signal in response to a stimulus that exceeds the neural receptive field.

Several hypotheses have been used to describe this phenomenon but corroboration was previously not possible. Neural activity was recorded using laminar electrodes in the V1 cortex in anaesthetised mice, and feedback signals were selectively inhibited through optogenetic interventions. For selective inhibition, light-gated cation channel channelrhodopsin-2 was expressed in inhibitory neurons using blue light for activation.

Results revealed that surround suppression consistently occurred after initial response, which is indicative of recurrent processing. The importance of intercortical communication was tested by interrupting feedback signals from higher visual areas such as the lateromedial or anterolateral areas during V1 recording. Preliminary findings confirmed surround suppression theory as no decreased V1 neural response to larger stimuli was seen during interruption of feedback signals.

Further analyses are ongoing to validate the findings. Tests will also be conducted on alert mice to supplement the preliminary findings.

Project activities have clearly revealed the potential of optogenetic interventions in unravelling complex brain functions through selective activation or inhibition. This could revolutionise the field of neurobiology. Future applications include treatment and rehabilitation of psychiatric and other mental disorders.