Neural mechanisms of spatial colour contrast processing and colour constancy in Drosophila

• Applicant: Dr. Christopher Schnaitmann
• Subject Area: Cognitive, Systems and Behavioural Neurobiology
• Term: from 2020 to 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449783245

Colour vision facilitates both scene segmentation and object recognition. It relies on complex neural computations, a key feature being the comparison of signals from photoreceptor classes with different spectral sensitivities. Postsynaptic to photoreceptors, spectral processing includes spatial and temporal computations, crucial for detecting spatial colour contrast which enhances segmentation and for ensuring colour constancy under varying illumination. However, the circuit architecture and computations enabling these functions remain largely unknown. We aim to address this problem by combining genetic, physiological and behavioural approaches. We have developed an physiological approach to study spatio-chromatic processing in Drosophila and identified key postsynaptic neurons with diverse response properties. Among these, Dm8 displays a double-opponent receptive field, indicating its role in encoding spatial colour contrast. Given that double-opponent neurons are characteristic of systems maintaining colour constancy, this finding suggests that Drosophila possesses colour constancy. Building on our recent work, this project now aims to unravel the microcircuits and mechanisms implementing the encoding of spatial colour contrast and colour constancy, and elucidate how chromatic and spatial information are integrated. Starting with Dm8 neurons, we will conduct a comprehensive analysis of its spatio-chromatic response properties, examining their sensitivity to spatial colour contrast, the influence of stimulus size and varying illumination. Recent connectomic studies have revealed several cell types that receive significant input from Dm8, forming parallel visual pathways. We will investigate the spatio-chromatic response properties of these cell types to determine the specific visual features they process. To elucidate the underlying circuit mechanisms, we will conduct physiological experiments combined with genetic tools that allow manipulation of neural activity. To link our physiological findings to the behavioural requirement, we will use a novel setup with precise control over spatial and chromatic patterns. Here, conditioning experiments will assess the role of spatial colour contrast in Drosophila’s colour discrimination and evaluate their ability to maintain consistent colour choice under varying lighting conditions. Through this multidisciplinary approach, our research aims to provide critical insights into the neural circuits that integrate spatial and chromatic information, thereby enhancing our understanding of visual perception and the underlying mechanisms that enable colour contrast processing and colour constancy.

• DFG Programme: Research Grants