State-dependent visual processing
Brain state can fundamentally control how visual cortex processes information. We have shown that the effects of locomotion extend throughout the mouse early visual system, where it affects pupil size, and modulates the activity of dLGN and decorrelates responses in primary visual cortex (Erisken et al. 2014).
In a project embedded in the SFB 870, we follow up on this work and consider the effects of locomotion within the thalamo-cortico-thalamic loop. Furthermore, we investigate thalamic activity as a function of arousal, which we infer from pupil size, whisker pad movements, and locomotion (funded by SmartStart2).
Together with Aman Saleem (UCL), we have organized a Mini-Symposium at SfN 2017 that has discussed novel perspectives of sensory processing during active, multi-dimensional behavior in different systems (fly vision, rodent vision, audition, somatosensation) and at different processing levels (fly lobula plate, mammalian thalamus and cortex).
Feedforward and feedback processing in thalamus
As an ideal model circuit to understand the role of feedback in the visual system, we study how cortico-thalamic feedback modulates activity in the dorsolateral geniculate (dLGN) of the thalamus and in the thalamic reticular nucleus (TRN). In ongoing projects, we work with transgenic mice expressing Cre-recombinase in L6 cortico-thalamic pyramidal cells and use optogenetic methods to causally probe their impact on thalamic activity (funded by DFG).
Neural basis of visual behavior
Neural activity, even in early sensory areas, is modulated by visual behavior (Khastkhodaei et al. 2016; Saleem et al. 2017). In the past, we have shown that visual behavior in mice does not only reflect stimulus properties, but can also heavily be influenced by non-sensory factors, such as past rewards or past choices (Busse et al. 2011). In a project within the RTG Perception in Context 2175, we follow up on this observation and combine electrophysiological recordings, optogenetics and computational modeling (in collaboration with Thomas Wachtler, LMU) to gain a deeper understanding in the neural circuits and mechanism underlying history-dependent visual processing.
We have summarized our views on the microcircuits in mouse primary visual cortex underlying visual behavior in a review for Current Opinion in Neurobiology.
Normalization in the visual system
The appropriate relationship between excitation and inhibition is crucial for normal brain function, including the processing of visual information. In the past, we have shown that parvalbumin-expressing (PV+) inhibitory interneurons in primary visual cortex contribute to contextual modulations, potentially via controlling stimulus drive (Vaiceliunaite et al. 2013).
In a project part of the DFG-funded priority program “Computational Connectomics”, we study in collaboration with Dr. Tatjana Tchumatchenko at the MPI for Brain Research in Frankfurt how we can infer connectivity from key response properties of excitatory and inhibitory neurons in mouse primary visual cortex.
Alterations of inhibitory activity have also been proposed to underlie several neuropsychiatric diseases, including schizophrenia. In ongoing work, we investigate the impact of impaired inhibitory circuits on network oscillations and visual processing.
Natural stimuli for mice
Across species, visual systems have evolved to efficiently cope with the specific information encountered in the animal’s natural habitat. Visual stimuli that are matched to natural conditions are therefore essential to understand how neurons process visual information. In a project with Thomas Euler (CIN, University of Tübingen), we explore the visual input received by the mouse visual system under natural conditions and how such input is processed along key stages of the early visual system (funded by SFB 1233).