Decoding Neural Circuit Structure and Function by Arzu Çelik & Mathias F. Wernet

Author:Arzu Çelik & Mathias F. Wernet
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

10.2.2 Arousal State Modulations in Visual Circuits in Flies

Octopamine (OA) in insects increases the general level of arousal of the animal (Roeder 2005). Many of the modulations of neural activity observed during the transition from quiescence into movement can be reproduced with OA agonists in non-behaving preparations. This may imply that such modulatory activity is associated with changes in arousal levels. However, in insects, it has not been possible to decouple arousal-related modulations from modulations induced by overt movement yet. Therefore, it is still possible that some aspect of OA-based modulations in visual circuits may be related to locomotion-induced motor feedback.

Motion vision is critical for the detection of moving objects in the world, and for monitoring self-movement (Lappe et al. 1999). During flight or walking, the retina is excited with visual flow, known as optic-flow. Optic-flow processing neurons are thought to be important for monitoring self-movement to correct deviations from the intended course. In flies, optic-flow processing neurons are located in the Lobula Plate (LoP) of the fly brain. Because of their large dendritic arbors, expanding across the retinotopical organization of the LoP, these neurons are called Lobula Plate Tangential cells (LPTCs) (Borst 2014; Silies et al. 2014). In each hemisphere of the Drosophila brain, there are three horizontal system cells (HS-cells) (Scott et al. 2002; Schnell et al. 2010), and six vertical system cells (VS-cells) processing optic-flow along the yaw, or the roll (and pitch) axis, respectively (Hausen 1982a, b; Joesch et al. 2008). These LPTCs show graded membrane potential changes upon wide-field visual motion stimuli, they are direction selective, and they are tuned to a preferred velocity of the moving visual stimuli. For example, HS-cells depolarize with front to back motion, and hyperpolarize with back to front motion, and the direction-selective response (the difference between the magnitude of the preferred- and the nulled-direction response) peaks at a best stimulus velocity (Joesch et al. 2008; Schnell et al. 2010). Likewise, VS-cells depolarize with downward motion and hyperpolarize with upward motion, and they also display temporal tuning properties. Recently, it has become possible to record from these neurons while the fly is walking (Seelig et al. 2010) or flying (Maimon et al. 2010). Experiments performed under these conditions have shown that locomotion modulates the activity of HS- and VS-cell. Flight induces a boost in the membrane potential of VS-cells in the absence of visual motion stimuli (Maimon et al. 2010; Suver et al. 2012). Walking and flight also induce an increase in the magnitude of the response of HS- and VS-cells to visual motion stimuli (Fig. 10.2b). Furthermore, during walking, this response increase scales monotonically with walking speed (Fig. 10.2e) (Chiappe et al. 2010; Longden et al. 2014). Last but not least, the temporal tuning properties of LPTCs are modified during locomotion. Walking and flight induce a shift in the sensitivity of HS- and VS-cells towards larger stimulus velocities (Chiappe et al. 2010; Suver et al. 2012), a phenomenon also observed in LPTCs of other fly species (Fig. 10.2b) (Jung et al.

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