Dynamic properties of compass neurons in the bee brain

• Applicant: Professor Dr. Keram Pfeiffer
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells ; Cognitive, Systems and Behavioural Neurobiology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 436624328

A fundamental requirement for the remarkable orientation skills, that many animals show is their ability to relate their heading direction to an external frame of reference. Neurons in the brain that accomplish this feat are called head-direction cells (in mammals) or compass neurons (in insects). Each compass neuron signals a specific angle between the animal and an external frame of reference, which in insects is the sky polarization pattern, the azimuth of the sun, or landmark-like cues. The preference direction of the neuron, i.e. the angle between the animal and the stimulus eliciting the highest activity, is usually assessed by slowly rotating a polarizer above, or a simulated sun around, the insect’s head. This is supposed to mimic a rotation of the animal underneath a natural sky. However, such stimuli neglect the dynamic features of natural movement. Both flying and walking insects change their heading not continuously, but abruptly at high angular velocities during so-called saccades, which alternate with segments of pure forward motion. It so far unknown, how insect compass neurons code sky-compass cues under naturally occurring dynamics of movement.Using intracellular recordings from compass neurons in the central complex of bumblebees, we could show that the angle of polarization that leads to the strongest excitation (preferred angle of polarization) is not a static property of the neurons but is strongly influenced by three parameters: 1. The direction of rotation of the polarized light, 2. The angular velocity of the polarized light 3. The previous activity state of the neuron (excited or inhibited). Changes in these parameters lead to shifts of the preferred angle of polarization of up to 60°. This raises the question, how such a system can reliably inform the animal about its current heading. To answer this question, we need to understand the dynamics of the neuronal responses in depth.The goal of this project is therefore to characterize how the velocity dynamics of sky-compass stimuli shape the response properties of compass neurons in the central-complex of bumblebees. We will use sky-compass stimuli such as polarized light (representing the sky) and an unpolarized green light spot (representing the sun) with a broad range of velocities, including naturalistic velocity profiles from published bumblebee flights. We will specifically characterize the tuning properties of compass neurons at different stages of the bumblebee central-complex network as a function of rotation direction and rotation velocity as well as the effects of the history of neuronal activity. The results of this study will help to understand how compass networks can generate consistent heading signals despite highly variable dynamics of their input signal.

• DFG Programme: Research Grants