Dr. Theo Mota (in cooperation with Benjamin Paffhausen)
Very little is known about the receptive field structure and its relation to spectral sensitivity in visual neurons of the central bee brain. Here we analyze these features by combining extracellular electrophysiological recording in central visual neuropils to precise stimulation of small visual-field regions with distinct colors. Visual stimuli are produced by three distinct monochromatic LEDs matching the absorption peaks of each bee photoreceptor in the UV, blue and green regions of the spectrum. These three LEDs are placed inside a small dark chamber with a circular window covered by UV-transmitting diffusing material, thus allowing different monochromatic or color mixture presentations. Two articulated arms connected to fast running DC motors allow presentation of chromatic stimuli subtending a visual angle of 10° within different regions of the visual field. After repeated random stimulation of the compound eye in all possible visual-field regions, we have been able to map the receptive field of recorded neurons for UV, blue or green. In addition, we perform stimulation with different color mixtures composed by these three monochromatic stimuli. By analyzing spectral sensitivity and receptive field structure, as well as other response properties of neurons in the lobula, lateral protocerebrum and vertical lobes, we aim at understanding how color coding is organized in these high-order integrative centers.