How polarization-sensitive interneurones of crickets perform at low degrees of polarization

In crickets, polarized-light information from the blue sky is processed by polarization-opponent interneurones (POL-neurones). These neurones receive input from the polarization-sensitive blue receptors found in the specialized dorsal rim area of the compound eye. Even under optimal conditions, the degree of polarization d does not exceed 0.75 in the blue region of the spectrum and it is normally much lower. The aim of this study is to assess how POL-neurones perform at low, physiologically relevant degrees of polarization. The spiking activity of POL-neurones is a sinusoidal function of e-vector orientation with a 180 ° period. The modulation amplitude of this function decreases strongly as the degree of polarization decreases. However, our data indicate that POL-neurones can signal e-vector information at d-values as low as 0.05, which would allow the polarization-sensitive system of crickets to exploit polarized light from the sky for orientation even under unfavourable meteorological conditions.