title: Non-linearities in response properties of insect visual cells: an analysis in time and frequency domain.
abstract: Intracellularly recorded voltage responses of the visual cells of the blowfly (Calliphora erythrocephala) were analysed in the time and frequency domains. The photoreceptors were stimulated with pulse (impulse), sine, sine-sweep and pseudorandomly (white noise) modulated green light. The blowfly photoreceptor responses, as analysed from the linear transfer functions, seem to arise from a system similar to that of cascaded low-pass filters, with a corner frequency at about 63 Hz (SD +/- 12 Hz). The system is likely to have at least five poles, including one linear second order term, and a pure delay element. Arising from the non-linearities a second harmonic can be seen in the power spectra of responses elicited by sine modulated light. This non-linearity is at least partly explained by the self-shunting property of the membrane voltage response. Light adaptation increases the non-linearities in frequencies lower than 20 Hz, as seen in the decrease of the coherence function with the signal-to-noise ratio remaining constant. Light adaptation also accelerates the transduction process and it appears in the linear transfer function in a form typical to negative feedback. With low stimulus frequencies it causes a 'phase lead'-type non-linearity. In addition, the sine-sweep responses show quite different frequency characteristics in respect of depolarization and repolarization. Lateral inhibition between photoreceptor responses recorded from retinular cell axons in the lamina appears as a drop in gain and as an increasing phase-lag in frequencies from 30 Hz upwards in linear transfer functions. The source of this capacitive-like coupling can be considered to be in the high resistance barriers compartmentalizing the second optic ganglion into discrete anatomical units.
authors.affiliation: Department of Physiology, University of Oulu, Finland.
authors.forename: M
authors.initials: M
authors.lastname: Weckström
authors.forename: E
authors.initials: E
authors.lastname: Kouvalainen
authors.forename: M
authors.initials: M
authors.lastname: Järvilehto
mesh_terms: D000221:Adaptation, Ocular; D000818:Animals; D004558:Electric Stimulation; D008027:Light; D009117:Muscidae; D010786:Photoreceptor Cells / Q000166:cytology / Q000502:physiology*