Wavelength-dependent waveform characteristics of tectal evoked potentials in rainbow trout

Abstract

Wavelength-dependent properties of tectal evoked potentials (TEPs) in rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), were examined. It was found that TEP waveforms show distinct variation as a function of wavelength. In addition, the data suggest that the On and Off channels of the tectum each possess different wavelength-dependent characteristics. Middle wavelength stimulation typically evoked a waveform similar to that reported for another anamniote vertebrate, the toad (genus Bufo Laurenti, 1768). For the On and Off responses, this waveform comprised two negative deflections, N1 and N2, which were interrupted by a positive deflection, P2. The N2 deflection was followed by a final positive deflection, P3. Principal component analysis revealed that the N2–P3 complex of the On response was significantly more pronounced at longer wavelengths. In contrast, the N2–P3 complex was most pronounced at middle wavelengths for the Off response. The N1 deflection was relatively invariant with respect to wavelength. Should colour-opponent tectal units provide a significant contribution to the TEP, it is probable that its waveform characteristics provide signs of underlying neural processes which facilitate colour discrimination.