Fig. 10.

Segment method to assess responsivity of tectal units to magnetic field (LFP signal). A tectal unit was stimulated by varying the vertical component of the magnetic field in 30 s for a complete 360° excursion (first row). To assess the existence of possible magnetic responses the 30 s segment was subdivided in six 5-s segments. For each segment we calculate, for control (no magnetic field, trace not shown) and stimulated conditions (magnetic field + blue light, second row), the histogram of amplitude values (third row) or the histogram for rectified amplitudes (fourth row) of the LFP signal. No differences were detected for direct or rectified amplitudes. The empirical distributions were similar for control (dot) or for stimulated (continuous curve) conditions (third and fourth rows). The small inset, third row, shows the standard deviations in both cases, and when they are taken into account, no significant differences are detected between control and experimental conditions. Thus, the magnetic field does not stimulate tectal neurons as it does not influence the amplitude of LFP signals (either direct or rectified) in specific phases of the magnetic field