Electrical activity in the optic tectum and colour change in the minnow (Phoxinus phoxinus L.)

The electrical activity of the optic tectum was recorded from the minnow under various conditions to investigate its relationship to colour change. The superficial E.E.G. was found to consist of two rhythms a 6–14 Hz (20–112 V) and a 18–24 Hz (6–18 μV). When the fish were deeply anaesthetized the E.E.G. was reduced virtually to nothing. Almost no activity was present in the optic tectum 30 min after bilateral blinding. There was an increase in activity after 5 h and this continued for 5 or more days but never returned to normal. In darkness the activity of the superficial E.E.G. first increased and then decreased, and when the eyes were re-exposed to light the activity increased again. The E.E.G. patterns were recorded and analysed from various depths and positions in the optic tectum during background reversal. In the stratum plexiforme et fibrosum externum, plexiforme internum and griseum internum no changes were observed. In the stratum fibrosum profundum and griseum periventriculare an increase in the high-frequency activity of approximately 10 Hz was observed on a black background.