Electroencephalographic studies on arousal in the goldfish (Carassius auratus).

Goldfish with implanted intracranial electroencephalographic (EEG) electrodes showed high-voltage slow activity of 6-9 Hz and a low-voltage fast activity of 16-24 Hz when resting in the dark. The former frequency was prevalent in the telencephalon, diencephalon, and midbrain but remained only in parts of the midbrain and cerebellum when the fish was left resting in an illuminated environment. In this latter condition the 16-24 Hz activity became predominant. Presentation of two stimuli, the onset of illumination and the passage of a moving edge across the source of illumination, caused bradycardia and a reduction in ventilatory rate, associated with behavioral arousal in this animal. An increase in the amplitude of 16-24 Hz activity in the EEG also occurred, most evident in the anterior and posterior tectum and dorsomedial and posterior telencephalon. Anterior tectal EEGs, on arousal, had the shortest latency and longest duration and were most resistant to habituation on repeated presentation of the moving-edge stimulus, the dorsomedial telencephalon showing similar characteristics to a lesser degree. It is suggested that these areas may be intimately concerned with the arousal response in teleosts.