Behavioural responses to electrical and visual stimulation of the toad tectum

Slow potential shifts in brain structures have been recorded and correlated with motivational state in several species. Previous studies have also found that application of an electrical current to the surface of brain tissue generates such slow potential shifts. The present study was conducted to examine if imposed dc shifts to the brain influenced motivation in the toad (Bufo bufo). Toads (B. bufo) had stimulating electrodes implanted on the surface of each optic rectum. After 1 day of recovery combined dc stimuli and a prey-like visual stimulus were presented to the animal. A current-dependent increase in prey-catching activities occurred with dc currents from 0.1 to 500 mu A and in avoidance behaviours from 50 to 500 mu A. There is also evidence of additivity of dc and visually induced negativity increasing some behaviours. The dc current was applied in order to start a movement of ions through the brain structure but more specifically through radial glia. The resulting flux of ions is thought to be responsible for the recorded slow potential shift associated with motivation and these experiments hopefully shed further light on the possible neuromodulatory role played by radial galia through the spatial buffering of potassium and the associated slow potential shifts. (c) 2006 Elsevier B.V. All rights reserved.