Figure 1

a) Schematic representation of the sequence of events in a single trial. The trial started with the onset of the center LED. The rat was required to poke its nose in the corresponding hole, and stay in this position for 500 ms. At this time, the peripheral stimulus was presented and the center LED was extinguished. The trial ended when the rat poked its nose and stayed for 200 ms in the hole adjacent to the center hole corresponding with the illuminated light. RT (ms) was defined as the time duration between onset of peripheral stimulation and the moment when the rat poked its nose in the correct response hole, provided that it remained there for 200 ms. b) Psychopharmacological data with systemic administration of MK-801. Data from nine rats that were able to reach the performance criterion of 80 correct trials for dosage levels of 0.04 mg/kg or less. At the highest dosage level, only four rats were able to complete more than 80 trials.