Improvement of Visual Short-Term Memory Characteristics in Monkeys: Effect of an Antioxidant

Visual short-term memory was tested in a delayed-discrimination task on rhesus monkeys before and after a systemic injection of the antioxidant oxymetacil (4 – 7 mg kg⁻¹). Monkeys had to discriminate stimuli with different visual attributes (colour, orientation, spatial frequency, size, contrast, spatial relationships between visual objects) by a delayed (0 – 32 s) instrumental reflex. Oxymetacil had no influence upon visual discrimination without delay, but after injection of this drug the delayed discrimination (associated with mechanisms of short-term memory) of different stimuli was significantly improved. Oxymetacil increased the duration of short-term storage of spatial information by a factor of 2 – 4 and decreased motor reaction time. Application of oxymetacil in the same doses produced similar results for delayed discrimination of black-and-white gratings, or geometrical figures of different orientations and size. The duration of short-term information storage was doubled or trebled and the motor reaction time was decreased. If monkeys were required to discriminate colour figures, the duration of short-term information storage was also doubled, being longer than for any of the other tasks. The results are discussed in terms of effects on cortical interregional synchronisation mechanisms responsible for control processes such as attention.