Neurophysiological correlates of improvements in cognitive characteristics in monkeys during modification of NMDA-ergic structures of the prefrontal cortex.

The effects of modification of NMDA-ergic structures by microdialysis perfusion in the prefrontal cortex (field 8) with NMDA glutamate (2 mM) on visual recognition and short-term memory (STM) were studied in rhesus macaques, using methods based on the deferred differentiation of stimuli of different colors. Impulse activity of neurons in the prefrontal and visual cortex was measured during these experiments, both before and after administration of NMDA. NMDA increased (2-fold) the duration of short-term retention of information and significantly reduced the latent period of the motor response at all delay periods, and also produced significant changes in neuron activity in the prefrontal cortex: depending on the stage of behavior, activity decreased in 60-75% of neurons and increased in 8-26%. NMDA produced significant increases in the cross-correlation coefficients between the responses of neurons in the visual and prefrontal cortex. The results showed that glutaminergic structures in the prefrontal cortex are involved in processes of visual recognition and STM in monkeys. The effect of NMDA, which synchronized cortical neuronal processes, improved the short-term understanding of visual information.