[Effect of norepinephrine on the frontal neuron activity related to delayed discrimination task in monkeys]

To study the role of norepinephrine (NE) in the cognitive function of the brain, the effects of NE, tolazoline (TOL) and propranolol (PR) on the activity of frontal neurons were examined in 3 rhesus monkeys (Macaca mulatta) during the performance of a delayed visual discrimination go/no-go task. Of the 230 task-related neurons recorded from the area medial to the superior ramus of the arcuate sulcus, 159 neurons were tested with NE applied microiontophoretically. Of these tested neurons, 11 neurons were related to starting period, 28 neurons to cue period, 66 neurons to delay period and 54 neurons to response period. About 2/3 of these neurons increased in discharge rate in the task, and the rest decreased. For most of the neurons with decrease of discharge rate in the delay period, the discharge rate was further decreased during application of NE. During application of TOL or PR, the discharge rate was increased and the effect of NE was antagonized. The present results suggest that NE may play a role in the cognitive function of the frontal neurons, particularly in attention and short-term memory, and may be involved in the inhibitory process of the neuronal activities.