Modulation of neuronal activities by iontophoretically applied catecholamines and acetylcholine in the primate motor cortex during a visual reaction-time task.

Single neuronal activities in the primate motor cortex were modulated by iontophoretically applied acetylcholine (ACh), noradrenaline (NA) or dopamine (DA) while monkeys were performing a visual reaction-time. task. ACh caused general increases of the discharge activities of both the background baseline and the task-related activity peaks, whereas NA caused decreases mainly of the baseline. DA caused activity increases in half of the tested neurons, and decreases in 25% of the neurons. NA modulated the firing rate to enhance the signal-to-noise ratio of the related activities. ACh and DA, by contrast, subserved to enhance the synaptic transmission in the motor cortex.