Andrianov V V
Fiziol Zh SSSR Im I M Sechenova. 1986 Nov;72(11):1486-92.
A directed visual attention of the cat towards the site of reinforcement entailed an increase of the firing rate of the visual cortex' neurons. Neurotransmitters applied microiontophoretically altered the firing rate within time intervals corresponding to the level of visual attention and perception of visual stimulus.