Spike rate modulation of locus coeruleus neurons associated with visual spatial attention in monkeys

Spike rate modulation of locus coeruleus neurons associated with visual spatial attention in monkeys. We trained two rhesus monkeys to selectively attend one of two visual stimulus locations while performing a visual orientation change detection task. Once the animal fixated, two Gabor sample stimuli appeared for 200 ms, one in each hemifield. After a brief delay (200-300 ms), a Gabor test stimulus appeared in one of the locations. The monkey had to report whether the test stimulus had a different orientation than the sample that had appeared in that location by making a saccade to one of two colored saccade targets after the fixation spot went off. The locations of the saccade targets were interchanged randomly across trials. Spatially selective attention was controlled in blocks of trials by different reward sizes and by varying the test stimulus probability for the two locations. While the monkeys did the attention task, we recorded simultaneously from populations of LC neurons (monkey S, n = 229; monkey P, n = 185). Recorded neurons were classified as phasic responsive to visual stimulus (phasic, monkey S, n = 89/229; monkey P, n = 74/185), pre-stimulus fixation responsive (non-phasic, monkey S, n = 88/229; monkey P, n = 53/185) or saccade related (saccade, monkey S, n = 104/229; monkey P, n = 124/185).