Behavior of luminance neurons in the pretectal olivary nucleus during the pupillary near response.

In cats and monkeys, extrastriate visual areas that have been reported to be involved in the near triad of pupilloconstriction, convergence, and accommodation have well-defined projections to the pretectal olivary nucleus (PON), the retinorecipient pretectal nucleus mediating the pupillary light reflex in mammals. We have therefore used alert, behaving primates to investigate the possibility that PON neurons are involved in the pupillary near response in addition to the pupillary light reflex. Single-unit recording revealed that PON luminance neurons significantly increased their firing rate with increases in retinal illumination and the resultant pupilloconstriction. In contrast, their activity did not significantly increase during pupilloconstriction elicited by near viewing. Thus the behavior of PON luminance neurons is appropriate for their participation in the pupillary light reflex, but is inappropriate for any proposed role in the pupillary near response. This result strongly suggests that neurons in the primate PON are solely related to the pupillary light reflex and that the cortical projections to this pretectal nucleus are related to this reflex and do not play a role in the pupillary near response.