Cortical modulation of retinal afferent signals that drive pupil responses in man

摘要

Objective The purpose of this study was to establish whether the pupil light reflex (PLR) response involves more than one component and the extent to which the effectiveness of such components is modulated by the cortex. Background Pupil responses to light in man have been associated entirely with subcortical projections, and this view was supported by some clinical observations which suggest that the pupils continue to respond normally to sudden changes in room illumination, even when the patients are cortically blind [Brindley et al. 1969]. This assumption is however inconsistent with other experimental observations which suggest that some aspects of the pupil light reflex response also require the normal functioning of the geniculostriate projection and the primary visual cortex [Harms 1951; Cibis etal. 1975; Kardon 1992]. In this study we carried out a number of diverse experiments to investigate whether the PLR response involves more than one component and the extent to which the effectiveness of these components is modulated by the cortex. Results The findings that have emerged from a number of different experiments reveal the existence of two pathways that drive the "sustained'' and "transient'' components of the PLR response. The transient component is either absent or reduced significantly in the absence of a normal geniculostriate input. Both components are however absent in patients with Parinaud's syndrome that involves damage to the pretectal region of the midbrain. Conclusion The "transient' component of the PLR response requires the normal functioning of the geniculostriate pathway and the visual cortex and is likely to be mediated through a direct projection from the cortex to the OPN. This hypothesis accounts for the absence of the transient PLR component in patients with damaged primary visual cortex and the absence of both components in Parinaud's patients.