Spatio‐temporal responses in the visual cortex evoked from first‐ and higher order thalamic nuclei in tree shrews: a voltage sensitive dyes study

Abstract

AbstractPurpose The primary visual cortex (V1) received its main thalamic drive from the lateral geniculate nucleus (LGN) through layer IV. In contrast, projections from the pulvinar end in layer I, suggesting that pulvinar exerts a diffuse modulatory influence on V1 activity. However, pulvinar projections to extrastriate areas (XC) mostly terminate in layer IV, suggesting that they provide a driver input to XC areas. Thus, one would expect the spatio‐temporal responses evoked by pulvinar activation to be different in striate and XC areas, reflecting the different connectivity pattern (driver vs modulator). We thus measured the spatiotemporal dynamics of voltage sensitive dyes activation in the visual cortex following thalamic electrical stimulation.Methods Tree shrews were anesthetised and bilateral craniotomies were made on the visual cortex. RH1691 was used to stain the cortex. Stimulating electrodes were placed in LGN and pulvinar.Results Stimulation of LGN induced fast and local responses in V1, which propagated to XC and contralateral cortex. The temporal profile of the responses was transient and monophasic in V1, and generally bimodal or tonic in XC. Stimulation of pulvinar induced fast and local responses in XC, followed by activation in V1 and contralateral cortex. The propagated waves in V1 were weak in amplitude and diffuse. Co‐stimulating pulvinar and LGN produced responses that were weaker than the sum of the responses evoked by the independent stimulation of LGN and pulvinar, even when pulvinar stimulation did not produce any responses in V1.Conclusion The pulvinar can exert a modulator influence in cortical processing of LGN inputs while it mainly provides driver inputs to XC.