Our main goal remains to understand dynamic relay functions of the LGN with a continued recent emphasis on the in vitro slice preparation. We have recently proposed that thalamic (and perhaps other brain) circuitry can be divided amongst drivers and modulators, and our proposed experiments are related, some more closely than others, to this theoretical framework. Drivers bring the main information to a thalamic nucleus to be relayed to cortex, and modulators are all other inputs, which affect the relay. In LGN for instance, the drivers are the retinal input, and the modulators are all nonretinal input. A closely related theme is the different function of ionotropic receptors, while modulators activate metabotropic (and often also ionotropic) receptors. We shall also explore how these different receptor types affect firing mode (burst or tonic) of relay cells. Our work will emphasize physiological and pharmacological experiments with a secondary emphasis on complementary morphological studies. We begin with an analysis of retinogeniculate transmission (driver input) in the context of local interneuron circuitry (a modulator), particularly the synaptic triadic arrangement between interneuron and retinal terminals and relay cells. We shall extend this approach to begin addressing questions of processing through the LP-PUL, both because this proves a powerful test of the hypothesis and also because we simply need to know much more about this important thalamic structure. As a way to help address these issues indirectly in LGN and LP-PUL by more powerful experimental means in analogous somatosensory thalamic structures (VG and POm), we shall develop a relatively new in vitro preparation with an intact thalamocortical circuit. Finally, we shall initiate experiments designed to test the possibility that the driver/modulator distinction can be extended to cortical circuitry. We shall begin by determining whether geniculocortical terminals in layers 4 and 6 of visual cortex activate ionotropic or metabotropic receptors, or both. We shall then begin to look at certain corticocortical pathways to and from various areas of visual cortex (areas 17, 18, 19, and the lateral suprasylvian area) to address the same question.