The PIM extends slightly above and behind the classically defined limit of the inferior pulvinar, the corticotectal tract. 
To determine whether this relative motion sensitivity depends on input to the colliculus from visual cortex, we studied colliculus cells in immobilized, anesthetized monkeys after unilateral thermocoagulation, or anesthetic blockade, of the corticotectal tract at the level of the pulvinar. In the colliculus ipsilateral to the corticotectal tract lesions, relative motion sensitivity was significantly reduced when compared either with the colliculus in intact animals or with the colliculus contralateral to the lesion. Anesthetic blockade of the corticotectal tract had similar effects; relative motion sensitivity, but not background motion sensitivity, was lost following injection of mepivacaine or bupivacaine. The corticotectal tract lesions, but not the anesthetic injections, also had minor effects on flash-evoked responses and spontaneous discharge rates; these effects may reflect a retrograde response of some tectopulvinar cells to injury of their axons by the corticotectal tract lesions. In the colliculus opposite the corticotectal tract lesion, relative motion sensitivity was similar to that in normal animals.
In addition, in some animals, cortical tracts, such as the anterior commissure, corpus callosum, and a corticotectal tract, were labeled.
Descending input by way of the corticotectal tract is probably essential for the detection process.
These results suggest that the corticotectal tract may inhibit the appearance of LTP via the GABAergic interneurons within the superficial gray layer (SGL)..
We conclude that whereas thermocoagulation of the pulvinar severely damages the corticotectal tract, kainic acid lesions spare these fibers of passage.
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