I don't shut out people. But somebody on here wrote that any object that hasn't been used/moved in the last 24-48 hours becomes invisible to the INTP and I am under the impression that it works the same way with people. It's: connect, exchange views and information on each other and then the intensity of the contact dwindles. The friendship can remain intact for many years if the other person isn't offended because I only call once every few months - not because I don't care about them but because it doesn't occur to me, either because I don't want to impose myself or, even more likely, because I am so absorbed in whatever else is going on in my head that I forget all about them. That doesn't mean I don't like them any more or don't want to see them or don't enjoy spending time with them. They just disappear from my radar for a while ...and I from theirs, involuntarily, for not calling often enough. But I am almost always grateful and happy when they contact me - it takes some of the burden of friendship maintenence off my shoulders, which is a great relief.
As for the exchange of knowledge and ideas. Usually a new person will spark my interest in certain new topics. But I don't probe them for information (unless they clearly want to talk about it) but rather use the encounter as an inspiration to do some independent research of my own.
I do need some amount of human contact, of course, but that is usually in the hands of 1-2 people at a time. Usually a partner and/or a best friend. Everybody else is a nice, pleasant bonus but work to maintain if they expect too much initiative from me. I don't mean any harm - it just usually doesn't occur to me to call no matter how much I like them.