Thinking is sledding
The brain-sled metaphor is conceptually similar to the brain-train metaphor. It associates thought patterns with paths a sled takes on a snowy hill. If a snow path has been followed repeatedly, it develops a form of attraction or magnetism, because of the snow trail which is differentially smooth. Similarly, thought patterns which have been followerd repeatedly are hard to break out of, because of the differentially luring trail in mental space. The abstract brain structure corresponds to the snowy hill itself and its trails.