The chemistry for right or left is specific in these worms, being on one side of the brain or another with some slight differences, and where these differences weigh only slightly they weigh enough to set the ingesting worm to favor connecting to one side of the brain or another. A transferred learned response, proving that the brain works by chemistry, chemical paths and chemical images. Emotions are chemistry, generated from within. Sensations, the power of the brain to retain ideas, is also intrinsically allied with chemical reactions. In fact, it forms the base.
Hormones stimulate feelings, and homones are created by nervous stimulation of the glands.
It is all intertwined. Senses receive light rays or heat, or other such stimuli that create chemical reactions that travel along nerves and are then stored in your brain by chemical changes. These chemical changes are so slow to deteriorate that you die before many of them do, which is why you have a memory. This is a chemical store, similar to a computer databank, in which chemical changes are virtually permanently etched in your brain. Complex thought can be broken down into thousands of steps, where sensory memories are related.