It is hard today to deny that perception and thinking are functions of the brain. We will never know the paths that signals take to generate a memory. That there are such paths, however, is not in question. Learning is indeed a private, internal process that takes place in the head of the learner, and therefore cannot be caused by an external agent, human or otherwise. To say that an external agent cannot cause learning is only to say that such an agent cannot itself stabilize the synaptic junctions needed for learning to occur.
External elements can of course have a remarkable influence on learning.
Indeed, learning in most cases is influenced, or stimulated, primarily by external agents. It is precisely here that teaching is critical. One unexpected and perhaps unwelcome result of seeing learning as a biological process is that we might begin to concentrate on the common aspects of learning in different people, not just on the differences among them. At one level, the idea is beyond challenge. Yet, the synaptic stabilization model suggests that when several people all learn the same thing, they all fire repeatedly whatever synaptic junctions they have available to enable understanding.