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Like Lauren, I was very suspicious of a narrow definition of an input as something generated outside the nervous system.   Although I understand that most input into the brain comes from outside the nervous system, I am skeptical of a definition of input that excludes input from one part of the brain to another part of the brain especially since the various parts of the brain are massively interconnected.  I also am skeptical as to how activities such as stomach growling, seizures, dreams, etc., which are considered to be “pure outputs” - outputs without inputs.   Although not directly generated by outside events – inputs, there is still an out of body event that indirectly contributes to the generation of these “pure outputs.” For instance, a stomach growl may be triggered by absence of food and dreams are influenced by what happened outside the nervous system sometimes in the distant past.  Therefore, I think one or both of the terms, input and/or output, should be broadened to somehow include what are considered “in body effects,” outputs that are produced by inputs from the body.”

The human brain is an example of a non-traditional stimulus/response system.  It does not always require external inputs to generate outputs. This allows for creativity and advantageous adaptations.   For example, when Galileo was reaching the end of his life, he lamented that his world was getting smaller because he was diminished to his shrinking five senses. Nevertheless he could reflect and powerfully express his situation.  Another example is Beethoven.  At a young age, he went deaf, but could generate powerful sensory outputs - some of the world’s greatest music!