The activity of neurons in any given region of the brain depends on, to a large extent, the stimuli that region receives from other regions. Because regional activity of one human subject to another may differ slightly when doing a sensory or cognitive task, not everyone starts at the same baseline. In animal experiments, which were done under very well controlled conditions, there are still slight variations in the baseline in the same region of the brain and the incremental changes from baseline alone cannot accurately reflect the amount of energy used. Only the total energy used can reflect the total activity within a region. However in analysis of functional imaging data (e.g., in cognitive neuroscience) the baseline signal is differenced away.