|MadSci Network: Neuroscience|
Let me first point out that you are correct in saying that our brains are capable of neurogenesis. However, the growth of new neurons throughout life only takes place in two distinct areas: First, the dentate gyrus of the hippocampus. This of course makes sense because this structure is involved in the learning of new short-term memories. Secondly, the subventricular zone generates new neurons for the olfactory bulb. So unfortunately we cannot utilize neurogenesis as treatment for ADD, or ADHD simply because the two structures meditating neurogenesis are not involved with the disorders.
Now, I don't know whom you are quoting in your question, but I think I can help you understand. When thinking about learning and memory and forming new memories it's important to try and see the "new connections" not as new neurons, but instead as the strenghthening or weakening or existing synaptic connections. Though the hippocampus might utilize neurogenesis for new memories, the cortex does not. So when short-term memories are consolidated into long-term memories in the cortex, the brain simply uses existing neurons. For instance a new spine may develop on an existing neuron. You might want to look up spines on the net...I have a feeling you'll be interested in them. Though semantics can be frustrating in neuroscience, be careful with using "neurogenesis" when speaking of new connections....if you read that, it usually means new connections on existing neurons. So finally, yes, the therapies in xistence for the disorders in question do appear to "mask" the problem, however when the problem is a simple imbalance in neurotransmitters, the stimulants prescribed often "fix" the problem perfectly. Plus, it's the best treatment we have other than behaviral therapy...which could take a looong time to work, and thus parents don't go for it. I sincerely hoped I helped in your understanding. If you need further clarification, I'm here.
Try the links in the MadSci Library for more information on Neuroscience.