How much benefit can one expect from three hours of investment? If this were about, say, weight resistance training, would you expect to have bigger muscles after this program?
Changes in Cortical Dopamine D1 Receptor Binding Associated with Cognitive Training
McNab et al. Science 6 February 2009: 800-802
Working memory is a key function for human cognition, dependent on adequate dopamine neurotransmission. Here we show that the training of working memory, which improves working memory capacity, is associated with changes in the density of cortical dopamine D1 receptors. Fourteen hours of training over 5 weeks was associated with changes in both prefrontal and parietal D1 binding potential. This plasticity of the dopamine D1 receptor system demonstrates a reciprocal interplay between mental activity and brain biochemistry in vivo.
Yes, absolutely, and you will have better muscles. You can have big changes in performance in a few days if you spend more time per day (but whether your muscles look bigger maybe not).
I'm not saying that you get significantly bigger muscles quickly, but you can get better muscles quickly (or perhaps it's due to the lungs/heart?).
BTW 10 lbs per year is a lot. It's more than 12 grams per day which is about 12 cm^3 per day. This is definitely noticeable. Where do you have this information from? Do you have other information like this? I'd be interested to know what exactly makes muscle tissue grow.