Something else that is interesting, is that you actually CAN exercise the brain and make new connections too.
Much of our life, if not all of our waking moments, is in response to stimulus. The brain has formed these synapses through a lifetime of training. We see, smell, feel, and generally "sense" the world around us, then we react accordingly.
As information, or instructions, move from one neuron to another, it passes through a void. This is where neurotransmitters, like dopamine, does its job: transferring the signal from a neuron to a receptor.
If we use a synapse a lot, the neurons actually grow. They can grow to the point where they touch each other, which quickens the reaction time. And there you have an automated response.
This system not only determines what we do, but how we feel about it.
Therefore, just by repetition, you can not only change a response to a stimulus, but how you feel about it.
For example, something I learned when doing my 30 day discipline challange was standing tall and putting my shoulders back a bit. Especially when talking to others. This was something that would enter my mind while talking to someone mostly. Well, a couple weeks ago, I caught myself doing that automatically as I was talking to a superior.
See... When I put my shoulders back a bit, I feel more confident. A lot more confident actually. To the point where I can say, or do, nothing wrong.
Same goes for me dwelling on the past. As soon as a negative thought of the past enters my mind now, I immediately become more aware of my surroundings. At first, I had to force myself to be in the "now" by taking deep breaths then purposely looking out at the weather if I could. Now, it's automatic.