"Evidence for the connection between happiness and attention is found in neuroscience: attentional control is located in the pre-frontal cortex. Those with a weak pre-frontal cortex also have an inability to inhibit their limbic system (to control their emotions). Most major mental health conditions are associated with a weak pre-frontal cortex.
Neuroscience has also found evidence for 'experience-dependent neuroplasticity.' In other words, our brains change with experience. We get good at (and grow thicker neuronetworks to support) the mental activities we engage in repeatedly. The most powerful way to change your brain is not medication, but behavior, and in particular, mental behavior.
With physical exercise, we can tell which muscles have become the strongest through exercise. Our strongest mental habits are the ones most easily activated, that are quickly and effortlessly available to our consciousness...the good news from neuroscience is that positive qualities of mind such as attention, kindness, and compassion are skills we can cultivate through practice and training. Contemplative studies point to an array of these practices to grow new mental habits."
See also: Britton Lab