The idea that our thoughts and moods are linked to an individual’s level of "happiness" has a surprising outcome rooted in genetic testing. Hedonic well-being (the subjective judgments of external experiences that produce a state of happiness) is determined to produces a cellular expression that produces more inflammatory cells in an immune response and less antibody production. In contract, eudaemonic well-being (intentional expression of interior beliefs and values that produce actions) produces .lower levels of inflammatory cells and greater levels of antibodies. 

Barbara L. Fredrickson, Karen M. Grewen, Kimberly A. Coffey, Sara B. Algoe, Ann M. Firestine, Jesusa M. G. Arevalo, Jeffrey Ma, and Steven W. Cole 
A functional genomic perspective on human well-being
PNAS 2013 110: 13684-13689.

The aging brain is a heterogenous process and varies individually, case by case. Neuroplasticity and neurogenesis aid the aging brain in creating new neural structure, thereby minimizing any impact of asymptomatic pre-clinical lesions.

• "Neuroplasticity, defined as the ability of the neuronal system to respond to intrinsic and external stimuli by reorganizing is structure, connections, and functions, is of great importance for the aging brain.
  
• Recent neuroimaging data have provided changes in aging brain that reflect compensatory mechanisms or neuronal restitution. Larger brain and hippocampal volumes and neuronal hypertrophy were associated with preserved cognition despite a high burden of AD pathology."
  

(Kurt A. Jellinger, MD, PhD; Johannes Attems, MD, PhD, 2013, Neuropathology, cerebral aging, and neuroplasticity ,Dialogues in Clinical Neuroscience - Vol 15- No. 1)

Experiencing stressful situations prompts a cascading neuropsychological response, in our brains and in our bodies.
During episodes of stressful encounters, the function of the hypothalamic-pituitary-adrenocortical (HPA) axis acts as a regulator,. The HPA is both influenced by and provide feedback to the hypothalamus, pituitary gland and adrenal glands. The HPA function is a primary aspect of the neuroendocrine system in the stress response cycle, including bodily regulation of digestion, the immune system, emotions and moods, sexuality and the inflow and outflow of energy. It serves as a central mechanism for the complex interactions of hormones, glands, and parts of the general adaptation syndrome (GAS). The HPA axis combined with corticosteroids produces the physiological response to stress. (Lange C, Zschucke E, Ising M, Uhr M, Bermpohl F, Adli M., 2013).

#hypothalamicpituitaryadrenocorticalaxis
http://www.ncbi.nlm.nih.gov/pubmed/23931983

Not only do our brains sprout new neurons based on experiences we have (via #neurogenesis and #neuroplasticity) but specific activities help protect your brain. This brain growth-protection is based on the "use it or lose it" premises:

1. Never stop learning. 
2. Immerse yourself in another culture. 
3. Seek out tough "stretch" assignments.
4. Manage stress. 
5. Have lots of friends. 

I'll add to this list, exercise, seek novelty in new experiences, and have fun!