I am very adamant with my clients about how to maintain their brain health!
I teach them that what we focus our attention on and how we focus our attention has a direct effect on the physical structure of the brain. Because of the brain's neuroplasticity, we can "sculpt" our brain. Generally, this "sculpting" is noticed most in our beliefs about ourselves which then impact our moods, emotions and even our behavior. If we believe mostly negative things about ourselves and we then focus on negatives to validate these beliefs then we are building neurocircuits in our brains that make it more likely for us to focus on and believe negative things about ourselves. Over time we begin to lose confidence, we are afraid to take beneficial risks...and our world gets very small and rigid. Now, certainly these changes don't occur over night -- these effects are subtle and occur over time. But, by being more conscious of where our minds go, we can use the brain's neuroplasticity to work for us -- not against us. Basically, "where we fire is where we wire." If we want to experience a bit more joy and delight - then we need to pay attention to what's going well in our life. If we are okay with misery - then we can focus on what's miserable about our life. By focusing on positive reality we support our amygdala (a little structure deep in the brain) helping it to settle down a bit. This is the structure that is associated with our flight/fight response and when we get too negative it gets very activated and starts telling the brain to release stress hormones. When this happens our nervous systems get a bit whacked. And if this process goes on too long it can have a profoundly negative impact on our physical and emotional health and well-being. Even our immune system can be negatively effected by this!
What can you do? When you notice you are having negative thoughts about yourself you can simply ask yourself, "What's more true?" (it's not all negative -- what's the little bit of positive?) and then bring your attention to that little positive truth about yourself, or to what's going well for you, or to that little bit of goodness you experienced today -- real stuff, not affirmation stuff. This real stuff can be very simple like that first taste of good coffee in the morning or a beautiful sunset or someone giving you a compliment, or knowing that you do your best in life. You bring your attention to that simple experience and notice how your body responds -- the actual physical sensations of your positive experience (warmth around the heart or a nice feeling in the gut) and then linger on those physical sensations for 20-30 seconds. This will allow your brain an opportunity to wire in something positive and over time will help balance out negative tendencies. Your amygdala will calm down as well and you'll have less of those stress hormones flowing through your system. Your confidence will grow, you'll feel more optimistic and life will just look and feel better!
Anyway, I go over this stuff all the time with people! And, it works...bringing them a little more peace, a little more well-being into their lives. Perhaps it'll be helpful for you too!