Three simple ways of decreasing cognitive decline....

As we age there are toxins that collect in the neurons.  These brain toxins are called Tau Proteins and Beta-Amyloid Plaques.  These gummy things can be increased by stress (I need to find a nursing home now), alcohol and lack of sleep (quality and quantity).
However, to counter-act this the brain uses a system that we call neuroplasticity.  What neuroplasticity can do is work with neurogenesis.  This means that the brain can create new brain cells.  This happens rapidly in babies and children.  The adult brain has this happen in the hippocampus, which is in charge of memories. 
Here are a few of the things that we can do to get this wonderful brain of ours up and running in the best manner possible. 
Get your heart rate up.  Do this in areas that are not polluted.  Pollution can create neural decline.
Increase your social interaction.  We are social beings that need others.  If you can get into an exercise with someone where you have to increase your hand to eye activity then you are getting a nice increase in your brain pathways and structure.  This helps to have a better thinking process.  Ping pong anyone?
Watch your eating patterns.  Intermittent fasting creates neurogenesis, which improves cognitive function and brain structure.  What to do?  Watch your refined sugar intake.  One time a month water fast for a day.  Reduce your calorie intake by 50 to 60 percent two days a week,  do this for a couple of months.  
Find two days a week that are non-consecutive and reduce your calories by 20 percent, do this 3 or 4 times a year.  
Eat only between 8 am and 8 pm or 12 noon to 8 pm.
Sleeping is the time that the brain uses to detox.  A lack of sleep can impact your I.Q.  Find a meditative or relaxing video on you tube if getting to sleep is your problem.  Aim for 7 to 9 hours a night.  If you like to nap then dig in.

LENS is like drano for the brain.  It helps it to detox and work better.