workout types - How much intensity is required when working out for cognitive/mental reasons?

I joined a gym because I code at a desk all day, and I want to keep my body active as I get older. I also read that physical activity can help preserve brain function and IQ : go to the gym three times per week and after 15 minutes of cardio warm up (2 miles on a bike, elliptical, etc.), I use three or four machines for different muscle groups (three sets of ten reps for each machine). So one day I may do triceps, calves, lower back. ...Read more