I have studied tony buzan and others’ work and had similar experiance to you until I started eating more healthy food.

Eating 8+ fruit per day… apples pears banana’s oranges plums kiwi and strawberries etc

Plus drink 2 -4 litres of water per day and exercise at the gym every other day for 1 hour.

My memory started working in ways I couldnt imagine… as did my concentration.

I could hear a telephone number or bank account number or similar just once and recall it days or weeks later. It actually got quite scary at first.

Then I went through a rough patch and dropped my gym sessions, started eating crap and smoking ciggarettes more and guess what … my memory and concentration plummeted. It was like having a hangover all day every day.

Try it for 2 weeks… You wont go back.