Answer: By constant & long meditation, Medha Nadi is developed & felt. Medha Nadi definitely improves intelligence and memory. But, you have to do a long practice for it. Swamiji was an extra ordinary person. He was a born perfect. So, the things were easy for him. Brahmacharya has to be practised not merely physically but it must be also mentally. The mind has to be absolutely pure. Then only the intelligence grows.

Response to above Reply: Thanks for your reply. I have another query :

I have been practising meditation for several weeks. Initially there used to be problem in controlling the mind because other thoughts came into my mind but now there is no such problem as these thoughts no more come.
But the greatest hurdle that I face now is my breath. Every time I exhale there is a slight wavering of the mind and one pointedness cannot be achieved. I consider this the greatest hurdle in my practise. Do people who are competent in meditation hold their breath.
Also I want to know what is the role of Pranayama ? I mean Pranayama is a separate exercise but how does it help in meditation ?
I would be grateful if you reply.
Reply to the Above Response: I appreciate your sincerity in Spiritual Practice. If you are able to control your thoughts without observing the breath, try to do that. Otherwise, continue to observe the breath. Gradually the wavering will stop.
Pranayama helps only to concentrate the mind ultimately. If you are able to do it without it, there is no need for Pranayama. Some practise Pranayama for the awakening of the Kundalini & its observation. But that is not very essential.