My wife shared this with me, something se saw posted on Facebook. I found it interesting.

Brain Substance of all men is not Equal”

Prabhupada: In psychology there is study brain substance. Brain substance of all men are not equal.

Svarupa Damodara: Yes. I think it is known because when Einstein died they tried to preserve the brain of Einstein. Thinking that his brain was different from others.

Prabhupada: If it was not different then how he became distinguished?

Svarupa Damodara: The brain substance is different just like everybodys intelligence different.

Prabhupada: Yes. According to the brain substance there is difference of intelligence. ( Morning Walk — September 23, 1972, Los Angeles)

Prabhupada: But Vyasadeva saw that next age, this Kali-yuga, people will be less intelligent. Here it is stated, the brain substance not in much quantity. This is psychologically true, that within the brain, the brain substance, if there is more, then one is more intelligent. Just see, modern scientific psychology, how it was known, long, long millions of years ago. At least five thousand years ago. And this is scientific fact. Those who are students of psychology, they know it. I was student of psychology, and our professor — he was a Scotman — he explained this brain substance, cerebular substance, Dr. Urquhart, that the more brain substance is there, more one becomes intelligent. ( Srimad-Bhagavatam 1.3.21 — September 26, 1972, Los Angeles)

Prabhupada: Regarding utilizing intelligence in devotional service, intelligence should be confirmed by the Spiritual Master. Therefore we accept the Spiritual Master for guidance. You should not depend on your own intelligence. Just like a child requires a parent to tell him the correct thing to do, similarly, a strict disciple should always use his intelligence in conformity with the instructions of the Spiritual Master. (Letter to: Sivananda — Los Angeles 13 February, 1969)