C. Olives cause forgetfulness similar to the body which causes coarseness: Torah Or p. 81a-82a

The Talmud states that the eating of olives causes one to forget 70 years worth of Torah learning. The reason for this is because the olive comes from the world of forgetfulness, which is the world of Kelipos. This corresponds to the human body and animal soul which come from Nogah and is called the serpents skin and causes one to forget his love for G-d.

D. Olive oil helps the memory due to the crushing:

Although olives cause one to forget 70 years worth Torah learning, the consumption of their oil causes one to remember 70 years worth of Torah learning. The reason for this is because the oil contained within olives corresponds to wisdom, Chochma. Prior to crushing the olive its oil is concealed and all that one consumes is the bitterness of the olive which comes from evil and causes one to forget Torah learning. However, when one crushes the olive the oil comes out. The reason that oil corresponds to wisdom and helps specifically with the aspect of memory is because wisdom known as Chochma, is the brain of memory. Now, just as it applies with regards to the olive so too it is with the body and animal soul. When one crushes his body and animal soul, and the pride, ego, and self-centeredness that comes with it, this helps to reveal the level of wisdom within the soul.