The three planets representing mental activity and intelligence are the Moon, Mercury and Uranus. To understand your mental abilities and quirks, look at the placement of these planets in your natal chart and the aspects they make with your other planets. (Link here if you don't know where the planets are placed in your birth chart).
Here is a partial excerpt on Mercury/Uranus aspects from Celestial Psychology. This is an excellent but little-known book on interpreting aspects in your birth chart.
"People with Mercury/Uranus contacts in their birth charts experience being different from others because of their unique mental processes and their way of expressing themselves. As children, their speeded-up thought patterns and modes of communication were dissimilar to others in the family, making them feel uncomfortable. Often they experienced frustration in trying to articulate ideas because their minds moved faster than their mouths. The parent's varying responses to these children were often perplexing. As adults, communication problems may manifest in personal, social and business relationships.
Mercury/Uranus people communicate using a kind of verbal shorthand developed from flashes of insight, a code rarely understood by others. For example, when talking with someone they often jump ahead to make their point, leaving out information essential for understanding. Impatient Uranus short circuits the information process, forgetting that other people have no idea how they arrived at their conclusions. This is why Mercury/Uranus people are so frequently misunderstood, misinterpreted and viewed as ultimately illogical. Their ideas seem to spring out of thin air, they have laid no cohesive groundwork to support their opinions and conclusions.
For Uranians to communicate effectively, they must stop assuming others possess mental telepathy. They need to explain or refer to the logical stages in the formulation of their ideas. Reconstructing this mental process is a boring and frustrating process for Uranians who have already done this internally. This same mental impatience frequently causes them to interrupt others who are talking. They need to be reminded that others have a right to express themselves in their own way and should be given a fair hearing before the Mercury/Uranus person jumps in...
Mercury/Uranus individuals can be very rigid in their thinking. Convinced of their own uniqueness, they tend to reject others' ideas and suggestions, which they believe cannot possibly apply to them. They also assume that if something works well for them, it must be right and will obviously work well for everyone else...
Mercury/Uranus people are inquisitive and experimental. They like to explore many varied intellectual areas, especially if it is their idea..."
The above image is "Spheres of Thought" by Marlene Healey