Some interesting info on Doodling (According to Wikipedia)

Idoodle |ˈdo͞odl|
verb [ no obj. ]
scribble absentmindedly: he was only doodling in the margin.
noun
a rough drawing made absentmindedly.For other uses, see Doodle (disambiguation).

Doodle by Luise von Mecklenburg-Strelitz, Queen of Prussia, c. 1795
A doodle is a drawing made while a person's attention is otherwise occupied. Doodles are simple drawings that can have concrete representational meaning or may just be abstract shapes.
Stereotypical examples of doodling are found in school notebooks, often in the margins, drawn by students daydreaming or losing interest during class.[1] Other common examples of doodling are produced during long telephone conversations if a pen and paper are available.
Popular kinds of doodles include cartoon versions of teachers or companions in a school, famous TV or comic characters, invented fictional beings, landscapes, geometric shapes, patterns and textures.

Etymology
The word doodle first appeared in the early 17th century to mean a fool or simpleton.[2] It may derive from the German Dudeltopf or Dudeldop, meaning simpleton or noodle (literally "nightcap").[2]
The meaning "fool, simpleton" is intended in the song title "Yankee Doodle", originally sung by British colonial troops prior to the American Revolutionary War. This is also the origin of the early eighteenth century verb to doodle, meaning "to swindle or to make a fool of". The modern meaning emerged in the 1930s either from this meaning or from the verb "to dawdle", which since the seventeenth century has had the meaning of wasting time or being lazy.

Effects on memory
According to a study published in the scientific journal Applied Cognitive Psychology, doodling can aid a person's memory by expending just enough energy to keep one from daydreaming, which demands a lot of the brain's processing power, as well as from not paying attention. Thus, it acts as a mediator between the spectrum of thinking too much or thinking too little and helps focus on the current situation. The study was done by Professor Jackie Andrade, of the School of Psychology at the University of Plymouth, who reported that doodlers in her experiment recalled 7.5 pieces of information (out of 16 total) on average, 29% more than the average of 5.8 recalled by the control group made of non-doodlers.[3]
 

Notable doodlers
Alexander Pushkin's notebooks are celebrated for their superabundance of marginal doodles, which include sketches of friends' profiles, hands, and feet. These notebooks are regarded as a work of art in their own right. Full editions of Pushkin's doodles have been undertaken on several occasions.[4] Some of Pushkin's doodles were animated by Andrei Khrzhanovsky and Yuriy Norshteyn in the 1987 film My Favorite Time.[5][6]
Nobel laureate (in literature, 1913) poet Rabindranath Tagore made huge number of doodles in his manuscript.[7] Poet and physician John Keats doodled in the margins of his medical notes; other literary doodlers have included Samuel Beckett and Sylvia Plath.[8] Mathematician Stanislaw Ulam developed the Ulam spiral for visualization of prime numbers while doodling during a boring presentation at a mathematics conference.[9] The American artist Cindy Hinant is known for her heart doodles.[10] Many American Presidents (including Thomas Jefferson, Ronald Reagan and Bill Clinton) have been known to doodle during meetings.[11]
Some doodles and drawings can be found in notebooks of Leonardo da Vinci.