@oristarA,
The impact of this caption stems from the word-play "on the brain" being equivalent to "always on the mind" i.e "preoccupied with". Also the words "mapped out" ( like "spelled out") don't merely refer to the brain scan data but imply a claim for "scientific or logical basis" for sexual techniques, which had previously lay in the realm of
ad hoc experiential "advice".
NB: Mathematics: A "mapping" is a correspondence (in this case "turn on"...more word play) between "an object set" (in this case sexual organs) and and "an image set" (in this case areas of the cortex).