Different levels of consciousness
Preconciousness is associated with intense activation, yet confined to sensori-motor processors ; 
 Occipito-temporal loops and local synchrony ; 
 Priming at multiple levels ; 
 No reportability while attention is occupied elsewhere ;

quora could also provide some answers : https://www.quora.com/What-is-the-core-of-human-consciousness/answer/Daisi-Lui ;

preconsciousness could have started earlier than consciousness ;

Freud, S., Strachey, J., In Freud, A., In Rothgeb, C. L., Richards, A., &amp; Scientific Literature Corporation. (1953). The standard edition of the complete psychological works of Sigmund Freud.