Assuming that ventral dominant brains allow for “filling in the gaps” of sensory information in a more efficient way, human brains were less metabolically intensive than extant species like Neanderthalensis.
During adverse environmental conditions which presented challenges to achieving the necessary calories to support those big brains, Sapiens were able to shift more work to these ventral structures (particularly cerebellar processing) which allowed Sapiens to shrink our brains (and bodies) faster than Neanderthals.
Sapiens survived not because they were “smarter” than Neadnerthals, but because these ventral brain structures allowed much lower metabolic requirements for the same data (even if the data was partially “artificial”).
The shift toward these ventral brain structures had a second effect – “filling in the blanks” enabled a much more sensorily decoupled experience, or a much more powerful “imagination”.
Perhaps the most powerful aspect of this shift compared to extant species was longer life spans. Humans are unusually long lived compared to similar species, and this extra time allowed more complex development and experience to occur in human brains.