Questions like "Who Am 'I'?" "What is this world around?" are as old as the dawn of capacity to 'abstract thinking' in man. The ancient Indian sages dwelt on these questions when the rest of the world was still at hunter-gatherer level. Except for building unfalsifiable but plausible 'models' with a greater intent (and emphasis) on creating a harmonious society, the sages could not provide straight answers to such fundamental "Why" questions. The ancients reasoned that 'misery and sorrow' were mainly at the back of such questioning and therefore, they went about finding ways and means of redemption of sorrow. Thus the basic inquiry got deflected.
But in the process the sages made tremendous contribution in understanding human mind (though not fully brain, neurons, synopses, ion channels and electrochemical activity of the brain at cell and molecular levels). Their conclusions were principally based on 'Gedankenexperiment' and answers on intuition. They could arrive at the fact that the sense of an 'individualized self' was a mere fiction, mind was the composite of 'thoughts' and "Consciousness" is the fundamental unchanging "Witness" of a changing phenomenal world. This was a great achievement based on the fact that the 'observational' tools at their disposal were only their 'senses' and a reasoning mind.
The ancients could drive to the limits of their thoughts under the available bandwidth and range of sensory observation in those times. The limit they reached was Brahman, the Oneness (Advaita) beyond which they could not go. Can present day science with capabilities of extensively extending the range of observation, experimentation and verification surpass this limit?