When attaining the first immaterial absorption, perception of form ceased. This means the perception of form exists in the first four material absorptions. And that is where the mind places it self (vitakka) and keep it connected (vicāra) in the first absorption. We called it nimitta. Hence this vitakka and vicāra are not the regular joe's thinkings and ponderings (also read here). This well proven by the AN 3.101.Material
For someone who has attained the first absorption, speech (vācā) has ceased.
For someone who has attained the second absorption, the placing of the mind (vitakka) and keeping it connected (vicāra) have ceased.
For someone who has attained the third absorption, rapture has ceased.
For someone who has attained the fourth absorption, breathing (assāsapassāsa) has ceased.
For someone who has attained the dimension of infinite space, the perception of form has ceased.
For someone who has attained the dimension of infinite consciousness, the perception of the dimension of infinite space has ceased.
For someone who has attained the dimension of nothingness, the perception of the dimension of infinite consciousness has ceased.
For someone who has attained the dimension of neither perception nor non-perception, the perception of the dimension of nothingness has ceased.
For someone who has attained the cessation of perception and feeling, perception and feeling have ceased.
For a mendicant who has ended the defilements, greed, hate, and delusion have ceased.
According to AN 3.101, Paṃsudhovaka-sutta (has 3 parallels), in order to achieve an internally stilled mind which is capable of realizing anything that can be realized by insight, we even have to let go of thoughts about the teachings (dhamma vitakkas).
mind has coarse corruptions: bad bodily, verbal, and mental conduct. A sincere, capable mendicant gives these up, gets rid of, eliminates, and exterminates them. When they’ve been given up and eliminated,
there are middling corruptions: sensual, malicious, or cruel thoughts. A sincere, capable mendicant...
there are fine corruptions: thoughts of family, country, and being looked up to. A sincere, capable mendicant…
only thoughts about the teaching (dhamma vitakka) are left. That samādhi is not peaceful or sublime or tranquil or unified, but is held in place by forceful suppression (So hoti samādhi na ceva santo na ca paṇīto nappaṭippassaddhaladdho na ekodibhāvādhigato sasaṅkhāraniggayhavāritagato).
But there comes a time when that mind is stilled internally; it settles, unifies, and becomes immersed in samādhi. That immersion is peaceful and sublime and tranquil and unified, not held in place by forceful suppression. They become capable of realizing anything that can be realized by insight to which they extend the mind, in each and every case.