yogaś citta-vṛtti-nirodhaḥ ||1.2||
(Yoga is the cessation of mental activities)
Yoga Sūtra, 1.2
Whole books have been written on the subject, so to answer your questions I would better refer you to those more competent than me to elaborate on this issue. I would suggest to start with M. Eliade’s ‘Yoga’, or J. Bronkhorst’s ‘The Two Traditions of Meditation in Ancient India’, and then go through his other publications and references on this topic. G. Polak’s ‘Reexamining Jhāna’ illustrates the point by means of current Theravāda meditation techniques derived from the Thai ‘kammaṭṭhāna’ movement. So let’s have a look at some relevant passages of Polak’s book:
Phra Ajahn Phut Thaniyo has maintained the following recollection of Ajahn Sao’s teaching style:
How did Phra Ajahn Sao teach? If it so happened that someone came to him, saying, ‘Ajahn, sir, I want to practice meditation. How should I go about it?’ he would answer, 'Meditate on the word ‘Buddho’. If the person asked, ‘What does ‘Buddho’ mean?’ Ajahn Sao would answer, ‘Don’t ask.’ 'What will happen after I’ve meditated on ‘Buddho’? ‘Don’t ask. Your only duty is simply to repeat the word ‘Buddho’ over and over in your mind.’ That’s how he taught: no long, drawn-out explanations (Phut Thaniyo, 1997: Access to Insight Website).
It appears that this form of meditation occupied a special place in the ‘kammaṭṭhāna’ tradition. It was also taught by Ajahn Chah, who advised the meditators to recite ‘Buddho’ until it penetrates deep into the heart of the consciousness (citta). The word ‘Buddho’ is supposed to represent the awareness and the wisdom of the Buddha. In practice, a meditator should depend on this word more than on anything else. The awareness it brings is supposed to lead the meditator to the understanding of the truth about one’s own mind (Chah, 2004: 300).
‘Buddho’ meditation was also taught by Ajahn Thate, Ajahn Maha Boowa, and Ajahn Lee. Ajahn Brahm has summed up this method of meditation in a following way:
In the Thai forest tradition, they add a mantra to breathing. As you breath in you think 'Bud” and as breath out you think ‘Dho’ (Brahm, 2006: 84).
Ajahn Brahm has rightly identified the true character of this form of meditation. ‘Buddho’ is indeed a mantra, just like ‘OM’ was a mantra. But this also means that we are not dealing here with the original Buddhist practice of ‘jhāna’, but with a practice of yoga. The basic method of yogic meditation is exactly the same.
The meditation on ‘Buddho’ is not present in any of the Suttas of the Pāli Canon. Even Buddhaghosa knew nothing about this form of meditation. The Visuddhimagga describes the subject of meditation known as ‘the recollection of the Buddha’, but it is developed in a completely different way. One should recollect the Buddha, by bringing to the mind his numerous unique qualities. These qualities should be then contemplated by active thinking and pondering. Due to the complexity of this method, it leads only to the attainment of ‘upacāra samādhi’. Ajahn Chah has stated that ‘Buddho’ should penetrate deep into the heart of consciousness. The idea that the mantra ‘Buddho’ should be merged into the heart was also preached by Ajahn Maha Boowa (cf. Kornfield, 1996: 167) and by Ajahn Thate. This notion is in fact a very old yogic idea. The Amṛtabindu Upaniṣad states that the mind should be controlled to such an extent, in which it gets merged in the heart. This is achieved by the meditation on the mantra ‘OM’ (ABU 5–7).
Ajahn Brahm has made several important comments about the state of ‘jhāna’, which is attained by his method of meditation. He points out, that all the five senses are totally shut down during ‘jhāna’. A meditator cannot feel, hear, see, smell of feel touch. Even if someone tapped a meditator absorbed in ‘jhāna’ on the shoulder, he wouldn’t feel a thing (Brahm, 2006: 154). In the state of ‘jhāna’, one cannot experience his own body, or feel any pain. As Ajahn Brahm points out, once the meditator is inside the ‘jhāna’, there is no more choice. One will be able to emerge only when the fuel of relinquishment will be all used up. Higher ‘jhāna’ usually persist for several hours (Brahm, 2006: 24–25). To illustrate his point, Ajahn Brahm recollects a fascinating story:
A lay disciple once told me how, completely by chance, he had fallen into a deep ‘jhāna’ while meditating at home. His wife thought he had died and sent for an ambulance. He was rushed to hospital in a loud wail of sirens. In the emergency room, no heartbeat registered on the ECG, and no brain activity was seen by EEG So the doctor on duty put defibrillators on his chest to reactivate his heart. Even though he was being bounced up and down on the hospital bed through the force of the electric shocks, he didn’t feel a thing. When he emerged from the ‘jhāna’ in the emergency room, perfectly all right, he had no knowledge of how he got there, nothing of ambulances and sirens. Nothing of body-jerking defibrillator (Brahm 2006, 154–155).
This account must seem all too familiar to us by now, but contrary to what Ajahn Brahm writes, it is not ‘jhāna’ that we are reminded of here. The complete inactivity of the senses, the resemblance to a dead person, the halt in the functioning of the most basic bodily operations are all the features of the highest yogic state of meditation, the very same state that was introduced by the later Buddhists under the name of ‘saññāvedayitanirodha’. There can be no doubt that Ajahn Brahm’s ‘jhāna’ possesses all the distinct features of yogic meditation.
The analysis of the meditative teachings of modern meditation masters shows that they contain many elements which have very little to do with the original form of early Buddhist meditation. In fact, many of these elements are explicitly criticized and rejected in the Suttapiṭaka. This is particularly the case with Ajahn Brahm’s view of ‘jhāna’ as a state in which the activity of the body comes to a halt, and with the painful methods of meditation developed by Sunlun Sayadaw.
(‘Reexamining Jhāna - Towards a Critical Reconstruction of Early Buddhist Soteriology’, 181-185)
I believe this also should answer your second question, since the topic of this thread relates to ‘jhāna’ meditation and the ‘jhāna’ factors ‘vitakka’ and ‘vicāra’ as they are understood in the EBT, and in the exegetical literature of the early Buddhist schools.