The original concept of Manasa purtra, as mentioned in Rig Veda, is different from that we find mention of in the subsequent literature, viz., Ramayana, Puranas, etc.
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In Rig Veda, rishi Vasiṣṭha, mentioned himself to be a mind-born son of Urvaśī.
उतासि मैत्रावरुणो वसिष्ठोर्वश्या ब्रह्मन्मनसोऽधि जातः । द्रप्सं स्कन्नं ब्रह्मणा दैव्येन विश्वे देवाः पुष्करे त्वाददन्त ॥
utāsi maitrāvaruṇo vasiṣṭhorvaśyā brahman manaso 'dhi jātaḥ | drapsaṃ skannam brahmaṇā daivyena viśve devāḥ puṣkare tvādadanta ||English translation:
And you are the descendant of Mitra and Varuṇa, o Vasiṣṭha, born from Urvaśī, from her mind, you formulator. Illumination spurted forth: with a heavenly formulation all the gods took you in mid-space /antariksha.
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Please note the words , o Vasiṣṭha, born from Urvaśī, from her mind - vasiṣṭhorvaśyā brahman manaso 'dhi jātaḥ
We have to remember that Urvaśī, mentioned in Rig Veda, is NOT the puranic celestial damsel Ūrvaśī, who was used by Indra to disturb the austerities of rishis, but the DIVINE Sarasvatī, the feminine form of the formless ENERGY/BRAHMAN.
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So, according to Rig Veda, mind-born son indicates, one who had attained SELF REALISATION and experiencing BLISS.
Rishi Vasiṣṭha attained BLISS, with the grace of Sarasvatī/Urvaśī, and hence he was the mind-born son of Sarasvatī/Urvaśī.
Hence, the mind-born son concept relates to pure SPIRITUALITY.
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By the time Ramayana was composed, had been converted to the birth of physical son.
Visravasa was described as the son of Pulastya, son born out of thought - र्मानसः सुतः
प्रजापतीनाम् षण्णं तु चतुर्थो यः प्रजापतिः |
मानसो ब्रह्मणः पुत्रः पुलस्त्य इति विश्रुतः || ५-२३-६
"Among th six Prajapatis, whichever son, the fourth Prajapati, born by the thought of Lord Brahma ,he is famous as Paulastya."
पुलस्त्यस्य तु तेजस्वी महार्षिर्मानसः सुतः |
नाम्ना स विश्रवा नाम प्रजापतिसमप्रभः || ५-२३-७
By the name, famous as Visrava, with a radiance equalling that of Lord Brahmathat glorious sage is the son born from the thought of Pulastya.
And, in Puranas the mind-born son concept was extended many rishis, prajapatis, etc, who were mentioned as mind-born sons of Brahma.
