The ancients had no understanding of brain function. In fact, when the Egyptians would mummify a person they scraped out and discarded the brain, then they put the lungs, liver, intestines and stomach in jars, to ensure that their breath was preserved for everlasting life:
Canopic jars
Canopic jars were made to contain the organs that were removed from the body in the process of mummification: the lungs, liver, intestines, and stomach. Each organ was protected by one of the Four Sons of Horus: Hapy (lungs), Imsety (liver), Duamutef (stomach), and Qebehsenuef (intestines).
This anatomy is evident in the Christian scriptures, however, they were more concerned with the heart and the reins (kidneys):
[Psa 7:9 KJV] [9] Oh let the wickedness of the wicked come to an end; but establish the just: for the righteous God trieth the hearts and reins.
[Psa 16:7 KJV] [7] I will bless the LORD, who hath given me counsel: my reins also instruct me in the night seasons.
[Psa 26:2 KJV] 2 Examine me, O LORD, and prove me; try my reins and my heart.
[Psa 73:21 KJV] [21] Thus my heart was grieved, and I was pricked in my reins.
[Psa 139:13 KJV] [13] For thou hast possessed my reins: thou hast covered me in my mother's womb.
[Pro 23:16 KJV] [16] Yea, my reins shall rejoice, when thy lips speak right things.
[Jer 11:20 KJV] [20] But, O LORD of hosts, that judgest righteously, that triest the reins and the heart, let me see thy vengeance on them: for unto thee have I revealed my cause.
[Jer 12:2 KJV] 2 Thou hast planted them, yea, they have taken root: they grow, yea, they bring forth fruit: thou [art] near in their mouth, and far from their reins.
[Jer 17:10 KJV] [10] I the LORD search the heart, [I] try the reins, even to give every man according to his ways, [and] according to the fruit of his doings.
[Rev 2:23 KJV] [23] And I will kill her children with death; and all the churches shall know that I am he which searcheth the reins and hearts: and I will give unto every one of you according to your works.
Jewish anatomy goes back to at least Genesis 2:7. Here Moses tells us that man is composed of two substance:
- clay/dirt/earth, which is thus "dirty"
- the breath of life, which animates the dirty statue of Elohim
[Gen 2:7 NASB95] [7] Then the LORD God formed man of dust from the ground, and breathed into his nostrils the breath of life; and man became a living being.
So where does the mind exist? It is a function of the animating breath of life. Paul call this "the principle of the Breath of Life":
[Rom 8:2 NASB95] 2 For the law of the Spirit [Gk: pneuma = "breath"] of life in Christ Jesus has set you free from the law of sin and of death.
See also all of these references:
[Job 33:4 NASB95] [4] "The Spirit of God has made me, And the breath of the Almighty gives me life.
[Pro 15:4 NASB95] [4] A soothing tongue is a tree of life, But perversion in it crushes the spirit.
[Isa 38:16 NASB95] [16] "O Lord, by [these] things [men] live, And in all these is the life of my spirit; O restore me to health and let me live!
[Rom 8:11 NASB95] [11] But if the Spirit of Him who raised Jesus from the dead dwells in you, He who raised Christ Jesus from the dead will also give life to your mortal bodies through His Spirit who dwells in you.
[2Co 3:6 NASB95] [6] who also made us adequate [as] servants of a new covenant, not of the letter but of the Spirit; for the letter kills, but the Spirit gives life.
So for Paul, like others before him, the control center of the body is the vital organs, where the thoughts and intent of a man reside.
[Pro 20:27 YLT] [27] The breath of man [is] a lamp of Jehovah, Searching all the inner parts of the heart.
Paul's burden in Romans is to convince the Romans that not only does the Torah not bring about justification and everlasting life, neither does the Torah bring about righteous behavior. For him, that isn't its purpose. For him, the purpose of the law is to turn sins into crimes, resulting in a death sentence. Sin is personified as an opportunistic enslaver of men into condemnation:

[Rom 7:21-25 YLT] [21] I find, then, the law, that when I desire to do what is right, with me the evil is present, [22] for I delight in the law of God according to the inward man, [23] and I behold another law in my members, warring against the law of my mind, and bringing me into captivity to the law of the sin that [is] in my members. [24] A wretched man I [am]! who shall deliver me out of the body of this death? [25] I thank God -- through Jesus Christ our Lord; so then, I myself indeed with the mind do serve the law of God, and with the flesh, the law of sin.
For Paul, freedom from sin comes by freedom from the Torah through death to the law, and resurrection, free from the body.