Enkephalos

Εἰδέναι δὲ χρὴ τοὺς ἀνθρώπους, ὅτι ἐξ οὐδενὸς ἡμῖν αἱ ἡδοναὶ γίνονται καὶ αἱ εὐφροσύναι καὶ γέλωτες καὶ παιδιαὶ ἢ ἐντεῦθεν καὶ λῦπαι καὶ ἀνίαι καὶ δυσφροσύναι καὶ κλαυθμοί. καὶ τούτῳ φρονεῦμεν μάλιστα καὶ νοεῦμεν καὶ βλέπομεν καὶ ἀκούομεν καὶ γινώσκομεν τά τε αἰσχρὰ καὶ τὰ καλὰ καὶ τὰ κακὰ καὶ ἀγαθὰ καὶ ἡδέα καὶ ἀηδέα, τὰ μὲν νόμῳ διακρίνοντες, τὰ δὲ τῷ ξυμφέροντι αἰσθανόμενοι, τῷ δὲ καὶ τὰς ἡδονὰς καὶ τὰς ἀηδίας τοῖσι καιροῖσι διαγινώσκοντες, καὶ οὐ ταὐτὰ ἀρέσκει ἡμῖν. τῷ δὲ αὐτῷ τούτῳ καὶ μαινόμεθα καὶ παραφρονέομεν, καὶ δείματα καὶ φόβοι παρίστανται ἡμῖν τὰ μὲν νύκτωρ, τὰ δὲ μεθ’ ἡμέρην, καὶ ἐνύπνια καὶ πλάνοι ἄκαιροι, καὶ φροντίδες οὐχ ἱκνεύμεναι, καὶ ἀγνωσίη τῶν καθεστεώτων καὶ ἀηθίη καὶ ἀπειρίη. καὶ ταῦτα πάσχομεν ἀπὸ τοῦ ἐγκεφάλου πάντα, ὅταν οὗτος μὴ ὑγιαίνῃ, ἀλλ’ ἢ θερμότερος τῆς φύσιος γένηται ἢ ψυχρότερος ἢ ὑγρότερος ἢ ξηρότερος, ἤ τι ἄλλο πεπόνθῃ πάθος παρὰ τὴν φύσιν ὃ μὴ ἐώθει. καὶ μαινόμεθα μὲν ὑπὸ ὑγρότητος· ὅταν γὰρ ὑγρότερος τῆς φύσιος ᾖ, ἀνάγκη κινεῖσθαι, κινευμένου δὲ μήτε τὴν ὄψιν ἀτρεμίζειν μήτε τὴν ἀκοήν, ἀλλ’ ἄλλοτε ἄλλα ὁρᾶν καὶ ἀκούειν, τήν τε γλῶσσαν τοιαῦτα διαλέγεσθαι οἷα ἂν βλέπῃ τε καὶ ἀκούῃ ἑκάστοτε· ὅσον δ’ ἂν ἀτρεμήσῃ ὁ ἐγκέφαλος χρόνον, τοσοῦτον καὶ φρονεῖ ὁ ἄνθρωπος.
(Hippocrates, Peri Hierēs Nousou 14)

And men ought to know that from nothing else but (from the brain) come joys, delights, laughter and sports, and sorrows, griefs, despondency, and lamentations. And by this, in an especial manner, we acquire wisdom and knowledge, and see and hear, and know what are foul and what are fair, what are bad and what are good, what are sweet, and what unsavory; some we discriminate by habit, and some we perceive by their utility. By this we distinguish objects of relish and disrelish, according to the seasons; and the same things do not always please us. And by the same organ we become mad and delirious, and fears and terrors assail us, some by night, and some by day, and dreams and untimely wanderings, and cares that are not suitable, and ignorance of present circumstances, desuetude, and unskilfulness. All these things we endure from the brain, when it is not healthy, but is more hot, more cold, more moist, or more dry than natural, or when it suffers any other preternatural and unusual affection. And we become mad from humidity (of the brain). For when it is more moist than natural, it is necessarily put into motion, and the affection being moved, neither the sight nor hearing can be at rest, and the tongue speaks in accordance with the sight and hearing. As long as the brain is at rest, the man enjoys his reason… (tr. Charles Darwin Adams)