Aeschylus, Prometheus Bound
788-789 (tr. Alan H. Sommerstein):
First, Io, I shall tell you about the wanderings on which you will be driven: inscribe them on the memory-tablets of your mind.
σοὶ πρῶτον, Ἰοῖ, πολύδονον πλάνην φράσω,
ἣν ἐγγράφου σὺ μνήμοσιν δέλτοις φρενῶν.
Mark Griffith, commentary on line 789:
The 'wax-tablets of the wits' are a conventional but vivid metaphor for the faculty of memory (so e.g. Pind. O. 10.2, Aesch. Cho. 450, Eum. 275, Soph. Ph. 1325; further Sansone 60-2, 'Aesch. has only one metaphor for memory, and he uses it at least six times.' The phrase here implies close attention, as much as memory.
The reference is to David Sansone, Aeschylean Metaphors for Intellectual Activity
(Wiesbaden: Franz Steiner, 1975).