Human prefrontal areas show enhanced activations when individuals are presented with images, under diverse task conditions. However, the functional role of these increased activations remains a deeply debated question. Here we addressed this question by comparing, dynamically, the relational structure of prefrontal activations and both visual and textual-trained deep neural networks (DNNs) during a visual memorization task. We analyzed intra-cranial recordings, conducted for clinical purposes, while patients viewed and memorized images of familiar faces and places. Our results reveal that relational structures in the frontal cortex elicited during visual memorization were predicted by text and not visual DNNs. Importantly, the temporal dynamics of these correlations showed striking differences, with a rapid decline over time for the visual component, but persistent dynamics including a significant image offset response for the text component. The results point to a dynamic text-related function of prefrontal cortex during visual memorization in the human brain.