Studies show that the PFC, mainly the dorsolateral prefrontal cortex, functions to downregulate the hippocampal activity to suppress unwanted thoughts 1) 2)

The frontal operculum rostral to the ascending ramus of the lateral fissure is associated with the prefrontal association cortex and plays a role in thought, cognition, and planning behavior.

1)
Schmitz TW, Correia MM, Ferreira CS, Prescot AP, Anderson MC. Hippocampal GABA enables inhibitory control over unwanted thoughts. Nat Commun. 2017 Nov 03;8(1):1311.
2)
De Raedt R, Remue J, Loeys T, Hooley JM, Baeken C. The effect of transcranial direct current stimulation of the prefrontal cortex on implicit self-esteem is mediated by rumination after criticism. Behav Res Ther. 2017 Dec;99:138-146.