Direction of oscillatory networks in the human medial temporal lobe reverses across verbal working memory phases

Working memory (WM) requires neural circuits to change how they interact as information is encoded, maintained and used. Directional oscillatory interactions in the medial temporal lobe (MTL) contribute to memory processing, but how these interactions are spatially organized during verbal WM remains unclear. Here, we analyzed intracranial electroencephalogram and neuronal spiking recorded from the human MTL during a verbal Sternberg task. Theta- and gamma-band activities in MTL showed predominant directionality in the posterior-to-anterior axis during WM encoding, but this direction was reversed to anterior-to-posterior during retrieval. Theta activities reflecting the WM load were more prevalent in left than right MTL, and theta in left MTL coordinated spike timings more strongly. Moreover, interhemispheric interactions showed a predominant left-to-right influence, with posterior-to-anterior interactions enhanced during encoding and anterior-to-posterior interactions enhanced during retrieval. Together, these findings suggest that verbal WM engages a spatially organized MTL network in which the predominant direction of oscillatory interactions changes across task phases.