The Role of the Hippocampus and Retrosplenial Cortex in Spatial Memory: A double blind anodal Transcranial Direct Current Stimulation (tDCS) Study

Rosalia De Biase¹Sara Esposito¹Emma Chiaramello²Marta Parazzini²Laura Sagliano^1*

• ¹University of Campania Luigi Vanvitelli, Caserta, Italy
• ²Istituto di Elettronica e di Ingegneria dell'Informazione e delle Telecomunicazioni Consiglio Nazionale delle Ricerche Sede di Milano, Milan, Italy

Spatial memory enables the encoding and retrieval of object locations across changing viewpoints by integrating multiple spatial reference frames. While neuroimaging and lesion studies have highlighted the role of the hippocampus and retrosplenial cortex (RSC) in these processes, causal evidence from non-invasive brain stimulation remains limited, particularly for the RSC, due to its deep cortical location. In this within-subject study, eighteen healthy participants performed a spatial localization task in a virtual room under three stimulation conditions: anodal transcranial direct current stimulation (tDCS) over the left RSC, anodal tDCS over the left hippocampus, and sham stimulation. The task varied in terms of both the spatial reference frame (viewer-, object-, or room-centered) and the degree of perspective change (0°, 45°, 135°). Results showed that performance declined with increasing viewpoint rotation, particularly under room-centered encoding. RSC stimulation selectively disrupted accuracy in room-centered trials with greater perspective shifts (45°, 135°), supporting its role in viewpoint-invariant updating and the integration of stable environmental cues. In contrast, hippocampal stimulation did not yield significant behavioral effects. These findings provide, to the best of our knowledge, one of the first causal evidence implicating the retrosplenial cortex in spatial memory transformations across perspectives and highlight the need for further research into its functional specificity and the neuromodulatory effects of tDCS on deep cortical structures.