Jeongyeol Ahn^1,2, Juhyoung Ryu¹, Sangjun Lee³, Chany Lee⁴, Chang-Hwan Im⁵, Elisha P Merriam², Sang-Hun Lee¹; ¹Seoul National University, Seoul, Republic of Korea, ²National Institute of Mental Health, ³University of Minnesota, ⁴Korea Brain Research Institute, Daegu, Republic of Korea, ⁵Hanyang University, Seoul, Republic of Korea

Receptive field properties in the human visual cortex are fundamental to sensory processing and perception. Recent advances in brain stimulation techniques have enabled non-invasive modulation of neural activity, offering new opportunities to explore how baseline neural activity influences receptive field properties. In this study, we examined the effects of experimentally modulated baseline activity using anodal transcranial direct current stimulation (tDCS) on population receptive fields (pRFs) in the visual cortex. Using fMRI responses to ring-shaped traveling-wave stimuli, we modeled pRFs for individual voxels and quantified key properties, including baseline activity, pRF width, and surround suppression strength. We previously found that anodal tDCS increased the baseline fMRI activity for a prolonged period. Further analyses revealed that the increment in baseline activity was positively correlated with a narrower width of pRF (z = -5.19, FDR-adjusted p < 0.05) and surround suppression strength (z = 4.47, FDR-adjusted p < 0.05). These findings suggest a possibility that baseline neural activity modulation contributes to spatial tuning by strengthening inhibitory mechanisms, such as surround suppression, within the visual cortex. This likely involves potential changes in the balance of lateral interactions among neurons, emphasizing the role of inhibitory-excitatory dynamics in shaping receptive field properties. Our work provides insights into the functional organization of the visual cortex and highlights how receptive field properties can adapt under varying neural activity states, contributing to a deeper understanding of the cortical computations that underlie visual perception.

Acknowledgements: S.-H. L was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(grant #: RS-2024-00349515) and by the Korea Basic Science Institute(National research Facilities and Equipment Center) grant funded by the Ministry of Education (grant # RS-2024-00435727).