Brando Sheldrick¹, Veronica Nacher¹, Jennifer Lin¹, Hongying Wang¹, Saihong Sun¹, Xiaogang Yan¹, Douglas Crawford¹; ¹York University

Neurons along the intraparietal sulcus (IPs) are known to encode visual targets in egocentric (e.g., eye-centered) coordinates, but the influence of allocentric (e.g. landmark-centered) cues is less studied. The purpose of the current study was to investigate how local field potential (LFP) activity along the mid-posterior IPs is modulated by stable or shifting visual landmarks before and during reaches to remembered visual targets. To investigate this question, we recorded LFPs from putative lateral, medial, and ventral IPs sites using 32-channel Plexon probes in two female Rhesus monkeys. Simultaneous array recordings in posterior ventrolateral prefrontal cortex (pvLPFC) were reported elsewhere (Lin et al. SFN 2025). A landmark (four identical dots positioned at the vertices of a virtual square) was displayed at one of fifteen locations within reach on a touch screen. A visual target then appeared, either within or outside of the landmark square, followed by a visual mask. After the mask disappeared, the landmark either reappeared at the same location (stable-landmark condition) or shifted by 8 degrees in one of eight possible directions (landmark-shift condition). Gaze and head position were allowed to move freely, but animals were rewarded for reaching within 4.7 cm of the target. Control trials employed the same procedures without the landmarks. For comparison, pvLPFC LFPs showed low-frequency modulations during the memory, planning and execution phases, with additional low-frequency synchronization after reaches in the landmark conditions (Lin et al., SFN 2025). Preliminary analysis of parietal LFP data in the first monkey suggests higher-frequency synchronization in the alpha- and beta-bands prior to target onset that fades during the hand movement in all visual conditions. Additionally, there was again low-frequency (delta and theta) synchronization after reach/before reward in the landmark task conditions compared to no-landmark controls. The latter might suggest visual feedback of reach errors relative to the landmark.

Acknowledgements: The Connected Minds Program, funded in part by the Canada First Research Excellence Fund.