Place-modulated activity among neurons in the hippocampal formation presents a means to organize contextual information in the service of memory formation and recall1,2. One particular spatial representation, that of grid cells, has been observed in the entorhinal cortex (EC) of rats and bats3–5, but has yet to be described in single units in primates. Here, we examined spatial representations in the EC of head-fixed monkeys performing a free-viewing visual memory task6,7. Individual neurons were identified in the primate EC that emitted action potentials when the monkey fixated multiple discrete locations in the visual field across the presentation of up to hundreds of novel images. These firing fields possess spatial periodicity similar to a triangular tiling with a corresponding well-defined hexagonal structure in the spatial autocorrelation. Further, these neurons demonstrated theta-band oscillatory activity and changing spatial scale as a function of distance from the rhinal sulcus, which is consistent with previous findings in rodents4,8–10. These spatial representations may provide a framework to anchor the encoding of stimulus content in a complex visual scene. Together, our results provide a direct demonstration of grid cells in the primate and suggest that EC neurons encode space during visual exploration, even without locomotion.

We recently demonstrated that position in visual space is represented by grid cells in the primate entorhinal cortex (EC), suggesting that visual exploration of complex scenes in primates may employ signaling mechanisms similar to those used during exploration of physical space via movement in rodents. Here, we describe a group of saccade direction (SD) cells that encode eye movement information in the monkey EC during free-viewing of complex images. Significant saccade direction encoding was found in 20% of the cells recorded in the posterior EC. SD cells were generally broadly tuned and two largely separate populations of SD cells encoded future and previous saccade direction. Some properties of these cells resemble those of head-direction cells in rodent EC, suggesting that the same neural circuitry may be capable of performing homologous spatial computations under different exploratory contexts.