Entorhinal cortex receptive fields are modulated by spatial attention, even without movement

Grid cells in the entorhinal cortex allow for the precise decoding of position in space. Along with potentially playing an important role in navigation, grid cells have recently been hypothesized to make a general contribution to mental operations. A prerequisite for this hypothesis is that grid cell activity does not critically depend on physical movement. Here, we show that movement of covert attention, without any physical movement, also elicits spatial receptive fields with a triangular tiling of space. In monkeys trained to maintain central fixation while covertly attending to a stimulus moving in the periphery we identified a significant population (20/141, 14% neurons at a FDR <5%) of entorhinal cells with spatially structured receptive fields. This contrasts with recordings obtained in the hippocampus, where grid-like representations were not observed. Our results provide evidence that neurons in macaque entorhinal cortex do not rely on physical movement.

The Ga-Nitride/air Two-Dimensional Photonic Quasi-crystals Fabricated on GaN-based Light Emitters

ABSTRACTThe two-dimensional (2D) Ga-nitride/air photonic quasi-crystals (PQC) were successfully fabricated by the technique of focused Ga ion beam (FIB) milling on GaN based epitaxial wafers. The effects of the PQC on the current injected edge emitting GaN-based light emitters were investigated. The quasi-crystal structures studied in this work are based on square-triangular tiling with 8-fold or 12-fold symmetry. The air hole diameter in the different PQC patterns was varied from 95nm up to 1200nm, the filling factor of air hole was in the range of 10% to 50% and the depth of the hole was 90nm to 370nm, respectively. Among these, the nearest center-to-center distance of the holes and/or the lattice constant was reached to be 170nm. The photonic quasi-crystals on the GaN-based light emitters demonstrated a two to three factor of magnitude enhancement of surface extractive emission. The blocking of the propagation of planar-guided modes by the photonic quasi-crystals was observed. By comparison of symmetry effect among the triangular lattice PC and PQCs, it was found that the GaN-based photonic quasi-crystal (PQC) with 12-fold symmetry provided a much favorable enhancement of the extractive light emission over that of triangle lattice PC and 8-fold symmetric PQC as well.