Grid cell mechanisms and function: contributions of entorhinal persistent spiking and phase resetting

Grid cell mechanisms and function: contributions of entorhinal persistent spiking and phase resetting. processingcontinues up into higher level association cortices, including those that provide the inputs to hippocampus. 2014, 5:207C219. doi: 10.1002/wcs.1272 INTRODUCTION Many of the cortical and hippocampal areas that are required for episodic memory function are also specialized for spatial processing. The shared anatomical substrates for memory and spatial processing have resulted in the notion that these two cognitive functions use similar neural computations.1C3 For example, remembering past events in rich detail GLPG0259 requires information from many sensory processing streams to be merged during learning. This is achieved through a cortical hierarchy in which information from primary sensory cortices first converges within higher association areas and then within the entorhinal cortex and hippocampus.4 Similarly, the emergence of spatial firing patterns also requires the convergence of information from many different sensory systems. A standard functionalCanatomical model has emerged in which information from higher visual, auditory, somatosensory, and olfactory association cortices first projects to the rhinal cortices, where it is segregated into two processing streams, one for objects, through perirhinal and lateral entorhinal cortex, and the second one for space, through the postrhinal, parasubicular, presubicular, and medial entorhinal cortices. Projections from the two (lateral and medial) entorhinal streams then converge in hippocampus where conjunctive representations for memories of objects, space, and time emerge.5C7 Despite the high degree of convergence toward the top of the processing GLPG0259 hierarchy, where a large number of cortical areas provide inputs to the next processing stage,8 a large fraction of neurons in parahippocampal regions have specialized spatial firing patterns (Figure ?(Figure1).1). The different cell types nonetheless converge in the hippocampus to result in the prototypical firing pattern of place cells.9 Place cells are active in one or few restricted areas of space, which can range, for cells in different positions along the dorsoventral axis, from 30?cm to several meters.10 Despite the feature of predominantly firing in a particular place, functional diversity may nonetheless persist in place cells because they can flexibly switch to non-spatial firing patterns11 or, more commonly, to different levels of average firing within the place field.12 We first describe the different cell types with spatial and directional firing patterns in the entorhinal cortex and hippocampus, and then discuss how these cell types may be functionally connected in the entorhino-hippocampal circuit. Open in a separate window Figure 1 Examples of cell types with spatial tuning in the hippocampus and in parahippocampal cortices. The left column displays data from each cell type during exploration of an open field arena. Within this column, the spatial selectivity of each cell type is shown by plotting the location of each spike (in red) GLPG0259 onto the trajectory of the animal (in black). The central panels are color-coded firing rate maps of the same arena with high firing rates in red and low firing rates in blue. Finally, the right panels are polar plots GLPG0259 showing firing rate as a function of the head direction of the animal during exploration in the environment. The right columns indicate in which regions each spatially tuned cell type is found. Grid cells fire in multiple spatial locations that form a triangular grid of the environment. Grid cells are found in the presubiculum, parasubiculum, and all layers of the medial entorhinal cortex. Head-direction cells fire throughout the environment ALK but only when the animal is definitely facing a specific direction. Head-direction cells are found in the presubiculum, parasubiculum, and layers III, V, and VI of the medial entorhinal cortex. Conjunctive cells open fire inside a triangular grid pattern only when the animal is facing a specific direction. Much like head-direction cells, conjunctive cells are found in the presubiculum, parasubiculum and layers III, V, and VI of the medial entorhinal cortex. Boundary/border cells open fire when the animal is located at a specific range from a wall in the environment. These cells are found in the subiculum (not demonstrated), presubiculum, parasubiculum, and all layers of the medial entorhinal cortex..