You will be presented with the abstract, introduction, and discussion section from a biomedical research article. Your task is to create a summary that a layperson can understand, capturing the essence of the research article. Keep essential scientific terms, but ensure that the language remains clear and the concepts are explained in an uncomplicated manner.

Title: Entorhinal cortex receptive fields are modulated by spatial attention, even without movement}
Article:
Abstract:
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.
Introduction:
Spatial representations, in the form of place cells and grid cells, have been identified in rodents( Hafting et al., 2005; O'Keefe and Dostrovsky, 1971), bats( Yartsev et al., 2011; Yartsev and Ulanovsky, 2013), macaque monkeys( Killian et al., 2012) and humans( Jacobs et al., 2013; Ekstrom et al., 2003). The hippocampal formation, however, also contributes to the processing of memories( Squire and Wixted, 2011), and conceptual similarities between spatial navigation and the processes involved in remembering and planning suggest that grid cells might support cognitive functions besides spatial navigation( Buzsáki et al., 2013). This idea resonates well with the recent demonstration that grid cells are active during the exploration of images with eye-movements, that is by overt attention( Killian et al., 2012). These findings revealed that grid cells do not only track an animal's location in space, but can also represent the gaze position of the animal. Shifts of gaze location usually correspond to shifts in attention( Hoffman, 1998; Rolfs et al., 2011), and the neural substrate for overt and covert attention is largely overlapping( Corbetta et al., 1998). Accordingly, grid cells in the entorhinal cortex are potentially capable of representing not only gaze location but the locus of attention in general. Here, we investigated whether firing fields of entorhinal cells are activated by movements of covert attention, in the absence of any physical movement. Attention functions as an important control for mental processes( Petersen and Posner, 2012); accordingly, the hypothesis that grid cells participate in a range of cognitive functions predicts that grid cells may be activated by movements of attention. Here, we tested this prediction by recording from single units in the entorhinal cortex in monkeys trained to perform a task of covert attention.
Discussion:
In summary, our results provide strong evidence that the activation of cells in entorhinal cortex with spatially structured firing fields does not require physical movement through an environment. Previous results demonstrated that, in stationary monkeys, grid cells can be activated by eye movements as monkeys visually explore complex scenes( Killian et al., 2012). Here, our findings suggest that even eye movements are not required to activate cells with grid-like firing fields and that firing fields in the entorhinal cortex cells can represent the location of attention. That spatial representations in the hippocampal formation can represent locations other than the animal’s current position has been shown in rodents through the identification of theta phase precession( O'Keefe and Recce, 1993) and the demonstration that ensembles of hippocampal place cells fire in sequence within a theta cycle, representing places in front of and behind the animal( Muller and Kubie, 1989; Skaggs and McNaughton, 1996; Jensen and Lisman, 1996). More recent studies have shown that sequential firing of hippocampal place cells can represent anticipation of upcoming locations( Diba and Buzsáki, 2007), future possible paths when the rat is at a choice point( Johnson and Redish, 2007; Singer et al., 2013), and even behavioral trajectories toward a remembered goal in a 2D environment( Pfeiffer and Foster, 2013). While it is difficult in rodents to assess the location of attention distinct from the location of the animal, these data are consistent with the idea that hippocampal sequences may reflect the animal’s attention being directed along a specific spatial trajectory. Paying attention to the just-completed trajectory could serve to enhance encoding of that experience. Correspondingly, directing attention to future possible paths could serve as a retrieval mechanism to enable optimal choice behavior. These findings also resonate well with reports of grid-like six-fold symmetric BOLD activity while participants imagine navigating in a familiar environment( Horner et al., 2016), imagine directions between locations in a large-scale virtual city( Bellmund et al., 2016), and navigate a purely abstract concept space( Constantinescu et al., 2016). The data presented here demonstrate that entorhinal cells with grid-like firing fields can similarly encode information apart from the animal’s current location. In agreement with Killian et al.( 2012), we found a percentage of grid cells( 14%) that is lower than reports from recording in rats( e. g. 32% in Sargolini et al., 2006). We see several possible explanations for this discrepancy. First, our task design is limited to detecting a subset of grid cells who’s firing fields match the size of the screen and the spacing of the dot’s trajectory, thereby potentially underestimating the true percentage of grid cells in macaque entorhinal cortex. Second, our task design does not attach significance to the spatial position of the dot. It is possible to solve the task without knowing where the color change occurs. Thus, it seems plausible that our observations reflect the entorhinal cortex in an attenuated state and that we would observe stronger grid cell activity if the precise dot position was relevant. Future work could address these points by enlarging the screen, including more fixation locations around which the moving dot needs to be observed, and by making the spatial position relevant. The latter might be achieved by introducing an invisible spatial reward field, such that the monkey does not need to detect a color change but only respond when the dot passes through high reward areas on the screen. A good strategy would thereby require integration of the spatial position of received reward to infer the layout of the reward field. Future experiments examining links between grid cell responses and behavior are critical for advancing our understanding of the function of the entorhinal cortex.
When driving home from work , we can easily tell where we are along our route . A network of regions deep within the brain acts a little like an inbuilt GPS and tracks our position relative to other objects in the environment . Cells in one of these brain regions , called the entorhinal cortex , construct a map of our surroundings . The map resembles a grid of tessellating triangles , and the cells that produce it are called grid cells . Whenever we move onto a corner of one of the triangles , the corresponding grid cells start to fire . This firing enables the brain to track our movements . But grid cells may do more than support navigation through the physical world . They may also help us navigate through our memories . Evidence suggests that we organize our knowledge and experiences into mental maps . These maps connect related concepts just as physical maps connect nearby locations . In principle , the brain systems that support physical navigation may also enable us to access the information within our mental maps . But for this to be true , cells such as grid cells must respond to movement in mental space as well as in physical space . Wilming et al . have now tested this possibility by training macaque monkeys to detect a color change in a dot moving across a screen . The monkeys had to keep their eyes fixed on the center of the screen throughout the task . This meant they could not move their eyes to track the dot . Instead they had to mentally move the focus of their attention . Wilming et al . monitored the activity of cells in the entorhinal cortex as the monkeys mentally followed the dot . As predicted , some of the cells fired in a triangular grid-like pattern similar to that seen when animals move through their environment . Grid cells can thus fire in the absence of physical movement . These findings bring us closer to understanding how brain circuits that code for spatial locations also support other mental processes . Evidence from many sources suggests that structures within the brain’s medial temporal lobe , including the entorhinal cortex , contribute to memory . The next challenge is to identify how these brain regions encode spatial and other types of information and use them to form memories .