Moving bar of light evokes vectorial spatial selectivity in the immobile rat hippocampus

Visual cortical neurons encode the position and motion direction of specific stimuli retrospectively, without any locomotion or task demand. Hippocampus, a part of visual system, is hypothesized to require self-motion or cognitive task to generate allocentric spatial selectivity that is scalar, abstract, and prospective. To bridge these seeming disparities, we measured rodent hippocampal selectivity to a moving bar of light in a body-fixed rat. About 70% of dorsal CA1 neurons showed stable activity modulation as a function of the bar angular position, independent of behavior and rewards. A third of tuned cells also encoded the direction of revolution. In other experiments, neurons encoded the distance of the bar, with preference for approaching motion. Collectively, these demonstrate visually evoked vectorial selectivity (VEVS). Unlike place cells, VEVS was retrospective. Changes in the visual stimulus or its trajectory did not cause remapping but only caused gradual changes. Most VEVS-tuned neurons behaved like place cells during spatial exploration and the two selectivities were correlated. Thus, VEVS could form the basic building block of hippocampal activity. When combined with self-motion, reward, or multisensory stimuli, it can generate the complexity of prospective representations including allocentric space, time, and episodes.

Decision-related feedback in visual cortex lacks spatial selectivity

Feedback in the brain is thought to convey contextual information that underlies our flexibility to perform different tasks. Empirical and computational work on the visual system suggests this is achieved by targeting task-relevant neuronal subpopulations. We combine two tasks, each resulting in selective modulation by feedback, to test whether the feedback reflected the combination of both selectivities. We used visual feature-discrimination specified at one of two possible locations and uncoupled the decision formation from motor plans to report it, while recording in macaque mid-level visual areas. Here we show that although the behavior is spatially selective, using only task-relevant information, modulation by decision-related feedback is spatially unselective. Population responses reveal similar stimulus-choice alignments irrespective of stimulus relevance. The results suggest a common mechanism across tasks, independent of the spatial selectivity these tasks demand. This may reflect biological constraints and facilitate generalization across tasks. Our findings also support a previously hypothesized link between feature-based attention and decision-related activity.

Neural responses to natural visual motion are spatially selective across the visual field, with selectivity differing across brain areas and task

It is well established that neural responses to visual stimuli are enhanced at select locations in the visual field. While spatial selectivity and the effects of spatial attention are well-understood for discrete tasks (e.g., visual cueing paradigms), little is known about neural response during a naturalistic visual experience that involves complex dynamic visual stimuli, for instance, driving. In this study, we assess the strength of neural responses across the visual space during a kart race video game. Specifically, we measure the correlation strength of scalp evoked potentials with optical flow magnitude at individual locations on the screen. We find the strongest neural responses for task-relevant locations in visual space, selectively extending to areas beyond the focus of overt attention: while the driver’s gaze is directed upon the heading direction at the center of the screen, we observe robust neural evoked responses also to peripheral areas such as the road and surrounding buildings. Importantly, this spatial selectivity of neural responses differs across scalp locations. Moreover, during active gameplay, the strength of the spatially-selective neural responses are enhanced compared to passive viewing. Spatially selective neural gains have previously been interpreted as an attentional gain mechanism. In this view, the present data suggest that different brain areas focus attention on different task-relevant portions of the visual field, reaching beyond the focus of overt attention.

Hippocampal representations of distance, space, and direction and their plasticity predict navigational performance

ABSTRACTThe hippocampus is implicated in episodic memory and allocentric spatial navigation. However, spatial selectivity is insufficient to navigate; one needs information about the distance and direction to the reward on a specific journey. The nature of these representations, whether they are expressed in an episodic-like sequence, and their relationship with navigational performance are unknown. We recorded single units from dorsal CA1 of the hippocampus while rats navigated to an unmarked reward zone defined solely by distal visual cues, similar to the classic water maze. The allocentric spatial selectivity was substantially weaker than in typical real world tasks, despite excellent navigational performance. Instead, the majority of cells encoded path distance from the start of trials. Cells also encoded the rat’s allocentric position and head angle. Often the same cells multiplexed and encoded path distance, head direction and allocentric position in a sequence, thus encoding a journey-specific episode. The strength of neural activity and tuning strongly correlated with performance, with a temporal relationship indicating neural responses influencing behavior and vice versa. Consistent with computational models of associative Hebbian learning, neural responses showed increasing clustering and became better predictors of behaviorally relevant variables, with neurometric curves exceeding and converging to psychometric curves. These findings demonstrate that hippocampal neurons multiplex and exhibit highly plastic, task- and experience-dependent tuning to path-centric and allocentric variables to form an episode, which could mediate navigation.

Analysis of the selectivity properties of volumetric holograms in radio-photonic devices

The importance of the use of radio-photonics in telecommunication equipment is shown. The place and tasks of volumetric holograms in radio-photonic devices are described. The urgency of the problem of studying the properties of selectivity of a volume hologram, which determine the influence of this hologram on the parameters of the light flux in a radio photonics device, has been substantiated. The analysis of the exposure conditions of the volume hologram for the formation of the structure of the striations, providing its spectral and spatial selectivity to the light flux. A reasonable choice of the type of photographic material of a volumetric hologram for its use in the construction of a radio-photonic device is shown. A variant of the optical scheme for recording a volume hologram with two counter propagating light beams with spherical wave fronts and the equation of this hologram are presented. The parameters that determine the structure of the striations of the volume hologram are listed. The analysis of the conditions for the reconstruction of the optical field exposed on the volume hologram is carried out. Conditions for optimal reconstruction of an optical field by a hologram and its destruction are considered. Diagrams of the angles of reconstruction of optical fields by a volumetric reflective hologram are presented. It is shown that when a reconstructing light beam with a spherical wave front is incident on a volume hologram, in order to provide the highest value of the energy of the reconstructed optical field, the reconstructing light beam must be narrowly directed, and its optical axis must coincide with one of the directions of optimal reconstruction. In this case, the reconstructing light beam should be located between the two directions of complete destruction of the optical field. It is concluded that a volume hologram possesses the properties of both spectral (to the wavelength of light) and spatial selectivity, which must be taken into account when using it in a radio-photonic device.