Biology subjects

Purandare, C.

Publications and source records attributed to Purandare, C..

3 recordsLinked to original sources

bioRxiv2025

Kinematic fields of the visuo-hippocampal circuit

The structure of focused receptive fields in retinotopic and allocentric space in the visual cortex and hippocampus is studied extensively to understand cognitive functions such as stimulus tracking and path-integration, respectively. These functions require accurate tracking of running speed and acceleration. While speed dependence in these areas is well-studied, the acceleration dependence has received little attention, and the joint effect of speed-acceleration is unknown. Hence, we assessed the joint influence of these kinematic variables by computing receptive fields in a novel, 2D phase space of speed-acceleration using the Allen Brain Visual Observatory data. Head-fixed mice ran spontaneously on a running wheel next to a monocular gray screen ensuring virtually no changes in the retinotopic or allocentric space. Remarkably, about half (44.3%, 6590/14862) of neurons in the visuo-hippocampal circuit (from LGN to subiculum) were significantly modulated by a specific combination of speed and acceleration to form receptive fields in the speed-acceleration phase space (called kinematic space). The prevalence of kinematic tuning is comparable to the fraction of place cells in this part of the mouse hippocampus, and the fraction of visually tuned neurons in higher visual areas. The kinematic field size ([~]30% of the sampled space) was also comparable to the place field size. Kinematic fields spanned the entire space but preferred either low-speed, high-acceleration or the high-speed, low-acceleration segments. Although pupil size too varied spontaneously, the kinematic tuning exceeded pupil size tuning in all brain areas. Surprisingly, pupil size modulated the activity of [~]20% of hippocampal neurons, which was comparable to that in LGN and visual cortical areas. Thus, all visuo-hippocampal areas have focused kinematic fields that are three times more prevalent than the pupil size fields in the absence of any vestibular, visual or spatial stimuli. This kinematic phase space could interface with retinotopic and allocentric spaces to guide natural behaviors involving movement.

neuroscience↗

bioRxiv2022

Mega-scale movie-fields in the mouse visuo-hippocampal network

Natural experience often involves a continuous series of related images while the subject is immobile. How does the cortico-hippocampal circuit process this information? The hippocampus is crucial for episodic memory1-3, but most rodent single unit studies require spatial exploration4-6 or active engagement7. Hence, we investigated neural responses to a silent, isoluminant, black and white movie in head-fixed mice without any task or locomotion demands, or rewards, from the Allen Brain Observatory. The activity of most neurons (97%, 6554/6785) in the thalamo-cortical visual areas was significantly modulated by the 30s long movie clip. Surprisingly, a third (33%, 3379/10263) of hippocampal -dentate gyrus, CA1 and subiculum- neurons showed movie-selectivity, with elevated firing in specific movie sub-segments, termed movie-fields. Movie-tuning remained intact when mice were immobile or ran spontaneously. On average, a tuned cell had more than 5 movie-fields in visual areas, but only 2 in hippocampal areas. The movie-field durations in all brain regions spanned an unprecedented 1000-fold range: from 0.02s to 20s, termed mega-scale coding. Yet, the total duration of all the movie-fields of a cell was comparable across neurons and brain regions. We hypothesize that hippocampal responses show greater continuous-sequence encoding than visual areas, as evidenced by fewer and broader movie-fields than in visual areas. Consistent with this hypothesis, repeated presentation of the movie images in a fixed, scrambled sequence virtually abolished hippocampal but not visual-cortical selectivity. The enhancement of continuous movie tuning compared to the scrambled sequence was eight-fold greater in hippocampal than visual areas, further supporting episodic-sequence encoding. Thus, all mouse-brain areas investigated encoded segments of the movie. Similar results are likely to hold in primates and humans. Hence, movies could provide a unified way to probe neural mechanisms of episodic information processing and memory, even in immobile subjects, across brain regions, and species.

neuroscience↗

bioRxiv2021

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 demand1. Hippocampus, a part of visual system, is hypothesized to require self-motion or cognitive task to generate allocentric spatial selectivity that is scalar, abstract2,3, and prospective4-7. 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 bars 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 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 selectivity were correlated. Thus, VEVS could form the basic building block of hippocampal activity. When combined with self-motion, reward, or multisensory stimuli8, it can generate the complexity of prospective representations including allocentric space9, time10,11, and episodes12.

neuroscience↗