Analysis of the principles governing the dimensionality reduction performed by Lobula Plate Tangential Cells

Lobula Plate Tangential Cells (LPTCs) are critical for visual navigation in flies, enabling efficient processing of optical flow. Unlike upstream neurons in the visual pathway, such as those in the Lobula, Medulla, and T4/T5 layers, which retain a retinotopic organisation, LPTCs perform the first major dimensionality reduction of visual signals. This reduction simplifies the vast amount of visual information into key motion signals essential for navigation. In this paper, we investigate the principles governing this dimensionality reduction and explore with a data-based approach the efficiency of LPTCs in compressing optical flow information while preserving critical motion cues for navigation and their role in transmitting information to descending neurons. More specifically, our contribution is as follows: (i) we demonstrate, using Principal Component Analysis (PCA) as a reference, that global optical flow patterns, as also found in LPTC response maps, are efficient to describe and encode the variation in the optical flow experienced during visual navigation tasks; (ii) we show that LPTCs present a strong alignment with Principal Components of the experienced optical flow, supporting the hypothesis that the LPTCs maximize the flow of signal energy from the T4/T5 cells to the descending neurons; and (iii) we show that whilst LPTCs encode optical flow information in a lossy fashion, it can be reconstructed. Using optical flow priors, such as the complementarity of LPTCs in contralateral hemispheres and continuity of the flow in navigation tasks, we performed a reconstruction of the original flow from LPTCs response. Our analysis reveals the dual potential of LPTCs: selectively relaying signals for navigation that are fine-tuned in relation to the flys own dynamics; and broadly compressing the optical flow information that is sensed by the flys visual system.