Biology subjects

Kempkes, E.

Publications and source records attributed to Kempkes, E..

3 recordsLinked to original sources

bioRxiv2026

Lateral-eyed tree shrews combine panoramic vision with an expanded oculomotor repertoire

Mammals differ in how they redirect gaze. Primates shift and hold gaze with rapid, precise eye movements that can be decoupled from the head. In lateral-eyed mammals studied to date, gaze is organized around the head: saccades are coupled to head rotation in freely moving animals and typically accompanied by attempted head movements even under head fixation. These observations suggest a trade-off: animals that keep a panoramic field give up the precise, eye-driven control of gaze typical of frontal-eyed animals. But because lateral eyes and head-centered gaze co-occur in every lateral-eyed species studied, it is unknown whether one follows from the other. Here we test this in the tree shrew, an arboreal mammal with laterally placed eyes. Using real-time eye tracking in head-fixed animals, we find that tree shrews saccade frequently under head fixation and that most saccades occur without detectable attempted head movement. Tree shrews make visually evoked saccades, along both the horizontal and vertical axes of the visual field, toward targets. They can also fixate on visual targets. Using widefield calcium imaging, we show that visual cortex over-represents the central visual field. Lastly, we show that extraocular muscles contain morphologically elaborate palisade endings, specialized nerve endings that are a constant feature of frontal-eyed species. Lateral eyes therefore do not preclude eye-driven gaze control. The two are separable dimensions of visual system design, a combination that may suit animals whose locomotion routinely points the head away from where they need to look.

neuroscience↗

bioRxiv2023

High-density recording reveals sparse clusters (but not columns) for shape and texture encoding in macaque V4

Macaque area V4 includes neurons that exhibit exquisite selectivity for visual form and surface texture, but their functional organization across laminae is unknown. We used high-density Neuropixels probes in two awake monkeys to characterize shape and texture tuning of dozens of neurons simultaneously across layers. We found sporadic clusters of neurons that exhibit similar tuning for shape and texture: [~]20% exhibited similar tuning with their neighbors. Importantly, these clusters were confined to a few layers, seldom columnar in structure. This was the case even when neurons were strongly driven, and exhibited robust contrast invariance for shape and texture tuning. We conclude that functional organization in area V4 is not columnar for shape and texture stimulus features and in general organization maybe at a coarse scale (e.g. encoding of 2D vs 3D shape) rather than at a fine scale in terms of similarity in tuning for specific features (as in the orientation columns in V1). We speculate that this may be a direct consequence of the great diversity of inputs integrated by V4 neurons to build variegated tuning manifolds in a high-dimensional space. Significance StatementIn primary visual cortex of the macaque monkey, studies have demonstrated columnar functional organization, i.e. shared tuning across layers for stimulus orientation, spatial frequency, ocular dominance, etc. In mid and higher level visual form processing stages, where neurons exhibit high-dimensional tuning, functional organization has been harder to evaluate. Here, leveraging the use of the high-density Neuropixels probes to record simultaneously from dozens of neurons across cortical layers, we demonstrate that functional organization is not columnar for shape and texture tuning in area V4, a midlevel stage critical for form processing. Our results contribute to the debate about the functional significance of cortical columns providing support to the idea that they emerge due to one-to-many representational expansion.

neuroscience↗

bioRxiv2023

Inserting a Neuropixels probe into awake monkey cortex: two probes, two methods

Neuropixels probes have revolutionized neurophysiological studies in the rodent, but inserting these probes through the much thicker primate dura remains a challenge. Here we describe two methods we have developed for the insertion of two types of Neuropixels probes acutely into the awake monkey cortex. For the fine rodent probe, which is unable to pierce native primate dura, we developed a duraleyelet method to insert the probe repeatedly without breakage. For the thicker NHP probe, we developed an artificial dura system to insert the probe. We have now conducted successful experiments in 3 animals across 7 recording chambers with the procedures described here and have achieved stable recordings over several months in each case. Here we describe our hardware, surgical preparation, methods for insertion and methods for removal of broken probe parts. We hope that our methods are of value to primate physiologists everywhere.

neuroscience↗