Why tree shrews?

Tree shrews are similar in size, appearance, and agility, to squirrels. However, their visual system resembles that of primates. This is because they are evolutionarily close to primates, and highly visual animals. Unlike rodents, they are diurnal. In fact, the large majority of the light sensors in their retinas are cones, which gives tree shrews relatively good vision during well-lit daylight conditions.

As model organisms in visual neuroscience and beyond, tree shrews offer many advantages. They can serve as a bridge between rodent and primate studies, aiding to distinguish species-specific findings from general principles. Their small size makes them amenable for laboratory studies. Their relatively short gestation, and immaturity at birth, make them ideal animals for developmental studies. Their smooth brains are ideal for optical approaches. Their general cleverness, relatively large hippocampus, and versatile 3D movements make them interesting organism for the study of learning and spatial processing. Their distinct vocalizations and social hierarchy leaves open many intriguing possibilities ...

Selected neuroscience publications using the tree shrew as a model organism

A sinusoidal transformation of the visual field is the basis for periodic maps in area V2. Sedigh-Sarvestani, Lee, Jaepel, Satterfield, Shultz & Fitzpatrick. Neuron 2021

This study took advantage of the smooth cortex of the tree shrew to characterize the map of visual space in the secondary visual cortex. A new type of visual space map was discovered. This mapping produces a striped pattern on the surface of secondary visual cortex which has been observed in primates and other animals.

Aspects of tree shrew consolidated sleep structure resemble human sleep. Marta M. Dimanico, Arndt-Lukas Klaassen, Jing Wang, Melanie Kaeser, Michael Harvey, Björn Rasch & Gregor Rainer. Comm Biology 2021

This paper used electrophysiological recordings to characterize the sleep patterns of tree shrews and rats, and compared them to known patters in humans. The findings suggest considerable homology of sleep structure between humans and tree shrews, but not rats, despite the large difference in body mass between these species.

The second visual system of the tree shrew. Petry & Bickford J Comp Neurol 2019

This paper offers an in-depth review of our knowledge of the tree shrew visual system, with a focus on the secondary visual pathway from the retina to the superior colliculus. Tree shrews are unique in their possession of a large and well structured secondary visual system, in addition to a large and well structured parimary visual system leading from the retina to the visual cortex.

This study took advantage of the tree shrew visual cortex's unique laminar structure to show that neural transformation of spatial information along the visual pathway accounts for the simultaneous generation of cortical columnar organization and new feature detect-ability. A similar result, using different methods, was found in cats.

This report shed further light on how the structure of long-range axon connections in visual cortex give rise to functional orientation maps by showing that long-range horizontal connections preferentially link neurons with co-oriented & co-axially aligned receptive fields.

Genome of the Chinese tree shrew. Fan et al. & Yong-Gang Yao Nature Commun 2013

This is the long-awaited publicly available genome sequence for the Chinese tree shrew, closely related tot he Northern tree shrew. The analysis of the data supports a close genetic relationship between tree shrews and primates.

This is the first report of long-range axon collateral in visual cortex that connect clusters of cells in a regular modular arrangement. Future studies linked this structural pattern to orientation maps. The same pattern is now recognized in the visual cortex of primates, cats, and other larger species.