Available Sensory Input Determines Motor Performance and Strategy in Early Blind and Sighted Short-Tailed Opossums

Conserved visual capacity of rats under red light

Recent studies examine the behavioral capacities of rats and mice with and without visual input, and the neuronal mechanisms underlying such capacities. These animals are assumed to be functionally blind under red light, an assumption that might originate in the fact that they are dichromats who possess ultraviolet and green cones, but not red cones. But the inability to see red as a color does not necessarily rule out form vision based on red light absorption. We measured Long-Evans rats’ capacity for visual form discrimination under red light of various wavelength bands. Upon viewing a black and white grating, they had to distinguish between two categories of orientation: horizontal and vertical. Psychometric curves plotting judged orientation versus angle demonstrate the conserved visual capacity of rats under red light. Investigations aiming to explore rodent physiological and behavioral functions in the absence of visual input should not assume red-light blindness.

Kinematic analysis of sensorimotor behavior during variable ladder rung walking in short-tailed opossums (Monodelphis domestica)

This protocol presents a workflow for detecting differences in kinematics between experimental conditions. It is tailored for short-tailed opossums but can be applied to any species capable of completing the ladder rung task. There are four phases of this protocol: (1) data collection, (2) pose tracking, (3) analysis of single trials, and (4) cross-condition comparisons. This pipeline implements aspects of machine learning and signal processing, allowing for rapid data analysis that provides insight into how animals perform this task.

For complete details on the use and execution of this protocol, please refer to Englund et al. (2020).

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Protocol uses a simple sensorimotor task for animal models that requires little training

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Provides a pipeline for rapid analysis of pose tracking data

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Implements supervised clustering, treating pose data as waveforms

Developmental plasticity of texture discrimination following early vision loss in the marsupial Monodelphis domestica

Behavioral strategies that depend on sensory information are not immutable; rather they can be shaped by the specific sensory context in which animals develop. This behavioral plasticity depends on the remarkable capacity of the brain to reorganize in response to alterations in the sensory environment, particularly when changes in sensory input occur at an early age. To study this phenomenon, we utilize the short-tailed opossum, a marsupial that has been a valuable animal model to study developmental plasticity due to the extremely immature state of its nervous system at birth. Previous studies in opossums have demonstrated that removal of retinal inputs early in development results in profound alterations to cortical connectivity and functional organization of visual and somatosensory cortex; however, behavioral consequences of this plasticity are not well understood. We trained early blind and sighted control opossums to perform a two-alternative forced choice texture discrimination task. Whisker trimming caused an acute deficit in discrimination accuracy for both groups, indicating the use of a primarily whisker-based strategy to guide choices based on tactile cues. Mystacial whiskers were important for performance in both groups; however, genal whiskers only contributed to behavioral performance in early blind animals. Early blind opossums significantly outperformed their sighted counterparts in discrimination accuracy, with discrimination thresholds that were lower by ∼75 μm. Our results support behavioral compensation following early blindness using tactile inputs, especially the whisker system.