The contribution of cross-modal sensory input to reaching and grasping in blind and sighted short-tailed opossums
Reaching and grasping are essential goal-directed behaviors that require the integration of visual, olfactory, and somatosensory inputs. Although the loss of vision can profoundly disrupt sensory-guided behaviors, mammals often exhibit compensatory cross-modal plasticity allowing them to reach and grasp with ease. To examine how early sensory loss shapes reaching behavior, we performed bilateral enucleations in short-tailed opossums (Monodelphis domestica) of either sex at postnatal day 4, before retino-thalamic and thalamocortical connections have formed. We assessed performance in early blind (EB) and sighted control (SC) animals using a semi-naturalistic reach-to-grasp task requiring precise unilateral limb targeting to retrieve a dead cricket. To isolate the contributions of specific sensory modalities to this task, we selectively disrupted olfactory and mystacial vibrissae inputs and manipulated lighting conditions during task performance. EB opossums were capable of accurate reaching and grasping and showed no significant differences in performance relative to SC animals. Both groups relied strongly on tactile input, as whisker trimming significantly increased targeting error. Removal of olfactory input also impaired performance, with a disproportionately greater effect in EB animals. These findings show that short-tailed opossums retain functional reach-to-grasp behavior after early vision loss and that accurate forelimb movements arise from enhanced spared sensory systems.