Elephant facial motor control

Abstract

We studied facial motor control in elephants, animals with muscular dexterous trunks. Facial nucleus neurons (~54,000 in Asian elephants, ~63,000 in African elephants) outnumbered those of other land-living mammals. The large-eared African elephants had more medial facial subnucleus neurons than Asian elephants, reflecting a numerically more extensive ear-motor control. Elephant dorsal and lateral facial subnuclei were unusual in elongation, neuron numerosity, and a proximal-to-distal neuron size increase. We suggest that this subnucleus organization is related to trunk representation, with the huge distal neurons innervating the trunk tip with long axons. African elephants pinch objects with two trunk tip fingers, whereas Asian elephants grasp/wrap objects with larger parts of their trunk. Finger “motor foveae” and a positional bias of neurons toward the trunk tip representation in African elephant facial nuclei reflect their motor strategy. Thus, elephant brains reveal neural adaptations to facial morphology, body size, and dexterity.

Elephant trunks use an adaptable prehensile grip

“…African and Asian elephants differ in their trunk anatomy in that African elephants are browsers, and Asian elephants are grazers. This specialization gives African elephants two prehensile trunk fingers, whereas Asian elephants have one, which leads to differences in facial motor control neurons [14].…”

“…Different postures present varying degrees of force, motion, and sensory information [13]. Like the human hand, the African elephant trunk can move with precision and high force due to its 60 000 facial neurons [14].…”

A Myelin Map of Trunk Folds in the Elephant Trigeminal Nucleus

“…Because of the level of detail of our topography suggestions, however, we think it will be relatively straightforward to test the validity of our topography suggestions. Specifically, we predict that the dorsal trunk finger representation of the principalis trunk module will be connected with the distal part of the dorsal subnucleus of the facial nucleus (which contains the putative motor representation of the dorsal trunk finger (Kaufmann et al, 2022)). We would also predict that the dorsal trunk finger representation of the principalis trunk module will be connected with the dorsal trunk finger representation of the oralis nucleus.…”

“…We also performed Golgi and cytochrome oxidase reactivity (Wong & Kaas, 2008;Wong-Riley, 1979). The antibody staining procedure followed the protocols described by Purkart et al, 2022 andKaufmann et al, 2022. For Golgi staining, brains were only minimally fixated (1 day 1% paraformaldehyde in 0.1 M phosphate buffer). Staining was performed with a commercial kit (Rapid Golgi Kit, Gentaur, Aachen Germany).…”

Elephant trunks use an adaptable prehensile grip

“…Different postures present varying degrees of force, motion, and sensory information [13]. Like the human hand, the elephant can move with precision and high force due to the African elephants’ abundant facial neural control from over 60,000 facial neurons[14].…”