title: Structure, function, and cortical representation of the rat submandibular whisker trident.
abstract: Although the neurobiology of rodent facial whiskers has been studied intensively, little is known about sensing in other vibrissae. Here we describe the under-investigated submandibular "whisker trident" on the rat's chin. In this three-whisker array, a unique unpaired midline whisker is laterally flanked by two slightly shorter whiskers. All three whiskers point to the ground and are curved backwards. Unlike other whiskers, the trident is not located on an exposed body part. Trident vibrissae are not whisked and do not touch anything over long stretches of time. However, trident whiskers engage in sustained ground contact during head-down running while the animal is exploring or foraging. In biomechanical experiments, trident whiskers follow caudal ground movement more smoothly than facial whiskers. Remarkably, deflection angles decrease with increasing ground velocity. We identified one putative trident barrel in the left somatosensory cortex and two barrels in the right somatosensory cortex. The elongated putative trident-midline barrel is the longest and largest whisker barrel, suggesting that the midline trident whisker is of great functional significance. Cortical postsynaptic air-puff responses in the trident representation show much less temporal precision than facial whisker responses. Trident whiskers do not provide as much high-resolution information about object contacts as facial whiskers. Instead, our observations suggest an idiothetic function: their biomechanics allow trident whiskers to derive continuous measurements about ego motion from ground contacts. The midline position offers unique advantages in sensing heading direction in a laterally symmetric manner. The changes in trident deflection angle with velocity suggest that trident whiskers might function as a tactile speedometer.
authors.affiliation: Neural Systems and Behavior, Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA.
authors.forename: Lydia
authors.initials: L
authors.lastname: Thé
authors.forename: Michael L
authors.initials: ML
authors.lastname: Wallace
authors.forename: Christopher H
authors.initials: CH
authors.lastname: Chen
authors.forename: Edith
authors.initials: E
authors.lastname: Chorev
authors.forename: Michael
authors.initials: M
authors.lastname: Brecht
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000344:Afferent Pathways / Q000502:physiology*; D000818:Animals; D001696:Biomechanical Phenomena; D001931:Brain Mapping; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D005260:Female; D007839:Functional Laterality; D053444:Inhibitory Postsynaptic Potentials / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009068:Movement / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D018408:Patch-Clamp Techniques; D010812:Physical Stimulation; D051381:Rats; D020318:Rats, Long-Evans; D013003:Somatosensory Cortex / Q000166:cytology / Q000502:physiology*; D014110:Touch; D055698:Touch Perception / Q000502:physiology; D014738:Vibrissae / Q000033:anatomy & histology* / Q000294:innervation*; D014741:Video Recording