Long and short whiskers differently guide snout/pellet interaction in rat oral grasping

Abstract

AbstractWe studied the role of rat whisker/snout tactile sense during oral grasping, comparing control data with those obtained, respectively, 1–3 and 5–7 days after bilateral long or short whisker trimming and 3–5 and 8–10 days after bilateral infraorbital nerve (ION) severing. Two behavioural phases were identified: whisker–snout contact by nose‐N or lip‐L and snout–tongue contact. The second phase involved either: snout passing over stationary pellet (Still pellet); pellet rolling as the snout passed over it (Rolling pellet); pellet being pushed forward by the snout (Pushed pellet); or pellet being hit and pushed away (Hit/Lost pellet). In controls, success was 100%, with N‐contact prevailing over L‐contact in the first phase and Still pellet in the second. In long whisker‐trimmed versus controls, success was still 100%, but L‐contact increased in frequency, Pushed pellet prevailed and the second phase duration increased. In short whisker‐trimmed versus controls, success remained 100%, with increased L‐contact frequency; the first phase duration did not change, but the second phase increased since in pushed trials, the pellet rolled around the snout. In ION‐severed versus controls, both phases changed drastically: L‐contact frequency increased, Pushed pellet prevailed and contact was persistently maintained; Hit/Lost pellet emerged, Still and Rolling pellets disappeared and the oral‐grasping sequence was not triggered. These results suggest that long and short whiskers, respectively, optimize the first and second phases of snout–pellet interaction and that whisker/snout sense is necessary to trigger oral grasping. Kinematic trajectory analysis supports the conclusion that movement from whisker to snout contact is an orientation response.