TRANSITION FROM SUCKLING TO DRINKING AT WEANING - A KINEMATIC AND ELECTROMYOGRAPHIC STUDY IN MINIATURE PIGS

The movements of the tongue, hyoid, and jaw were recorded cineradiogra phically in preweaning pigs as they suckled bariumized milk from a vet erinary teat or drank it from a bowl. The movements were quantified by measuring the X, Y coordinates of radioopaque markers embedded in the tongue and attached to both jaws and to the hyoid. EMG activity in ma sseter, anterior digastric, geniohyoid, genioglossus, hyoglossus, ster nohyoid, stylohyoid, and omohyoid muscles was recorded synchronously w ith cineradiography at 100 frames/sec. In both suckling and drinking, the movements were characterized by minimal movements of the jaw and h yoid but extensive movements of the tongue. In suckling, the movements were largely confined to the mid-posterior part of the tongue. A seal was formed between the posterior tongue and soft palate while a depre ssion formed in the mid-tongue; this was associated with fluid moving into the depression probably because of a reduced intraoral pressure. The depression was associated with increased EMG activity in the genio glossus muscle and overlapping activity in digastric, geniohyoid, hyog lossus, and sternohyoid muscles. In drinking cycles, significant movem ent occurred in all parts of the tongue; milk ingestion was associated with tongue movements that combined elements characteristic both of s uckling (mid-tongue depression with a posterior seal) and of lapping ( extensive anteroposterior movements within the tongue itself). In drin king, compared to suckling, there was a major reduction in EMG activit y in masseter, digastric, geniohyoid, and sternohyoid muscles. After m ilk had accumulated in the valleculae, swallows usually occurred in ev ery other cycle during suckling and in every third or fourth cycle dur ing drinking. The emptying of the valleculae was an event that was emb edded in the early jaw-opening phase of an otherwise normal suckling o r drinking cycle. Emptying of the valleculae was associated with poste riorly directed movement of the back of the tongue and increased EMG a ctivity in hyoglossus, styloglossus, and omohyoid muscles. No differen ces were noted in the kinematics associated with swallowing in the two activities, but, in the normalized and averaged EMG data, there were significant differences in the timing of genioglossus activity and in the relative balance of hyoglossal and stylohyoid activity. (C) 1998 W iley-Liss, Inc.