Meeting Abstract

LBS1.4  Thursday, Jan. 3  Variation in EMG Activity during Feeding: A Hierarchical Approach GERMAN, R.Z.*; CROMPTON, A.W.; THEXTON, A.J.; Johns Hopkins University; Harvard University; King’s College, London rz.german@jhmi.edu

During repetitions of apparently identical movements, there are several potential sources of temporal variation in the rectified and integrated EMG signals recorded by a single bipolar intramuscular wire electrode. These sources include the selective detection of different types of motor units, their differential recruitment, their differential fatigue and the unspoken problem of micro-changes in electrode position relative to nearby muscle fibers. Differences in EMG signals also occur between electrodes at different sites within an individual muscle as well as between individuals, reflecting anatomical differences. We assessed the relative significance of these factors using a hierarchical nested model of existing EMG activity data recorded from 16 oropharyngeal muscles in infant pigs during feeding. We used two infant pig models: 1) a supra-collicular decerebrate with an isolated pharyngeal swallow but no rhythmic activity 2) an intact infant exhibiting both swallowing and rhythmic suckling. In some muscles the variation was minimal within signals from a single electrode over time, among signals from multiple electrodes in the same muscle, and among signals from different individuals. In other muscles, variation existed at all levels. Intra-muscle variation was sometimes as great as inter-individual variation. Muscles with variable EMG signals appeared to subserve multiple functions and they presumably contained different task units. In this situation, statistical methods were essential to characterize the overall patterns of EMG activity. These results suggest that a single bipolar electrode is generally insufficient to characterize the function of a particular muscle.