Swallowing problems, and the often-associated sequelae including pneumonia, malnutrition, and dehydration are common, potentially life-threatening conditions suffered by many elderly individuals. The combination of cognitive, physical, and sensory impairments commonly seen in individuals with dementia and following stroke often results in eating needs going unmet, leading to increased morbidity and premature mortality. The functional limitations of many of these individuals frequently result in decreased mealtime independence and necessitate extensive or total assistance (i.e., dependence) with consuming food and liquids. Despite the implication of increased safety associated with feeding assistance, the influence and potential risk of absent pre-oral cues are unclear, especially in an already taxed system. This study investigated the cooperative relationships between the sequential sensorimotor acts involved in eating and swallowing, focusing on the anticipatory stage, under various sensory-loss conditions.
Kinematic data from the lips, jaw, and hand were obtained from 24 healthy younger adults (ages 18-30) and 24 healthy older adults (ages 70-85) under four different conditions: typical self-feeding, typical assisted feeding (i.e., loss of proprioceptive cues), sensory loss self-feeding (i.e., loss of visual cues and degradation of auditory cues), and sensory loss assisted feeding (i.e., loss/degradation of auditory, proprioceptive, and visual cues). During typical self-feeding, all participants began the mouth opening gesture shortly after the onset of hand movement toward the mouth and prior to the onset of oral sensation. However, differences in the timing of anticipatory onset and offset lip movements were observed between older and younger adults and also on the basis of the presence/absence of feeding dependency and sensory loss. Older adults initiated lowering movement earlier than younger adults given the availability of proprioceptive and/or visual cues. In addition to demonstrating earlier lip lowering, during both self-feeding conditions older adults more consistently attended to the timing between lip lowering onset and hand movement onset as compared to both the younger adults and other relative timing pairs. Given the absence of proprioceptive cues (i.e., during assisted feeding), the onset of anticipatory lip movement was delayed. Sensory loss (i.e., loss of visual cues, reduction in auditory cues) alone did not negatively impact the onset of lip movement for either group as compared to typical self-feeding. Conversely, the presence of sensory loss more negatively impacted the offset of lip movement as compared to the absence of proprioception (e.g., the offset of lip movement was later given only visual/auditory loss as compared to assisted feeding). The presence of both feeding dependence and sensory loss had the greatest negative impact on the timing of both the onset and offset of anticipatory lip movement.
These findings suggest that deglutition should be considered as beginning prior to the onset of oral sensation and highlight the necessity of better understanding the role that pre-oral, or anticipatory, sensorimotor information may play in the overall eating and deglutitory process. As older adults consistently demonstrated a "compensatory advantage" via earlier and less variable movement onset given the availability of proprioceptive and/or visual cues, continued investigation into these age-related differences is important. This study provides a first step in clarifying the relationship between these pre-oral cues and anticipatory oral posturing during eating and swallowing, allowing for a better understanding of the potential for increased risk assisted feeding recommendations may elicit. However, the differences observed between older and younger adults, particularly under conditions of sensory loss, may be further exacerbated in a taxed system, potentially increasing risk for various patient populations.