An Investigation of the Effect of Chewing on Rhythmic Motor Tasks

Chewing gum and walking has traditionally been cited as the quintessentially difficult dual task, but little is known regarding chewing effects on motor control. The aims of this dissertation include describing chewing patterns across adulthood, describing chewing’s influence on secondary motor tasks, and investigate entrainment patterns of chewing and gait per established patterns of coupled oscillators. Three experiments were conducted to describe chewing patterns and to examine the effect chewing has on other motor tasks, particularly walking, in young and old adults. The first experiment used a metronome to manipulate chewing rates and measured associated gait parameters. This experiment established that chewing affects gait. As chewing speed increases or decreases, step rate also changes accordingly. Tasks such as walking, finger tapping, and simple reaction time all slow with advancing age. This experiment established chewing as a task resistant to neuromotor slowing with age. The second experiment examined the effect of chewing on a variety of secondary motor tasks. This experiment confirmed that chewing interferes with performance of a discrete secondary task, such as reaction time, whereas chewing entrains with cyclic movements, like finger tapping and gait. The final experiment varied the timing of when chewing was initiated to highlight the inherent organization of task influence. This experiment confirmed that chewing consistently impacts gait, but not vice versa. A top-down hierarchy where chewing drives changes in gait was substantiated. The physiological basis for the observed behavior is discussed in terms of coupled neural oscillators, such as the central pattern generators in the hindbrain and spinal cord. The findings from the series of experiments highlights oral sensory information as a potentially novel method of influencing movement patterns throughout adulthood. The functional implications of chewing are paramount to survival, but the connection between the mouth and the legs has not been well documented. Understanding the mechanisms associated with this inimitable relationship whereby the mouth is driving leg motion during gait could lead to innovative rehabilitative techniques for gait training

Chewing Speed Does Not Follow Typical Patterns of Motor Slowing with Age

Aging adults experience gradual structural changes in nerve and muscle tissues that impair their ability to exploit speed as an effective movement strategy. The aim of the study was to examine whether chewing rates demonstrate a level of age-related neuromotor decline similar to other motor tasks. Fifteen young (20-40 years) and fifteen healthy older adults (60+ years) completed a battery of motor tasks including: walking, finger tapping, simple reaction time, postural sway, and chewing. Gait metrics were collected using a 20-foot pressure-sensitive walkway. All walking was performed at a preferred speed. Participants tapped an accelerometer affixed to a table at a preferred rate. Upper extremity reaction time was recorded by depressing a mouse button with an associated timing mechanism, whereas a similar foot pedal interface was used to measure lower extremity reaction time. Postural sway data was collected using a force plate. Surface electromyography of the masseter was used to record fast(2Hz), slow(1Hz), and preferred chewing rates. Fast and slow chewing rates were set using an auditory metronome which was switched off during recording. Age comparisons for each task were performed using general linear modeling, with additional considerations for chewing speed effects and interactions for the chewing task. The results reveal that older adults demonstrate a general slowing of movement with the exception of chewing speed which appears to be preserved with aging. Regardless of age, preferred chewing rates were nearly identical. Preservation of chewing rates compared to other motor tasks may be due to the difference in anatomical innervation between muscles of mastication and the limbs. Masticatory muscles receive bilateral innervation including ipsilateral and contralateral inputs from the motor cortices, whereas limb muscles receive mainly unilateral innervation from the contralateral cortex. The neural redundancy may preserve chewing rates despite age-related degradation of the system.https://digitalcommons.odu.edu/health_sciences/1009/thumbnail.jp

The Impact of Chewing on Neuromotor Function in Children

Reaction time is a common measure used to assess the speed of cognitive processing in individuals of all ages. Typically the latency for simple reaction time changes with age with children exhibiting slower simple reaction times compared to adults. Chewing gum is a common behavior which many people perform on a daily basis. Evidence suggests that this activity has benefits on attention and memory in children and adults. However, any definitive benefits of chewing for reaction time remain unclear. The current study was designed to examine the effect of chewing at different speeds on simple reaction time in a cohort of typically developing children (n=16, aged 10-17 years). Individuals completed a simple reaction time task under the following conditions: 1) no chewing (control), 2) slow chewing (1 Hz), 3) fast chewing (2.2 Hz), and 4) preferred chewing. A repeated measures, mixed generalized linear model was used to assess differences in reaction time across the four conditions. Results revealed that all chewing conditions led to a significant increase in reaction time values compared to the no-chew (control) condition. Conversely, the reaction time values during the slow and fast chewing conditions were slower than the preferred chewing condition. While these results indicate that chewing gum can have a negative effect on reaction times, systematically instructing children to increase or decrease their chewing rate from their preferred frequency amplified this interference. One possibility is that chewing requires more attention which may result in decreased cognitive resources allocated for the reaction time task. Completing a concurrent oral motor task during a simple reaction time degrades performance.https://digitalcommons.odu.edu/health_sciences/1008/thumbnail.jp