Mastoid vibration affects dynamic postural control during gait in healthy older adults

Abstract

Vestibular disorders are difficult to diagnose early due to the lack of a systematic assessment. Our previous work has developed a reliable experimental design and the result shows promising results that vestibular sensory input while walking could be affected through mastoid vibration (MV) and changes are in the direction of motion. In the present paper, we wanted to extend this work to older adults and investigate how manipulating sensory input through mastoid vibration (MV) could affect dynamic postural control during walking. Three levels of MV (none, unilateral, and bilateral) applied via vibrating elements placed on the mastoid processes were combined with the Locomotor Sensory Organization Test (LSOT) paradigm to challenge the visual and somatosensory systems. We hypothesized that the MV would affect sway variability during walking in older adults. Our results revealed that MV significantly not only increased the amount of sway variability but also decreased the temporal structure of sway variability only in anterior-posterior direction. Importantly, the bilateral MV stimulation generally produced larger effects than the unilateral. This is an important finding that confirmed our experimental design and the results produced could guide a more reliable screening of vestibular system deterioration.

Figure 1

(A) Marginal means (averaging the three MV conditions) for the coefficient of variation of the six LSOT conditions. Error bars show standard deviations. The post hoc differences are indicated over the bars with the number of the condition with which differences were found. (B) Bar charts showing the marginal means (averaging the six LSOT condition) of the coefficient of variation of the three MV conditions. Error bars show standard deviations. The post hoc differences are indicated over the bars with the type of the condition with which differences were found. (C) Group means (cell means in terms of the two-way ANOVA) for all conditions with brackets over the bars to identify significant differences between conditions. **: <0.01; ***: <0.0001.

Figure 2. Marginal means (averaging the three MV conditions) for the Sample Entropy in the AP direction for the six LSOT conditions.

Error bars are standard deviations. The post hoc differences are indicated over the bars with the number of the condition with which differences were found. (B) Marginal means (averaging the six LSOT condition) for the Sample Entropy in the AP direction for the three MV conditions. Error bars show standard deviations. The post hoc differences are indicated over the bars with the type of the condition with which differences were found. (C) Group means (cell means in terms of the two-way ANOVA) for all conditions. Brackets indicate significant differences between conditions. **: <0.01; ***: <0.0001.

Figure 3

(A) Marginal means (averaging the three MV conditions) for the Sample Entropy in the ML direction for the six LSOT conditions. Error bars show standard deviations. The post hoc differences are indicated over the bars with the number of the condition with which differences were found. (B) Marginal means (averaging the six LSOT condition) for the Sample Entropy in the ML direction for the three MV conditions. Error bars show standard deviations. No significant main effect was found. (C) Group means (cell means in terms of the two-way ANOVA) for all conditions. No significant interaction was found.

Figure 4. The tactor system contains two tactors and a controller unit for communication with the computer through Bluetooth and transmission of stimulus control signals to the tactors.

Figure 5. The netCOP sway area was composed from the two triangle areas that are represented by the dotted lines.

Five points were used to generate these two-triangle areas as following: intersection point (IP), right heel-strike (RHS), right toe-off (RTO), left heel-strike (LHS), left toe-off (LTO).