Age-Related Changes in Presynaptic Inhibition During Gait Initiation

Abstract

Age-related changes in presynaptic inhibition (PSI) have not been observed during gait initiation, which requires anticipatory postural adjustment (APA). As APA is centrally modulated and is impaired in older compared to young adults, here we aimed to study the presynaptic control and co-contraction levels in the ankle muscles during gait initiation in older compared to young adults. Fifteen older (age range 65–80 years) and 15 young adults (age range 19–30 years) performed a gait initiation task on a force platform under 3 conditions: (i) without electrical stimulation; (ii) test Hoffman reflex (H-reflex); and (iii) conditioned H-reflex. H-reflexes were evoked on the soleus muscle when the APA amplitude exceeded 10%–20% of the average baseline mediolateral force. Participants also performed quiet stance as a control task. Results showed that both age groups presented similar PSI levels during quiet stance (p = .941), while in the gait initiation older adults presented higher PSI levels, longer duration, and lower amplitude of APA than young adults (p < .05). Older adults presented higher co-contraction ratio in both tasks than young adults (p < .05). Correlations between the PSI levels and the APA amplitude (r = −0.61, p = .008), and between the PSI levels and the co-contraction ratio during gait initiation (r = −0.64, p = .005) were found for older adults only. APA amplitude explained 49% of the variance of the PSI levels (p = .003). Our findings suggest that older compared to young adults have increased presynaptic control to compensate for the decreased supraspinal modulation on impaired APAs during gait initiation.

Age-Related Differences in Corticospinal Excitability and Anticipatory Postural Adjustments of the Trunk

“…What are the possible mechanisms underlying delayed APAs seen with ageing? Work has shown increased presynaptic inhibition in spinal circuits prior to gait initiation (i.e., during APAs) in older adults compared with young adults and levels of the inhibition correlating with amplitudes of APAs (Filho et al, 2021). Other studies also reported age differences in the modulation of presynaptic inhibition during an upper-limb postural task (Baudry et al, 2010) and standing (Degani et al, 2020).…”

Reply from Jumes Leopoldino Oliveira Lira, Carlos Ugrinowitsch, Daniel Boari Coelho, Luis Augusto Teixeira, Andrea Cristina de Lima‐Pardini, Fernando Henrique Magalhães, Egberto Reis Barbosa, Fay B. Horak, and Carla Silva‐Batista

“…Regarding the second question, we agree that restoring PSI may compensate for supraspinal dysfunction during FOG episodes, as we have recently demonstrated that healthy elderly individuals have higher PSI levels associated with weaker APAs compared to healthy young individuals (Filho et al 2021). The increase in PSI levels in elderly individuals has been considered an adaptive/compensatory phenomenon, due to age-related deterioration of supraspinal modulation (Morita et al 1995;Filho et al 2021). It is important to highlight that although we assessed PSI in the ON-medication state during no FOG episodes, we will test the hypothesis that the loss of PSI is greater during OFF-medication state than in ON state, as levodopa changes the excitability of the H-reflex in PD (McLeod & Walsh, 1972).…”

“…Regarding the second question, we agree that restoring PSI may compensate for supraspinal dysfunction during FOG episodes, as we have recently demonstrated that healthy elderly individuals have higher PSI levels associated with weaker APAs compared to healthy young individuals (Filho et al . 2021). The increase in PSI levels in elderly individuals has been considered an adaptive/compensatory phenomenon, due to age‐related deterioration of supraspinal modulation (Morita et al .…”

“…1995; Filho et al . 2021). It is important to highlight that although we assessed PSI in the ON‐medication state during no FOG episodes, we will test the hypothesis that the loss of PSI is greater during OFF‐medication state than in ON state, as levodopa changes the excitability of the H‐reflex in PD (McLeod & Walsh, 1972).…”

Revisiting the use of Hoffmann reflex in motor control research on humans

“…In contrast, using tendon vibration and D1 inhibition, Butchart et al (1993) and Earles et al (2001) reported a decrease in Ia presynaptic inhibition in older adults for the soleus. However, others found no difference in Ia presynaptic inhibition between young and older adults in upper and lower limb muscles (Baudry et al 2010;Baudry and Duchateau 2012;Filho et al 2021). These divergent results do not support Ia presynaptic inhibition as a primary contributor to the lesser H-reflex amplitude in older adults.…”