Abstract
BackgroundIncreasing attention is payed to the contribution of somatosensory processing in motor control. In particular, temporal somatosensory discrimination has been found to be altered differentially in common movement disorders. To date, there have only been speculations as to how impaired temporal discrimination and clinical motor signs may relate to each other. Prior to disentangling this relationship, potential confounders of temporal discrimination, in particular age and peripheral nerve conduction, should be assessed, and a quantifiable measure of proprioceptive performance should be established.ObjectiveTo assess the influence of age and polyneuropathy (PNP) on somatosensory temporal discrimination threshold (STDT), temporal discrimination movement threshold (TDMT), and behavioral measures of proprioception of upper and lower limbs.MethodsSTDT and TDMT were assessed in 79 subjects (54 healthy, 25 with PNP; age 30–79 years). STDT was tested with surface electrodes over the thenar or dorsal foot region. TDMT was probed with needle electrodes in flexor carpi radialis (FCR) and tibialis anterior (TA) muscle. Goniometer-based devices were used to assess limb proprioception during (i) active pointing to LED markers, (ii) active movements in response to variable visual cues, and (iii) estimation of limb position following passive movements. Pointing (or estimation) error was taken as a measure of proprioceptive performance.ResultsIn healthy subjects, higher age was associated with higher STDT and TDMT at upper and lower extremities, while age did not correlate with proprioceptive performance. Patients with PNP showed higher STDT and TDMT values and decreased proprioceptive performance in active pointing tasks compared to matched healthy subjects. As an additional finding, there was a significant correlation between performance in active pointing tasks and temporal discrimination thresholds.ConclusionGiven their notable impact on measures of temporal discrimination, age and peripheral nerve conduction need to be accounted for if STDT and TDMT are applied in patients with movement disorders. As a side observation, the correlation between measures of proprioception and temporal discrimination may prompt further studies on the presumptive link between these two domains.
Highlights
Increasing attention is payed to the contribution of somatosensory processing in motor control
The results of somatosensory temporal discrimination threshold (STDT) and temporal discrimination movement threshold (TDMT) assessment are presented in the upper part of Table 1
Screening the entire data for a potential correlation between the two domains, we found higher temporal discrimination thresholds to be associated with higher pointing errors in the ARROW task at upper (STDT right hand: r = 0.477; p < 0.001; Figure 4A/TDMT right flexor carpi radialis muscle (FCR) muscle: r = 0.546; p < 0.001; Figure 5A) and lower limbs (STDT right foot: r = 0.336; p = 0.002; Figure 4B/TDMT right tibialis anterior muscle (TA) muscle: r = 0.523; p < 0.001; Figure 5B)
Summary
Increasing attention is payed to the contribution of somatosensory processing in motor control. Temporal somatosensory discrimination has been found to be altered differentially in common movement disorders. There have only been speculations as to how impaired temporal discrimination and clinical motor signs may relate to each other. Prior to disentangling this relationship, potential confounders of temporal discrimination, in particular age and peripheral nerve conduction, should be assessed, and a quantifiable measure of proprioceptive performance should be established. Temporal aspects of somatosensory processing have drawn increasing interest as potential markers in the differential diagnostic workup of movement disorders. TDMT is defined as the shortest interval at which a subject perceives two externally induced passive movements as separate (Tinazzi et al, 2005). TDMT has been shown to be increased in PD patients (Fiorio et al, 2007) and patients with essential or functional tremor (Tinazzi et al, 2013a, 2014), whereas it was found normal in patients with writer’s cramp (Tinazzi et al, 2006) and dystonia with tremor (Tinazzi et al, 2013a)
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