Dry immersion as a model of deafferentation: A neurophysiology study using somatosensory evoked potentials

Introduction
Dry immersion is a ground-based experiment simulating the effects of weightlessness, and it is a model of acute symmetrical bilateral deafferentation. This exploratory study aimed to investigate the effects of three days of dry immersion (DI) on sensory thresholds and the functioning of lemniscal pathways, assessed by somatosensory evoked potentials (SEPs).
Methods
Twelve healthy male volunteers (32+/-4.8 years) participated in the study. Sensory thresholds and SEPs of the tibial nerve of both limbs were recorded before (D-1) and on the third day of dry immersion (D3).
Results
Sensory thresholds significantly decreased on D3 (-20.75 +/-21.7%; z = -2.54; p = 0.0109 on the right side and -22.18+/-17.28%; z = -3.059; p = 0.002 on the left side). The amplitude of P40 responses did not differ between D-1 and D3. Latencies of all central responses until P30 were shortened on D3 (N21 right:-0.57+/-0.31; z = -3.06; p = 0.002; N21 left -0.83+/-0.53; z = -2.94; p = 0.003; P30 right: -1.26+/-1.42; z = -3.059; p = 0.002; P30 left: -1.11+/-1.55; z = -2.27; p = 0.02)
Conclusion
Three days of dry immersion can induce hyperexcitability of lemniscal pathways.
Significance
This may be explained by a change in the expression of membrane channels and/or medullar plasticity and/or hypersensitization of peripheral sensory receptors induced by this acute deafferentation. Additional studies are needed to further elucidate the mechanisms.