Previous studies showed reorganised and/or altered activity in the primary sensorimotor cortex after a spinal cord injury (SCI), suggested to reflect abnormal processing. However, little is known about whether somatotopically-specific representations can be activated despite reduced or absent afferent hand inputs. In this observational study we used functional MRI and an (attempted) finger movement task in tetraplegic patients to characterise the somatotopic hand layout in primary somatosensory cortex. We further used structural MRI to assess spared spinal tissue bridges. We found that somatotopic hand representations can be activated through attempted finger movements in absence of sensory and motor hand functioning, and no spared spinal tissue bridges. Such preserved hand somatotopy could be exploited by rehabilitation approaches that aim to establish new hand-brain functional connections after SCI (e.g., neuroprosthetics). However, over years since SCI the hand representation somatotopy deteriorated, suggesting that somatotopic hand representations are more easily targeted within the first years after SCI.

Following spinal cord injury (SCI), the motor output flow to the limb(s) and sensory input to the brain is largely lost. While attempted movements with the paralysed and sensory deprived body part can still evoke signals in the sensorimotor system, this task-related 'net' brain activity of SCI patients differs substantially from healthy controls. Such reorganised and/or altered activity is thought to reflect abnormal processing. It is however possible that this altered net sensorimotor activity in SCI patients conceals preserved somatotopically-specific representations of the paralysed and sensory deprived body parts that could be exploited in a functionally meaningful manner (e.g. via neuroprosthetics). In this cross-sectional study, we investigated whether a functional connection between the periphery and the brain is necessary to maintain somatosensory representations. We used functional MRI and an (attempted) finger movement task to characterise the somatotopic hand layout in the primary somatosensory cortex and structural MRI to assess spared spinal tissue bridges. We tested 14 tetraplegic SCI patients (mean age, s.e.m.=55, 3.6; 1 female) who differed in terms of lesion completeness, retained sensorimotor functioning, and time since injury, as well as 18 healthy control participants (mean age, s.e.m.=56, 3.6 years; 1 female). Our results revealed somatotopically organised representations of patients' hands in which neighbouring clusters showed selectivity for neighbouring fingers in contralateral S1, qualitatively similar to those observed in healthy controls. To quantify whether these representations were normal in tetraplegic SCI patients we correlated each participant's intricate representational distance pattern across all fingers (revealed using representational similarity analysis) with a canonical inter-finger distance pattern obtained from an independent sample. The resulting hand representation typicality scores were not significantly different between patients and controls. This was even true when considering two individual patients with no sensory hand functioning, no hand motor functioning, and no spared spinal tissue bridges. However, a correlational analysis revealed that over years since SCI the hand representation typicality in primary somatosensory cortex deteriorates. We show that somatosensory representations can be maintained for several years following SCI even in the absence of perhiperhal inputs. Such preserved cortical hand representations could therefore be exploited in a functionally meaningful way by rehabilitation approaches that attempt to establish new functional connections between the hand and the brain after an SCI (e.g. through neuroprosthetics). However, time since injury may critically influence the somatotopic representations of SCI patients and might thereby impact the success of such rehabilitation approaches.

Bioimpedance monitoring provides a non-invasive, safe and affordable opportunity to monitor total body water for a wide range of clinical applications. However, the measurement is susceptible to variations in posture and movement. Existing devices do not account for these variations and are therefore unsuitable to perform continuous measurements to depict trend changes. We developed a wearable bioimpedance monitoring system with embedded real-time posture detection using a distributed accelerometer network. We tested the device on 14 healthy volunteers following a standardized protocol of posture change and evaluated the agreement with a commercial device. The impedance showed a high correlation (r>0.98), a bias of -4.5 Ω, and limits of agreement of -30 and 21 Ω. Context-awareness was achieved with an accuracy of 94.6% by classifying data from two accelerometers placed at the upper and lower leg. The calculated current consumption of the system was as low as 10 mA during continuous measurement operation, suggesting that the system can be used for continuous measurements over multiple days without charging. The proposed motion-aware design will enable the measurement of relevant bioimpedance parameters over long periods and support informed clinical decision making.

<div>Bioimpedance monitoring provides a non-invasive,</div><div>safe and affordable opportunity to monitor total body water for a wide range of clinical applications. However, the measurement is susceptible to variations in posture and movement. Existing devices do not account for the variations and are therefore unsuitable to perform continuous measurements to depict trend changes. We developed a wearable bioimpedance monitoring system with embedded real-time posture detection using a distributed accelerometer network. We tested the device on 14 healthy volunteers following a standardized protocol of posture change and compared the obtained measurements with an existing commercial device. The impedance measured with both systems had a high correlation (r>0.98) and a Bland-Altman analysis revealed a bias of -4.5 and limits of agreement of -30 and 21. Context-awareness was achieved with processing accelerometer data placed at the upper and lower leg with an accuracy >95%. The calculated current consumption is as low as 10 mA during continuous measurement operation, suggesting that without recharge the system can be used for multiple days. The proposed motion-aware design will enable the measurement of relevant bioimpedance parameters continuously over long periods and aid in informed clinical decision making.</div>

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