Background: Traumatic brachial plexus injury (TBPI) is a potentially debilitating event, that usually affects young men following car or motorbike accidents. TBPI interferes with hand sensorimotor function, is associated with chronic pain, and causes cortical reorganization. Interactions between the somatosensory and motor cortices are of fundamental importance for motor control. The hands and face stand out as regions of high functionality with a privileged interaction existing between them, as reflected by the proximity and extension of their representations. Face-hand sensorimotor interactions have been demonstrated in healthy subjects. Objective: The aim of this study was to investigate changes in the sensorimotor interaction in the hand and between the face and the hand in TBPI patients in order to better understand the plasticity of face-hand sensorimotor circuits following TBPI. Method: The experimental design consisted of activating the representation of a hand muscle using transcranial magnetic stimulation (TMS) preceded by an electrical stimulation (ES) applied to the hand or face, which allows the investigation of the cortical reorganization resulting from TBPI. In the paradigm called afferent inhibition (AI), the motor evoked potential (MEP) in a target muscle is significantly reduced by a previous peripheral ES. AI can be evoked in short-latency (SAI) or long-latency (LAI) interstimulus intervals. Nine TBPI patients participated: five had partial sensorimotor function in their hands and were evaluated on the injured side (TBPI-I group) and four had complete loss of sensorimotor function in their hands and were evaluated on the uninjured side (TBPI-UI group). A control group (CG) included 18 healthy adults. A detailed clinical evaluation complemented the analysis. Results: The results showed preserved hand sensorimotor integration for TBPI patients at SAI intervals, but not at LAI intervals. For the face-to-hand sensorimotor integration, the results showed no inhibition at SAI intervals for the TBPI patients. For LAI intervals, a facilitation effect was observed for the TBPI patients, an effect we termed long afferent facilitation or LAF. LAF positively correlated with results in the Central Sensitization Inventory and in the Disabilities Arm, Shoulder, and Hand questionnaire. Conclusion: These results point to the existence of an inhibitory regulation system between the representations of the face and the hand that seems to be suppressed in TBPI and correlates with pain. Moreover, brain changes arising from TBPI are not restricted to the hemisphere contralateral to the injured limb, but extend to both hemispheres.

BackgroundInteractions between the somatosensory and motor cortices are of fundamental importance for motor control. Although physically distant, face and hand representations are side by side in the sensorimotor cortex and interact functionally. Traumatic brachial plexus injury (TBPI) interferes with upper limb sensorimotor function, causes bilateral cortical reorganization, and is associated with chronic pain. Thus, TBPI may affect sensorimotor interactions between face and hand representations.ObjectiveThe aim of this study was to investigate changes in hand–hand and face–hand sensorimotor integration in TBPI patients using an afferent inhibition (AI) paradigm.MethodThe experimental design consisted of electrical stimulation (ES) applied to the hand or face followed by transcranial magnetic stimulation (TMS) to the primary motor cortex to activate a hand muscle representation. In the AI paradigm, the motor evoked potential (MEP) in a target muscle is significantly reduced when preceded by an ES at short-latency (SAI) or long-latency (LAI) interstimulus intervals. We tested 18 healthy adults (control group, CG), evaluated on the dominant upper limb, and nine TBPI patients, evaluated on the injured or the uninjured limb. A detailed clinical evaluation complemented the physiological investigation.ResultsAlthough hand–hand SAI was present in both the CG and the TBPI groups, hand–hand LAI was present in the CG only. Moreover, less AI was observed in TBPI patients than the CG both for face–hand SAI and LAI.ConclusionOur results indicate that sensorimotor integration involving both hand and face sensorimotor representations is affected by TBPI.