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Evidence indicates attention can alter afferent inhibition, a Transcranial Magnetic Stimulation (TMS) evoked measure of cortical inhibition following somatosensory input. This measure is emerging as a valuable tool for clinical assessment of sensorimotor function. However, the reliability of the measure remains relatively low. Further, attention is capable of modifying the magnitude of afferent inhibition. Therefore, for afferent inhibition to become an assessment with translation within and beyond the research lab, the reliability of the measure must be improved. Controlling the focus of attention may be one method to improve the reliability of afferent inhibition. In the present study, two experiments were conducted. One to assess the biological effects of attention on SAI and LAI, and the other to address whether the reliability of SAI and LAI are altered in the presence of varying attentional demands. The magnitude of short- and long-latency afferent inhibition (SAI and LAI, respectively) was assessed under four conditions with varying attentional demands focused on the somatosensory input that mediates SAI and LAI circuits. Further, the reliability of SAI and LAI was assessed with and without directed attention to the relevant somatosensory input to explore whether attention to the tactile stimulation can improve intrasession and intersession reliability of these measures. Thirty individuals participated in four conditions; three conditions were identical in their physical parameters and varied only in the focus of directed attention (visual attend, tactile attend, non- directed attend) and one condition consisted of no external physical parameters (no stimulation). Reliability was measured by repeating conditions at three time points to assess intrasession and intersession reliability. Results indicate the magnitude of SAI and LAI were not modulated by varied attention. Reliability assessments demonstrated that the attention manipulations increased intrasession and intersession reliability of SAI and LAI compared to the no stimulation condition. This research exposes the influence of attention, and its impact on the reliability of afferent inhibition. By quantifying these influences, this research has identified new information to inform the design of TMS research in sensorimotor integration. / Thesis / Master of Science in Kinesiology / Attention can alter transcranial magnetic stimulation (TMS) evoked afferent inhibition. Measures of afferent inhibition are emerging as valuable tools for clinical assessments of sensorimotor function. However, the reliability of afferent inhibition remains relatively low, limiting its value in the clinic. Afferent inhibition is increased when the one’s attention is focused on the peripheral nerve stimulation used to elicit afferent inhibition. However, it is unknown whether afferent inhibition, with attention directed to somatosensory input, will improve the reliability of these measures. This is important as it suggests that changes to the methodology used to acquire afferent inhibition can improve the reliability of this measure, thereby increasing the opportunity for translation to the clinic. The goal of this study was to assess the influence of attention on afferent inhibition circuits, short afferent inhibition (SAI) and long afferent inhibition (LAI) and determine whether attention modulation would increase the reliability of afferent inhibition.

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The main objective of this project was to develop a method for soft neural probe insertion into a nerve. These soft probes are made of a silicon elastomer that is a few orders of magnitude less stiff than the nerve, which makes the insertion process particularly challenging. To overcome this challenge a tungsten microwire was used as an insertion shuttle to help penetrate the nerve by increasing the overall stiffness of the probe. At a first stage, the insertion process was tested on a nerve phantom (e.g. agarose gel with PDMS membrane) to control the insertion parameters and validate the insertion platform. Once the envisioned insertion method was established, the probe was implanted in a real rodent nerve. / <p>Examensarbetet är utfört vid Institutionen för teknik och naturvetenskap (ITN) vid Tekniska fakulteten, Linköpings universitet</p>

Cortical representations are plastic and are allocated based on the proportional use or disuse of a pathway. A steady stream of sensory input maintains the integrity of cortical networks; while in contrast, alterations in afferent activation promote sensorimotor reorganization. After an incomplete spinal cord injury (SCI), damage to the ascending and/or descending pathways induces widespread modifications to the sensorimotor system. Strengthening these spared sensorimotor pathways may be therapeutic by promoting functional recovery after injury. Using a technique called transcranial magnetic stimulation (TMS), we show that the leg motor cortex is facilitated by peripheral sensory inputs via disinhibition and potentiation of excitatory intracortical circuits. Hence, in addition to its crucial role in sensory perception, excitation from peripheral sensory afferents can reinforce muscle activity by engaging, and possibly shaping, the activity of the human motor cortex. After SCI, the amount of excitation produced by afferent stimulation reaching the motor cortex is expectantly reduced and delayed. This reduction of sensory inflow to the motor cortex may contribute to our findings that cortical inhibition is down-regulated after SCI, and this compensation may aid in the recruitment of excitatory networks in the motor cortex as a result of the damage to its output neurons. By repeatedly pairing sensory inputs from a peripheral nerve in the leg with direct cortical activation by TMS, in an intervention called paired associative stimulation, we show that the motor system can be potentiated in both uninjured individuals and after SCI. In the uninjured subjects, we show that in order to produce associative facilitation, the time window required for coincident activation of the motor cortex by TMS and peripheral sensory inputs is not as narrow as previously thought (~100 vs. ~20 ms), likely due to the persistent activation of cortical neurons following activation by TMS. The potential to condition the nervous system with convergent afferent and cortical inputs suggests that paired associative stimulation may serve as a priming tool for motor plasticity and rehabilitation following SCI.

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