Yazar "Turker, Kemal S." seçeneğine göre listele
Listeleniyor 1 - 11 / 11
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Activation properties of trigeminal motoneurons in participants with and without bruxism(Amer Physiological Soc, 2013) D'Amico, Jessica M.; Yavuz, S. Utku; Saracoglu, Ahmet; Atis, Elif Sibel; Gorassini, Monica A.; Turker, Kemal S.In animals, sodium-and calcium-mediated persistent inward currents (PICs), which produce long-lasting periods of depolarization under conditions of low synaptic drive, can be activated in trigeminal motoneurons following the application of the monoamine serotonin. Here we examined if PICs are activated in human trigeminal motoneurons during voluntary contractions and under physiological levels of monoaminergic drive (e. g., serotonin and norepinephrine) using a paired motor unit analysis technique. We also examined if PICs activated during voluntary contractions are larger in participants who demonstrate involuntary chewing during sleep (bruxism), which is accompanied by periods of high monoaminergic drive. In control participants, during a slowly increasing and then decreasing isometric contraction, the firing rate of an earlier-recruited masseter motor unit, which served as a measure of synaptic input to a later-recruited test unit, was consistently lower during derecruitment of the test unit compared with at recruitment (Delta F = 4.6 +/- 1.5 imp/s). The Delta F, therefore, is a measure of the reduction in synaptic input needed to counteract the depolarization from the PIC to provide an indirect estimate of PIC amplitude. The range of Delta F values measured in the bruxer participants during similar voluntary contractions was the same as in controls, suggesting that abnormally high levels of monoaminergic drive are not continually present in the absence of involuntary motor activity. We also observed a consistent "onion skin effect" during the moderately sized contractions (<20% of maximal), whereby the firing rate of higher threshold motor units discharged at slower rates (by 4-7 imp/s) compared with motor units with relatively lower thresholds. The presence of lower firing rates in the more fatigue-prone, higher threshold trigeminal motoneurons, in addition to the activation of PICs, likely facilitates the activation of the masseter muscle during motor activities such as eating, nonnutritive chewing, clenching, and yawning.Öğe Comparison of the inhibitory response to tendon and cutaneous afferent stimulation in the human lower limb(Amer Physiological Soc, 2012) Rogasch, Nigel C.; Burne, John A.; Turker, Kemal S.Rogasch NC, Burne JA, Turker KS. Comparison of the inhibitory response to tendon and cutaneous afferent stimulation in the human lower limb. J Neurophysiol 107: 564-572, 2012. First published October 26, 2011; doi:10.1152/jn.00751.2011.-A powerful early inhibition is seen in triceps surae after transcutaneous electrical stimulation of the Achilles tendon [tendon electrical stimulation (TES)]. The aim of the present study was to confirm results from surface electromyogram (SEMG) recordings that the inhibition is not wholly or partly due to stimulation of cutaneous afferents that may lie within range of the tendon electrodes. Because of methodological limitations, SEMG does not reliably identify the time course of inhibitory and excitatory reflex components. This issue was revisited here with an analysis of changes in single motor unit (SMU) firing rate [peristimulus frequencygram (PSF)] and probability [peristimulus time histogram (PSTH)] to reexamine the time course of inhibitory SMU events that follow purely cutaneous (superficial sural) nerve stimulation. Results were then compared with similar data from TES. When compared with the reflex response to TES, sural nerve stimulation resulted in a longer onset latency of the primary inhibition and a weaker effect on SMU firing probability and rate. PSF also revealed that decreased SMU firing rates persisted during the excitation phase in SEMG, suggesting that the initial inhibition was more prolonged than previously reported. In a further study, the transcutaneous SEMG Achilles tendon response was compared with that from direct intra-tendon stimulation with insulated needle electrodes. This method should attenuate the SEMG response if it is wholly or partly dependent on cutaneous afferents. However, subcutaneous stimulation of the tendon produced similar components in the SEMG, confirming that cutaneous afferents made little or no contribution to the initial inhibition following TES.Öğe Compound group I excitatory input is differentially distributed to human soleus motoneurons(Elsevier Ireland Ltd, 2012) Binboga, Erdal; Turker, Kemal S.Objective: We studied whether the distribution of synaptic input from compound group I afferents onto the various-sized motoneurons in the human soleus muscle supports the size principle. Methods: The subject lay prone on a physiotherapy table and electrical stimuli were delivered to the tibial nerve. The recordings were taken with surface electromyography (SEMG) and single motor unit (SMU) potentials. The relative sizes of SMUs were estimated using four different methods. After identifying the relative size of each SMU of the pair, normalised size of the H-reflex was determined using the extra spike per trigger (ESPT) method. Results: In total 33 SMU pairs were studied to compare results obtained in each pair. It was found that, although the stimulus intensity was identical for each pair, the ESPT values were statistically larger in the bigger SMUs compared with the relatively smaller SMUs (p < 0.05). Conclusions: We conclude that, within the limits of this study, compound group I excitatory input to soleus motoneurons in human subjects does not support the size principle which governs the recruitment order of motoneurons in the reduced animal preparations. Significance: This study illustrates the importance of performing human experiments to confirm or reject principles obtained using reduced animal preparations. (C) 2012 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.Öğe Cutaneous silent period in human FDI motor units(Springer, 2010) Kahya, Mehmet C.; Yavuz, S. Utku; Turker, Kemal S.In this study, we aimed to use both the probability-based and the frequency-based analyses methods simultaneously to examine cutaneous silent period (CSP) induced by strong electrical currents. Subjects were asked to contract their first dorsal interosseus muscles so that one motor unit monitored via intramuscular wire electrodes discharged at a rate of approximately 8 Hz. Strong electrical stimuli were delivered to the back of the hand that created a subjective discomfort level of between 4 and 7 [0-10 visual analogue scale] and induced cutaneous silent period in all units. It was found that the duration of the CSP was significantly longer when the same data were analysed using frequency-based analysis method compared with the probability-based methods. Frequency-based analysis indicated that the strong electrical stimuli induce longer lasting inhibitory currents than what was indicated using the probability-based analyses such as surface electromyogram and peristimulus time histogram. Usage of frequency-based analysis for bringing out the synaptic activity underlying CSP seems essential as its characteristics have been subject to a large number of studies in experimental and clinical settings.Öğe Human stretch reflex pathways reexamined(Amer Physiological Soc, 2014) Yavuz, S. Utku; Mrachacz-Kersting, Natalie; Sebik, Oguz; Unver, M. Berna; Farina, Dario; Turker, Kemal S.Reflex responses of tibialis anterior motor units to stretch stimuli were investigated in human subjects. Three types of stretch stimuli were applied (tap-like, ramp-and-hold, and half-sine stretch). Stimulus-induced responses in single motor units were analyzed using the classical technique, which involved building average surface electromyogram (SEMG) and peristimulus time histograms (PSTH) from the discharge times of motor units and peristimulus frequencygrams (PSF) from the instantaneous discharge rates of single motor units. With the use of SEMG and PSTH, the tap-like stretch stimulus induced five separate reflex responses, on average. With the same single motor unit data, the PSF technique indicated that the tap stimulus induced only three reflex responses. Similar to the finding using the tap-like stretch stimuli, ramp-and-hold stimuli induced several peaks and troughs in the SEMG and PSTH. The PSF analyses displayed genuine increases in discharge rates underlying the peaks but not underlying the troughs. Half-sine stretch stimuli induced a long-lasting excitation followed by a long-lasting silent period in SEMG and PSTH. The increase in the discharge rate, however, lasted for the entire duration of the stimulus and continued during the silent period. The results are discussed in the light of the fact that the discharge rate of a motoneuron has a strong positive linear association with the effective synaptic current it receives and hence represents changes in the membrane potential more directly and accurately than the other indirect measures. This study suggests that the neuronal pathway of the human stretch reflex does not include inhibitory pathways.Öğe Is Myofascial Pain in Temporomandibular Disorder Patients a Manifestation of Delayed-onset Muscle Soreness?(Lippincott Williams & Wilkins, 2013) Koutris, Michail; Lobbezoo, Frank; Sumer, Nevruz Ceren; Atis, Elif Sibel; Turker, Kemal S.; Naeije, MachielObjective: In a study to the possible role of overuse of the jaw muscles in the pathogenesis of jaw muscle pain, we used a protocol involving concentric and eccentric muscle contractions to provoke a state of delayed-onset muscle soreness (DOMS) in the jaw muscles of healthy individuals. We tested whether the accompanying signs and symptoms would yield the temporary diagnosis of myofascial pain according to the research diagnostic criteria for temporomandibular disorders (RDC/TMD) in these individuals. Methods: Forty persons (mean age +/- SD = 27.7 +/- 7.5 y) performed six, 5-minute bouts of eccentric and concentric jaw muscle contractions. Before and immediately after the exercise, and 24 hours, 48 hours, and 1 week later, self-reported muscle fatigue and pain, pain-free maximum mouth opening, pressure-pain thresholds, and the number of painful jaw muscle palpation sites were recorded. Results: Significant signs and symptoms of DOMS in the jaw muscles were found, which all had resolved after 1 week. In 31 (77.5%) of the participants, these signs and symptoms also gave rise to a temporary diagnosis of myofascial pain according to the RDC/TMD. Conclusions: The results of this study demonstrate that an experimental protocol involving concentric and eccentric muscle contractions can provoke DOMS in the jaw muscles and the temporary diagnosis of myofascial pain according to the RDC/TMD. The results observed strengthen the supposition that the myofascial pain in TMD patients may be a manifestation of DOMS in the jaw muscles.Öğe Mimicking human neuronal pathways in silico: an emergent model on the effective connectivity(Springer, 2014) Gurcan, Onder; Turker, Kemal S.; Mano, Jean-Pierre; Bernon, Carole; Dikenelli, Oguz; Glize, PierreWe present a novel computational model that detects temporal configurations of a given human neuronal pathway and constructs its artificial replication. This poses a great challenge since direct recordings from individual neurons are impossible in the human central nervous system and therefore the underlying neuronal pathway has to be considered as a black box. For tackling this challenge, we used a branch of complex systems modeling called artificial self-organization in which large sets of software entities interacting locally give rise to bottom-up collective behaviors. The result is an emergent model where each software entity represents an integrate-and-fire neuron. We then applied the model to the reflex responses of single motor units obtained from conscious human subjects. Experimental results show that the model recovers functionality of real human neuronal pathways by comparing it to appropriate surrogate data. What makes the model promising is the fact that, to the best of our knowledge, it is the first realistic model to self-wire an artificial neuronal network by efficiently combining neuroscience with artificial self-organization. Although there is no evidence yet of the model's connectivity mapping onto the human connectivity, we anticipate this model will help neuroscientists to learn much more about human neuronal networks, and could also be used for predicting hypotheses to lead future experiments.Öğe Muscle pain theories: Is there a third dimension?(Elsevier Ireland Ltd, 2010) Turker, Kemal S.Öğe Provocation of delayed-onset muscle soreness in the human jaw-closing muscles(Pergamon-Elsevier Science Ltd, 2010) Turker, Kemal S.; Koutris, Michail; Sumer, N. Ceren; Atis, E. Sibel; Linke, Ian R.; Lobbezoo, Frank; Naeije, MachielEccentric contractions of jaw-closing muscles are difficult to perform. This may explain why fatigue-inducing experiments performed so far suggest the jaw-closing muscles to be fatigue resistant. Aim of this study was to construct an apparatus that can impose intense eccentric contractions to the jaw-closing muscles, and to test the hypothesis that eccentric contractions can provoke symptoms of delayed-onset muscle soreness (DOMS) in these muscles. The provocation apparatus consists of two tungsten arms connected by a hinge axis on one end. Participants bite with their anterior teeth on biting plates located on the other end. Each time the experimenter gradually releases the compression force of the apparatus' rubber tubings, the mouth is forced open and the jaw-closing muscles perform an eccentric contraction. Six male participants performed eccentric contractions of their jaw-closing muscles in six sets of exercises, each lasting 5 min, and with 1 mm of rest in between. Each set consisted of 60 open-close movements. Before and after the exercises, and after 24 h, 48 h, and 1 week, feelings of fatigue and pain, the maximum mouth opening without pain, muscles' tenderness to palpation and the maximum voluntary bite force were recorded. After 24 h and 48 h, the levels of fatigue and pain were elevated, the maximum mouth opening without pain was smaller, and five of the participants reported tenderness to palpation. The maximum voluntary bite force was also smaller after 24 h. These findings indicate that this novel apparatus is successful in inducing DOMS in the jaw-closing muscles. (C) 2010 Elsevier Ltd. All rights reserved.Öğe Responses of human soleus motor units to low-threshold stimulation of the tibial nerve(Springer, 2011) Binboga, Erdal; Prasartwuth, Orawan; Pehlivan, Murat; Turker, Kemal S.The peristimulus frequencygram (PSF) has recently been shown to illustrate postsynaptic potentials of motoneurones much more reliably than the peristimulus time histogram (PSTH). The aim of this investigation was to examine the profile of the postsynaptic potential (PSP) in soleus motoneurones in response to an H-reflex with and without accompanying M waves of different magnitude by using PSTH and PSF profiles of single motor units. Nine men and five women healthy subjects participated in this study. Electrical stimuli were delivered to the tibial nerve in the popliteal fossa. The reflex response of the soleus muscle was recorded using both surface electromyogram and single motor unit potentials. The PSTH analysis demonstrated that there were four different synaptic events following low-intensity stimulation of the tibial nerve: primary enhancement in firing probability (H-reflex or E1), primary reduction in firing probability (primary silent period or SP1), secondary reduction in firing probability (secondary silent period or SP2), and secondary enhancement in firing probability (E2). On the other hand, the PSF analysis indicated only two reflex responses, long-lasting enhancement in discharge rate including the H-reflex (LLE) and long-lasting decrease in discharge rate (LLD). The results of the two analyses methods are compared and contrasted. While the PSTH demonstrated that there was a silent period (SP1) immediately following the H-reflex, the PSF indicated an increase in discharge rate during the same period. The PSF also indicated that, during SP2 and E2, the discharge rate actually decreased (LLD). It was therefore suggested that LLD involved activation of several inhibitory pathways including the autogenic inhibition of units via the Golgi tendon organs. It was concluded that the PSF could indicate the details of the postsynaptic potentials and is very useful for bringing out previously unknown effects of electrical stimulation of muscle nerves.Öğe Synaptic potentials contributing to reflex inhibition in gastrocnemius following tendon electrical stimulation(Elsevier Ireland Ltd, 2011) Rogasch, Nigel C.; Burne, John A.; Binboga, Erdal; Turker, Kemal S.Objective: To investigate the synaptic potentials underlying reflex inhibition in gastrocnemius following electrical stimulation of the Achilles tendon using single motor unit recordings. Methods: Surface electromyography (SEMG) and single motor unit (SMU) action potentials were recorded from the medial head of left gastrocnemius muscle in eight healthy human subjects. The left Achilles tendon was stimulated electrically while subjects maintained a low contraction level sufficient to record one or two motor units. SMU responses were analysed using peri-stimulus time histogram (PSTH) and peri-stimulus frequencygram (PSF) techniques and compared with SEMG results. Results: A total of 22 SMU experiments were completed. In all trials, a large reflex inhibition (I1) was observed in both SEMG and PSTH followed by a later inhibition (I2). In 50% of trials, SEMG and PSTH showed that both I1 and I2 were followed by excitation (E1 and E2, respectively). PSF analysis showed only a prolonged reduction in SMU discharge rate. This inhibition had a latency of 38 ms and duration of 130 ms, extending into the E1 period in 14 units and more than 200 ms extending into the E2 period in six units. Conclusions: PSF data suggest that tendon electrical stimulation results in a long-lasting inhibition, most likely through the autogenic inhibitory reflex pathway mediated by group I tendon afferents. Significance: These findings emphasise the importance of using both probability (SEMG, PSTH) and frequency (PSF) based techniques in error free estimation of synaptic potentials. (C) 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.
