Researcher:
Sebik, Oğuz

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Oğuz

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Sebik

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Sebik, Oğuz

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2012 - 201821

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Researcher Of Publications: search.filters.isAuthorOfPublication.419fde73-9ab8-43dd-89cc-d75bf8da8f7f

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    Chiropractic alters TMS induced motor neuronal excitability: preliminary findings
    (Springer International Publishing Ag, 2014) Haavik, Heidi; Niazi, Imran Khan; Duehr, Jens; Kinget, Mat; Ugincius, Paulius; Department of Physics; N/A; Sebik, Oğuz; Yılmaz, Gizem; Türker, Kemal Sıtkı; Researcher; PhD Student; Faculty Member; Department of Physics; College of Sciences; Graduate School of Health Sciences; School of Medicine; Koç University Hospital; N/A; N/A; 6741
    The objective of this study was to use the electromyography (EMG) via surface and intramuscular single motor unit recordings to further characterize the immediate sensorimotor effects of spinal manipulation and a control intervention using TMS. The results provide evidence that spinal manipulation of dysfunctional spinal segments increases low threshold motoneurone excitability.
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    Rectification of SEMG as a tool to demonstrate synchronous motor unit activity during vibration
    (Elsevier Sci Ltd, 2013) Karacan, İlhan; Çidem, Muharrem; Department of Physics; N/A; Sebik, Oğuz; Türker, Kemal Sıtkı; Researcher; Faculty Member; Department of Physics; College of Sciences; School of Medicine; N/A; 6741
    The use of surface electromyography (SEMG) in vibration studies is problematic since motion artifacts occupy the same frequency band with the SEMG signal containing information on synchronous motor unit activity. We hypothesize that using a harsher, 80-500 Hz band-pass filter and using rectification can help eliminate motion artifacts and provide a way to observe synchronous motor unit activity that is phase locked to vibration using SEMG recordings only. Multi Motor Unit (MMU) action potentials using intramuscular electrodes along with SEMG were recorded from the gastrocnemius medialis (GM) of six healthy male volunteers. Data were collected during whole body vibration, using vibration frequencies of 30 Hz, 35 Hz, 40 Hz or 50 Hz. A computer simulation was used to investigate the efficacy of filtering under different scenarios: with or without artifacts and/or motor unit synchronization. Our findings indicate that motor unit synchronization took place during WBV as verified by MMU recordings. A harsh filtering regimen along with rectification proved successful in demonstrating motor unit synchronization in SEMG recordings. Our findings were further supported by the results from the computer simulation, which indicated that filtering and rectification was efficient in discriminating motion artifacts from motor unit synchronization. We suggest that the proposed signal processing technique may provide a new methodology to evaluate the effects of vibration treatments using only SEMG. This is a major advantage, as this non-intrusive method is able to overcome movement artifacts and also indicate the synchronization of underlying motor units.
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    Cutaneous silent period evoked in human first dorsal interosseous muscle motor units by laser stimulation
    (Elsevier, 2016) Kahya, Mehmet Cemal; Department of Physics; N/A; Sebik, Oğuz; Türker, Kemal Sıtkı; Researcher; Faculty Member; Department of Physics; College of Sciences; School of Medicine; N/A; 6741
    Painful stimulation of the hand results in an inhibitory response in the hand muscles known as the cutaneous silent period (CSP). In this study, we employed probability- and frequency-based analysis methods to examine the CSP induced by laser stimuli. Subjects were asked to contract their first dorsal interosseous muscle so that selected motor units discharged at a rate of about 8 Hz. Laser pulses were delivered to the palm of the hand, and reflex responses were recorded. The stimuli generated CSP in all test subjects. We found that the latency of the CSP evoked using laser stimulation was longer than that the previously published latency values of the CSP evoked using electrical stimulation. Using only the presently generated laser induced CSP data, the CSP duration was longer when analyzed via peristimulus frequencygram method compared to the probability-based methods such as peristimulus time histogram and surface electromyogram. In the light of the current results, we suggest that laser stimulation could be used when studying pain pathways in human subjects and the frequency-based analysis methods can be preferred because they are previously shown to be more reliable for obtaining the synaptic activity profile. These results can be used to standardize the CSP methods in basic and clinical research.
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    Investigation of the effects of 50 Hz magnetic fields on platelet aggregation using a modified aggregometer
    (Taylor & Francis Inc, 2012) Sağdilek, Engin; Çelebi, Gürbüz; Department of Physics; Sebik, Oğuz; Researcher; Department of Physics; College of Sciences; N/A
    Purpose: Electromagnetic fields have various effects on intracellular calcium levels, free oxygen radicals and various enzymes. The platelet activation pathway involves an increase in intracellular calcium levels and protein kinase C activation; and free oxygen radicals play a mediating role in this pathway. This study investigated whether 1 mT and 6 mT, 50 Hz magnetic fields had any effects on platelet aggregation. Materials and Methods: Blood from healthy volunteers was anticoagulated with either citrate or heparin. Each sample was divided in half and assigned to exposure and control groups. Platelet rich plasma samples in the exposure group were exposed to a 1 mT or a 6 mT, 50 Hz magnetic field for 1.5 or 1 h, respectively. The samples from both exposure and control groups were simultaneously evaluated using a modified optical aggregometer. Adenosine-diphosphate, collagen, and epinephrine were used as inducing agents. The slopes of the aggregation curve, the maximum values and the areas under the curves were recorded and compared. Results: A significant effect was observed only in the 1 mT-citrate group. It was found that magnetic field exposure significantly increased the maximum values and slopes of the collagen-induced aggregations. Conclusions: It was found that magnetic field exposure has an activating effect on platelet aggregation.
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    Whole-body vibration-induced muscular reflex: is it a stretch-induced reflex?
    (Soc Physical Therapy Science, 2015) Department of Physics; N/A; Sebik, Oğuz; Yılmaz, Gizem; Türker, Kemal Sıtkı; Researcher; PhD Student; Faculty Member; Department of Physics; College of Sciences; Graduate School of Health Sciences; School of Medicine; N/A; N/A; 6741
    Purpose: Whole-body vibration (WBV) can induce reflex responses in muscles. A number of studies have reported that the physiological mechanisms underlying this type of reflex activity can be explained by reference to a stretch-induced reflex. Thus, the primary objective of this study was to test whether the WBV-induced muscular reflex (WBV-IMR) can be explained as a stretch-induced reflex. Subjects and Methods: The present study assessed 20 healthy males using surface electrodes placed on their right soleus muscle. The latency of the tendon reflex (T-reflex) as a stretch-induced reflex was compared with the reflex latency of the WBV-IMR. In addition, simulations were performed at 25, 30, 35, 40, 45, and 50 Hz to determine the stretch frequency of the muscle during WBV. Results: WBV-IMR latency (40.5 +/- 0.8 ms; 95% confidence interval [CI]: 39.0-41.9 ms) was significantly longer than T-reflex latency (34.6 +/- 0.5 ms; 95% CI: 33.6-35.5 ms) and the mean difference was 6.2 ms (95% CI of the difference: 4.7-7.7 ms). The simulations performed in the present study demonstrated that the frequency of the stretch signal would be twice the frequency of the vibration. Conclusion: These findings do not support the notion that WBV-IMR can be explained by reference to a stretch-induced reflex.
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    Discharge rate and synaptic noise affect reflex response regime of motor unit population
    (Wiley-Blackwell, 2015) Yavuz, Utku Şükrü; Negro, Francesco; Froemmel, Cornelius; Farina, Dario; Department of Physics; N/A; Sebik, Oğuz; Türker, Kemal Sıtkı; Researcher; Faculty Member; Department of Physics; College of Sciences; School of Medicine; N/A; 6741
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    Chiropractic spinal manipulation alters TMS induced i-wave excitability and shortens the cortical silent period
    (2018) Haavik, Heidi; Niazi, Imran Khan; Jochumsen, Mads; Ugincius, Paulius; Navid, Muhammad Samran; Department of Physics; N/A; N/A; N/A; Sebik, Oğuz; Yılmaz, Gizem; Özyurt, Mustafa Görkem; Türker, Kemal Sıtkı; Researcher; PhD Student; PhD Student; Faculty Member; Department of Physics; College of Sciences; Graduate School of Health Sciences; Graduate School of Sciences and Engineering; School of Medicine; Koc University Hospital; N/A; N/A; N/A; 6741
    The objective of this study was to construct peristimulus time histogram (PSTH) and peristimulus frequencygram (PSF) using single motor unit recordings to further characterize the previously documented immediate sensorimotor effects of spinal manipulation. Single pulse transcranial magnetic stimulation (TMS) via a double cone coil over the tibialis anterior (TA) motor area during weak isometric dorsiflexion of the foot was used on two different days in random order; pre/post spinal manipulation (in eighteen subjects) and pre/post a control (in twelve subjects) condition. TA electromyography (EMG) was recorded with surface and intramuscular fine wire electrodes. Three subjects also received sham double cone coil TMS pre and post a spinal manipulation intervention. From the averaged surface EMG data cortical silent periods (CSP) were constructed and analysed. Twenty-one single motor units were identified for the spinal manipulation intervention and twelve single motor units were identified for the control intervention. Following spinal manipulations there was a shortening of the silent period and an increase in the single unit I-wave amplitude. No changes were observed following the control condition. The results provide evidence that spinal manipulation reduces the TMS-induced cortical silent period and increases low threshold motoneurone excitability in the lower limb muscle. These finding may have important clinical implications as they provide support that spinal manipulation can be used to strengthen muscles. This could be followed up on populations that have reduced muscle strength, such as stroke victims.
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    Human stretch reflex pathways reexamined
    (Amer Physiological Soc, 2014) Yavuz, Ş. Utku; Mrachacz-Kersting, Natalie; Ünver, M. Berna; Farina, Dario; Department of Physics; N/A; Sebik, Oğuz; Türker, Kemal Sıtkı; Researcher; Faculty Member; Department of Physics; College of Sciences; School of Medicine; N/A; 6741
    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.
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    The new technique for accurate estimation of the spinal cord circuitry: recording reflex responses of large motor unit populations
    (Wiley, 2015) Yavuz, Utku Şükrü.; Negro, Francesco; Holobar, Ales; Frömmel, Cornelius; Farina, Dario; Department of Physics; N/A; Sebik, Oğuz; Türker, Kemal Sıtkı; Researcher; Faculty Member; Department of Physics; College of Sciences; School of Medicine; N/A; 6741
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    Estimating reflex responses in large populations of motor units by decomposition of the high-density surface electromyogram
    (Wiley, 2015) Yavuz, Utku Şükrü; Negro, Francesco; Holobar, Ales; Frömmel, Cornelius; Farina, Dario; Department of Physics; N/A; Sebik, Oğuz; Türker, Kemal Sıtkı; Researcher; Faculty Member; Department of Physics; College of Sciences; School of Medicine; N/A; 6741
    We propose and validate a non-invasive method that enables accurate detection of the discharge times of a relatively large number of motor units during excitatory and inhibitory reflex stimulations. High-density surface electromyography (HDsEMG) and intramuscular EMG (iEMG) were recorded from the tibialis anterior muscle during ankle dorsiflexions performed at 5%, 10% and 20% of the maximum voluntary contraction (MVC) force, in nine healthy subjects. The tibial nerve (inhibitory reflex) and the peroneal nerve (excitatory reflex) were stimulated with constant current stimuli. In total, 416 motor units were identified from the automatic decomposition of the HDsEMG. The iEMG was decomposed using a state-of-the-art decomposition tool and provided 84 motor units (average of two recording sites). The reflex responses of the detected motor units were analysed using the peri-stimulus time histogram (PSTH) and the peri-stimulus frequencygram (PSF). The reflex responses of the common motor units identified concurrently from the HDsEMG and the iEMG signals showed an average disagreement (the difference between number of observed spikes in each bin relative to the mean) of 8.2 +/- 2.2% (5% MVC), 6.8 +/- 1.0% (10% MVC) and 7.5 +/- 2.2% (20% MVC), for reflex inhibition, and 6.5 +/- 4.1%, 12.0 +/- 1.8% and 13.9 +/- 2.4%, for reflex excitation. There was no significant difference between the characteristics of the reflex responses, such as latency, amplitude and duration, for the motor units identified by both techniques. Finally, reflex responses could be identified at higher force (4 of the 9 subjects performed contraction up to 50% MVC) using HDsEMG but not iEMG, because of the difficulty in decomposing the iEMG at high forces. In conclusion, single motor unit reflex responses can be estimated accurately and non-invasively in relatively large populations of motor units using HDsEMG. This non-invasive approach may enable a more thorough investigation of the synaptic input distribution on active motor units at various force levels.