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Publication Metadata only 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; 6741The 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.Publication Metadata only 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; 6741Painful 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.Publication Metadata only 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; 6741We 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.Publication Metadata only High pass filtering and rectification of SEMG as a tool to demonstrate synchronous motor unit activity during vibration(Elsevier Sci Ltd, 2014) 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; 6741N/APublication Metadata only 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; 6741Reflex 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.Publication Metadata only NEUROD2 regulates stim1 expression and store-operated calcium entry in cortical neurons(Soc Neuroscience, 2017) N/A; N/A; N/A; N/A; N/A; N/A; N/A; N/A; Department of Physics; Department of Molecular Biology and Genetics; Güner, Gökhan; Güzelsoy, Gizem; İşleyen, Fatma Sadife; Şahin, Gülcan Semra; Akkaya, Cansu; Bayam, Efil; Kotan, Ilgın Eser; Kabakçıoğlu, Alkan; Dunn, Gülayşe İnce; Master Student; Master Student; Master Student; Master Student; PhD Student; Researcher; Master Student; Faculty Member; Other; Department of Physics; Department of Molecular Biology and Genetics; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Sciences; N/A; N/A; N/A; N/A; N/A; N/A; N/A; 49854; N/ACalcium signaling controls many key processes in neurons, including gene expression, axon guidance, and synaptic plasticity. In contrast to calcium influx through voltage- or neurotransmitter-gated channels, regulatory pathways that control store-operated calcium entry (SOCE) in neurons are poorly understood. Here, we report a transcriptional control of Stim1 (stromal interaction molecule 1) gene, which is a major sensor of endoplasmic reticulum (ER) calcium levels and a regulator of SOCE. By using a genome-wide chromatin immunoprecipitation and sequencing approach in mice, we find that NEUROD2, a neurogenic transcription factor, binds to an intronic element within the Stim1 gene. We show that NEUROD2 limits Stim1 expression in cortical neurons and consequently fine-tunes the SOCE response upon depletion of ER calcium. Our findings reveal a novel mechanism that regulates neuronal calcium homeostasis during cortical development.Publication Metadata only 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; 6741The 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.Publication Metadata only Reorganization of brain connectivity across the spectrum of clinical cognitive decline(SPRINGER-VERLAG ITALIA SRL, 2024) Dal, Demet Yüksel; Yıldırım, Zerrin; Gurvit, Hakan; Acar, Burak; Department of Physics; Kabakçıoğlu, Alkan; Department of Physics; ; College of Sciences;Clinical cognitive decline, leading to Alzheimer's Disease Dementia (ADD), has long been interpreted as a disconnection syndrome, hindering the information flow capacity of the brain, hence leading to the well-known symptoms of ADD. The structural and functional brain connectome analyses play a central role in studies of brain from this perspective. However, most current research implicitly assumes that the changes accompanying the progression of cognitive decline are monotonous in time, whether measured across the entire brain or in fixed cortical regions. We investigate the structural and functional connectivity-wise reorganization of the brain without such assumptions across the entire spectrum. We utilize nodal assortativity as a local topological measure of connectivity and follow a data-centric approach to identify and verify relevant local regions, as well as to understand the nature of underlying reorganization. The analysis of our preliminary experimental data points to statistically significant, hyper and hypo-assortativity regions that depend on the disease's stage, and differ for structural and functional connectomes. Our results suggest a new perspective into the dynamic, potentially a mix of degenerative and compensatory, topological alterations that occur in the brain as cognitive decline progresses.Publication Metadata only Tendon reflex is suppressed during whole-body vibration(Elsevier Sci Ltd, 2016) Karacan, Ilhan; Cidem, Muharrem; Cakar, Halil Ibrahim; N/A; Department of Physics; N/A; Yılmaz, Gizem; Sebik, Oğuz; Türker, Kemal Sıtkı; PhD Student; Researcher; Faculty Member; Department of Physics; Graduate School of Health Sciences; College of Sciences; School of Medicine; N/A; N/A; 6741In this study we have investigated the effect of whole body vibration (WBV) on the tendon reflex (T-reflex) amplitude. Fifteen young adult healthy volunteer males were included in this study. Records of surface EMG of the right soleus muscle and accelerometer taped onto the right Achilles tendon were obtained while participant stood upright with the knees in extension, on the vibration platform. Tendon reflex was elicited before and during WBV. Subjects completed a set of WBV. Each WBV set consisted of six vibration sessions using different frequencies (25, 30, 35, 40, 45, 50 Hz) applied randomly. In each WBV session the Achilles tendon was tapped five times with a custom-made reflex hammer. The mean peak-to-peak (PP) amplitude of T-reflex was 1139.11 +/- 498.99 mu V before vibration. It decreased significantly during WBV (p < 0.0001). The maximum PP amplitude of T-reflex was 1333 +/- 515 mu V before vibration. It decreased significantly during WBV (p < 0.0001). No significant differences were obtained in the mean acceleration values of Achilles tendon with tapping between before and during vibration sessions. This study showed that T-reflex is suppressed during WBV. T-reflex suppression indicates that the spindle primary afferents must have been pre-synaptically inhibited during WBV similar to the findings in high frequency tendon vibration studies.Publication Metadata only Vibration parameters affecting vibration-induced reflex muscle activity(Taylor and Francis Ltd, 2017) Çidem, Muharrem; Karacan, İlhan; Çakar, Halil Ibrahim; Çidem, Mehmet; KaramehmetoĞlu, Şafak Sahir; 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; 6741Purpose: To determine vibration parameters affecting the amplitude of the reflex activity of soleus muscle during low-amplitude whole-body vibration (WBV). Materials and methods: This study was conducted on 19 participants. Vibration frequencies of 25, 30, 35, 40, 45, and 50Hz were used. Surface electromyography, collision force between vibration platform and participant's heel measured using a force sensor, and acceleration measured using an accelerometer fixed to the vibration platform were simultaneously recorded. Results: The collision force was the main independent predictor of electromyographic amplitude. Conclusion: The essential parameter of vibration affecting the amplitude of the reflex muscle activity is the collision force.