Researcher:
Yılmaz, Gizem

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PhD Student

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Gizem

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Yılmaz

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Yılmaz, Gizem

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2014 - 201917

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Now showing 1 - 10 of 17
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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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    Jaw reflexes originating from the periodontal and muscle spindle receptors to the jaw muscles
    (Springer International Publishing Ag, 2017) Ugincius, P.; Yılmaz, Gizem; Türker, Kemal Sıtkı; PhD Student; Faculty Member; Graduate School of Health Sciences; School of Medicine; N/A; 6741
    We investigated the jaw reflexes using both the probability- and the discharge rate-based analysis methods. While recording the masseter muscle activity, computer controlled slow-rate "push" and rapid rate "tap" stimuli were delivered to the upper right central incisor before and during local anesthetic block. While preceding local anesthesia, the tap stimuli induced inhibitory reflex responses; during local anesthetic block, the same stimulus induced excitatory and inhibitory reflex responses. The push stimuli generated a combination of inhibitory and excitatory responses that disappeared during the local anesthetic block. We found that the discharge rate-based method was better for indicating the duration of earlier responses and the existence, sign, and duration of later responses.
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    Facial muscle activity contaminates EEG signal at rest: evidence from frontalis and temporalis motor units
    (Iop Publishing Ltd, 2019) N/A; N/A; N/A; N/A; N/A; Yılmaz, Gizem; Budan, Abdullah Salih; Ungan, Pekcan; Topkara, Betilay; Türker, Kemal Sıtkı; PhD Student; Undergraduate Student; Faculty Member; PhD Student; Faculty Member; Graduate School of Health Sciences; School of Medicine; School of Medicine; Graduate School of Health Sciences; School of Medicine; N/A; N/A; N/A; 353320; 6741
    Objective: In order to reach electroencephalography (EEG) electrodes on the scalp, synchronized activity of neurons needs to pass thorough several tissue layers, including the skull and muscles covering the scalp. the contamination of EEG signal by temporalis and frontalis muscles has been well documented for voluntary muscle contraction even at low contraction levels. the extent of myogenic contamination during postural and/or rest activity of the temporalis and frontalis remains an impediment for EEG research. Approach: In this study, we first aimed to observe involuntary, continuous motor unit activity of the frontalis muscle at rest and evaluate motor unit level frontalis interference on the EEG electrodes. Second, we compared motor unit interference from the frontalis before and after artefact pruning via an independent component analysis (ICa) algorithm. Main Results: We demonstrated that motor unit activity of the frontalis muscle produces interference potentials on the frontal electrodes at rest and the interference was significantly reduced after ICa on the frontal electrodes, but not completely eliminated. Likewise, the temporalis interference at rest was significantly smaller after ICa on the fronto-temporal electrodes, but not completely removed. Significance: We documented the existence of resting involuntary activity of the temporalis and frontalis muscles underneath EEG electrodes and the removal of the EEG signal from their contiguous interference is not possible even after the use of ICa technology. We recommend that EEG researchers readdress the definition of 'rest' for EEG recordings and the ICa experts should extend their electromyography removal strategies to motor unit level interference.
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    EEG-like signals can be synthesized from surface representations of single motor units of facial muscles
    (Springer, 2018) N/A; Yılmaz, Gizem; Ungan, Pekcan; Türker, Kemal Sıtkı; PhD Student; Faculty Member; Faculty Member; Graduate School of Health Sciences; School of Medicine; School of Medicine; N/A; N/A; 6741
    Electrodes for recording electroencephalogram (EEG) are placed on or around cranial muscles; hence, their electrical activity may contaminate the EEG signal even at rest conditions. Due to its role in maintaining mandibular posture, tonic activity of temporalis muscle interferes with the EEG signal particularly at fronto-temporal locations at single motor unit (SMU) level. By obtaining surface representation of a motor unit, we can evaluate its interference in EEG and if we could sum surface representations of several tonically active motor units, we could estimate the overall myogenic contamination in EEG. Therefore, in this study, we followed re-composition (RC) approach and generated EEG-like artefact model using surface representations of single motor units (RC). Furthermore, we compared signal characteristics of RC signals with simultaneously recorded EEG signal at different locations in terms of power spectral density and coherence. First, we found that RC signal represented the power spectral distribution of an EMG signal. Second, RC signal reflected the discharge rate of a SMU giving the greatest surface representation amplitude and strongest interference appeared as distinguishable frequency peak on RC power spectra. Moreover, for strong interferences, RC also contaminated the EEG at F7 and other EEG electrodes. These findings are important to illustrate the susceptibility of EEG signal to myogenic artefacts even at rest and the research using EEG coherence comparisons should consider muscle activity while drawing conclusions about neuronal interactions and oscillations.
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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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    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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    Periodontal mechanoreceptors and bruxism at low bite forces
    (Pergamon-Elsevier Science Ltd, 2019) Laine, Christopher M.; Tinastepe, Neslihan; N/A; N/A; N/A; Yılmaz, Gizem; Özyurt, Mustafa Görkem; Türker, Kemal Sıtkı; PhD Student; PhD Student; Faculty Member; Graduate School of Health Sciences; Graduate School of Sciences and Engineering; School of Medicine; Koç University Hospital; N/A; N/A; 6741
    Objective: In this study, we examined if 6-9 Hz jaw tremor, an indirect indicator of Periodontal Mechanoreceptor (PMR) activity, is different in bruxists compared to healthy participants during production of a low-level constant bite force. Methods: Bite force and surface EMG from the masseter muscle were recorded simultaneously as participants (13 patients, 15 controls) held a force transducer between the upper and lower incisors very gently. Results: Tremor in 6-9 Hz band for bruxists was greater on average compared to controls, but the difference was not significant, both for force recordings and EMG activity. Conclusions: The low effect sizes measured with the current protocol contrast highly with those of our previous study, where larger, dynamic bite forces were used, and where jaw tremor was markedly different in bruxists compared with controls. Significance: We have now gained important insight into the conditions under which abnormal jaw tremor can be elicited in bruxism. From a scientific standpoint, this is critical for understanding the 'abnormality' of PMR feedback in bruxism. Prom a clinical perspective, our results represent progress towards the development of an optimal protocol in which jaw tremor can serve as a biological marker of bruxism.
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    Reevaluation of reflex responses of the human masseter muscle to electrical lip stimulation
    (Amer Physiological Soc, 2017) Ugincius, Paulius; Yılmaz, Gizem; Sebik, Oğuz; Türker, Kemal Sıtkı; PhD Student; Researcher; Faculty Member; Graduate School of Health Sciences; School of Medicine; School of Medicine; N/A; N/A; 6741
    We examined the reflex response of the human masseter muscle to electrical stimulation of the lip using both single motor unit and surface electromyogram based methods. Using the classical analysis methods, reflex response to mild electrical stimuli generated two distinct short-lasting inhibitions. This pattern may reflect the development of combinations of short-and long-latency inhibitory postsynaptic potentials as a result of the mildly painful electrical lip stimulation. However, this pattern appearing in the classical analysis methods may have developed as a consequence of earlier responses and may not be genuine. This study examined the genuineness of these responses using both the classical analysis methods and the discharge rate method to uncover the realistic postsynaptic potentials in human trigeminal motor nucleus. Using the discharge rate method, we found that the electrical lip stimulation only generated a long-lasting single or compound inhibitory response that is followed by late, long-lasting excitation. These findings have important implications on the redrawing of the neuronal pathways of the trigeminal nerve that are frequently used to judge neuromuscular disorders of the trigeminal region. NEW & NOTEWORTHY We examined the human masseter reflex response to electrical stimulation of lower lip to uncover realistic postsynaptic potentials in the trigeminal motor nucleus. We found that the stimulation generates a long-lasting single or compound inhibitory response that is followed by a late, long-lasting excitation. These findings have important implications on the redrawing of the neuronal pathways of the trigeminal nerve that are frequently used to judge neuromuscular disorders of the trigeminal region.
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    Discharge rate method for error free estimation of the synaptic potentials in human motor neurons
    (Wiley-Blackwell, 2015) Yavuz, Utku; Ugincius, Paulius; N/A; Department of Physics; N/A; Türker, Kemal Sıtkı; Sebik, Oğuz; Yılmaz, Gizem; Faculty Member; Researcher; PhD Student; Department of Physics; School of Medicine; College of Sciences; Graduate School of Health Sciences; 6741; N/A; N/A
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    Re-examination of the periodontal reflexes using frequency analyses
    (Wiley-Blackwell, 2015) Ugincius, Paulius; Atış, Elif Sibel; Stankevicius, Edgaras; 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; 6741
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