The effects of stimulus rates on high frequency oscillations of median nerve somatosensory-evoked potentials--direct recording study from the human cerebral cortex.
ABSTRACT To study the effects of different stimulus rates on high-frequency oscillations (HFOs) of somatosensory-evoked potentials (SEPs), we recorded median nerve SEPs directly from the human cerebral cortex.
SEPs were recorded from subdural electrodes in 5 patients with intractable epilepsy, under the conditions of low (3.3Hz) and high (12.3Hz) stimulus rates.
Increased stimulus rates to the median nerve from 3.3 to 12.3Hz showed a pronounced amplitude reduction of HFOs when compared with the primary N20-P20, area 3b, and P25, area 1, responses.
HFOs were more sensitive to a high stimulus rate than the primary cortical responses, suggesting that the post-synaptic intracortical activities may greatly contribute to the HFO generation.
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ABSTRACT: A brief review of previous studies is presented on high frequency oscillations (HFOs)>300 Hz overlying the cortical response in the somatosensory evoked potential (SEP) or magnetic field (SEF) in humans as well as other mammals. The characteristics of somatosensory HFOs are described about reproducibility and origin (area 3b and 1) of the HFOs, changes during a wake-sleep cycle, effects of stimulus rate or tactile interference, and pharmacological effects. Also, several hypotheses on the neural mechanisms of the HFOs are reconsidered; the early HFO burst is probably generated from action potentials of thalamocortical fibers at the time when they arrive at the area 3b (and 1), since this component is resistant to higher stimulus rate >10 Hz, general anesthesia, or application of glutamatergic receptor antagonist: by contrast, the late HFO burst is sensitive to higher stimulus rate and eliminated after application of glutamatergic receptor antagonist, reflecting activities of a postsynaptic neural network in areas 3b and 1 of the somatosensory cortex. In view of physiological features of the somatosensory HFOs and their pathological or pharmacological changes, possible mechanisms of the late HFO burst genesis are discussed: a fast-spiking interneuron hypothesis, a fast pyramidal cell IPSP hypothesis and a chattering cell hypothesis.Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 07/2011; 122(10):1908-23. DOI:10.1016/j.clinph.2011.05.023 · 2.98 Impact Factor
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ABSTRACT: Increasing evidence from invasive intracranial recordings suggests that the matured brain generates both physiological and pathological high-frequency signals. The present study was designed to detect high-frequency brain signals in the developing brain using newly developed magnetoencephalography (MEG) methods. Twenty healthy children were studied with a high-sampling rate MEG system. Functional high-frequency brain signals were evoked by electrical stimulation applied to the index fingers. To determine if the high-frequency neuromagnetic signals are true brain responses in high-frequency range, we analyzed the MEG data using the conventional averaging as well as newly developed time-frequency analysis along with beamforming. The data of healthy children showed that very high-frequency brain signals (>1000 Hz) in the somatosensory cortex in the developing brain could be detected and localized using MEG. The amplitude of very high-frequency brain signals was significantly weaker than that of the low-frequency brain signals. Very high-frequency brain signals showed a much earlier latency than those of a low-frequency. Magnetic source imaging (MSI) revealed that a portion of the high-frequency signals was from the somatosensory cortex, another portion of the high-frequency signals was probably from the thalamus. Our results provide evidence that the developing brain generates high-frequency signals that can be detected with the non-invasive technique of MEG. MEG detection of high-frequency brain signals may open a new window for the study of developing brain function.Frontiers in Human Neuroscience 12/2014; 8:969. DOI:10.3389/fnhum.2014.00969 · 2.90 Impact Factor
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ABSTRACT: This study is addressed to define postoperative pattern of blood flow in free microvascular flaps by using a laser Doppler flowmetry (LDF) and to reveal effects of the prostaglandin E1 (PGE1) administration on the blood flow. Postoperative blood flows in the flaps were monitored with LDF in 14 patients, who were administrated PGE1 twice a day for 7 days after the operation. The average blood flow rates in the flaps gradually increased after the operation, reached peak at 7 days after the operation, and then become stable until 21 days after the operation. After the PGE1 administration, the blood flow rates in all of the patients increased within 15min and reached the peak between 75min and 105min. These results suggest that PGE1 is useful to increase the blood flow in the flap. Furthermore, the present study revealed these postoperative patterns of the changes in the blood flow in the flaps, careful monitoring of the flaps with LDF as performed in the present study will provide significant information to identify a disturbance of circulation in the flaps as soon as possible.Asian Journal of Oral and Maxillofacial Surgery 08/2011; 23(3):113-116. DOI:10.1016/j.ajoms.2011.03.001