scholarly journals From unspecific to adjusted, how the BOLD response in the rat hippocampus develops during consecutive stimulations

2016 ◽  
Vol 37 (2) ◽  
pp. 590-604 ◽  
Author(s):  
Stephanie Riemann ◽  
Cornelia Helbing ◽  
Frank Angenstein
Keyword(s):  
High Frequency ◽  
Pulse Sequences ◽  
Low Frequency ◽  
Bold Response ◽  
Deconvolution Analysis ◽  
Bold Responses ◽  
Electrical Pulses ◽  
Stimulation Period ◽  
Frequency Pulse ◽  
Spiking Activity

To determine the possibility to deconvolve measured BOLD responses to neuronal signals, the rat perforant pathway was electrically stimulated with 10 related stimulation protocols. All stimulation protocols were composed of low-frequency pulse sequences with superimposed high-frequency pulse bursts. Because high-frequency pulse bursts trigger only one synchronized spiking of granular cells, variations of the stimulation protocol were used: (a) to keep the spiking activity similar during the presentation of different numbers of pulses, (b) to apply identical numbers of pulses to induce different amounts of spiking activity, and (c) to concurrently vary the number of applied electrical pulses and resultant spiking activity. When complex pulse sequences enter the hippocampus, an unspecific default-like BOLD response is first generated, which relates neither to the number of incoming pulses nor to the induced spiking activity. Only during subsequent stimulations does the initial unspecific response adjust to a more adequate response, which in turn either strongly related to spiking activity when low-frequency pulses were applied or depended on the incoming activity when high-frequency pulse bursts were presented. Thus, only the development of BOLD responses during repetitive stimulations can predict the underlying neuronal activity and deconvolution analysis should not be performed during an initial stimulation period.

scholarly journals The cholinergic system modulates negative BOLD responses in the prefrontal cortex once electrical perforant pathway stimulation triggers neuronal afterdischarges in the hippocampus

2021 ◽  
pp. 0271678X2110498
Author(s):  
Alberto Arboit ◽  
Karla Krautwald ◽  
Frank Angenstein
Keyword(s):  
Prefrontal Cortex ◽  
Neuronal Activity ◽  
Cerebral Blood Volume ◽  
Bold Response ◽  
Perforant Pathway ◽  
Bold Responses ◽  
Stimulation Period ◽  
Negative Bold ◽  
The Right ◽  
Frequency Pulse

Repeated high-frequency pulse-burst stimulations of the rat perforant pathway elicited positive BOLD responses in the right hippocampus, septum and prefrontal cortex. However, when the first stimulation period also triggered neuronal afterdischarges in the hippocampus, then a delayed negative BOLD response in the prefrontal cortex was generated. While neuronal activity and cerebral blood volume (CBV) increased in the hippocampus during the period of hippocampal neuronal afterdischarges (h-nAD), CBV decreased in the prefrontal cortex, although neuronal activity did not decrease. Only after termination of h-nAD did CBV in the prefrontal cortex increase again. Thus, h-nAD triggered neuronal activity in the prefrontal cortex that counteracted the usual neuronal activity-related functional hyperemia. This process was significantly enhanced by pilocarpine, a mACh receptor agonist, and completely blocked when pilocarpine was co-administered with scopolamine, a mACh receptor antagonist. Scopolamine did not prevent the formation of the negative BOLD response, thus mACh receptors modulate the strength of the negative BOLD response.

scholarly journals Low Frequency Stimulation of the Perforant Pathway Generates Anesthesia-Specific Variations in Neural Activity and BOLD Responses in the Rat Dentate Gyrus

2011 ◽  
Vol 32 (2) ◽  
pp. 291-305 ◽  
Author(s):  
Karla Krautwald ◽  
Frank Angenstein
Keyword(s):  
Dentate Gyrus ◽  
Stimulus Frequency ◽  
Low Frequency ◽  
Blood Oxygen Level Dependent ◽  
Bold Response ◽  
Blood Oxygen Level ◽  
Perforant Pathway ◽  
Bold Responses ◽  
Dependent Signal ◽  
Frequency Stimulation

To study how various anesthetics affect the relationship between stimulus frequency and generated functional magnetic resonance imaging (fMRI) signals in the rat dentate gyrus, the perforant pathway was electrically stimulated with repetitive low frequency (i.e., 0.625, 1.25, 2.5, 5, and 10 Hz) stimulation trains under isoflurane/N2O, isoflurane, medetomidine, and α-chloralose. During stimulation, the blood oxygen level-dependent signal intensity (BOLD response) and local field potentials in the dentate gyrus were simultaneously recorded to prove whether the present anesthetic controls the generation of a BOLD response via targeting general hemodynamic parameters, by affecting mechanisms of neurovascular coupling, or by disrupting local signal processing. Using this combined electrophysiological/fMRI approach, we found that the threshold frequency (i.e., the minimal frequency required to trigger significant BOLD responses), the optimal frequency (i.e., the frequency that elicit the strongest BOLD response), and the spatial distribution of generated BOLD responses are specific for each anesthetic used. Concurrent with anesthetic-dependent characteristics of the BOLD response, we found the pattern of stimulus-induced neuronal activity in the dentate gyrus is also specific for each anesthetic. Consequently, the anesthetic-specific influence on local signaling processes is the underlying cause for the observation that an identical stimulus elicits different BOLD responses under various anesthetics.

Fatigue of Paralyzed and Control Thenar Muscles Induced by Variable or Constant Frequency Stimulation

2003 ◽  
Vol 89 (4) ◽  
pp. 2055-2064 ◽  
Author(s):  
Christine K. Thomas ◽  
Lisa Griffin ◽  
Sharlene Godfrey ◽  
Edith Ribot-Ciscar ◽  
Jane E. Butler
Keyword(s):  
Spinal Cord ◽  
High Frequency ◽  
Low Frequency ◽  
Constant Frequency ◽  
Time Integral ◽  
Frequency Stimulation ◽  
Force Time ◽  
And Control ◽  
Frequency Pulse ◽  
Force Time Integral

Muscles paralyzed by chronic (>1 yr) spinal cord injury fatigue readily. Our aim was to evaluate whether the fatigability of paralyzed thenar muscles ( n = 10) could be reduced by the repeated delivery of variable versus constant frequency pulse trains. Fatigue was induced in four ways. Intermittent supramaximal median nerve stimulation (300-ms-duration trains) was delivered at 1) constant high frequency (13 pulses at 40 Hz each second for 2 min); 2) variable high frequency (each second for 2 min). The first two intervals of each variable frequency train were 5 and 20 ms. The remaining pulses were evenly distributed in time across 275 ms. The number of pulses varied for each subject such that the force time integral in the unfatigued state matched that evoked by a constant 40-Hz train; 3) constant low frequency (7 pulses at 20 Hz each second for 4 min); and 4) variable low frequency (each second for 4 min). The pulse pattern was the same as that for variable high frequency except that the force-time integral was matched to that produced by the constant low-frequency stimulation. These same experiments were performed on the thenar muscles of five able-bodied control subjects. The variable high-frequency trains used to fatigue paralyzed and control muscles had an average (± SE) of 12 ± 2 and 10 ± 1 pulses, respectively. Variable low-frequency trains had 7 ± 1 and 6 ± 1 pulses, respectively. Significant mean force declines of comparable magnitude (to 20–25% initial fatigue force or to 13–21% initial 50 Hz force) were seen in paralyzed muscles with all four stimulation protocols. The force reductions in paralyzed muscles were always accompanied by significant increases in half-relaxation time and decreases in force-time integral, irrespective of the stimulation protocol. Significant force decreases also occurred in control muscles during each fatigue test. Again, these force declines were similar whether constant or variable pulse patterns were used at high or low frequencies (to 40–60% initial fatigue force or to 29–36% initial 50 Hz force). The force reductions in control muscles were significantly less than those seen in paralyzed muscles, except when constant high-frequency stimulation was used. The variations in stimulation frequency, pulse pattern, and pulse number used in this study therefore had little influence on thenar muscle fatigue in control subjects or in spinal cord–injured subjects with chronic paralysis.

ADDENDUM TO “STUDIES OF ELASTIC WAVE ATTENUATION IN POROUS MEDIA” BY M. R. J. WYLLIE, G. H. F. GARDNER, AND A. R. GREGORY (GEOPHYSICS, OCTOBER, 1962, PP. 569–589)

Geophysics ◽  
1963 ◽  
Vol 28 (6) ◽  
pp. 1074-1074 ◽  
Author(s):  
M. R. J. Wyllie ◽  
G. H. F. Gardner ◽  
A. R. Gregory
Keyword(s):  
High Frequency ◽  
Critical Angle ◽  
Wave Attenuation ◽  
Low Frequency ◽  
Shear Velocity ◽  
Confining Pressure ◽  
Biot’S Theory ◽  
Biot's Theory ◽  
Angle Method ◽  
Frequency Pulse

In the paper published last year we noted that the shear velocity through liquid‐saturated rocks often appeared to exceed the shear velocity through the same rocks when dry. Our results were based on measurements made by the critical‐angle method on rocks subjected to heavy confining pressure. We felt constrained to observe that, if shear velocities through liquid‐saturated rocks were higher than through their dry counterparts, the applicability of Biot’s theory to any but low‐frequency resonating systems was open to question. Because Biot’s theory will be of maximum use only if it can be applied to systems in which velocities are measured by high‐frequency pulse techniques, our warning diminished the practical value of our other results.

scholarly journals Postsynaptic and Spiking Activity of Pyramidal Cells, the Principal Neurons in the Rat Hippocampal CA1 Region, Does Not Control the Resultant BOLD Response: A Combined Electrophysiologic and fMRI Approach

2015 ◽  
Vol 35 (4) ◽  
pp. 565-575 ◽  
Author(s):  
Thomas Scherf ◽  
Frank Angenstein
Keyword(s):  
Pyramidal Cells ◽  
Bold Response ◽  
Ca1 Pyramidal Cells ◽  
Ca1 Region ◽  
Hippocampal Ca1 Region ◽  
Postsynaptic Activity ◽  
Hippocampal Ca1 ◽  
Bold Responses ◽  
Stimulation Of ◽  
Spiking Activity

The specific role of postsynaptic activity for the generation of a functional magnetic resonance imaging (fMRI) response was determined by a simultaneous measurement of generated field excitatory postsynaptic potentials (fEPSPs) and blood oxygen level-dependent (BOLD) response in the rat hippocampal CA1 region during electrical stimulation of the contralateral CA3 region. The stimulation electrode was placed either in the left CA3a/b or CA3c, causing the preferentially basal or apical dendrites of the pyramidal cells in the right CA1 to be activated. Consecutive stimulations with low-intensity stimulation trains (i.e., 16 pulses for 8 seconds) resulted in clear postsynaptic responses of CA1 pyramidal cells, but in no significant BOLD responses. In contrast, consecutive high-intensity stimulation trains resulted in stronger postsynaptic responses that came along with minor (during stimulation of the left CA3a/b) or substantial (during stimulation of the left CA3c) spiking activity of the CA1 pyramidal cells, and resulted in the generation of significant BOLD responses in the left and right hippocampus. Correlating the electrophysiologic parameters of CA1 pyramidal cell activity (fEPSP and spiking activity) with the resultant BOLD response revealed no positive correlation. Consequently, postsynaptic activity of pyramidal cells, the most abundant neurons in the CA1, is not directly linked to the measured BOLD response.

Design and Implementation of a Dimmable LED Driver with Low-Frequency PWM Control

2013 ◽  
Vol 284-287 ◽  
pp. 2538-2542
Author(s):  
Hung Liang Cheng ◽  
Chun An Cheng ◽  
Chao Shun Chen ◽  
Kuan Lung Huang
Keyword(s):  
High Frequency ◽  
High Efficiency ◽  
Low Frequency ◽  
Buck Converter ◽  
Duty Ratio ◽  
Buck Converters ◽  
Resonant Converter ◽  
Switching Loss ◽  
Led Driver ◽  
Frequency Pulse

This paper proposes a high-efficiency dimmable LED driver for light emitting diodes (LED). The developed LED driver consists of a full-bridge resonant converter and six buck converters. The function of the full-bridge resonant converter is to obtain a smooth dc-link voltage for the buck converters by phase-shift modulation (PSM) while that of the six buck converters is to drive six LED modules, respectively. The gate voltage of the active switch of each buck converter is a combination of high-frequency and low-frequency pulses. The duty ratio of the high-frequency pulse controls the LED voltage and thereby, controls the amplitude of LED current. LEDs are dimmed by low-frequency pulse-width modulation (PWM) to vary the average current flowing through LED. Circuit equations are derived and circuit parameters are designed. High circuit efficiency is ensured by operating the active switches at zero-voltage switching-on to reduce the switching loss. Finally, a prototype circuit was built to verify the accuracy and feasibility of the proposed LED driver.

Simulations of high-resolution images of amorphous silicon films

1986 ◽  
Vol 44 ◽  
pp. 544-545
Author(s):  
G. Y. Fan ◽  
J. M. Cowley
Keyword(s):  
Electron Microscope ◽  
High Frequency ◽  
Fourier Transformation ◽  
Amorphous Materials ◽  
Low Frequency ◽  
Chromatic Aberration ◽  
Structure Information ◽  
Frequency Components ◽  
High Resolution Images ◽  
Spatial Frequency Spectrum

It is well known that the structure information on the specimen is not always faithfully transferred through the electron microscope. Firstly, the spatial frequency spectrum is modulated by the transfer function (TF) at the focal plane. Secondly, the spectrum suffers high frequency cut-off by the aperture (or effectively damping terms such as chromatic aberration). While these do not have essential effect on imaging crystal periodicity as long as the low order Bragg spots are inside the aperture, although the contrast may be reversed, they may change the appearance of images of amorphous materials completely. Because the spectrum of amorphous materials is continuous, modulation of it emphasizes some components while weakening others. Especially the cut-off of high frequency components, which contribute to amorphous image just as strongly as low frequency components can have a fundamental effect. This can be illustrated through computer simulation. Imaging of a whitenoise object with an electron microscope without TF limitation gives Fig. 1a, which is obtained by Fourier transformation of a constant amplitude combined with random phases generated by computer.

SEM image sharpness analysis

1996 ◽  
Vol 54 ◽  
pp. 142-143
Author(s):  
M. T. Postek ◽  
A. E. Vladar
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Quantitative Information ◽  
Primary Electron ◽  
Image Sharpness ◽  
Critical Dimensions ◽  
Sem Image ◽  
Frequency Changes ◽  
Electron Microscopes ◽  
Scanning Electron

Fully automated or semi-automated scanning electron microscopes (SEM) are now commonly used in semiconductor production and other forms of manufacturing. The industry requires that an automated instrument must be routinely capable of 5 nm resolution (or better) at 1.0 kV accelerating voltage for the measurement of nominal 0.25-0.35 micrometer semiconductor critical dimensions. Testing and proving that the instrument is performing at this level on a day-by-day basis is an industry need and concern which has been the object of a study at NIST and the fundamentals and results are discussed in this paper.In scanning electron microscopy, two of the most important instrument parameters are the size and shape of the primary electron beam and any image taken in a scanning electron microscope is the result of the sample and electron probe interaction. The low frequency changes in the video signal, collected from the sample, contains information about the larger features and the high frequency changes carry information of finer details. The sharper the image, the larger the number of high frequency components making up that image. Fast Fourier Transform (FFT) analysis of an SEM image can be employed to provide qualitiative and ultimately quantitative information regarding the SEM image quality.

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