Frequency-dependent Changes Research Articles

Effective Masking Levels for 500 and 2000 Hz Bone Conduction Auditory Steady State Responses in Infants and Adults With Normal Hearing

Few studies have investigated effective masking levels (EMLs) needed to isolate the test ear for bone conduction assessments in infants. The objective of this study was to determine EMLs for 500 and 2000 Hz bone conduction auditory steady state responses (ASSRs) to amplitude (AM)/frequency-modulated (FM) stimuli for infants and adults with normal hearing. Maturational factors that contribute to infant-adult differences in EMLs will also be investigated. The present study and previously published 1000 and 4000 Hz EML data will be compared to investigate EML across four frequencies. These findings will provide a starting point for implementing clinical masking for infant bone conduction testing using physiological measures. Participants were 15 infants (7 to 35 weeks) and 15 adults (21 to 56 years) with normal hearing. Bone-conducted single ASSR stimuli (research MASTER) were 100% AM and 25% FM at 85 and 101 Hz for 500 and 2000 Hz carrier frequencies, respectively. They were presented at 25 and 35 dB HL for 500 Hz and at 35 and 45 dB HL for 2000 Hz for both infants and adults (approximately 10 and 20 dB SL at each frequency for infants). Air-conducted narrowband maskers were presented to both ears simultaneously. Real-ear to coupler differences were measured to account for differences in the sound pressure developed in infant and adult ear canals as a result of ear-canal size. Data analyses were conducted for mean EMLs across frequency (500 to 4000 Hz) and between age groups. Masked and unmasked ASSR amplitudes were compared for 500 and 2000 Hz. Both infants and adults required much more masking (25 to 33 dB) to eliminate responses at 500 compared with 2000 Hz. On average, infants required 16 dB more masking at 500 Hz and similar amounts of masking at 2000 Hz compared with adults. When adjusted for ear-canal size and bone conduction sensitivity, the pattern of results did not change. Across all four frequencies, infants showed a systematic decrease in mean EMLs with an increase in frequency; all pair-wise comparisons were significant except 2000 versus 4000 Hz. Adults showed smaller frequency-dependent changes in EML (only significantly greater for 500 versus 2000 Hz and 4000 Hz). When ear-canal size and bone conduction sensitivity were taken into account, only 500 Hz required more masking than other frequencies in infants; there were no significant frequency-dependent trends for adults, although the greater EMLs at 1000 versus 2000 Hz and 4000 Hz approached significance. Unmasked and masked amplitudes tended to be larger for 2000 Hz but not for 500 Hz when comparing infants with adults. EMLs appropriate for infants for bone conduction ASSRs elicited to AM/FM stimuli are considerably higher at 500 compared with 2000 Hz. Infants also need more masking at 500 Hz compared with adults but the same amount of masking at 2000 Hz. Comparisons across four frequencies reveal a systematic decrease in EML with an increase in frequency in infants, which is not apparent in adults. Recommended EMLs for AM/FM bone-conducted ASSR stimuli presented at 35 dB HL for 500, 1000, 2000, and 4000 Hz, respectively, are: (1) infants: 81, 68, 59, and 45 dB SPL, and (2) adults: 66, 63, 59, and 55 dB SPL.

Study on the effect of delayed recovery of extracellular potassium ion concentration on spiral wave

Frequency-dependent changes in the extracellular potassium ion concentration have been added to the Luo-Rudy phase I heart model. Effects of the delayed restoration of extracellular potassium ion concentration on spiral waves are studied. Numerical simulation results show that due to the state of spiral wave, the delayed restoration of extracellular potassium ion concentration can lead to periodic oscillations of concentration, and the period and amplitude of the oscillation increase with the delayed recovery time, resulting in the emergence of various phenomena, such as the breathing spiral wave, the coexistence of multiple spiral waves, the meandering of spiral waves in the manner of Lévy flight, and the disappearance of spiral wave through different ways. These results are compatible with the experimental results.

Selective changes of resting-state brain oscillations in aMCI: an fMRI study using ALFF.

Mild cognitive impairment (MCI) refers to a transitional state between normal aging and dementia and is a syndrome with cognitive decline greater than expected for an individual's age and educational level. As a subtype of MCI, amnestic mild cognitive impairment (aMCI) most often leads to Alzheimer's disease. This study aims to elucidate the altered brain activation in patients with aMCI using resting-state functional magnetic resonance. We observed Frequency-dependent changes in the amplitude of low-frequency fluctuations in aMCI patients (n = 20), and normal subjects (n = 18). At the same time, we took gray matter volume as a covariate. We found that aMCI patients had decreased amplitude of low-frequency fluctuation signal in left superior temporal gyrus, right middle temporal gyrus, right inferior parietal lobe, and right postcentral gyrus compared to the control group. Specially, aMCI patients showed increased signal in left superior and middle frontal gyrus. Our results suggested that increased activation in frontal lobe of aMCI patients may indicate effective recruitment of compensatory brain resources. This finding and interpretation may lead to the better understanding of cognitive changes of aMCI.

Capacitive detection of living microalgae in a microfluidic chip

Capacitive detection of living microalgae from the sample suspension in a microfluidic chip is presented in this paper. A three-dimension capacitance sensor was designed by placing two cylindrical copper wires across the microfluidic channel. The frequency-dependent capacitive changes for both living and dead Dunaliella Salina were analyzed with Maxwell mixture theory and measured experimentally in this study. The results show that the amplitude of capacitive change is mainly influenced by algae's size, living status and the applied alternative current frequency. Specifically, capacitive change increases with the increase in algae size and decreases with the increase in frequency. For the same kind of algae, the capacitance change caused by the living algal, however, is larger than that of the dead one under the same frequency, which can be used to differentiate the living algae from the sample suspension. The method of frequency-dependent capacitive detection of live algae described in this paper is simple and sensitive. The experimentally determined frequency window can serve as a guideline to differentiate the living algal from the dead one.

Role of phase angle measurement in electrical impedance spectroscopy

Abstract Importance of phase angle measurement during the application of electrical impedance spectroscopy was studied by executing pot experiments with maize. Electrical impedance, phase angle (strength of capacitive character), and dissipation factor in the plant-soil system were scanned between 100 and 10 000 Hz current frequency. The frequency-dependent change in the phase angle could be described by optimum curves culminating within 920-3 650 Hz. Since the rate of energy dissipation is independent of root extent, the higher phase angle and lower energy dissipation were associated with the higher coefficient of determination achieved for the root electrical impedance - root system size (root dry mass and root surface area) regressions. The characteristic frequency selected on the basis of phase angle spectra provided a higher significance level at statistical comparison of plant groups subjected to stress conditions influencing root development. Due to the physicochemical changes observable in aging root tissue, the apex of phase angle spectra, thus the characteristic frequency, shifted continuously toward the higher frequencies over time. Consequently, the regularly repeated phase angle measurement is advisable in time-course studies for effective application of the electrical impedance method, and the systematic operation at the same frequency without determination of phase angle spectra should be avoided.

An Integrated Mitochondrial ROS Production and Scavenging Model: Implications for Heart Failure

It has been observed experimentally that cells from failing hearts exhibit elevated levels of reactive oxygen species (ROS) upon increases in energetic workload. One proposed mechanism for this behavior is mitochondrial Ca2+ mismanagement that leads to depletion of ROS scavengers. Here, we present a computational model to test this hypothesis. Previously published models of ROS production and scavenging were combined and reparameterized to describe ROS regulation in the cellular environment. Extramitochondrial Ca2+ pulses were applied to simulate frequency-dependent changes in cytosolic Ca2+. Model results show that decreased mitochondrial Ca2+uptake due to mitochondrial Ca2+ uniporter inhibition (simulating Ru360) or elevated cytosolic Na+, as in heart failure, leads to a decreased supply of NADH and NADPH upon increasing cellular workload. Oxidation of NADPH leads to oxidation of glutathione (GSH) and increased mitochondrial ROS levels, validating the Ca2+ mismanagement hypothesis. The model goes on to predict that the ratio of steady-state [H2O2]m during 3Hz pacing to [H2O2]m at rest is highly sensitive to the size of the GSH pool. The largest relative increase in [H2O2]m in response to pacing is shown to occur when the total GSH and GSSG is close to 1 mM, whereas pool sizes below 0.9 mM result in high resting H2O2 levels, a quantitative prediction only possible with a computational model.

Changes in Large Pulmonary Arterial Viscoelasticity in Chronic Pulmonary Hypertension

Conduit pulmonary artery (PA) stiffening is characteristic of pulmonary arterial hypertension (PAH) and is an excellent predictor of mortality due to right ventricular (RV) overload. To better understand the impact of conduit PA stiffening on RV afterload, it is critical to examine the arterial viscoelastic properties, which require measurements of elasticity (energy storage behavior) and viscosity (energy dissipation behavior). Here we hypothesize that PAH leads to frequency-dependent changes in arterial stiffness (related to elasticity) and damping ratio (related to viscosity) in large PAs. To test our hypothesis, PAH was induced by the combination of chronic hypoxia and an antiangiogenic compound (SU5416) treatment in mice. Static and sinusoidal pressure-inflation tests were performed on isolated conduit PAs at various frequencies (0.01–20 Hz) to obtain the mechanical properties in the absence of smooth muscle contraction. Static mechanical tests showed significant stiffening of large PAs with PAH, as expected. In dynamic mechanical tests, structural stiffness (κ) increased and damping ratio (D) decreased at a physiologically relevant frequency (10 Hz) in hypertensive PAs. The dynamic elastic modulus (E), a material stiffness, did not increase significantly with PAH. All dynamic mechanical properties were strong functions of frequency. In particular, κ, E and D increased with increasing frequency in control PAs. While this behavior remained for D in hypertensive PAs, it reversed for κ and E. Since these novel dynamic mechanical property changes were found in the absence of changes in smooth muscle cell content or contraction, changes in collagen and proteoglycans and their interactions are likely critical to arterial viscoelasticity in a way that has not been previously described. The impact of these changes in PA viscoelasticity on RV afterload in PAH awaits further investigation.

Development of an antenna coil type sensor device for hydrogen leakage detection

An antenna coil type hydrogen gas sensor device was fabricated and evaluated for applying to radio frequency identification (RFID) tag which can easily realize highly reliable and multipoint hydrogen leakage detection system. An antenna coil composed of platinum thin film was formed by photolithography onto a quartz-glass substrate. Then, a platinum-supported tungsten trioxide thin film was deposited on that coil by spin coating method. A frequency dependence of electrical properties (S-parameters) of the sensor device in air and in 4vol.% hydrogen balanced with nitrogen gas was investigated in the range from 300kHz to 3GHz. The considerably change in frequency dependence of S11 with the exposure to hydrogen gas was observed. The result indicated high sensitivity of this sensor device and the possibility of wireless transmission of the information about hydrogen leakage. The 90% response time was about 3s at 188MHz. The sensitivity to hydrogen in air was lower than that in nitrogen atmosphere. It could result from the competitive oxidation reaction of tungsten bronze by oxygen. However, the sensor device was able to detect hydrogen gas in concentration range below lower explosion limit. In addition, the change in S21 between the sensor device and a conventional antenna coil was also demonstrated.

Abstract 445: Increased Dietary Salt Intake Enhances Sympathetic and Cardiovascular Responses to Various Stressors

Previous studies indicate that increased dietary salt intake enhances sympathetic nerve activity (SNA) and arterial blood pressure (ABP) responses evoked from sympathetic neurons of the rostral ventrolateral medulla. The present study sought to extend these findings and determine whether dietary salt intake enhances SNA and ABP responses various sympathetic reflexes that depend on RVLM neurotransmission. Male Sprague-Dawley rats were fed 0.1% (n=6-8) or 4.0% (n=6-8) NaCl diets for 14-21 days. Then, animals were anesthetized with Inactin. Electrical stimulation (1-20 Hz, 1 ms pulse, 500 uA) of sciatic afferents produced frequency-dependent changes in SNA and ABP in both groups. However, rats ingesting 4% versus 0.1% NaCl displayed significantly larger increases in lumbar SNA (5Hz: 213±25 vs 146±25%, P<0.05), renal SNA (5Hz: 187±24 vs 120±11%), splanchnic SNA (5Hz: 203±21 vs 136±9%), and mean ABP (5Hz: 28±2 vs 12±2 mmHg). Rats ingesting 4% vs 0.1% NaCl also displayed greater increases in lumbar SNA (24±6 vs 13±2%, P<0.05) and mean ABP (12.1±0.9 vs 8.2±1.3mmHg, P<0.05) during increases in cerebrospinal fluid sodium concentration produced by intracerebroventricular infusion of 1M NaCl (5ul/10min). Lastly, hypercapnia (7% CO2, 33% O2, 63% N2, 60s) produced greater increases in lumbar SNA in rats ingesting 4% versus 0.1% NaCl (24±2% versus 9±3%, respectively; P<0.01). These findings suggest increased dietary salt intake enhances several sympathetic and cardiovascular reflexes.

Toughening strategies of carbon nanotube/polycarbonate composites with electromagnetic interference shielding properties

The effect of different toughening strategies on the mechanical properties of multiwalled carbon nanotube/polycarbonate composite (PC/MWNT) for electromagnetic interference shielding was analyzed from the mechanical and fracture tests using linear elastic fracture mechanics. The effect of processing (injection and compression molding) and manufacturing (annealing) conditions in the mechanical properties and electrical conductivity has been studied. The classic electromagnetic theory predicts a shielding effectiveness around 40 dB for nanocomposites with 5 wt% of MWNT in the frequency range studied. These values make these compounds to be very interesting materials for potential applications as electronic housings. Therefore, a combination of cyclic form of polybutylene terephthalate addition and annealing strategies let to optimize flexural parameters and improve the flexural modulus of PC composites. The rheology results showed that the dynamic moduli and the viscosity grew with increasing MWNT content. A significant change in frequency dependence of the moduli was observed, with respect to pure PC, which indicates a transition from a liquid‐like to a solid‐like behavior.Finally, the morphological study proves that the composites display different toughening mechanisms as function of carbon nanotube quantity. This fact could explain the different fracture behaviors of materials. In summary, it has been proved that it is possible to obtain PC/MWNT nanocomposites with relatively high conductivity, minimizing the loss of mechanical properties, using processing techniques easily scalable at industrial level. POLYM. COMPOS., 34:1938–1949, 2013. © 2013 Society of Plastics Engineers

Dietary salt intake enhances sympathetic responses to central sodium and sciatic afferent activation

Previous studies indicate that increased dietary salt intake enhances sympathetic nerve activity (SNA) and arterial blood pressure (ABP) responses evoked from the rostral ventrolateral medulla. The present study sought to extend these observations and determine whether SNA and ABP responses to physiological stimuli are also enhanced. Male Sprague‐Dawley rats were fed 0.1% (low) or 4.0% (high) NaCl chow for 14–16 days. Then, animals were anesthetized with Inactin, and various sympathetic reflexes were tested. Electrical stimulation (1–20 Hz, 1 ms pulse, 500 uA) of sciatic afferents produced frequency‐dependent changes in SNA and ABP in both groups. However, rats ingesting 4% versus 0.1% NaCl displayed significantly larger increase in lumbar SNA (5Hz: 213±25 vs 146±15%), renal SNA (5Hz: 187±24 vs 120±11%), splanchnic SNA (5Hz: 203±21 vs 136±9%), heart rate (5Hz: 21±4 vs 13±2 bpm), and mean ABP (5Hz: 28±2 vs 12±2mmHg). Similarly, rats ingesting 4% versus 1% NaCl displayed greater increases in lumbar SNA (128±9 vs 112±2%) and mean ABP (12±1 vs 7±2mmHg) in response to intracerebroventricular infusion of 1M NaCl (5ul/10min). These findings suggest that increased dietary NaCl sensitizes central sympathetic networks to produce larger changes in SNA and ABP.

Electrical measurements of dielectric nonlinearities in ferroelectric bilayer thin films

Frequency dependence of the dielectric response is studied for ferroelectric bilayer thin-film capacitors under a cyclic bias voltage. The approach used in this work enables probing strong dielectric nonlinearities at millisecond and microsecond time scales during polarization switching in thin films. The frequency-dependent changes that are observed in the relative dielectric permittivity of PbZr0.8Ti0.2O3/PbZr0.6Ti0.4O3 and PbZr0.6Ti0.4O3/PbZr0.2Ti0.8O3 epitaxial bilayers without applying the cyclic bias are small in the kHz-to-MHz frequency range. When the bias is applied, a strong frequency dependence of the relative dielectric permittivity is observed during polarization switching. For instance, the permittivity of the PbZr0.6Ti0.4O3/PbZr0.2Ti0.8O3 bilayer changes from εr≈300 at 100 kHz to εr≈1600 at 2 kHz. The observed frequency dependence of the permittivity can be described by [1+TT+Tcln(1ωt0)]2 that has been proposed for dynamic response in systems involving pinning at two-dimensional domain walls.

Electrical tissue property imaging using MRI at dc and Larmor frequency

Cross-sectional imaging of conductivity and permittivity distributions inside the human body has been actively investigated in impedance imaging areas such as electrical impedance tomography (EIT) and magnetic induction tomography (MIT). Since the conductivity and permittivity values exhibit frequency-dependent changes, it is worthwhile to perform spectroscopic imaging from almost dc to hundreds of MHz. To probe the human body, we may inject current using surface electrodes or induce current using external coils. In EIT and MIT, measured data are only available on the boundary or exterior of the body unless we invasively place sensors inside the body. Their image reconstruction problems are nonlinear and ill-posed to result in images with a relatively low spatial resolution. Noting that an MRI scanner can noninvasively measure magnetic fields inside the human body, electrical tissue property imaging methods using MRI have lately been proposed. Magnetic resonance EIT (MREIT) performs conductivity imaging at dc or below 1 kHz by externally injecting current into the human body and measuring induced internal magnetic flux density data using an MRI scanner. Magnetic resonance electrical property tomography (MREPT) produces both conductivity and permittivity images at the Larmor frequency of an MRI scanner based on B1-mapping techniques. Since internal data are only available in MREIT and MREPT, we may formulate well-posed inverse problems for image reconstructions. To develop related imaging techniques, we should clearly understand the basic principles of MREIT and MREPT, which are based on coupled physics of bioelectromagnetism and MRI as well as associated mathematical methods. In this paper, we describe the physical principles of MREIT and MREPT in a unified way and associate measurable quantities with the conductivity and permittivity. Clarifying the key relations among them, we examine existing image reconstruction algorithms to reveal their capabilities and limitations. We discuss technical issues in MREIT and MREPT and suggest future research directions to improve the quality of cross-sectional images of the electrical tissue properties.

Depth-resolved cellular microrheology using HiLo microscopy

It is increasingly important to measure cell mechanical properties in three-dimensional environments. Particle tracking microrheology (PTM) can measure cellular viscoelastic properties; however, out-of-plane data can introduce artifacts into these measurements. We developed a technique that employs HiLo microscopy to reduce out-of-plane contributions. This method eliminated signals from 90% of probes 0.5 μm or further from the focal plane, while retaining all in-plane probes. We used this technique to characterize live-cell bilayers and found that there were significant, frequency-dependent changes to the extracted cell moduli when compared to conventional analysis. Our results indicate that removal of out-of-plane information is vital for accurate assessments of cell mechanical properties.

Amygdala hyperactivity and tonotopic shift after salicylate exposure

The amygdala, important in forming and storing memories of aversive events, is believed to play a major role in debilitating tinnitus and hyperacusis. To explore this hypothesis, we recorded from the lateral amygdala (LA) and auditory cortex (AC) before and after treating rats with a dose of salicylate that induces tinnitus and hyperacusis-like behavior. Salicylate unexpectedly increased the amplitude of the local field potential (LFP) in the LA making it hyperactive to sounds≥60 dB SPL. Frequency receptive fields (FRFs) of multiunit (MU) clusters in the LA were also dramatically altered by salicylate. Neuronal activity at frequencies below 10 kHz and above 20 kHz was depressed at low intensities, but was greatly enhanced for stimuli between 10 and 20 kHz (frequencies near the pitch of the salicylate-induced tinnitus in the rat). These frequency-dependent changes caused the FRF of many LA neurons to migrate towards 10-20 kHz thereby amplifying activity from this region. To determine if salicylate-induced changes restricted to the LA would remotely affect neural activity in the AC, we used a micropipette to infuse salicylate (20 μl, 2.8 mM) into the amygdala. Local delivery of salicylate to the amygdala significantly increased the amplitude of the LFP recorded in the AC and selectively enhanced the neuronal activity of AC neurons at the mid-frequencies (10-20 kHz), frequencies associated with the tinnitus pitch. Taken together, these results indicate that systemic salicylate treatment can induce hyperactivity and tonotopic shift in the amygdala and infusion of salicylate into the amygdala can profoundly enhance sound-evoked activity in AC, changes likely to increase the perception and emotional salience of tinnitus and loud sounds. This article is part of a Special Issue entitled: Tinnitus Neuroscience.

Quadri-pulse stimulation induces stimulation frequency dependent cortical hemoglobin concentration changes within the ipsilateral motor cortical network

BackgroundImaging studies investigating repetitive transcranial magnetic stimulation (rTMS) mediated hemodynamic consequences revealed inconsistent results, mainly due to differences in rTMS parameters and technical difficulties with simultaneous recordings during rTMS. Objective/HypothesisQuadri-pulse rTMS (QPS) induces bidirectional long-term plasticity of the human primary motor cortex (M1). To evaluate its on-line effects, near infrared spectroscopy (NIRS) recordings were performed during QPS. We hypothesized that on-line effects during QPS are different from long-term aftereffects. MethodsUsing a novel TMS - on-line multi-channel NIRS setup we recorded hemoglobin concentration [Hb] changes at the stimulated M1 and adjacent sensory-motor areas during QPS protocols inducing oppositely directed aftereffects (QPS-5: interstimulus interval (ISI) 5 ms, potentiation; QPS-50: ISI 50 ms, depression). In two experiments we studied NIRS changes during either single or repeated QPS bursts. ResultsThe repetitive QPS-5 bursts significantly decreased oxyhemoglobin concentration ([oxy-Hb]) in the ipsilateral M1. A single QPS-5 burst decreased [oxy-Hb] in the M1 and premotor cortex. QPS-50 induced no significant NIRS changes at any sites. ConclusionsQPS can significantly alter cortical hemodynamics depending on the stimulation frequency. While bidirectional long-term aftereffects of QPS reflect synaptic efficacy changes, unidirectional on-line effects during QPS may represent pure electrophysiological property changes within the cell membrane or synapse. Since neuronal postexcitatory inhibitory postsynaptic potentials typically peak within the first 10–20 ms, only pulses delivered at higher frequencies may lead to summation of the inhibitory effects, resulting in [oxy-Hb] decrease only after QPS-5. Our new TMS-NIRS setup may be valuable to investigate TMS induced neurovascular coupling mechanisms in humans.

Bioelectrical Impedance as a Diagnostic Factor in the Clinical Practice and Prognostic Factor for Survival in Cancer Patients: Prediction, Accuracy and Reliability

Bioimpedance analysis could provide a clear figure about changes in cells and tissues based on frequencydependent changes, due to their electrical resistances for the applied electrical current. This review explains the physical principle of bioimpedance. And to monitor the progression of radiation induced tissue injury, particularly in radiotherapies. The interaction of radiation with the biological tissues and a prediction for their earlier and later alterations due to exposure are discussed. As well as, an overview for tissue identification by bioelectrical impedance analysis (BIA) is proposed. Bioimpedance analysis “applications and its limitations” in the health care, clinical practice and prognosis of overall survival in cancer patients are discussed.

Reflection and transmission coefficients of a fracture in transversely isotropic media

We obtain the reflection and transmission coefficients at a fracture in transversely isotropic media, whose symmetry axis is perpendicular to the fracture surface. We consider dissimilar upper and lower media. The fracture is modeled as an interface with boundary discontinuities in the displacement and the particle velocity. The stress components are proportional to the displacement and velocity discontinuities through the specific stiffnesses and specific viscosities, respectively. The stiffness introduces frequency-dependence and phase changes in the fracture response and the viscosity is related to the energy loss. We also calculate the energy balance at the fracture and the dissipated energy. The theory is illustrated by computing the reflection coefficient of a fracture present in the Antarctic ice cap. In this case, the reflection coefficient decreases with increasing incidence angle and then approaches 1 at grazing angle.

Functional PET Evaluation of the Photosensitive Baboon

The baboon provides a unique, natural model of epilepsy in nonhuman primates. Additionally, photosensitivity of the epileptic baboon provides an important window into the mechanism of human idiopathic generalized epilepsies. In order to better understand the networks underlying this model, our group utilized functional positron emission tomography (PET) to compare cerebral blood flow (CBF) changes occurring during intermittent light stimulation (ILS) and rest between baboons photosensitive, epileptic (PS) and asymptomatic, control (CTL) animals. Our studies utilized subtraction and covariance analyses to evaluate CBF changes occurring during ILS across activation and resting states, but also evaluated CBF correlations with ketamine doses and interictal epileptic discharge (IED) rate during the resting state. Furthermore, our group also assessed the CBF responses related to variation of ILS in PS and CTL animals. CBF changes in the subtraction and covariance analyses reveal the physiological response and visual connectivity in CTL animals and pathophysiological networks underlying responses associated with the activation of ictal and interictal epileptic discharges in PS animals. The correlation with ketamine dose is essential to understanding differences in CBF responses between both groups, and correlations with IED rate provides an insight into an epileptic network independent of visual activation. Finally, the ILS frequency dependent changes can help develop a framework to study not only spatial connectivity but also the temporal sequence of regional activations and deactivations related to ILS. The maps generated by the CBF analyses will be used to target specific nodes in the epileptic network for electrophysiological evaluation using intracranial electrodes.

Probing mouse brain microstructure using oscillating gradient diffusion MRI

High resolution diffusion tensor images of the mouse brain were acquired using the pulsed gradient spin echo sequence and the oscillating gradient spin echo sequence. The oscillating gradient spin echo tensor images demonstrated frequency-dependent changes in diffusion measurements, including apparent diffusion coefficient and fractional anisotropy, in major brain structures. Maps of the rate of change in apparent diffusion coefficient with oscillating gradient frequency revealed novel tissue contrast in the mouse hippocampus, cerebellum, and cerebral cortex. The observed frequency-dependent contrasts resembled neuronal soma-specific Nissl staining and nuclei-specific 4',6-diamidino-2-phenylindole (DAPI) staining in the mouse brain, which suggests that the contrasts might be related to key features of cytoarchitecture in the brain. In the mouse cuprizone model, oscillating gradient spin echo-based diffusion MRI revealed significantly higher frequency-dependence of perpendicular diffusivity (λ(⊥) ) in the demyelinated caudal corpus callosum at 4 weeks after cuprizone treatment when compared with control mice and mice at 6 weeks after cuprizone treatment. The elevated frequency-dependence of λ(⊥) coincided with the infiltration of activated microglia/macrophages and disruption of axons during acute demyelination in the caudal corpus callosum. The results demonstrate the potential of oscillating gradient spin echo-based diffusion MRI for providing tissue contrasts complimentary to conventional pulsed gradient spin echo-based diffusion MRI.