Low-frequency Stimuli Research Articles

Temporal Frequency Abnormalities in Early-Stage Diabetic Retinopathy Assessed by Electroretinography.

PurposeTo define the nature and extent of temporal frequency abnormalities in diabetics who have mild or no nonproliferative diabetic retinopathy (NPDR) by using the flicker electroretinogram (ERG).MethodsLight-adapted flicker ERGs were recorded from 20 diabetics who have no clinically apparent retinopathy, 20 diabetics who have mild NPDR, and 20 nondiabetic, age-equivalent controls. ERGs were elicited by full-field sinusoidal flicker across the temporal frequency range of 6 to 100 Hz and were recorded using conventional techniques. The amplitude and phase of the fundamental and harmonic response components were derived by Fourier analysis and compared among the groups.ResultsAnalysis of variance indicated that compared with the controls, both patient groups had significant amplitude reductions of the fundamental ERG component for temporal frequencies greater than 56 Hz (all P ≤ 0.03). Modeling the amplitude measurements indicated that both patient groups had significant reductions in the high-frequency response cutoff. Response phase, however, did not differ significantly among the groups at any frequency. The amplitude and phase of the high-frequency harmonics (32–96 Hz) of the patients' responses to a low-frequency stimulus (16 Hz) were normal over the temporal frequency range that the fundamental response was abnormal.ConclusionsTaken together, the diabetics' fundamental amplitude attenuation for rapid flicker combined with their normal high-frequency harmonic responses generated by slow flicker suggest that the likely site of the abnormal temporal filtering occurs prior to the nonlinearity that generates the harmonic components of the ERG, implicating a photoreceptor origin.

An Adaptive SSVEP-Based Brain-Computer Interface to Compensate Fatigue-Induced Decline of Performance in Practical Application.

Brain-computer interfaces based on steady-state visual evoked potentials are promising communication systems for people with speech and motor disabilities. However, reliable SSVEP response requires user's attention, which degrades over time due to significant eye-fatigue when low-frequency visual stimuli (5-15 Hz) are used. Previous studies have shown that eye-fatigue can be reduced using high-frequency flickering stimuli (>25 Hz). Here, it is quantitatively demonstrated that the performance of a high-frequency SSVEP BCI decreases over time, but this amount of decrease can be compensated effectively by using two proposed adaptive algorithms. This leaded to a robust alternative communication system for practical applications. The asynchronous spelling system implemented in this study uses a threshold-based version of LASSO algorithm for frequency recognition. In long online experiments, when participants typed a sentence with the BCI system for 16 times, accuracy of the system was close to its maximum along the experiment. However, regression analysis on typing speed of each sentence demonstrated a significant decrease in all 7 subjects ( ) when thresholds obtained from a calibration test were kept fixed over the experiment. In comparison, no significant change in typing speed was observed when the proposed adaptive algorithms were used. The analysis of variances revealed that the average typing speed of the last four sentences when using adaptive relational algorithm (8.7 char/min) was significantly higher than the tolerance-based algorithm (8.1 char/min) and significantly above 6 char/min when the fixed thresholds were used. Therefore, the relational algorithm proposed in this paper could successfully compensate for the effect of fatigue on performance of the SSVEP BCI system.

Organ of Corti vibration within the intact gerbil cochlea measured by volumetric optical coherence tomography and vibrometry.

There is indirect evidence that the mammalian cochlea in the low-frequency apical and the more commonly studied high-frequency basal regions function in fundamentally different ways. Here, we directly tested this hypothesis by measuring sound-induced vibrations of the organ of Corti (OoC) at three turns of the gerbil cochlea using volumetric optical coherence tomography vibrometry (VOCTV), an approach that permits noninvasive imaging through the bone. In the apical turn, there was little frequency selectivity, and the displacement-vs.-frequency curves had low-pass filter characteristics with a corner frequency of ~0.5-0.9 kHz. The vibratory magnitudes increased compressively with increasing stimulus intensity at all frequencies. In the middle turn, responses were similar except for a slight peak in the response at ~2.5 kHz. The gain was ~50 dB at the peak and 30-40 dB at lower frequencies. In the basal turn, responses were sharply tuned and compressively nonlinear, consistent with observations in the literature. These data demonstrated that there is a transition of the mechanical response of the OoC along the length of the cochlea such that frequency tuning is sharper in the base than in the apex. Because the responses are fundamentally different, it is not appropriate to simply frequency shift vibratory data measured at one cochlear location to predict the cochlear responses at other locations. Furthermore, this means that the number of hair cells stimulated by sound is larger for low-frequency stimuli and smaller for high-frequency stimuli for the same intensity level. Thus the mechanisms of central processing of sounds must vary with frequency. NEW & NOTEWORTHY A volumetric optical coherence tomography and vibrometry system was used to probe cochlear mechanics within the intact gerbil cochlea. We found a gradual transition of the mechanical response of the organ of Corti along the length of the cochlea such that tuning at the base is dramatically sharper than that at the apex. These data help to explain discrepancies in the literature regarding how the cochlea processes low-frequency sounds.

Vision During Saccadic Eye Movements

The perceptual consequences of eye movements are manifold: Each large saccade is accompanied by a drop of sensitivity to luminance-contrast, low-frequency stimuli, impacting both conscious vision and involuntary responses, including pupillary constrictions. They also produce transient distortions of space, time, and number, which cannot be attributed to the mere motion on the retinae. All these are signs that the visual system evokes active processes to predict and counteract the consequences of saccades. We propose that a key mechanism is the reorganization of spatiotemporal visual fields, which transiently increases the temporal and spatial uncertainty of visual representations just before and during saccades. On one hand, this accounts for the spatiotemporal distortions of visual perception; on the other hand, it implements a mechanism for fusing pre- and postsaccadic stimuli. This, together with the active suppression of motion signals, ensures the stability and continuity of our visual experience.

Functional MRI Investigation of Audiovisual Interactions in Auditory Midbrain.

The brain integrates information from different sensory modalities to form a representation of the environment and facilitate behavioral responses. The auditory midbrain or inferior colliculus (IC) is a pivotal station in the auditory system, integrating ascending and descending information from various auditory sources and cortical systems. The present study investigated the modulation of auditory responses in the IC by visual stimuli of different frequencies and intensities in rats using functional MRI (fMRI). Low-frequency (1 Hz) high-intensity visual stimulus suppressed IC auditory responses. However, high-frequency (10 Hz) or low-intensity visual stimuli did not alter the IC auditory responses. This finding demonstrates that cross-modal processing occurs in the IC in a manner that depends on the stimulus. Furthermore, only low-frequency high-intensity visual stimulus elicited responses in non-visual cortical regions, suggesting that the above cross-modal modulation effect may arise from top-down cortical feedback. These fMRI results provide insight to guide future studies of cross-modal processing in sensory pathways.

Whole Body Vibration Exposure on Markers of Bone Turnover, Body Composition, and Physical Functioning in Breast Cancer Patients Receiving Aromatase Inhibitor Therapy: A Randomized Controlled Trial.

Introduction: Women with breast cancer are often prescribed aromatase inhibitors, which can cause rapid loss of bone mass leading to significant potential for morbidity. Vibration training has been shown to be helpful in reducing bone turnover in postmenopausal women without cancer. Aim: To examine the effect of vibration stimulus on markers of bone turnover in breast cancer patients receiving aromatase inhibitors. Methods: Thirty-one breast cancer survivors undergoing treatment with aromatase inhibitors were randomized to vibration stimulus (n = 14) or usual care control (n = 17). Low-frequency and low-magnitude vibration stimulus (27-32 Hz, 0.3g) was delivered in supervised sessions via standing on a vibration platform for 20 minutes, 3 times per week for 12 weeks. The primary outcome was blood markers of bone resorption (serum N-telopeptide X/creatine) and formation (serum type 1 procollagen N-terminal propeptide; P1NP). Other study outcomes body composition as well as measures of physical functioning. Outcomes were compared between groups using analysis of covariance adjusted for baseline values as well as time on aromatase inhibitors. Outcomes: On average, participants were 61.5 years old and overweight (ie, body mass index = 28.5 kg/m2). Following vibration training, there was no significant difference between groups for bone resorption (adjusted group difference 0.5, P = .929) or formation (adjusted group difference 5.3, P = .286). There were also no changes in any measure of physical functioning body composition. Conclusions: Short-term low-magnitude vibration stimulus does not appear to be useful for reducing markers of bone turnover secondary to aromatase inhibitors in breast cancer patients; nor is it useful in improving physical function or symptoms. However, further investigations with larger samples and higher doses of vibration are warranted. Trial Registration: Australian and New Zealand Clinical Trials Registry (ACTRN12611001094965).

Hybrid stimulation enhances torque as a function of muscle fusion in human paralyzed and non-paralyzed skeletal muscle

ObjectiveAfter spinal cord injury (SCI), hybrid stimulation patterns that interpose paired-pulse doublets over a constant-frequency background may enhance the metabolic “work” (muscle torque) performed by paralyzed muscle. This study examined the effect of background stimulation frequency on the torque contribution of the doublet before and after fatigue.DesignCross-sectional study.SettingResearch laboratory in an academic medical center.ParticipantsFive men with chronic sensory and motor-complete SCI and ten non-SCI controls (6 males, 4 females). SCI subjects were recruited from a long-term study of unilateral plantar-flexor training; both limbs were tested for the present study.InterventionsSubjects underwent plantar flexor stimulation at 5, 7, 9, and 12 Hz. The four background frequencies were overlaid with 6 ms doublets delivered at the start, middle, or at both the start and middle of each train. The 5 Hz and 12 Hz frequencies were analyzed after fatigue.Outcome MeasuresMean torque, peak torque, torque fusion index, doublet torque.ResultsTrains with doublets at both the start and middle yielded the most consistent enhancement of torque (all P < 0.028). Torque contribution of the doublet was greatest at low stimulus frequencies (all P < 0.016). The low relative fusion of untrained paralyzed muscle preserved the efficacy of the doublet even during fatigue.ConclusionHybrid stimulus trains may be an effective way to increase contractile work in paralyzed muscle, even after fatigue. They may be useful for rehabilitation strategies designed to enhance the metabolic work performed by paralyzed skeletal muscle.

Idiothetic signal processing and spatial orientation in patients with unilateral hippocampal sclerosis.

The role of the hippocampus in spatial navigation and the presence of vestibular-responsive neurons in limbic areas are well-established from animal experiments. However, hippocampal spatial processing in humans is not fully understood. Here, we employed real whole body and head-on-trunk rotations to investigate how vestibular signals, either alone or in combination with neck-proprioceptive stimulation, shape the spatial frame of reference in patients with unilateral hippocampal sclerosis (HS). Patients were asked to point in darkness with a light spot, moved on a cylindrical screen by means of a joystick, into their visual straight-ahead direction (VSA), to remember this direction in space, and to revert back to this point after the rotations. Estimates in patients with HS were compared with those of healthy controls and of patients with epilepsy without hippocampal involvement. All groups produced similar errors after low-frequency vestibular stimuli. These errors were eliminated when rotations involved concurrent neck stimulation. Significantly increased variability was observed, however, in both the VSA and reposition estimates after the rotations in patients with HS compared with controls. These results suggest that cognitive processing of idiothetic signals for self-motion perception is inaccurate in patients with HS. Importantly, however, the responses of patients with HS showed no spatial lateralization with regard to right or left HS, suggesting that the underlying neuronal loss attenuates the precision of head-direction signal decoding in a nondirectional manner. Hence, patients are unable to use these signals as efficiently as normal subjects in the construction of a stable head-centric spatial frame of reference. NEW & NOTEWORTHY Spatial perception relies on combined processing of various idiothetic (vestibular and proprioceptive) and allothetic (visual and auditory) sensory signals. Despite the established knowledge of rodent vestibular-hippocampal interactions, human data are lacking. We investigated idiothetic orientational processing in subjects with unilateral hippocampal sclerosis using various combinations of vestibular and proprioceptive stimuli. Hippocampal impairment leads to less accurate, noisy decoding of the signal related to idiothetic orientation. However, patients did not show any lateralized deficits of visual straight-ahead perception or of target/self-displacement perception after idiothetic stimulation.

Amyloid fibrils induce dysfunction of hippocampal glutamatergic silent synapses.

Silent glutamatergic synapses lacking functional AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazoleproprionate) receptors exist in several brain regions including the hippocampus. Their involvement in the dysfunction of hippocampal glutamatergic transmission in the setting of Alzheimer's disease (AD) is unknown. This study demonstrated a decrease in the percentage of silent synapses in rats microinjected with amyloid fibrils (Aβ1-40 ) into the hippocampal CA1. Also, pairing low-frequency electric stimuli failed to induce activation of the hippocampal silent synapses in the modeled rats. Immunoblotting studies revealed a decreased expression of GluR1 subunits in the hippocampal CA1 synaptosomal preparation, indicating a potential reduction in the GluR1 subunits anchoring in postsynaptic density in the modeled rats. We also noted a decreased expression of phosphorylated cofilin, which regulates the function of actin cytoskeleton and receptor trafficking, and reduced expression of the scaffolding protein PSD95 in the hippocampal CA1 synaptosome in rats injected with Aβ1-40 . Taken together, this study illustrates dysfunction of hippocampal silent synapse in the rodent model of AD, which might result from the impairments of actin cytoskeleton and postsynaptic scaffolding proteins induced by amyloid fibrils.

T75. The relationship between Motor Unit (MU) behaviour and nerve conduction velocity follow cooling at the elbow: An exploration of conduction dependent MUs rate block

Nerve conduction velocity is a common assessment of peripheral demyelinating conditions used to locate the lesions and assess severity. Considering measurements involve low frequency or single stimuli, changes due to continuous activity would remain out of their scope. Accordingly, slowing of conduction velocity is not thought to result in weakness, but may account for loss of deep tendon reflexes leading to neural transmission failure. It has previously been shown that a decrease in temperature of 1 °C can cause a 2.4 m/s reduction in nerve conduction velocity, however little is known on the neuromuscular effects, specifically the behavior of individual Motor Units (MUs). This study explored the relationship between the MU behavior and motor-sensory nerve conduction velocities following the application of a standard therapeutic cooling technique at the elbow. Eleven healthy individuals, aged 20–49, were tested using two non-invasive Nerve Conduction Studies (NCS); compound muscle action potentials of the First Dorsal Interosseous (FDI) muscle and sensory nerve action potentials, and a non-invasive investigation of the firing of MU using surface EMG decomposition (dEMG, Delsys Inc.) of FDI. Testing was performed prior to cooling, immediately after cooling and after 15 min of rewarming. Cooling was performed for 15 min using crushed ice and water to a skin temperature between 10 and 15 °C. Repeated measures ANOVAs with post hoc pairwise comparisons showed significant reductions in the MU firing between pre-cooling and post-cooling and between pre-cooling and re-warming (p = 0.013, p = 0.045) respectively. Similar patterns were seen in both the Motor and Sensory NCS with significant differences between pre-cooling and post-cooling, pre-cooling and re-warming, and between post-cooling and 15 min of re-warming in the Sensory assessment, although the latter is of questionable clinical importance (p < 0.01), Fig. 1. This showed a 22% delay in the Sensory and 26% delay in the Motor nerve conduction, which caused a corresponding 12% mean MUs firing rate decay. Further analysis separating MUs in tertiles revealed higher firing MUs were significantly reduced after cooling, leaving lower firing MUs unchanged (Table 1). There appears to be a clear relationship between the motor and sensory NCS and the MU firing rate. In contrast to high stimulation frequencies used clinically or activity dependent conduction block, this study shows conduction dependent MUs rate block (CDRB) verifying motor deficit whilst only nerve conduction slowing is evident, and revealing the first recruited MUs are affected more than the later recruited ones. This highlights the potential for dEMG as a novel neurological assessment, which could be used when conduction velocity is difficult to measure and motor control is affected, especially early in the clinical state before axonal degeneration is evident, which is still challenging for routine neurophysiological methods.

Amphibian sacculus and the forced Kuramoto model with intrinsic noise and frequency dispersion.

The amphibian sacculus (AS) is an end organ that specializes in the detection of low-frequency auditory and vestibular signals. In this paper, we propose a model for the AS in the form of an array of phase oscillators with long-range coupling, subject to a steady load that suppresses spontaneous oscillations. The array is exposed to significant levels of frequency dispersion and intrinsic noise. We show that such an array can be a sensitive and robust subthreshold detector of low-frequency stimuli, though without significant frequency selectivity. The effects of intrinsic noise and frequency dispersion are contrasted. Intermediate levels of intrinsic noise greatly enhance the sensitivity through stochastic resonance. Frequency dispersion, on the other hand, only degrades detection sensitivity. However, frequency dispersion can play a useful role in terms of the suppression of spontaneous activity. As a model for the AS, the array parameters are such that the system is poised near a saddle-node bifurcation on an invariant circle. However, by a change of array parameters, the same system also can be poised near an emergent Andronov-Hopf bifurcation and thereby function as a frequency-selective detector.

Pannexin's Role in Mediating Skeletal Muscle Active Hyperaemia

The dynamic metabolic rate of skeletal muscle coupled with the fact that discrete motor units can be recruited within a larger muscle bed necessitates a level of vascular control that allows blood flow to be directed to single muscle fibers. While the locus of blood flow regulation is undetermined, mounting evidence suggests capillaries (CAPS) may play a central role in blood flow coordination. This stems from CAPS close proximity to muscle fibres and, that CAPS can be stimulated by products of contraction to increase their own perfusion, via initiating a vasodilatory signal conducted upstream to its controlling arteriole. This cell‐cell communication is necessary to achieve the coordination needed to distribute blood flow to active skeletal muscle fibres. Gap junction dependent spread of hyperpolarization is prevalent in microvascular cell‐cell signaling, however the archetypal characteristics consistent with hyperpolarization are not always observed during conducted responses elicited by muscle contraction. This may suggest a 2nd pathway involved in conducted signaling. Pannexin (PANX) channels have been implicated in cell‐cell signaling in other tissues. PANX allow the cellular release of ATP into the interstitial space to activate purinergic receptors on neighboring cells. Activated receptors increase intracellular Ca2+ leading to PANX‐mediated ATP release and propagation of the signal to adjacent cells. We sought to determine if there was a role of PANX in CAP‐initiated condcuted responses. Using intravital microscopy of the hamster cremaster we stimulated CAPS with 1) vasoactive agents relevant to muscle contraction and 2) muscle contraction itself, while observing changes in diameter of the upstream arteriole associated with the stimulated CAP. 1) Micropipetting vasoactive agents; potassium chloride (KCl; 10 mM; n=7), adenosine (ADO, 10−4 M; n=9), pinacidil (10−5 M; n=8), SNAP (nitric oxide donor; 10−6 M; n=13), and acetylcholine (10−4 M; n=7) produced an upstream arteriolar dilation. However, when PANX blocker, mefloquine (MEF, 10−5 M) was applied between the CAP stimulation site and observation site, the conducted responses elicited by KCl and ADO were inhibited by 111% and 67% respectively, while having no effect on the conducted response of other dilators. 2) Conducted responses were elicited by contracting muscle fibres underlying CAPS for 2 min while altering contraction frequency (6, 15 &amp; 60 contractions per minute (CPM)) or stimulus frequency (4, 20 &amp; 40 Hz). While each contraction parameter produced an upstream arteriolar dilation, we found that, in the presence of MEF, conducted responses at low (6CPM, n=15) and intermediate (15CPM; n=15) contraction frequency were unaffected but at high (60CPM; n=15) vasodilation was blunted by 35%. Further, MEF blunted the conducted response at low (4 Hz; n=7) and intermediate (20 Hz; n=7) stimulus frequency by 88% and 73%, respectively but not at high (40 Hz; n=7). These data show CAPS elicit a conducted response involving PANX channel signaling, and that this signal is physiologically relevant during skeletal muscle contraction. Evidence of a 2nd pathway involved in mediating the conducted response begs the question of why 2 pathways exist when they seem to be mediating the same function.Support or Funding InformationNSERC Canada.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Effects of Social Experience on the Habituation Rate of Zebrafish Startle Escape Response: Empirical and Computational Analyses.

While the effects of social experience on nervous system function have been extensively investigated in both vertebrate and invertebrate systems, our understanding of how social status differentially affects learning remains limited. In the context of habituation, a well-characterized form of non-associative learning, we investigated how the learning processes differ between socially dominant and subordinate in zebrafish (Danio rerio). We found that social status and frequency of stimulus inputs influence the habituation rate of short latency C-start escape response that is initiated by the Mauthner neuron (M-cell). Socially dominant animals exhibited higher habituation rates compared to socially subordinate animals at a moderate stimulus frequency, but low stimulus frequency eliminated this difference of habituation rates between the two social phenotypes. Moreover, habituation rates of both dominants and subordinates were higher at a moderate stimulus frequency compared to those at a low stimulus frequency. We investigated a potential mechanism underlying these status-dependent differences by constructing a simplified neurocomputational model of the M-cell escape circuit. The computational study showed that the change in total net excitability of the model M-cell was able to replicate the experimental results. At moderate stimulus frequency, the model M-cell with lower total net excitability, that mimicked a dominant-like phenotype, exhibited higher habituation rates. On the other hand, the model with higher total net excitability, that mimicked the subordinate-like phenotype, exhibited lower habituation rates. The relationship between habituation rates and characteristics (frequency and amplitude) of the repeated stimulus were also investigated. We found that habituation rates are decreasing functions of amplitude and increasing functions of frequency while these rates depend on social status (higher for dominants and lower for subordinates). Our results show that social status affects habituative learning in zebrafish, which could be mediated by a summative neuromodulatory input to the M-cell escape circuit, which enables animals to readily learn to adapt to changes in their social environment.

Assessment of Cochlear Function during Cochlear Implantation by Extra- and Intracochlear Electrocochleography.

Objective: The aims of this study were: (1) To investigate the correlation between electrophysiological changes during cochlear implantation and postoperative hearing loss, and (2) to detect the time points that electrophysiological changes occur during cochlear implantation.Material and Methods: Extra- and intracochlear electrocochleography (ECoG) were used to detect electrophysiological changes during cochlear implantation. Extracochlear ECoG recordings were conducted through a needle electrode placed on the promontory; for intracochlear ECoG recordings, the most apical contact of the cochlear implant (CI) electrode itself was used as the recording electrode. Tone bursts at 250, 500, 750, and 1000 Hz were used as low-frequency acoustic stimuli and clicks as high-frequency acoustic stimuli. Changes of extracochlear ECoG recordings after full insertion of the CI electrode were correlated with pure-tone audiometric findings 4 weeks after surgery.Results: Changes in extracochlear ECoG recordings correlated with postoperative hearing change (r = −0.44, p = 0.055, n = 20). Mean hearing loss in subjects without decrease or loss of extracochlear ECoG signals was 12 dB, compared to a mean hearing loss of 22 dB in subjects with a detectable decrease or a loss of ECoG signals (p = 0.0058, n = 51). In extracochlear ECoG recordings, a mean increase of the ECoG signal of 4.4 dB occurred after opening the cochlea. If a decrease of ECoG signals occurred during insertion of the CI electrode, the decrease was detectable during the second half of the insertion.Conclusion: ECoG recordings allow detection of electrophysiological changes in the cochlea during cochlear implantation. Decrease of extracochlear ECoG recordings during surgery has a significant correlation with hearing loss 4 weeks after surgery. Trauma to cochlear structures seems to occur during the final phase of the CI electrode insertion. Baseline recordings for extracochlear ECoG recordings should be conducted after opening the cochlea. ECoG responses can be recorded from an intracochlear site using the CI electrode as recording electrode. This technique may prove useful for monitoring cochlear trauma intraoperatively in the future.

Functional Change in the Caudal Pontine Reticular Nucleus Induced by Age-Related Hearing Loss.

Increased acoustic startle responses (ASR), which represent reduced uncomfortable loudness level in humans, have been reported in middle-aged C57BL/6J mice with sensorineural hearing loss. Although neural plasticity changes in the central auditory system after the peripheral lesions were suggested to underlie this phenomenon, the neurological cause of exaggerated ASR is still not clear. In this study, the local field potentials and firing rates of the caudal pontine reticular nucleus (PnC), which plays a major role in the ASR pathway, were recorded in 2-month- and 6-month-old C57BL/6 J mice. Consistent with our previous studies, the amplitude of ASR increased, and the threshold of ASR decreased in the 6-month-old mice after developing 20–40 dB hearing loss. The PnC response induced by high-frequency stimuli (>20 kHz) decreased in the 6-month group, whereas the PnC response induced by low-frequency stimuli (<12 kHz) showed a significant increase in the 6-month group compared to the 2-month group. The enhancement of PnC response is similar to the ASR increase found in the 6-month-old C57 mice. Our results suggest that the high-frequency hearing loss caused an increase in PnC sensitivity in the C57 mice which may enhance ASRs.

Cardiac Arrest Induces Ischemic Long-Term Potentiation of Hippocampal CA1 Neurons That Occludes Physiological Long-Term Potentiation.

Ischemic long-term potentiation (iLTP) is a form of synaptic plasticity that occurs in acute brain slices following oxygen-glucose deprivation. In vitro, iLTP can occlude physiological LTP (pLTP) through saturation of plasticity mechanisms. We used our murine cardiac arrest and cardiopulmonary resuscitation (CA/CPR) model to produce global brain ischemia and assess whether iLTP is induced in vivo, contributing to the functionally relevant impairment of pLTP. Adult male mice were subjected to CA/CPR, and slice electrophysiology was performed in the hippocampal CA1 region 7 or 30 days later. We observed increased miniature excitatory postsynaptic current amplitudes, suggesting a potentiation of postsynaptic AMPA receptor function after CA/CPR. We also observed increased phosphorylated GluR1 in the postsynaptic density of hippocampi after CA/CPR. These data support the in vivo induction of ischemia-induced plasticity. Application of a low-frequency stimulus (LFS) to CA1 inputs reduced excitatory postsynaptic potentials in slices from mice subjected to CA/CPR, while having no effects in sham controls. These results are consistent with a reversal, or depotentiation, of iLTP. Further, depotentiation with LFS partially restored induction of pLTP with theta burst stimulation. These data provide evidence for iLTP following in vivo ischemia, which occludes pLTP and likely contributes to network disruptions that underlie memory impairments.

Further Characterization of the Predominant Inner Retinal Degeneration of Aging Cln3 Δex7/8 Knock-In Mice.

Neuronal ceroid lipofuscinosis (NCL) is the most common group of neurogenetic storage diseases typically beginning in childhood. The juvenile form (JNCL), also known as Batten disease, is the most common form. Vision-related problems are often an early sign, appearing prior to motor and mental deficits. We have previously investigated disease progression with age in the Cln3 Δex7/8 KI mouse model for JNCL and showed a decline of visual acuity and a predominant decline of the inner retinal function in mice, similar to human disease. The aim of this study was to further characterize this degeneration by means of flicker ERGs. For the scotopic flicker ERG, we found a significantly lower magnitude for Cln3 Δex7/8 KI mice already at 6months of age for low stimulus frequencies, while the difference declines with increasing frequency. Under photopic conditions there was no magnitude difference at 6months, but a cumulative magnitude reduction with further aging. For both conditions the phases were similar for both groups. There was a similar magnitude reduction for the responses of both the slow and fast rod pathway in the 15 Hz experiments, and there were no differences in response phase. Low-frequency flicker responses seem to be sensitive to very early disease manifestations, and while the degeneration is associated with a reduction of predominating inner retinal responses in the scotopic flash ERG, this predominance seems not to be related to a selective involvement of the slow and fast rod pathways.

Chirping and asymmetric jamming avoidance responses in the electric fish Distocyclus conirostris.

Electrosensory systems of weakly electric fish must accommodate competing demands of sensing the environment (electrolocation) and receiving social information (electrocommunication). The jamming avoidance response (JAR) is a behavioral strategy thought to reduce electrosensory interference from conspecific signals close in frequency. We used playback experiments to characterize electric organ discharge frequency (EODf), chirping behavior and the JAR of Distocyclus conirostris, a gregarious electric fish species. EODs of D. conirostris had low frequencies (∼80-200 Hz) that shifted in response to playback stimuli. Fish consistently lowered EODf in response to higher-frequency stimuli but inconsistently raised or lowered EODf in response to lower-frequency stimuli. This led to jamming avoidance or anti-jamming avoidance, respectively. We compare these behaviors with those of closely related electric fish (Eigenmannia and Sternopygus) and suggest that the JAR may have additional social functions and may not solely minimize the deleterious effects of jamming, as its name suggests.

An experimentally validated model for geometrically nonlinear plucking-based frequency up-conversion in energy harvesting

It is well known that plucking-based frequency up-conversion can enhance the power output in piezoelectric energy harvesting by enabling cyclic free vibration at the fundamental bending mode of the harvester even for very low excitation frequencies. In this work, we present a geometrically nonlinear plucking-based framework for frequency up-conversion in piezoelectric energy harvesting under quasistatic excitations associated with low-frequency stimuli such as walking and similar rigid body motions. Axial shortening of the plectrum is essential to enable plucking excitation, which requires a nonlinear framework relating the plectrum parameters (e.g. overlap length between the plectrum and harvester) to the overall electrical power output. Von Kármán-type geometrically nonlinear deformation of the flexible plectrum cantilever is employed to relate the overlap length between the flexible (nonlinear) plectrum and the stiff (linear) harvester to the transverse quasistatic tip displacement of the plectrum, and thereby the tip load on the linear harvester in each plucking cycle. By combining the nonlinear plectrum mechanics and linear harvester dynamics with two-way electromechanical coupling, the electrical power output is obtained directly in terms of the overlap length. Experimental case studies and validations are presented for various overlap lengths and a set of electrical load resistance values. Further analysis results are reported regarding the combined effects of plectrum thickness and overlap length on the plucking force and harvested power output. The experimentally validated nonlinear plectrum–linear harvester framework proposed herein can be employed to design and optimize frequency up-conversion by properly choosing the plectrum parameters (geometry, material, overlap length, etc) as well as the harvester parameters.

Mode transition in electrical activities of neuron driven by high and low frequency stimulus in the presence of electromagnetic induction and radiation

The Hindmarsh–Rose (HR) neuron model has been improved to investigate the complex electrophysiological and various physical phenomena at the level of single cell, for example, time-varying action potential can be induced by the exchange of ion currents and the fluctuation of ions concentration in the cell. When the magnetic flux is considered as a new variable associated to magnetic field, the improved HR neuron model can describe the effects of electromagnetic induction and radiation on membrane potential, where a memristor is used to bridge the membrane potential and the magnetic flux. In this paper, considering the magnetic flux driven, respectively, by the periodic high and low frequency electromagnetic radiation and the Gaussian white noise, the improved HR neuron model is employed to study the modes transition in electrical activities of neuron. The thought-provoking phenomena are detected and discussed by using bifurcation analysis on sampled time series of membrane potential. It is found that the electrical modes of HR neuron model under various parameters have different responses to the periodic high–low frequency electromagnetic radiation and the Gaussian white noise.