What We Can Learn from the Exported Cases in Detecting Disease Outbreaks - A Case Study of the COVID-19 Epidemic

Purpose

Early warning in the travel origins is crucial to prevent disease spreading. When travel origins have delays in reporting disease outbreaks, the exported cases could be used to estimate the epidemic.

Methods

We developed a Bayesian model to jointly estimate the epidemic prevalence and detection delay using the exported cases and their arrival and detection dates. We used simulation studies to discuss potential biases generated by the exported cases. We proposed a hypothesis testing framework to determine the epidemic severity.

Results

We applied the method to the early phase of the COVID-19 epidemic of Wuhan, United States, Italy, and Iran and found that the indicators estimated from the exported cases were consistent with the domestic data under certain scenarios. The exported cases could generate various biases if not modeled properly. We presented the required number of exported cases for determining different severity levels of the outbreak.

Conclusions

The exported case data is a good addition to the domestic data but also has its drawbacks. Utilizing the diagnosis resources from all countries, we advocate that countries work collaboratively to strengthen the global infectious disease surveillance system.

The Adaptive Olfactory Measure of Threshold (ArOMa-T): A rapid test of olfactory function

PURPOSE

Many widely-used psychophysical tests of olfaction have limitations that can create barriers to adoption outside research settings. For example, tests that measure the ability to identify odors may confound sensory performance with memory recall, verbal ability, and past experience with the odor. Conversely, threshold-based tests typically avoid these issues, but are labor intensive. Additionally, many commercially available olfactory tests are slow and may require a trained administrator, making them impractical for use in a short wellness visit or other broad clinical assessment.

METHODS

We tested the performance of the Adaptive Olfactory Measure of Threshold (ArOMa-T) -- a novel odor detection threshold test that employs an adaptive Bayesian algorithm paired with a disposable odor-delivery card -- in a non-clinical sample of individuals (n=534) at the 2021 Twins Day Festival in Twinsburg, OH.

RESULTS

Participants successfully completed the test in under 3 min with a false alarm rate of 9.6% and a test-retest reliability of 0.61. Odor detection thresholds differed by sex (~3.2-fold) and between the youngest and oldest age groups (~8.7-fold), consistent with prior work. In an exploratory analysis, we failed to observe evidence of detection threshold differences between participants who reported a history of COVID-19 and matched controls who did not. We also found evidence for broad-sense heritability of odor detection thresholds.

CONCLUSION

Together, these data indicate the ArOMa-T can determine odor detection thresholds. The ArOMa-T may be particularly valuable in clinical or field settings where rapid and portable assessment of olfactory function is needed.

The Adaptive Olfactory Measure of Threshold (ArOMa-T): a rapid test of olfactory function

Many widely used psychophysical olfactory tests have limitations that can create barriers to adoption. For example, tests that measure the ability to identify odors may confound sensory performance with memory recall, verbal ability, and prior experience with the odor. Conversely, classic threshold-based tests avoid these issues, but are labor intensive. Additionally, many commercially available tests are slow and may require a trained administrator, making them impractical for use in situations where time is at a premium or self-administration is required. We tested the performance of the Adaptive Olfactory Measure of Threshold (ArOMa-T)-a novel odor detection threshold test that employs an adaptive Bayesian algorithm paired with a disposable odorant delivery card-in a non-clinical sample of individuals (n = 534) at the 2021 Twins Day Festival in Twinsburg, OH. Participants successfully completed the test in under 3 min with a false alarm rate of 7.5% and a test-retest reliability of 0.61. Odor detection thresholds differed by sex (~3.2-fold lower for females) and age (~8.7-fold lower for the youngest versus the oldest age group), consistent with prior studies. In an exploratory analysis, we failed to observe evidence of detection threshold differences between participants who reported a history of COVID-19 and matched controls who did not. We also found evidence for broad-sense heritability of odor detection thresholds. Together, this study suggests the ArOMa-T can determine odor detection thresholds. Additional validation studies are needed to confirm the value of ArOMa-T in clinical or field settings where rapid and portable assessment of olfactory function is needed.

Methodological and Conceptual Progresses in Studies on the Latent Tracks in PADC

Modified structure along latent tracks and track formation process have been investigated in poly (allyl diglycol carbonate), PADC, which is well recognized as a sensitive etched track detector. This knowledge is essential to develop novel detectors with improved track registration property. The track structures of protons and heavy ions (He, C, Ne, Ar, Fe, Kr and Xe) have been examined by means of FT-IR spectrometry, covering the stopping power region between 1.2 to 12,000 eV/nm. Through a set of experiments on low-LET radiations—such as gamma ray-, multi-step damage process by electron hits was confirmed in the radiation-sensitive parts of the PADC repeat-unit. From this result, we unveiled for the first-time the layered structure in tracks, in relation with the number of secondary electrons. We also proved that the etch pit was formed when at least two repeat-units were destroyed along the track radial direction. To evaluate the number of secondary electrons around the tracks, a series of numerical simulations were performed with Geant4-DNA. Therefore, we are proposing new physical criterions to describe the detection thresholds. Furthermore, we propose a present issue of the definition of detection threshold for semi-relativistic C ions. Additionally, as a possible chemical criterion, formation density of hydroxyl group is suggested to express the response of PADC.

Older and Young Adults Experience Similar Long-Term Olfactory Habituation

Olfactory habituation corresponds to a decreased behavioral or perceptual response to an odor after a prolonged exposure to this odor. Our aim was to investigate whether long-term olfactory habituation and its recovery are similar in young (<35 years old) and older adults (>50). Fifty-seven participants were recruited for a 5-week longitudinal study. They were exposed to one of the two odors (manzanate alpha [MA], irone alpha [IA]) for 2 weeks at home. Olfactory detection thresholds for both odors were measured before and after exposure. Results showed that the two age groups behaved similarly. The long-term exposure to an odor led to a temporary increase of its detection threshold (lower sensitivity to the odor). IA thresholds were more sensitive to the duration of exposure with the odor than MA thresholds. One week after termination of exposure, participants fully recovered and even became more sensitive to both odors. No cross-habituation was found between the two odors. Our findings highlight that long-term habituation is specific to the odor exposed, behaves the same in young and older adults, and is fully reversible in both age groups after 1 week.

Reducing the Number of Mismatches between Hairs and Buccal References When Analysing mtDNA Heteroplasmic Variation by Massively Parallel Sequencing

In forensics, mitochondrial DNA (mtDNA) analysis is foremost applied to rootless hairs often lacking detectable nuclear DNA. Sanger sequencing is the routine mtDNA method in most forensic laboratories, even though interpretation of mixed samples and heteroplasmic sites can be challenging. Individuals may hold cells with low-level heteroplasmy variants below the detection threshold and other cells where this minor variant is the major one. This difference may be interpreted as a mismatch between reference and evidentiary trace samples, such as buccal specimens and rootless hairs. Such mismatches may be solved by Massively Parallel Sequencing (MPS), allowing more sensitive quantitative analysis for mixed positions than Sanger. The mtDNA control region was analysed in buccal reference samples from 26 individuals and 475 corresponding hairs by MPS and compared to Sanger sequencing data generated on the same samples. With MPS, mixed contributions down to 3% were regarded, leading to a substantial increase in the frequency of heteroplasmy. Our results demonstrate that previously reported mismatches between buccal reference and hair shaft samples by Sanger are detected as low-level heteroplasmy by MPS. A detailed overview of buccal and hair heteroplasmy is provided and implications for MPS-based mtDNA analysis in the context of forensic cases are discussed.

Prefrontal Responses to Odors in Individuals With Autism Spectrum Disorders: Functional NIRS Measurement Combined With a Fragrance Pulse Ejection System

Individuals with autism spectrum disorders (ASD) are impaired not only in social competencies but also in sensory perception, particularly olfaction. The olfactory ability of individuals with ASD has been examined in several psychophysical studies, but the results have been highly variable, which might be primarily due to methodological difficulties in the control of odor stimuli (e.g., the problem of lingering scents). In addition, the neural correlates of olfactory specificities in individuals with ASD remain largely unknown. To date, only one study has investigated this issue using functional magnetic resonance imaging (fMRI). The present study utilized a sophisticated method-a pulse ejection system-to present well-controlled odor stimuli to participants with ASD using an ASD-friendly application. With this advantageous system, we examined their odor detection, identification, and evaluation abilities and measured their brain activity evoked by odors using functional near-infrared spectroscopy (fNIRS). As the odor detection threshold (DT) of participants with ASD was highly variable, these participants were divided into two groups according to their DT: an ASD-Low DT group and an ASD-High DT group. Behavioral results showed that the ASD-High DT group had a significantly higher DT than the typically developing (control) group and the ASD-Low DT group, indicating their insensitivity to the tested odors. In addition, while there was no significant difference in the odor identification ability between groups, there was some discrepancy between the groups' evaluations of odor pleasantness. The brain data identified, for the first time, that neural activity in the right dorsolateral prefrontal cortex (DLPFC) was significantly weaker in the ASD-High DT group than in the control group. Moreover, the strength of activity in the right DLPFC was negatively correlated with the DT. These findings suggest that participants with ASD have impairments in the higher-order function of olfactory processing, such as olfactory working memory and/or attention.

Relationship between Sucrose Taste Detection Thresholds and Preferences in Children, Adolescents, and Adults

To address gaps in knowledge, our objectives were to (1) to determine whether there are age-related changes in sweet taste detection thresholds, as has been observed for sweet taste preferences, and (2) determine whether detection thresholds and taste preferences were significantly related to each other from childhood to adulthood. We combined data from studies that used the same validated psychophysical techniques to measure sucrose taste detection threshold and the most preferred sucrose concentration in children (n = 108), adolescents (n = 172), and adults (n = 205). There were significant effects of age group on both sucrose detection thresholds (p < 0.001) and most preferred sucrose concentration (p < 0.001). While children had higher sucrose detection thresholds than adolescents, who in turn tended to have higher detection thresholds than adults, both children and adolescent most preferred sucrose concentrations were higher than that of adults (all p < 0.05). Among each age group, and when combined, the lowest sucrose concentration detected was not significantly correlated with the most preferred sucrose concentration (all p > 0.18). These data provide further evidence that age-related changes in sucrose taste preferences that occur during adolescence cannot be explained by changes in taste sensitivity and that these two dimensions of sweet taste undergo distinct developmental trajectories from childhood to adulthood.

Establishing Meaningful Limits of Detection for Ion-Selective Electrodes and Other Nonlinear Sensors

Although IUPAC has recommended a probabilistic approach to determining limit of detection (LOD) based on false-positive and false-negative rates for more than 20 years, the LOD definition for ion-selective electrodes (ISEs) long predates these recommendations and conflicts substantively with them. Although it is well known that the ISE LOD definition does not follow best practice, it continues to be used due to simplicity and a lack of available methods for estimating LOD for nonlinear sensors. Here, we use ISEs as a model system for estimation of LOD for nonlinear sensors that is consistent with broad IUPAC recommendations and justified using statistical theory. Using freely available software, the new approach and updated definition is demonstrated through theory, simulation, and an environmental application. The results show that the current LOD definition for ISEs performs substantially worse than the proposed definition when assessed against IUPAC recommendations, including ignoring sensor noise and LOD uncertainty, leading to bias of an order of magnitude or more. Further, the environmental application shows that the new definition, which includes estimates of LOD uncertainty, allows more objective assessment of sensor response and fitness for purpose. The growing demand for ultrasensitive sensors that operate in complex matrices has pushed the boundaries of traditional calibration approaches. These sensors often operate near their limit of detection (LOD), with additional challenges created if their response is nonlinear. These challenges are amplified when assessing new sensors, since they may be less reproducible and noisier than benchmark techniques.

The Psychoacoustics of Profound Hearing Impairment

A group of profoundly hearing-impaired adults is being studied in order to determine their residual auditory capabilities. Most tests use acoustic contrasts that have relevance for the perception of speech, so that the results obtained may be used to guide the development of appropriate hearing aids. All the listeners are postlingually deafened, with losses >95 dB HL at and above 500 Hz, and least loss at low frequencies. Trends in detection thresholds, discomfort levels, dynamic ranges, intensity discrimination (both static and dynamic), frequency selectivity, spectral shape discrimination, gap detection, tone/noise discrimination, frequency discrimination and phase sensitivity are reported and discussed. Generally speaking, temporal resolving power seems to be more resistant to degradation than mechanisms of frequency selectivity. Furthermore, at least some of the differences in performance between normal and profoundly-impaired listeners may be attributable to the loss of frequency selectivity. Implications are drawn for hearing aid fitting and design, and comparisons made to the electro-auditory abilities of users of single-channel cochlear implants.

Target Tracking in Clutter with Extremum Seeking Control for Adaptive Detection Thresholding

If the signal strength obtained from sonar is higher than the predefined detection threshold, it is considered as a candidate for target tracking. This detection threshold is a parameter that affects the detection probability of targets and the distribution of clutter measurements, so it is important to determine a proper threshold to improve target tracking performance. There are various techniques for adjusting the detection threshold. To apply these techniques, it is assumed that the probability density functions of the signal strength for clutter are known in advance. However, in a real environment, the probability density function of the signal strength is unknown in general. In this paper, we propose a detection threshold control method using extremum seeking control in realistic environments. The extremum seeking control is a method used in complex nonlinear systems. We propose a new structure for extremum seeking control that is applicable to detection processes with nonlinear characteristics. This structure is used to adjust the detection threshold of the received signal amplitude to make the estimated clutter measurement density converge to a designed clutter measurement density to achieve the best target tracking performance in the current environment. Simulation studies for the proposed extremum seeking control applied to target tracking in an unknown clutter signal distribution demonstrate the effectiveness and improved target tracking performance.

Cause or prevention of breast cancer with estrogens: analysis from tumor biologic data, growth kinetic model and Women's Health Initiative study

The existing medical literature suggests that estrogens may cause breast cancer but, paradoxically, can also prevent this neoplasm under specific circumstances. Appropriate interpretation of this complex data requires an understanding of emerging concepts of tumor biology. A substantial body of data, including animal models and epidemiologic studies, suggests that estrogens contribute to the development of breast cancer. Additionally, pre-clinical experiments indicate that the responsible mechanisms include both estrogen receptor α-dependent and -independent effects (ERα-dependent and ERα-independent effects). We recently developed two models to describe the growth kinetics of occult breast tumors, one based on autopsy studies and tumor doubling time and the other, computer-based. Validation of the models involved comparison of the predicted incidence of breast cancer with the actual incidence in population-based studies. Utilization of these models allowed us to determine that 16 years on average are required for tumors to undergo the 30 doubling times necessary for the occult tumors to reach the threshold for clinical detection. These models suggest that menopausal hormone therapy with estrogen plus a progestogen in the Women's Health Initiative (WHI) study accelerated the doubling time of occult, pre-existing tumors from 200 to 150 days and thus, increased the rate of tumor diagnosis. Based on estrogen-induced apoptosis data, the model accurately predicted the prevention of diagnosed breast cancer in the estrogen-alone arm of the WHI. Notably, pre-clinical studies demonstrated that conjugated equine estrogen, as used in the WHI, has unique, pro-apoptotic properties compared to the anti-apoptotic effects of estradiol, a finding providing an explanation for the reduction in breast cancer with conjugated equine estrogen.

Sensitivity of Small RNA-Based Detection of Plant Viruses

Plants recognize unrelated viruses by the antiviral defense system called RNA interference (RNAi). RNAi processes double-stranded viral RNA into small RNAs (sRNAs) of 21–24 nucleotides, the reassembly of which into longer strands in silico allows virus identification by comparison with the sequences available in databases. The aim of this study was to compare the virus detection sensitivity of sRNA-based virus diagnosis with the established virus species-specific polymerase chain reaction (PCR) approach. Viruses propagated in tobacco plants included three engineered, infectious clones of Potato virus A (PVA), each carrying a different marker gene, and an infectious clone of Potato virus Y (PVY). Total RNA (containing sRNA) was isolated and subjected to reverse-transcription real-time PCR (RT-RT-PCR) and sRNA deep-sequencing at different concentrations. RNA extracted from various crop plants was included in the reactions to normalize RNA concentrations. Targeted detection of selected viruses showed a similar threshold for the sRNA and reverse-transcription quantitative PCR (RT-qPCR) analyses. The detection limit for PVY and PVA by RT-qPCR in this study was 3 and 1.5 fg of viral RNA, respectively, in 50 ng of total RNA per PCR reaction. When knowledge was available about the viruses likely present in the samples, sRNA-based virus detection was 10 times more sensitive than RT-RT-PCR. The advantage of sRNA analysis is the detection of all tested viruses without the need for virus-specific primers or probes.

Forward Masking in Cochlear Implant Users: Electrophysiological and Psychophysical Data Using Pulse Train Maskers

Electrical stimulation of auditory nerve fibers using cochlear implants (CI) shows psychophysical forward masking (pFM) up to several hundreds of milliseconds. By contrast, recovery of electrically evoked compound action potentials (eCAPs) from forward masking (eFM) was shown to be more rapid, with time constants no greater than a few milliseconds. These discrepancies suggested two main contributors to pFM: a rapid-recovery process due to refractory properties of the auditory nerve and a slow-recovery process arising from more central structures. In the present study, we investigate whether the use of different maskers between eCAP and psychophysical measures, specifically single-pulse versus pulse train maskers, may have been a source of confound.In experiment 1, we measured eFM using the following: a single-pulse masker, a 300-ms low-rate pulse train masker (LTM, 250 pps), and a 300-ms high-rate pulse train masker (HTM, 5000 pps). The maskers were presented either at same physical current (Φ) or at same perceptual (Ψ) level corresponding to comfortable loudness. Responses to a single-pulse probe were measured for masker-probe intervals ranging from 1 to 512 ms. Recovery from masking was much slower for pulse trains than for the single-pulse masker. When presented at Φ level, HTM produced more and longer-lasting masking than LTM. However, results were inconsistent when LTM and HTM were compared at Ψ level. In experiment 2, masked detection thresholds of single-pulse probes were measured using the same pulse train masker conditions. In line with our eFM findings, masked thresholds for HTM were higher than those for LTM at Φ level. However, the opposite result was found when the pulse trains were presented at Ψ level.Our results confirm the presence of slow-recovery phenomena at the level of the auditory nerve in CI users, as previously shown in animal studies. Inconsistencies between eFM and pFM results, despite using the same masking conditions, further underline the importance of comparing electrophysiological and psychophysical measures with identical stimulation paradigms.

Dependence of Nociceptive Detection Thresholds on Physiological Parameters and Capsaicin-Induced Neuroplasticity: A Computational Study

Physiological properties of peripheral and central nociceptive subsystems can be altered over time due to medical interventions. The effective change for the whole nociceptive system can be reflected in changes of psychophysical characteristics, e.g., detection thresholds. However, it is challenging to separate contributions of distinct altered mechanisms with measurements of thresholds only. Here, we aim to understand how these alterations affect Aδ-fiber-mediated nociceptive detection of electrocutaneous stimuli. First, with a neurophysiology-based model, we study the effects of single-model parameters on detection thresholds. Second, we derive an expression of model parameters determining the functional relationship between detection thresholds and the interpulse interval for double-pulse stimuli. Third, in a case study with topical capsaicin treatment, we translate neuroplasticity into plausible changes of model parameters. Model simulations qualitatively agree with changes in experimental detection thresholds. The simulations with individual forms of neuroplasticity confirm that nerve degeneration is the dominant mechanism for capsaicin-induced increases in detection thresholds. In addition, our study suggests that capsaicin-induced central plasticity may last at least 1 month.

Effects of Matrix Composition on Detection Threshold Estimates for Methyl Anthranilate and 2-Aminoacetophenone

Conceptually, a detection threshold represents the lowest concentration at which an individual or a group of individuals can reliably perceive a given stimulus, with a commonly used operational definition of 50% performance above chance. Estimated detection thresholds (DTs), however, are often reported in the literature with little attention given to the matrix in which the stimuli were evaluated. Here, we highlight the influence of matrix effects on DTs for two odor-active compounds commonly found in Vitis Labrusca wines. Differences in orthonasal DTs for methyl anthranilate (MA) and 2-aminoacetophenone (2AAP) in water, a model wine system, and wine were demonstrated using a within-subject design and forced choice (i.e., criterion free) psychophysical methods. Six sample triads, each containing two blanks and one spiked sample, were presented to participants with the instructions to choose the “different” sample, and this was repeated in different matrices (water, model wine, and wine). The estimated DTs for both compounds were significantly lower in water versus the model wine system and wine. This finding recapitulates the strong need to carefully consider the nature of the delivery matrix when determining and comparing threshold estimates across studies. Additionally, data from prior reports have suggested DTs for MA and 2AAP may differ by two orders of magnitude in spite of their structural similarity. We failed to confirm this difference here: although 2AAP thresholds were somewhat lower than MA thresholds, differences were much smaller than what had been suggested previously. This, again, emphasizes the need to make comparisons within the same individuals, using appropriate methods with sufficient numbers of participants.

Metabolic and Sensory Influences on Odor Sensitivity in Humans

Our olfactory sense plays an important role in eating behavior by modulating our food preferences and intake. However, hunger or satiety may also influence how we perceive odors. Albeit speculative, contradictory results found in the past may have resulted from confounding by type of meal that participants ate to induce satiety. We aimed to investigate the influence of hunger state on olfactory sensitivity, comparing hunger to satiety using 2 different types of lunch to control for sensory-specific satiety. Odor detection thresholds were measured in 2 groups of participants (39 per group, 18-40 years), under 3 conditions: when hungry (twice), after a sweet lunch, and after a savory lunch. One group had their detection thresholds tested for a sweet odor, whereas in the other group, sensitivity to a savory odor was measured. Differences in olfactory sensitivity conditions were analyzed using linear mixed models. Participants had higher scores on the odor sensitivity task in a hungry versus satiated state (P = 0.001). Within the satiated condition, there was no effect of type of lunch on odor sensitivity. In conclusion, hunger slightly enhances sensitivity to food odors, but did not significantly depend on the type of food participants ate, suggesting no clear influence of sensory-specific satiety.

Sweet taste sensitivity in pre-diabetics, diabetics and normoglycemic controls: a comparative cross sectional study

BACKGROUND

Increasing prevalence of pre-diabetes is an emerging public health problem. Decrease in sweet taste sensitivity which can lead to an increase in sugar intake might be a factor driving them to overt diabetes. The aim of the present study was to assess the sweet taste sensitivity in pre-diabetics in comparison with diabetics and with normoglycemic controls.

METHODS

Forty pre-diabetics, 40 diabetics and 34 normoglycemic controls were studied. The three groups were matched for age, sex and BMI. The division into groups was based on their glycated hemoglobin levels. The detection and recognition thresholds were determined by the multiple forced-choice method using sucrose solutions prepared in ¼ log dilutions. The intensities of perceived sensations for a series of suprathreshold concentrations of sucrose solutions prepared in ½ log dilution were determined by rating on a visual analogue scale. Statistical analyses were performed by SPSS version 21.

RESULTS

The mean (SD) detection thresholds of diabetic, pre-diabetic and normoglycemic groups were 0.025 (0.01), 0.018 (0.01) and 0.015 (0.01) respectively with a significant increase in diabetic group compared to normoglycemic group (p = 0.03). The mean recognition thresholds were not different among the three groups. When the intensity ratings for suprathreshold concentrations of sucrose were compared between the three groups, for all suprathreshold concentrations tested, significant differences were observed across the four concentrations (p < 0.001) and between groups in suprathreshold ratings (p < 0.05). Further analysis showed that the diabetic group had significantly lower suprathreshold ratings than the normoglycemic group (p < 0.001). Although all mean suprathreshold intensity ratings of the pre-diabetic group were between the normoglycemic and diabetic groups, the differences were not significant.

CONCLUSIONS

This is the first study to demonstrate the sweet taste sensitivity in pre-diabetics. The findings of the present study do not support the hypothesis of decreased sweet taste sensitivity of pre-diabetics. However, the results confirm the previous findings of blunted taste response in diabetics. The observation of pre-diabetics having intermediate values for all taste thresholds and suprathreshold ratings warrants a future investigation with a larger pre-diabetic sample recruited with more specific screening criteria to test this hypothesis further.

Behaviorally gated reduction of spontaneous discharge can improve detection thresholds in auditory cortex

Animals often listen selectively for particular sounds, a strategy that could alter neural encoding mechanisms to maximize the ability to detect the target. Here, we recorded auditory cortex neuron responses in well trained, freely moving gerbils as they performed a tone detection task. Each trial was initiated by the animal, providing a predictable time window during which to listen. No sound was presented on nogo trials, permitting us to assess spontaneous activity on trials in which a signal could have been expected, but was not delivered. Immediately after animals initiated a trial, auditory cortex neurons displayed a 26% reduction in spontaneous activity. Moreover, when stimulus-driven discharge rate was referenced to this reduced baseline, a larger fraction of auditory cortex neurons displayed a detection threshold within 10 dB of the behavioral threshold. These findings suggest that auditory cortex spontaneous discharge rate can be modulated transiently during task performance, thereby increasing the signal-to-noise ratio and enhancing signal detection.

Simultaneous stability and sensitivity in model cortical networks is achieved through anti-correlations between the in- and out-degree of connectivity

Neuronal networks in rodent barrel cortex are characterized by stable low baseline firing rates. However, they are sensitive to the action potentials of single neurons as suggested by recent single-cell stimulation experiments that reported quantifiable behavioral responses in response to short spike trains elicited in single neurons. Hence, these networks are stable against internally generated fluctuations in firing rate but at the same time remain sensitive to similarly-sized externally induced perturbations. We investigated stability and sensitivity in a simple recurrent network of stochastic binary neurons and determined numerically the effects of correlation between the number of afferent (“in-degree”) and efferent (“out-degree”) connections in neurons. The key advance reported in this work is that anti-correlation between in-/out-degree distributions increased the stability of the network in comparison to networks with no correlation or positive correlations, while being able to achieve the same level of sensitivity. The experimental characterization of degree distributions is difficult because all pre-synaptic and post-synaptic neurons have to be identified and counted. We explored whether the statistics of network motifs, which requires the characterization of connections between small subsets of neurons, could be used to detect evidence for degree anti-correlations. We find that the sample frequency of the 3-neuron “ring” motif (1→2→3→1), can be used to detect degree anti-correlation for sub-networks of size 30 using about 50 samples, which is of significance because the necessary measurements are achievable experimentally in the near future. Taken together, we hypothesize that barrel cortex networks exhibit degree anti-correlations and specific network motif statistics.

Detection of Near-Threshold Sounds is Independent of EEG Phase in Common Frequency Bands

Low-frequency oscillations in the electroencephalogram (EEG) are thought to reflect periodic excitability changes of large neural networks. Consistent with this notion, detection probability of near-threshold somatosensory, visual, and auditory targets has been reported to co-vary with the phase of oscillations in the EEG. In audition, entrainment of δ-oscillations to the periodic occurrence of sounds has been suggested to function as a mechanism of attentional selection. Here, we examine in humans whether the detection of brief near-threshold sounds in quiet depends on the phase of EEG oscillations. When stimuli were presented at irregular intervals, we did not find a systematic relationship between detection probability and phase. When stimuli were presented at regular intervals (2-s), reaction times were significantly shorter and we observed phase entrainment of EEG oscillations corresponding to the frequency of stimulus presentation (0.5 Hz), revealing an adjustment of the system to the regular stimulation. The amplitude of the entrained oscillation was higher for hits than for misses, suggesting a link between entrainment and stimulus detection. However, detection was independent of phase at frequencies ≥1 Hz. Furthermore, we show that when the data are analyzed using acausal, though common, algorithms, an apparent "entrainment" of the δ-phase to presented stimuli emerges and detection probability appears to depend on δ-phase, similar to reports in the literature. We show that these effects are artifacts from phase distortion at stimulus onset by contamination with the event-related potential, which differs markedly for hits and misses. This highlights the need to carefully deal with this common problem, since otherwise it might bias and mislead this exciting field of research.

To pool or not to pool, from whether to when: applications of pooling to biospecimens subject to a limit of detection

Pooling of biological specimens has been utilised as a cost-efficient sampling strategy, but cost is not the unique limiting factor in biomarker development and evaluation. We examine the effect of different sampling strategies of biospecimens for exposure assessment that cannot be detected below a detection threshold (DT). The paper compares use of pooled samples to a randomly selected sample from a cohort in order to evaluate the efficiency of parameter estimates. The proposed approach shows that a pooling design is more efficient than a random sample strategy under certain circumstances. Moreover, because pooling minimises the amount of information lost below the DT, the use of pooled data is preferable (in a context of a parametric estimation) to using all available individual measurements, for certain values of the DT. We propose a combined design, which applies pooled and unpooled biospecimens, in order to capture the strengths of the different sampling strategies and overcome instrument limitations (i.e. DT). Several Monte Carlo simulations and an example based on actual biomarker data illustrate the results of the article.

Psychophysical assessment of stimulation sites in auditory prosthesis electrode arrays

Auditory prostheses use implanted electrode arrays that permit stimulation at many sites along the tonotopic axis of auditory neurons. Psychophysical studies demonstrate that measures of implant function, such as detection and discrimination thresholds, vary considerably across these sites, that the across-site patterns of these measures differ across subjects, and that the likely mechanisms underlying this variability differ across measures. Psychophysical and speech recognition studies suggest that not all stimulation sites contribute equally to perception with the prosthesis and that some sites might have negative effects on perception. Studies that reduce the number of active stimulation sites indicate that most cochlear implant users can effectively utilize a maximum of only about seven sites in their processors. These findings support a strategy for improving implant performance by selecting only the best stimulation sites for the processor map. Another approach is to revise stimulation parameters for ineffective sites in an effort to improve acuity at those sites. In this paper, we discuss data supporting these approaches and some potential pitfalls.

Neural variability, detection thresholds, and information transmission in the vestibular system

A fundamental issue in neural coding is the role of spike timing variation in information transmission of sensory stimuli. Vestibular afferents are particularly well suited to study this issue because they are classified as either regular or irregular based on resting discharge variability as well as morphology. Here, we compared the responses of each afferent class to sinusoidal and random head rotations using both information theoretic and gain measures. Information theoretic measures demonstrated that regular afferents transmitted, on average, two times more information than irregular afferents, despite having significantly lower gains. Moreover, consistent with information theoretic measures, regular afferents had angular velocity detection thresholds that were 50% lower than those of irregular afferents (approximately 4 vs 8 degrees/s). Finally, to quantify the information carried by spike times, we added spike-timing jitter to the spike trains of both regular and irregular afferents. Our results showed that this significantly reduced information transmitted by regular afferents whereas it had little effect on irregular afferents. Thus, information is carried in the spike times of regular but not irregular afferents. Using a simple leaky integrate and fire model with a dynamic threshold, we show that differential levels of intrinsic noise can explain differences in the resting discharge, the responses to sensory stimuli, as well as the information carried by action potential timings of each afferent class. Our experimental and modeling results provide new insights as to how neural variability influences the strategy used by two different classes of sensory neurons to encode behaviorally relevant stimuli.