A robust sound perception model suitable for neuromorphic implementation

Coath M, Sheik S, Chicca E, Indiveri G, Denham S, Wennekers T. A robust sound perception model suitable for neuromorphic implementation. Neuromorphic Engineering. 2014;7(278):1-10.We have recently demonstrated the emergence of dynamic feature sensitivity through exposure to formative stimuli in a real-time neuromorphic system implementing a hybrid analog/digital network of spiking neurons. This network, inspired by models of auditory processing in mammals, includes several mutually connected layers with distance-dependent transmission delays and learning in the form of spike timing dependent plasticity, which effects stimulus-driven changes in the network connectivity. Here we present results that demonstrate that the network is robust to a range of variations in the stimulus pattern, such as are found in naturalistic stimuli and neural responses. This robustness is a property critical to the development of realistic, electronic neuromorphic systems. We analyze the variability of the response of the network to “noisy” stimuli which allows us to characterize the acuity in information-theoretic terms. This provides an objective basis for the quantitative comparison of networks, their connectivity patterns, and learning strategies, which can inform future design decisions. We also show, using stimuli derived from speech samples, that the principles are robust to other challenges, such as variable presentation rate, that would have to be met by systems deployed in the real world. Finally we demonstrate the potential applicability of the approach to real sounds

Strontium concentration, radiogenic (⁸⁷Sr/86Sr) and stable (<i>δ</i>⁸⁸Sr) strontium isotope systematics in a controlled feeding study.

Transhumance and palaeodiet are two central themes in archaeology and using chemical analysis of bones and teeth to reconstruct trends and patterns in diet and mobility has become a cornerstone of bioarchaeology. This study has investigated strontium concentration ([Sr]), radiogenic (87Sr/86Sr) and stable strontium (δ88Sr) isotope systematics in a controlled feeding experiment on domestic pigs designed to simulate terrestrial versus marine protein consumption. The results of the radiogenic (87Sr/86Sr) analysis offer a validation of the strontium isotope methodology. The study confirms that the radiogenic strontium isotope composition of dental enamel does represent the radiogenic strontium isotope composition of the diet. The results of the δ88Sr analysis have revealed a distinct shift of 0.322 ± 0.060 ‰ towards isotopically light Sr with trophic level. The magnitude of this shift is consistent with the predictions from the analogous shift observed in calcium isotopes. This is the first time that trophic level fractionation in δ88Sr has been identified in a controlled setting. Although still in its infancy, δ88Sr analysis has great potential to inform on trophic level systematics, to investigate dietary trends in early life and is potentially useful in examining diagenetic alteration

Strontium concentration, radiogenic (⁸⁷Sr/86Sr) and stable (<i>δ</i>⁸⁸Sr) strontium isotope systematics in a controlled feeding study.

Transhumance and palaeodiet are two central themes in archaeology and using chemical analysis of bones and teeth to reconstruct trends and patterns in diet and mobility has become a cornerstone of bioarchaeology. This study has investigated strontium concentration ([Sr]), radiogenic (87Sr/86Sr) and stable strontium (δ88Sr) isotope systematics in a controlled feeding experiment on domestic pigs designed to simulate terrestrial versus marine protein consumption. The results of the radiogenic (87Sr/86Sr) analysis offer a validation of the strontium isotope methodology. The study confirms that the radiogenic strontium isotope composition of dental enamel does represent the radiogenic strontium isotope composition of the diet. The results of the δ88Sr analysis have revealed a distinct shift of 0.322 ± 0.060 ‰ towards isotopically light Sr with trophic level. The magnitude of this shift is consistent with the predictions from the analogous shift observed in calcium isotopes. This is the first time that trophic level fractionation in δ88Sr has been identified in a controlled setting. Although still in its infancy, δ88Sr analysis has great potential to inform on trophic level systematics, to investigate dietary trends in early life and is potentially useful in examining diagenetic alteration

Evaluation of novel data-driven metrics of amyloid β deposition for longitudinal PET studies

PURPOSE: Positron emission tomography (PET) provides in vivo quantification of amyloid-β (Aβ) pathology. Established methods for assessing Aβ burden can be affected by physiological and technical factors. Novel, data-driven metrics have been developed to account for these sources of variability. We aimed to evaluate the performance of four data-driven amyloid PET metrics against conventional techniques, using a common set of criteria. METHODS: Three cohorts were used for evaluation: Insight 46 (N=464, [18F]florbetapir), AIBL (N=277, [18F]flutemetamol), and an independent test-retest data (N=10, [18F]flutemetamol). Established metrics of amyloid tracer uptake included the Centiloid (CL) and where dynamic data was available, the non-displaceable binding potential (BPND). The four data driven metrics computed were the amyloid load (Aβ load), the Aβ PET pathology accumulation index (Aβ index), the Centiloid derived from non-negative matrix factorisation (CLNMF), and the amyloid pattern similarity score (AMPSS). These metrics were evaluated using reliability and repeatability in test-retest data, associations with BPND and CL, and sample size estimates to detect a 25% slowing in Aβ accumulation. RESULTS: All metrics showed good reliability. Aβ load, Aβ index and CLNMF were strong associated with the BPND. The associations with CL suggests that cross-sectional measures of CLNMF, Aβ index and Aβ load are robust across studies. Sample size estimates for secondary prevention trial scenarios were the lowest for CLNMF and Aβ load compared to the CL. CONCLUSION: Among the novel data-driven metrics evaluated, the Aβ load, the Aβ index and the CLNMF can provide comparable performance to more established quantification methods of Aβ PET tracer uptake. The CLNMF and Aβ load could offer a more precise alternative to CL, although further studies in larger cohorts should be conducted

Automated quantitative MRI volumetry reports support diagnostic interpretation in dementia: a multi-rater, clinical accuracy study

Objectives: We examined whether providing a quantitative report (QReport) of regional brain volumes improves radiologists’ accuracy and confidence in detecting volume loss, and in differentiating Alzheimer’s disease (AD) and frontotemporal dementia (FTD), compared with visual assessment alone. Methods: Our forced-choice multi-rater clinical accuracy study used MRI from 16 AD patients, 14 FTD patients, and 15 healthy controls; age range 52–81. Our QReport was presented to raters with regional grey matter volumes plotted as percentiles against data from a normative population (n = 461). Nine raters with varying radiological experience (3 each: consultants, registrars, ‘non-clinical image analysts’) assessed each case twice (with and without the QReport). Raters were blinded to clinical and demographic information; they classified scans as ‘normal’ or ‘abnormal’ and if ‘abnormal’ as ‘AD’ or ‘FTD’. Results: The QReport improved sensitivity for detecting volume loss and AD across all raters combined (p = 0.015* and p = 0.002*, respectively). Only the consultant group’s accuracy increased significantly when using the QReport (p = 0.02*). Overall, raters’ agreement (Cohen’s κ) with the ‘gold standard’ was not significantly affected by the QReport; only the consultant group improved significantly (κs 0.41➔0.55, p = 0.04*). Cronbach’s alpha for interrater agreement improved from 0.886 to 0.925, corresponding to an improvement from ‘good’ to ‘excellent’. Conclusion: Our QReport referencing single-subject results to normative data alongside visual assessment improved sensitivity, accuracy, and interrater agreement for detecting volume loss. The QReport was most effective in the consultants, suggesting that experience is needed to fully benefit from the additional information provided by quantitative analyses. Key Points: • The use of quantitative report alongside routine visual MRI assessment improves sensitivity and accuracy for detecting volume loss and AD vs visual assessment alone. • Consultant neuroradiologists’ assessment accuracy and agreement (kappa scores) significantly improved with the use of quantitative atrophy reports. • First multi-rater radiological clinical evaluation of visual quantitative MRI atrophy report for use as a diagnostic aid in dementia

In situ ion microprobe ²⁰⁷Pb/²⁰⁶Pb dating of monazite from Precambrian metamorphic suites, Tobacco Root Mountains, Montana

The Precambrian rocks of the Tobacco Root Mountains have been separated into three suites: the Indian Creek Metamorphic Suite, the Pony-Middle Mountain Metamorphic Suite, and the Spuhler Peak Metamorphic Suite. The Indian Creek and Pony-Middle Mountain Metamorphic Suites are quartzofeldspathic gneiss suites that contain variable amounts of metasupracrustal rocks. The Spuhler Peak Metamorphic Suite contains primarily mafic rocks and is possibly ocean crust. Metamorphosed mafic dikes and sills that intruded the Indian Creek and Pony-Middle Mountain Meta morphic Suites, but not the Spuhler Peak Metamorphic Suite, indicate juxtaposition of the Spuhler Peak Metamorphic Suite with the other two suites after intrusion of the dikes at ca. 2060 Ma. All rocks have been deformed and metamorphosed together, initially at pressures greater than 1.0 GPa and temperatures greater than 750 °C, followed by differential reequilibration at ∼0.6 GPa on a clockwise pressure-temperature path. Two-hundred-seventy-two 207Pb/206Pb spot ages of monazite grains from seventeen Spuhler Peak Metamorphic Suite, five Pony-Middle Mountain Metamorphic Suite, and eight Indian Creek Metamorphic Suite rocks have been obtained from the University of California at Los Angeles ion microprobe. Based on the distribution of the ages, the samples can be divided into three groups. (1) All seventeen Spuhler Peak Metamorphic Suite, one Pony-Middle Mountain Metamorphic Suite, and two Indian Creek Metamorphic Suite samples have relatively homogeneous spot age populations that vary from ca. 1720 to ca. 1780 Ma. (2) A group of seven Indian Creek and Pony-Middle Mountain Metamorphic Suite samples has spot ages from monazite grains that form an array near 2450 Ma. (3) A group of four Indian Creek and Pony-Middle Mountain Metamorphic Suite samples are bimodal in that they contain spot ages from both the 1720-1780 Ma group and the 2450 Ma array. There are younger and a few older spot ages in these samples that likely represent mixed age domains, the former between the 1720-1780 Ma and the 2450 Ma age domains and the latter between older detrital grain cores and the 2450 Ma array. Monazite grains in the matrix have similar ages to those that occur as inclusions in garnet and kyanite. Thus, the monazite in these rocks, as well as the peak metamorphic minerals, either grew or re-equilibrated during the higher-pressure (>1.0 GPa) metamorphism. The near absence of 207Pb/206Pb ages older than 1780 Ma in the Spuhler Peak Metamorphic Suite and the common occurrence of older ages in monazite from the Indian Creek and Pony-Middle Mountain Metamorphic Suites are consistent with assembly of the Tobacco Root terrane during a prolonged (60 m.y. long) collision event, the Big Sky orogeny, beginning at ca. 1780 Ma and culminating at ca. 1720 Ma. The Early Proterozoic Big Sky orogeny significantly overprinted the effects of an earlier ca. 2450 Ma orogeny in both the Pony-Middle Mountain and Indian Creek Metamorphic Suites. This older event modified pre-existing Archean rocks. However, of the 272 spot ages on monazite grains reported here, only six are significantly older than 2450 Ma and only one of these is older than 2600 Ma - a 2988 Ma spot age from a monazite inclusion in a garnet from a Pony-Middle Mountain Metamorphic Suite sample. There is no evidence of widespread Archean events recorded in the monazite grains of the Tobacco Root Mountains. © 2004 Geological Society of America.Link_to_subscribed_fulltex