2,858 research outputs found
The effect of neural adaptation of population coding accuracy
Most neurons in the primary visual cortex initially respond vigorously when a
preferred stimulus is presented, but adapt as stimulation continues. The
functional consequences of adaptation are unclear. Typically a reduction of
firing rate would reduce single neuron accuracy as less spikes are available
for decoding, but it has been suggested that on the population level,
adaptation increases coding accuracy. This question requires careful analysis
as adaptation not only changes the firing rates of neurons, but also the neural
variability and correlations between neurons, which affect coding accuracy as
well. We calculate the coding accuracy using a computational model that
implements two forms of adaptation: spike frequency adaptation and synaptic
adaptation in the form of short-term synaptic plasticity. We find that the net
effect of adaptation is subtle and heterogeneous. Depending on adaptation
mechanism and test stimulus, adaptation can either increase or decrease coding
accuracy. We discuss the neurophysiological and psychophysical implications of
the findings and relate it to published experimental data.Comment: 35 pages, 8 figure
Event-driven simulations of a plastic, spiking neural network
We consider a fully-connected network of leaky integrate-and-fire neurons
with spike-timing-dependent plasticity. The plasticity is controlled by a
parameter representing the expected weight of a synapse between neurons that
are firing randomly with the same mean frequency. For low values of the
plasticity parameter, the activities of the system are dominated by noise,
while large values of the plasticity parameter lead to self-sustaining activity
in the network. We perform event-driven simulations on finite-size networks
with up to 128 neurons to find the stationary synaptic weight conformations for
different values of the plasticity parameter. In both the low and high activity
regimes, the synaptic weights are narrowly distributed around the plasticity
parameter value consistent with the predictions of mean-field theory. However,
the distribution broadens in the transition region between the two regimes,
representing emergent network structures. Using a pseudophysical approach for
visualization, we show that the emergent structures are of "path" or "hub"
type, observed at different values of the plasticity parameter in the
transition region.Comment: 9 pages, 6 figure
Voice and speech outcomes of chemoradiation for advanced head and neck cancer: a systematic review
Purpose of this review is to systematically assess the effects on voice and speech of advanced head and neck cancer and its treatment by means of chemoradiotherapy (CRT). The databases Medline, Embase and Cochrane were searched (1991–2009) for terms head and neck cancer, chemoradiation, voice and speech rehabilitation. Twenty articles met the inclusion criteria, whereof 14 reported on voice outcomes and 10 on speech. Within the selected 20 studies, 18 different tools were used for speech or voice evaluation. Most studies assessed their data by means of patient questionnaires. Four studies presented outcome measures in more than one dimension. Most studies summarised the outcomes of posttreatment data that were assessed at various points in time after treatment. Except for four studies, pre-treatment measurements were lacking. This and the fact that most studies combined the outcomes of patients with radiated laryngeal cancers with outcome data of non-laryngeal cancer patients impedes an interpretation in terms of the effects of radiation versus the effects of the disease itself on voice or speech. Overall, the studies indicated that voice and speech degenerated during CRT, improved again 1–2 months after treatment and exceeded pre-treatment levels after 1 year or longer. However, voice and speech measures do not show normal values before or after treatment. Given the large-ranged posttreatment data, missing baseline assessment and the lacking separation of tumour/radiation sites, there is an urgent need for structured standardised multi-dimensional speech and voice assessment protocols in patients with advanced head and neck cancer treated with CRT
Deviations from the Gaussian distribution of mesoscopic conductance fluctuations
The conductance distribution of metallic mesoscopic systems is considered.
The variance of this distribution describes the universal conductance
fluctuations, yielding a Gaussian distribution of the conductance. We calculate
diagrammatically the third cumulant of this distribution, the leading deviation
from the Gaussian. We confirm random matrix theory calculations that the
leading contribution in quasi-one dimension vanishes. However, in quasi two
dimensions the third cumulant is negative, whereas in three dimensions it is
positive.Comment: 9 pages, Revtex, with eps figures,to appear in Phys Rev
Collimation and asymmetry of the hot blast wave from the recurrent nova V745 Scorpii
The recurrent symbiotic nova V745 Sco exploded on 2014 February 6 and was
observed on February 22 and 23 by the Chandra X-ray Observatory Transmission
Grating Spectrometers. By that time the supersoft source phase had already
ended and Chandra spectra are consistent with emission from a hot, shock-heated
circumstellar medium with temperatures exceeding 10^7K. X-ray line profiles are
more sharply peaked than expected for a spherically-symmetric blast wave, with
a full width at zero intensity of approximately 2400 km/s, a full width at half
maximum of 1200 +/- 30 km/s and an average net blueshift of 165 +/- 10 km/s.
The red wings of lines are increasingly absorbed toward longer wavelengths by
material within the remnant. We conclude that the blast wave was sculpted by an
aspherical circumstellar medium in which an equatorial density enhancement
plays a role, as in earlier symbiotic nova explosions. Expansion of the
dominant X-ray emitting material is aligned close to the plane of the sky and
most consistent with an orbit seen close to face-on. Comparison of an
analytical blast wave model with the X-ray spectra, Swift observations and
near-infrared line widths indicates the explosion energy was approximately
10^43 erg, and confirms an ejected mass of approximately 10^-7 Msun. The total
mass lost is an order of magnitude lower than the accreted mass required to
have initiated the explosion, indicating the white dwarf is gaining mass and is
a supernova Type 1a progenitor candidate.Comment: To appear in the Astrophysical Journa
The influence of a PHI-5-loaded silicone membrane, on cutaneous wound healing in vivo
This study investigated whether a novel ionogenic substance, containing amongst others zinc and rubidium (PHI-5; Dermagenics Inc, Memphis, TN, USA), could improve the healing of full-thickness skin wounds. Uniform wounds were created on the right flank of guinea pigs. Micro-grooved silicone rubber membranes, containing 0 (controls), 1.25, 5.00, or 10.00 μg PHI-5, were sutured onto this wound. Standardized digital wound photographs were made after 1, 3, and 6 weeks. Also, wound biopsies were taken after 3 and 6 weeks for histological and histomorphometrical evaluation. For all study groups, 6 animals were used. Analysis of the 1-week digital photographs showed that the surface area of the wounds decreased significantly, with an increasing PHI-5 concentration. No other differences were found in the wound photographs. Also, no differences were measured in histomorphometry at 3 and 6 weeks. Concluding, in our study model a single application of PHI-5 did have a significant positive influence on initial wound healing
Clinical Characteristics of Cutaneous Melanoma and Second Primary Malignancies in a Dutch Hospital-Based Cohort of Cutaneous Melanoma Patients
The increasing number of living cutaneous melanoma patients and the increased risk of developing a second primary tumour incited us to analyse the clinical characteristics of cutaneous melanoma and define the frequency, site, and type of second primary cancers in cutaneous melanoma patients. We collected data on patients who visited the Department of Dermatology at the Radboud University Nijmegen Medical Centre and were newly diagnosed with cutaneous melanoma or metastasis of melanoma with unknown primary localization between 2002 and 2006. A total of 194 cases were included; eleven patients developed a subsequent melanoma, 24 had at least one basal cell carcinoma, three had at least one squamous cell carcinoma, and 21 patients had a second non-cutaneous primary malignancy. In conclusion, 48 patients developed a subsequent malignancy. As nonmelanoma skin cancer is the most frequent second malignancy, our results subscribe to the necessity of follow-up by a dermatologist
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