An improved method for the estimation of firing rate dynamics using an optimal digital filter

In most neural systems, neurons communicate by means of sequences of action potentials or 'spikes'. Information encoded by spike trains is often quantified in terms of the firing rate which emphasizes the frequency of occurrence of action potentials rather than their exact timing. Common methods for estimating firing rates include the rate histogram, the reciprocal interspike interval, and the spike density function. In this study, we demonstrate the limitations of these aforementioned techniques and propose a simple yet more robust alternative. By convolving the spike train with an optimally designed Kaiser window, we show that more robust estimates of firing rate are obtained for both low and high-frequency inputs. We illustrate our approach by considering spike trains generated by simulated as well as experimental data obtained from single-unit recordings of first-order sensory neurons in the vestibular system. Improvements were seen in the prevention of aliasing, phase and amplitude distortion, as well as in the noise reduction for sinusoidal and more complex input profiles. We review the generality of the approach, and show that it can be adapted to describe neurons with sensory or motor responses that are characterized by marked nonlinearities. We conclude that our method permits more robust estimates of neural dynamics than conventional techniques across all stimulus conditions.     

Quantitative analysis of whole-tumor Gd enhancement histograms predicts malignant transformation in low-grade gliomas

PURPOSE: To quantify subtle gadolinium (Gd) enhancement (signal increase) in whole-tumor histograms and optimize their ability to predict subsequent malignant transformation in low-grade gliomas (LGGs). MATERIALS AND METHODS: We analyzed histograms from 21 adult subjects with LGGs (eight nontransformers and 13 transformers) who had been imaged every six months for periods of two to five years. Before transformation these tumors were reported as radiologically non-enhancing. Imaging included a T(1)-weighted volume sequence before and after a double dose of Gd-DTPA contrast agent. Image data sets were spatially registered and subtracted to obtain maps of percent enhancement (%E). Tumor outlines were defined on fluid-attenuated inversion recovery (FLAIR) images, and the volumes were calculated. Histogram tails were analyzed to obtain the volume (mL) of subtly enhancing tissue (%E > 10%). RESULTS: Baseline enhancing volumes were higher for Ts than for NTs (P < 0.005). Kaplan-Meier survival curves for a threshold of 4 mL showed clear differences at five years (P < 0.04). Pretransformation examinations predicted transformation (corrected threshold = 3.0 mL, P = 0.011). CONCLUSION: Clear histogram differences at presentation suggest that the process of transformation starts very early. It is now possible to identify individuals at high risk for transformation at baseline by quantifying the volume of subtly enhancing tumor tissue, and such findings could have an impact on patient management.     

Risk factors for neovascular glaucoma after carbon ion radiotherapy of choroidal melanoma using dose-volume histogram analysis

PURPOSE: To determine the risk factors for neovascular glaucoma (NVG) after carbon ion radiotherapy (C-ion RT) of choroidal melanoma. METHODS AND MATERIALS: A total of 55 patients with choroidal melanoma were treated between 2001 and 2005 with C-ion RT based on computed tomography treatment planning. All patients had a tumor of large size or one located close to the optic disk. Univariate and multivariate analyses were performed to identify the risk factors of NVG for the following parameters; gender, age, dose-volumes of the iris-ciliary body and the wall of eyeball, and irradiation of the optic disk (ODI). RESULTS: Neovascular glaucoma occurred in 23 patients and the 3-year cumulative NVG rate was 42.6 +/- 6.8% (standard error), but enucleation from NVG was performed in only three eyes. Multivariate analysis revealed that the significant risk factors for NVG were V50IC (volume irradiated > or =50 GyE to iris-ciliary body) (p = 0.002) and ODI (p = 0.036). The 3-year NVG rate for patients with V50IC > or =0.127 mL and those with V50IC <0.127 mL were 71.4 +/- 8.5% and 11.5 +/- 6.3%, respectively. The corresponding rate for the patients with and without ODI were 62.9 +/- 10.4% and 28.4 +/- 8.0%, respectively. CONCLUSION: Dose-volume histogram analysis with computed tomography indicated that V50IC and ODI were independent risk factors for NVG. An irradiation system that can reduce the dose to both the anterior segment and the optic disk might be worth adopting to investigate whether or not incidence of NVG can be decreased with it.     

Haemodialysis-induced changes in red blood cell size-distribution histograms

Treatment by haemodialysis may result in changes of the red blood cell size- distribution histograms in most subjects. After maintenance haemodialysis a statistically significant shift to the left is observed for the mean size distribution histogram in a group consisting of sixteen women. The shift is in agreement with the finding of significantly higher values for the microcyte fraction, as well as with significantly lower mean cell volume (MCV) values. No significant changes were observed for the macrocytic fractions of red blood cells.     

Matching visual induction effects on screens of different size

In the film industry, the same movie is expected to be watched on displays of vastly different sizes, from cinema screens to mobile phones. But visual induction, the perceptual phenomenon by which the appearance of a scene region is affected by its surroundings, will be different for the same image shown on two displays of different dimensions. This phenomenon presents a practical challenge for the preservation of the artistic intentions of filmmakers, because it can lead to shifts in image appearance between viewing destinations. In this work, we show that a neural field model based on the efficient representation principle is able to predict induction effects and how, by regularizing its associated energy functional, the model is still able to represent induction but is now invertible. From this finding, we propose a method to preprocess an image in a screen–size dependent way so that its perception, in terms of visual induction, may remain constant across displays of different size. The potential of the method is demonstrated through psychophysical experiments on synthetic images and qualitative examples on natural images.     

Prostate volume change after radioactive seed implantation: possible benefit of improved dose volume histogram with perioperative steroid

Purpose: To evaluate the changes in prostate volume associated with radioactive seed implantation and identify factors that influence prostate swelling.

Methods and Materials: Between June 1997 and August 1999, 161 patients implanted for prostate carcinoma at the University of California, San Francisco, had prostate volume measurements taken at 4 time points (preplan, preimplant, postimplant, postimplant dosimetry). Patient records were reviewed for treatment with perioperative steroids, hormone therapy (nHT), and external beam radiotherapy (EBRT). One and 2-way analysis of variance (ANOVA) methods were used to test differences in mean effects among patient subsets.

Results: A mean 20% volume increase was noted immediately postimplant overall (p < 0.0001), and even with EBRT and/or HT. Steroids were associated with a mean volume decrease of 19.9%, by 3–4 weeks post-procedure (p < 0.0001). Without steroids, only a 3.8% mean change was seen (p = ns). Steroid use resulted in a significant increase in mean dose-volume histogram (DVH) (p = 0.001); however, this benefit was only observed among patients who did not receive steroid. A consistently high DVH occurred with steroid use.

Conclusion: A significant decrease in prostate volume and improved DVH are associated with steroid use. The diminished benefit of steroid use and higher mean DVH achieved in later years suggests the existence of a significant “learning curve” for brachytherapy procedures.     

Dose to Bone Marrow Using IMRT Techniques in Prostate Cancer Patients

Purpose: To investigate the dose distribution in active bone marrow of patients undergoing intensity-modulated radiotherapy (IMRT) for prostate cancer and compare it to the distribution in the same patients, if they had been treated using conformal plans, in order to develop criteria for optimization to minimize the estimated risk of secondary leukemia. Patients and Methods: Mean bone marrow doses were calculated for ten patients with localized prostate cancer who underwent whole-pelvis IMRT and compared to three-dimensional conformal (3-D CRT) plans prepared for the same patients. Also for comparison, the IMRT and 3-D CRT plans were produced to simulate the treatment of the prostate gland only. To measure the dose to extrapelvic bone marrow, three thermoluminescent diode (TLD) chips were placed in the middle of the sternum region inside the Rando phantom. Results: For both the pelvic and prostate-only volumes, the IMRT plans were superior to 3-D CRT plans in reducing the high dose volume to the rectum, the bladder and the small bowel while maintaining acceptable coverage of the planning target volume (PTV). For the pelvic treatment group the IMRT plans, compared to 3-D CRT, reduced the high dose volume (> 20 Gy) to os coxae, which is the main contributor of dose to pelvic bone marrow, but increased the middle dose volume (10–20 Gy). No statistically significant differences were observed for lower dose volumes (< 5 Gy). For the prostate-only treatment the IMRT plan increased the high dose volume and slightly decreased the low dose volume of pelvic bone marrow. However, for both treatments the leakage dose to extrapelvic sites was higher by a factor of 2 in IMRT plans. Conclusion: There are significant differences in the dose-volume histograms of bone marrow doses from 3-D CRT and from IMRT. Pronounced dose inhomogeneity reduces the risk of leukemia compared to homogeneous radiation exposure of the bone marrow. The mean bone marrow dose is therefore not a useful criterion to judge plan quality, since scattered low doses to distant sites may be more critical than the high dose volumes receiving > 10 Gy. The number of monitor units needed to deliver an IMRT plan affects leakage dose and their incorporation into planning constraints should be considered.     

Septal connections with identified oxytocin and vasopressin neurones in the supraoptic nucleus of the rat. An electrophysiological investigation

Neurosecretory cells in the supraoptic nucleus of the lactating rat were identified by antidromic stimulation and differentiated as oxytocin or vasopressin secreting by their electrical activity during suckling. Oxytocin-containing neurones show a slow irregular or fast continuous pattern of electrical activity which is interrupted every 5–15 min by a synchronous high-frequency discharge of action potentials, precipitating the reflex milk ejections. Vasopressin-containing neurones never react to suckling. They usually exhibit a slow irregular electrical activity, but under stimulation for vasopressin release, evolve a phasic pattern of neuronal discharge. In both types of neurone, electrical stimulation of the neurohypophysial tract elicited an antidromic activation followed by inhibition.Possible relations of these neurosecretory cells with the septum were investigated by studying their electrophysiological responses to electrical stimulation of the septum. Single pulse septal stimulation caused a short term inhibition in both vasopressin- and oxytocin-containing cells. Repetitive stimulation of the septum at low frequency decreased the background firing rates of oxytocin-containing neurones without affecting the high-frequency discharges at the time of milk ejections. In phasically firing vasopressin-containing neurones, such stimulation decreased the intraburst firing rates; at higher stimulus intensity, the phasic pattern was altogether disrupted. In slow firing vasopressin-containing neurones, stimulation produced a reduction of their firing rates.The septum appears, therefore, to exert an inhibitory action on both oxytocin and vasopressin systems. The observed effects of septal stimulation on vasopressin-containing neurones suggest that the septum could participate in the control of phasic activity, thus modulating the rate of hormone release. The role of the septum in oxytocin release remains unclear since, in our experiments, septal stimulation did not affect the reflex milk ejection induced by suckling. However, the inhibition of the background activity of oxytocin-containing neurones suggests that the septum could be involved in other situations where oxytocin might be released.