Biomedical subjects

S R Schultz

Publications and source records attributed to S R Schultz.

10 recordsLinked to original sources

PubMed2001

Temporal correlations and neural spike train entropy.

Sampling considerations limit the experimental conditions under which information theoretic analyses of neurophysiological data yield reliable results. We develop a procedure for computing the full temporal entropy and information of ensembles of neural spike trains, which performs reliably for limited samples of data. This approach also yields insight to the role of correlations between spikes in temporal coding mechanisms. The method, when applied to recordings from complex cells of the monkey primary visual cortex, results in lower rms error information estimates in comparison to a "brute force" approach.

Action Potentials↗

PubMed2001

The role of spike timing in the coding of stimulus location in rat somatosensory cortex.

Although the timing of single spikes is known to code for time-varying features of a sensory stimulus, it remains unclear whether time is also exploited in the neuronal coding of the spatial structure of the environment, where nontemporal stimulus features are fundamental. This report demonstrates that, in the whisker representation of rat cortex, precise spike timing of single neurons increases the information transmitted about stimulus location by 44%, compared to that transmitted only by the total number of spikes. Crucial to this code is the timing of the first spike after whisker movement. Complex, single neuron spike patterns play a smaller, synergistic role. Timing permits very few spikes to transmit high quantities of information about a behaviorally significant, spatial stimulus.

Action Potentials↗

PubMed2001

A unified approach to the study of temporal, correlational, and rate coding.

We demonstrate that the information contained in the spike occurrence times of a population of neurons can be broken up into a series of terms, each reflecting something about potential coding mechanisms. This is possible in the coding regime in which few spikes are emitted in the relevant time window. This approach allows us to study the additional information contributed by spike timing beyond that present in the spike counts and to examine the contributions to the whole information of different statistical properties of spike trains, such as firing rates and correlation functions. It thus forms the basis for a new quantitative procedure for analyzing simultaneous multiple neuron recordings and provides theoretical constraints on neural coding strategies. We find a transition between two coding regimes, depending on the size of the relevant observation timescale. For time windows shorter than the timescale of the stimulus-induced response fluctuations, there exists a spike count coding phase, in which the purely temporal information is of third order in time. For time windows much longer than the characteristic timescale, there can be additional timing information of first order, leading to a temporal coding phase in which timing information may affect the instantaneous information rate. In this new framework, we study the relative contributions of the dynamic firing rate and correlation variables to the full temporal information, the interaction of signal and noise correlations in temporal coding, synergy between spikes and between cells, and the effect of refractoriness. We illustrate the utility of the technique by analyzing a few cells from the rat barrel cortex.

Animals↗

PubMed1999

Correlations and the encoding of information in the nervous system.

Is the information transmitted by an ensemble of neurons determined solely by the number of spikes fired by each cell, or do correlations in the emission of action potentials also play a significant role? We derive a simple formula which enables this question to be answered rigorously for short time-scales. The formula quantifies the corrections to the instantaneous information rate which result from correlations in spike emission between pairs of neurons. The mutual information that the ensemble of neurons conveys about external stimuli can thus be broken down into firing rate and correlation components. This analysis provides fundamental constraints upon the nature of information coding, showing that over short time-scales correlations cannot dominate information representation, that stimulus-independent correlations may lead to synergy (where the neurons together convey more information than they would if they were considered independently), but that only certain combinations of the different sources of correlation result in significant synergy rather than in redundancy or in negligible effects. This analysis leads to a new quantification procedure which is directly applicable to simultaneous multiple neuron recordings.

Action Potentials↗

PubMed1999

Analysis of information transmission in the Schaffer collaterals.

Hippocampal region CA1 seems from comparative studies to be particularly important in the primate brain, in addition to being crucial to memory function. Thus, it is an extremely appropriate place to begin a quantitative investigation of the information representation and transmission capabilities of cerebral neural networks. In this study, a mathematical model of the Schaffer collateral projection from CA3 to CA1 is described. From the model, the amount of information that can be conveyed by the Schaffer collaterals is calculated, i.e., the information that a pattern of firing in CA1 conveys about a pattern of firing in CA3, because of the connections between them. The calculation is performed analytically for an arbitrary probability distribution describing the pattern of CA3 firing and then solved numerically for particular input distributions. The effect of a number of issues on the information conveyed is examined. Consideration of the effect of the amount of analog resolution of firing rates in the patterns of activity in CA3 confirmed information transmission to be most efficient for binary codes, to a degree that depends on the sparseness of activity. For very sparse codes, a binary code allows more information to be received even in absolute terms, but for more distributed codes, slightly more information can be received by CA1 by making use of analog resolution. The pattern of convergence of connections from CA3 to CA1 is examined, i.e., the spatial distribution of the number of connections each CA1 neuron receives. It is found that the effect of the difference between a uniform convergence model and a proposed real convergence pattern (Bernard and Wheal, Hippocampus 1994;4:497-529) is minimal. The effect of the ratio of expansion between CA3 and CA1 due to the relative numbers of neurons in these two areas is studied. The Schaffer collaterals in all mammalian species reported in the literature seem to operate in a regime in which there is at least the scope for efficient transfer of information. In addition, the effect of topography (with respect to the transverse hippocampal axis) in the Schaffer collateral connectivity is examined. In the absence of spatial correlations, topography is found to have essentially no effect on information transmission. If spatial correlations in firing were present in CA3 (which, however, would be less efficient for memory storage in the recurrent collaterals), information transmission would be maximized by matching the topographic spread to the spatial scale of correlation.

Animals↗

PubMed1994

Mineral content of Louisiana white-tailed deer.

Water, lipid, and mineral composition were determined for metacarpals, phalanges, livers, and antlers from 219 free-ranging white-tailed deer (Odocoileus virginianus) collected on six properties in East Feliciana Parish, Louisiana (USA) to provide baseline data and to identify sources of composition variation. Metacarpal and phalangeal composition varied primarily with deer age; liver composition varied with deer sex.

Age Factors↗

PubMed1986

Further observations in the ultrasound evaluation of renal allograft rejection.

In order to determine whether sonographic parenchymal changes and volume changes are reliable predictors of acute transplant rejection, 36 recipients of renal allografts were studied. The significance of graft volume changes was evaluated, since most previous studies have not utilized routine immediate postoperative baseline scans for comparison to follow-up scans. All patients had baseline scans within 24 hours of the transplant. All 24 acute rejection patients had biopsy proof of rejection within three days of the follow-up scans. Seven clinically normal and five clinically designated acute tubular necrosis (ATN) patients were studied for comparison. A retrospective blind review utilizing three sonologists and previously described criteria combined with calculated volume changes demonstrated an overall sensitivity of 85 per cent and specificity of 94 per cent for the detection of acute rejection. The kidneys with acute rejection had an average volume increase of 73 per cent vs. 27 per cent for ATN patients and 24 per cent for normal patients, a statistically significant difference.

Acute Disease↗

PubMedDate not supplied

Anatomy of the portal vein bifurcation: intra- versus extrahepatic location--implications for transjugular intrahepatic portosystemic shunts.

PURPOSE: To delineate the relationship of the main portal vein bifurcation to the liver capsule, an anatomic study of the portal vein bifurcation was undertaken in 31 cadavers. MATERIALS AND METHODS: The portal bifurcation was characterized as intrahepatic, extrahepatic, or at the liver capsule (junctional). When the bifurcation was extrahepatic, the exposed portions of the right and left portal veins were measured. RESULTS: The portal bifurcation was intrahepatic in eight cadavers (25.8%), at the liver capsule in eight cadavers (25.8%), and extrahepatic in 15 cadavers (48.4%). The maximum lengths of exposed extrahepatic right and left portal veins were 3.0 cm and 2.5 cm, respectively. CONCLUSION: These findings suggest that for transjugular intrahepatic portosystemic shunt placement, a portal vein puncture site 3 cm from the portal bifurcation will be intrahepatic in most cases.

Aged↗

PubMedDate not supplied

CT detection of skeletal muscle metastases.

The CT appearance of skeletal muscle metastases, proven by biopsy, is presented in a series of 11 patients. Primary sites of neoplasm included chest, head and neck, breast, esophagus, uterus, ovary, prostate, and lymph nodes. Computed tomographic guided biopsies were performed in seven patients and four patients underwent open biopsy. The CT findings consisted primarily of muscle enlargement with the masses containing low density and loss of normal fat and vascular planes. Invasion of adjacent bony structures

Esophageal Neoplasms↗

PubMedDate not supplied

Large infiltrating renal transitional cell carcinomas: CT and ultrasound features.

A series of nine patients with large infiltrating renal transitional cell carcinomas is presented. These large tumors are rare but important in the differential diagnosis of renal masses. The average tumor size was 8.5 cm. In six patients the tumor involved almost the entire kidney. Seven masses were centrally located but two were peripheral. With CT the masses exhibited low attenuation relative to the normal or opposite renal parenchyma. Four masses exhibited necrosis. Lymphadenopathy, venous invasion, calcification, and spontaneous hemorrhage were all seen in this series. The major differential diagnostic possibility was renal cell carcinoma but lymphoma and metastatic disease were included. The diagnosis was confirmed in six patients by fine needle aspiration biopsy because of the presence of metastatic disease or the possibility of lymphoma. In the remaining three patients the diagnosis was made at surgery. The recognition that a large infiltrating renal mass may represent a transitional cell neoplasm is important in the eventual surgical management, and accurate preoperative diagnosis is stressed.

Biopsy, Needle↗