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164 results on '"Cowan, J. D."'

2. Self-organized criticality in a network of interacting neurons

Author

Cowan, J D, Neuman, J, and van Drongelen, W

Subjects
Quantitative Biology - Neurons and Cognition, Physics - Biological Physics
Abstract

This paper contains an analysis of a simple neural network that exhibits self-organized criticality. Such criticality follows from the combination of a simple neural network with an excitatory feedback loop that generates bistability, in combination with an anti-Hebbian synapse in its input pathway. Using the methods of statistical field theory, we show how one can formulate the stochastic dynamics of such a network as the action of a path integral, which we then investigate using renormalization group methods. The results indicate that the network exhibits hysteresis in switching back and forward between its two stable states, each of which loses its stability at a saddle-node bifurcation. The renormalization group analysis shows that the fluctuations in the neighborhood of such bifurcations have the signature of directed percolation. Thus the network states undergo the neural analog of a phase transition in the universality class of directed percolation. The network replicates precisely the behavior of the original sand-pile model of Bak, Tang & Wiesenfeld., Comment: 17 pages, 4 figures, submitted to Journal of Statistical Mechanics

Published
2012
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21. Neurophysiology

Author

Blum, M., Howland, Bradford H., Cowan, J. D., Pitts, Walter H., Gesteland, R. C., Verbeek, L. A. M., Lettvin, Jerome Y., Berendsen, H. J. C., McCulloch, Warren S., Blum, M., Howland, Bradford H., Cowan, J. D., Pitts, Walter H., Gesteland, R. C., Verbeek, L. A. M., Lettvin, Jerome Y., Berendsen, H. J. C., and McCulloch, Warren S.

Abstract

Contains reports on five research projects., Bell Telephone Laboratories, Incorporated, National Institutes of Health, Teagle Foundation, Incorporated

Published
2010

22. Neurophysiology

Author

Cowan, J. D., Winograd, S., Arbib, M. A., Cowan, J. D., Winograd, S., and Arbib, M. A.

Abstract

Contains reports on three research projects., Bell Telephone Laboratories, Incorporated, National Institutes of Health, Teagle Foundation, Incorporated, United States Air Force (WADD Contract AF33(616)-7783)

Published
2010

23. Neurophysiology

Author

Gesteland, R. C., Howland, Bradford H., Onesto, N. M., Maturana, Humberto R., Wall, P. D., Melzack, R., Winograd, S., Cowan, J. D., Berendsen, H. J. C., McCulloch, Warren S., Verbeek, L. A. M., Lettvin, Jerome Y., Axelrod, F. S., Rossoni, Paola, Pitts, Walter H., Aldrich, J. A., Blum, M., Gesteland, R. C., Howland, Bradford H., Onesto, N. M., Maturana, Humberto R., Wall, P. D., Melzack, R., Winograd, S., Cowan, J. D., Berendsen, H. J. C., McCulloch, Warren S., Verbeek, L. A. M., Lettvin, Jerome Y., Axelrod, F. S., Rossoni, Paola, Pitts, Walter H., Aldrich, J. A., and Blum, M.

Abstract

Contains research objectives and reports on three research projects., U. S. Air Force Office of Scientific Research under Contract AF49(638)-398, National Institutes of Health, Teagle Foundation, Incorporated, Bell Telephone Laboratories, Incorporated

Published
2010

24. Neurophysiology

Author

McCulloch, Warren S., Berendsen, H. J. C., Blum, M., Cowan, J. D., Verbeek, L. A. M., Lettvin, Jerome Y., Maturana, Humberto R., Gesteland, R. C., Pitts, Walter H., McCulloch, Warren S., Berendsen, H. J. C., Blum, M., Cowan, J. D., Verbeek, L. A. M., Lettvin, Jerome Y., Maturana, Humberto R., Gesteland, R. C., and Pitts, Walter H.

Abstract

Contains reports on ten research projects., Bell Telephone Laboratories, Incorporated, National Institutes of Health, Teagle Foundation, Incorporated

Published
2010

25. Neurophysiology

Author

Lettvin, Jerome Y., Goodall, M. C., Howland, Howard C., Howland, Bradford H., Cowan, J. D., Winograd, S., Lettvin, Jerome Y., Goodall, M. C., Howland, Howard C., Howland, Bradford H., Cowan, J. D., and Winograd, S.

Abstract

Contains reports on four research projects., National Institutes of Health (Grant B-1865-(C3), Grant MH-04737-02), United States Air Force, Aeronautical Systems Division (Contract AF33(616)-7783), Teagle Foundation, Incorporated, Bell Telephone Laboratories, Incorporated

Published
2010

26. Neurophysiology

Author

Pitts, Walter H., Brown, J. E., III, Major, Diane, Howland, Bradford H., von Dechend, Herta, Blum, M., Aldrich, J. A., Wall, P. D., Onesto, N. M., Rojas, J. A., Melzack, R., Taub, A., Cowan, J. D., Lettvin, Jerome Y., McCulloch, Warren S., Gesteland, R. C., Maturana, Humberto R., Kornacker, K., Pitts, Walter H., Brown, J. E., III, Major, Diane, Howland, Bradford H., von Dechend, Herta, Blum, M., Aldrich, J. A., Wall, P. D., Onesto, N. M., Rojas, J. A., Melzack, R., Taub, A., Cowan, J. D., Lettvin, Jerome Y., McCulloch, Warren S., Gesteland, R. C., Maturana, Humberto R., and Kornacker, K.

Abstract

Contains research objectives and reports on nine research projects., The Teagle Foundation, Inc., U.S. Air Force (Aeronautical Systems Division) under Contract AF33(616)-7783, Bell Telephone Laboratories, Inc., National Institutes of Health [Grant M-4235-(C1)], National Institutes of Health (Grant B-1865-(C3)), National Institutes of Health (Grant MP-4737), National Institutes of Health (Grant B-2480(C1))

Published
2010

34. Terminal sedation in palliative medicine--definition and review of the literature.

Author

Cowan, John, Walsh, Declan, Cowan, J D, and Walsh, D

Abstract

This paper reviews the reported use of nonopioid medications for terminal sedation. To provide a summary of the available literature, an electronic database search was performed. Thirteen series and 1 4 case reports were identified. Various symptoms, including agitation, pain, and confusion, required terminal sedation. Eleven drugs were used in 342 patients. Most patients were also treated with concurrent opioids and received terminal sedation in an inpatient hospice unit. Midazolam was the most common sedative employed. A good response--defined as adequate sedation--ranged between 75% and 100%. The median time to death following the introduction of terminal sedation was greater than 1 day. No agent appears to have superior efficacy or limiting toxicity. [ABSTRACT FROM AUTHOR]

Published
2001
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37. Bone marrow necrosis.

Author

Cowan, John D., Rubin, Ronald N., Kies, Merrill S., Cerezo, Lizardo, Cowan, J D, Rubin, R N, Kies, M S, and Cerezo, L

Published
1980
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42. Localized effects of spatial-frequency adaptation

Author

Williams, D. W., Wilson, H. R., and Cowan, J. D.

Abstract

The spatially localized threshold-elevation aftereffect of spatial-frequency adaptation was measured by using localized, aperiodic test patterns that have bandpass Fourier transforms. At a given retinal location, the threshold-elevation curves are consistent with the fatigue of size-tuned mechanisms with center-surround sensitivity profile. Only a few different sizes of such mechanisms were required to fit the local results. The local aftereffect was also measured as a function of eccentricity near the fovea. The results indicate that the threshold-elevation aftereffect of spatial-frequency adaptation is not spatially homogeneous.

Published
1982

43. Further evidence for four mechanisms mediating vision at threshold: Sensitivities to complex gratings and aperiodic stimuli

Author

Bergen, J. R., Wilson, H. R., and Cowan, J. D.

Abstract

It is now generally accepted that several mechanisms mediate contrast detection at threshold. Many attempts to measure the bandwidths of these mechanisms using subthreshold summation have yielded estimates suggesting very narrow frequency tuning. We have measured thresholds for three classes of stimuli: gratings containing two sinusoidal components, sums of “difference of Gaussian” (DOG) patterns, and square waves. The results of the subthreshold summation experiments with gratings are consistent with those of other studies. All of these thresholds can be predicted by a model requiring only four center-surround-type mechanisms at each retinal locus. These mechanisms have a full bandwidth at a half-height of about 1.75 octaves. Quantitative prediction of sensitivities depends critically upon spatial probability summation. It is this spatial nonlinearity that yields these somewhat counterintuitive results. The much narrower bandwidths inferred by others are due to the assumption of linearity used in their analyses.

Published
1979

45. Osteomyelitis in children: comparison of hematogenous and secondary osteomyelitis

Author

Fitzgerald, R. H., Landells, D. G., and Cowan, J. D.

Subjects
Male, Adolescent, Bacteria, Arthritis, Infant, Osteomyelitis, Blood Sedimentation, Penicillins, Staphylococcal Infections, Abscess, Debridement, Child, Preschool, Sepsis, Wound Infection, Humans, Female, Child, Research Article, Retrospective Studies
Abstract

Summary: A review of osteomyelitis in 54 patients treated at the Dr. Charles A. Janeway Child Health Centre over a 4-year period revealed equal frequencies of secondary and hematogenous osteomyelitis. Although the clinical picture in patients with hematogenous osteomyelitis was classic, patients with secondary osteomyelitis presented with an altered clinical response. Patients with secondary osteomyelitis have a history of an antecedent puncture wound or an inadequately treated contiguous focus of infection; antistaphylococcal antimicrobial therapy was ineffective for most because gram-negative bacilli were isolated in this group of patients. In contrast to patients with hematogenous osteomyelitis, who frequently respond to intensive antimicrobial therapy, those with secondary osteomyelitis will frequently require surgical intervention to eradicate the infection.

Published
1975

47. A phase II study of bisantrene in malignant lymphomas. A Southwest Oncology Group Study.

Author

Miller, Thomas, Cowan, John, Neilan, Barbara, Jones, Stephen, Miller, T P, Cowan, J D, Neilan, B A, and Jones, S E

Abstract

Forty evaluable patients with malignant lymphoma (ML) were treated with bisantrene at a dose of 260 mg/m2 every 3 weeks (18 patients) or 208 mg/m2 every 3 weeks (22 patients). The initial dose rate was determined on the basis of expected myelosuppression. Patients were heavily pretreated and had advanced disease (92% had stage IV). The overall response rate was 10% and included 1 partial response (PR) in 17 patients with Hodgkin's disease (HD), 1 PR and 1 complete response (CR) in 5 patients with favorable histology in non-Hodgkin's lymphoma (NHL), and 1 PR in 18 patients with unfavorable histology in NHL. Neutropenia (WBC less than or equal to 3000 cells/microliter) was the most common toxicity, occurring in 50% of patients. Phlebitis was a common side effect in patients treated with bisantrene administered by way of peripheral veins. Bisantrene has limited activity in heavily pretreated patients with HD or unfavorable histology in NHL. The role of bisantrene for treatment of NHL with favorable histology or for treatment at an earlier point in the natural history of ML is unknown. [ABSTRACT FROM AUTHOR]

Published
1986
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50. What matters in neuronal locking?

Author

Gerstner, W., van Hemmen, J. L., and Cowan, J. D.

Subjects
Quantitative Biology::Neurons and Cognition
Abstract

Exploiting local stability we show what neuronal characteristics are essential to ensure that coherent oscillations are asymptotically stable in a spatially homogeneous network of {\em spiking\/} neurons. Under standard conditions, a necessary and in the limit of a large number of interacting neighbors also sufficient condition is that the postsynaptic potential is increasing in time as the neurons fire. If the postsynaptic potential is decreasing, oscillations are bound to be unstable. This is a kind of locking theorem and boils down to a subtle interplay of axonal delays, postsynaptic potentials, and refractory behavior. The theorem also allows for mixtures of excitatory and inhibitory interactions. On the basis of the locking theorem we present a simple geometric method to verify existence and local stability of a coherent oscillation.

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