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Biomedical subjects

R Granger

Publications and source records attributed to R Granger.

10 recordsLinked to original sources
PubMed1995

Necrotizing fasciitis in childhood.

Necrotizing fasciitis is a rare entity in the pediatric population. Five cases of this soft tissue infection were treated at the authors' institution between January and December 1993. Three of the children were profoundly neutropenic secondary to chemotherapy. All five were treated with aggressive surgical debridement, frequent dressing changes, broad-spectrum antibiotics, and nutritional support. In addition, the patients with neutropenia received a combination of granulocyte-colony stimulating factor and granulocyte transfusions. One child died of overwhelming sepsis and bone marrow graft failure. The others eventually made a complete recovery. Necrotizing fasciitis may be becoming a more common problem in children. Aggressive chemotherapeutic regimens and more frequent use of bone marrow transplantation could be a factor in this. Early diagnosis and aggressive surgical therapy is critical. However, mortality may be significant, especially in patients with neutropenia. Leukocyte response to the infection may be a prognostic marker. Pseudomonas and enteric gram-negative organisms are seen frequently in immunocompromised children with necrotizing fasciitis. Antimicrobial selection should supply adequate coverage of these organisms.

Adolescent↗
PubMed1994

Non-Hebbian properties of long-term potentiation enable high-capacity encoding of temporal sequences.

A hypothesis commonly found in biological and computational studies of synaptic plasticity embodies a version of the 1949 postulate of Hebb that coactivity of pre- and postsynaptic elements results in increased efficacy of their synaptic contacts. This general proposal presaged the identification of the first and still only known long-lasting synaptic plasticity mechanism, long-term potentiation (LTP). Yet the detailed physiology of LTP induction and expression differs in many specifics from Hebb's rule. Incorporation of these physiological LTP constraints into a simple non-Hebbian network model enabled development of "sequence detectors" that respond preferentially to the sequences on which they were trained. The network was found to have unexpected capacity (e.g., 50 x 10(6) random sequences in a network of 10(5) cells), which scales linearly with network size, thereby addressing the question of memory capacity in brain circuitry of realistic size.

Algorithms↗
PubMed1991

Computation of frequency-to-spatial transform by olfactory bulb glomeruli.

A physiological simulation of 2.5% of the input and inhibitory neurons and 25% of the primary mitral/tufted cells in a single mammalian olfactory bulb glomerulus was constructed. This physiological simulation used the integrate-and-fire paradigm with realistic activation curves and synaptic delays. The dendritic integration incorporated non-linear interactive effects of individual cell excitatory and inhibitory post-synaptic potentials (PSPs) from both axodendritic and dendro-dendritic synaptic contacts. Refractory periods for granule-cell inhibition of mitral/tufted cell activity lead to relatively fixed-frequency rhythmic activity in the glomerulus, independent of the input frequency from the olfactory nerve. Though the frequency of mitral/tufted cell firing in bulb was approximately independent of input frequency, the number of cells active in the glomerulus was a roughly-linear function of input frequency to the glomerulus, indicating the mechanism's ability to function as a frequency-to-spatial encoder.

Animals↗
PubMed1991

Higher olfactory processes: perceptual learning and memory.

The past year has seen several important findings emerge from studies of higher olfactory processes. The identification of synaptic long-term potentiation in the olfactory cortex, induced via repetitive burst stimulation at the theta rhythm, and physiological activity patterns associated with learning, some of which mimic long-term potentiation induction patterns, have suggested relationships between rhythmic activity, behavioral learning and synaptic plasticity. In addition, the construction of computational models of the olfactory bulb and cortex have generated testable behavioral and physiological predictions which have been supported by experimental evidence.

Animals↗
PubMed1990

Simulation of paleocortex performs hierarchical clustering.

Simulations were performed of layers I and II of olfactory paleocortex, as connected to its primary input structure, olfactory bulb. Induction of synaptic long-term potentiation by means of repetitive sampling of inputs caused the simulation to organize encodings of learned cues into a hierarchical memory that uncovered statistical relationships in the cue environment, corresponding to the performance of hierarchical clustering by the biological network. Simplification led to characterization of those parts of the network responsible for the mechanism, resulting in a novel, efficient algorithm for hierarchical clustering. The hypothesis is put forward that these corticobulbar networks and circuitry of similar design in other brain regions contain computational elements sufficient to construct perceptual hierarchies for use in recognizing environmental cues.

Animals↗
PubMed1978

The Brighton resuscitation ambulances: review of 40 consecutive survivors of out-of-hospital cardiac arrest.

In three years 40 patients were resuscitated by ambulancemen after out-of-hospital cardiac arrest and survived to be discharged. Twenty-six of these had had circulatory arrest before an ambulance arrived and a further three had developed ventricular fibrillation before they were moved. Thirty-two patients were alive at the time of review six months to three and a half years later. Resuscitation by ambulancemen can be effective for patients with unheralded sudden cardiac arrest as well as for patients with recent myocardial infarction. Survivors of out-of-hospital ventricular fibrillation may have a favourable long-term prognosis.

Adult↗