Information transport by sine-Gordon solitons in microtubules

We study the problem of information propagation in brain microtubules. After considering the propagation of electromagnetic waves in a fluid of permanent electric dipoles, the problem reduces to the sine-Gordon wave equation in one space and one time dimensions. The problem of propagation of information is thus set.Comment: 3 page

Forced Moves or Good Tricks in Design Space? Landmarks in the Evolution of Neural Mechanisms for Action Selection

This review considers some important landmarks in animal evolution, asking to what extent specialized action-selection mechanisms play a role in the functional architecture of different nervous system plans, and looking for “forced moves” or “good tricks” (see Dennett, D., 1995, Darwin’s Dangerous Idea, Penguin Books, London) that could possibly transfer to the design of robot control systems. A key conclusion is that while cnidarians (e.g. jellyfish) appear to have discovered some good tricks for the design of behavior-based control systems—largely lacking specialized selection mechanisms—the emergence of bilaterians may have forced the evolution of a central ganglion, or “archaic brain”, whose main function is to resolve conflicts between peripheral systems. Whilst vertebrates have many interesting selection substrates it is likely that here too the evolution of centralized structures such as the medial reticular formation and the basal ganglia may have been a forced move because of the need to limit connection costs as brains increased in size

Waves, Pulses, and the Theory of Neural Masses

 It is a truism that systems as complex as vertebrate nervous systems are more than the sum of their parts. What is meant is that the interconnection of numbers of neurons gives rise to collective properties belonging to the neural populations and not to the neurons taken one at a time. The purpose of this essay is to explore some facets of the nature of neural collective properties.   Conventional wisdom holds that such properties emerge from the interconnection of finite numbers of neurons in discrete chains and networks, which are logical and anatomical counterparts of the Jacksonian-Sherringtonian heirarchy of reflex arcs. According to a popular analogy, neurons are like the electronic components of a television receiver which can be connected in a certain way or set of ways to give the properties of the receiver. The central thesis of this essay is the idea that, when neurons strongly interact in sufficiently large numbers (on the order of 10' or more), new collective properties emerge that demand a different kind or level of conceptualization.   An analogy equivalent to that given above is the notion that temperature and pressure exist only for a mass, in contrast to the thermal kinetic energy of molecules in the mass. The suggestion is that certain interactive phenomena in vertebrate brains occur only as broadly distributed and continuous events or waves across masses of neurons, and that in some instances these cooperative phenomena may be essential aspects of normal brain function. The task is to describe some of these wave phenomena in terms of underlying collective properties, and to do so in such a way as to minimize confusion between observables and principles. Again by analogy, brain potentials (EEG waves) appear to have somewhat the relation to wave activity of neural masses that flow patterns have to temperature and pressure waves in atmospheric storms. They are observable side effects that are of interest mainly because they give access to the internal dynamics.   The approach used is to review the historical interplay between ideas concerning neural networks and masses, to develop a set of rules for describing neural masses as dynamic entities, and then to discuss some of the implications of those rules for neurophysiology.   Throughout the development the emphasis is placed on the idea of graded neural synaptic interaction, because it is interaction of neurons that gives rise to something more than the sum of parts. Neurons are connected to each other by structural synaptic linkages. For each neuron there is a certain density of these anatomical connections, referring to the number and size of contacts of each neuron with its neighbors within each unit volume of neural mass. But the significant quantity is the momentary functional or effective connection density, which denotes the level of transfer of influence across a given set of connections at a given time and place. If, for example, a volley arrives on an afferent path to a neuron that is in an absolute refractory state, the functional connection density is zero, even though the anatomical connection density is nonzero.   Two kinds of massive connections are distinguished. The first is a one-way or forward connection from one neuron to neurons in another mass; the second is feedback connection of one neuron with many others in the same mass. Both types give rise to mass actions of many neurons, but only the second gives rise to the collective properties of interest in the present context. That is, neural interactions based on functional interconnection densities give rise to wave phenomena, and, as is shown for some of the neural masses in the mammalian olfactory system, the observable effects of wave patterns in turn provide the means for measuring the intensities of interactions

Endoscopic Placement of Feeding Tubes

It is no exaggeration to say that percutaneous gastrostomy has revolutionized the feeding of disabled patients with intact gastrointestinal tracts. The most common indication is inability to swallow. It is generally best to place a gastrostomy tube early to prevent malnutrition and minimize complications of procedures on poorly nourished tissue. If a patient is expected to live for only weeks to months, nasoenteric feedings are the nutritional route of choice. Contraindications to percutaneous gastrostomy include coagulation disorders, upper gastrointestinal fistulas, intestinal obstruction, varices, peritoneal dialysis, septicemia and esophageal obstruction. Three techniques are described: 'pull,' 'push' and 'introducer.' The most frequently reported complications are wound infection and pneumoperitoneum. Now that multiple methods for successful insertion of endoscopic percutaneous feeding tubes have been described, the literature appears to be concentrating on complications of the various techniques. Nevertheless, compared to the other options available for patients unable to swallow (allowing malnutrition to proceed, tube feeding, surgical gastrostomy, parenteral nutrition), percutaneous gastrostomy is the procedure of choice in virtually all cases if the intestine is functioning

An Approach to Iron-Deficiency Anemia

Iron-deficiency anemia is a common reason for referral to a gastroenterologist. In adult men and postmenopausal women, gastrointestinal tract pathology is often the cause of iron-deficiency anemia, so patients are frequently referred for endoscopic evaluation. Endoscopy may be costly and at times difficult for the patient. Therefore, physicians need to know what lesions can be identified reliably and, more importantly, the importance of ruling out life-threatening conditions such as occult malignancy. Over the past decade, a number of prospective studies have been completed that examined the yield of endoscopy in the investigation of iron-deficiency anemia. The present article provides a broad overview of iron-deficiency anemia, with particular emphasis on hematological diagnosis, etiology, the use of endoscopy in identifying lesions and iron-repletion therapy. Other clinical scenarios, including assessment of patients on anti-inflammatory or anticoagulation therapy and patients with bleeding of obscure origin, are also addressed. The present article provides a diagnostic algorithm to iron-deficiency anemia, which describes a more systematic manner in which to approach iron-deficiency anemia

Does Whipworm Increase the Pathogenicity of Campylobacter jejuni? A Clinical Correlate of an Experimental Observation

Campylobacter jejuni is a leading cause of acute diarrhea worldwide, usually mild and self-limiting. No adequate hypothesis has yet been formulated to explain why in an otherwise healthy host this infection is occasionally severe. In a pig model, C jejuni has been shown to be pathogenic only in the presence of swine whipworm. A human case of life-threatening C jejuni colitis leading to toxic megacolon and acute renal failure, associated with concomitant whipworm (Trichuris suis) ova in the feces, is reported. The potential of T suis to potentiate C jejuni in humans deserves further study

Common Symptoms from an Uncommon Infection: Gastrointestinal Anisakiasis

Clinicians can be forgiven for thinking of anisakiasis as a rare condition low in the differential diagnosis of abdominal pain. Gastrointestinal anisakiasis is a zoonotic parasitic disease caused by consumption of raw or undercooked seafood infected with nematodes of the genus Anisakis. Even though the reported cases indicate that this is a rare disease, the true incidence of the disease could be potentially higher than what is reported in the literature as cases can go undiagnosed. Diagnosis and treatment of gastric anisakiasis are made by a compatible dietary history, direct visualization, and removal of the larvae via gastroscopy. Serologic testing and imaging studies are useful in the diagnosis of intestinal anisakiasis and conservative management should be considered. This disease may mimic other diseases and lead to unnecessary surgery. This emphasizes the importance of suspecting gastrointestinal anisakiasis by history taking and by other diagnostic modalities

Double-balloon enteroscopy following capsule endoscopy in the management of obscure gastrointestinal bleeding: Outcome of a combined approach

BACKGROUND: There is no consensus on the relative accuracy of capsule endoscopy (CE) versus double-balloon enteroscopy (DBE) to investigate obscure gastrointestinal bleeding (GIB). CE is less invasive, but DBE more directly examines the small bowel, and allows tissue sampling plus therapeutic intervention