Sleep to forget teacher, or sleep to remember grandmother?

December 10th, 2017

It seems that a lack of sleep may prevent the brain from forgetting unimportant information. A lack of sleep may also prevent the brain from remembering important information. How can scientists make sense of this seemingly-nonsensical seeming-contradiction?

Imagine you just met your child’s teacher, who is named Gwen. The name Gwen, however, is firmly associated in your memory networks with your grandmother, who is also named Gwen.

Under such conditions, you may unintentionally think that your grandmother has no children, or that the teacher is in fact your grandmother. Researcher Gina Poe poses this example in the paper, “Sleep Is for Forgetting,”  as well as a diagram of this example:

Figure 2: Disambiguating the teacher Gwen from the grandmother Gwen requires sleep-dependent consolidation of the novel information while protecting the grandmother schema.

Poe claims that when the brain is asleep, ‘garbage’ memories and links can be deleted. Hormones that activate during rest could protect long held memories from deletion, in this case protecting the grandmother from the new teacher. Sleep could prevent unintentional overlaps in memory, and socially problematic mix-ups.

Don’t forget to remember to read the companion paper by Susan Sara, “Sleep to Remember.” Sara reviews the literature, taking a dig at the ancient Greeks:

According to Aristotle, the sleep state was “a boarder-land between living and not-living: a person who is asleep would appear to be neither completely non-existent nor completely existent” (Sprague, 1977). Clearly, ancient Greek thought did not attribute any important functional role to the sleep state.

Sara’s article covers a history of studies suggesting that rapid eye movement (REM) sleep helps consolidate memories by making some connections stronger. More recent examples are used, as well as the early experiments of sleep depriving rats that “… involved constraining the animal on an inverted flower pot surrounded by a pool of water.”

Each researcher comments on the other’s paper, pointing out details that are seemingly-reasonable reasons for their analysis.

Dicey, and then some: Stirred, not shaken (physics)

December 10th, 2017

Dice Become Ordered When Stirred, Not Shaken” is a headline on a snappy summary of a new physics paper. The headline, and the summary, are published in Physics Focus. Their own summary of their summary: “A jumble of thousands of cubic dice, agitated by an oscillating rotation, can rapidly become completely ordered, a result that is hard to produce with more conventional shaking.”

The researchers produced an action video:


The study itself is “Experimental Study of Ordering of Hard Cubes by Shearing,” K. Asencio, M. Acevedo, I. Zuriguel, and D. Maza, Physical Review Letters, epub December 1, 2017. The authors, at Universidad de Navarra, Spain and Unidad Monterrey, Mexico report:

“We experimentally analyze the compaction dynamics of an ensemble of cubic particles submitted to a novel type of excitation. Instead of the standard tapping procedure used in granular materials we apply alternative twists to the cylindrical container. Under this agitation, the development of shear forces among the different layers of cubes leads to particle alignment. As a result, the packing fraction grows monotonically with the number of twists. If the intensity of the excitations is sufficiently large, an ordered final state is reached where the volume fraction is the densest possible compatible with the boundary condition.”

(Thanks to Mason Porter for bringing this to our attention.)

Modelling heat loss from a semi-spherical cow udder

December 8th, 2017

Theoretical physicists are sometimes accused of making over-simplifications for mathematical models. This has lead to many variations on the spherical cow story, where a physicist claims to be able to cure a sick cow, but only if it is a spherical cow in a vacuum. Oddly, most iterations of this tale ignore heat radiated from a cow.

In a classic case of life semi imitating art, researchers Kifle Gebremedhin and Binxin Wu focus on heat radiated from only one part of a dairy cow in the paper titled “Modelling heat loss from the udder of a dairy cow.” Since they are using a semi cow, they decided to use a semi sphere to model the udder.

According to the researchers, it only takes ten assumptions to reduce a fully functioning, mooing, milk producing cow into a semi spherical udder model:

1. Cow udder is semi sphere.
2. Radius of the semi sphere is 0.17 m.
3. An outer layer of 10-mm thickness of tissue was assumed for
heat transfer between the udder and ambient air (Fig. 1).
4. A one-dimensional transient (a function of time) heat flow was
assumed through the thickness of the tissue (Fig. 1).
5. Heat lost from the udder skin surface when the cow is standing is by evaporation and convection.
6. Core temperature of udder tissue is 38.6°C.
7. Metabolic heat production rate in the tissue is 1946 W/m3.
8. Blood-flow time through the udder takes between 2 and 4 min.
9. The physical and thermal properties are assumed to be constant.
10.Temperature of blood entering the udder is equal to core temperature.

As noted here before, other models for determining heat loss from whole cows have been around for some time. Some models treated cows as cylinders, while others ignored cow geometry completely and used temperatures and humidity. This particular model is unique in that it simplifies the the cow to a single organ. But how was that organ selected?

Dairy cows are usually cooled off by spraying water from above to wet their bodies. Gebremedhin tried the inverted tactic of wetting the cows from below in “Alternative Cooling of Dairy Cows by udder Wetting,

Thermal images of an udder before and after wetting.

Cooling  the udder was just as effective as trying to cool off the entire body of the cow. Gebremedhin found that the massive amount of blood flowing through the udder likely distributes the cooling quickly.

The semi-spherical udder model paper shares the result:

… the udder could be considered as a heat sink, and thus, in time of heat stress, a dairy cow could be cooled by cooling the udder…

 

Cardinal Ludovico Trevisan’s earlobe crease (study)

December 7th, 2017

Attention was recently drawn to the fact that Robert E. Lee had a crease in his right earlobe, and that he died from cardiovascular disease. But Lee was by no means the only historical figure who showed such signs. Francesco M. Galassi, Dr. who is a Postdoc assistant in the Paleopathology and Mummy Studies Group at the University of Zurich, reminds us that there are abundant opportunities for paleopathological research in this area. He has recently discovered, for example, that Cardinal Ludovico Trevisan (1401–1465) [pictured] not only had a crease across his auricular lobe, but also :

“[…] the cardinal’s death, which occurred five to six years after the portrait was made, in Rome on 22nd March 1465, might very well have been the result of oedema, once known by the currently obsolete term ‘dropsy’, a common final pathophysiological step of several organ failures such as hepatic and renal, and well known to be associated with cardiovascular disease.”

See: Palaeopathology of the earlobe crease (Frank’s sign): New insights from Renaissance art, International Journal of Cardiology, Volume 236, 1 June 2017, Pages 82-84.

Bonus assignment [optional] List historical individuals (aside from Robert E. Lee and Cardinal Ludovico Trevisan) for whom there is existing visual evidence of earlobe creases and who are also recorded as having died as a result of cardiovascular problems.

A refreshing medical report about detox tea

December 6th, 2017

A new medical paper says that one popular brand of what’s called “detox tea” is pretty tox. The study is called “Yogi Detox Tea: A Potential Cause of Acute Liver Failure.” It’s published in the journal Case Reports in Gastrointestinal Medicine.

The study’s authors, at Drexel University Hospital, in Philadelphia, say: “We present a case of acute fulminant liver failure from a liver detoxification tea. We present a 60-year-old female with weakness, lethargy, scleral icterus, jaundice, and worsening mental status. She drank herbal tea three times a day for 14 days prior to symptom development. Liver tests were elevated. Remaining laboratory tests and imaging were negative for other etiologies. An ultrasound-guided liver biopsy showed submassive necrosis. A literature search on the ingredients shows six ingredients as having hepatotoxic effects and remaining ingredients as having very sparse hepatoprotective data.”