Neurons in the rat hippocampus show activity related to the rat's position in its environment. As with the memory theory, there is now almost universal agreement that spatial coding plays an important role in hippocampal function, but the details are widely debated.
Studies conducted on freely moving rats and mice have shown that many hippocampal neurons have "place fields", that is, they fire bursts of action potentials when a rat passes through a particular part of the environment. In humans, cells with location-specific firing patterns have been reported in a study. Patients with drug-resistant epilepsy had diagnostic electrodes put in their hippocampus. Then a computer was used to move them around in a virtual reality town.
The discovery of place cells in the 1970s led to a theory that the hippocampus might act as a cognitive map a neural representation of the layout of the environment. The "cognitive map hypothesis" has been further advanced by recent discoveries of direction cells in several parts of the rodent brain which are strongly connected to the hippocampus.
The hippocampus has a generally similar appearance across the mammals from monotremes such as the echidna to primates such as humans. The hippocampal size to body-size ratio increases: it is about twice as large for primates as for the echidna. It does not, however, increase at anywhere close to the rate of the neocortex to body-size ratio. Therefore, the hippocampus takes up a larger fraction of the cortex in rodents than in primates.
Other vertebrates have areas which may be homologous to the hippocampus of mammals. Some insects, and cephalopods such as the octopus, have strong spatial learning and navigation abilities. These appear to work differently from the mammalian spatial system, and have evolved independently of the mammalian system.
Superparamagnetism
Superparamagnetism is a form of magnetism. A superparamagnetic material has many small clusters of magnetic things in its structure, but they are not all pointed the same way, so the material is not magnetic by itself. If a magnetic field is applied to the material, then the clusters change direction to match the magnetic field and the material becomes magnetic. Superparamagnetism is like paramagnetism, except it can happen at near room temperature. It happens when materials are made up of very small parts (1-10 nm).
Safety
Safety is a feeling that no bad things will happen. Security avoids things to happen that you don't want to. The police keep public safety, which stops crimes happen. Safety hats protect the head from injury. Houses provide safety from the weather.
Heidi
Heidi is a book written by Johanna Spyri, published between 1880 and 1881. It is about a young orphan girl who grows up in the Swiss Alps (mountains in Switzerland) with her grandfather.
When her guardians die, Heidi must live in the mountains with her grandfather, Alm-Uncle, who does not like people. He slowly changes and becomes more caring because of Heidi. Then, Heidi must move to Frankfurt, Germany to be the friend of Clara, a girl who is sick and cannot walk. Clara’s grandmother encourages Heidi to learn to read, and she also learns about God. She becomes very homesick, and a kind doctor says that she must return home to her grandfather. Later, Clara visits Heidi in the Alps and becomes strong enough to walk.
Johanna Spyri wrote this story for her son, Berhard Diethelm Spyri. People and places in the story come from Spyry's own life. Catherine Eayrs, a literary critic, thinks that the village of Dorfli may come from Jenins in Switzerland, a place that Spyri visited as a child, however Dorfli is an actual town in Switzerland. Also, the kindly doctor is similar to Spyri's own father, and Klara's grandmother is a good storyteller, just like Spyri's own mother.
Immediately after the book was published, "Heidi" was popular, both with children and adults. It continues to be popular, and translations are available in more than fifty languages. About 50 million books have been sold. The story has also been told on movie and television. There is even a musical version.
Visitors to Switzerland can visit a tourist village called Heididorf in Maienfeld. The name means "Heidi's village" in German.
Some readers think that one problem of "Heidi" is that the book teaches the Christian religion. Malcolm Usrey, a literary critic, thinks that nature is as important as Christianity in helping people, because Klara’s paralysis and Heidi’s home sickness are both healed in the “clean air of the Swiss mountains”.
Hans von Bülow
Hans von Bülow (born Dresden, 8 January 1830 ; died Cairo, 12 February 1894) was a German conductor and pianist. He was one of the most famous conductors of the 19th century as well as being a famous pianist. He is especially remembered for his conducting of the operas of Richard Wagner.
Bülow was born in Dresden. His family belonged to the nobility: he had the title of “Freiherr” (similar to the English Baron). When he was nine he had music lessons from Friedrich Wieck who was the father of Clara Schumann. However, his parents said that he had to study law instead of music, and they sent him to Leipzig.
During this time he met Franz Liszt in Weimar and he heard him conduct the music of Wagner. He decided to study music even though his parents did not want him to. He went to Zürich where Wagner was living in exile. Wagner thought he was very talented and got him some conducting jobs. In 1851 he went to Weimar to study the piano with Liszt. He worked very hard at his piano technique. He also wrote articles about music. Liszt also thought that von Bülow would become a great musician.
In 1853 Bülow made his first concert tour. He played in Vienna, Pest, Dresden, Karlsruhe, Bremen, Hamburg and Berlin. He taught the piano in Berlin and gave a lot of support to young composers who had new ideas about music. He toured as pianist and conductor in Germany and Russia. In 1857 he married Liszt’s daughter, Cosima. They had two daughters.
In 1864 he became the Hofkapellmeister in Munich. This was a very important conducting job and it made him extremely famous. He conducted the first performances of two Wagner operas: "Tristan und Isolde" (1865) and "Die Meistersinger von Nürnberg" (1868). These were extremely successful. Meanwhile Cosima was having a love affair with Richard Wagner. In 1868 she left her husband to live with Wagner, taking their daughters with her. She divorced Bülow, who went to Florence for a while to recover from the shock. However, he always continued to show great respect for Wagner and continued to conduct his music. When Wagner died in 1883 he was terribly sad.
In 1872 Bülow toured again. He visited England and the USA where, as the solo pianist, he gave the first performance (world premiere) of Tchaikovsky’s Piano Concerto No. 1 in Boston in 1875.
From 1878 to 1880 he was conductor in Hanover, but had to leave after a quarrel with a tenor. In 1880 he went to Meiningen where he conducted the orchestra, making it one of the best orchestras in Germany. He made the players perform from memory. He often conducted the music of Johannes Brahms. He thought about every detail of the pieces he conducted. He liked to have two pianos on the stage so that he could face the audience or have his back to them, whichever he wanted.
During this time he met Richard Strauss in Berlin. He helped Strauss, who was a young man at the time, to make his music well known
He did new things with his orchestra, such as introducing a double bass with five strings (this is now normal in most European orchestras). He also introduced timpani with pedals. In the late 1880s he settled in Hamburg, but continued to tour, both conducting and performing on the piano.
Bülow had health problems which gave him very bad headaches. He went to warmer countries to try to get better. He died in a hotel in Cairo, Egypt, ten months after his last concert performance.