Howard Eichenbaum, a neuroscientist at Boston University, and collaborators showed that cells in rats that form the brain’s internal GPS system, known as grid cells, are more malleable than had been anticipated. Typically these cells act like a dead-reckoning system, with certain neurons firing when an animal is in a specific place. (The researchers who discovered this shared the Nobel Prize in 2014.) Eichenbaum found that when an animal is kept in place — such as when it runs on a treadmill — the cells keep track of both distance and time. The work suggests that the brain’s sense of space and time are intertwined.
The findings help to broaden our understanding of how the brain’s memory and navigation systems work. Perhaps both grid cells and other GPS-like cells aren’t tuned only to space but are capable of encoding any relevant property: time, smell or even taste. “It probably points to a broad thing the hippocampus does,” said Loren Frank, a neuroscientist at the University of California, San Francisco, who studies memory and the hippocampus. “It figures out the relevant axis for encoding experiences and then uses the cells to map those experiences.”
Buzsáki points out that it may not even make sense to think of hippocampal cells as independently coding for space or time. The human brain often considers time and distance interchangeably. “If one asks how far New York is from LA, the answers you get vary: 3,000 miles, six hours by flight,” he said. “In older language, distances were typically given by time — the days it takes to go from one valley to another — since it was not distance but the number of sunsets that was easy to calculate.”
For Buzsáki, the issue goes beyond neuroscience and reaches into physics. Physicists consider space-time as a cohesive, four-dimensional entity, a fabric upon which the objects and events of the universe are embedded. “Neuroscience must converge back to the old problem of physics: Are there place and time cells? Or is there only a single time-space-continuum representation in the brain?” Buzsáki said.
During Running in Place, Grid Cells Integrate Elapsed Time and Distance Run
Benjamin J. Kraus, Mark P. Brandon, Robert J. Robinson II, Michael A. Connerney, Michael E. Hasselmo, Howard Eichenbaum
•Time and distance coding by grid cells can be studied in rats running in place •In this task, grid cell activity reflects a combination of time and distance coding •Grid cells are more sharply tuned to time and distance than non-grid cells •Many grid cells exhibit multiple time and distance fields
The spatial scale of grid cells may be provided by self-generated motion information or by external sensory information from environmental cues. To determine whether grid cell activity reflects distance traveled or elapsed time independent of external information, we recorded grid cells as animals ran in place on a treadmill. Grid cell activity was only weakly influenced by location, but most grid cells and other neurons recorded from the same electrodes strongly signaled a combination of distance and time, with some signaling only distance or time. Grid cells were more sharply tuned to time and distance than non-grid cells. Many grid cells exhibited multiple firing fields during treadmill running, parallel to the periodic firing fields observed in open fields, suggesting a common mode of information processing. These observations indicate that, in the absence of external dynamic cues, grid cells integrate self-generated distance and time information to encode a representation of experience.
Just how do you navigate in open waters without a compass when it is cloudy? Sunstones have been proposed. In theory you can use polarization of the available light and combine that information with a sundial to figure out where the Sun is.
Several researchers have tried to duplicate this over the years with poor results. Another attempt appear in the Royal Society Open Science journal. They find it is sort of possible with very clear cordierite crystals with tourmaline crystals being the next choice. It is still very iffy.
Adjustment errors of sunstones in the rst step of sky-polarimetric Viking navigation: studies with dichroic cordierite/ tourmaline and birefringent calcite crystals
Dénes Száz1, Alexandra Farkas1,2, Miklós Blahó1, András Barta1,3, Ádám Egri1,2,3, Balázs Kretzer1, Tibor Hegedüs4, Zoltán Jäger4 and Gábor Horváth1
1Environmental Optics Laboratory, Department of Biological Physics, Physical Institute, Eötvös University, Pázmány sétány 1, Budapest 1117, Hungary 2 Danube Research Institute, MTA Centre for Ecological Research, Karolina út 29–31, Budapest 1113, Hungary 3Estrato Research and Development Ltd, Nemetvolgyi ut 91/c, Budapest 1124, Hungary 4Astronomical Observatory of Baja, University of Szeged, Pf. 766, Baja 6500, Hungary
According to an old but still unproven theory, Viking navigators analysed the skylight polarization with dichroic cordierite or tourmaline, or birefringent calcite sunstones in cloudy/foggy weather. Combining these sunstones with their sun-dial, they could determine the position of the occluded sun, from which the geographical northern direction could be guessed. In psychophysical laboratory experiments, we studied the accuracy of the first step of this sky-polarimetric Viking navigation. We measured the adjustment error e of rotatable cordierite, tourmaline and calcite crystals when the task was to determine the direction of polarization of white light as a function of the degree of linear polarization p. From the obtained error functions e(p), the thresholds p* above which the first step can still function (i.e. when the intensity change seen through the rotating analyser can be sensed) were derived. Cordierite is about twice as reliable as tourmaline. Calcite sunstones have smaller adjustment errors if the navigator looks for that orientation of the crystal where the intensity difference between the two spots seen in the crystal is maximal, rather than minimal. For higher p (greater than pcrit) of incident light, the adjustment errors of calcite are larger than those of the dichroic cordierite (pcrit=20%) and tourmaline (pcrit=45%), while for lower p (less than pcrit) calcite usually has lower adjustment errors than dichroic sunstones. We showed that real calcite crystals are not as ideal sunstones as it was believed earlier, because they usually contain scratches, impurities and crystal defects which increase considerably their adjustment errors. Thus, cordierite and tourmaline can also be at least as good sunstones as calcite. Using the psychophysical e(p) functions and the patterns of the degree of skylight polarization measured by full-sky imaging polarimetry, we computed how accurately the northern direction can be determined with the use of the Viking sun-dial under 10 different sky conditions at 61° latitude, which was one of the main Viking sailing routes. According to our expermiments, under clear skies, using calcite or cordierite or tourmaline sunstones, Viking sailors could navigate with net orientation errors |Σmax|≤3°. Under overcast conditions, their net navigation error depends on the sunstone type: |Σmax(calcite)|≤6° , |Σmax(cordierite)|≤10° and |Σmax(tourmaline)|≤17°∘
While you can measure the energy content of food understanding how a specific metabolism handles specific foods and measuring what a person eats are inexact. It can be useful if it enforces mindful eating, but something better is needed. An excellent post in Mosaic from an episode of the Gastropod podcast.
By delving into older, purely mathematical Babylonian texts written between 1800 B.C.E. and 1600 B.C.E., which also described computations with a trapezoid, he realized that the astronomers who made the tablets had gone a step further. To compute the time at which Jupiter would have moved halfway along its ecliptic path, the astronomers divided the 60-day trapezoid into two smaller ones of equal area. The vertical line dividing the two trapezoids marked the halfway time; because of the different shapes of the trapezoids, it indicated not 30 days but slightly fewer.
The Babylonians had developed “abstract mathematical, geometrical ideas about the connection between motion, position and time that are so common to any modern physicist or mathematician,” Ossendrijver says.
Indeed, compared with the complex geometry embraced by the ancient Greeks a few centuries later, with its cycles and epicycles, the inscriptions reflect “a more abstract and profound conception of a geometrical object in which one dimension represents time,” says historian Alexander Jones of New York University in New York City. “Such concepts have not been found earlier than in 14th century European texts on moving bodies,” he adds. “Their presence … testifies to the revolutionary brilliance of the unknown Mesopotamian scholars who constructed Babylonian mathematical astronomy.”
Mr Stuart, a theatrical mask-maker and scenic artist, founded Mechanimals at his Bluegate Studio in Thaxted in the early 1950s after watching donkeys taking children for rides at the seaside.
He set about making petrol-driven pachyderms, modelled on Asiatic elephants, each capable of taking up to 12 passengers for pleasure rides in a howdah, an elephant carriage.
He thought although it was cheaper to buy a real elephant, feeding and stable costs would be much greater than the cost of petrol, making his creations a bargain for seaside and theme park operators. He was not happy with the initial stiff-legged elephants as they were not realistic enough, so his employee Maurice Radburn came up with a working, walking model.
An eight-foot-tall and 12-foot-wide elephant was then constructed.