Friendship ornaments from the Stone Age

Roughly 6,000 years ago, hunter-gatherer communities in northeast Europe produced skillfully manufactured slate ring ornaments in great numbers. While these ornaments are commonly referred to as 'slate rings', they were rarely used as intact rings. Instead, the ornaments were fragmented on purpose, using pieces of rings as tokens. These fragments were further processed into pendants.

The fragments have most likely served as symbols of the social relations of Stone Age hunter-gatherers.

Purposeful fragmentation of ornaments

As most archaeological material is found in a fragmented state, the phenomenon has been considered a natural consequence of objects' having been long buried underground. However, according to Postdoctoral Researcher Marja Ahola from the University of Helsinki, not all objects have necessarily been broken by accident. Instead, it is possible some were fragmented on purpose as part of maintaining social relations, bartering or ritual activities. The research now completed has demonstrated that a substantial number of ornaments have been found in extensive and central locations. As some of the ornaments originate in Lake Onega region and have been transported to Finland through a widespread exchange network, it is possible that they symbolise the connections established within the network.

By matching pieces of slate ring ornaments, analysing their geochemical composition and investigating traces of use and manufacture in the objects, a research group at the University of Helsinki and the University of Turku demonstrated that the ornaments had not only been worn, but also intentionally broken. Because fragments from the same ornament were found in two different locations, it is possible that they were worn by two different individuals. Another indication of this is the fact that one of the fragments had been worked on more finely than the other.

"These fragments of the same object may show the handprint and preferences of two individuals. Perhaps they wore the ornaments as a symbol of a connection established," Ahola muses.

A similar link was found in slate ring ornaments created during the same manufacturing process, one of which was found in a settlement-site context and the other in a burial site investigated near the settlement.

"What we see here may be one way of maintaining connection between the living and the dead. This is also the first clear material connection between a certain place of residence and a burial site. In other words, the people who lived there most likely buried their dead in a site close to them," Ahola explains.

An X-ray fluorescence analysis (XRF) of a little over 50 slate ring ornaments demonstrated that some of the ornaments or fragments thereof had been imported from Lake Onega region, Russia, hundreds of kilometres from the site where they were found. XRF analyses can be used to determine the element concentrations and raw materials of inorganic archaeological materials with a very high precision. The technique can be applied as an entirely non-invasive surface analysis, which makes it perfectly suited to the study of archaeological objects.

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'Math neurons' identified in the brain

The brain has neurons that fire specifically during certain mathematical operations. This is shown by a recent study conducted by the Universities of Tübingen and Bonn. The findings indicate that some of the neurons detected are active exclusively during additions, while others are active during subtractions. They do not care whether the calculation instruction is written down as a word or a symbol. The results have now been published in the journal Current Biology.

Most elementary school children probably already know that three apples plus two apples add up to five apples. However, what happens in the brain during such calculations is still largely unknown. The current study by the Universities of Bonn and Tübingen now sheds light on this issue.

The researchers benefited from a special feature of the Department of Epileptology at the University Hospital Bonn. It specializes in surgical procedures on the brains of people with epilepsy. In some patients, seizures always originate from the same area of the brain. In order to precisely localize this defective area, the doctors implant several electrodes into the patients. The probes can be used to precisely determine the origin of the spasm. In addition, the activity of individual neurons can be measured via the wiring.

Some neurons fire only when summing up

Five women and four men participated in the current study. They had electrodes implanted in the so-called temporal lobe of the brain to record the activity of nerve cells. Meanwhile, the participants had to perform simple arithmetic tasks. "We found that different neurons fired during additions than during subtractions," explains Prof. Florian Mormann from the Department of Epileptology at the University Hospital Bonn.

It was not the case that some neurons responded only to a "+" sign and others only to a "-" sign: "Even when we replaced the mathematical symbols with words, the effect remained the same," explains Esther Kutter, who is doing her doctorate in Prof. Mormann's research group. "For example, when subjects were asked to calculate '5 and 3', their addition neurons sprang back into action; whereas for '7 less 4,' their subtraction neurons did."

This shows that the cells discovered actually encode a mathematical instruction for action. The brain activity thus showed with great accuracy what kind of tasks the test subjects were currently calculating: The researchers fed the cells' activity patterns into a self-learning computer program. At the same time, they told the software whether the subjects were currently calculating a sum or a difference. When the algorithm was confronted with new activity data after this training phase, it was able to accurately identify during which computational operation it had been recorded.

Prof. Andreas Nieder from the University of Tübingen supervised the study together with Prof. Mormann. "We know from experiments with monkeys that neurons specific to certain computational rules also exist in their brains," he says. "In humans, however, there is hardly any data in this regard." During their analysis, the two working groups came across an interesting phenomenon: One of the brain regions studied was the so-called parahippocampal cortex. There, too, the researchers found nerve cells that fired specifically during addition or subtraction. However, when summing up, different addition neurons became alternately active during one and the same arithmetic task. Figuratively speaking, it is as if the plus key on the calculator were constantly changing its location. It was the same with subtraction. Researchers also refer to this as "dynamic coding."

"This study marks an important step towards a better understanding of one of our most important symbolic abilities, namely calculating with numbers," stresses Mormann. The two teams from Bonn and Tübingen now want to investigate exactly what role the nerve cells found play in this.

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