Ziolkowski, M. | bioRxiv Science

bioRxiv2021

A four-point measurement probe for brain tissue conductivity and permittivity characterization

We present a measurement probe consisting of four platinum electrodes fused into soda-lime glass. The probe is based on a four-terminal sensing technique that uses separate pairs of current-carrying and voltage-sensing electrodes and performs more accurate measurements than the simpler and more usual two-terminal sensing technique. The electrodes are aranged within an area of 1 mm2 allowing for local characterization of different brain tissues. The operation of the probe is demonstrated in situ on post mortem porcine brain tissue by measuring the impedance spectra of grey and white matter in a frequency range of 1 kHz < f < 1 MHz. The conductivity and relative permittivity are derived from the impedance spectra using the geometry factor of the probe. The geometry factor is obtained experimentally by measuring the impedances of an electrolytical dilution series with known conductivities. The obtained conductivity of grey matter is in the order of 0.11 S/m and of white matter is in the order of 0.07 S/m over the acquired frequency range.

neuroscience↗

bioRxiv2021

Ancient genomes reveal long range influence of the site and culture of Tiwanaku

Tiwanaku was a civilization that flourished in the Lake Titicaca Basin (present-day Bolivia) between 500 and 1000 CE. At its apogee, Tiwanaku controlled the lakes southern shores and influenced certain areas of the Southern Andes. There is a considerable amount of archaeological and anthropological data concerning the Tiwanaku culture; however, our understanding of the population of the site of Tiwanaku is limited. To understand the population dynamics at different stages of the Tiwanaku cultural development, we analyzed 17 low-coverage genomes from individuals dated between 300 and 1500 CE. We found that the population from the Lake Titicaca Basin remained genetically unchanged throughout more than 1200 years, indicating that significant cultural and political changes were not associated with large scale population movements. In contrast, individuals excavated from Tiwanakus ritual core were highly heterogeneous, some with genetic ancestry from as far away as the Amazon, supporting the proposition of foreign presence at the site. However, mixed-ancestry individuals presence suggests they were local descendants of incomers from afar rather than captives or visiting pilgrims. A number of human offerings from the Akapana Platform dating to ca. 950 CE mark the end of active construction and maintenance of the monumental core and the wane of Tiwanaku culture. Significance StatementTiwanaku was an important pre-Inca polity in South America and an example of primary social complexity on par with civilizations in the Indus and Nile river valley. Flourishing between 500 and 1000 CE, Tiwanaku exercised control in the south Titicaca basin and influenced a vast area in southern Peru, Bolivia, and northern Chile. Comprehensive archeological studies provided information about the rise, expansion, and fall of the Tiwanaku culture, but little is known about the monumental sites population. To address this lacuna, we generated low coverage genomes for 17 individuals, revealing that while the Titicaca basins residential population was homogenous, the individuals excavated from the ritual core of Tiwanaku drew their ancestry from distant regions.

genomics↗

bioRxiv2020

In situ impedance measurements on postmortem porcine brain

The paper presents an experimental study where the distinctness of grey and white matter of an in situ postmortem porcine brain by impedance measurements is investigated. Experimental conditions that would allow to conduct the same experiment on in vivo human brain tissue are replicated. https://doi.org/10.1515/cdbme-2019-XXXX

neuroscience↗