Haaretz reports that Yafit Kedar and Ran Barkai of Tel Aviv University suggest that Europe’s Paleolithic artists may have experienced hypoxia, or lack of oxygen, while painting by torchlight in remote areas of caves.

The researchers simulated deep caves entered through narrow mouths and long corridors with software created to plan ventilation for underground parking lots. They found that the use of fire deep in a cave would have caused a significant drop in oxygen levels.

The dark cave spaces may have been chosen, the researchers explained, because this lack of oxygen produced euphoric, transformative experiences, and perhaps even hallucinations, making them sacred spaces. The caves were thus painted, Kedar and Barkai explain, to reflect their significance. The rock face itself may have been understood as a connection to another world.