Standing outside the low, gray industrial building, she watched as horses went in one side and, about 15 minutes later, a worker appeared on the other end, holding a head, neurons and all.“It was precisely as revolting as it sounds,” she says.Spalding would then spend hours chipping away to extract the necessary cells, a grisly procedure that was just the first in a decade-long stretch of hurdles she had to surmount.
But Spalding persevered, and her hard work eventually paid off.Last June, she published a paper in which she conclusively stated that adult human did indeed build new neurons in their brains.The human hippocampus, Spalding and Frisén discovered, was continually creating small numbers of neurons.Our bodies are prolific artists, creating new cells throughout the body.Some cells, like those found in skin, hair, and the lining of the gut, are produced and discarded on a regular basis, like doodles on scrap paper. Kirsty Spalding was one of the scientists who doubted that assessment.
Other cells, like those in the adult brain and nervous system, have been viewed as more like the Mona Lisa. Spalding, once a postdoc at the Karolinska Institute in Stockholm, Sweden and now a professor there, knew there were tantalizing hints that the adult hippocampus—a seahorse-shaped region deep in the brain that is important for memory and learning—could regenerate neurons.
But without knowing exactly when each neuron was created, scientists couldn’t say with any certainty that this was true.
Spalding and her postdoc advisor Jonas Frisén had a hunch that a pulse of radioactive carbon created by above-ground nuclear tests during the Cold War could help solve the riddle.
“A geopolitical phenomenon—this Cold War bomb testing—has, in a way, put a date stamp on everything and everybody,” Spalding says.
The bomb pulse has been declining since the 1963 above-ground test ban treaty, creating a sort of clock they could exploit.
By determining how many radioactive carbon atoms a cell contained, Spalding and Frisén hoped they could calculate its birthdate. Spalding’s curiosity eventually leading her to a slaughterhouse on the outskirts of Stockholm.