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Smart Sperm Memory
If human sperm turn in one direction, they will turn in the opposite direction at the next opportunity, Peter Brugger, a neurobiologist at University Hospital, Zurich, has found.
"It's certainly not cognitive memory," he says. But they must have some kind of memory.
This kind of behaviour, known as spontaneous alternation behaviour, is found in a wide range of creatures. To see whether human sperm cells exhibit it, Brugger recorded which way 714 healthy sperm cells turned when confronted with a left or right choice in a T-shaped channel. As expected, half the sperm went left and half went right.
But in a maze that forced the sperm to turn right before they reached the T-junction, 58 per cent turned left.
Brugger, whose work will appear in Behavioural Brain Research, thinks the percentage that "remember" which way to turn would be even greater if the maze were smaller. The sperm had to swim 10 times their body length after the forced turn, so some of them may already be "forgetting".
One simple explanation could be that each turn causes an asymmetry in the mechanism that controls a cell's tail, or flagellum. It then compensates by turning in the opposite direction next time.
But it is also possible that the sperm are somehow communicating. "They could be flocking," Brugger says. To test this, he plans to repeat the experiment one sperm at a time.
In the body, sperm follow a chemical trail to the egg. "But they may have choices [of which way to turn] when they get very close to the egg," says reproductive biologist Harry Moore of the University of Sheffield. Testing for alternation behaviour could be a way to check the health of sperm used for IVF, he adds.
Paul Ellis - Men's Health
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