Clucking sound wakes chick embryos
Chick embryos can be "woken up" in the egg long before hatching by rousing them with the sound of clucking hens, a study has shown.
The findings may have important implications for premature babies, researchers believe. "This work showed that embryo brains can function in a waking-like manner earlier than previously thought - well before birth," said study leader Dr Evan Balaban, from McGill University in Montreal, Canada.
"Like adult brains, embryo brains also have neural circuitry that monitors the environment to selectively wake the brain up during important events."
Dr Balaban's team devised experiments in which brain activity in unhatched chick embryos was monitored using an advanced PET (positron emission tomography) scanning technique.
The researchers found that during the final 20% of life before hatching, the chicks displayed brain activity that mirrored being asleep or awake. Wakefulness was only induced by "meaningful" recorded sounds of chickens clucking. "Non-vocal" noises had no effect.
Prior to this point in development, embryos were in a state that was "neither like sleep nor waking", said Dr Balaban. It was more akin to being comatose, or under anaesthetic.
Another surprise was that while their higher brain regions were inactive, the chicks showed a lot of spontaneous movement. Once they reached the threshold of 80% of development, movement ceased as they entered a "sleep-like state". At the same time, their higher brain regions burst into activity.
"The last 30% of foetal brain development is a more interesting time than we previously thought, because it's when complex whole-brain functions that depend on co-ordination of widely separated brain areas first emerge," said Dr Balaban. "Embryos begin to cycle through a variety of brain states and are even capable of showing waking-like brain activity."
The findings, published in the journal Current Biology, may explain instances of complex foetal and pre-birth learning, he said.
Dr Balaban added: "It also raises questions about the longer-term developmental consequences that such brain activity may have, if it is induced before intrinsic brain wiring is sufficiently completed, for example, in babies born very prematurely. We are excited by the possibility that the techniques developed here can now be used to provide answers to these questions."