Repeated exposure to a common anaesthesia drug early in life leads to visual recognition memory impairment, which may persist for a long time, a new study warns.

Impairment in visual recognition memory emerges after the first year of life, researchers said.

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"Our results confirm that multiple anaesthesia exposures alone result in memory impairment in a highly translational animal model," said Mark Baxter, professor at Icahn School of Medicine at Mount Sinai in the US.

Researchers exposed 10 non-human primate subjects to a common paediatric anaesthetic for four hours, the length of time required for a significant surgical procedure in humans.

The primates were exposed to the anaesthetic at postnatal day seven and then again two and four weeks later. This was done because human data indicates that repeated anaesthesia results in a greater risk of cognitive disability relative to a single anaesthetic exposure.

Researchers evaluated the visual recognition memory of exposed subjects compared with that of healthy controls at 6- 10 months of age, 12-18 months of age and again at 24-30 months of age using the visual paired comparison test, which measures memory by assessing preference for looking at a new image over a previously viewed one.

They found the anaesthesia-exposed infants displayed no memory impairment when tested at 6-10 months, but demonstrated significant memory impairment (reduced time looking at the novel image) after the first year of life compared with the control group.

"Interestingly, the anaesthesia-exposed group had normal visual memory at six months of age. Visual memory impairment didn't emerge until the second year of life, corresponding roughly to the age of three to six years old in humans," Baxter said.

Researchers used rhesus monkeys as at birth they are in a stage of neurodevelopment that is more similar to that of human infants than are neonatal rodents, with respect to brain growth, a six-week-old rhesus monkey corresponds to a human 6 to 12 months of age.

The study was published in the British Journal of Anaesthesia.