Ultrasound exposure of the foetal chick brain: effects on learning and memory.

Ultrasound imaging of the brain is routinely used to monitor the development and resolution of brain lesions among premature and compromised newborn human babies. However, animal studies have shown that ultrasound can cause damage to developing foetal and neonatal tissues. In this study we investigated if ultrasound of the chick brain can lead to learning and memory impairment after hatch. We exposed the brains of chicks on day 19 of a 21 day incubation period to 5 or 10 min of B-mode, or to 1, 2, 3, 4 or 5 min of pulsed Doppler ultrasound in ovo. Learning and memory function were assessed at day 2 post-hatch. Our results show that B-mode exposure at E19 does not affect memory function. On the other hand, 2h after training, significant memory impairment occurred following 4 and 5 min of pulsed Doppler exposure at E19. In separate groups of chicks, short-, intermediate- and long-term memory was equally impaired suggesting an inability to learn. Further, the chicks were still unable to learn with a second training session 5 min after completion of the initial testing. These results demonstrate that extended exposure to pulsed Doppler ultrasound can adversely affect cognitive function in the chick when exposure occurs close to the time of hatch.