Objective: The aim of this study was to investigate if cranial ultrasound during development can impair learning and memory.
Methods: The brains of chick embryos were scanned in either B-mode or Pulsed Doppler (PD) mode for various durations during gestation at E19 of the 21 day incubation. Brains were exposed to B-mode for either 5 or 10 minutes or to PD-mode for 1,2,3,4 or 5 minutes using a Philips ATL 5000 and a 15-7 MHz linear array transducer. Control animals were sham exposed. Chicks were allowed to hatch and at 2 days post hatch, the bead discrimination test was used to assess short-, intermediate- and long-term memory as well as re-training ability. Statistical analyses were carried out using one-way ANOVA.
Results: Chicks exposed to B-mode demonstrated normal memory retention (p>0.05). Exposure to Pulsed Doppler mode, however, resulted in a duration-dependant reduction in long-term memory. When exposed to more than 4 minutes of Pulsed Doppler mode, long-term memory loss was highly significant (p=0.004). The finding that short-and intermediate memory were affected after extended exposure to PD ultrasound suggested that their ability to learn in the first place was impaired. Hence, after a second training trial, these chicks were still unable to learn.
Conclusion: These results show that learning in newborn chicks is significantly impaired after extended exposure to PD ultrasound. Until further evidence is available, it would seem prudent to minimise PD use among premature newborns as well as term babies who have been compromised during delivery.