Science Image (image) Salk Institute Share Print E-Mail Caption Nuclei (blue) of the medial prefrontal cortex neurons projecting their axons (green) to the periaqueductal gray area. Credit Salk Institute Usage Restrictions with credit and related coverage. Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.