While similar neurological blueprints exist for primates, MRI technology hadn't been used before to determine the precise volume and layout of brain structures in other species. Montie is especially interested in the size and positioning of the sea lion hippocampus, which plays a fundamental role in spatial memory and navigation.

"We don't know if there's a difference in the size of the hippocampus between (sea lion) males and females, or if there's a difference between young and old animals," Montie says. "We need to get an idea of what a normal hippocampus is supposed to look like throughout its lifetime."

Determining what's "normal" is the first step in tracing abnormal changes in the brain. Domoic acid poisoning occurs in other marine species and sea birds, but Montie says that sea lions seem to be more affected by domoic acid than related pinnipeds, including seals and walruses.

Exposure to manmade chemicals could be the key variable that makes them particularly vulnerable to the neurotoxin.

Sea lions breed around the Channel Islands off the California coast. Dr. John Ramsdell, a supervisory research physiologist who studies algal toxins at the National Oceanic and Atmospheric Administration, says that waters around the islands contain abnormally high levels of DDT and PCBs since nearby factories were once allowed to dump chemical waste directly into the sewage systems.

As a result, California sea lions have absorbed "monstrous levels" of the contaminants, Ramsdell explains. Female sea lions pass along harmful chemicals, especially DDT, to pups in utero and when they nurse.