For the study, different doses of low-level lead, cadmium, and mercury were administered to Sprague-Dawley rats via drinking water during the critical stage of brain development, late stage, and after maturation. The findings showed that exposure to the toxic heavy metals decreased the density of memory- and learning-related dendritic spines in the hippocampus during the critical period of brain development, resulting in hippocampus-dependent spatial memory deficits. During the late phase of brain development, only the density of learning-related dendritic spines was reduced and higher doses of the metals were required to cause an effect, which led to hippocampus-independent spatial memory abnormalities.

However, exposure to lead, cadmium, and mercury after brain maturation revealed no significant change in dendritic spines or cognitive function. The study’s authors recommend focusing on mitigating exposure to lead, cadmium, and mercury from water or food during early brain development as much as possible.