Toxic disorders and encephalopathy

The purpose of the present chapter is to selectively review the literature on the neuroanatomical, neuropsychological, and emotional/behavioral effects of exposure to four different substances: Organic solvents, lead, manganese_ (Mn), and carbon monoxide (CO). A discussion of all toxins is beyond the scope of this chapter. Rather, we chose to focus on the most common, the best researched, and, in our opinion, the most interesting. Recent research regarding each of these substances has provided a window into the mechanisms for changes in behavior and cognition. There are far too many substances known to affect the central nervous system to review them all here. In addition, the volume of literature on each of the substances we discuss is too large for comprehensive review. Rather, our goal is to provide clinicians with a theoretical background of the changes in behavior/emotions and cognition commonly observed with exposure to these substances, and to provide guidance for assessing exposed individuals. In this updated chapter, we have added a discussion of manganese, as there is a rapidly expanding literature on cognitive dysfunction with strong neuroimaging studies. We have also updated the other substances with some worthwhile additions to the literature. We will start with a general conceptualization of the cognitive neuroscience of toxic exposure before addressing each of the four substances. For each substance, we will review the particulars of exposure and symptom expression, the neurobehavioral symptoms, the neuroimaging changes, and the relationship among these. Based upon these findings, where possible, we will recommend areas to focus on and hypotheses to explore when evaluating patients with such exposures. We will address general themes for the assessment of patients with a history of toxic exposure, including measurement of exposure, determination of effort in medical-legal cases, and collaboration with occupational medicine specialists. Finally, we will comment where the field should focus on going forward.