Behavioral and psychophysiological markers of disordered attention.

Behavioral and psychophysiological assays provide the most sensitive indication of whether a presumed neurotoxin has a deleterious effect on the nervous system. The effects of lead on the nervous system are strongly suggestive that this agent can produce disturbances in attention; moreover, there are clinical reports of such effects. The action of lead is also manifest in behaviors described as "hyperactive," or reflecting "minimal brain damage." The core symptom in both disorders is probably impairment in attention. The recent Diagnostic and Statistical Manual (DSM-III) of the American Psychiatric Association uses the term Attention Deficit Disorder to replace such terms as hyperactivity and minimal brain damage. Prior studies of the behavioral toxicity of lead may have used inadequate or incomplete assays of attention; this could in part account for the variability in outcomes. Recent research on attention suggests that it is a complex behavior consisting of a number of elements or components, each of which may be in part dependent upon a different region of the central nervous system. Behavioral assays should examine the components of attentive behavior using tests which are sensitive to the different elements. It is recommended that psychophysiological assays (using cognitive event-related potentials), although more difficult and costly to implement, be used as well. These assays may provide a more dynamic view of altered information processing in the brain and help to localize and characterize the behavioral impairment.