Academic journal article Environmental Health Perspectives

Prenatal PCB Exposure, the Corpus Callosum, and Response Inhibition

Academic journal article Environmental Health Perspectives

Prenatal PCB Exposure, the Corpus Callosum, and Response Inhibition

Article excerpt

The present study reports the association between prenatal exposure to polychlorinated biphenyls (PCBs), the corpus callosum, and response inhibition in children who are 4.5 years old. Children (n = 189) enrolled in the Oswego study were tested using a continuous performance test. We measured (square millimeters) the splenium of the corpus callosum, a pathway implicated in the regulation of response inhibition, using magnetic resonance imaging. Results indicated a dose-dependent association between cord blood PCBs and errors of commission. Splenium size but not other brain areas predicted errors of commission ([r.sup.2] = 0.20), with smaller size associated with more errors of commission. There was an interaction between splenium size and PCB exposure. The smaller the splenium, the larger the association between PCBs and errors of commission. If the association between PCBs and response inhibition is indeed causal, then children with suboptimal development of the splenium are particularly vulnerable to these effects. These data await replication. Key words: corpus callosum, impulsivity, inhibition, PCBs, polychlorinated biphenyls, splenium. Environ Health Perspect 111:1670-1677 (2003). doi:10.1289/ehp.6173 available via http://dx.doi.org/[Online 16 June 2003]

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Response inhibition is a behavioral process characterized by active termination of prepotent, ongoing, or otherwise routinized behaviors (Barkley 1997). As such, response inhibition is crucial to the ongoing regulation of behavior--the ability to change behavior in response to changing environmental contingencies, to withhold or delay responding when appropriate, and to inhibit responses that are no longer relevant or adaptive in new contexts. Response inhibition is a key behavioral process for the successful completion of many tasks such as the continuous performance task (Losier et al. 1996), fixed-interval (FI) schedules of reinforcement (Darcheville et al. 1992; Rice 1997; Sagvolden et al. 1998), and delayed-response paradigms (Rice 1999a). At a more molar level of behavioral analysis, Barkley (1997) has theorized that response inhibition is required for several downstream behavioral processes, including working memory, regulation of affect, and performance of rule-governed behavior. This is in large part because disruptive or potentially competing behaviors must be inhibited during the execution of these processes. Not surprisingly, response inhibition is frequently impaired in children with attention-deficit hyperactivity disorder (ADHD) (Klorman et al. 1991; Losier et al. 1996; Mota and Schachar 2000; Sagvolden et al. 1998; Schachar and Logan 1990; Schachar and Tannock 1993) and in animal models of this disorder (Berger and Sagvolden 1998; Sagvolden et al. 1992).

Evidence suggests that common neurotoxicants such as lead and polychlorinated biphenyls (PCBs) impair response inhibition in animals. Lead, in particular, has been reliably associated with impaired response inhibition in FI schedules of reinforcement (Cory-Slechta and Pokora 1991; Cory-Slechta et al. 2002), where low levels of lead cause rats to respond far in excess of the requirements of the reinforcement schedule. PCBs, a ubiquitous organochlorine contaminant in the environment, have also been associated with impaired response inhibition in rats in several studies (Berger 2001; Lilienthal et al. 1990). Possibly owing to differences in dosing and methodology, however, these results have not always been detected (Bushnell 2002; Holene et al. 1999). Most relevant to humans, however, is the work conducted with nonhuman primates, whose behavioral and physiologic characteristics are much closer to humans than are those of rats. Mele et al. (1986) showed that monkeys exposed to PCBs in utero responded excessively and inappropriately after reinforcement omission during schedule-controlled behavior. Even more pertinent is the work of Rice (1997, 1999b), who demonstrated PCB-induced impairments in response inhibition in monkeys on both FI and differential reinforcements of low rates. …

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