Boucher et al. are no longer adequate to meet the demands of the task (Norman and Shallice 1986). In the current review, four aspects of EFs were considered: response inhibition, planning, set shifting, and the executive component of working memory. Associations between prenatal PCB exposure and these functions are summarized in Table 7. Poorer response inhibition has been consistently related to prenatal PCB exposure in both the Michigan and the Oswego cohorts. The significant effect reported in Oswego, one of the leaste­xposed cohorts, suggests that this aspect is likely to be very sensitive to PCB exposure. Effects on task planning were also observed in both cohorts that documented this EF (Netherlands and Michigan). However, in the Netherlands, planning effects were reported using the Tower of London test but not the copy of the Rey Complex Figure. These different tasks solicit different processes. For instance, the Tower of London test is more likely to require response inhibition (Miyake et al. 2000). Finally, set shifting and working memory, documented in 11­year­old children from the Michigan cohort, were affected by PCB exposure in non­ breast­f ed children. Altogether, these observations may suggest that EFs are par­ ticularly affected by prenatal PCB exposure. Replication of these results is needed before definite conclusions can be drawn. Sensory and motor functions. Performance on many neurobehavioral cognitive tasks can be affected by sensory impairments or motor dif­ ficulties. It thus appears important to make sure that the aforementioned PCB effects are not the indirect consequences of alterations in those modalities. This is the object of the final step of the present neuropsychological analysis. Studies documenting effects of PCB exposure on sen­ sory functions are summarized in Table 8. Results suggest that it is possible that prenatal PCB exposure alters the auditory system in a very subtle manner. However, this effect, if present, is unlikely to be strong enough as to influence performance on neurobehavioral tasks requiring the auditory modality (e.g., language assessments and auditory spans). Table 7. Study results on EF. EF Response inhibition Cohorta Oswego Michigan Netherlands Michigan Michigan Michigan Planning Set shifting Working memory 12 Results from psychomotor development and motor functioning assessments are pre­ sented in Table 9. The global portrait of results suggests that motor functions during childhood are not particularly affected by prenatal PCB exposure. Thus, decreased per­ formance on neurobehavioral tests requiring physical (e.g., hand, fingers) response (e.g., Continuous Performance Test, Tower of London) is more likely to be related to actual cognitive impairments rather than to specific motor dysfunction. Discussion The present review suggests that prenatal expo­ sure to PCBs is associated with a fairly specific profile of cognitive impairments in children. Among the cognitive functions assessed in the different studies, detrimental effects have been established more clearly for EFs. In many cases, negative effects have also been observed for speed of information processing, verbal abili­ ties, and visual recognition memory. However, there is relatively little evidence of effects on visual–spatial abilities, episodic memory, and sustained attention. Effects appear to be inde­ pendent of sensory and motor functions. More data are needed to document effects on other cognitive functions. Most consistent results across studies sug­ gest particular vulnerability of EFs to prenatal PCB exposure. Different studies have found that efficiency in planning, executive working memory, set shifting, and especially response inhibition decrease as a function of levels of PCBs. Because the prefrontal structures of the brain are thought to be of particular impor­ tance in these highero­rder functions (Jurado and Rosselli 2007), one can hypothesize that the development of the prefrontal cortex is affected by PCB exposure. This hypothesis is in accordance with animal studies that showed disturbance in dopamine levels of the prefron­ tal cortex (Seegal et al. 2005) in rats exposed to PCB congeners in utero. However, other structures are also involved in the execution of controlled behaviors in humans (Pillon and Dubois 2005), and specific injury to prefrontal cortex alone is not likely to explain other partic­ ularities of the cognitive profile associated with prenatal PCB exposure (e.g., decreased process­ ing speed; Vreugdenhil et al. 2004b). Thus, direct evidence of brain structural or functional alterations could help in relating prenatal PCB exposure to prefrontal cortex integrity (e.g., Cecil et al. 2008; Jonkman et al. 2007). EFs are sensitive to several disorders such as atten­ tion deficit and hyperactivity disorder, autism, and obsessive­compulsive disorder (Barkley 1997; Happé et al. 2006; Hughes et al. 1994; Olley et al. 2007), and to other neurotoxicants such as lead, marijuana, and cocaine (Canfield et al. 2004; Fried and Smith 2001; Mayes et al. 2005). This greater sensitivity to tasks designed to assess EFs may be related to their dependence on the integrity of multiple neural systems. Use of more focused tests would further our under­ standing of the specific end points responsible for the aforementioned deficits. In addition, failure to observe detrimental effects of PCB exposure on child cognition in the CPP, North Carolina, and Faroese cohorts might be related to the absence of specific EF assessments in those studies. Although the effects of PCBs on the speed of information processing are strongly suggested by the present review, some ques­ tions still remain for another central aspect of attention—selective attention. First, only the Michigan study used specific tests of selec­ tive attention, and the results obtained were inconsistent. Second, the present literature review did not succeed in discriminating the relative contribution of attention allocation, working memory, and shortt­erm memory to the effects observed on memory performance. For the moment, one can hypothesize that the documented effects on EFs are responsible for effects observed on numeric span subtests when the backward condition is used. Other specific impairments caused by prenatal PCB exposure are highlighted by the distinction between verbal and visual­ spatial functions; in most studies, the former are affected, whereas the latter are not. The distinction between verbal and visual–spatial Measurement CPT commission errors CPT commission errors DRL inter-response times CPT commission errors Sternberg Memory errors of commission CPT commission errors Tower of London Rey Complex Figure Test copy strategy WISC-R Labyrinth WCST perseverative errors WISC-R Arithmetic Reference Stewart et al. 2003a Stewart et al. 2005 Stewart et al. 2006 Jacobson and Jacobson 2003 Jacobson and Jacobson 2003 Jacobson and Jacobson 2003 Vreugdenhil et al. 2004a Vreugdenhil et al. 2004a Jacobson and Jacobson 1996 Jacobson and Jacobson 2003 Jacobson and Jacobson 2003 ovlume 117 | number 1 | January 2009 • Environmental Health Perspectives Age (years) Effect 4.5 8, 9.5 9.5 4 4 11 9 9 11 11 11 ↓ ↓ ↓ – ↓ ↓b ↓ – ↓ ↓b ↓b Abbreviations: ↓, statistically significant decreased performance on the measure; –, absence of significant effect. Tests: DRL, Differential reinforcement of low rates schedules [based on Sagvolden et al. (1998)]; Tower of London (Shallice 1982); WCST, Wisconsin Card Sorting Test (Grant and Berg 1948); WISC, Wechsler Intelligence Scale for Children (Wechsler 1991). aCohorts are presented in ascending order of median prenatal PCB exposure. bDecrease is significant only in non-breast-fed children.