Prenatal exposure to marihuana and tobacco during infancy, early and middle childhood: effects and an attempt at synthesis.

Both marihuana and cigarettes appear implicated, in a differential fashion, in the neurobehaviour of infants and children born to women who used these substances during pregnancy. In a low-risk upper middle class sample, marihuana use was associated, in the newborn, with mild withdrawal symptoms and some autonomic disruption of nervous system state regulation. However, between 6 months and 3 years of age no behavioural consequences of marihuana exposure (once confounding factors were controlled) were noted. At four years of age, although global tests of intelligence did not differentiate exposed from non-marihuana exposed children, verbal ability and memory were associated with in utero marihuana exposure. At five and six years of age these general areas were also noted to be associated with maternal cannabis use as was sustained attention. These areas of neurobehavior that appear affected by marihuana exposure during fetal development are ones that are consistent with the cognitive construct of 'executive functioning' which is thought to be a marker of prefrontal lobe functioning. Consistent with the observations derived from these children is that prefrontal functioning may not be apparent until approximately four years of age and that executive functioning is disassociated from measures of global intelligence. Exposure to cigarettes during pregnancy appears to be associated with neurobehavioural deficits in the auditory domain. In the newborn this is manifested by decreased responsivity to sound and altered auditory habituation. Between the ages of one and 11 years the performance on auditory related tasks (verbal memory, language, auditory processing) were consistently the domains that differentiated the cigarette exposed from the non exposed children. The possible role of the cholinergic mediated efferent auditory system is discussed. Also associated with in utero exposure to cigarettes were general cognitive performance and parental reports and objectively derived measures of impulsivity. The striking degree of consistency over the years lends strength to the interpretation that the observations in childhood have, at least as their partial etiology, the prenatal exposure to cigarettes. However, in interpreting the evidence presented it must be recognized that the alterations in the child's behaviour may well affect the parenting behaviour. This potential transactional interaction must remain an integral part of drawing conclusions about both marihuana and cigarette's effects.