Development and Psychopathology, 12 (2000), 695–712
Copyright 2000 Cambridge University Press
Printed in the United States of America
The role of early experience in shaping
behavioral and brain development and its
implications for social policy
GERALDINE DAWSON, SHARON B. ASHMAN,
LESLIE J. CARVER
University of Washington
This article provides a targeted review of the scientific literature on the effects of experience on early brain and
behavioral development and later outcome as it pertains to risk for some forms of child psychopathology. It is
argued that ample evidence exists indicating that the prenatal and early postnatal years likely represent a sensitive
period with respect to the effects of stress on the developing nervous system and behavioral outcome, and with
respect to the long-term beneficial effects of early interventions on brain and behavioral development for some
genetically based disorders, such as phenylketonuria and autism. Moreover, evidence suggests that parental mental
health during the first years of life has a significant influence on early brain activity and behavior, and long-term
behavioral outcome. It is concluded that, although prevention and early intervention efforts should not exclusively
focus on the earliest years of development, such efforts should begin during this period. By directing such efforts
toward promoting optimal prenatal and infant–toddler development, the long-term negative consequences of factors
that have their greatest influences during early development and which set the stage for future development can be
minimized or avoided entirely. Several recommendations for public policy and future research pertaining to the
effects of early experience on child outcome are offered.
from birth to 3 years; the Family and Medical
Leave Act enacted in 1993, which recognized
In the past few decades, efforts at promoting
optimal development in children have increas-
ingly focused on the earliest years of life, the importance of parents spending time with
their young infants after birth before returningincluding the prenatal period, infancy, and
toddlerhood. Broad-based policy changes re- to work; and Early Head Start created in
1994, which provided education and childcareflecting a focus on early development have
included PL 99-457 enacted in 1986, which to at-risk children from birth to 3 years. The
rationale behind these efforts has been basedprovided services to handicapped children
largely on an increased understanding of nor-
mal infant behavior and development and of
The writing of this article and the research on the effects the negative influences of factors such as poor
of maternal depression on infant brain activity reported
nutrition, drug exposure, abuse and neglect,
herein were supported by grants from the National Insti-
and parent psychopathology and stress on
tute of Mental Health (MH47117) and the National Insti-
early development and later outcome (Nelson,
tutes of Child Health and Human Development, and
Deafness and Communication Disorders (POIHD34565).
Lara Embry, Karin Frey, Lili Lengua, Charles Nelson, The idea that early experience is important
and Joanna Self provided helpful critiques of early ver-
for promoting optimal long-term outcomes for
sions of this paper.
children has been supported by studies of be-
Address correspondence and reprint requests to: G.
havioral outcomes and early intervention in
Dawson, Department of Psychology and Center on Hu-
various at-risk and developmentally disabled
man Development and Disability, Box 357920, Univer-
sity of Washington, Seattle, WA 98195. populations. Examples of such research in-
G. Dawson, S. B. Ashman, and L. J. Carver696
clude studies of (a) the effects of prenatal nu- tion discussed the importance of the new
brain science for understanding children’s de-trition and exposure to toxic substances on
brain and behavioral development (Morgan & velopment and for public policy. As a result,
leaders in several states enacted policyGibson, 1991; Sonderegger, 1992; Spohr,
Williams, & Steinhausen, 1993); (b) the ef- changes based on what they viewed as the
new research on brain development. Numer-fects of maternal depression during pregnancy
and infancy on later cognitive and emotional ous policy initiatives and exploratory panels
emerged to address the issue of early experi-functioning in children (Goodman & Gotlib,
1999); and (c) the effects of early interven- ence and brain development in several states
(Groginsky, Christian, & McConnell, 1998).tions for improving cognitive, social, and aca-
demic functioning in children from economi- In 1997, the Federal Early Childhood Devel-
opment Act was introduced, stressing the im-cally and socially disadvantaged backgrounds
(Campbell & Ramey, 1994) and in children portance of early experience on brain devel-
opment and outcome for children.with genetic disorders that affect brain devel-
opment, such as autism and phenylketonuria The recent public and political enthusiasm
over the effects of early environment on brain(PKU; Dawson & Osterling, 1997; Wappner,
Cho, Kronmal, Schuett, & Seashore, 1999). development subsequently led to a backlash
among some scientists who were concernedAt the same time that research and policy
have increasingly stressed the importance of that the public and policymakers have over-
simplified a complex issue. In fact, the publicearly experience in the development of chil-
dren, new techniques for studying infant be- hype over the implications of brain science
and the resulting recent critiques and contro-havior and brain activity have been devel-
oped, allowing developmental scientists to versy may have had the unfortunate effect of
a waning of interest in early childhood, withbegin to learn more about relations between
biology and behavior in infants and children a loss of policies with the potential to benefit
children (Thompson & Nelson, in press).(reviewed in Dawson & Fischer, 1994). In the
1990s, as these intriguing studies were pub- Nevertheless, scientists such as Bruer (1999),
Greenough (1997), and others have raised im-lished and discussed in the popular media,
public interest in early brain development and portant questions regarding what is actually
known about the effects of early experiencebehavior began to swell. The effects of early
experience on the developing brain, in partic- on brain development. In his recent book,
Bruer (1999) argues that the media have beenular, became of interest after a White House
conference on the topic was held in the spring misguided in promoting the myth that the first
3 years of a baby’s life can determine aof 1997. The White House conference coin-
cided with a national media campaign focused child’s long-range outcome. He further de-
scribes what he refers to as “three neuroscien-on early development, which included broad-
casts on “Good Morning America” and fea- tific strands” that taken together form the
“myth of the first three years.” In this article,ture articles in Newsweek. Concurrently, pub-
lic policy documents on the relation between we will discuss each of these strands and what
can be scientifically concluded about their im-brain science and early development were
published by major foundations interested in portance for understanding the effects of early
experience on later outcome. We will coverpromoting the health and welfare of children,
including Starting Points, published by the in some detail what is known about the devel-
opment and underlying mechanisms involvedCarnegie Corporation, and Rethinking the
Brain: New Insights Into Early Development, in synaptic formation and efficiency. We will,
in addition, describe the growing body of evi-published in conjunction with the White
House conference. These documents were dence demonstrating that exposure to early
maladaptive experiences, such as prenatal andcovered in the popular media and read by pol-
icymakers and politicians interested in public postnatal stress and parental psychopathology,
does indeed have long-term implications forhealth and child development. Keynote speak-
ers at the 1997 National Governor’s Associa- brain and behavioral development. The impli-
Role of experience 697
cations of the research pertaining to the ef- aptic formation and pruning and behavioral
development. First, it is known that some dis-fects of early experience on brain and behav-
ior for public policy will be considered in the orders that involve mental retardation, such as
Fragile X, are associated with abnormal syn-concluding section of this paper.
aptic pruning, specifically with excess syn-
Synaptogenesis and the Remarkable
apses (Comery, Harris, Willems, Oostra, Ir-
Period of Early Brain Growth
win, Weiler, & Greenough, 1997). While
these disorders are caused by genetic abnor-The first neuroscientific strand that Bruer de-
scribes pertains to the fact that the brain de- malities rather than faulty early experiences,
it is noteworthy that there does appear to be avelops rapidly during the prenatal and early
postnatal months. Remarkably, early in a relation between synaptic density and intelli-
gence, with higher numbers of synapses asso-child’s life the brain produces trillions more
synapses than are found in adulthood. During ciated with lower intelligence.
Second, it appears that increased early en-the first 3 years of life, synapses form at a
phenomenal rate. In humans, it appears that vironmental stimulation does not necessarily
lead to increases in synaptic formation duringrapid synapse formation begins during the
first few postnatal months and reaches highest the period of rapid synaptic proliferation and
pruning, at least for the visual system in non-densities at about 3 months for sensory cortex
and about 2–3.5 years for frontal cortex (Hut- human primates (Bourgeois, Jastreboff, &
Rakic, 1989). It is clear, however, that experi-tenlocher, 1994; Huttenlocher & Dabholkar,
1997; Rakic, Bourgeois, & Goldman–Rakic, ence in some instances can alter the synaptic
formation and organization in the cortex (see1994). Furthermore, this period of peak syn-
aptic density coincides in time with the emer- Kolb, Forgie, Gibb, Gorny, & Rowntree,
1998, for a review of this rich set of data).gence of important cognitive skills, including
early manifestations of working memory (Di- Animals raised in complex, enriched environ-
ments have more synapses in certain parts ofamond & Goldman–Rakic, 1989). For exam-
ple, a study by Bell and Fox (1994) showed their brains compared to animals raised in
nonenriched environments (Greenough, Black,that infants who are able to achieve early
frontal tasks involving working memory dis- & Wallace, 1987). Furthermore, changes in
synaptic organization as a result of experienceplayed increased electrical brain activity over
the frontal scalp region. Put simply, neurosci- are correlated with changes in behavioral per-
formance in both animals and humans (Kolbence and developmental science have shown
that early life is a time of truly remarkable et al., 1998). For example, Jacobs and
Scheibel (1993) and Jacobs, Schall, andgrowth in terms of both brain and behavior.
However, as Bruer points out, there is still rel- Scheibel (1993) reported a relation between
extent of dendritic arborization (which wouldatively little known about how early experi-
ences, such as parenting, actually affect brain act to increase the number of synapses) and
the amount of education received. Interest-development, such as the rate or patterns of
synaptic formation and pruning, or even about ingly, research has shown that the effect of
enriched experience on synaptic number andthe relation between changes in regional syn-
aptic densities and specific cognitive skills organization is highly dependent upon the
age. Enriched experience during early postna-(e.g., peak synaptic densities in the frontal re-
gion and the emergence of early frontal lobe tal life appears to lead to a decrease in spine
density on the neuron but to have no effect onskills). Although it is intriguing that certain
biological events such as rapid synaptic pro- dendritic length (Kolb et al., 1998).
Science is still addressing the question ofliferation and the emergence of certain cogni-
tive skills co-occur in development, such a co- precisely how experiences affect the pattern
of selective elimination and responsiveness ofoccurrence does not prove that there is any
causal relation between these two processes. neural networks formed during early develop-
ment, as opposed to the sheer quantity of syn-There are, however, several things that are
known about the relation between early syn- apses, which appears, in large part, to be
G. Dawson, S. B. Ashman, and L. J. Carver698
under genetic control. It is known that experi- ute to memory. A recent report described the
formation of new dendritic spines followingence can and does play a role in selecting and
establishing preferentially active synapses. LTP (Toni, Buchs, Nikonenko, Bron, & Mul-
ler, 1999). This morphological synapticSelective amplification of specific neural
groups occurs via a competitive process as a change may also lead to changes in synapse
responsiveness.result of the frequency and intensity of stimu-
lation (Edelman, 1987; Hebb, 1949). Once a Consistent with the idea that LTP underlies
the formation of memories, a number of stud-specific pattern of neuronal groups is selected
in a mapped area, exposure to the same or ies have shown that blocking LTP through re-
ceptor antagonists or genetic manipulationssimilar stimuli is likely to preferentially acti-
vate previously selected neuronal groups. In leads to impaired memory performance in ex-
perimental animals (Lu, Jia, Janus, Hender-this way, it is hypothesized, developing neural
patterns become stabilized and less suscepti- son, Gerlai, Wojtowicz, & Roder, 1997; May-
ford, Bach, Huang, Wang, Hawkins, &ble to change over time (Edelman, 1989).
Such maps are believed to involve cortical Kandel, 1996). In addition, enhancing LTP by
manipulating second-messenger cascades in-sensory and motor maps as well as the brain
regions with which these cortical areas inter- volved in LTP is correlated with improved
memory performance (Barad, Bourtchou-act, such as limbic regions. Research is shed-
ding light on the mechanisms involved in se- ladze, Winder, Golan, & Kandel, 1998). In
addition to memory formation, some researchlecting and establishing preferentially active
neural patterns. Repeated and synchronous ac- suggests that components of LTP that are in-
volved in gene regulation are important fortivation of neighboring neurons strengthens
the connections between them, and allows consolidation of memory traces (Bourtchou-
ladze, Frenguelli, Blendy, Cioffi, Schutz, &them to fire more efficiently.
Decades ago, Hebb (1949) suggested that Silva, 1994). Thus, although there are some
reports that eliminating or decreasing LTPeither morphological or metabolic changes
might underlie changes in synaptic efficiency. does not affect memory (Meiri, Sun, Segal, &
Alkon, 1998), most research suggests thatMuch attention has been focused on long-
term potentiation (LTP), which may be a met- they are related.
Although it is becoming increasingly clearabolic mechanism for memory formation
(Chen & Tonegawa, 1997; Malenka & Nicoll, that LTP is likely involved in memory forma-
tion, there are a number of aspects of the1999). In LTP, high-frequency activation of
glutamate receptors results in a long-lasting physiological basis of memory that still must
be understood. LTP is most frequently studiedstrengthening of the synaptic connection such
that for intervals of up to hours the synapse in the hippocampus, a structure thought to be
involved in the formation of memory tracesresponds more readily and efficiently to acti-
vation. In LTP, non-N-methyl-
-aspartate (Chen & Tonegawa, 1997; Malenka & Nicoll,
1999). It has yet to be determined, however,(NMDA) glutamate receptors are activated,
depolarizing the postsynaptic membrane and how memory traces are stored in long-term
memory and what role, if any, synaptic plas-allowing for activation of NMDA glutamate
receptors. Most likely, both postsynaptic and ticity plays in the storage process. There is
some suggestion that, in addition to memory,presynaptic mechanisms are involved in this
process. Removal of the magnesium block LTP may be involved in activity-dependent
formation of neural circuitry, certainly in sen-that typically prevents activation of the
NMDA receptor allows calcium to enter the sory systems (Chen & Tonegawa, 1997;
Katz & Shatz, 1996). One hypothesis yet topostsynaptic cell, beginning a cascade of sec-
ond-messenger events that ultimately leads to be tested is that experience-dependent mecha-
nisms such as LTP might also be involved inlong-lasting changes in synaptic strength. In
addition to the metabolic changes that are in- building associative networks that form the
basis for memories as well.volved in LTP, structural changes have been
identified and such changes may also contrib- In summary, ample scientific evidence in-
Role of experience 699
dicates that experiences can influence the for- development, such as PKU and autism, have
shown that optimal long-term outcome inmation, strength, and efficiency of synapses.
Research is revealing the mechanisms in- terms of IQ and adaptive behavior critically
depends on intervention during the early yearsvolved in experience-dependent changes in
synaptic efficiency. However, it is unknown of life. For PKU, intervention must begin
when the infant is less than 21 days old (Wap-to what extent the early years of life, because
of the tremendous changes in the sheer num- pner et al., 1999). It has been demonstrated
that children with autism who receive inten-ber of synapses that take place during this
time, represent a particularly sensitive period sive interventions by 2–3 years of age fare
substantially better than those who receive in-for selecting and establishing preferentially
active patterns of neural networks that are less tervention after this age (see Dawson & Os-
terling, 1997, for review of early interventionsusceptible to change later in life.
studies in autism). Moreover, recent research
has shown that relatively common variations
Sensitive Periods and Long-Term
in early experience related to stress and mal-
Effect of Early Experience
adaptive parenting can have long-term effects
on development. In the next sections, we willThis brings us to the second and third neuros-
cientific strands that, according to Bruer, form review in detail what is known about the in-
fluences of early stress and maternal depres-the “myth of the first three years.” These per-
tain to the related notions that (a) the early sion on development. It will be concluded that
early stress and maternal depression representyears of development represent a sensitive pe-
riod for brain and behavioral development and relatively common deviations in early experi-
ence that appear to negatively influence both(b) early experiences can have long-term in-
fluences on brain and behavioral develop- brain and behavioral development.
ment. To begin, it is known that there are sen-
sitive periods in brain development (Knudsen,
Effects of early stress
1999); that is, there are periods in develop-
ment during which specific types of experi- Numerous studies, most involving animals
but some in humans, have documented theence are needed for the brain to develop
normally. The term “experience-expectant” de- negative effects of early exposure to stress
and social deprivation on both brain and be-velopment has been used to refer to develop-
mental processes that involve a readiness of the havioral development, and on long-term out-
come. Prenatal stress, for example, has beenbrain to receive specific types of information
from the environment (Greenough et al., 1987). shown to have numerous and varied effects
on the subsequent development of offspring.This readiness occurs during sensitive periods
in which specific types of information are reli- The function of the hypothalamic–pituitary–
adrenal (HPA) axis, the major hormonal stressably present for most members of the species.
This information can be visual, social, affec- response system, is affected in the offspring
of rats exposed to high levels of stress hor-tive, and cognitive. It has been argued that the
overproliferation of synapses during early post- mones either by injection or by exposure to
stress-inducing events (e.g., handling, re-natal life reflects the brain’s readiness to re-
ceive expected information during this period, straint, light, heat, cold). Offspring of preg-
nant rats injected with adrenocorticotropinwith the subset of synapses being selectively
retained depending on experience (Black, hormone (ACTH) showed increased basal
levels of corticosterone and decreased levelsJones, Nelson, & Greenough, 1998).
Studies have clearly demonstrated sensi- in response to stress (Fameli, Kitraki, & Styli-
anopoulou, 1994). In these offspring, the HPAtive periods for the development of language
and visual systems (Levay, Wiesel, & Hubel, system was hyperaroused during baseline
conditions and was overwhelmed and unable1980; Newport, 1990). Also, studies of chil-
dren at risk for cognitive and social impair- to respond during stressful conditions. This
result suggests that the systems that typicallyment due to genetic disorders that affect brain
G. Dawson, S. B. Ashman, and L. J. Carver700
regulate the activity of the HPA system do not prenatal stress on regulation of the HPA axis
and on brain development seem to be strongerfunction normally in cases of prenatal stress.
The HPA axis is regulated by a complex sys- for females than for males (e.g., Fride &
Weinstock, 1989; Kinsley, Mann, & Bridges,tem involving Type I glucocorticoid receptors
in the hippocampus and Type II receptors 1989). The maternal behavior of rats that were
themselves stressed prenatally clearly differsthroughout the brain (Weinstock, 1997). Dis-
regulation of this feedback system can lead to from that of nonprenatally stressed dams
(Weinstock, Fride, & Hertzberg, 1988). Thisincreased response to stressors, as well as an
inability to adapt to ongoing stress (Wein- raises the interesting possibility of multigen-
erational effects of prenatal stress, an issuestock, 1997).
In nonhuman primates, prenatal stress is that has yet to be well examined in the litera-
ture. In summary, there is evidence to suggestassociated with increased basal levels of
ACTH in plasma, as well as increased ACTH that prenatal stress results in long-term
changes in both brain and behavior in ani-levels in response to stress situations of vary-
ing degree in the offspring (Clarke, Wittwer, mals.
In comparison to the animal literature, lessAbbott, & Schneider, 1994). Behavioral ef-
fects have also been reported in infant mon- is known about the effects of prenatal stress
in humans. The majority of research in thekeys born to mothers that were stressed dur-
ing pregnancy. Monkeys that were exposed to area is retrospective, such as studies in which
parents respond to questionnaires about theirrepeated unpredictable noise in a darkened
room gave birth to infants that exhibited in- pregnancy history (Lobel, 1994). Children
whose mothers’ were exposed to a variety ofcreased behaviors associated with disturbance
(clinging to another monkey, clinging to an stressors during pregnancy were found to
have less optimal outcomes, including emo-artificial surrogate monkey, or self-directed
motor activity) and decreased motor and ex- tion regulation problems and motor delays
(Meier, 1985; Stott, 1973). The prospectiveploratory behaviors (locomotion, play, explo-
ration of the environment, and climbing) com- studies that have been done have primarily fo-
cused on very basic indicators of health andpared to infant monkeys born to nonstressed
mothers (Schneider, 1992a). Changes in cog- brain development such as birth weight, head
size, and risk for prematurity. Although thesenitive ability have also been noted in prena-
tally stressed rats and monkeys. In rats, per- are likely important factors in the future cog-
nitive and social development of the child,formance on a delayed alteration task was
impaired in the offspring of females exposed there is little direct evidence from studies in-
vestigating outcomes in children exposed toto the presence of a cat during the gestational
period (Lordi, Protais, Mellier, & Caston, stress in prenatal or early life. Indirect links
between head size and HPA responsiveness1997). In prenatally stressed rhesus monkeys,
the development of object permanence was (Ramsay & Lewis, 1995) suggest that prenatal
stress may be related to later HPA responsive-delayed compared to controls (Schneider,
1992b). ness (Glover, 1997), but the relation between
stress and head size is not made directly inThe mechanism responsible for these be-
havioral changes may lie in brain develop- the Ramsay and Lewis study. Thus, a relation
between stress response and prenatal stress inment changes that occur as a result of prenatal
stress. In rats exposed to prenatal stress, mild the human is hypothetical at best: infants pre-
natally exposed to stress have small heads,stressors resulted in an increase in acetylcho-
line in the hippocampus (Day, Koehl, De- and infants with small heads have abnormal
stress responses. Direct measures of the activ-roche, Le Moal, & Maccari, 1998). In addi-
tion, decreases in levels of dopamine and ity of the HPA axis are required to determine
precisely the effects on the system of prenatalincreases in levels of serotonin were discov-
ered in the brains of adult rats exposed to stress in the developing human before it can
concluded that results are truly parallel tostress hormones prenatally (Fameli et al.,
1994). those found in nonhuman primates and rats.
Studies of animals and humans also haveInterestingly, in many studies the effects of
Role of experience 701
demonstrated that early social deprivation and tions as well as changes in CRF neural sys-
tems. Similarly, Plotsky and Meaney (1993)exposure to high levels of stress during the
early postnatal period are related to poor so- found that maternal separation during the first
2 weeks of life resulted in elevated stress re-cial outcomes and alterations in psychobio-
logical functioning. Exposure to stress during sponses in adult rats.
Studies of nonhuman primates have dem-the postnatal period is associated with in-
creased levels of glucocorticoids, and gluco- onstrated similar long-term consequences of
early life stress (Capitanio, Rasmussen, Sny-corticoids have been shown to have harmful
effects on the developing brain. Evidence now der, Laudenslager, & Reite, 1986; Coplan,
Andrews, Rosenblum, Owens, Friedman,indicates that maternal behavior is important
for regulation of the stress response. In rats, Gorman, & Nemeroff, 1996). Coplan et al.
(1996) exposed bonnet macaques to eithermaternal separation stimulates HPA axis
activity and leads to elevated corticosterone predictable or unpredictable rearing condi-
tions by varying the amount and predictabilitylevels, as well as changes in, corticotropin re-
leasing factor (CRF) concentrations and re- of foraging that mothers needed to do to ac-
quire food. Years later, compared to primatesceptor number (Kuhn, Pauk, & Schanberg,
1990; Kuhn & Schanberg, 1998; Pihoker, exposed to predictable high foraging or pre-
dictable low foraging conditions, primatesOwens, Kuhn, Schanberg, & Nemeroff,
1993). Maternal behaviors, such as feeding exposed to variable foraging conditions ex-
hibited elevated cerebrospinal fluid concentra-and stroking, can weaken this adrenocortical
response to maternal separation. Suchecki, tions of CRF. Capitanio et al. (1986) reported
that monkeys who had experienced maternalRosenfeld, and Levine (1993) have shown
that, in maternally deprived rat pups, feeding separations as infants displayed more dis-
turbed behavior as adults.inhibits corticosterone secretion, while strok-
ing suppresses ACTH secretion. Moreover, What is known about the influence of early
postnatal stress on human development? Re-the attenuating effects of tactile stimulation
appear to be specific to maternal stimulation searchers have investigated how the mother–
infant relationship affects cortisol levels by(Stanton & Levine, 1990).
Similar research with nonhuman primates exploring the relationship between attachment
security and cortisol reactivity. Nachmias,has shown that plasma cortisol increases fol-
lowing maternal separation as a function of its Gunnar, Mangelsdorf, Parritz, and Buss
(1996) reported that a secure attachment rela-duration (Levine & Wiener, 1988). In nonhu-
man primates, the presence of a familiar so- tionship buffers the cortisol responses of be-
haviorally inhibited 18-month-olds to a novelcial group can serve to reduce the endocrine
effects of maternal separation. Monkeys who situation. Only the inhibited toddlers who
were also insecurely attached to their motherswere separated from their mothers and then
isolated displayed a more profound increase exhibited significant elevations in salivary
cortisol. Gunnar, Brodersen, Nachmias, Buss,in plasma cortisol levels and a slower return
to baseline. It has been hypothesized that the and Rigatuso (1996) found that attachment se-
curity moderates the cortisol response of 15-lower stress response in the presence of a fa-
miliar social group reflects the continued month-olds to inoculation distress. Fearful
toddlers who were also insecurely attachedavailability of a stable, predictable social en-
vironment (Levine & Wiener, 1988). exhibited elevated cortisol levels. These data
suggest that, especially for temperamentallyImportantly, animal studies involving both
rodents and nonhuman primates indicate that inhibited or fearful children, sensitive, respon-
sive caretaking may be an important factor inthe effects of maternal separation can persist
into adulthood (Anisman, Zaharia, Meaney, & the modulation of the HPA axis.
One of the most profound, long-term natu-Merali, 1998; Ladd, Owens, & Nemeroff,
1996; Plotsky & Meaney, 1993). Ladd et al. ralistic studies of early deprivation has oc-
curred with Romanian orphanage children.(1996) found that adult rats who had been ma-
ternally deprived showed increased baseline These children experienced significant depri-
vation until their adoption into homes in Eu-and stress-induced plasma ACTH concentra-
G. Dawson, S. B. Ashman, and L. J. Carver702
rope, Canada, and the United States. About Lynch, & Fielding, 1993; Grunebaum,
Cohler, Kaufman, & Gallant, 1978; Hammen,6 years after adoption, Gunnar and Chisholm
(1999) examined the effects of early institu- Burge, Burney, & Adrian, 1990; Orvaschel,
Welsh–Allis, & Weijai, 1988; Redding, Har-tional rearing on cortisol levels and attach-
ment quality. They found that children who mon, & Morgan, 1990). By early childhood,
children of depressed mothers have a 29%had experienced 8 or more months of institu-
tional rearing had significantly higher salivary chance of developing an emotional or behav-
ioral disorder, compared to an 8% chance forcortisol compared to sex, age, and socioeco-
nomic status matched controls and compared children of medically ill parents (Hammen et
al., 1990). Later, we will review evidence thatto children who had experienced 4 or fewer
months of institutional life. Also, there was a maternal depression is associated not only
with risk for maladaptive behavior but alsosignificant positive correlation between eve-
ning cortisol levels and time in institution, with risk for alterations in brain activity.
The behavioral disturbances associatedsuggesting that the longer exposure to depri-
vation is related to greater effects on the HPA with maternal depression are evident even in
young infants. Infants of depressed mothersaxis. Moreover, securely attached institution-
alized children were more likely to show nor- tend to be withdrawn and less active and to
display lower levels of positive affect (Field,mal cortisol levels.
1986, 1992; Field, Healy, Goldstein, Perry,
Bendall, Schanberg, Zimmerman, & Kuhn,
Effects of maternal depression
1988; Field, Healy, Goldstein, & Guthertz,
1990). They also have difficulty sustainingBruer argues that examples involving such
unusual and severe deprivation as occurs in their attention and exhibit poor mastery moti-
vation (Radke–Yarrow, Cummings, Kuczyn-the studies of children in orphanages cited
above do not really bear upon the concerns ski, & Chapman, 1985; Zahn–Waxler, Cum-
mings, McKnew, & Radke–Yarrow, 1984).that typical parents might have about the ap-
propriate kinds of emotional stimulation and Cognitive and language delays have been ob-
served by 1 year of age (Radke–Yarrow et al.,responsiveness they should provide their chil-
dren. But, in fact, even less extreme variations 1985; Zahn–Waxler et al., 1984).
Thus, it appears that maternal depressionin early parenting related to the parent’s own
emotional well-being appear to have signifi- may have adverse consequences on a young
infant’s early development and increase thecant long-term influence on children’s emo-
tional development, and possibly on their risk for affective or behavioral disorder in
childhood (Hammen et al., 1990). The biolog-brain development as well. Evidence for this
comes from studies of the effects of maternal ical and social mechanisms mediating these
effects are not yet understood. One proposeddepression, which is a fairly common risk fac-
tor for children, even for those children who mechanism involves the influence of the
mother’s depression on her ability to interactgrow up in otherwise advantaged environ-
ments. Children of mothers experiencing af- with her infant in a way that facilitates emo-
tional and cognitive development. Numerousfective disorders, including depression and bi-
polar disorder, during the early postnatal studies have shown that a mother experienc-
ing depression is less likely to interact in anyears are at risk for developing problems in
self-regulation, peer relationships, and sleep adaptive way with her young infant. De-
pressed mothers often find it difficult to pro-regulation, and for having behavioral prob-
lems, academic difficulties, and affective dis- vide contingent responses and optimal levels
of stimulation, and tend to show less positiveorders (Alpern & Lyons–Ruth, 1993; Coghill,
Caplan, Alexandra, Robson, & Kumar, 1986; and more negative affect when interacting
with their infants (Cohn, Matias, Tronick,Denham, Zahn–Waxler, Cummings, & Ian-
notti, 1991; Downey & Coyne, 1990; Erick- Connell, & Lyons–Ruth, 1986; Cohn & Tron-
ick, 1989; Field et al., 1988, 1990; Field,son, Sroufe, & Egeland, 1985; Ghodsian, Zaj-
icek, & Wolkind, 1984; Goodman, Brogan, Sandberg, Garcia, Vega–Lahr, Goldstein, &
Role of experience 703
Guy, 1985). During mother–infant interac- emotion and attention regulation and that poor
regulatory skills contribute to several differenttions, there is less frequent sharing of positive
emotional states and more frequent matching types of psychopathology (Dawson, 1994).
Furthermore, there is increasing evidence thatof negative emotional states (Field et al.,
1990). parents play a central role in facilitating the
development of self-regulatory skills in youngWhen the child reaches toddlerhood, it has
been found that toddlers of depressed mothers infants and children (Cicchetti, Ganiban, &
Barnett, 1991; Malatesta & Haviland, 1982;are less likely to maintain interactions and
display less coordinated interactions. Toddlers Tronick & Gianino, 1986; Tronick, 1989). In
the case of maternal depression, it is likelyof depressed mothers have also been found to
display fewer positive affiliative behaviors to- that the inability to provide adequate positive
emotion and regulatory input affects not onlyward their mothers and higher levels of hos-
tile and aggressive behavior (Dawson, Frey, the infant’s behavioral regulation abilities but
also the brain systems that underlie these abil-Self, Panagiotides, Hessl, Yamada, & Rinaldi,
1999). Depressed mothers also are less likely ities (Dawson, 1994).
Although the studies described above haveto repair interrupted interactions (Jameson,
Gelfand, Kulcsar, & Teti, 1997). When inter- focused on the role of the depressed mother’s
behavior, other mechanisms mediating the ef-acting with their preschool-aged children, de-
pressed mothers have been found to use a less fects of maternal depression on children must
be considered. Research has shown, for exam-positive tone, display more negative affect,
express more anxiety, and provide fewer di- ple, that neonates born to depressed mothers
tend to be less active, less socially responsive,rect commands (Cox, Puckering, Pound, &
Mills, 1987; Kochanska, Kuczynski, & Ma- and fussier than those born to nondepressed
mothers (Field et al., 1985; Whiffen & Gott-guire, 1989; Radke–Yarrow, Nottelmann,
Belmont, & Welsh, 1993). lib, 1989; Zuckerman, Als, Bauchner, Par-
ker, & Cabral, 1990). Prenatal exposure toTo explain the effect of maternal depres-
sion on children’s behavior, some investiga- maternal depression may be associated with a
less than optimal intrauterine environment.tors have suggested that children may be imi-
tating the mother’s depressed behavior. The contribution of genetic factors that in-
crease risk for depression is another importantOthers have hypothesized that children of de-
pressed mothers may fail to develop adequate factor, although it is unlikely that genetic fac-
tors alone can account for the high risk formeans for regulating arousal and negative af-
fect because of the mother’s difficulty in pro- emotional and behavioral disturbances found
in children of depressed mothers (Moldin,viding appropriate levels of stimulation, re-
sponsiveness, and arousal modulation. Later, Reich, & Rice, 1991; Todd, Neuman, Geller,
Fox, & Hickok, 1993).in toddlerhood, these mothers may have diffi-
culty helping the young child to develop ade- There is some evidence that the first few
years of life may represent a time of increasedquate self-regulatory strategies, leading to
maladaptive affective, attentional, social, and vulnerability for enduring effects of maternal
depression (Alpern & Lyons–Ruth, 1993).cognitive behavior. Early in the toddler years,
a major achievement is the ability to inhibit Wolkind, Zajicek–Coleman, and Ghodsian
(1980) reported that maternal depression oc-inappropriate responses and the use of self-
generated mental images to guide appropriate curring when the infants were 14 months old
was predictive of later behavioral problemsbehavior. For example, Piaget’s A not B task,
believed to be an early prefrontal task that re- during the preschool years, even when the de-
pression was absent by the time the childrenquires both inhibition of a prepotent response
and working memory to guide behavior, is were in preschool. Coghill and colleagues
(1986) found that maternal depression duringachieved some time in the 2nd year of life
(Diamond & Goldman–Rakic, 1989). It has the infant’s 1st year of life was predictive of
lower cognitive ability at 4 years of age, re-been hypothesized that inhibitory skills medi-
ated by the frontal lobe play a central role in gardless of mother’s depression status when
G. Dawson, S. B. Ashman, and L. J. Carver704
the child was 4 years old. Similarly, Alpern tively structured conditions. Thus, it does not
appear that the differences in brain activityand Lyons–Ruth (1993) found that infants of
mothers who were depressed when their in- were simply the result of differences in the
infants’ patterns of emotional expression dur-fants were 18–24 months but not depressed
when their children were 5 years were never- ing EEG recording.
Dawson and her coworkers also examinedtheless at increased risk for anxiety symptoms
at age 5 years. the relation between individual differences in
frontal brain activity and infant behavior,As stated earlier, children of depressed
mothers are not only a higher risk for cogni- which were observed in naturalistic situations
involving mother–infant play outside the psy-tive, social, and affective disturbances; they
also exhibit changes in brain activity early in chophysiology laboratory. Based on previous
theoretical and experimental work linking thelife. Dawson and colleagues have demon-
strated that 13- to 15-month-old infants of de- left frontal region with approach behaviors
and the right frontal region with withdrawalpressed mothers show reduced electrical brain
activity over the left frontal scalp region, as behaviors (Davidson, Ekman, Saron, Sen-
ulis, & Freisen, 1990; Fox, 1991), it was pre-compared to infants of nondepressed mothers
(Dawson, Grofer–Klinger, Panagiotides, Hill, dicted that reduced left frontal activity would
be related to lower frequencies of positive ap-& Spieker, 1992; Dawson, Frey, Panagiotides,
Osterling, & Hessl, 1997). This finding has proach behaviors in the infants. In addition,
based on a previous finding from our labora-been demonstrated in two independent sam-
ples, one involving teenaged mothers with tory that infants of depressed mothers also
show increased generalized frontal activationmultiple risk factors and another involving
middle-income, primarily married, adult during the expression of negative emotions
(Dawson, Panagiotides, Grofer–Klinger, &mothers who were carefully screened for a va-
riety of other risk factors that could poten- Spieker, 1997), it was predicted that increased
levels of generalized frontal activation wouldtially influence infant behavior and brain ac-
tivity (e.g., other major psychiatric disorders, be related to increased levels of intense nega-
tive affect.substance abuse, contact with Child Protective
Services, and prenatal and birth difficulties). In this study (Dawson, Frey, Self, et al.,
1999), it was found that infants of depressedIn the latter longitudinal study involving 159
mothers and their infants, Dawson and col- mothers were less affectionate and less likely
to touch their mothers during free play. Theyleagues (1997) found that infants’ atypical
frontal electroencephalogram (EEG) patterns also had more difficulty quietly occupying
themselves while their mothers filled out awere linearly related to the severity of mater-
nal depression. Interestingly, infant frontal questionnaire, and thus appeared to have more
difficulty with self-regulation. Reduced leftEEG patterns were not found to be related to
mothers’ levels of anxiety or hostility, even frontal activity was correlated with lower lev-
els of positive approach behaviors (affectionthough depressed mothers reported signifi-
cantly higher levels of these symptoms (Daw- toward mother during free play) and higher
frequencies of negative bids for attentionson et al., 1997). It was also found that the
pattern of atypical frontal electrical brain ac- (grabbing mother’s clipboard or pen while she
attempted to fill out questionnaire). In addi-tivity in infants of depressed mothers general-
ized to a range of situations in which we re- tion, increased generalized frontal brain activ-
ity was associated with higher levels of nega-corded brain activity, including a “nonsocial”
baseline condition and a standardized playful tive affect, hostility, tantrums, and aggression.
Thus, the behaviors that were found to be as-condition carried out with a familiar experi-
menter (Dawson, Frey, Panagiotides, Ya- sociated with frontal brain activity appear to
reflect the dimensions of positive approachmada, Hessl, & Osterling, 1999). Importantly,
infants of depressed and nondepressed moth- and affiliative behaviors and regulation of
negative emotions. These findings suggesters were not found to differ in terms of their
affective behavior during these brief, rela- that maternal depression is associated with al-
Role of experience 705
terations in infant brain activity and that atyp- evaluate assumptions at the intersection of
science, policy, and clinical practice. First, theical frontal brain activity is associated with
lower levels of approach behaviors and in- current state of scientific findings on the issue
must be understood. Second, reasonablecreased intensity of negative affect or diffi-
culty in regulating negative affect. hypotheses can be generated as logical exten-
sions of these scientific findings. Finally, un-Dawson (1999) also found that mothers ex-
periencing depression displayed higher levels warranted assertions need to be assessed.
Such an analysis can then lead to well-justi-of insensitive behaviors when interacting with
their infants. Insensitive behaviors broadly in- fied policy recommendations. Let us consider
such an analysis and its implications for socialcluded behaviors that reflected a difficulty in
sensitively following the cues of the infant, policy recommendations.
Regarding the current state of the science,including behaviors such as poking, tickling,
responding to infant’s bid for attention by critics agree that from the perspective of es-
tablished scientific knowledge our under-withdrawing from or rejecting solicited physi-
cal contact, and unsolicited holding. Further- standing of the neurobiology of the effects of
early experience on developmental outcome ismore, path analyses indicated that mother’s
insensitivity with her infant mediated the rela- still in its infancy (Bruer, 1999; Nelson,
1999a, 1999b; Shonkoff, in press). Neverthe-tion between maternal depression and infant
frontal EEG activity (Dawson, 1999). These less, a number of reasonable assertions and
hypotheses can be generated from what isresults provide support for the hypothesis that
the behavior of a depressed mother toward her known based on both brain and behavioral
science. First, it is clear that the prenatal andinfant—in particular, the degree of maternal
insensitivity—can influence patterns of infant early postnatal years are a time during which
remarkable growth in multiple domains offrontal brain activity. Specifically, high levels
of maternal insensitivity appear to be associ- functioning (e.g., social, linguistic, cognitive,
motor) occurs in terms of both brain and be-ated with lower levels of infant left frontal
electrical brain activity. These results, taken havioral development. Second, ample evi-
dence exists indicating that these years likelytogether with previous studies on the effects
of maternal depression on infant behavior and represent a sensitive period with respect to the
effects of nutrition, exposure to toxins, andbrain activity, suggest that relatively common
variations in early parenting that are related to possibly stress. Third, this period also seems
to represent a sensitive period with respect toa parent’s emotional well-being are associated
with alterations in infant brain activity and be- the long-term beneficial effects of early inter-
vention on brain and behavioral developmenthavior. Other studies have shown that mater-
nal depression early in life is a risk factor for for some genetically based disorders, such as
PKU and autism. Fourth, evidence suggestslater psychopathology in childhood (Good-
man & Gotlib, 1999). The question of that parental mental health during the first
years of life is a significant factor with respectwhether altered brain activity early in life
constitutes a risk factor for later psychopath- to early brain activity and behavior and long-
term behavioral outcome. This paper has fo-ology is as yet unanswered and is currently
being addressed in a longitudinal study being cused on early stress and maternal depression,
but similar evidence exists with respect to theconducted by Dawson and colleagues.
influence of other forms of maladaptive par-
enting, such as maltreatment (DeBellis, Kes-
Implications for Social Policy and
havan, Clark, Casey, Giedd, Boring, Frus-
taci, & Ryan, 1999; Pollak, Cicchetti,
Klorman, & Brumaghim, 1997).What can we say about the effects of early
experience on brain development and later Understanding the factors that determine
social and emotional outcome in humans is aoutcome and their implications for social pol-
icy? Shonkoff (in press) outlined three levels complex task that requires integrating infor-
mation about the genetic, physical, and socialof analysis that should be applied to critically
G. Dawson, S. B. Ashman, and L. J. Carver706
environment. Outcome is variable because of 1999). As Cicchetti and Cannon (1999) point
out, our hopes of finding new avenues for in-the nondeterministic, probabilistic nature of
development. As Cicchetti and Cannon (1999) tervention rest on discovery of the mecha-
nisms that constrain plasticity and change.state, “Epigenesis is viewed as probabilistic
rather than predetermined or preformational, Early development is a period that is com-
prised of many fundamental “experience ex-with the bidirectional and transactional nature
of genetic, neural, behavioral, and environ- pectant” processes. Unfortunately, there are
many conditions, such as autism, in which ge-mental influence over the life course captur-
ing the essence of probabilistic epigensis” (p. netic or acquired brain abnormalities preclude
having a normal experience of an otherwise377). Although early experiences are impor-
tant for later outcome, this does not imply that normal environment. As described by Black
et al. (1998), neuropathology can result inthe effects of any one type of early experience
are necessarily causal or permanent. Systems
theory principles such as the notion that mul-
...adevelopmental “groove” that will carry devel-
opment forward. Therapeutic manipulations may
tiple pathways can converge on a common
perturb this trajectory initially, but development
outcome (equifinality) and vice versa (multifi-
will fall back into the existing track if the canaliza-
nality) are well accepted by developmental
tion is sufficiently entrenched. However, if the per-
psychopathologists and must be incorporated
turbation is large enough, then the trajectory can
into any theory about the effects of early ex-
be shifted out of one equilibrium into another, and
perience on later outcome (Cicchetti & Ro-
from there brain development will proceed down a
gosch, 1996). In developmental psychopathol-
different pathway. As development proceeds, canal-
ogy, the term “pathway” is used to refer to
ization generally deepens—developmental trajec-
the cumulative influence of an individual’s
tories progressively become more difficult to redi-
specific genetic makeup and experiences that
rect by experience. This perspective supports the
together operate in a complex and probabilis-
common therapeutic strategies that early interven-
tion is better than late and that more intervention
tic fashion to influence outcome (Gottlieb,
may work better than less. (pp. 46–47)
1991, 1992). An experience involving a de-
pressed mother most likely is moderated by a
host of other factors, including genetic fac- The substantial effect of early intervention
has been dramatically demonstrated in thetors, other significant relationships, the child’s
intelligence and schooling, peers, and so on. case of autism. If very intensive behavioral
intervention is commenced by 2 years of age,Each individual has a unique combination of
factors influencing outcome. Thus, in most a substantial number of children with autism
show a remarkable improvement in this con-cases it is not reasonable to consider one type
of experience as having a permanent and spe- dition (see Dawson & Osterling, 1997).
Furthermore, there are many common con-cific effect on later outcome. On the other
hand, the term “pathway” implies that, at any ditions, such as exposure to stress and mater-
nal depression, in which the variation in early,point in an individual’s development, that in-
dividual has, indeed, developed along a spe- expected environment falls outside the norm,
and these conditions do appear to have an in-cific pathway involving a complex set of risk
and protective factors, and to alter this trajec- fluence on long-term outcome. Because we
have the knowledge of many early factors thattory one must intervene through planned ther-
apeutic activities that focus on changing be- promote optimal development, it is imperative
that we translate that knowledge into socialhavioral and neural patterns of conditioning,
through insight and self-will, or through ser- policy so that society can benefit from the sci-
entific knowledge that has been gained. In theendipitous advantageous experiences (a posi-
tive role model or mentor). However it oc- case of our understanding of the importance
of early experience on brain and behavioralcurs, real energy is required; it rarely, if ever,
happens spontaneously or easily. Fortunately, development, evidence from the neurosci-
ences and the behavioral sciences offers ainherent plasticity appears to be a characteris-
tic of at least some brain structures (Johnson, firm base for identifying optimal conditions
Role of experience 707
for children’s development. Public under- tervention programs for pregnant women
suffering from alcohol or drug addictionstanding of the importance of such conditions
is a critical first step that must be followed by are needed.
the design and implementation of policy and
3. Similarly, a brief assessment of mother’s
intervention efforts. There is much more we
mental health should be included as part of
do as a society to provide an optimal environ-
the regular well-baby checkups, along with
ment in the first years of life and beyond. Pol-
educational materials related to infant nutri-
icy should focus on primary prevention of ad-
tion and behavioral development. Contin-
verse outcomes by reducing known risk
ued efforts to improve identification of psy-
factors related to early environment and expe-
chopathology in infants during well-baby
rience so that such factors can be thwarted be-
checkups should also be supported.
fore they have any influence on outcome, as
well as on secondary prevention by identify-
4. Increased efforts to train health care work-
ing environmental factors that are modifiable
ers in how to detect and respond when par-
moderators or mediators of outcome so that
ents are experiencing mental health prob-
we can mitigate the negative influence of such
lems are needed.
risk factors on children’s development and
5. Communities struggling with poverty and
outcome. Specifically, we believe that the fol-
the host of associated problems that are as-
lowing policy recommendations are well jus-
sociated with poverty (stress, violence,
tified based on the current state of knowledge
poor nutrition, parental psychopathology,
regarding the effects of early experience on
impoverished educational opportunities)
brain and behavioral development.
should be a direct and substantial focus of
programs related to optimal prenatal and
1. In general, although prevention and early
early postnatal environments because chil-
intervention efforts should not exclusively
dren growing up in such communities are
focus on the earliest years of development,
most likely to be exposed to multiple risk
it is clear from the research discussed
factors that are associated with poor long-
above that such efforts should begin as
early as possible. By directing such efforts
6. Because the prenatal and early postnatal
toward promoting optimal prenatal and in-
years represent a sensitive period with re-
fant–toddler development, the long-term
spect to the long-term beneficial effects of
negative consequences of factors that have
early intervention on brain and behavioral
their greatest influences during early devel-
development for some genetically based
opment and which set the stage for future
disorders, such as autism, increased efforts
development can be minimized or avoided
at early identification of such disorders is
needed. Greater public awareness and edu-
2. Prevention efforts that promote healthy pre-
cation of health care providers with respect
natal development should focus on increas-
how to detect developmental disorders dur-
ing public awareness, outreach efforts, and
ing infancy and toddlerhood and how to fa-
intervention programs related to improving
cilitate access to appropriate interventions
prenatal nutrition, reducing fetal exposure
to toxins (alcohol, drugs), and minimizing
maternal stress and psychopathology dur- 7. Efforts aimed at early identification, pre-
vention, and remediation of developmentaling pregnancy. In light of findings that pre-
natal depression and stress can influence disorders should be enhanced. To provide
one example, autism has become recog-fetal and neonatal behavior, prenatal
screening should include a brief assessment nized as a relatively prevalent (1 in 500–
1000 persons) developmental disorder thatof maternal mental health so that appro-
priate medical or psychological interven- can and should be detected during infancy
in most cases (Osterling & Dawson, 1994,tions can begin at this time. Moreover, in-
G. Dawson, S. B. Ashman, and L. J. Carver708
1999). Unfortunately, autism is not typi- tribution of parenting factors to the devel-
opment of self-regulatory brain mecha-cally diagnosed in children until around the
age of 3–4 years (Siegel, Pliner, Eschler, & nisms that have been hypothesized to relate
to affective and attentional disorders is stillElliot, 1988). Pediatricians and other health
care professionals need to be aware of how poorly understood.
to assess early symptoms of autism in in-
3. It needs to be determined whether psycho-
fants and toddlers so that appropriate
biological measures such as neuropsycho-
screening and referral can occur. Moreover,
logical performance, cortisol levels, auto-
given the dramatic impact of early interven-
nomic responses, and brain electrical
tion in autism, funding for early behavioral
activity will be useful in identifying chil-
intervention programs for infants and tod-
dren at risk for psychopathology.
dlers at risk for autism is clearly justified
and cost effective.
4. Continued research on the neurobiological
bases of different types of child psycho-
8. In general, financial, emotional, and practi-
pathology will be important for understand-
cal support needs to be provided to families
ing the etiology, nature, and treatment of
who are struggling to access appropriate in-
such disorders. Such research will lay the
tervention for their children who have been
foundation for identifying phenotypic
identified as having a developmental disor-
markers for childhood disorders, which will
der, chronic illness, or mental health prob-
be essential for early identification, design-
lem. Denial of such support to families by
ing interventions, and discovering genetic
insurance companies and government agen-
cies is shortsighted on the part of these
health care systems in light of what is
5. There is also a need to develop neurobio-
known about the critical impact of early in-
logical frameworks for interventions for
tervention on long-term outcome.
children at risk for psychopathology be-
cause of genetic or environmental factors.
Future research should focus on increasing
For example, the use of neurocognitive and
our understanding of the multiple influences
psychophysiological assessments that target
on children’s development and outcome, and
specific brain regions, such as prefrontal
thus will depend upon multidisciplinary, lon-
functioning, may allow us to design indi-
gitudinal approaches that integrate biological
vidualized treatment approaches based on
and environmental factors. Among the impor-
tant issues that need to be addressed in future
research are the following:
6. Similarly, measures of response to inter-
ventions should include neuropsychological
1. Given that different biological systems de-
and psychophysiological indices of brain
velop on different timetables, it needs to be
function to determine whether and how
determined whether and how specific envi-
specific brain systems may be influenced
ronmental events, such as exposure to
stress and maternal depression, selectively
affect the development of specific neurobi-
7. The degree of plasticity in neural systems
ological systems depending on the timing
as it relates to risk for child psychopathol-
and duration of the exposure to such events
ogy needs to be understood. For example,
and whether and how timing influences risk
issues related to timing, duration, and type
for psychopathology. In particular, studies
of early interventions that may influence
that address these issues in humans are
outcome in children at risk for psychopath-
ology need to be explored.
2. The role of the environment in promoting
optimal brain function in children needs to In conclusion, technological advances in
brain research continue to make this an excit-be better understood. For example, the con-
Role of experience 709
ing time with respect to our ability to under- ing of brain and behavioral development but
rather the translation of that knowledge intostand the neural bases of normal and abnor-
mal development. As science continues to meaningful policy and action. This responsi-
bility, shared by the general public, scientists,move this effort forward at a remarkably fast
pace, it has become apparent that our most practitioners, and policymakers, should be a
central focus of our efforts.difficult challenge will not be the understand-
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