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ArticleMedia Violence Effects on
Brain Development: What
Neuroimaging Has
Revealed and What Lies
Ahead

American Behavioral Scientist
1–16© 2015 SAGE Publications
Reprints and permissions:sagepub.com/journalsPermissions.nav
DOI: 10.1177/0002764215596553
abs.sagepub.com

Tom A. Hummer1

Abstract
Substantial research has indicated that media violence induces both short- and longterm increases in aggressive thoughts, feelings, and behaviors. Recently, neuroimaging
techniques have begun to identify the mechanisms driving these changes. An
important avenue that these neuroimaging tools can address is how exposure to
media violence in childhood affects brain development, which can have lifelong
behavioral consequences. This review highlights neuroimaging research examining
how media violence exposure affects the pediatric brain. While such research islimited, evidence suggests that prefrontal mechanisms for controlling emotion andbehavior are altered by exposure to violent media. Therefore, long-term increases inaggression and decreases in inhibitory control due to excessive media violence
exposure may result from impaired development of prefrontal regions. However,additional neuroimaging research is necessary to establish whether and how
exposure to media violence specifically shapes subsequent neural maturation. To
optimize the use of neuroimaging in this inquiry, imaging studies should not stand on
their own, but instead must be integrated with more traditional research paradigms
to establish a more complete picture of effects. Future research must employ more
longitudinal approaches to better characterize long-term effects that high exposure
to violent screen media may have on brain development, particularly prefrontal andlimbic brain regions.
Keywords
media violence, MRI, neuroimaging
Characterizing the effects of various forms of violent media on children’s thoughts
and behaviors has been a focus of psychological research for more than 50 years.
1

Indiana University School of Medicine, Indianapolis, IN, USA

Corresponding Author:
Tom A. Hummer, Department of Psychiatry, Indiana University School of Medicine, 705 Riley Hospital
Drive, Riley Outpatient Center Room 4300, Indianapolis, IN 46202, USA.
Email: thummer@iupui.edu__________________________________________________________________________________________
This is the author's manuscript of the article published in final edited form as:
Hummer, T. A. (2015). Media Violence Effects on Brain Development What Neuroimaging Has Revealed and What
Lies Ahead. American Behavioral Scientist, 59(14), 1790-1806. http://dx.doi.org/10.1177/0002764215596553

2American Behavioral Scientist

Tremendous advances have been made through a variety of scientific methods, such as
behavioral observation, physiological monitoring, and computerized reaction-timetasks. These methods have enabled researchers to provide substantial evidence that
exposure to television, film, and computer/video game violence, which involves
purposeful injury of one character by another, can increase aggressive thoughts,
feelings, and behaviors (Anderson et al., 2003; Huesmann, Moise-Titus, Podolski, &Eron, 2003; Paik & Comstock, 1994; Wood, Wong, & Chachere, 1991).
As this research has progressed, newer tools have been developed to increase ourunderstanding of how children are influenced by media exposure. Most notably,
technological advances now allow us to more directly examine how children’s brains
are affected by prior or current violent media exposure, using various neuroimaging
methods. By integrating neuroimaging techniques into existing research knowledge, amore complete picture of media violence effects on the brain and behavior can beformed.
The most substantial potential consequences of media violence exposure are thosethat extend beyond the immediate impact of watching a violent show or playing a
violent video game. Clarifying long-term effects of violence exposure is one of the
primary goals of media violence research, since an enduring impact on behavior
patterns or personality traits is much more problematic for the individual and forsociety. The most critical potential influence of violence exposure is on childhood
brain development, as alterations to the developmental trajectory of relevant brain
regions will influence individual characteristics and behaviors for many years to come,into and through adulthood. The potential for violence exposure to have a significant
impact on brain development is strong, as a confluence of children’s increasing media
exposure and greater independence combine with the heightened sensitivity of thedeveloping pediatric brain.
If used properly, neuroimaging provides an optimal method for understanding how
brain development is influenced by exposure to media violence during childhood andadolescence. Neuroimaging encompasses multiple techniques, including
electroencephalography (EEG), magnetic resonance imaging (MRI), and positronemission tomography (PET), among others, which enable us to characterize thestructure and function of the brain in vivo. Advances in technology and computational
power over the past couple of decades have made data collection with these methods
more feasible, precise, and usable, leading more scientists to embrace neuroimaging as
the next progression in psychological research. The result has been a flood of exciting
contributions to the field that have pulled back the curtain on the brain, revealing brain
structure and function with increasingly detailed images.
Beyond the excitement derived from the novelty and beauty of imaging the brain,
we must evaluate how useful neuroimaging can be as a scientific tool to assess shortand long-term developmental effects of exposure to violent media. In particular, it isnecessary to clarify the added value that neuroimaging tools bring to more traditional
psychological techniques in understanding effects of violent media. How doneuroimaging techniques help us achieve our goals within media effects research, andhow can we ensure that we are maximizing the potential of these tools to informscientific knowledge?

Hummer3What is Neuroimaging?
Brain imaging techniques measure neural characteristics by detecting naturally
occurring signals emanating from the brain, or via the interaction of neural properties
with exogenous material, such as radioactive isotopes. The most commonly utilizedneuroimaging methods, particularly within media violence research, are EEG and
MRI. This article focuses primarily on these two methods, which are more widelyused due to their relative ease of use and noninvasive characteristics.
In EEG, participants wear headgear that contains a matrix of electrodes that record
ongoing electric activity through the scalp. This activity is the result of synchronizedoscillations of neuronal activity, emanating primarily from cortical origins. Theseelectric signals can reflect spontaneous activity recorded over an extended period oftime (minutes to hours), or activity in response to specific stimuli, such as presented
pictures or words. EEG activity recorded with this latter approach is known as eventrelated potential (ERP), since it is time-locked to stimulus “events.” ERP signals areaveraged over many trials during an experiment. In this manner, investigators candetermine the brain’s response to specific conditions (such as negatively valenced
images), including the strength, latency, and duration of the neural response. Because
ERP records activity generated directly by the firing of groups of neurons, the method
provides high temporal resolution, on the order of milliseconds. This excellent
resolution enables investigators to differentiate immediate sensory responses to a
stimulus from subsequent, higher level responses, such as cognitive processes that
follow immediate perception. However, electrical signals from neuronal activity
disperse as they reach the surface of the scalp, so each electrode measures potentialchanges that arise over a relatively widespread area of the brain. Thus, spatial
resolution is poorer than that of other imaging techniques. In other words, EEG is
excellent at determining when activity is taking place, but can only indicate
approximately where in the brain neurons are firing.
An MRI scanner is essentially a large tube that contains a very powerful magnet.
This magnet moves rapidly in a closed field around a biological target (e.g., the brain),
exciting atomic nuclei within the field. The scanner then measures radio frequency
signals emitted by these nuclei as they “relax” to their equilibrium state. Different
tissue types—including gray matter, white matter, and cerebrospinal fluid—havedistinct magnetic susceptibilities and relaxation rates, and generate distinct signals.
Using this information, we can reconstruct high-resolution three-dimensional maps ofthe brain.
To examine brain activity, investigators take advantage of changes in blood flow,
blood volume, and oxygen metabolism that accompany neuronal activity. Thesechanges alter the blood-oxygen level-dependent (BOLD) signal, which is collectedduring functional MRI (fMRI). During fMRI, BOLD signal is quantified during
spontaneous activity (“resting state”) or in response to specific presented stimuli.
fMRI has better spatial resolution than EEG, typically quantifying the BOLD signal
with a resolution of 2 to 3 mm. Because the BOLD signal is based on hemodynamics
and lags the actual firing of neurons, fMRI is an indirect measure of brain activity.
Moreover, signal detection across the entire brain in fMRI takes 1 to 3 seconds, due tothe relaxation time required. Therefore, the temporal resolution of brain activity with

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American Behavioral Scientist

fMRI is on the order of 2 to 3 seconds, poorer than that of EEG, but its spatial
resolution is better, detecting much more precisely where activity is occurring.
In addition, MRI can characterize gross structural characteristics of the brain,including gray matter and white matter. Gray matter consists primarily of brain cellbodies, where neural computations and interactions take place. White matter is thefatty tissue, called myelin, which insulates long-range brain connections (axons).
Specialized MRI techniques can be employed to gather data on architecturalcharacteristics that help elucidate neurodevelopment, particularly within white matter
tracts. Specifically, diffusion tensor imaging (DTI) quantifies diffusion of watermolecules within the brain to provide detailed information about microstructuralproperties. Quantifying this diffusion yields data on the degree of myelination andaxonal organization of white matter tracts, as molecule diffusion is more directed
when extracellular space is limited by increased myelination. For instance, fractional
anisotropy (FA), one commonly used measure of neurodevelopment, represents thedegree to which diffusion progresses axially (parallel to fiber tracts) relative to theradial direction (perpendicular to the tract). FA normally increases throughout
childhood and adolescence, and thus is a widely used measure of neurodevelopment
during these time periods.
In adults, imaging techniques, such as PET or single-photon emission computed
tomography (SPECT), can also provide useful information, including neurotransmitter
receptor concentrations or brain metabolism. However, these methods are not typicallyavailable for pediatric research, as the lightly radioactive contrasts used are avoided inchildren.

Childhood Brain Development
Neuroimaging tools, particularly MRI, have been vital in mapping out how brain
development progresses through childhood and adolescence. The development ofcortical volume throughout childhood and adolescence is complex, but there is an
overall trend characterized by an average peak in cortical gray matter in earlyadolescence (Giedd et al., 1999; Reiss, Abrams, Singer, Ross, & Denckla, 1996). This
peak timing and subsequent decrease in cortical volume is regionally specific. For
instance, volume of the frontal lobe—which is central to such higher order processes
as attention, planning, organization, and behavioral control—is highest around age 11
in girls and age 12 in boys (Giedd, 2004; Giedd et al., 1999), though this trajectory
may differ slightly with intelligence level (Shaw et al., 2006). This cortical thinning islikely related to the process of pruning, which removes unnecessary neuronalconnections, and development of white matter tracts (myelination) that occur as thebrain matures (Sowell et al., 2003). Myelination increases, improving the efficiency ofneuronal transmission, throughout childhood and adolescence. This development isparticularly strong in association fibers, which connect two separate areas of cortex(the surface of the brain), improving function of higher order brain processes (Asato,
Terwilliger, Woo, & Luna, 2010; Benes, 1989; Yakovlev & Lecours, 1967). As areflection of increased myelination, white matter density has a generally linear
increase throughout adolescence and beyond (Giedd et al., 1999; Sowell et al., 1999).

Hummer

5

The maturation of white matter tracts improves the efficiency of communication
between brain regions, with connections between association areas (such as frontal
and parietal cortices) strengthening especially during adolescence (Asato et al., 2010).
This improved neural communication is associated with improved executivefunctioning capabilities, including working memory, inhibitory control, and attention.
Microstructural properties of white matter, measured via DTI, reflect the degree of
myelination and organization of tracts that are associated with neurocognitive
performance on a variety of tasks (Mabbott, Noseworthy, Bouffet, Laughlin, &Rockel, 2006; Nagy, Westerberg, & Klingberg, 2004; Olson et al., 2009; Silveri et al.,2006; Tamnes et al., 2010). Moreover, delayed neurodevelopment throughout
childhood, as reflected both by the trajectory of cortical thickness and DTI-derived
white matter measures, is a key feature of clinical manifestations of executive
dysfunction, such as attention deficit hyperactivity disorder (Shaw et al., 2007; Shawet al., 2011).
Current theory suggests that brain regions primarily responsible for more
evolutionarily ancient functions, such as motivation, emotion, and reward sensitivity,
mature earlier than those neural regions (most notably prefrontal cortex) that help
control these drives. Development of the prefrontal cortex continues into the mid-20s,
so psychological processes mediated by prefrontal mechanisms, including attention,
inhibitory control, and emotion or behavior regulation, are particularly vulnerable
during adolescence.
Environmental factors apart from media violence, such as drugs of abuse (Squeglia,
Jacobus, & Tapert, 2009) or stress (Eiland & Romeo, 2013) have extensive long-term
effects on brain structure and function when encountered during one’s teenage years,
particularly early adolescence. There are several reasons why this time period is
especially sensitive to long-term effects. First, as noted above, maturation of theprefrontal cortex and associational tracts is particularly robust during this time period,
and disruptions of this development have extended consequences on communication
between higher level brain regions. Second, the onset of puberty brings about a host of
hormonal changes that drive organization of the adolescent brain (Sisk & Zehr, 2005),
and hormones play an increasing role in emotion and stress regulation following
puberty (Amin, Epperson, Constable, & Canli, 2006; Dedovic, Duchesne, Andrews,
Engert, & Pruessner, 2009; Kajantie & Phillips, 2006; Young & Altemus, 2004).
These changes typically coincide with increasing independence, which intensifies
social pressures and other life stressors. This combination of evolving neurobiologicaldevelopment with psychosocial and environmental changes creates a sensitive period
for enduring effects on the brain. While media violence is certainly not the only factor
that may alter brain development during adolescence, its prevalence and potential for
impact make it an important research topic.

Neuroimaging of Media Violence Effects in Children andAdolescents
Pediatric neuroimaging studies of media violence have built on the existing body ofpsychological research, in an attempt to determine what is driving the observed
cognitive and behavioral effects and to identify effects that may not be detectable

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American Behavioral Scientist

through more traditional techniques. To date, the number of neuroimaging researchstudies that directly examine neurobiological outcomes of media violence exposure on
children and adolescents has been limited, but promising.
The first neuroimaging study to examine the relationship between media violence
exposure and brain activity was a correlational study involving aggressive adolescents with
disruptive behavior disorder and nonaggressive control youth (aged 13-17 years; Mathews
et al., 2005). Past exposure to video game and television violence was quantified via selfand parent-report, and groups were split into low- and high-violence exposure groups
based on a median split. During fMRI, participants performed a counting Stroop task, aninterference task known to engage the anterior cingulate. This task required participants topress a button corresponding to the number of digits (interference condition) or letters(control condition) in a presented stimulus (e.g., press Button 3 for 111 or XXX).
Participants with lower past violent media exposure had a greater anterior cingulate
response (interference activity–control activity) than the high-exposure group. This study
provided useful preliminary evidence that dysfunction of top-down control regions was
related to media violence exposure. However, the study design made it impossible todetermine the direction of effects; differences in anterior cingulate function could havebeen caused by violence exposure, or existing characteristics associated with the different
brain activity may have predisposed these youth toward more violent programs or games.
A subsequent fMRI investigation revealed that the presence of a disruptive behavior
disorder influenced how past media violence exposure was related to brain activity (Kalnin
et al., 2011). These adolescents performed an emotional Stroop task, in which they were
presented with aggressive (e.g., hit, harm) or nonaggressive (run, walk) action words, forwhich they identified, via button-press, the color of the ink with which they were printed.
Aggressive words required participants to suppress any emotional response in order to
respond as quickly as possible. In control youth, the amygdala, which responds strongly toemotionally arousing stimuli, had a greater response to violent words than in youth withhigh past media violence exposure. However, youth with a disruptive behavior disorder
showed the opposite finding, with higher amygdala activity in the low-violence group,suggesting psychopathology may interact with the effects of media violence on the brain.
To better establish whether exposure to violent content could influence subsequentadolescent brain activity, a controlled fMRI experiment was designed. In this study,adolescents were randomly assigned to play one of two equally exciting, action-packed
games for 30 minutes: an exciting, but nonviolent racing game, or a violent first-person
shooter game (Hummer et al., 2010; Wang et al., 2009). Immediately after game play,teens were scanned with fMRI while performing counting and emotional Stroop tasks
related to emotional and cognitive control, each of which requires regulating automatic
responses in order to respond correctly. The group that played violent games had lower
interference-related dorsolateral prefrontal cortex activity during the counting Stroop, andhigher amygdala activity to aggressive words during the emotional Stroop, relative to thenonviolent game group. In addition, medial prefrontal cortex activity had lower
connectivity with the amygdala in the violent game group. These results suggest that
inhibitory mechanisms were altered by violent game play, including the ability ofprefrontal regions to inhibit the amygdala response to negative stimuli.

Hummer7

During a Go/No-Go task, participants were instructed to press a button to eachpresented letter (“Go”) except when the letter was an X (“No-Go”). Because No-Go
trials were less common, cognitive or behavioral inhibition mediated in part by lateralprefrontal cortex was required to stop the more automatic button-press response.
Nonviolent game players had greater right lateral prefrontal activity during No-Go
trials compared with the violent game group. Since both games were rated to be
similarly exciting, these results have indicated that the violent characteristics of thegame may have triggered the different neural responses, indicating that playing a
violent video game may attenuate inhibition.
In an fMRI study of healthy male adolescents (Strenziok et al., 2011), response anddesensitization to violent videos were examined. Participants watched videos andjudged whether the level of aggression was higher or lower compared with theprevious video. Response to aggression on video was associated with activity across awide set of regions, including bilateral inferior frontal cortices, anterior cingulate,fusiform gyrus, and occipital cortex. Investigators then examined for activity changes
related to desensitization, diminished response to emotionally arousing stimuli
following repeated exposures. A time-by-aggression level interaction was found in theleft orbitofrontal cortex and bilateral parietal cortices, where activity decreased overtime for more aggressive videos. This result provides evidence that brain activity
related to both emotion (orbitofrontal) and attention-related (parietal) aspects of theviolent film clips decreased as time went on, indicating neural desensitization.
This group also reported a relationship between brain structure and past selfreported media violence exposure (Strenziok et al., 2010). Gray matter density in theleft lateral orbitofrontal cortex was higher with lower levels of reported television andmovie violence in adolescence. In addition, recent work in our laboratory indicatedthat higher violent television exposure is related to lower frontoparietal white mattervolume (Hummer, Kronenberger, Wang, Anderson, & Mathews, 2014). While thisrecent study was conducted in young adult males, the structural characteristics
identified suggest that brain development prior to participation, much of which
occurred during adolescence, was associated with violence exposure. Similarly,
research has found exposure to real-life violence to be related to occipital cortex
volume or maturity of visual-limbic tracts in young adults (Choi, Jeong, Polcari,
Rohan, & Teicher, 2012; Tomoda, Polcari, Anderson, & Teicher, 2012).
This research fits into a somewhat larger pool of adult neuroimaging research
regarding media violence, which has focused on mechanisms regarding desensitizationand inhibitory control. For instance, adults with higher past exposure to violent video
games have a reduced ERP response to violent images (Bartholow, Bushman, &Sestir, 2006), and the lower ERP responses were correlated with subsequently
delivering a more aggressive, intense noise blast to opponents in a competitive game.
A recent fMRI study examined brain activity in adults who viewed a violent film clip
and compared their responses with those from individuals who watched a nonviolent
clip (Guo et al., 2013). The violent clip group had a reduced neural response to images
depicting pain in others in the sensorimotor cortex and insula, a brain network
involved in evaluating pain in self and others.

8American Behavioral Scientist

Neuroimaging studies of adults have also found a relationship between cognitive
control mechanisms and violent media exposure. For instance, Bailey, West, andAnderson (2010) reported that adults with high video game violence exposure had
attenuated frontal ERP responses during high-conflict trials which required thegreatest cognitive control mechanisms. These studies and others (Engelhardt,
Bartholow, & Saults, 2011; Kelly, Grinband, & Hirsch, 2007; Mathiak & Weber,2006) highlight the relationship between exposure to media violence and brain
function, with a consistent association found between decreased activity in prefrontal
control mechanisms in participants with greater media violence exposure cumulatively
or immediately prior to testing. However, due to the dynamic nature of childhood
brain development, it is not so easy to simply assume that neural findings from adults,
even young adults, translate easily to children or adolescents.
The degree to which this adult research helps us understand how children’s brains
are affected by media violence is dependent on the similarities and differences
between developing pediatric brains and more stable adult brains. Of course, thefundamental differences between children’s and adult brains are precisely the reasons
why studying how media violence affects young brains is of particular interest. The
complex trajectory of childhood brain development, as outlined earlier, makes thistime period more vulnerable to substantial, long-term effects of environmental stimuli,
including media violence.

Interpreting Imaging Research Through a
Neurodevelopment Lens
Given the significant evidence associating greater media violence exposure with both
short- and long-term increases in aggressive thoughts, feelings, and behaviors, there isa strong need to understand the mechanisms underlying emotional and behavioral
control and how these mechanisms are influenced by media violence. Thus, researchhighlighting effects of media violence on prefrontal executive function, and prefrontal
interaction with emotion-sensitive regions, may be especially valuable tocharacterizing media violence effects.
For instance, playing a violent video game was found to reduce subsequent
prefrontal activity (compared with a nonviolent game) by Wang et al. (2009) andHummer et al. (2010) during tasks requiring control of cognitive processes or
behavior. These tasks were specifically designed and implemented to engage
prefrontal control capabilities. Prefrontal activity during similar tasks has been shown
to change across childhood and adolescence (Luna et al., 2001). To understand what
this exposure-related reduction in prefrontal activity means in terms ofneurodevelopment, additional research must be carried out at different ages, or ideally,at multiple ages within the same participants. Moreover, we must strive to clarify how
any prefrontal changes found are related to real-world psychological and behavioral
traits of interest.
The interaction of prefrontal regions with emotion-sensitive limbic regions is a key
part of emotion regulation (Banks, Eddy, Angstadt, Nathan, & Phan, 2007; Gross,
2002; Hariri, Bookheimer, & Mazziotta, 2000). Characterizing how exposure to media
violence may affect maturation of the relationship between these regions during

Hummer9childhood and adolescence is an important focus of neuroimaging research. Teens whoplayed a violent game for 30 minutes were found to have lower medial prefrontal
cortex control over the amygdala during presentation of aggressive words (Wang etal., 2009). The amygdala acts as an alert system for the brain, activating strongest in
response to stimuli that demand immediate attention or a behavioral response.
Appropriate control of the amygdala by prefrontal regions helps limit overly
impulsive, emotional responses to provocation. Since the adolescent prefrontal cortex
has not yet reached full maturity, extensive media violence exposure duringadolescence may impair prefrontal-limbic communication and have detrimental effects
on emotion regulation into adulthood. However, neuroimaging research has yet to
examine long-term causal effects of media violence exposure on prefrontal
capabilities, partially due to methodological limitations in what we can ascertain withan experimental design.
This framework is helpful for interpreting research regarding long-term effects ofmedia violence exposure (Gentile, Coyne, & Walsh, 2011; Huesmann et al., 2003).
Longitudinal research has indicated that, even when controlling for childhood
aggression levels, adults with greater exposure to television violence as children
exhibited more aggressive behaviors as adults (Huesmann et al., 2003). This long-term
outcome may be due to altering the neurodevelopmental trajectory of the prefrontal
cortex (Figure 1), resulting in diminished inhibitory control of negative behaviors andan increased likelihood of aggressive behavior.

Figure 1. A hypothesized model for neurodevelopmental effects of media violence.
Note. One potential model for media violence effects on brain development is depicted. Individuals
demonstrating poor or delayed development may be more susceptible to potential effects of high levels of
media violence, particularly during a sensitive period in early adolescence. Brain development may bequantified by a variety of neuroimaging methods, including diffusion tensor imaging indicators of
microstructural properties of white matter tracts.

10American Behavioral Scientist

Optimizing Neuroimaging in Media Effects Research
As with any research method, neuroimaging has its limitations. Participants are lying
alone in an enclosed space and must remain still, so it is difficult to simulate realworld exposure to violent media, limiting external validity. Laboratory or
epidemiologic data may better reflect or quantify real-world outcomes, but cannot
elucidate underlying biological mechanisms. The research value of neuroimaging isdependent on our ability to integrate the neurobiological and neurodevelopmental
information it can glean with research using other methodologies to investigate
cognitive, emotional, and behavioral processes.
It is also important to triangulate neuroimaging data with results from othermethodologies in order to generate meaningful findings on real clinical outcomes.
Investigators must take care not to overestimate the novelty or significance of findings
simply because, for instance, fMRI images are presented. One early brain imaging
primer laid out this notion in a straight-forward, yet necessary, principle: “ . . .
investigations that simply show there are changes in brain activation that correspondto some aspect of social cognition, emotion, or behavior contribute little—after all,what scientific theory would predict otherwise!” (Cacioppo et al., 2003, p. 652). In
other words, finding brain activity changes in response to media violence is not, on its
own, novel evidence that media violence exposure is having a meaningful effect. Afterall, substantial behavioral research already provides evidence that increased levels of
aggression can follow exposure to media violence—so of course the brain is involved.
The key is in using neuroimaging to contribute to understanding the nature andmechanism of the effect.
In other words, altered brain activity following violent video game exposure does
not provide definitive proof that the games are “good” or “bad” for players, or eventhat the games increase aggression. These studies do, however, provide evidence that
inhibitory control deficits may drive increases in aggression found with other researchparadigms. Interpreting neuroimaging results in studying media effects is best
performed with a full understanding of the limitations of the approach and of the
background psychological literature.
Similarly, investigators should not shy away from imaging paradigms based on alack of complexity alone—relatively simple paradigms can provide results with moreclarity, even if external validity is lower. During cognitive control fMRI paradigms,
such as the Go/No-Go, the in-scanner tasks are not overly difficult and the participants
are in a relaxed state, so the true capacity of prefrontal cortex is likely not reached. Yet
we hope to extrapolate findings to how the region would act during heightened statesof arousal and/or peer-influenced situations, when overt aggressive behavior is more
likely and prefrontal control more necessary. This principal is similar to a physician’s
stethoscope, which is often used on a still, relaxed patient in the doctor’s office todetect potential concerns, even though the risk of heart problems is greatest when aperson is much more active. Establishing ecological validity in fMRI paradigms canbe even more problematic than psychological laboratory experiments, given theconstraints of testing immobile participants in an MRI scanner. Nevertheless, clearly
identifying changes in inhibitory control mechanisms provides an excellent
complement to existing psychological research.

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We must take care to not overextend the conclusions we draw from such findings.
To maximize the generalizability of results, one option is to examine the relationshipbetween behavior measured outside the scanner with brain activity data. In thismanner, the strengths of multiple methods can be more easily combined. If repeatedattempts to find a relationship between brain activity changes and physiological,
emotional, or behavioral changes outside the scanner are unsuccessful, it is possiblethat the importance of neural changes is minimal. That said, it would certainly be
difficult to ascertain that an identified neural change has absolutely no effect on realworld thoughts or behaviors.

Future Directions
Ultimately, a main purpose of such research is to identify and limit any potential
detrimental effects that exposure to media violence may have on the developing brain.
Neuroimaging research on the topic should therefore focus on precisely characterizing
how violent media affects the brain, establishing what characteristics of viewing or
game play are most influential, and determining who is most at risk for negative
effects. Answering these questions will provide direction on where to focus
prevention, interventions, and policy recommendations in order to limit negative longterm effects on the brain.
One consistent difficulty in studying long-term effects of media violence research
is distinguishing whether exposure to large amounts of media violence actuallycontributes to increases in aggression (Anderson et al., 2003; Paik & Comstock, 1994)
or poorer executive function (Kronenberger et al., 2005), or whether individuals withworse attention and weaker self-control are drawn to violent media. Unfortunately, it
is ethically impossible to develop a longitudinal experimental investigation of theeffects of exposure to media violence. We cannot assign randomized groups to solely
watch educational programming or violent programming for several years duringchildhood and see what happens. Instead, evidence must be combined fromcomplementary sources: observational studies that identify the outcomes with whichpast media violence exposure is correlated; longitudinal designs that follow media
habits and measure behaviors over many years; experimental investigations that canmore directly pinpoint violence exposure as a cause of short-term effects; and training
or intervention studies that can determine whether long-term effects can be reduced.
To date, neuroimaging studies have started to address several of these avenues inchildren and adults, particularly long-term correlational and short-term experimental
research (Hummer et al., 2010; Mathews et al., 2005; Strenziok et al., 2011). Goingforward, such work should continue to examine prefrontal-limbic interactions inparticular, in order to investigate control of aggressive thoughts and behaviors.
Extended neuroimaging studies, with repeated measures within the same
individuals, would be immensely helpful in completing the story in whether and how
media violence exposure influences brain development. Longitudinal neuroimaging
studies, which measure neural characteristics at several points during childhood, havebeen essential to outlining the trajectory of childhood and adolescent brain
development (Giedd, 2004; Giedd et al., 1999; Gogtay et al., 2004). Similar research,adding continuous measurements of television, film, and video game habits, can help

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American Behavioral Scientist

ascertain whether ongoing neurodevelopmental changes are influenced by current
violence exposure. For example, if structural characteristics indicating delayeddevelopment (e.g., lower FA measured by DTI) predict later levels of violent video
game play, then media violence exposure may be viewed as the result, rather than thecause of developmental issues. On the other hand, if violence exposure predicts neuralchanges after controlling for age-related developments, then the evidence would
support the hypothesis that such exposure affects brain development. These questions
are significant given that the trajectory of cortical thickness and white mattermaturation is linked to attention problems (Konrad & Eickhoff, 2010; Shaw et al.,2007) or other neurocognitive functions (Mabbott et al., 2006; Olson et al., 2009;
Silveri, Tzilos, & Yurgelun-Todd, 2008), and both experimental and correlational
research link media violence to deficits in attention and other facets of self-control(Bailey et al., 2010; Bushman & Huesmann, 2006; Kronenberger et al., 2005).
One can also propose a model in which children who demonstrate somewhat
delayed development and/or have a higher vulnerability to the impact ofenvironmental factors are driven either further “off-course” by extensive exposure to
media violence (Piotrowski & Valkenburg, IN PRESS[PE: Please include year of
publication and provide complete reference details for Piotrowski & Valkenburg,
IN PRESS at the proof stage.]). A similar model is used in characterizing the effectthat adolescent substance abuse may have on long-term brain development (Figure 1).
Longitudinal neuroimaging investigations could clarify whether such a model isappropriate for media violence.
Along these lines, it is important to identify any potential risk factors that alter the
degree to which media violence may influence a person’s brain. Media violence is justlike any other experience, such as an exercise regimen, that enacts biological changes,
with the strength and manner of effects based on a combination of an individual’sbaseline characteristics, susceptibility to change, and features of the experience. In thiscase, baseline factors of interest include not only existing neurobiologicalcharacteristics which can be assessed through imaging techniques but also genetic,
family environment, and personality variables.
Moreover, the effects of various contextual features of television or video game
exposure, including whether games are played in individual or social/multiplayer
settings, are also important factors to explore in future neuroimaging investigations.
Considering the many nuances of video games, distinguishing the impact of eachspecific aspect of game play on subsequent brain function is increasingly difficult, andinvestigators should always take care not to lose the scientific forest for the trees. In
addition, while the focus of this review is to identify potential effects of violent media
exposure on brain development, the influence of positive or prosocial video games orother media interactions should not be ignored. Certainly, violence is not the only
game characteristic that may shape the brain. Indeed, neuroimaging evidence has
indicated that cognitive training games may strengthen maturation of prefrontal
regions (McNab et al., 2009; Mozolic, Hayasaka, & Laurienti, 2010).

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Summary
Neuroimaging tools are vital to characterizing brain development during childhood
and adolescence. Neurodevelopment is affected by a variety of external influences,including the potential impact of various forms of media violence. Neuroimaging
techniques provide an essential tool to investigate how high levels of media violence
exposure may modify brain development. To optimize the utility of neuroimaging
tools, investigators must design and interpret imaging studies integrated with othermedia violence research methods, including survey data, behavioral measurements,
and physiological recordings. To date, neuroimaging research suggests that increased
exposure to violent media content is associated with lower prefrontal control ofemotions or behaviors and with delayed development of frontal or frontoparietal
regions. As neuroimaging techniques evolve and measurement resolution of brain
form and function continue to improve, researchers should integrate these methods
with diverse research tools to focus on understanding long-term effects of exposure toviolent media on the development of young brains, focusing on prefrontal and limbic
regions and their interactions.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship,
and/or publication of this article.

Funding
The author(s) received no financial support for the research, authorship, and/or publication ofthis article.

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Author Biography
Tom A. Hummer is an assistant research professor in the Department of Psychiatry at Indiana
University School of Medicine. Before coming to Indianapolis, he received his undergraduate
degree in psychology from the Ohio State University and a PhD in computational neurosciencefrom the University of Chicago. His primary interests are in utilizing neuroimaging techniques
to characterize biological and environmental effects on adolescent brain development. He has
employed MRI techniques to examine short- and long-term effects of violent video game playor television violence, and future aims include identifying how media violence affects neuraland hormonal mechanisms involved in emotion and stress regulation.