We all heard the warning as kids: “That TV will rot your brain!” You may even find yourself repeating the threat when you see young eyes glued to the tube instead of exploring the real world. The parental scolding dates back to the black-and-white days of I Love Lucy, and today concern is growing amid a flood of video streaming on portable devices. But are young minds really being harmed?
With brain imaging, the effects of regular TV viewing on a child's neural circuits are plain to see. Studies suggest watching television for prolonged periods changes the anatomical structure of a child's brain and lowers verbal abilities. Behaviorally, even more detrimental effects may exist: although a cause-and-effect relation is hard to prove, higher rates of antisocial behavior, obesity and mental health problems correlate with hours in front of the set.
Now a new study hits the pause button on this line of thinking. The researchers conclude that the entire body of research up to now has overlooked an important confounding variable, heredity, that could call into question the conventional wisdom that TV is bad for the brain. Further study will be needed to evaluate this claim, but the combined evidence suggests we need a more nuanced attitude toward our viewing habits.
Replaying the evidence
To understand the argument against television, we should rewind to 2013, when a team ofresearchers at Tohoku University in Japan, led by neuroscientist Hikaru Takeuchi, first published findings from a study in which the brains of 290 children between the ages of five and 18 were imaged. The kids' TV viewing habits, ranging from zero to four hours each day, were also taken into account. Takeuchi and his colleagues found that the more television these kids watched, the bulkier the brain's hypothalamus, septum, sensorimotor area and visual cortex became. These areas are implicated in multiple processes, including emotional responses, arousal, aggression and vision, respectively. In addition, the brain showed thickening in a frontal lobe region, the frontopolar cortex, that is known to lower language-based reasoning ability. Testing confirmed that verbal IQ scores, which measure vocabulary and language skills, fell in proportion to the hours of TV the children watched. The changes in brain tissue occurred regardless of the child's sex or age or his or her family's income.
Some of these brain differences could be benign: an increase in the visual cortex's volume is likely caused by exercising eyesight while watching TV. But thickening in the hypothalamus is characteristic of patients with borderline personality disorder, increased aggressiveness and mood disorders. Perhaps watching TV shows, with their high density of drama, action and comedy, engages circuits of arousal and emotion such that these areas, rather than circuits of intellect, strengthen. This change could lead to psychological and behavioral issues. Previous studies have shown that for each additional hour of television watched in childhood, the odds of developing symptoms of depression increase by 8 percent and the odds of being convicted of a crime increase by 27 percent. And other findings suggest that for every two hours watched in one's youth, the odds of developing type 2 diabetes increase by 20 percent.
There are many possible explanations for these links. TV viewing is generally sedentary and solitary, denying children many health benefits of physical activity and socialization. The development of verbal proficiency, reasoning and other intellectual abilities could atrophy from passively viewing a screen. “Guardians of children should consider these effects when children view TV for long periods,” Takeuchi and his colleagues concluded.
But the correlation between TV viewing and brain and behavioral changes does not necessarily tell us the whole story. The quandary scientists face is determining whether TV viewing causes changes in brain and behavior or whether preexisting personal traits or other conditions underlie binge watching.
Fast-forward to the new study, by criminologists Joseph Schwartz of the University of Nebraska Omaha and Kevin Beaver of Florida State University. Schwartz and Beaver analyzed middle and high school students to look for associations between TV viewing and a range of factors such as race, gender, antisocial behavior and incarceration for violent crimes. Researchers checked back with nearly 15,000 of these children about two years later and again after they had reached adulthood, between the ages of 18 and 26. Much like previous studies, they found that young adults who had watched more television during early adolescence were more likely to engage in antisocial behavior, to be arrested at least once and to be incarcerated as an adult.
The researchers then added one more factor to their analysis. The study included more than 3,000 sibling pairs (that is, half-siblings, full siblings, and identical and nonidentical twins). The correlation between nearly all the negative behavior and time spent watching TV vanished after the researchers statistically accounted for relatedness. Genetics, they concluded, shapes brain and behavior, which in turn has wide-ranging consequences, including how many hours of TV individual children tend to watch and how their brains respond to it. “For example,” Schwartz says, “children with increased predisposition toward aggressive behavior may be more drawn to TV.” Similarly, those who are genetically inclined to depression or obesity may be more likely to spend their free time watching TV in the family room rather than shooting hoops on the basketball court.
Research suggests that heredity accounts for approximately half of the risk of developing antisocial behavior, with the remaining risk explained by environmental influences. In particular, genes that influence neural signaling involving dopamine and serotonin are associated with increased criminality, antisocial behavior and psychological disorders. “[Our findings] suggest that the changes in neurobiological functioning observed by Takeuchi et al. would have occurred regardless of the actual amount of television watched,” Schwartz says.
It would appear that researchers have been weighing the evidence out of balance by neglecting the important factor of heredity in TV habits. But this chicken-or-egg dilemma resolves as it does with real chickens: this is an interdependent cycle. For instance, a 1990 study comparing adopted and nonadopted children raised in the same home found that genetics was the most important factor in determining how many hours of TV kids watched. But the study also found that the higher a mother's IQ, the fewer hours both her biological and adopted children spent glued to the tube.
Everyone's brain is different, and what you do with your brain—especially at a young age, when it is developing—does affect its physical structure and function. If a child has inherited risk factors predisposing him or her to behavioral difficulties, he or she will likely spend more time watching TV, but doing that is not helping the situation. “Watching more TV may trigger various neurobiological changes that ultimately exacerbate any underlying inclinations toward aggressive behavior,” Schwartz warns. In such cases, limiting exposure to TV could be helpful. For other children, TV may not have this risk.
Recognizing this fact, parents will want to regulate their children's TV viewing in the context of those children as individuals. Ultimately, Mom is right: the more time spent sitting on the couch, the less time spent in physical activity, reading, and interacting with friends. The lack of physical activity and intellectual pursuits has obvious physical and cognitive consequences. TV may or may not rot the brain, but sitting perched in front of the screen for so long does seem to waste it.
Television (TV) viewing is known to affect children's verbal abilities and other physical, cognitive, and emotional development in psychological studies. However, the brain structural development associated with TV viewing has never been investigated. Here we examined cross-sectional correlations between the duration of TV viewing and regional gray/white matter volume (rGMV/rWMV) among 133 boys and 143 girls as well as correlations between the duration of TV viewing and longitudinal changes that occurred a few years later among 111 boys and 105 girls. After correcting for confounding factors, we found positive effects of TV viewing on rGMV of the frontopolar and medial prefrontal areas in cross-sectional and longitudinal analyses, positive effects of TV viewing on rGMV/rWMV of areas of the visual cortex in cross-sectional analyses, and positive effects of TV viewing on rGMV of the hypothalamus/septum and sensorimotor areas in longitudinal analyses. We also confirmed negative effects of TV viewing on verbal intelligence quotient (IQ) in cross-sectional and longitudinal analyses. These anatomical correlates may be linked to previously known effects of TV viewing on verbal competence, aggression, and physical activity. In particular, the present results showed effects of TV viewing on the frontopolar area of the brain, which has been associated with intellectual abilities.
children, gray matter volume, television, verbal, white matter volume
Many cross-sectional and longitudinal studies have reported deleterious effects of television (TV) viewing on the cognitive abilities, attention, behaviors, and academic performance of children (Johnson et al. 2002, 2007; Christakis et al. 2004). Longer TV viewing was associated with lower intelligence quotient (IQ) and reading grades in a cross-sectional study (Ridley-Johnson et al. 1983). However, the longitudinal effects of TV viewing on Full Scale IQ (FSIQ) are less clear (Gortmaker et al. 1990). In an intervention study, restricting children's TV viewing for a short period improved their cognitive abilities (Gadberry 1981) and another longitudinal study showed that TV viewing affected attention (Landhuis et al. 2007), which in turn is correlated with a wide range of cognitive performances (Sergeant et al. 2002). Finally, longitudinal studies have shown that TV viewing has detrimental effects on verbal abilities including verbal working memory (Zimmerman and Christakis 2005).
As described above, TV viewing during infancy and childhood is considered to be detrimental to the development of intellectual abilities, particularly verbal ones. Thus, revealing the effects of TV viewing on neural systems and revealing the mechanisms by which TV viewing affects children's intellectual abilities is socially and scientifically important. However, despite numerous related psychological and functional magnetic resonance imaging (fMRI) studies of brain activities in children watching certain content, the effects of TV viewing on brain structures in children are unknown.
The medial prefrontal cortex (mPFC), frontopolar areas, posterior parietal areas, and the left inferior frontal gyrus (IFG) are considered to be important for the development of intelligence and verbal intelligence in children. The frontopolar area, which is the most anterior part of the brain, is considered to be involved in the evaluation of internally generated information as well as with higher functioning associated with hierarchical organization of the prefrontal functions (for review, see Christoff and Gabrieli 2000). Regional gray matter structures in medial and lateral areas around the frontal pole have also been rather consistently correlated with intelligence in adults (Haier et al. 2004; Gong et al. 2005; Colom et al. 2006; Narr et al. 2007) and children (Wilke et al. 2003; Frangou et al. 2004; Karama et al. 2011; Menary et al. 2013). These areas show developmental cortical thinning during development, and children with superior IQs show the most vigorous cortical thinning in this area (Shaw et al. 2006). In addition, the posterior parietal areas have rather consistently been shown to be correlated with intelligence together with other less consistent findings across the brain (Jung and Haier 2007), which may suggest the importance of the fronto-parietal areas and the associated functional network in intelligence (Jung and Haier 2007). On the other hand, the left IFG has been shown to be critical in a wide range of verbal cognitions (phonological, semantic, and syntax-related) (Vigneau et al. 2006). Regional gray matter structures have also been correlated with the verbal intelligence quotient (VIQ) (Konrad et al. 2012). Furthermore, children whose verbal IQ improved in a longitudinal developmental study showed a greater increase in regional gray matter volume (rGMV) in the left IFG (Ramsden et al. 2011). Considering the association between the duration of TV viewing and IQ/VIQ that TV viewing is less associated with cognitions such as monitoring and the evaluation of internally generated information, which is covered by the frontopolar area, we hypothesized that the duration of TV viewing would be apparent in the mPFC, posterior parietal areas, and left IFG areas.
The purpose of this study was to test these hypotheses and reveal the effects of TV viewing using cross-sectional and longitudinal analyses of brain structures in children. For this purpose, we employed cross-sectional analyses to identify associations between the duration of TV viewing and rGMV/regional white matter volume (rWMV) and then analyzed associations between the duration of TV viewing and rGMV/rWMV changes a few years later using a longitudinal design. We also investigated associations between the duration of TV viewing and VIQ/IQ using similar analyses to determine the nature of the associations between the duration of TV viewing and brain structural changes. We used voxel-based morphometry (VBM) to evaluate rGMV/rWMV (Good et al. 2001).
All subjects were healthy Japanese children and the details related to their initial recruitment (preexperiment) were described elsewhere (Taki et al. 2010). In brief, we collected brain magnetic resonance (MR) images from 290 subjects (145 boys and 145 girls; age range, 5.6–18.4 years) who did not have any history of malignant tumors or head traumas involving loss of consciousness. We stipulated that only right-handed children could participate in the study in an advertisement used for subject recruitment and also confirmed that all subjects were right-handed using the self-report questionnaire, the “Edinburgh Handedness Inventory” (Oldfield 1971). As per the Declaration of Helsinki (1991), written informed consent was obtained from each subject and his/her parent prior to MR scanning after a full explanation of the purpose and procedures of the study was provided. Approval for these experiments was obtained from the Institutional Review Board of Tohoku University. A few years after the preexperiment, the postexperiment was conducted and 235 subjects participated.
Due to issues with the quality of the imaging data or lack of effective data of psychological variables, the cross-sectional imaging analyses were performed with 276 subjects (133 boys and 143 girls) and the longitudinal imaging analyses were performed with 216 subjects (111 boys and 105 girls). Ten of the cases of missing data were due to a lack of effective psychological data in the preexperiment and the remaining was due to the poor quality of imaging data.
Assessments of Psychological Variables
In both the pre- and postexperiments, we measured the Full Scale intelligence quotient (IQ) using the Japanese version of the Wechsler Adult Intelligence Scale-Third Edition (WAIS-III) for subjects aged 16 years or older or the Wechsler Intelligence Scale for Children-Third Edition (WISC-III) for subjects younger than 16 years (Azuma et al. 1998). The tests were administered by trained examiners (Fujita et al. 2006