Association of excessive social media use with abnormal white matter integrity of the corpus callosum
Introduction
The use of social media sites can excite the reward centers of the brain (Meshi et al., 2013, Meshi et al., 2015). Hence, some people may develop excessive use patterns that may provide immediate reinforcing rewards but be disadvantageous in the long-run, and infringe users' normal functioning (Turel et al., 2018b, Turel et al., 2016, Turel and Serenko, 2012, Turel et al., 2011, Xu et al., 2012). Excessive social media use (ESMU) is defined as an excessive behavioral pattern of social media use that has adverse effects on individuals by producing addiction-like symptoms, including salience, withdrawal, mood modification, relapse, conflict, and tolerance" (He et al., 2017b). It can be viewed as a sub-category in the broader spectrum of problematic excessive use of the Internet. We use the term ESMU because agreement regarding the use of the term "addiction" to describe such issues, especially in the context of social media use, is still lacking (Turel, 2015) and we want to avoid over-pathologizing common, but excessive behaviors (Kardefelt-Winther et al., 2017) until the definition, classification conditions and boundaries of technology addictions mature.
Behaviorally, ESMU can manifest in an imbalance between reward and inhibition brain systems, which results in impaired decision making such that a person emphasizes short-term reinforcing rewards over larger long-term utilitarian rewards (Turel and Qahri-Saremi, 2016, Turel and Bechara, 2016a, Turel and Bechara, 2016b). Such disadvantageous decisions underlie many excessive behaviors (Chen et al., 2018, Wei et al., 2017). Functionally, ESMU has been associated with hyper-active amygdala-striatal system (Turel et al., 2014); structurally, it has been associated with differences in the amygdala-striatal system and in the posterior parts of the insular cortex (Turel et al., 2018c), but to a lesser extent with prefrontal abnormalities (He et al., 2017a, He et al., 2017b, Montag et al., 2017, Montag et al., 2018).
Another, yet largely overlooked possibility, is the idea that ESMU may also relate to impaired inter-hemispheric connections (Yip et al., 2013). The logic is that when the communication between hemispheres is suboptimal (e.g., when molecule diffusion is isotropic), transfers of information may be too slow or ineffective for analyzing the situation and to mobilize the needed inhibition resources (Zorlu et al., 2013). Such inter-hemispheric connectivity issues (as often manifested in impaired integrity of the corpus callosum) result in deficient decision making ability, as reflected in increased delay discounting (Olson et al., 2009) and poor performance on the Iowa Gambling Task (Brown et al., 2012). Indeed, reduced effectiveness of the corpus callosum has been demonstrated across many behaviors that involve deficient decision making. These include opiate addiction (Bora et al., 2012), alcoholism (Harris et al., 2008), marijuana use (Arnone et al., 2008), gambling (Joutsa et al., 2011b), substance abuse (Kaag et al., 2017), kleptomania (Grant et al., 2006) and trichotillomania (Chamberlain et al., 2010).
Recent research has also demonstrated that corpus callosum white matter integrity can be associated with excessive use of technologies, including the Internet (Lin et al., 2012a, Shin et al., 2013, Yuan et al., 2011), videogames (Jeong et al., 2016; Weng et al.), and smartphones (Hu et al., 2017). Nevertheless, results have not been consistent. While some point to increased corpus callosum effectiveness in excessive gamers (Jeong et al., 2016), others found decreased effectiveness in excessive Internet users (Bi et al., 2015, Lin et al., 2012a) and gamers (Weng et al., 2013), and others found no corpus callosum microstructure changes in excessive Internet (Yuan et al., 2011) or smartphone (Hu et al., 2017) users. It is noteworthy that such inconsistencies are common in the study of the corpus callosum's role in other problematic behaviors; they may stem from differences in samples, duration of behavior and processing methods (Yu et al., 2016), or merely from the idea that diffusivity measures in this area are notoriously difficult due to the “kissing axons” problem (Jbabdi and Johansen-Berg, 2011).
These results imply that corpus callosum structural changes that promote decision making deficits (as often manifested in measures of isotropic diffusivity) may underlie excessive use of technologies, but that such corpus callosum effects may vary from one technology, sample and context to another. Hence, focusing on ESMU is research-worthy, because this is a new context that has not been addressed in prior corpus callosum research. Moreover, if we assume that ESMU is similar to other behaviors in which deficits in weighing short- vs. long-term rewards and punishments prevail (e.g., substance abuse, excessive gambling), we can expect to find white matter changes in the corpus callosum that are associated with ESMU.
We focus on corpus callosum white matter integrity in terms of Fractional Anisotropy (FA) and Mean Diffusivity (MD). FA captures the degree of restrictiveness of molecule diffusion along the axon axis. When its value is 0 it means that the diffusion is sporadic in all directions and isotropic; when it is 1, it means that the diffusion is efficient and runs only along the axonal axis. Isotropic diffusion can reflect issues in myelination, axonal integrity and density, axon diameter and fiber crossings (Zatorre et al., 2012). FA is a common index of white matter integrity. Studies found significant association between FA in the corpus callosum and behavioral measures, including addiction (El-Hage et al., 2017, Lin et al., 2012b). For example, Lin et al. (2012b) found that an Internet addiction group had significantly lower FA in the corpus callosum than controls. El-Hage et al. (2017) found that COMT male Val homozygotes had significantly higher FA in the corpus callosum compared to Met-carriers. MD captures the total diffusion, in all directions, within a voxel. It is hence an inverse measure to FA; high values of MD are associated with low myelination (or high demyelination), reduced axonal density and may be indicative of axonal degeneration (Landman et al., 2007). We expect inefficient interhemispheric communication, manifested in reduced FA (Bi et al., 2015) and increased MD (Joutsa et al., 2011a), in people with higher levels of ESMU.
To test this hypothesis, we conduct a DTI study of 20 social media users, which was part of a larger study program that involved functional (Turel et al., 2014) and structural (He et al., 2017a) features of ESMU. We start with hypothesis-driven Region of Interest (ROI) analysis of the three core subdivisions of the corpus callosum (genu, body, and splenium). This split is guided by neurological and neuropsychological evidence that these parts are not functionally equivalent (Eliassen et al., 2000, Fabri and Polonara, 2013). The anterior parts of the corpus callosum are well known to relate to prefrontal and executive function processing, while the middle is more concerned with sensory-motor processing, and the posterior part is more concerned with vision-related processing. Hence, lumping together all tracts in the corpus callosum may be misleading and present a birds-eye-view of white matter integrity rather than point to specific areas involved in ESMU. We then proceed with a whole-brain voxel-wise analysis (Tract Based Spatial Statistics; TBSS) as a supplemental approach. This is done to provide further support to our ROI analysis, and also to detect if there are other relevant regions, beyond our hypothesized ones, that emerge as significant; these may inform future research. In these analyses we correlate the ESMU scores with white matter integrity measures (FA and MD), after corrections for multiple comparisons and accounting for controls.
Section snippets
Participants
Twenty normal participants (10 females, Avgage = 20.3 years, SDAge = 2.25 years, 18–23) who reported using Facebook and who were free of current and lifetime Axis I diagnoses (as per a short version of the Structural Clinical Interview for DSM-IV we administered) were recruited to participate in this study. The broader study program, which is beyond the scope of this study, employed the same participants for studying functional activations (Turel et al., 2014) and structural changes (He et al.,
Results
After controlling for age, we found in the ROI-based analysis a significant positive correlation between the MD in both the body and the splenium of corpus callosum (CC) and ESMU score (Table 1). However, the correlation between the MD in the body of CC and ESMU score was not significant after FDR correction. No other correlations were significant.
In the TBSS analysis, after controlling for age, we found that the FA of right corticospinal tract (MNI coordinates 10, -25, 55, Table 2 and Fig. 1)
Discussion
This study sought to extend the understanding of the neural basis of ESMU. Prior research indicated that ESMU can be associated with changes in functional activation and grey matter structure of reward systems in the brain (He et al., 2017a, He et al., 2017b, Turel et al., 2014, Turel et al., 2018c). We posited that it is also possible that ESMU is linked to changes in white matter microstructure, especially in the corpus callosum, because reduced corpus callosum white matter integrity
Conclusion
This study demonstrated that ESMU may be associated with deficits in interhemispheric connection and in the communication along the ventral semantic path. These are reflected in increased mean diffusivity in key regions of the corpus callosum, extending to the forceps minor, and increased mean diffusivity of the left Superior and Inferior Longitudinal Fasciculi. We call for future research to further examine the important emerging issue of ESMU.
Disclosure statement
The authors declare no conflict of interest.
Author contributions
Conception and design of the study: OT, QH, AB; acquisition and analysis of data: OT, QH; drafting the manuscript or figures: OT, QH, AB.
Funding information
QH was supported by research grants from the National Natural Science Foundation of China (31400959), Entrepreneurship and Innovation Program for Chongqing Overseas Returned Scholars(cx2017049), and Fundamental Research Funds for Central Universities (SWU1809003 and SWU1709106).
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These authors contributed equally to this work.