Increasing evidence supports the notion that both internalizing (e.g., anxiety) and externalizing (e.g., aggression) behavioral dysregulation are associated with abnormal communication between brain regions. Electroencephalographic (EEG) signals across two electrode sites are said to be coherent with one another when they show consistent phase relations. However, periods of desynchrony with shifting of phase relations are a necessary aspect of information processing. The components of EEG phase reset (‘locking’ when two regions remain in synchrony, and ‘shifting’ when the two regions desynchronize momentarily) show dramatic changes across development. We collected resting EEG data from typically developing 12 to 15-year-olds and calculated phase shift and lock values in the alpha frequency band across 14 pairs of electrodes varying in inter-electrode distance. A composite measure of participants’ aggression levels was positively associated with phase shifting, particularly in the low alpha frequency range, most strongly over the left hemisphere, consistent with the relatively greater left-prefrontal activity reported in aggressive adults. A composite measure of anxiety levels was positively associated with alpha phase locking at sites over both hemispheres, consistent with changes in connectivity reported during anxious thinking in adults. Associations with anxiety could not be explained by traditional EEG coherence measures and suggest that phase shifting and locking might provide an important non-invasive associate of clinically problematic behavior.
Adolescence is a period characterized by major biological, psychological and social changes that can affect the developing adolescent’s ability to self-regulate and these changes coincide with the onset of many forms of psychopathology (Lewinsohn, Clarke, Seeley, & Rohde, 1994; Paus, Keshavan, & Giedd, 2008). Of particular interest here are increased incidence of anxiety and aggression, markers of emotional and social dysregulation respectively.
Both anxiety and aggression have been associated with specific patterns of communication between neural regions. Aberrant connectivity has been observed in some anxiety disorders (Liao et al., 2010 and Marchand, 2010) and in some of those prone to aggressive behavior (Hofman and Schutter, 2009 and van Honk et al., 2010), using fMRI and TMS connectivity techniques. The direction of these aberrations varies across studies with Liao et al. (2010) reporting decreased connectivity in those with social anxiety disorder relative to controls within both motor and visual networks, and increased connectivity in a self-referential network involving medial prefrontal regions. The strength of the coherent activity in some of these networks is associated with symptom severity. Two other research groups (Decety et al., 2009 and Shannon et al., 2009) report that youth prone to aggressive behavior show reduced intrahemispheric connectivity (specifically between limbic and prefrontal structures important to emotion regulation).
There are, however, electroencephalographic (EEG) coherence and other connectivity measures that may better capture the moment to moment changes in functional connectivity that occur between neural regions (see e.g., Sporns, Tononi, & Edelman, 2000). Examples include the work of Hinrichs and Machleidt (1992) who used traditional alpha EEG coherence measures and observed globally decreased alpha coherence together with increases in peak alpha frequency during anxious thinking in an adult sample. Knyazev, Savostyanov, and Levin (2005), however, found increased levels of low alpha coherence (adjusted to each participant’s peak frequency, but generally 8–10 Hz) correlated positively with increased levels of state anxiety in an adult sample. Thus, the specific direction of coherence patterns associated with anxiety is unclear at present, and discordant results may be partially attributable to which frequencies within the alpha range are examined.
With respect to aggression, Hinrichs and Machleidt (1992) observed globally increased alpha coherence in participants during aggressive cognition, but their results did not address whether these relations would extend to trait measures of the same construct. Little other work has addressed the association between EEG measures of connectivity and aggressive behavior.
In sum, aberrant connectivity may be associated with anxiety and increased connectivity may be associated with aggressive states. Important for the present work, both Hinrichs and Machleidt (1992) and Knyazev et al. (2005) report on average coherence values across the whole scalp providing little to no information on the scalp locations of group and state differences despite fMRI and TMS work suggesting that these differences may be regionally specific (e.g., Hofman and Schutter, 2009, Liao et al., 2010, Marchand, 2010 and van Honk et al., 2010). In the present study we test whether these reported state differences in coherence extend to stable trait measures and we aim to provide improved topographical detail on the observed effects.
Given the rapid biological and psychological changes during adolescence, we first wished to determine whether variance in anxiety and aggression could be predicted by age, pubertal status, sex, and/or their interaction, and to then examine neurophysiological effects in light of these. Females reported significantly higher levels of anxiety than males (t(83) = 2.85, p = .006). Anxiety levels were not correlated with age, pubertal status, or the interaction of pubertal status and sex (see Table 1 for values). Males and females did not differ in levels of reported aggression (t(83) = 1.51, p = .13). Aggression scores were significantly correlated with pubertal status and the interaction of pubertal status and sex. Aggression and anxiety scores were highly correlated with one another (see Table 1) and remained highly correlated once pubertal status, sex and their interaction were partialled out, (r(80) = .47, p < .001).
