EEG during different emotions in 10-month-old infants of depressed mothers

EEG activity of 10-month-old infants of depressed and non-depressed mothers was compared during stimuli designed to produce happy and sad responses. During a baseline recording and during their happy facial expressions, infants of depressed mothers showed greater relative right frontal EEG asymmetry compared to infants of non-depressed mothers. The greater relative right frontal EEG asymmetry was also noted during a play interaction with their mothers. Infants of depressed mothers also showed more negative and less positive expressions. These findings are discussed in relation to the theory that frontal EEG activity may be a biological marker for symptoms associated with depression. The literature linking brain activity patterns (as measured by an electroencephalograph, EEG) and depressive symptoms suggests that asymmetric hemisphere activity of frontal regions of the brain is one potential marker for vulnerability to depression (Davidson, 1994, 1998). Specifically, greater right frontal EEG asymmetries, due to suppressed left hemisphere activity, are associated with a depressive style of behaviour. 296 N. A. JONES ET AL. Greater right frontal EEG asymmetries have been noted in infants of depressed mothers (Dawson et al., 1999; Field et al., 1995) and as early as 1 week of age (Jones et al., 1998). However, because a recent report, based on two studies, has found inconsistent relationships between adult depression and EEG asymmetry (Reid et al., 1998), those data may call into question whether infants of depressed mothers would display this pattern if their depressed mothers did not. Previous research by Davidson and his colleagues (Davidson, 1994), Dawson and her colleagues (Dawson, 1994), and our own work with infants (Field et al., 1995; Jones et al., 1997a,b, 1998) and children of depressed mothers (Jones et al., 2000) has suggested a link between greater relative right frontal EEG asymmetry and depressive symptoms. These studies are especially important because finding infant risk factors that may be precursors for later depressive disorders may help identify those children in need of early intervention. Besides basal EEG patterns associated with depressive symptoms, it is also important to assess individual differences in the reactions to affective elicitors and their link to EEG patterns and vulnerabilities for depressive symptoms. The present study examined baseline affective responses and EEG patterns in infants of depressed mothers and those that occurred during conditions designed to induce positive and negative emotions. These data may contribute to a model of vulnerability for depression that highlights both tonic and state-activated affective bio-regulatory capabilities. The present study was conducted for several reasons. It was designed to be a downward extension in infant age of recent Dawson et al. (1999) studies to suggest that even younger infants exhibit an aberrant style of affective and physiological responding. In addition, we specifically chose emotion-eliciting situations that have previously shown state-induced affective variation for infants of depressed and non-depressed mothers. In previous research, Dawson (Dawson et al., 1992, 1999) has reported limited variation in affective responses between infants of depressed and non-depressed mothers. One of the goals of the present investigation was to examine EEG activity during tonic, non-reactive states and during tasks that would elicit variation in positive and negative responses. In a rejoinder to Reid, Davidson (1998) has suggested that it is imperative to use tasks that produce variations in behavioural responses to examine the theorized association between emotions and neural circuitry. Moreover, Davidson (1988) has suggested that verification of the emotional response and comparing at least two emotions during at least two distinct methods are important methods when examining emotion± physiology relationships. In several of the studies with infants of depressed mothers, minimal affective responses were noted, thus calling into question the methods used to produce emotional responses (Dawson et al., 1999). In the present study we used a very specific group of depressed mothers and examined the infant’s physiology in correspondence with their affective style of responding. We also used clearly defined positive or negative stimulus conditions, including at least two or three stimulus conditions for both positive responses and negative responses. In addition, we attempted to verify the existence of the emotional responses before linking the emotional response to the EEG activity. Doing this, we felt would improve our understanding the affective responses of infants of depressed mothers and the neural processing associated with those emotions. The present study examined right and left frontal EEG patterns in 10-month-old infants of depressed and non-depressed mothers during baseline and emotion-eliciting conditions. Based on our previous studies, we expected that infants of depressed mothers would show greater relative right frontal EEG asymmetry (due to left EEG DURING DIFFERENT EMOTIONS 297 hemisphere hypoactivation) compared to infants of non-depressed mothers during the baseline condition. During the viewing of sad facial expressions, we expected that the infants of depressed mothers would show greater relative right frontal EEG asymmetry and during the viewing of happy facial expressions infants of non-depressed mothers would show greater relative left frontal EEG asymmetry. Further, infants of depressed mothers were expected to show less positive affect and greater negative affect during play interactions with their mothers. Associations between affect and EEG activity would also be noted during the play interactions and maternal separation procedures.