Cerebral laterality in adolescent major depression

Novel mechanism-based treatments for pediatric anxiety and depressive disorders

Pediatric anxiety and depressive disorders are common, can be highly impairing, and can persist despite the best available treatments. Here, we review research into novel treatments for childhood anxiety and depressive disorders designed to target underlying cognitive, emotional, and neural circuit mechanisms. We highlight three novel treatments lying along a continuum relating to clinical impact of the disorder and the intensity of clinical management required. We review cognitive training, which involves the lowest risk and may be applicable for problems with mild to moderate impact; psychotherapy, which includes a higher level of clinical involvement and may be sufficient for problems with moderate impact; and brain stimulation, which has the highest potential risks and is therefore most appropriate for problems with high impact. For each treatment, we review the specific underlying cognitive, emotional, and brain circuit mechanisms that are being targeted, whether treatments modify those underlying mechanisms, and efficacy in reducing symptoms. We conclude by highlighting future directions, including the importance of work that leverages developmental windows of high brain plasticity to time interventions to the specific epochs in childhood that have the largest and most enduring life-long impact.

Handedness and depression: A meta-analysis across 87 studies

Alterations in functional brain lateralization, often indicated by an increased prevalence of left- and/or mixed-handedness, have been demonstrated in several psychiatric and neurodevelopmental disorders like schizophrenia or autism spectrum disorder. For depression, however, this relationship is largely unclear. While a few studies found evidence that handedness and depression are associated, both the effect size and the direction of this association remain elusive. Here, we collected data from 87 studies totaling 35,501 individuals to provide a precise estimate of differences in left-, mixed- and non-right-handedness between depressed and healthy samples and computed odds ratios (ORs) between these groups. Here, an OR > 1 signifies higher rates of atypical handedness in depressed compared to healthy samples. We found no differences in left- (OR = 1.04, 95% CI = [0.95, 1.15], p = .384), mixed- (OR = 1.64, 95% CI = [0.98, 2.74], p = .060) or non-right-handedness (OR = 1.05, 95% CI = [0.96, 1.15], p = .309) between the two groups. We could thus find no link between handedness and depression on the meta-analytical level.

Right brain, left brain in depressive disorders: Clinical and theoretical implications of behavioral, electrophysiological and neuroimaging findings

The right and left side of the brain are asymmetric in anatomy and function. We review electrophysiological (EEG and event-related potential), behavioral (dichotic and visual perceptual asymmetry), and neuroimaging (PET, MRI, NIRS) evidence of right-left asymmetry in depressive disorders. Recent electrophysiological and fMRI studies of emotional processing have provided new evidence of altered laterality in depressive disorders. EEG alpha asymmetry and neuroimaging findings at rest and during cognitive or emotional tasks are consistent with reduced left prefrontal activity in depressed patients, which may impair downregulation of amygdala response to negative emotional information. Dichotic listening and visual hemifield findings for non-verbal or emotional processing have revealed abnormal perceptual asymmetry in depressive disorders, and electrophysiological findings have shown reduced right-lateralized responsivity to emotional stimuli in occipitotemporal or parietotemporal cortex. We discuss models of neural networks underlying these alterations. Of clinical relevance, individual differences among depressed patients on measures of right-left brain function are related to diagnostic subtype of depression, comorbidity with anxiety disorders, and clinical response to antidepressants or cognitive behavioral therapy.

Brain laterality, depression and anxiety disorders: New findings for emotional and verbal dichotic listening in individuals at risk for depression

Studies using dichotic listening tests and electroencephalographic (EEG) measures of hemispheric asymmetry have reported evidence of abnormal brain laterality in patients having depressive disorders. We present new findings from a multigenerational study of risk for depression, in which perceptual asymmetry was measured in dichotic listening tests of emotional and verbal processing. Biological offspring and grandchildren of probands with a major depressive disorder (MDD) who were at high risk and those of nondepressed controls who were at low risk were tested on dichotic emotional recognition and consonant-vowel syllable tests. In the emotion test, individuals with a lifetime diagnosis of MDD had a smaller right hemisphere advantage than those without a MDD, but there was no difference between high- and low-risk groups or between those with or without an anxiety disorder. In the syllable test, a smaller left hemisphere advantage was found in individuals with an anxiety disorder compared to those without an anxiety disorder, but there was no difference between high- and low-risk groups or between those with or without a MDD. This double dissociation indicates that lifetime diagnosis of MDD and anxiety disorders have a differential impact on lateralized hemispheric processing of emotional and verbal information.

Visuospatial and mathematical dysfunction in major depressive disorder and/or panic disorder: A study of parietal functioning

The parietal cortex is critical for several different cognitive functions, including visuospatial processing and mathematical abilities. There is strong evidence indicating parietal dysfunction in depression. However, it is less clear whether anxiety is associated with parietal dysfunction and whether comorbid depression and anxiety are associated with greater impairment. The present study compared participants with major depression (MDD), panic disorder (PD), comorbid MDD/PD and controls on neuropsychological measures of visuospatial processing, Judgement of Line Orientation (JLO), and mathematical abilities, Wide Range Achievement Test (WRAT) Arithmetic. Only comorbid MDD/PD was associated with decreased performance on JLO, whereas all psychopathological groups exhibited comparably decreased performance on WRAT Arithmetic. Furthermore, the results were not accounted for by other comorbid disorders, medication use or psychopathology severity. The present study suggests comorbid depression and anxious arousal are associated with impairment in visuospatial processing and provides novel evidence indicating mathematical deficits across depression and/or anxiety. Implications for understanding parietal dysfunction in internalising psychopathology are discussed.

Mood modulates auditory laterality of hemodynamic mismatch responses during dichotic listening

Hemodynamic mismatch responses can be elicited by deviant stimuli in a sequence of standard stimuli even during cognitive demanding tasks. Emotional context is known to modulate lateralized processing. Right-hemispheric negative emotion processing may bias attention to the right and enhance processing of right-ear stimuli. The present study examined the influence of induced mood on lateralized pre-attentive auditory processing of dichotic stimuli using functional magnetic resonance imaging (fMRI). Faces expressing emotions (sad/happy/neutral) were presented in a blocked design while a dichotic oddball sequence with consonant-vowel (CV) syllables in an event-related design was simultaneously administered. Twenty healthy participants were instructed to feel the emotion perceived on the images and to ignore the syllables. Deviant sounds reliably activated bilateral auditory cortices and confirmed attention effects by modulation of visual activity. Sad mood induction activated visual, limbic and right prefrontal areas. A lateralization effect of emotion-attention interaction was reflected in a stronger response to right-ear deviants in the right auditory cortex during sad mood. This imbalance of resources may be a neurophysiological correlate of laterality in sad mood and depression. Conceivably, the compensatory right-hemispheric enhancement of resources elicits increased ipsilateral processing.

The sad, the angry, and the asymmetrical brain: dichotic listening studies of negative affect and depression

Dichotic Listening (DL) is a valuable tool to study emotional brain lateralization. Regarding the perception of sadness and anger through affective prosody, the main finding has been a left ear advantage (LEA) for the sad but contradictory data for the anger prosody. Regarding an induced mood in the laboratory, its consequences upon DL were a diminished right ear advantage (REA) for the induction of sadness and an increased REA for the induction of anger. The global results fit with the approach-withdrawal motivational model of emotional processing, pointing to sadness as a right hemisphere emotion but anger processed bilaterally or even in the left hemisphere, depending on the subject's preferred mode of expression. On the other hand, the study of DL in clinically depressed patients found an abnormally larger REA in verbal DL tasks which was predictive of therapeutic pharmacological response. However, the mobilization of the available left hemisphere resources in these responders (reflected in a higher REA) would indicate a remission of the episode but would not assure the absence of new relapses.

Emerging depression is associated with face memory deficits in adolescent girls

OBJECTIVE

To examine the association between memory for previously encoded emotional faces and depression symptoms assessed over 4 years in adolescent girls. Investigating the interface between memory deficits and depression in adolescent girls may provide clues about depression pathophysiology.

METHOD

Participants were 213 girls recruited from a longitudinal, community-based study; the majority were African American. Scores on depressive screening measures at age 8 were used to increase the base rate of depression. Depression symptoms and diagnoses were assessed annually for 4 years. In year 4, when the girls were 12 to 13 years old, a face emotion encoding task was administered during which ratings were generated in response to sad, fearful, angry, and happy faces. A surprise memory task followed whereby participants identified which of two faces, displaying neutral expressions, they had seen previously.

RESULTS

Girls with higher depression symptom levels from ages 9 to 12 years evidenced lower accuracy in identifying previously encoded emotional faces. Controlling for IQ, higher depression symptom level was associated with a memory deficit specific to previously encoded sad and happy faces. These effects were not moderated by race.

CONCLUSIONS

Individual differences in face memory deficits relate to individual differences in emerging, early adolescent depression, and may be vulnerability markers for depression.

Dichotic listening performance suggests right hemisphere involvement in PTSD

The present study focuses on language laterality as measured with dichotic listening (DL) to consonant-vowel syllables (CV syllables) in refugees with post-traumatic stress disorder (PTSD). PTSD is associated with impaired callosal transfer and with increased right hemisphere activation and impaired executive skills that could influence the processing of dichotic stimuli. A total of 22 participants with PTSD were compared to 23 participants without a diagnosis of PTSD. All participants had similar experiences of acts of war and political violence. They were tested with dichotic listening to CV syllables with free recall and directed attention following the forced attention paradigm. The PTSD group showed increased right ear advantage due to impaired left ear reporting and also smaller attention modulation compared to the control group, and the performance shared variance with self-report measures of arousal and intrusive memories. The results are discussed towards a model of impaired functionality of the frontal lobe and right hemisphere versus impaired callosal transfer, both yielding predictions for the processing of the left ear input and the ability to attention modulation of the performance.

EEG hemispheric asymmetries during cognitive tasks in depressed patients with high versus low trait anxiety

Studies of regional hemispheric asymmetries point to relatively less activity in left frontal and right posterior regions in depression. Anxiety was associated with increased right posterior activity, which may be related to arousal and, in anxious-depressed individuals, offset the posterior asymmetry typically seen in depression. These asymmetries have been indexed by resting EEG or inferred through the use of lateralized auditory and visual tasks (e.g., dichotic listening and chimeric faces). However, associations between regional EEG activity and neurocognitive function in depression or anxiety remain unclear. The present study used matched verbal (Word Finding) and spatial (Dot Localization) tasks to compare task-related alpha asymmetries in depressed patients grouped according to level of trait anxiety. EEG and behavioral performance were recorded from depressed patients with high anxiety (n = 14) or low anxiety (n = 14) and 21 age- and education-matched healthy adults during the two tasks, and alpha power was averaged within each task. As predicted, the two patient groups exhibited opposite patterns of regional hemispheric alpha asymmetry. Greater right than left central-parietal activation was seen in the high-anxiety depressed group during the spatial task, whereas greater left than right frontal-central activation was found in the low-anxiety depressed group during the verbal task. Group differences in task performance were in the expected direction but did not reach statistical significance. These results are consistent with Heller's two-dimensional model of depression and anxiety and highlight the sensitivity of task-related EEG alpha in discriminating among subgroups of depressed patients differing in trait anxiety.

Functional brain asymmetry as a determinative factor in the treatment of depression: theoretical implications

Depression is characterized by the functional insufficiency of both left and right hemispheres. Patients who respond to antidepressants are characterized by a relatively higher left hemisphere activity in comparison to non-responders, and successful treatment with antidepressants increases left hemisphere activity. Left hemisphere is responsible for the goal-oriented behavior that includes search activity as a state opposite to depression, which accounts for the positive outcome in depression following activation of the left hemisphere. However, it is not a pathogenetic but a palliative treatment, because the core reason for depression is the inability of the right hemisphere to correspond to the demands of the polydimensional environment. The article suggests that in order to achieve stability, treatment has to combine methods that restore left hemisphere activity with methods that restore right hemisphere efficiency.

Lateralization of the serotonin-1A receptor distribution in language areas revealed by PET

Lateralization is a well described aspect of the human brain. A plethora of morphological, cytological and functional studies describes hemispheric asymmetry in auditory and language areas. However, no study has reported cortical lateralization in the healthy human brain in vivo on the level of neurotransmitter receptors and in relation to functional organization so far. In this study, we assessed the distribution of the main inhibitory serotonergic receptor (the 5-HT1A receptor) and analyzed its regional binding with regard to hemisphere, sex and plasma levels of sex steroid hormones (testosterone, estradiol, progesterone). We quantified the 5-HT1A receptor binding potential by positron emission tomography (PET) using the highly selective and specific radioligand [carbonyl-11C]WAY-100635 and measured hormone levels in thirty-four (16 females, 18 males) healthy right-handed subjects. The obtained data were analyzed in an automated region of interest (ROI) based approach investigating 14 auditory, language and limbic areas. We found significantly higher 5-HT1A receptor binding in the superior and middle frontal gyri of the right hemisphere, the triangular and orbital parts of the inferior frontal gyrus, the supramarginal gyrus, the superior gyrus of the temporal pole and the middle temporal gyrus. Regions of the primary and secondary auditory cortex (Heschl's gyrus and superior temporal gyrus) and the Rolandic operculum displayed significantly higher receptor binding in the left hemisphere. 5-HT1A receptor binding was 1.8-2.9% higher in right frontal ROIs and 2-3.6% higher in left primary and secondary auditory regions. There was no hemispheric difference in 5-HT(1A) receptor binding in the hippocampus, amygdala, and insula. Post-hoc testing suggested that lateralization of 5-HT1A receptor binding differed between the sexes in the triangular part of the inferior frontal gyrus. For the first time, this PET study shows lateralization of the main inhibitory receptor of the serotonergic system in functionally asymmetric organized regions of the healthy human brain in vivo.

Association study of theta EEG asymmetry and brain-derived neurotrophic factor gene variants in childhood-onset mood disorder

BACKGROUND

Childhood-onset mood disorders (COMD) include various serious, disabling psychiatric conditions that are heterogeneous in presentation and etiology. Because intermediate phenotypes may help to identify genetic contributors to COMD, we tested for an association between variants in the brain-derived neurotrophic factor (BDNF) gene and theta EEG asymmetry, both of which have been independently implicated in affective disorders.

METHODS

Theta EEG asymmetry measures were calculated for a total of 191 individuals with COMD and 93 controls, who were also genotyped at seven BDNF single-nucleotide polymorphism (SNPs), two intergenic flanking SNPs, and one SNP in the lin-7 homolog C (Caenorhabditis elegans) (LIN7C) gene.

RESULTS

Adjusting for sex and ethnicity in linear models of asymmetry scores at ten brain regions, significant genotype and genotype-by-ethnicity interactions were observed for marker Val66Met in two parietal (P3/4 and P7/8) regions in the depressed group only.

CONCLUSIONS

Our results suggest that the functional Val66Met polymorphism affects theta EEG asymmetry in parietal brain regions specifically in individuals with COMD.

Pharmacotherapy of depressed children and adolescents: current issues and potential directions

The recent deliberations by the U.S. Food and Drug Administration (FDA) regarding the relationship between antidepressants and suicidality in children have incited debates about the safety of these medications for the treatment of pediatric depression. In light of these events, this review discusses four issues pertaining to pharmacotherapy for pediatric depression. First, we summarize pertinent data from randomized controlled trials of antidepressants for pediatric depression. These data provide strong support for fluoxetine and modest support for the other antidepressants. Second, we examine the outcome of the FDA meta-analysis of the data on antidepressant-induced suicidality, with specific emphasis on the methodological limitations of this analysis. Third, we consider the collective implications of the antidepressant efficacy and suicidality data on clinical practice. Specifically, we present several compelling arguments that justify the continued use of antidepressants for pediatric depression, despite the inherent limitations of these medications. Finally, we review several pathophysiological factors that might provide insights into treatment response and impact the design of future pharmacotherapy studies of depression. These factors relate to diagnostic heterogeneity, developmental consistency, and psychobiology. Potentially novel pharmacotherapies are also discussed.

Face-memory and emotion: associations with major depression in children and adolescents

BACKGROUND

Studies in adults with major depressive disorder (MDD) document abnormalities in both memory and face-emotion processing. The current study used a novel face-memory task to test the hypothesis that adolescent MDD is associated with a deficit in memory for face-emotions. The study also examines the relationship between parental MDD and memory performance in offspring.

METHODS

Subjects were 152 offspring (ages 9-19) of adults with either MDD, anxiety disorders, both MDD and anxiety, or no disorder. Parents and offspring were assessed for mental disorders. Collection of face-memory data was blind to offspring and parent diagnosis. A computerized task was developed that required rating of facial photographs depicting 'happy,"fearful,' or 'angry' emotions followed by a memory recall test. Recall accuracy was examined as a function of face-emotion type.

RESULTS

Age and gender independently predicted memory, with better recall in older and female subjects. Controlling for age and gender, offspring with a history of MDD (n = 19) demonstrated significant deficits in memory selectively for fearful faces, but not happy or angry faces. Parental MDD was not associated with face-memory accuracy.

DISCUSSION

This study found an association between MDD in childhood or adolescence and perturbed encoding of fearful faces. MDD in young individuals may predispose to subtle anomalies in a neural circuit encompassing the amygdala, a brain region implicated in the processing of fearful facial expressions. These findings suggest that brain imaging studies using similar face-emotion paradigms should test whether deficits in processing of fearful faces relate to amygdala dysfunction in children and adolescents with MDD.

Dichotic listening tests of functional brain asymmetry predict response to fluoxetine in depressed women and men

Patients having a depressive disorder vary widely in their therapeutic responsiveness to a selective serotonin reuptake inhibitor (SSRI), but there are no clinical predictors of treatment outcome. Studies using dichotic listening, electrophysiologic and neuroimaging measures suggest that pretreatment differences among depressed patients in functional brain asymmetry are related to responsiveness to antidepressants. Two new studies replicate differences in dichotic listening asymmetry between fluoxetine responders and nonresponders, and demonstrate the importance of gender in this context. Right-handed outpatients who met DSM-IV criteria for major depression, dysthymia, or depression not otherwise specified were tested on dichotic fused-words and complex tones tests before completing 12 weeks of fluoxetine treatment. Perceptual asymmetry (PA) scores were compared for 75 patients (38 women) who responded to treatment and 39 patients (14 women) who were nonresponders. Normative data were also obtained for 101 healthy adults (61 women). Patients who responded to fluoxetine differed from nonresponders and healthy adults in favoring left- over right-hemisphere processing of dichotic stimuli, and this difference was dependent on gender and test. Heightened left-hemisphere advantage for dichotic words in responders was present among women but not men, whereas reduced right-hemisphere advantage for dichotic tones in responders was present among men but not women. Pretreatment PA was also predictive of change in depression severity following treatment. Responder vs nonresponder differences for verbal dichotic listening in women and nonverbal dichotic listening in men are discussed in terms of differences in cognitive function, hemispheric organization, and neurotransmitter function.

The neuropsychology of depression: a literature review and preliminary model

Neuropsychological research provides a useful framework to study emotional problems, such as depression, and their correlates. This paper reviews several prominent neuropsychological theories. Functional neuroanatomical systems of emotion and depression are reviewed, including those that describe cerebral asymmetries in emotional processing. Following the review, a model that is composed of three neuroanatomical divisions (left frontal, right frontal, and right posterior) and corresponding neuropsychological emotional sequelae within each quadrant is presented. It is proposed that dysfunction in any of these quadrants could lead to symptomatology consistent with a diagnosis of depression. The proposed model combines theories of arousal, lateralization, and functional cerebral space and lends itself to scientific methods of investigation. Accordingly, research, prevention, and treatment programs in accordance with the proposed model may promote an improved understanding of the neuropsychological mechanisms involved in depression.

Superior temporal gyrus volumes in pediatric generalized anxiety disorder

BACKGROUND

The essential symptoms of generalized anxiety disorder (GAD) are intrusive worry about everyday life circumstances and social competence, and associated autonomic hyperarousal. The amygdala, a brain region involved in fear and fear-related behaviors in animals, and its projections to the superior temporal gyrus (STG), thalamus, and to the prefrontal cortex are thought to comprise the neural basis of our abilities to interpret social behaviors. Larger amygdala volumes were previously reported in pediatric GAD; however, the brain regions involved in social intelligence were not examined in this pilot study.

METHODS

Magnetic resonance imaging (MRI) was used to measure the STG, thalamus, and prefrontal volumes in 13 medically healthy child and adolescent subjects with generalized anxiety disorder (GAD) and 98 comparison subjects, who were at low familial risk for mood and psychotic disorders. Groups were similar in age, gender, height, weight, handedness, socioeconomic status, and full-scale IQ.

RESULTS

The total, white matter, and gray matter STG volumes were significantly larger in GAD subjects compared with control subjects. Thalamus and prefrontal lobe volumes did not differ between groups. Findings of significant side-by-diagnosis interactions for STG and STG white matter volumes suggest that there is a more pronounced right > left asymmetry in total and STG white matter volumes in pediatric GAD subjects compared with control subjects. A significant correlation between the STG white matter percent asymmetry index with the child report of the Screen for Child Anxiety Related Emotional Disorders Scale was seen.

CONCLUSIONS

These data agree with previous work implicating posterior right-hemispheric regions in anxiety disorders and may suggest developmental alterations in pediatric GAD.

Interhemispheric asymmetry of regional cerebral blood flow in prepubescent boys with attention deficit hyperactivity disorder

The prefrontal cortex is asymmetric in both structure and function. In normal subjects, the right prefrontal cortex is activated more than the left during response inhibition. Patients with attention deficit hyperactivity disorder (ADHD) have impaired response inhibition and altered structural interhemispheric asymmetry. This study was conducted to examine the functional interhemispheric asymmetry during response inhibition in children with ADHD. Subjects were divided into three groups according to the level of motor hyperactivity. Blood flow tracer (99m)Tc-ethyl cysteinate dimer was injected while subjects were performing a response inhibition task (RIT), followed by single photon emission computerized tomography (SPECT). After three-dimensional reconstruction, filtering and smoothing, individual scans were morphed to a template. Three average group images were created from individual scans. Each average group image was subtracted voxel-by-voxel from its mirror image to compare the regional cerebral blood flow (rCBF) in the right and left cerebral hemispheres, yielding images of significant interhemispheric rCBF asymmetry. The severe hyperactivity group exhibited most prefrontal left>right rCBF asymmetry and left>right occipitoparietal asymmetry. Reversal of functional prefrontal asymmetry in boys with severe motor hyperactivity supports the hypothesis of right prefrontal cortex dysfunction in ADHD.

Affective neuroscience and the development of social anxiety disorder

Recent studies on the familial distribution and longitudinal outcome of SAD emphasize developmental aspects of the syndrome, consistent with the developmental psychopathology perspective. Key questions in this area concern factors that mediate familial transmission and that predict outcome. Prior studies provide incomplete answers to these questions. Recent studies in affective neuroscience suggest potential avenues for answering these questions. As reviewed in the current article, fMRI studies of face processing provide examples of such potentially informative research directions.

Electroencephalographic and perceptual asymmetry differences between responders and nonresponders to an SSRI antidepressant

BACKGROUND

Recent reports suggest the value of electroencephalographic and dichotic listening measures as predictors of response to antidepressants. This study examines the potential of electroencephalographic alpha asymmetry and dichotic measures of perceptual asymmetry as predictors of clinical response to 12 weeks of treatment with fluoxetine (Prozac).

METHODS

Resting electroencephalography (eyes open and eyes closed) and dichotic listening with word or complex tone stimuli were assessed in depressed outpatients during a pretreatment period.

RESULTS

Fluoxetine responders (n = 34) differed from nonresponders (n = 19) in favoring left over right hemisphere processing of dichotic stimuli. They also differed in their resting electroencephalographic alpha asymmetry, particularly in the eyes open condition. Nonresponders showed an alpha asymmetry indicative of overall greater activation of the right hemisphere than the left, whereas responders did not. The relationship between hemispheric asymmetry and treatment response interacted with gender, being evident among depressed women but not men.

CONCLUSIONS

The results are consistent with the hypothesis that a characteristic tendency toward greater left than right hemisphere activation is associated with favorable response to fluoxetine, whereas the opposite hemispheric asymmetry predicts poor response.

Volumetric asymmetries in late-onset mood disorders: an attenuation of frontal asymmetry with depression severity

The purpose of the study was to examine global and regional volumetric asymmetries in patients with late-onset mood disorders and non-depressed control subjects. Our sample comprised 34 patients with late-onset major depression, 18 patients diagnosed with late-onset minor depression and 30 control subjects. All subjects were scanned using a 1.5 Tesla GE Scanner, and quantitative estimates of global and focal brain volumes were obtained. Control subjects and patients displayed significant right-left volumetric differences across several regions, with right-sided regions being larger than the left. In the frontal lobes, the asymmetry differed significantly in the three groups (P=0.02). It was most pronounced in the control group and decreased significantly in the minor and major depression groups. There was a significant trend (P=0.005) in the magnitude of frontal asymmetry across groups, with the frontal asymmetry decreasing with increasing severity of depression. Hemispheric and temporal asymmetries were comparable in all three groups. These data suggest that an attenuation of the 'normal' volumetric asymmetry in the frontal regions may provide a structural basis to late-onset mood disorders