James P. Towey

Regional brain asymmetries in major depression with or without an anxiety disorder: A quantitative electroencephalographic study

Studies of brain activity in affective disorders need to distinguish between effects of depression and anxiety because of the substantial comorbidity of these disorders. Based on a model of asymmetric hemispheric activity in depression and anxiety, it was predicted that anxious and nonanxious depressed patients would differ on electroencephalographic (EEG) measures of parietotemporal activity. Resting EEG (eyes closed and eyes open) was recorded from 44 unmedicated outpatients having a unipolar major depressive disorder (19 with and 25 without an anxiety disorder), and 26 normal controls using 30 scalp electrodes (13 homologous pairs over the two hemispheres and four midline sites). As predicted, depressed patients with an anxiety disorder differed from those without an anxiety disorder in alpha asymmetry. Nonanxious depressed patients showed an alpha asymmetry indicative of less activation over right than left posterior sites, whereas anxious depressed patients showed evidence of greater activation over right than left anterior and posterior sites. The findings are discussed in terms of a model in which specific symptom features of depression and anxiety are related to different patterns of regional brain activity.

Event-related potentials in depression : influence of task, stimulus hemifield and clinical features on P3 latency

P3 latency, a brain event-related potential (ERP) correlate of stimulus evaluation time, was measured in 25 unmedicated depressed patients and 27 normal controls during auditory temporal and spatial discrimination tasks. Patients were divided into two subgroups, one having a typical major depression (melancholia or simple mood reactive depression) and one having an atypical depression. Typical depressives had abnormally long P3 latency for the spatial task but not the temporal task. They also showed an abnormal lateral asymmetry, with longer P3 latency for stimuli in the right hemifield than the left. In contrast, atypical depressives did not differ from normals in either respect. Longer P3 latency correlated with ratings of insomnia, while abnormal lateral asymmetry correlated with reduced right visual field advantage for syllables. The P3 latency findings point to a task-related slowing of perceptual decisions in a subgroup of depression.

Brain ERPs of depressed patients to complex tones in an oddball task : Relation of reduced P3 asymmetry to physical anhedonia

Event-related potentials to binaural complex tones were recorded from 40 depressed outpatients and 22 normal control participants at 30 electrode sites. Patients did not differ from control participants in N1 or P3 amplitude but showed greater N2. N2 was greater over right than over the left hemisphere at lateral sites in patients and control participants. A P3 asymmetry was found for control participants and patients with low scores on a physical anhedonia scale, but not for patients with high anhedonia scores. Topographic (local Laplacian) maps corresponding to P3 showed greater radial current flow over right than over left central regions in control participants. Patients with high anhedonia did not show this asymmetry, whereas patients with low anhedonia showed an intermediate asymmetry. These findings support the hypothesis that anhedonic depression is associated with dysfunction of right hemisphere mechanisms mediating the processing of complex pitch information.

Abnormal cerebral laterality in bipolar depression : Convergence of behavioral and brain event-related potential findings

Cerebral laterality in bipolar and unipolar major depression was compared using visual half-field and dichotic listening measures of perceptual asymmetry. The results replicate our prior finding of abnormal laterality in bipolar depressed patients on a visuospatial test. Bipolar patients (n = 11) failed to show the left visual field (right hemisphere) advantage for dot enumeration seen for both unipolar patients (n = 43) and normal controls (n = 24). Bipolar patients performed significantly poorer than unipolar patients on normal controls for left visual field, but not right visual field stimuli. An electrophysiological correlate of abnormal visual field asymmetry in bipolar depression was found in brain event-related potentials recorded during audiospatial and temporal discrimination tasks. Bipolar patients had smaller N100 amplitudes for test stimuli in the left than right hemifield, whereas unipolar patients and normals did not. The origins of left hemifield deficits in bipolar depression are discussed in terms of right-sided dysfunction of an arousal/attentional system involving temporoparietal and possibly frontal regions.

N250 latency and decision time

Eight subjects counted the rarer of two clicks under two levels of difficulty of discrimination. Event-related potentials showed a significant lengthening of N250 and P300 latency when the discrimination was more difficult. These findings confirm those of Ritter et al. !1979} despite the following procedural differences: {1} Stimuli differed in intensity rather than pitch, 12} the task involved silent counting rather than reaction time, and 13} statistical analyses were computed across subjects rather than within subjects. We conclude that the N250 latency shift reflects an increase in decision time as a consequence of greater difficulty. The current findings also support the Ritter et al. I1979} conclusion that the P300 latency increase is secondary to the N250 increase. Although P300 amplitude decreased with increased task difficulty, as predicted by the equivocation formulation of Ruchkin and Sutton 11979}, this trend failed to reach the required .01 level of statistical significance.

Response- and stimulus-related ERP asymmetries in a tonal oddball task: a Laplacian analysis.

Previous studies have found greater P3 amplitude over right than left hemisphere sites in a tonal oddball task with a reaction time (RT) response. This asymmetry had a central topography, and interacted with response hand. Identification of the processes underlying these asymmetries requires the use of additional methods for separating response- and stimulus-related contributions. We applied local Hjorth and spherical spline algorithms to compute surface Laplacian topographies of ERP data recorded from 30 scalp electrodes in a pooled sample of 46 right-handed healthy adults. For both methods, the current sources underlying the late positive complex were largest at medial parietal regions, but were asymmetric at central and frontocentral sites. Although a frontocentral sink contralateral to the response hand contributed to the asymmetry of the classic P3 peak, the source asymmetry was most robust after the sink had resolved. The late source was largest at electrode C4 for right hand responses, and was further enhanced in subjects showing a dichotic left ear advantage, but was unrelated to response speed. We conclude that the right hemisphere source reflects an interaction of response-related asymmetries with right hemisphere processes responsible for pitch discrimination.

Abnormality of EEG alpha asymmetry in female adolescent suicide attempters

Abnormal electroencephalographic (EEG) activity has been associated with various psychiatric disorders and behaviors, including depression, suicide, and aggression. We examined quantitative resting EEG in Hispanic female adolescent suicide attempters and matched normal controls. Computerized EEG measures were recorded at 11 scalp sites during eyes open and eyes closed periods from 16 suicide attempters and 22 normal controls. Suicide attempters differed from normal controls in alpha asymmetry. Normal adolescents had greater alpha (less activation) over right than left hemisphere, whereas suicidal adolescents had a nonsignificant asymmetry in the opposite direction. Nondepressed attempters were distinguished from depressed attempters in that they accounted for the preponderance of abnormal asymmetry, particularly in posterior regions. Alpha asymmetry over posterior regions was related to ratings of suicidal intent, but not depression severity. The alpha asymmetry in suicidal adolescents resembled that seen for depressed adults in its abnormal direction, but not in its regional distribution. Findings for suicidal adolescents are discussed in terms of a hypothesis of reduced left posterior activation, which is not related to depression but to suicidal or aggressive behavior.

Expectancy in humans in multisecond peak-interval timing with gaps

In two experiments, the peak-interval procedure was used with humans to test effects related to gaps in multisecond timing. In Experiment 1, peak times of response distributions were shorter when the gap occurred later during the encoding of the criterion time to be reproduced, suggesting that gap expectancy shortened perceived durations. Peak times were also positively related to objective target durations. Spreads of response distributions were generally related to estimated durations. In Experiment 2, peak times were shortest when gaps were expected but did not occur, confirming that the shortening effect of gap expectancy is independent of the gap occurrence. High positive start-stop correlations and moderate positive peak-time-spread correlations showed strong memory variability, whereas low and negative start-spread correlations suggest small response-threshold variability. Correlations seemed not to be influenced by expectancy. Overall, the peak-interval procedure with gaps provided relevant information on similarities and differences in timing in humans and other animals.

Left hemispheric activation in depersonalization disorder: A case report

Depersonalization disorder is classified in DSM-III-R (APA 1987) as a dissociative disorder characterized by altered perception or experience of the self. To date, there are no known reports of the neurobiological features of this disorder. We report clinical and biological correlates in a patient with depersonalization disorder previously unresponsive to a variety of anticonvulsant, monoamine oxidase inhibitor, and tricyclic antidepressant trials, but for whom fluoxetine partially reduced depersonalization symptoms, but not associated anxiety and depression. Neurophysiological, neuroanatomical and neuropsychological findings revealed left hemispheric frontal-temporal activation and decreased left caudate perfusion. These findings suggest a similarity to the neuropsychiatric data reported in obsessive-compulsive disorder patients.