Pattern-reversed visual evoked potentials in subtypes of major depression
Introduction
Modern classification systems recognize melancholic (‘somatic’) and atypical features (Fountoulakis et al., 1999b). In spite of early reports (Dally and Rohde, 1961, Liebowitz et al., 1988, Sargant, 1960, West and Dally, 1959) concerning the ‘atypical syndrome’ (with reverse neurovegetative symptoms), today the only finding that continues to be robust is not the favorable response of atypical patients to monoamine oxidase inhibitors, but their resistance to tricyclic antidepressants. Atypical depression is considered to constitute a risk factor for further mental suffering (Tsolaki et al., 1997, Fountoulakis et al., 2000). It is suggested that the subtype of depression is also of prime importance in event-related potential (ERP) studies (Shagass, 1981).
Electrophysiological methods, although spatially removed from the events they record, are possibly closer in time to these events in comparison to cerebrospinal fluid, urine and peripheral blood testing. Relationships between electrophysiological testing and peripheral biological markers have been reported in depression (Buchsbaum et al., 1971a, Buchsbaum et al., 1973a, Buchsbaum and Wender, 1973b). Studies on primates also support the usefulness of these methods and the relationship of catecholaminergic activity with visual information processing (Redmond et al., 1975), possibly reflecting a secondary elaboration or process enabling the organism to choose the appropriate motoric or affective response (Bruder et al., 1992). However, although some features of the ERP (e.g. the amplitude and latency response to varying levels of stimulus intensity; Buchsbaum, 1974) might be heritable, ERPs are generally considered to reflect state-related rather than trait-related processes (Shagass, 1979).
Articles on the visual system of depressives (Buchsbaum et al., 1971a, Buchsbaum et al., 1977, Fotiou et al., 1999, Fountoulakis et al., 1999a) and Alzheimer's disease patients (Fotiou et al., 2000) have shown that the assessment of the visual system may provide valuable information about different diseases affecting the central nervous system (CNS).
The hypothesis under investigation in the current study was that melancholic patients may manifest reduced conduction velocity in the brain, and this could be related to differences in their response to life events as suggested by several authors (Buchsbaum et al., 1973a, Buchsbaum, 1975, Fotiou et al., 1999). Another hypothesis under investigation in the current study was whether there is a difference in the conduction velocity between hemispheres, since this could lead to a disruption in the flow and processing of information in the brain and thus could lead to affective disorders.
The rationale behind the use of pattern-reversed visual evoked potentials (PR-VEPs) was that they constitute a marker for the conduction velocity in the CNS, are highly reliable (compared with flash-VEPs), are short-latency potentials (below 200 ms), and thus demand minimum effort and collaboration from the subject (in contrast to long-latency potentials).
Since severity is frequently confounded with specific clinical features (e.g. suicidality and psychomotor changes), and different scales and criteria sets reflect different approaches to this problem, the simultaneous use of multiple rating scales was judged to be necessary.
Section snippets
Subjects
Fifty (15 males and 35 females) patients suffering from major depression according to DSM-IV (American Psychiatric Association, 1994) and depression according to ICD-10 criteria (World Health Organization, 1993) took part in the study. The patients ranged in age from 21 to 60 years (mean=41.0, S.D.=11.4). The patients were compared with a control group (n=20 controls, 7 males and 13 females, aged 20–55 years, mean=36.7, S.D.=8.9). All subjects provided written informed consent. Fourteen of the
Results
Depressed patients and controls had similar gender composition and did not differ significantly in age (P=0.107). Patients of the melancholic subtype tended to be older than the other subjects, but not significantly so (Table 1). However, age was entered in the analysis as a covariate to rule out the possibility that it might constitute a confounder. There were twice as many women as men in the sample (70% vs. 30%), which is a common problem in studies of depression (Zimmerman et al., 1985).
A
Discussion
Melancholic patients might have reduced transmission velocity in the CNS, as is suggested by prolonged latency of the b-wave of the electroretinogram (Fotiou et al., 1999). The present study provides further data to support this. The main finding was that melancholic patients had prolonged, while atypical patients had shorter PR-VEP latencies especially from the dominant right eye (Fig. 1). This, together with the normal values of the ratio O1/O2 latencies, in all depressed subtypes (Table 2),
Acknowledgements
The authors wish to thank the Editor and three anonymous reviewers for their assistance in the interpretation of the results and the final formation of the manuscript.
References (59)
- et al.
Auditory laterality in depression: relation to circadian patterns and EEG sleep
Biological Psychiatry
(1985) - et al.
Laterarized auditory processing in depression: dichotic click detection
Psychiatry Research
(1981) - et al.
Regional brain asymmetries in major depression with or without an anxiety disorder: a quantitative EEG study
Biological Psychiatry
(1997) - et al.
Abnormal cerebral laterality in bipolar depression: convergence of behavioral and brain event related potential findings
Biological Psychiatry
(1992) - et al.
Event related potentials in depression: influence of task, stimulus hemifield and clinical features on P3 latency
Biological Psychiatry
(1991) - et al.
Hemispheric differences in evoked potentials to verbal and non-verbal stimuli in the left and right visual fields
Physiology and Behavior
(1970) - et al.
Comparison of antidepressant drugs in depressive illnesses
Lancet
(1961) - et al.
Neuronal generators of the visual evoked potentials: intracerebral recording in awake humans
Electroencephalography and Clinical Neurophysiology
(1988) - et al.
Changes in pupil reaction to light in Alzheimer's disease patients: a preliminary report
International Journal of Psychophysiology
(2000) - et al.
Changes in pupil reaction to light in melancholic patients
International Journal of Psychophysiology
(1999)