Attentional asymmetries following ECT in patients with major depression

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Abstract

Neuropsychological abnormalities of lateralization have been reported after right unilateral electroconvulsive therapy (ECT), that may reflect temporary disruption of the treated hemisphere. A visuospatial task sensitive to lateralization of spatial attention was administered in a test–retest design to patients with unipolar major depression and a group of age and gender matched controls. The patient group underwent right unilateral ECT between the two test sessions. The patient and control groups did not differ significantly at the initial baseline testing. After ECT, the patient group showed a significant shift of attentional bias toward the left, while the control group showed no significant shift in the second session relative to the first. The results suggest that ≈1 h after termination of ictus there is a leftward attentional bias, possibly reflecting a change in right hemisphere cerebral activity.

Introduction

Electroconvulsive therapy (ECT) has proven to be a highly successful therapeutic intervention in the treatment of a range of psychiatric and neurological conditions including major mood disorder. While its therapeutic mode of action remains unclear, there are a number of physiological effects of ECT, which may be antidepressant in action with serotinergic, adrenergic and dopaminergic effects all being observed [1].

With onset of seizure, there is rapid and marked increase in cerebral blood flow and metabolism. The post ictal period is marked by a reduction in cerebral blood flow below resting levels [6], which are themselves frequently reported to be lower in patients with depression compared to normal healthy controls [8]. Post ictal reduction in cerebral blood flow and metabolism following unilateral ECT appears to be most marked in the treated hemisphere [6].

Such alterations in cerebral activity might account for findings of transient abnormalities of neuropsychological performance in the period immediately following ECT. Kriss et al. [3] reported a number of abnormalities following right unilateral ECT including left paresis, left hemianopia, and, in one third of cases, evidence of left neglect on a clock drawing task. These abnormalities had all resolved by ≈20 min following seizure termination. Sackeim et al. [9] reported neglect of the left side in visual cancellation tasks, which was greater with increasing stimulus intensity. Such abnormalities might reflect reduced right cerebral hemisphere activity in the immediate post ictal period.

To further examine issues of attentional asymmetry, now at a purely perceptual level, following right unilateral ECT, a visuospatial task (grey scales) known to be sensitive to lateralization of attention [4] was employed with a group of patients undergoing right unilateral ECT, and a group of age and gender matched controls. The grey scales have been found to be capable of detecting asymmetries in right hemisphere patients not revealed by standard tests and do not involve any directional motor component. The grey scales consist of a series of pairs of mirror-image rectangles shaded from pure black at one end to pure white at the other. Participants indicated verbally, which rectangle in each pair appeared overall the darker. An attentional bias to one direction should be reflected in a tendency to select the rectangle, which is darker at the preferred end. It was predicted that the patient group would show a rightward attentional bias following right unilateral ECT.

Section snippets

Participants

Participants were five patients with unipolar major depression (DSM-IV) and five aged and NART matched healthy controls (see Table 1 for clinical details of the patient group). The control participants had no known psychiatric or neurological history, and all participants were right-handed [7] and had normal or corrected to normal vision.

Materials

Participants viewed a series of 32 stimuli each consisting of two rectangles presented one above the other and shaded in a semicontinuous grey scale from pure

Results

Asymmetry scores indicating the extent and direction of lateralization of attention were calculated for each of the patients and controls. An asymmetry index of zero indicates no consistent bias, while scores of +1 and−1 would indicate complete rightward and leftward lateralization, respectively.

A two-way mixed model ANOVA with factors of group (patients, controls) and test session (pre, post) found a significant interaction of group X test session, F(1,8)=11.552, P<0.01. Fig. 2 indicates that

Discussion

At the initial testing session both the patient and the control groups showed a slight leftward bias, a finding previously reported in a healthy control group [4]. While the control group showed no difference at the second test session, the patient group showed a marked and significant shift in attentional asymmetry. This shift was to the left, the direction opposite to that predicted.

In the first instance, findings of an increased leftward attentional bias might suggest a change in the

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