Influence of mood on visually evoked potentials: a prospective longitudinal study

Retinal dysfunction of contrast processing in major depression also apparent in cortical activity

Depressive disorder is often associated with the subjective experience of altered visual perception. Recent research has produced growing evidence for involvement of the visual system in the pathophysiology of depressive disorder. Using the pattern electroretinogram (PERG), we found reduced retinal contrast response in patients with major depression. Based on this observation, the question arises whether this change has a cortical correlate. To evaluate this, we analyzed the visual evoked potential (VEP) of the occipital cortex in 40 patients with depressive disorder and 28 healthy controls. As visual stimuli, checkerboard stimuli of 0.51° check size, 12.5 reversals per second and a contrast of 3-80% was used. In addition to the PERG, we recorded the VEP with an Oz versus FPz derivation. The amplitude versus contrast transfer function was compared across the two groups and correlated with the severity of depression, as measured by the Hamilton Depression Rating Scale and the Beck Depression Inventory. Patients with major depression displayed significantly reduced VEP amplitudes at all contrast levels compared to control subjects (p = 0.029). The VEP amplitude correlated with psychometric measures for severity of depression. The degree of depression reduced the contrast transfer function in the VEP to a lesser extent than in the PERG: While the PERG is reduced to ≈50%, the VEP is reduced to 75%. Our results suggest that depression affects the cortical response in major depression, but less so than the retinal responses. Modified contrast adaptation in the lateral geniculate nucleus or cortex possibly moderates the increased losses in the retina.

Effect of antidepressive therapy on retinal contrast processing in depressive disorder

BACKGROUND

Recently, we reported a reduced retinal contrast gain in unmedicated and medicated patients with major depression.

AIMS

To analyse whether the contrast gain normalises after successful antidepressive therapy by recording the pattern electroretinogram (PERG) in healthy controls and patients with depression before and after antidepressive therapy.

METHOD

Fourteen patients diagnosed with major depression were repeatedly scanned and the results compared with that from 40 matched controls.

RESULTS

The retinal contrast gain was lower at baseline in patients with depression, was normalised with remission and correlated with the severity of depression. Patients who did not achieve remission retained significantly lower contrast gain at follow-up.

CONCLUSIONS

The study provides evidence for a state-dependent modulation of retinal contrast gain in patients with major depression. Reduced contrast gain normalised after therapy. A PERG-based contrast gain could serve as a state marker of depression.

Emotion and the auditory brainstem response to speech

Effects of emotion have been reported as early as 20 ms after an auditory stimulus onset for negative valence, and bivalent effects between 30 and 130 ms. To understand how emotional state influences the listener's brainstem evoked responses to speech, subjects looked at emotion-evoking pictures while listening to an unchanging auditory stimulus (danny). The pictures (positive, negative, or neutral valence) were selected from the IAPS database and controlled for dominance and arousal. Utilizing an array of measurements to assess subcortical modulation, we have found that emotion does not substantially alter brainstem alter although there is a subtle effect of background noise suppression in both emotional conditions.

Emotion modulates early auditory response to speech

In order to understand how emotional state influences the listener's physiological response to speech, subjects looked at emotion-evoking pictures while 32-channel EEG evoked responses (ERPs) to an unchanging auditory stimulus ("danny") were collected. The pictures were selected from the International Affective Picture System database. They were rated by participants and differed in valence (positive, negative, neutral), but not in dominance and arousal. Effects of viewing negative emotion pictures were seen as early as 20 msec (p = .006). An analysis of the global field power highlighted a time period of interest (30.4-129.0 msec) where the effects of emotion are likely to be the most robust. At the cortical level, the responses differed significantly depending on the valence ratings the subjects provided for the visual stimuli, which divided them into the high valence intensity group and the low valence intensity group. The high valence intensity group exhibited a clear divergent bivalent effect of emotion (ERPs at Cz during viewing neutral pictures subtracted from ERPs during viewing positive or negative pictures) in the time period of interest (r(Phi) = .534, p < .01). Moreover, group differences emerged in the pattern of global activation during this time period. Although both groups demonstrated a significant effect of emotion (ANOVA, p = .004 and .006, low valence intensity and high valence intensity, respectively), the high valence intensity group exhibited a much larger effect. Whereas the low valence intensity group exhibited its smaller effect predominantly in frontal areas, the larger effect in the high valence intensity group was found globally, especially in the left temporal areas, with the largest divergent bivalent effects (ANOVA, p < .00001) in high valence intensity subjects around the midline. Thus, divergent bivalent effects were observed between 30 and 130 msec, and were dependent on the subject's subjective state, whereas the effects at 20 msec were evident only for negative emotion, independent of the subject's behavioral responses. Taken together, it appears that emotion can affect auditory function early in the sensory processing stream.

Differential effects of mood on cortical cerebral blood flow: a 133xenon clearance study

Studies of healthy and clinical populations have suggested valence-specific cortical and subcortical neural systems regulating emotions. In a study of 12 normal volunteers, the 133xenon clearance method for measuring regional cerebral blood flow (CBF) was used to study the effects of experimentally controlled mood states on regional brain activity within superficial cortex. CBF was measured with 254 detectors and bolus infusion during a happy mood induction task, a sad mood induction task, a sex differentiation task, and a resting baseline condition. CBF increased during sad and decreased during happy mood induction, relative to the activated (sex differentiation) and the nonactivated (resting) nonemotional control conditions. Increased CBF during sad mood induction was correlated with greater negative mood changes. Conversely, increased CBF was associated with a stronger subjective experience of positive affect during happy mood induction. This suggests that cortical arousal may serve to intensify the conscious experience of emotion. Heart rate accelerated during happy and sad mood induction and during sex differentiation relative to a pretask baseline condition. Some regional specificity of effects was also observed. The occipital temporal region showed higher overall CBF during sad mood induction than during happy mood induction. The only region that showed specific lateralized changes in CBF which differentiated sad from happy states was the frontal pole, with left CBF being higher during sad and lower during happy mood induction relative to right CBF. For sad mood induction, there were significant regional differences among correlations between CBF and self-ratings. These were attributable to higher negative correlations (i.e., higher CBF correlates with negative self-rating) in midtemporal, occipital temporal, and postcentral regions. These correlations did not vary across the 15 regions for happy mood induction. For sad mood induction, heart rate correlated positively with CBF increase and with negative affect. Correlations were opposite for happy mood induction. The results suggest high cortical and autonomic arousal during negative/sad mood and low cortical and high autonomic arousal during positive/happy mood. They underscore the value of integrating emotional experience with physiologic measures in neuroimaging activation studies.