Affective startle modulation in clinical depression: preliminary findings

Abstract

Background: Modulation of the startle reflex by affective foreground stimuli was investigated in a group receiving inpatient treatment for major depressive episodes (n = 14) and an age and gender matched nondepressed group (n = 14).

Methods: Participants viewed 27 pleasant, neutral, and unpleasant pictures chosen from the International Affective Picture System. Acoustic startle probes were presented during picture viewing, and participants also rated the affective qualities of the pictures.

Results: While ratings of the pictures were largely similar between the depressed and nondepressed groups, they displayed dissimilar patterns of startle modulation. In the nondepressed group, blinks elicited during unpleasant pictures were significantly larger than during pleasant pictures, whereas the depressed group failed to show this effect. Analyses, which separated the depressed participants into moderate and severe groups based on Beck Depression Inventory scores, revealed that while the moderately depressed group also showed a normal pattern of startle modulation, the severely depressed showed potentiated startles during the pleasant pictures.

Conclusions: These preliminary results suggest that severely depressed patients may respond to some pleasant stimuli as if they are aversive, possibly because such stimuli are seen as signals of frustrative nonreward.

Introduction

Depression is understood to be characterized by heightened activity and sensitivity of aversive emotional systems and lowered activity and sensitivity of appetitive emotional systems Clark and Watson 1991, Fowles 1988, Gray 1994. Research has confirmed that depression is associated with high levels of self-rated negative affect and low levels of self-rated positive affect (e.g., Allen et al unpublished data; Watson et al 1988), heightened responsiveness to aversive stimuli Gatchel et al 1977, Lewinsohn et al 1973, and reduced responsiveness to pleasant stimuli Henriques et al 1994, Schwartz et al 1976.

In the present study, we attempted to extend these findings by examining the impact of depression on modulation of the startle reflex while viewing affective pictures. The magnitude of the eye blink component of the startle response varies as a function of both attentional and emotional processes (Filion et al 1998). However, when the time between the onset of a foreground stimulus, such as picture, and the startle probe is relatively long (i.e, greater than 2000 msec), the emotional valence of the foreground stimuli will affect startle magnitude, larger blinks being associated with more negative valence (Vrana et al 1988). This affect-startle effect has been replicated many times using a variety of startle probes and emotive foreground stimuli Bradley et al 1990, Cook et al 1991, Ehrlichman et al 1995, Jansen and Frijda 1994. It has been proposed that the magnitude of the startle reflex varies as a function of the activation of aversive and appetitive motivational systems, due to “response matching” between the defensive response to the aversive probe and the ongoing motivational state of the individual (i.e., startle responses will be inhibited during “mismatched” appetitive states and potentiated during “matched” aversive states; Lang et al 1992).

Animal research has clearly shown that startle potentiation is associated with the amygdaloid fear system (Davis 1989). In humans, potentiation of the startle reflex during negative foregrounds has been shown to be greater for high-trait fearful individuals during imagery (Cook et al 1991) and picture viewing Cook et al 1992, Corr et al 1995, Greenwald et al 1991. By contrast, potentiation of the startle reflex during negative foregrounds has been shown to be reduced or absent in highly psychopathic individuals, a group thought to have a deficit in trait fearfulness (Patrick 1994). The only published study thus far to examine associations between depression and startle modulation is that by Cook and co-workers (1991). Although this study chiefly examined individual differences in trait fearfulness, subjects also completed inventories assessing levels of depression and anger. They found similar results for both depression and anger as they had for fear. High scoring subjects showed significantly greater potentiation of the startle reflex during aversive imagery than did low depression and low anger subjects respectively. Taken together, these results suggest that affective startle potentiation is related to levels of negative affect generally, rather than fear in particular.

It is less clear what effect, if any, variations in levels of positive affect will have on affective startle modulation. This is a critical matter for predictions regarding the effects of depression on affective startle modulation. As it has been proposed that startle magnitude is affected by the activation of aversive and appetitive motivational systems (Lang et al 1992), relative inhibition of startle during pleasant foreground stimuli (compared to neutral foreground stimuli) may act as an index of the capacity for positive affect. Cook and Gautier (1992) examined startle modulation in a nonclinical sample of individuals who varied on both negative and positive affectivity, and found that individuals low in positive affect showed greater valence modulation during highly arousing affective materials, and larger overall startles. To date, no study has described the effects of clinically depressed states, which can include extreme deficits in positive affect such as refractory anhedonia, on affective modulation of the startle reflex.

In the present study, we hypothesized that while nondepressed participants would show the usual pattern of increasing startle probe responses with increasing negative picture valence, depressed participants would show a pattern of heightened aversive responses (as indexed by greater startle potentiation) to viewing unpleasant pictures, and decreased appetitive responses (as indexed by less startle inhibition) while viewing pleasant pictures, when compared with the nondepressed group. Given suggestions that levels of negative affectivity and positive affectivity will affect startle modulation, we also hypothesized that the severity of emotional symptoms related to these dimensions would affect patterns of affective startle modulation. Participants rated their symptoms using the Beck Depression Inventory (BDI; Beck and Steer 1987) and the Beck Anxiety Inventory (BAI; Beck et al 1988). While both of these instruments have been shown to index general negative affect, they respectively assess unique depression-specific (BDI; low positive affect) and anxiety-specific (BAI; physiologic hyperarousal) components of emotional symptoms Clark et al 1994, Steer et al 1995. In order to assess anhedonia, participants completed the Physical Anhedonia Inventory (PAI; Chapman et al 1976). We hypothesized that measures associated with negative affect (BDI, BAI) would be associated with greater startle potentiation during aversive pictures, and that measures associated with low positive affect (BDI, PAI) would be associated with less startle inhibition during pleasant pictures.