Alcohol selectively reduces anxiety but not fear: startle response during unpredictable versus predictable threat

Abstract

Recent theory and empirical research have suggested that fear and anxiety are distinct processes with separable neurobiological substrates. Furthermore, a laboratory procedure has been developed to manipulate fear versus anxiety independently via administration of predictable or unpredictable electric shock, respectively. Benzodiazepines appear to selectively reduce anxiety but not fear in this procedure. The primary aim of this experiment was to determine if alcohol produced a similar selective reduction in anxiety. Intoxicated (target blood alcohol concentration of .08%) and nonintoxicated participants viewed a series of colored squares separated by variable intertrial intervals (ITIs) in 3 conditions. In the predictable shock condition, shocks were administered contingently during every square. In the unpredictable shock condition, shocks were administered noncontingently during both squares and ITIs. In the no-shock condition, no shocks were administered at any time. Alcohol significantly reduced startle potentiation during cues signaling unpredictable but not predictable shock, consistent with the thesis that alcohol selectively reduces anxiety but not fear. In addition, alcohol's effect on startle potentiation during unpredictable shock was mediated by vigilance. This anxiolytic effect may clarify the nature of alcohol's reinforcing effects in social and problem drinkers.

Figure 1. Startle Response and Startle Potentiation during Predictable Shock Cues

Left Panel: Raw startle response is displayed for Predictable shock (gray) and No-shock (white) cues by Beverage group. Startle potentiation difference scores (Predictable shock cue – No-shock cue) are displayed (hatched) with standard errors for the Beverage group effect. Predictable shock cues produced significant startle potentiation relative to No-shock cues (difference > 0; p< .001). The non-significant Beverage Group effect on startle potentiation indicates that alcohol does not reduce startle potentiation to predictable shock cues relative to no-shock cues. For all figures, the Beverage group effect on startle potentiation difference scores is statistically equivalent to the Beverage group × Cue type interaction for raw startle response. Right Panel: Raw startle response is displayed for Predictable shock cues (gray) and Predictable shock ITIs (white) by Beverage group. Startle potentiation difference scores (Predictable cue – Predictable ITI) are displayed (hatched) with standard errors for the Beverage group effect. Predictable shock cues produced significant startle potentiation relative to the Predictable shock ITI period (difference > 0; p< .001). The non-significant Beverage group effect on startle potentiation indicates that alcohol does not reduce startle potentiation to predictable shock cues relative to the ITI period in the same predictable blocks.

Figure 2. Startle Response and Startle Potentiation during Unpredictable Shock Cues and ITI

Left Panel: Raw startle response is displayed for Unpredictable shock (gray) and No-shock (white) cues by Beverage group. Startle potentiation difference scores (Unpredictable cue – No-shock cue) are displayed (hatched) with standard errors for the Beverage group effect. Unpredictable shock cues produced significant startle potentiation relative to No-shock cues (difference > 0; p< .001). The significant Beverage Group effect (p= .021) on startle potentiation indicates that alcohol selectively reduces startle potentiation to Unpredictable shock cues relative to No-shock cues. Right Panel: Raw startle response is displayed for the Unpredictable ITI period (gray) and No-shock ITIs period (white) by Beverage group. Startle potentiation difference scores (Unpredictable ITI – No-shock ITI) are displayed (hatched) with standard errors for the Beverage group effect. Unpredictable ITIs produced significant startle potentiation relative to the No-shock ITI period (difference > 0; p< .001). The test non-significant Beverage Group effect on startle potentiation indicates that alcohol does not reduce startle potentiation during the unpredictable ITI period relative to the comparable ITI period in the No-shock blocks.

Figure 3. Startle Potentiation to Predictable and Unpredictable Shock Cues by Beverage Group

Startle potentiation difference scores are displayed for Predictable (Predictable cue – No-shock cue) and Unpredictable (Unpredictable cue – No-shock cue) shock conditions. These startle potentiation differences scores were displayed separately in the left panels of Figure 1 & Figure 2. These data are presented here together to facilitate direct comparison of startle potentiation magnitude across the two manipulations. Error bars represent standard errors of the Beverage group effects. The significant Beverage Group × Block Type interaction (p= .032) indicates that alcohol has a larger effect on Unpredictable vs. Predictable shock cue startle potentiation. The simple effect of Beverage Group is significant for Unpredictable shock cues (p=.021) but not for Predictable shock cues (p= .716).

Figure 4. Startle Response and Startle Inhibition during No-shock Blocks

Raw startle response is displayed for No-shock cues (gray) and the No-s hock ITI period (white) by Beverage group. Startle inhibition difference scores (No-shock cue – No-shock ITI) are displayed (hatched) with standard errors for the Beverage group effect. No-shock cues produced significant startle inhibition relative to the No-shock ITI period (difference scores < 0; p< .001). The significant Beverage Group effect (p< .001) on startle inhibition difference scores indicates that alcohol reduced startle inhibition associated with attention to the visual no-shock cues.