Amygdala fMRI Signal as a Predictor of Reaction Time

Philipp Riedel,Nora C Vetter,Michael Marxen,Dirk K Müller,Michael N Smolka,Mark J Jacob

doi:10.3389/fnhum.2016.00516

Abstract

Reaction times (RTs) are a valuable measure for assessing cognitive processes. However, RTs are susceptible to confounds and therefore variable. Exposure to threat, for example, speeds up or slows down responses. Distinct task types to some extent account for differential effects of threat on RTs. But also do inter-individual differences like trait anxiety. In this functional magnetic resonance imaging (fMRI) study, we investigated whether activation within the amygdala, a brain region closely linked to the processing of threat, may also function as a predictor of RTs, similar to trait anxiety scores. After threat conditioning by means of aversive electric shocks, 45 participants performed a choice RT task during alternating 30 s blocks in the presence of the threat conditioned stimulus [CS+] or of the safe control stimulus [CS-]. Trait anxiety was assessed with the State-Trait Anxiety Inventory and participants were median split into a high- and a low-anxiety subgroup. We tested three hypotheses: (1) RTs will be faster during the exposure to threat compared to the safe condition in individuals with high trait anxiety. (2) The amygdala fMRI signal will be higher in the threat condition compared to the safe condition. (3) Amygdala fMRI signal prior to a RT trial will be correlated with the corresponding RT. We found that, the high-anxious subgroup showed faster responses in the threat condition compared to the safe condition, while the low-anxious subgroup showed no significant difference in RTs in the threat condition compared to the safe condition. Though the fMRI analysis did not reveal an effect of condition on amygdala activity, we found a trial-by-trial correlation between blood-oxygen-level-dependent signal within the right amygdala prior to the CRT task and the subsequent RT. Taken together, the results of this study showed that exposure to threat modulates task performance. This modulation is influenced by personality trait. Additionally and most importantly, activation in the amygdala predicts behavior in a simple task that is performed during the exposure to threat. This finding is in line with “attentional capture by threat”—a model that includes the amygdala as a key brain region for the process that causes the response slowing.

Highlights

There is great variability in reaction times (RTs) between and within participants, even in RT tasks where a simple motoric reaction to a cue is required (SRT task) or in RT tasks with two possible stimuli and two possible simple reactions (CRT task) (Rabbitt et al, 2001; Salthouse and Berish, 2005)
In line with the literature, the current study showed that trait anxiety affects performance in a simple CRT task during exposure to continuous threat
Higher BOLD signal within the right amygdala prior to a CRT task was related to longer RTs on the respective trial

Summary

INTRODUCTION

There is great variability in reaction times (RTs) between and within participants, even in RT tasks where a simple motoric reaction to a cue is required (SRT task) or in RT tasks with two possible stimuli and two possible simple reactions (CRT task) (Rabbitt et al, 2001; Salthouse and Berish, 2005). When threat-conditioned stimuli are presented as transient distractors in RT tasks, faster RTs (Notebaert et al, 2011), slower RTs (Schmidt et al, 2015) or no significant difference in RTs (Koster et al, 2005a) have been observed when compared to unconditioned distractors. Etkin et al (2004) reported that participants with high trait anxiety responded faster toward fearful compared to neutral face distractors This effect was only true for masked faces as distractors, that is, in case of unaware or indirect threat.

Participants

RESULTS

Evaluation of Threat Conditioning

DISCUSSION