Does the amygdala response correlate with the personality trait 'harm avoidance' while evaluating emotional stimuli explicitly?

Background: The affective personality trait 'harm avoidance' (HA) from Cloninger's psychobiological personality model determines how an individual deals with emotional stimuli. Emotional stimuli are processed by a neural network that include the left and right amygdalae as important key nodes. Explicit, implicit and passive processing of affective stimuli are known to activate the amygdalae differently reflecting differences in attention, level of detailed analysis of the stimuli and the cognitive control needed to perform the required task. Previous studies revealed that implicit processing or passive viewing of affective stimuli, induce a left amygdala response that correlates with HA. In this new study we have tried to extend these findings to the situation in which the subjects were required to explicitly process emotional stimuli. Methods: A group of healthy female participants was asked to rate the valence of positive and negative stimuli while undergoing fMRI. Afterwards the neural responses of the participants to the positive and to the negative stimuli were separately correlated to their HA scores and compared between the low and high HA participants. Results: Both analyses revealed increased neural activity in the left laterobasal (LB) amygdala of the high HA participants while they were rating the positive and the negative stimuli. Conclusions: Our results indicate that the left amygdala response to explicit processing of affective stimuli does correlate with HA

Human brain structure predicts individual differences in preconscious evaluation of facial dominance and trustworthiness.

Social cues conveyed by the human face, such as eye gaze direction, are evaluated even before they are consciously perceived. While there is substantial individual variability in such evaluation, its neural basis is unknown. Here we asked whether individual differences in preconscious evaluation of social face traits were associated with local variability in brain structure. Adult human participants (n = 36) monocularly viewed faces varying in dominance and trustworthiness, which were suppressed from awareness by a dynamic noise pattern shown to the other eye. The time taken for faces to emerge from suppression and become visible (t2e) was used as a measure of potency in competing for visual awareness. Both dominant and untrustworthy faces resulted in slower t2e than neutral faces, with substantial individual variability in these effects. Individual differences in t2e were correlated with gray matter volume in right insula for dominant faces, and with gray matter volume in medial prefrontal cortex, right temporoparietal junction and bilateral fusiform face area for untrustworthy faces. Thus, individual differences in preconscious social processing can be predicted from local brain structure, and separable correlates for facial dominance and untrustworthiness suggest distinct mechanisms of preconscious processing

Social Anxiety: Understanding the Attentional Bias to Threat

Biased attention toward threatening facial expressions is an important maintaining and possibly aetiological factor for social anxiety. However, little is known about the underlying mechanisms. To develop our understanding of this threat bias, the relative contributions of top-down attention, bottom-up attention, and selection history were differentiated across four studies. In Study One, the roles of top-down attention, bottom-up attention, and selection history were tested in an unselected sample using a modification of the dot-probe task, in which participants were cued to attend to a happy or angry face on each trial. Results showed that attentional orienting toward facial expressions was not exclusively driven by bottom-up attentional capture as some previous theories suggest; but instead, participants could shift attention toward emotional faces in a top-down manner. This effect was eliminated when the faces were inverted, demonstrating that top-down attention relies on holistic face processing. Study One found no evidence of selection history (i.e., no improvement on repeated trials or blocks of trials in which the task was to orient to the same expression). Study Two tested whether this ability to use top-down attention to orient to emotional faces is impaired for individuals with social anxiety. Using the same task as Study One, Study Two found that participants with higher levels of social anxiety were selectively impaired in attentional shifting toward a cued happy face when it was paired with an angry face, but not when paired with a neutral face. These results indicate that high social anxiety is associated with deficits in top-down control of attention, which are selectively revealed in the presence of non-task-relevant threat. The results of Study Two could be explained by bottom-up attention to threat or a top-down set for threat that could not be overcome by the instruction to attend to a happy face. To test this, Study Three utilised a modified dot-probe task in which participants were presented with an upright face paired with an inverted face (displaying a disgust or neutral expression) and engagement with and disengagement of attention from threatening faces were measured separately. The task was performed under no, low, and high working-memory load conditions. Since working-memory load draws on the same resources as top-down attention, interference from increasing working-memory load on attentional orienting would point to a role for top-down attention. Social anxiety was not associated with delayed disengagement from threat. However, surprisingly, high social anxiety was associated with an engagement bias away from threat, while low social anxiety was associated with a bias toward threat. These results were unaffected by the working-memory load manipulation. However, some methodological issues were identified with the study. Study Four overcame these methodological issues by using a paired angry and neutral face under no, low and high working-memory load conditions. Higher levels of social anxiety were associated with increased engagement with threat under no-load, but not under low- and high-load conditions. Thus, this body of research provides evidence that social anxiety is associated with an engagement bias to threat, which is driven by top-down attention

Testing a goal-driven account of involuntary attentional capture by motivationally salient stimuli

Traditionally, mainstream models of attention have neglected the role of motivationally meaningful stimuli (e.g. threat/reward). These stimuli can cause the rapid and involuntary attraction of attention (attentional capture), and can hence be said to have motivational salience. It is sometimes considered that this capture occurs in a stimulus-driven manner (versus goal-driven). I, however, suggest that attentional capture by motivational salience could be caused by a goal-driven mechanism. To test this we asked three overarching questions: 1) Is detecting motivationally salient stimuli considered important? By using a novel concurrent forced choice task, which isolates the priority of an individual’s explicit search goals, we found that individuals believed that it was advantageous to detect and search for motivationally salient stimuli. 2) Can voluntary search goals induce attentional capture? In Chapter 2 we revealed that task-irrelevant threatening stimuli only captured attention, versus neutral distractors, when participants were searching for that category of threatening stimuli. This goal-driven capture effect was robust yet highly specific, affecting only the single specific semantic category, rather than generalising across all related stimuli (Chapter 3). We found an identical pattern of results for reward associated stimuli (alcohol in social drinkers) in Chapter 4, with capture only occurring in the goal-driven condition. The same was true for smoking related images in Chapter 5, and this occurred independently of current nicotine dependence. Additionally, self-selected search goals were capable of inducing attentional capture, not just instructed goals (Chapter 7). 3) How are top-down search goals initially selected? Chapter 6 revealed that search goal priority was positively predicted by stimulus importance and expectancy. This task also revealed a contextual cueing effect on search goal priority, whereby threat was prioritised more in a threatening context (versus safe). On the basis of my findings we propose a novel Importance-Expectancy model of attentional goal selection