Studies using emotionally salient stimuli have demonstrated neural activation in limbic and paralimbic brain regions. In some studies, subjects passively perceive evocative stimuli, while in other studies, they perform specific cognitive tasks. Evidence is emerging that even a simple cognitive task performed on emotionally salient stimuli can affect neural activation in emotion-associated brain regions. We tested the hypothesis that rating the subjective experience of an aversive visual stimulus would decrease limbic/paralimbic activation and increase activity in medial frontal regions. Ten healthy subjects underwent (15)O PET scans while they viewed pictures of aversive (AV) and nonaversive (NA) content, taken from the International Affective Picture System. Subjects appraised pictures on a scale of pleasantness/unpleasantness during one set of scans (RTNG), and they passively viewed pictures during another set (PSVW). After each scan, emotional responses were assessed. RTNG was associated with significantly less intensity of sadness and significantly less activation (AV - NA) of the right insula/amygdala and left insula, relative to PSVW. RTNG also activated the dorsal medial prefrontal cortex and the anterior cingulate sulcus, which were not differentially activated during PSVW. For both RTNG and PSVW, subjects activated the left fusiform gyrus. The results support the proposition that task instructions about how subjects should process evocative stimuli can affect neural activity.
" , it provided us with the personal ratings of emotional intensity felt by our participants for each stimulus . Verbal recordings of experienced intensity after scanning have been shown to reliably represent emotional experiences during scanning ( Phan et al . , 2004 ) and avoid biases introduced by monitoring one ' s own emotion during scanning ( Taylor et al . , 2003 ; Phan et al . , 2004 ) ."
[Show abstract][Hide abstract] ABSTRACT: The specific role of the amygdala remains controversial even though the development of functional imaging techniques has established its implication in the emotional process. The aim of this study was to highlight the sensitivity of the amygdala to emotional intensity (arousal). We conducted an analysis of the modulation of amygdala activation according to variation in emotional intensity via an fMRI event-related protocol. Monitoring of electrodermal activity, a marker of psychophysiological emotional perception and a reflection of the activation of the autonomic nervous system, was carried out concurrently. Eighteen subjects (10 men; aged from 22 to 29 years) looked at emotionally positive photographs. We demonstrated that the left and right amygdalae were sensitive to changes in emotional intensity, activating more in response to stimuli with higher intensity. Furthermore, electrodermal responses were more frequent for the most intense stimuli, demonstrating the concomitant activation of the autonomic nervous system. These results highlight the sensitivity of the amygdala to the intensity of positively valenced visual stimuli, and in conjunction with results in the literature on negative emotions, reinforce the role of the amygdala in the perception of intensity.
"Second, the shock likelihood ratings were not collected during the fear generalization procedure but immediately afterwards. This was done in order to avoid suppression of fear responses by evaluative processes (Lange et al., 2003; Taylor et al., 2003), but this aspect of our design may have affected our results. However, because previous studies that used on-line shock likelihood or fear ratings found qualitatively similar results (i.e., more apparent fear generalization in ratings than in physiological measures) (Lissek et al., 2008; Haddad et al., 2013), this seems unlikely to have had a large effect. "
[Show abstract][Hide abstract] ABSTRACT: Fear generalization is the production of fear responses to a stimulus that is similar – but not identical - to a threatening stimulus. Although prior studies have found that fear generalization magnitudes are qualitatively related to the degree of perceptual similarity to the threatening stimulus, the precise relationship between these two functions has not been measured systematically. Also, it remains unknown whether fear generalization mechanisms differ for social and non-social information. To examine these questions, we measured perceptual discrimination and fear generalization in the same subjects, using images of human faces and non-face control stimuli (“blobs”) that were perceptually matched to the faces. First, each subject’s ability to discriminate between pairs of faces or blobs was measured. Each subject then underwent a Pavlovian fear conditioning procedure, in which each of the paired stimuli were either followed (CS+) or not followed (CS-) by a shock. Skin conductance responses (SCRs) were also measured. Subjects were then presented with the CS+, CS- and five levels of a CS+-to-CS- morph continuum between the paired stimuli, based on individual discrimination thresholds. Finally, subjects rated the likelihood that each stimulus had been followed by a shock. Subjects showed both autonomic (SCR-based) and conscious (ratings-based) fear responses to morphs that they could not discriminate from the CS+ (generalization). For both faces and non-face objects, fear generalization was not found above discrimination thresholds. However, subjects exhibited greater fear generalization in the shock likelihood ratings compared to the SCRs, particularly for faces. These findings reveal that autonomic threat detection mechanisms in humans are highly sensitive to small perceptual differences between stimuli. Also, the conscious evaluation of threat shows broader generalization than autonomic responses, biased towards labeling a stimulus as threatening.
Frontiers in Human Neuroscience 09/2014; 8:624. DOI:10.3389/fnhum.2014.00624 · 3.63 Impact Factor
"The dACC is thought to play a role in the regulation of both cognitive and emotional processing (Phan et al. 2002; Etkin et al. 2011). Increased dACC activity was associated with increased attention to negative emotions (Etkin et al. 2011), and reappraisal or rating of emotional stimuli v. passive viewing (Ochsner et al. 2002; Taylor et al. 2003; Hutcherson et al. 2005). The increased dACC activation we observed during presentation of negative v. neutral pictures in PTSD is therefore thought to reflect an attentional bias to negative stimuli, previously demonstrated as attentional bias to threat stimuli (Fani et al. 2012). "
[Show abstract][Hide abstract] ABSTRACT: Background:
Post-traumatic stress disorder (PTSD) is thought to be characterized by general heightened amygdala activation. However, this hypothesis is mainly based on specific studies presenting fear or trauma-related stimuli, hence, a thorough investigation of trauma-unrelated emotional processing in PTSD is needed.
In this study, 31 male medication-naive veterans with PTSD, 28 male control veterans (combat controls; CC) and 25 non-military men (healthy controls; HC) were included. Participants underwent functional MRI while trauma-unrelated neutral, negative and positive emotional pictures were presented. In addition to the group analyses, PTSD patients with and without major depressive disorder (MDD) were compared.
All groups showed an increased amygdala response to negative and positive contrasts, but amygdala activation did not differ between groups. However, a heightened dorsal anterior cingulate cortex (dACC) response for negative contrasts was observed in PTSD patients compared to HC. The medial superior frontal gyrus was deactivated in the negative contrast in HC, but not in veterans. PTSD+MDD patients showed decreased subgenual ACC (sgACC) activation to all pictures compared to PTSD-MDD.
Our findings do not support the hypothesis that increased amygdala activation in PTSD generalizes to trauma-unrelated emotional processing. Instead, the increased dACC response found in PTSD patients implicates an attentional bias that extends to trauma-unrelated negative stimuli. Only HC showed decreased medial superior frontal gyrus activation. Finally, decreased sgACC activation was related to MDD status within the PTSD group.
Psychological Medicine 07/2014; DOI:10.1017/S0033291714001706 · 5.94 Impact Factor
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