Academic journal article Cognitive, Affective and Behavioral Neuroscience

Coarse Threat Images Reveal Theta Oscillations in the Amygdala: A Magnetoencephalography Study

Academic journal article Cognitive, Affective and Behavioral Neuroscience

Coarse Threat Images Reveal Theta Oscillations in the Amygdala: A Magnetoencephalography Study

Article excerpt

Neurocognitive models propose a specialized neural system for processing threat-related information, in which the amygdala plays a key role in the analysis of threat cues. fMRI research indicates that the amygdala is sensitive to coarse visual threat relevant information-for example, low spatial frequency (LSF) fearful faces. However, fMRI cannot determine the temporal or spectral characteristics of neural responses. Consequently, we used magnetoencephalography to explore spatiotemporal patterns of activity in the amygdala and cortical regions with blurry (LSF) and normal angry, fearful, and neutral faces. Results demonstrated differences in amygdala activity between LSF threat-related and LSF neutral faces (50-250 msec after face onset). These differences were evident in the theta range (4-8 Hz) and were accompanied by power changes within visual and frontal regions. Our results support the view that the amygdala is involved in the early processing of coarse threat related information and that theta is important in integrating activity within emotion-processing networks.

It is now well established that the amygdala plays a key role in the processing of emotional information, regulates emotional responses, and controls fear reactions in a range of species (for reviews, see Aggleton & Young, 2000; Davis & Whalen, 2001; Phelps & LeDoux, 2005; Zald, 2003). The amygdala is proposed to be part of a network of cortical and subcortical structures that allow efficient processing of, and rapid responding to, crude visual representations of potentially threatening stimuli (LeDoux, 1998, 2000). Within this network, cortical regions, including the ventral visual system, allow for the fine-grained analysis of stimuli and provide more refined, detailed information about the emotional significance of a perceived stimulus (Price & Amaral, 1981; Winston, Vuilleumier, & Dolan, 2003). Frontal regions, such as the prefrontal cortex, are also proposed to play an important role in regulating amygdala activity in response to threat-related information (Bishop, 2007; Hariri, Mattay, Tessitore, Fera, & Weinberger, 2003).

There is now considerable research that shows differential amygdala activation to threat-related cues compared with that to neutral cues (for a review, see Phan, Wager, Taylor, & Liberzon, 2002). Such responses have also been found when awareness of the threat cue is restricted by masking (Williams, Das, et al., 2006) and when the threatening stimulus is unattended (Vuilleumier, 2005), but not always. That is, in contrast to Williams, Das, et al., Pessoa, Japee, Sturman, and Ungerleider (2006) showed that amygdala responses were greater for fearful than for neutral faces, but only when participants were able to reliably detect those stimuli. Amygdala activation has also been observed for both direct-threat cues (e.g., an angry face) and indirect-threat cues (e.g., a fearful face that signals threat in the environment, but is not threatening per se; Yang et al., 2002); there is, however, more consistent evidence for amygdala activation by fearful facial expressions (Davis & Whalen, 2001; Phan et al., 2002; Whalen et al., 2001).

In recent neuroimaging work, the spatial frequency of stimuli has been manipulated in order to test the hypothesis that the amygdala response to threatening stimuli is driven by coarse visual information, which is primarily contained in low spatial frequencies (LeDoux, 2000). Using fMRI, Vuilleumier, Armony, Driver, and Dolan (2003) demonstrated increased activation of the amygdala in response to blurry, low spatial frequency (LSF) fearful faces compared with fine-grained, high spatial frequency (HSF) fearful faces. This finding contrasted with evidence of greater activation of the fusiform cortex by HSF faces compared with that by LSF faces, irrespective of their emotional expressions. Such findings are consistent with the idea that the amygdala is particularly sensitive to crude visual representations of threat cues, such as those represented by LSF information (Vuilleumier & Pourtois, 2007). …

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