We have demonstrated a meta-analysis of the activation states of anxiety under emotional stimulations by the ALE method to compare the brain activation in different subtypes of anxiety.
We found that anxiety disorders displayed increased activation in the bilateral amygdala, anterior cingulate gyrus, parahippocampal gyrus, and common decreased activation mainly in the posterior cingulate, lingual gyrus, and precuneus. These conclusions are consistent with the previous studies [14, 20–30].
Although activations in the amygdala always appear in anxiety disorders involving emotional stimulations, there was a divergence in the activation of the left and right amygdala. For instance, some studies have highlighted the hyperactivity of the two-sided amygdala in anxiety disorders [23, 24, 27, 29, 31–33], while other studies have only found it in the unilateral amygdala. This may be related to the different functions of the left and right amygdala [34]. The right amygdala is related to sensory-driven, bottom-up processing [35]. And the left amygdala is associated with the cognitive evaluation of emotional stimulations [36, 37]. Our meta-analysis showed the activation of the bilateral amygdala increases when anxiety were stimulated by emotional facial pictures.
We also detected more activation in the parahippocampal gyrus (BA 34) in anxiety, this is consistent with the structure in Pavlov fear conditioning in animals and humans [38]. An earlier review and meta-analysis of fMRI data in anxiety disorders also pointed out that the activation of the parahippocampal gyrus was significantly increased [39, 40].
Additionally, we also found that under the stimulative tasks, the activation of the cingulate cortex of anxiety disorders was significantly different from HCs. As previous studies [41–44] reported that the cingulate cortex is related to emotional processing and participates in emotional regulation in depression and anxiety. Our results have once again verified this theory.
We also found that anxiety disorders showed markedly increased activations in the anterior cingulate cortex. As reported that the anterior cingulate cortex plays a key role in regulating mood in individuals, especially anxiety [45]. In the insula (BA 13) of anxiety, we found an increased activation. This also confirms the evidence from studies [46] and [47] that the insula has an impact on facial emotional processing. We also found a decreased activation in the anterior wedge (BA 7) and the visual associative cortex (BA 19) of anxiety disorders. This may be related to the inherent functional structure of the front wedge in humans [48], [49]. The size of the anterior right wedge is positively correlated with the individuals’ linguistic creativity [50]. This also reflects the remarkable characteristics of anxiety disorders’ avoidance behavioral response and impaired cognition, speech, and various related physiological reactions.
However, our meta-analysis has some limitations that must be considered. Primarily, due to the timing of selecting studies, some related publications may be missed. Moreover, the age of the participants included in the meta-analysis was not divided in detail. Because anxiety problems, particularly negative cognitions problems, increased with age, and are significantly higher among females [51].