Human thalamic and amygdala modulation in emotional scene perception

A 5-min paradigm to evoke robust emotional reactivity in neuroimaging studies

The advent of the Research Domain Criteria (RDoC) approach to funding translational neuroscience has highlighted a need for research that includes measures across multiple task types. However, the duration of any given experiment is quite limited, particularly in neuroimaging contexts, and therefore robust estimates of multiple behavioral domains are often difficult to achieve. Here we offer a "turn-key" emotion-evoking paradigm suitable for neuroimaging experiments that demonstrates strong effect sizes across widespread cortical and subcortical structures. This short series could be easily added to existing fMRI protocols, and yield a reliable estimate of emotional reactivity to complement research in other behavioral domains. This experimental adjunct could be used to enable an initial comparison of emotional modulation with the primary behavioral focus of an investigator's work, and potentially identify new relationships between domains of behavior that have not previously been recognized.

fMRI replicability during emotional scene viewing: Functional regions and sample size

Recent findings have questioned the replicability of functional magnetic resonance imaging (fMRI) in the study of affective processing, reporting low replicability of emotional enhancement during a face-matching task. However, poor replicability may instead reflect a lack of emotional engagement for face matching. In the current study, replicability of emotional enhancement was tested in a large (N = 160) sample when emotional engagement was assessed during pleasant, neutral, and unpleasant picture viewing, which reliably engages affective reactions in both the brain and the body. Replicability was computed using a subsampling technique, in which random sets of subjects of different sample sizes (N = 20, 40, 60, 80) were selected from the entire dataset, and replicability of emotional enhancement for peaks, clusters, and voxels were averaged across 500 permutations for each sample size. Consistent with previous findings, fMRI replicability increased with increasing sample size. On the other hand, even with relatively small samples, fMRI replicability for peaks, clusters, and voxels during emotional, compared to neutral, scene viewing was good to excellent. Importantly, replicability varied in different brain regions, with excellent replicability at both the cluster and peak level with an N of 40, at the most conservative threshold (p < .001), in the amygdala and the visual cortex. The data argue against general recommendations regarding sample size in fMRI studies of emotion, suggesting instead that degree of replicability depends on successful emotional engagement in task-related brain regions.

Structural assessment of thalamus morphology in brain disorders: A review and recommendation of thalamic nucleus segmentation and shape analysis

The thalamus is a central brain structure crucially involved in cognitive, emotional, sensory, and motor functions and is often reported to be involved in the pathophysiology of neurological and psychiatric disorders. The functional subdivision of the thalamus warrants morphological investigation on the level of individual subnuclei. In addition to volumetric measures, the investigation of other morphological features may give additional insights into thalamic morphology. For instance, shape features offer a higher spatial resolution by revealing small, regional differences that are left undetected in volumetric analyses. In this review, we discuss the benefits and limitations of recent advances in neuroimaging techniques to investigate thalamic morphology in vivo, leading to our proposed methodology. This methodology consists of available pipelines for volume and shape analysis, focussing on the morphological features of volume, thickness, and surface area. We demonstrate this combined approach in a Parkinson's disease cohort to illustrate their complementarity. Considering our findings, we recommend a combined methodology as it allows for more sensitive investigation of thalamic morphology in clinical populations.

The Missing Link in Early Emotional Processing

Initial evaluation structures (IESs) currently proposed as the earliest detectors of affective stimuli (e.g., amygdala, orbitofrontal cortex, or insula) are high-order structures (a) whose response latency cannot account for the first visual cortex emotion-related response (~80 ms), and (b) lack the necessary infrastructure to locally analyze the visual features that define emotional stimuli. Several thalamic structures accomplish both criteria. The lateral geniculate nucleus (LGN), a first-order thalamic nucleus that actively processes visual information, with the complement of the thalamic reticular nucleus (TRN) are proposed as core IESs. This LGN–TRN tandem could be supported by the pulvinar, a second-order thalamic structure, and by other extrathalamic nuclei. The visual thalamus, scarcely explored in affective neurosciences, seems crucial in early emotional evaluation.

The Amygdala Responds Rapidly to Flashes Linked to Direct Retinal Innervation: A Flash-evoked Potential Study Across Cortical and Subcortical Visual Pathways

Rapid detection and response to visual threats are critical for survival in animals. The amygdala (AMY) is hypothesized to be involved in this process, but how it interacts with the visual system to do this remains unclear. By recording flash-evoked potentials simultaneously from the superior colliculus (SC), lateral posterior nucleus of the thalamus, AMY, lateral geniculate nucleus (LGN) and visual cortex, which belong to the cortical and subcortical pathways for visual fear processing, we investigated the temporal relationship between these regions in visual processing in rats. A quick flash-evoked potential (FEP) component was identified in the AMY. This emerged as early as in the LGN and was approximately 25 ms prior to the earliest component recorded in the SC, which was assumed to be an important area in visual fear. This quick P1 component in the AMY was not affected by restraint stress or corticosterone injection, but was diminished by RU38486, a glucocorticoid receptor blocker. By injecting a monosynaptic retrograde AAV tracer into the AMY, we found that it received a direct projection from the retina. These results confirm the existence of a direct connection from the retina to the AMY, that the latency in the AMY to flashes is equivalent to that in the sensory thalamus, and that the response is modulated by glucocorticoids.

Humor and emotion: Quantitative meta analyses of functional neuroimaging studies

Humor is a ubiquitous aspect of human behavior that is infrequently the focus of neuroscience research. To localize human brain structures associated with the experience of humor, we conducted quantitative activation likelihood estimate (ALE) meta analyses of 57 fMRI studies (n = 1248) reporting enhanced regional brain activity evoked by humorous cues versus matched control cues. We performed separate ALE analyses of studies that employed picture-driven, text-based, and auditory laughter cues to evoke humor. A primary finding was that complex humor activates supramodal areas of the brain strongly associated with emotional processes, including bilateral amygdala and inferior frontal gyrus. Moreover, activation in brain regions associated with language, semantic knowledge, and theory of mind were differentially modulated by text and picture-driven humor cues, while hearing laughter enhances activation in auditory association cortex. The identification of humor-driven brain networks has the potential to expand brain-derived models of human emotion and could provide useful targets in translational research and therapy.

Assessing the role of the amygdala in fear of pain: Neural activation under threat of shock

INTRODUCTION

The DSM-5 explicitly states that the neural system model of specific phobia is centered on the amygdala. However, this hypothesis is predominantly supported by human studies on animal phobia, whereas visual cuing of other specific phobias, such as dental fear, do not consistently show amygdala activation. Considering that fear of anticipated pain is one of the best predictors of dental phobia, the current study investigated neural and autonomic activity of pain anticipation in individuals varying in the degree of fear of dental pain.

METHOD

Functional brain activity (fMRI) was measured in women (n = 31) selected to vary in the degree of self-reported fear of dental pain when under the threat of shock, in which one color signaled the possibility of receiving a painful electric shock and another color signaled safety.

RESULTS

Enhanced functional activity during threat, compared to safety, was found in regions including anterior insula and anterior/mid cingulate cortex. Importantly, threat reactivity in the anterior insula increased as reported fear of pain increased and further predicted skin conductance changes during pain anticipation.

LIMITATIONS

The sample was comprised of women.

CONCLUSIONS

Individual differences in fear of pain vary with activation in the anterior insula, rather than with the amygdala, indicating that fear is not uniquely associated with amygdala activation. Whereas coping techniques such as emotion regulation have been found to vary with activation in a frontal-amygdala circuit when confronted with visual cues, precision psychiatry may need to target specific brain circuits to diagnose and treat different types of specific phobia.

Common circuit or paradigm shift? The functional brain in emotional scene perception and emotional imagery

Meta-analytic and experimental studies investigating the neural basis of emotion often compare functional activation in different emotional induction contexts, assessing evidence for a "core affect" or "salience" network. Meta-analyses necessarily aggregate effects across diverse paradigms and different samples, which ignore potential neural differences specific to the method of affect induction. Data from repeated measures designs are few, reporting contradictory results with a small N. In the current study, functional brain activity is assessed in a large (N = 61) group of healthy participants during two common emotion inductions-scene perception and narrative imagery-to evaluate cross-paradigm consistency. Results indicate that limbic and paralimbic regions, together with visual and parietal cortex, are reliably engaged during emotional scene perception. For emotional imagery, in contrast, enhanced functional activity is found in several cerebellar regions, hippocampus, caudate, and dorsomedial prefrontal cortex, consistent with the conception that imagery is an action disposition. Taken together, the data suggest that a common emotion network is not engaged across paradigms, but that the specific neural regions activated during emotional processing can vary significantly with the context of the emotional induction.

Directional interconnectivity of the human amygdala, fusiform gyrus, and orbitofrontal cortex in emotional scene perception

The perception of emotionally arousing scenes modulates neural activity in ventral visual areas via reentrant signals from the amygdala. The orbitofrontal cortex (OFC) shares dense interconnections with amygdala and has been strongly implicated in emotional stimulus processing in primates, but our understanding of the functional contribution of this region to emotional perception in humans is poorly defined. In this study we acquired targeted rapid functional imaging from lateral OFC, amygdala, and fusiform gyrus (FG) over multiple scanning sessions (resulting in over 1,000 trials per participant) in an effort to define the activation amplitude and directional connectivity among these regions during naturalistic scene perception. All regions of interest showed enhanced activation during emotionally arousing, compared with neutral scenes. In addition, we identified bidirectional connectivity between amygdala, FG, and OFC in the great majority of individual subjects, suggesting that human emotional perception is implemented in part via nonhierarchical causal interactions across these three regions.NEW & NOTEWORTHY Due to the practical limitations of noninvasive recording methodologies, there is a scarcity of data regarding the interactions of human amygdala and orbitofrontal cortex (OFC). Using rapid functional MRI sampling and directional connectivity, we found that the human amygdala influences emotional perception via distinct interactions with late-stage ventral visual cortex and OFC, in addition to distinct interactions between OFC and fusiform gyrus. Future efforts may leverage these patterns of directional connectivity to noninvasively distinguish clinical groups from controls with respect to network causal hierarchy.

Trait anger modulates neural activity in the fronto-parietal attention network

Anger is considered a unique high-arousal and approach-related negative emotion. The influence of individual differences in trait anger on the processing of visual stimuli is relevant to questions about emotional processing and remains to be explored. Using functional magnetic resonance imaging (fMRI), we explored the neural responses to standardized images, selected based on valence and arousal ratings in a group of men with high trait anger compared to those with normative to low anger scores (controls). Results show increased activation in the left-lateralized ventral fronto-parietal attention network to unpleasant images by individuals with high trait anger. There was also a group by arousal interaction in the left thalamus/pulvinar such that individuals with high trait anger had increased pulvinar activation to the high-arousal (versus low arousal) unpleasant images as compared to controls. Thus, individual differences in trait anger in men are associated with brain regions subserving executive attentional and sensory integration during the processing of unpleasant emotional stimuli, particularly to high arousal images.

Primate Visual Perception: Motivated Attention in Naturalistic Scenes

Research has consistently revealed enhanced neural activation corresponding to attended cues coupled with suppression to unattended cues. This attention effect depends both on the spatial features of stimuli and internal task goals. However, a large majority of research supporting this effect involves circumscribed tasks that possess few ecologically relevant characteristics. By comparison, natural scenes have the potential to engage an evolved attention system, which may be characterized by supplemental neural processing and integration compared to mechanisms engaged during reduced experimental paradigms. Here, we describe recent animal and human studies of naturalistic scene viewing to highlight the specific impact of social and affective processes on the neural mechanisms of attention modulation.

A shared neural network for emotional expression and perception: an anatomical study in the macaque monkey

Over the past two decades, the insula has been described as the sensory “interoceptive cortex”. As a consequence, human brain imaging studies have focused on its role in the sensory perception of emotions. However, evidence from neurophysiological studies in non-human primates have shown that the insula is also involved in generating emotional and communicative facial expressions. In particular, a recent study demonstrated that electrical stimulation of the mid-ventral sector of the insula evoked affiliative facial expressions. The present study aimed to describe the cortical connections of this “affiliative field”. To this aim, we identified the region with electrical stimulation and injected neural tracers to label incoming and outgoing projections. Our results show that the insular field underlying emotional expression is part of a network involving specific frontal, cingulate, temporal, and parietal areas, as well as the amygdala, the basal ganglia, and thalamus, indicating that this sector of the insula is a site of integration of motor, emotional, sensory and social information. Together with our previous functional studies, this result challenges the classic view of the insula as a multisensory area merely reflecting bodily and internal visceral states. In contrast, it supports an alternative perspective; that the emotional responses classically attributed to the insular cortex are endowed with an enactive component intrinsic to each social and emotional behavior.

Brief learning induces a memory bias for arousing-negative words: an fMRI study in high and low trait anxious persons

Persons suffering from anxiety disorders display facilitated processing of arousing and negative stimuli, such as negative words. This memory bias is reflected in better recall and increased amygdala activity in response to such stimuli. However, individual learning histories were not considered in most studies, a concern that we meet here. Thirty-four female persons (half with high-, half with low trait anxiety) participated in a criterion-based associative word-learning paradigm, in which neutral pseudowords were paired with aversive or neutral pictures, which should lead to a valence change for the negatively paired pseudowords. After learning, pseudowords were tested with fMRI to investigate differential brain activation of the amygdala evoked by the newly acquired valence. Explicit and implicit memory was assessed directly after training and in three follow-ups at 4-day intervals. The behavioral results demonstrate that associative word-learning leads to an explicit (but no implicit) memory bias for negatively linked pseudowords, relative to neutral ones, which confirms earlier studies. Bilateral amygdala activation underlines the behavioral effect: Higher trait anxiety is correlated with stronger amygdala activation for negatively linked pseudowords than for neutrally linked ones. Most interestingly, this effect is also present for negatively paired pseudowords that participants could not remember well. Moreover, neutrally paired pseudowords evoked higher amygdala reactivity than completely novel ones in highly anxious persons, which can be taken as evidence for generalization. These findings demonstrate that few word-learning trials generate a memory bias for emotional stimuli, indexed both behaviorally and neurophysiologically. Importantly, the typical memory bias for emotional stimuli and the generalization to neutral ones is larger in high anxious persons.