Relating experimentally-induced fear to pre-existing phobic fear in the human brain

Altered amygdalar emotion space in borderline personality disorder normalizes following dialectical behaviour therapy

BACKGROUND

Borderline personality disorder (BPD) is a mental health condition characterized by an inability to regulate emotions or accurately process the emotional states of others. Previous neuroimaging studies using classical univariate analyses have tied such emotion dysregulation to aberrant activity levels in the amygdala of patients with BPD. However, multivariate analyses have not yet been used to investigate how representational spaces of emotion information may be systematically altered in patients with BPD.

METHODS

Patients with BPD performed an emotional face matching task while undergoing MRI before and after a 10-week inpatient program of dialectical behavioural therapy. Representational similarity analysis (RSA) was applied to activity patterns (evoked by angry, fearful, neutral and surprised faces) in the amygdala and temporo-occipital fusiform gyrus of patients with BPD and in the amygdala of healthy controls.

RESULTS

We recruited 15 patients with BPD (8 females, 6 males, 1 transgender male) to participate in the study, and we obtained a neuroimaging data set for 25 healthy controls for a comparative analysis. The RSA of the amygdala revealed a negative bias in the underlying affective space (in that activity patterns evoked by angry, fearful and neutral faces were more similar to each other than to patterns evoked by surprised faces), which normalized after therapy. This bias-to-normalization effect was present neither in activity patterns of the temporo-occipital fusiform gyrus of patients nor in amygdalar activity patterns of healthy controls.

LIMITATIONS

Larger samples and additional questionnaires would help to better characterize the association between specific aspects of therapy and changes in the neural representational space.

CONCLUSION

Our findings suggest a more refined role for the amygdala in the pathological processing of perceived emotions and may provide new diagnostic and prognostic imaging-based markers of emotion dysregulation and personality disorders.Clinical trial registration: DRKS00019821, German Clinical Trials Register (Deutsches Register Klinischer Studien).

Neurosteroids and translocator protein 18 kDa (TSPO) in depression: implications for synaptic plasticity, cognition, and treatment options

There is need for novel fast acting treatment options in affective disorders. 3α-reduced neurosteroids such as allopregnanolone are powerful positive allosteric modulators of GABAA receptors and target also extrasynaptic receptors. Their synthesis is mediated by the translocator protein 18 kDa (TSPO). TSPO ligands not only promote endogenous neurosteroidogenesis, but also exert a broad spectrum of functions involving modulation of mitochondrial activity and acting as anti-inflammatory and neuroregenerative agents. Besides affective symptoms, in depression cognitive impairment can be frequently observed, which may be ameliorated through targeting of extrasynaptic GABAA receptors either via TSPO ligands or exogenously administered 3α-reduced neurosteroids. Interestingly, recent findings indicate an enhanced activation of the complement system, e.g., enhanced expression of C1q, both in depression and dementia. It is of note that benzodiazepines have been shown to reduce long-term potentiation and to cause cognitive decline. Intriguingly, TSPO may be crucial in mediating the effects of benzodiazepines on synaptic pruning. Here, we discuss how benzodiazepines and TSPO may interfere with synaptic pruning. Moreover, we highlight recent developments of TSPO ligands and 3α-reduced neurosteroids as therapeutic agents. Etifoxine is the only clinically available TSPO ligand so far and has been studied in anxiety disorders. Regarding 3α-reduced neurosteroids, brexanolone, an intravenous formulation of allopregnanolone, has been approved for the treatment of postpartum depression and zuranolone, an orally available 3α-reduced neurosteroid, is currently being studied in major depressive disorder and postpartum depression. As such, 3α-reduced neurosteroids and TSPO ligands may constitute promising treatment approaches for affective disorders.

Threat induction biases processing of emotional expressions

Threats can derive from our physical or social surroundings and bias the way we perceive and interpret a given situation. They can be signaled by peers through facial expressions, as expressed anger or fear can represent the source of perceived threat. The current study seeks to investigate enhanced attentional state and defensive reflexes associated with contextual threat induced through aversive sounds presented in an emotion recognition paradigm. In a sample of 120 healthy participants, response and gaze behavior revealed differences in perceiving emotional facial expressions between threat and safety conditions: Responses were slower under threat and less accurate. Happy and neutral facial expressions were classified correctly more often in a safety context and misclassified more often as fearful under threat. This unidirectional misclassification suggests that threat applies a negative filter to the perception of neutral and positive information. Eye movements were initiated later under threat, but fixation changes were more frequent and dwell times shorter compared to a safety context. These findings demonstrate that such experimental paradigms are capable of providing insight into how context alters emotion processing at cognitive, physiological, and behavioral levels. Such alterations may derive from evolutionary adaptations necessary for biasing cognitive processing to survive disadvantageous situations. This perspective sets up new testable hypotheses regarding how such levels of explanation may be dysfunctional in patient populations.

Individualizing Representational Similarity Analysis

Representational similarity analysis (RSA) is a popular multivariate analysis technique in cognitive neuroscience that uses functional neuroimaging to investigate the informational content encoded in brain activity. As RSA is increasingly being used to investigate more clinically-geared questions, the focus of such translational studies turns toward the importance of individual differences and their optimization within the experimental design. In this perspective, we focus on two design aspects: applying individual vs. averaged behavioral dissimilarity matrices to multiple participants' neuroimaging data and ensuring the congruency between tasks when measuring behavioral and neural representational spaces. Incorporating these methods permits the detection of individual differences in representational spaces and yields a better-defined transfer of information from representational spaces onto multivoxel patterns. Such design adaptations are prerequisites for optimal translation of RSA to the field of precision psychiatry.

Supracategorical fear information revealed by aversively conditioning multiple categories

Fear-generalization is a critical function for survival, in which an organism extracts information from a specific instantiation of a threat (e.g., the western diamondback rattlesnake in my front yard on Sunday) and learns to fear - and accordingly respond to - pertinent higher-order information (e.g., snakes live in my yard). Previous work investigating fear-conditioning in humans has used functional magnetic resonance imaging (fMRI) to demonstrate that activity patterns representing stimuli from an aversively-conditioned category (CS+) are more similar to each other than those of a neutral category (CS-). Here we used fMRI and multiple aversively-conditioned categories to ask whether we would find only similarity increases within the CS+ categories or also similarity increases between the CS+ categories. Using representational similarity analysis, we correlated several models to activity patterns underlying different brain regions and found that, following fear-conditioning, between-category and within-category similarity increased for the CS+ categories in the insula, superior frontal gyrus (SFG), and the right temporal pole. When specifically investigating fear-generalization, these between- and within-category effects were detected in the SFG. These results advance prior pattern-based neuroimaging work by exploring the effect of aversively-conditioning multiple categories and indicate an extended role for such regions in potentially representing supracategorical information during fear-learning.

Linking Personality Traits to Individual Differences in Affective Spaces

Different individuals respond differently to emotional stimuli in their environment. Therefore, to understand how emotions are represented mentally will ultimately require investigations into individual-level information. Here we tasked participants with freely arranging emotionally charged images on a computer screen according to their subjective emotional similarity (yielding a unique affective space for each participant) and subsequently sought external validity of the layout of the individuals’ affective spaces through the five-factor personality model (Neuroticism, Extraversion, Openness to Experience, Agreeableness, Conscientiousness) assessed via the NEO Five-Factor Inventory. Applying agglomerative hierarchical clustering to the group-level affective space revealed a set of underlying affective clusters whose within-cluster dissimilarity, per individual, was then correlated with individuals’ personality scores. These cluster-based analyses predominantly revealed that the dispersion of the negative cluster showed a positive relationship with Neuroticism and a negative relationship with Conscientiousness, a finding that would be predicted by prior work. Such results demonstrate the non-spurious structure of individualized emotion information revealed by data-driven analyses of a behavioral task (and validated by incorporating psychological measures of personality) and corroborate prior knowledge of the interaction between affect and personality. Future investigations can similarly combine hypothesis- and data-driven methods to extend such findings, potentially yielding new perspectives on underlying cognitive processes, disease susceptibility, or even diagnostic/prognostic markers for mental disorders involving emotion dysregulation.