The effect of one left-sided dorsolateral prefrontal sham-controlled HF-rTMS session on approach and withdrawal related emotional neuronal processes

Neuromodulation as an Augmenting Strategy for Behavioral Therapies for Anxiety and PTSD: a Narrative Review

PURPOSE OF REVIEW

Post-traumatic stress disorder (PTSD) is a prevalent problem. Despite current treatments, symptoms may persist, and neuromodulation therapies show great potential. A growing body of research suggests that transcranial magnetic stimulation (TMS) is effective as a standalone treatment for PTSD, with recent research demonstrating promising use when combined synergistically with behavioral treatments. In this review, we survey this literature including data suggesting mechanisms involved in anxiety and PTSD that may be targeted by neurostimulation.

RECENT FINDINGS

Evidence suggests the mechanism of action for TMS that contributes to behavioral change may be enhanced neural plasticity via increased functionality of prefrontal and subcortical/limbic structures and associated networks. Some research has demonstrated a behavioral change in PTSD and anxiety due to enhanced extinction learning or improved ability to think flexibly and reduce ruminative tendencies. Growing evidence suggests TMS may be best used as a therapeutic adjunct, at least acutely, for extinction-based exposure therapies in patients by accelerating therapy response.

SUMMARY

While TMS has shown promise as a standalone intervention, augmentation with psychotherapy is one avenue of interest. Non-responders to current EBPs might particularly benefit from this sort of targeted approach, and it may shorten treatment length, which would help the successful completion of a course of therapy.

Effect of Intermittent Theta Burst Stimulation on the Neural Processing of Emotional Stimuli in Healthy Volunteers

BACKGROUND

Intermittent theta burst stimulation (iTBS) is a form of repetitive transcranial magnetic stimulation that has shown to be effective in treatment-resistant depression. Through studying the effect of iTBS on healthy subjects, we wished to attain a greater understanding of its impact on the brain. Our objective was to assess whether 10 iTBS sessions altered the neural processing of emotional stimuli, mood and brain anatomy in healthy subjects.

METHODS

In this double-blind randomized sham-controlled study, 30 subjects received either active iTBS treatment (10 sessions, two sessions a day) or sham treatment over the left dorsolateral prefrontal cortex. Assessments of mood, structural magnetic resonance imaging (MRI) and functional MRI (fMRI) were performed before and after iTBS sessions. During the fMRI, three different categories of stimuli were presented: positive, negative and neutral photographs.

RESULTS

This study showed that, during the presentation of negative stimuli (compared with neutral stimuli), 10 sessions of iTBS increased activity in the left anterior insula. However, iTBS did not induce any change in mood, regional gray matter volume or cortical thickness.

CONCLUSIONS

iTBS modifies healthy subjects' brain activity in a key region that processes emotional stimuli. (AFSSAPS: ID-RCB 2010A01032-37).

Influence of theta-burst transcranial magnetic stimulation over the dorsolateral prefrontal cortex on emotion processing in healthy volunteers

Repetitive transcranial magnetic stimulation is a potential treatment option for depression, with the newer intermittent theta-burst stimulation (iTBS) protocols providing brief intervention. However, their mechanism of action remains unclear. We investigated the hypothesis that iTBS influences brain circuits involved in emotion processing that are also affected by antidepressants. We predicted that iTBS would lead to changes in performance on emotion-processing tasks. We investigated the effects of intermittent TBS (iTBS) over the left dorsolateral prefrontal cortex (DLPFC) on the processing of emotional information (word recall and categorization, facial emotion recognition, and decision-making) in 28 healthy volunteers by contrasting these effects with those of sham stimulation. Each volunteer received iTBS and sham stimulation in a blinded crossover design and completed the emotion-processing tasks before and after stimulation. Compared to sham stimulation, iTBS increased positive affective processing for word recall, yet had an unexpected effect on facial emotion recognition for happy and sad faces. There was no evidence of an effect on decision-making or word categorization. We found support for our hypothesis that iTBS influences emotion processing, though some changes were not in the expected direction. These findings suggest a possible common mechanism of action between iTBS and antidepressants, and a complex neural circuitry involved in emotion processing that could potentially be tapped into via brain stimulation. Future research should investigate the neural correlates of emotion processing more closely to inform future iTBS protocols.

The effect of interbrain synchronization in gesture observation: A fNIRS study

INTRODUCTION

Gestures characterize individuals' nonverbal communicative exchanges, taking on different functions. Several types of research in the neuroscientific field have been interested in the investigation of the neural correlates underlying the observation and implementation of different gestures categories. In particular, different studies have focused on the neural correlates underlying gestures observation, emphasizing the presence of mirroring mechanisms in specific brain areas, which appear to be involved in gesture observation and planning mechanisms.

MATERIALS AND METHODS

Specifically, the present study aimed to investigate the neural mechanisms, through the use of functional Near-Infrared Spectroscopy (fNIRS), underlying the observation of affective, social, and informative gestures with positive and negative valence in individuals' dyads composed by encoder and decoder. The variations of oxygenated (O2Hb) and deoxygenated (HHb) hemoglobin concentrations of both individuals were collected simultaneously through the use of hyperscanning paradigm, allowing the recording of brain responsiveness and interbrain connectivity.

RESULTS

The results showed a different brain activation and an increase of interbrain connectivity according to the type of gestures observed, with a significant increase of O2Hb brain responsiveness and interbrain connectivity and a decrease of HHb brain responsiveness for affective gestures in the dorsolateral prefrontal cortex (DLPFC) and for social gestures in the superior frontal gyrus (SFG). Furthermore, concerning the valence of the observed gestures, an increase of O2Hb brain activity and interbrain connectivity was observed in the left DLPFC for positive affective gestures compared to negative ones.

CONCLUSION

In conclusion, the present study showed different brain responses underlying the observation of different types of positive and negative gestures. Moreover, interbrain connectivity calculation allowed us to underline the presence of mirroring mechanisms involved in gesture-specific frontal regions during gestures observation and action planning.

The "gift effect" on functional brain connectivity. Inter-brain synchronization when prosocial behavior is in action

The gift exchange represents a moment that characterizes interpersonal interactions. In particular, research in psychological and neuroscientific fields aimed to observe the social function of gift exchange. Specifically, the present study aimed to investigate the effects of prosocial behavior, experienced during gift exchange, on individuals’ cognitive performance and brain activity. To this aim, behavioral performance and neural activity of 15 dyads of participants, with a consolidated friendship, were collected during the execution of an attentional cooperative task before or after a gift exchange. Individuals’ brain activity was recorded through the use of Functional Near Infrared Spectroscopy (fNIRS) in hyperscanning. Results showed an increase of perceived cooperation and cognitive performance, in terms of accuracy (ACC), after gift exchange. The increase of interpersonal tuning and cooperation was also shown by neural activity with an increase of oxygenated hemoglobin (O2Hb) intra-brain and inter-brain connectivity in the dorsolateral prefrontal cortex (DLPFC) following the gift exchange. Moreover, from ConIndex analysis emerged an increase of inter-brain connectivity compared to intra-brain in DLPFC area. The present study, therefore, highlights how prosocial behavior can have positive effects on cognitive performance improvement and interpersonal relationships and neural coordination strengthen, increasing intra and inter-brain connectivity mechanisms.

Effects of Left Versus Right Dorsolateral Prefrontal Cortex Repetitive Transcranial Magnetic Stimulation on Affective Flexibility in Healthy Women: A Pilot Study

OBJECTIVE

To determine the antidepressant mechanism of action for repetitive transcranial magnetic stimulation (rTMS) to the left dorsolateral prefrontal cortex (DLPFC) in healthy women. Our primary hypothesis was that a single session of left DLPFC rTMS, compared with a session of right DLPFC rTMS, would result in better (reduced) negative nonaffective switch costs in healthy women.

BACKGROUND

The antidepressant mechanism of action for rTMS is not clear. It is possible that rTMS to the DLPFC improves emotion regulation, which could be a part of its antidepressant mechanism.

METHODS

Twenty-five healthy women were randomized to receive left high-frequency (HF) rTMS versus right HF rTMS in one session and then contralateral stimulation during a second session. Emotion regulation was assessed via switch costs for reappraisal of negatively valenced information on an affective flexibility task.

RESULTS

For negative nonaffective switch costs, the interaction effect in the two-way ANOVA was not significant (F1,19=3.053, P=0.097). Given that left HF rTMS is the approved treatment for depression, post hoc t tests were completed with particular interest in the left-side findings. These tests confirmed that negative nonaffective switch costs significantly improved immediately after left rTMS (t1,19=2.664, P=0.015) but not right rTMS.

CONCLUSIONS

These findings suggest that left DLPFC HF rTMS may lead to antidepressant effects by improving the regulation of emotion.

The individual contribution of DSM 5 symptom clusters of PTSD, life events, and childhood adversity to frontal oscillatory brain asymmetry in a large sample of active combatants

Post-Traumatic Stress Disorder (PTSD) has been linked to deviations in lateralized frontal functional oscillatory activity. This is possibly because left and right DLPFC have differential roles in regulating both memory and stress response, which are both dysfunctional in PTSD. However, previous results are heterogeneous, and could be attributable to individual symptom clusters, traumatic or aggressive life events, early life stress, or the interaction of these factors. In a large sample of active combatants (N=401), we regressed these factors on frontal electroencephalography (EEG) asymmetry across 5 frequency bands (delta: 2-4Hz; theta: 4-8Hz; alpha: 8-12Hz; beta: 12-24Hz; gamma: 24-48Hz). Negative cognition and mood was associated with stronger relative left delta and theta band power. Traumatic life events showed stronger right alpha and beta band power. Traumatic life events in interaction with hyperarousal predicted stronger relative right left-right imbalance (theta, alpha, and beta bands), whereas childhood adversity, in interaction with negative cognition and mood, predicted stronger relative left left-right imbalance (delta, theta, alpha and beta bands). The contribution of lateralized DLPFC dysfunction to PTSD is thus dependent on the individual complexities of subsymptom clusters and life history, and future studies need to take these factors into account.

Effects of Transcranial Magnetic Stimulation on the Cognitive Control of Emotion: Potential Antidepressant Mechanisms

Depression negatively impacts quality of life and is associated with high mortality rates. Recent research has demonstrated that improvement in depression symptoms with transcranial magnetic stimulation (TMS) to the dorsolateral prefrontal cortex (DLPFC) may involve changes in the cognitive control network, a regulatory system modulating the function of cognitive and emotional systems, composed of the DLPFC, dorsal anterior cingulate, and posterior parietal cortices. Transcranial magnetic stimulation to the DLPFC node of the cognitive control network may have antidepressant efficacy via direct effects on cognitive control processes involved in emotion regulation. This review provides a review of the impact of TMS on cognitive control processes, especially those related to emotion regulation, and posits that these effects are critical to the mechanism of action of TMS for depression. Treatment implications and future directions for study are discussed.

The role of frontal EEG asymmetry in post-traumatic stress disorder

Frontal alpha asymmetry, a biomarker derived from electroencephalography (EEG) recordings, has often been associated with psychological adjustment, with more left-sided frontal activity predicting approach motivation and lower levels of depression and anxiety. This suggests high relevance to post-traumatic stress disorder (PTSD), a disorder comprising anxiety and dysphoria symptoms. We review this relationship and show that frontal asymmetry can be plausibly linked to neuropsychological abnormalities seen in PTSD. However, surprisingly few studies (k = 8) have directly addressed frontal asymmetry in PTSD, mostly reporting that trait frontal asymmetry has little (if any) predictive value. Meanwhile, preliminary evidence suggest that state-dependent asymmetry during trauma-relevant stimulation distinguishes PTSD patients from resilient individuals. Thus, exploring links between provocation-induced EEG asymmetry and PTSD appears particularly promising. Additionally, we recommend more fine-grained analyses into PTSD symptom clusters in relation to frontal asymmetry. Finally, we highlight hypotheses that may guide future research and help to fully apprehend the practical and theoretical relevance of this biological marker.

Re-appraisal of negative emotions in cocaine dependence: dysfunctional corticolimbic activation and connectivity

Cocaine dependence is associated with pronounced elevations of negative affect and deficient regulation of negative emotions. We aimed to investigate the neural substrates of negative emotion regulation in cocaine-dependent individuals (CDI), as compared to non-drug-using controls, using functional magnetic resonance imaging (fMRI) during a re-appraisal task. Seventeen CDI abstinent for at least 15 days and without other psychiatric co-morbidities and 18 intelligence quotient-matched non-drug-using controls participated in the study. Participants performed the re-appraisal task during fMRI scanning: they were exposed to 24 blocks of negative affective or neutral pictures that they should Observe (neutral pictures), Maintain (sustain the emotion elicited by negative pictures) or Suppress (regulate the emotion elicited by negative pictures through previously trained re-appraisal techniques). Task-related activations during two conditions of interest (Maintain>Observe and Suppress>Maintain) were analyzed using the general linear model in SPM8 software. We also performed psychophysiological interaction (PPI) seed-based analyses based on one region from each condition: the dorsolateral prefrontal cortex (dlPFC-Maintain>Observe) and the inferior frontal gyrus (IFG-Suppress>Maintain). Results showed that cocaine users had increased right dlPFC and bilateral temporoparietal junction activations during Maintain>Observe, whereas they showed decreased right IFG, posterior cingulate cortex, insula and fusiform gyrus activations during Suppress>Maintain. PPI analyses showed that cocaine users had increased functional coupling between the dlPFC and emotion-related regions during Maintain>Observe, whereas they showed decreased functional coupling between the right IFG and the amygdala during Suppress>Maintain. These findings indicate that CDI have dysfunctional corticolimbic activation and connectivity during negative emotion experience and re-appraisal.