Increased amygdala activation to neutral faces is associated with better face memory performance

The impact of focused attention on subsequent emotional recollection: A functional MRI investigation

In his seminal works, Endel Tulving argued that functionally distinct memory systems give rise to subjective experiences of remembering and knowing (i.e., recollection- vs. familiarity-based memory, respectively). Evidence shows that emotion specifically enhances recollection, and this effect is subserved by a synergistic mechanism involving the amygdala (AMY) and hippocampus (HC). In extreme circumstances, however, uncontrolled recollection of highly distressing memories may lead to symptoms of affective disorders. Therefore, it is important to understand the factors that can diminish such detrimental effects. Here, we investigated the effects of Focused Attention (FA) on emotional recollection. FA is an emotion regulation strategy that has been proven quite effective in reducing the impact of emotional responses associated with the recollection of distressing autobiographical memories, but its impact during emotional memory encoding is not known. Functional MRI and eye-tracking data were recorded while participants viewed a series of composite negative and neutral images with distinguishable foreground (FG) and background (BG) areas. Participants were instructed to focus either on the FG or BG content of the images and to rate their emotional responses. About 4 days later, participants' memory was assessed using the R/K procedure, to indicate whether they Recollected specific contextual details about the encoded images or the images were just familiar to them - i.e., participants only Knew that they saw the pictures without being able to remember specific contextual details. First, results revealed that FA was successful in decreasing memory for emotional pictures viewed in BG Focus condition, and this effect was driven by recollection-based retrieval. Second, the BG Focus condition was associated with decreased activity in the AMY, HC, and anterior parahippocampal gyrus for subsequently recollected emotional items. Moreover, correlation analyses also showed that reduced activity in these regions predicted greater reduction in emotional recollection following FA. These results demonstrate the effectiveness of FA in mitigating emotional experiences and emotional recollection associated with unpleasant emotional events.

Emerging Directions in Emotional Episodic Memory

Building upon the existing literature on emotional memory, the present review examines emerging evidence from brain imaging investigations regarding four research directions: (1) Social Emotional Memory, (2) The Role of Emotion Regulation in the Impact of Emotion on Memory, (3) The Impact of Emotion on Associative or Relational Memory, and (4) The Role of Individual Differences in Emotional Memory. Across these four domains, available evidence demonstrates that emotion- and memory-related medial temporal lobe brain regions (amygdala and hippocampus, respectively), together with prefrontal cortical regions, play a pivotal role during both encoding and retrieval of emotional episodic memories. This evidence sheds light on the neural mechanisms of emotional memories in healthy functioning, and has important implications for understanding clinical conditions that are associated with negative affective biases in encoding and retrieving emotional memories.

Memory for emotional material in temporal lobe epilepsy

Several studies suggest that highly emotional information could facilitate long-term memory encoding and consolidation processes via an amygdala-hippocampal network. Our aim was to assess emotional perception and episodic memory for emotionally arousing material in patients with temporal lobe epilepsy (TLE) who are candidates for surgical treatment. We did this by using an audiovisual paradigm. Forty-six patients with medically resistant TLE (26 with left TLE and 20 with right TLE) and 19 healthy controls were assessed with a standard narrative test of emotional memory. The experimental task consisted of sequential picture slides with an accompanying narrative depicting a story that has an emotional central section. Subjects were asked to rate their emotional arousal reaction to each stimulus after the story was shown, while emotional memory (EM) was assessed a week later with a multiple choice questionnaire and a visual recognition task. Our results showed that ratings for emotional stimuli for the patients with TLE were significantly higher than for neutral stimuli (p=0.000). It was also observed that patients with TLE recalled significantly less information from each slide compared with controls, with a trend to lower scores on the questionnaire task for the group with LTLE, as well as poorer performance on the visual recognition task for the group with RLTE. Emotional memory was preserved in patients with RTLE despite having generally poorer memory performance compared with controls, while it was found to be impaired in patients with LTLE.

A brain-computer interface for potential non-verbal facial communication based on EEG signals related to specific emotions

Unlike assistive technology for verbal communication, the brain-machine or brain-computer interface (BMI/BCI) has not been established as a non-verbal communication tool for amyotrophic lateral sclerosis (ALS) patients. Face-to-face communication enables access to rich emotional information, but individuals suffering from neurological disorders, such as ALS and autism, may not express their emotions or communicate their negative feelings. Although emotions may be inferred by looking at facial expressions, emotional prediction for neutral faces necessitates advanced judgment. The process that underlies brain neuronal responses to neutral faces and causes emotional changes remains unknown. To address this problem, therefore, this study attempted to decode conditioned emotional reactions to neutral face stimuli. This direction was motivated by the assumption that if electroencephalogram (EEG) signals can be used to detect patients' emotional responses to specific inexpressive faces, the results could be incorporated into the design and development of BMI/BCI-based non-verbal communication tools. To these ends, this study investigated how a neutral face associated with a negative emotion modulates rapid central responses in face processing and then identified cortical activities. The conditioned neutral face-triggered event-related potentials that originated from the posterior temporal lobe statistically significantly changed during late face processing (600–700 ms) after stimulus, rather than in early face processing activities, such as P1 and N170 responses. Source localization revealed that the conditioned neutral faces increased activity in the right fusiform gyrus (FG). This study also developed an efficient method for detecting implicit negative emotional responses to specific faces by using EEG signals. A classification method based on a support vector machine enables the easy classification of neutral faces that trigger specific individual emotions. In accordance with this classification, a face on a computer morphs into a sad or displeased countenance. The proposed method could be incorporated as a part of non-verbal communication tools to enable emotional expression.

Effects of methamphetamine abuse and serotonin transporter gene variants on aggression and emotion-processing neurocircuitry

Individuals who abuse methamphetamine (MA) exhibit heightened aggression, but the neurobiological underpinnings are poorly understood. As variability in the serotonin transporter (SERT) gene can influence aggression, this study assessed possible contributions of this gene to MA-related aggression. In all, 53 MA-dependent and 47 control participants provided self-reports of aggression, and underwent functional magnetic resonance imaging while viewing pictures of faces. Participants were genotyped at two functional polymorphic loci in the SERT gene: the SERT-linked polymorphic region (SERT-LPR) and the intron 2 variable number tandem repeat polymorphism (STin2 VNTR); participants were then classified as having high or low risk for aggression according to individual SERT risk allele combinations. Comparison of SERT risk allele loads between groups showed no difference between MA-dependent and control participants. Comparison of self-report scores showed greater aggression in MA-dependent than control participants, and in high genetic risk than low-risk participants. Signal change in the amygdala was lower in high genetic risk than low-risk participants, but showed no main effect of MA abuse; however, signal change correlated negatively with MA use measures. Whole-brain differences in activation were observed between MA-dependent and control groups in the occipital and prefrontal cortex, and between genetic high- and low-risk groups in the occipital, fusiform, supramarginal and prefrontal cortex, with effects overlapping in a small region in the right ventrolateral prefrontal cortex. The findings suggest that the investigated SERT risk allele loads are comparable between MA-dependent and healthy individuals, and that MA and genetic risk influence aggression independently, with minimal overlap in associated neural substrates.

The human likeness dimension of the "uncanny valley hypothesis": behavioral and functional MRI findings

The uncanny valley hypothesis (Mori, 1970) predicts differential experience of negative and positive affect as a function of human likeness. Affective experience of humanlike robots and computer-generated characters (avatars) dominates "uncanny" research, but findings are inconsistent. Importantly, it is unknown how objects are actually perceived along the hypothesis' dimension of human likeness (DOH), defined in terms of human physical similarity. To examine whether the DOH can also be defined in terms of effects of categorical perception (CP), stimuli from morph continua with controlled differences in physical human likeness between avatar and human faces as endpoints were presented. Two behavioral studies found a sharp category boundary along the DOH and enhanced visual discrimination (i.e., CP) of fine-grained differences between pairs of faces at the category boundary. Discrimination was better for face pairs presenting category change in the human-to-avatar than avatar-to-human direction along the DOH. To investigate brain representation of physical change and category change along the DOH, an event-related functional magnetic resonance imaging study used the same stimuli in a pair-repetition priming paradigm. Bilateral mid-fusiform areas and a different right mid-fusiform area were sensitive to physical change within the human and avatar categories, respectively, whereas entirely different regions were sensitive to the human-to-avatar (caudate head, putamen, thalamus, red nucleus) and avatar-to-human (hippocampus, amygdala, mid-insula) direction of category change. These findings show that Mori's DOH definition does not reflect subjective perception of human likeness and suggest that future "uncanny" studies consider CP and the DOH's category structure in guiding experience of non-human objects.

Arousal enhanced memory retention is eliminated following temporal lobe resection

The amygdala, situated in the anterior medial temporal lobe (MTL), is involved in the emotional enhancement of memory. The present study evaluated whether anterior MTL-resections attenuated arousal induced memory enhancement for pictures. Also, the effect of MTL-resections on response latencies at retrieval was assessed. Thirty-one patients with unilateral MTL-resections (17 left, 14 right) together with 16 controls participated in a forced choice memory task with pictorial stimuli varying in arousal. Response latencies increased with stimulus arousal in controls but not in patients. This was paralleled by attenuated recognition memory for moderately and highly arousing pictures in MTL-resectioned patients as compared to healthy controls. However, patients and controls did not differ in memory performance for non-arousing pictures. These results suggest that the MTL is necessary for arousal induced memory enhancement.

The effect of acute citalopram on face emotion processing in remitted depression: a pharmacoMRI study

Both reduced serotonergic (5-HT) function and negative emotional biases have been associated with vulnerability to depression. In order to investigate whether these might be related we examined 5-HT modulation of affective processing in 14 remitted depressed subjects compared with 12 never depressed controls matched for age and sex. Participants underwent function magnetic resonance imaging (fMRI) during a covert face emotion task with and without intravenous citalopram (7.5mg) pretreatment. Compared with viewing neutral faces, and irrespective of group, citalopram enhanced left anterior cingulate blood oxygen level dependent (BOLD) response to happy faces, right posterior insula and right lateral orbitofrontal responses to sad faces, and reduced amygdala responses bilaterally to fearful faces. In controls, relative to remitted depressed subjects, citalopram increased bilateral hippocampal responses to happy faces and increased right anterior insula response to sad faces. These findings were not accounted for by changes in BOLD responses to viewing neutral faces. These results are consistent with previous findings showing 5-HT modulation of affective processing; differences found in previously depressed participants compared with controls may contribute to emotional processing biases underlying vulnerability to depressive relapse.

Does it make a difference if I have an eye contact with you or with your picture? An ERP study

Several recent studies have begun to examine the neurocognitive mechanisms involved in perceiving and responding to eye contact, a salient social signal of interest and readiness for interaction. Laboratory experiments measuring observers' responses to pictorial instead of live eye gaze cues may, however, only vaguely approximate the real-life affective significance of gaze direction cues. To take this into account, we measured event-related brain potentials and subjective affective responses in healthy adults while viewing live faces with a neutral expression through an electronic shutter and faces as pictures on a computer screen. Direct gaze elicited greater face-sensitive N170 amplitudes and early posterior negativity potentials than averted gaze or closed eyes, but only in the live condition. The results show that early-stage processing of facial information is enhanced by another person's direct gaze when the person is faced live. We propose that seeing a live face with a direct gaze is processed more intensely than a face with averted gaze or closed eyes, as the direct gaze is capable of intensifying the feeling of being the target of the other's interest and intentions. These results may have implications for the use of pictorial stimuli in the social cognition studies.

An investigation of the relationship between fMRI and ERP source localized measurements of brain activity during face processing

Brain activity patterns during face processing have been extensively explored with functional magnetic resonance imaging (fMRI) and event-related potentials (ERPs). ERP source localization adds a spatial dimension to the ERP time series recordings, which allows for a more direct comparison and integration with fMRI findings. The goals for this study were (1) to compare the spatial descriptions of neuronal activity during face processing obtained with fMRI and ERP source localization using low-resolution electromagnetic tomography (LORETA), and (2) to use the combined information from source localization and fMRI to explore how the temporal sequence of brain activity during face processing is summarized in fMRI activation maps. fMRI and high-density ERP data were acquired in separate sessions for 17 healthy adult males for a face and object processing task. LORETA statistical maps for the comparison of viewing faces and viewing houses were coregistered and compared to fMRI statistical maps for the same conditions. The spatial locations of face processing-sensitive activity measured by fMRI and LORETA were found to overlap in a number of areas including the bilateral fusiform gyri, the right superior, middle and inferior temporal gyri, and the bilateral precuneus. Both the fMRI and LORETA solutions additionally demonstrated activity in regions that did not overlap. fMRI and LORETA statistical maps of face processing-sensitive brain activity were found to converge spatially primarily at LORETA solution latencies that were within 18 ms of the N170 latency. The combination of data from these techniques suggested that electrical brain activity at the latency of the N170 is highly represented in fMRI statistical maps.

Emotional face processing and emotion regulation in children: an ERP study

Emotion regulation is a critical component of healthy development, yet few studies examine neural correlates of emotion regulation in childhood. In the present study, we assessed whether children's neurophysiological responses to salient and socially significant emotional distracters-emotional faces-were related to broader emotion regulation capacities. Emotion regulation was measured as attention performance following emotional distracters and as maternal report of child emotional dysregulation. Electroencephalography was recorded while participants (15 children aged 5-9) performed an attention task. Scalp-recorded event related potentials (ERPs) were time-locked to emotional distracters (fearful, sad, and neutral faces) and reflected a range of rapid attentional and face processing operations (P1, N1, N170, and Nc). P1 latencies were faster whereas N1 amplitudes were reduced to fearful compared to sad faces. Larger P1 and Nc amplitudes to fearful and sad faces were correlated with more effective emotion regulation. Results are discussed in terms of mechanisms in emotion regulation and the use of ERPs to detect early risk for psychopathology and inform intervention efforts.

T2 relaxation time correlates of face recognition deficits in temporal lobe epilepsy

This study explored structural correlates of immediate and delayed face recognition in 22 nonsurgical patients with nonlesional, unilateral mesial temporal lobe epilepsy (TLE, 10 left/12 right). We measured T2 relaxation time bilaterally in the hippocampus, the amygdala, and the fusiform gyrus. Apart from raised T2 values in the ipsilateral hippocampus, we found increased T2 values in the ipsilateral amygdala. Patients with right TLE exhibited impaired face recognition as a result of a decrease from immediate to delayed recognition. Higher T2 values in the right than left fusiform gyrus or hippocampus were related to worse immediate face recognition, but did not correlate with 24-hour face recognition. These preliminary results indicate that structural changes in the fusiform gyrus and hippocampus may influence immediate face recognition deficits, but have no linear influence on long-term face recognition in TLE. We suggest that long-term face recognition depends on a right hemispheric network encompassing structures outside the temporal lobe.

Electrophysiological correlates of spatial orienting towards angry faces: a source localization study

The goal of this study was to examine behavioral and electrophysiological correlates of involuntary orienting toward rapidly presented angry faces in non-anxious, healthy adults using a dot-probe task in conjunction with high-density event-related potentials and a distributed source localization technique. Consistent with previous studies, participants showed hypervigilance toward angry faces, as indexed by facilitated response time for validly cued probes following angry faces and an enhanced P1 component. An opposite pattern was found for happy faces suggesting that attention was directed toward the relatively more threatening stimuli within the visual field (neutral faces). Source localization of the P1 effect for angry faces indicated increased activity within the anterior cingulate cortex, possibly reflecting conflict experienced during invalidly cued trials. No modulation of the early C1 component was found for affect or spatial attention. Furthermore, the face-sensitive N170 was not modulated by emotional expression. Results suggest that the earliest modulation of spatial attention by face stimuli is manifested in the P1 component, and provide insights about mechanisms underlying attentional orienting toward cues of threat and social disapproval.