Yingying Tang

Abnormal functional connectivity of EEG gamma band in patients with depression during emotional face processing.

OBJECTIVEnThis paper evaluates the large-scale structure of functional brain networks using graph theoretical concepts and investigates the difference in brain functional networks between patients with depression and healthy controls while they were processing emotional stimuli.nnnMETHODSnElectroencephalography (EEG) activities were recorded from 16 patients with depression and 14 healthy controls when they performed a spatial search task for facial expressions. Correlations between all possible pairs of 59 electrodes were determined by coherence, and the coherence matrices were calculated in delta, theta, alpha, beta, and gamma bands (low gamma: 30-50Hz and high gamma: 50-80Hz, respectively). Graph theoretical analysis was applied to these matrices by using two indexes: the clustering coefficient and the characteristic path length.nnnRESULTSnThe global EEG coherence of patients with depression was significantly higher than that of healthy controls in both gamma bands, especially in the high gamma band. The global coherence in both gamma bands from healthy controls appeared higher in negative conditions than in positive conditions. All the brain networks were found to hold a regular and ordered topology during emotion processing. However, the brain network of patients with depression appeared randomized compared with the normal one. The abnormal network topology of patients with depression was detected in both the prefrontal and occipital regions. The negative bias from healthy controls occurred in both gamma bands during emotion processing, while it disappeared in patients with depression.nnnCONCLUSIONSnThe proposed work studied abnormally increased connectivity of brain functional networks in patients with depression. By combing the clustering coefficient and the characteristic path length, we found that the brain networks of patients with depression and healthy controls had regular networks during emotion processing. Yet the brain networks of the depressed group presented randomization trends. Moreover, negative bias was detected in the healthy controls during emotion processing, while it was not detected in patients with depression, which might be related to the types of negative stimuli used in this study.nnnSIGNIFICANCEnThe brain networks from both patients with depression and healthy controls were found to hold a regular and ordered topology. Yet the brain networks of patients with depression had randomization trends.

More normal EEGs of depression patients during mental arithmetic than rest

The aim of this study is to compare the brain activities in depression patients and healthy controls by a quantitative method. In the present study, the wavelet entropy (WE) and subband segmentation analysis are proposed to characterize the degree of disorder and complexity of the electroencephalographic (EEG) signals recorded from 16 scalp electrodes in 20 depression patients and 20 normal controls at rest and during mental arithmetic. The WE analysis demonstrates the EEGs of the depression subjects have higher WE than those of the controls at rest, which indicates a less rhythmic and ordered status in depression, whereas such difference is not significant during mental arithmetic. These results provide evidence that depression patients have more regular brain wave during mental arithmetic than rest. Furthermore, the WE of the depression patients is higher during rest than mental arithmetic at almost all electrodes, and this phenomenon is not found in the controls. It may suggest that larger parts of the brain of the patients are active during rest than performing a cognitive task. In addition, marginal effect of hemisphere is detected for the patients during mental arithmetic. Our results show that the we could be a useful tool in cognitive process analysis, especially in depression.

The time-frequency representation of the ERPs of face processing

In ERP studies of face processing, N170 and VPP were considered to reflect the structural encoding of faces in many researches. However, whether the VPP is the positive counterpart of the N170 from the same brain source is still a matter of debate. In present study, in order to address the debate we studied the oscillatory activities of event-related potentials (ERPs) during face processing. We recorded the ERPs in response to upright and inverted faces, and analyzed the time-frequency representation (TFR) by using the Smoothed Pseudo Wigner-Ville Distribution (SPWVD). The TFR of ERPs suggests that the oscillations at occipito-temporal sites (T5/T6) where the N170 was observed, were centralized in a higher frequency band (4–10Hz) while the oscillations at the fronto-central site (Cz) with salient VPP, were more centralized in a lower frequency range(0–5Hz). Therefore, we concluded that the face-sensitive N170 and VPP, associated with “the structural encoding” stage of the face processing in Bruce & Youngs model, reflect the activities from two different sources. Furthermore, different oscillatory activities were obtained at different face processing stages: 0–10Hz oscillations around 100–200ms post-stimulus are involved in face encoding processing, 0–4Hz oscillations around 300–400ms post-stimulus are involved in the later face identification and the enhanced activities in response to the inverted faces indicate a higher number of synchronous neuronal populations.

The altered cortical connectivity during spatial search for facial expressions in major depressive disorder

To characterize the altered directed connectivity within a distributed cortical network, as is associated with the impaired attention modulation involved in the manifestation of mood disorder in depression, short-window partial directed coherence (PDC) combining with the event-related brain potentials (ERPs) was applied in this study. ERPs were recorded from 13 normal subjects and 12 depressed patients during visual search for facial expressions. The evoked N2 component of ERPs by responding to all neutral faces (F(1,22)=5.51, P<0.05) and the positive face was reduced in the depressed patients as compared to the normal subjects (F(1,22)=5.71, P<0.05), while the evoked N2 component by detecting the negative face showed no significant between-group effect (F(1,22)=2.10, P=0.16). The reduced N2 amplitude reflected deficits in effortful attentional modulation in depression. Obtained PDC values within the N2 time-window (150-300 ms post stimulus) showed weaker intra-frontal and intra-central directed interactions and enhanced occipital information output when responding to all neutral faces in depression relative to those in the normal group. Few decreased intra-frontal directed interactions were observed when detecting the emotional face in depression. The altered cortical directed connectivity contributed to the impairment occurring in the effortful attention modulation in depression. Our findings supported that the impaired attention modulation processing in depression was associated with the altered cortical connectivity.

Early perceptual anomaly of negative facial expression in depression: An event-related potential study.

Depressed patients have a demonstrated cognitive bias in emotional information processing. However, it is unknown how early perceptual processing is modulated by emotional stimuli in depression. To examine this question, we studied 22 depressed patients and 22 healthy controls performing a cued target-response task with emotional facial expression as the cue. The early perceptual processes were examined using event-related potential (ERP) components, i.e., P1 and N170. Results showed that depressed patients had larger P1 amplitudes than healthy controls, implying that early perceptual abnormality for face processing in depression may occur as early as the P1 stage. There was no significant interaction between emotion types and groups on P1 amplitudes, which suggested that cognitive biases in depression might not yet have arisen. Following the P1 stage, N170 amplitudes for sad faces were larger than for other emotion types in depressed patients, whereas N170 amplitudes for happy faces were larger than for other emotion types in healthy controls. These results implied that depressed patients might have a perceptual bias associated with sad emotions, which may be detectable from the N170 time window. In summary, this study provides new insights for understanding the negative cognitive bias in depression using the electroneurophysiological biomarker N170.

Different time courses of event-related potentials in spatial search for emotionally loaded faces

Recognition of facial expressions has been investigated extensively over the last decade. However, the mechanism of advanced processing of emotional expressions as compared to neutral ones remains unclear. In our study, a face-in-the-crowd task with crowds of neutral and emotionally biased faces was performed by 18 normal subjects. Event-related potentials were recorded and analyzed in response to (a) different facial expressions (positive/negative) and (b) different detection difficulties induced by varying the number of faces. Results show that: (1) When responding to negative faces the late component (500-800 ms post-stimulus) showed a positive shift compared to positive faces; (2) A unique negative component for negative faces was observed at approximately 400 ms in fronto-central regions. In addition, no significant influence of emotional expressions on the early cognitive stages was observed. The N2 amplitude decreased only with increasing detection difficulty in processing the all neutral faces. Our results suggest that the time courses of ERPs to negative and positive faces differ, which implies different search strategies for negative and positive faces.

The Race Effect on the Emotion-Induced Gamma Oscillation in The EEG

Emotion and race are two major aspects of human mental life that are widely regarded as distinct. However, it is still under debate whether the race affects emotion processing or not. The studies based on Event-related potentials indicated many interesting results, but conflicting conclusions to some degree. This paper presents a study on how race influences emotion cognition during a cognitive task through a time-frequency analysis of event-related electroencephalograph. In our study, a recognition task with racial facial stimuli was utilized to address the influence of race-effect and emotion on working memory. Three expressions of each face (happy-positive, sad-negative and neutral) from different races were chosen for the experiments. Since depression is characterized as a typical mental disease with emotion processing deficits, fifteen patients with depression and eighteen normal controls were chosen to participate in the experiment. The repeated measure analysis of variance (ANOVA) of Gamma EEG revealed that a significant interaction between race and emotion in the time-window 200-300ms at the low gamma band (30-60Hz). Subsequent analysis showed that, with other race stimuli, the average iGBA of low gamma band revealed different emotion effects, i.e. positive> negative > neutral. In addition, two trend effects were found, the emotion effect (positive>neutral>negative) for depression patients in the window of 500ms-600ms at high iGBA(65-90Hz), and the interaction between group and race in the 200ms-300ms window. To depressed participants, average high iGBA between 200ms-300ms for other-race faces was larger than that for own race faces, while which didn’t happened to the normal controls. In summary we suppose that race-effect did affect the iGBA of the depressed participants while they performing emotion tasks, especially the negative ones. Keywords-EEG oscillation; other-race effect; emotion cognition; iGBA

The coherence changes in the depressed patients in response to different facial expressions

To characterize the changes of information transfer between different brain regions during facial expressions processing between the depressed patients and the normal subjects, we applied partial-directed coherence analysis (PDC) Participants were 16 depressed patients and 26 normal subjects, age–matched between groups An emotion recognition task with different facial expressions (positive and negative) was utilized as stimuli Lower frontal output PDC values in the alpha band reflected the poor frontal cortexs regulation of parieto-occipital regions in depressed patients, while the enhanced outflow from the posterior regions to the frontal regions could be taken as an indicator that the depressed group attempted to achieve the normal performance These topographic patterns of electrical coupling might indicate the changing functional cooperation between the brain areas in depressed patients The depressed patients may have abnormal brain areas comprising bilateral frontal, right temporal, parietal and occipital regions.

The theta burst transcranial magnetic stimulation over the right PFC affects electroencephalogram oscillation during emotional processing

&NA; Prefrontal cortex (PFC) plays an important role in emotional processing and therefore is one of the most frequently targeted regions for non‐invasive brain stimulation such as repetitive transcranial magnetic stimulation (rTMS) in clinical trials, especially in the treatment of emotional disorders. As an approach to enhance the effectiveness of rTMS, continuous theta burst stimulation (cTBS) has been demonstrated to be efficient and safe. However, it is unclear how cTBS affects brain processes related to emotion. In particular, psychophysiological studies on the underlying neural mechanisms are sparse. In the current study, we investigated how the cTBS influences emotional processing when applied over the right PFC. Participants performed an emotion recognition Go/NoGo task, which asked them to select a GO response to either happy or fearful faces after the cTBS or after sham stimulation, while 64‐channel electroencephalogram (EEG) was recorded. EEG oscillation was examined using event‐related spectral perturbation (ERSP) in a time‐interval between 170 and 310 ms after face stimuli onset. In the sham group, we found a significant difference in the alpha band between response to happy and fearful stimuli but that effect did not exist in the cTBS group. The alpha band activity at the scalp was reduced suggesting the excitatory effect at the brain level. The beta and gamma band activity was not sensitive to cTBS intervention. The results of the current study demonstrate that cTBS does affect emotion processing and the effect is reflected in changes in EEG oscillations in the alpha band specifically. The results confirm the role of prefrontal cortex in emotion processing. We also suggest that this pattern of cTBS results elucidates mechanisms by which mood improvement in depressive disorders is achieved using cTBS intervention. HighlightscTBS intervention affects the neural response to emotional stimuli as reflected in the scalp‐recorded alpha band changes.Differences in the alpha band response to happy and fearful stimuli in the sham group disappeared post‐cTBS.Absence of emotion‐related differences post‐cTBS was due to the reduced scalp‐recorded alpha band activity to happy faces.Reduced happy‐specific activity in the scalp‐recorded alpha band post‐cTBS suggests excitatory effects at the brain level.

Continuous theta burst transcranial magnetic stimulation affects brain functional connectivity

Prefrontal cortex (PFC) plays an important role in the emotional processing as well as in the functional brain network. Hyperactivity in the right dorsolateral prefrontal cortex (DLPFC) would be found in anxious participants. However, it is still unclear what the role of PFC played in a resting functional network. Continuous theta burst transcranial magnetic stimulation (cTBS) is an effective tool to create virtual lesions on brain regions. In this paper, we applied cTBS over right prefrontal area, and investigated the effects of cTBS on the brain activity for functional connectivity by the method of graph theory. We recorded 64-channels EEG on thirteen healthy participants in the resting condition and emotional tasks before and after 40 s of cTBS. This work focused on the effect of cTBS on cortical activities in the resting condition by calculating the coherence between EEG channels and building functional networks before and after cTBS in the delta, theta, alpha and beta bands. Results revealed that 1) The functional connectivity after cTBS was significantly increased compared with that before cTBS in delta, theta, alpha and beta bands in the resting condition; 2) The efficiency-cost reached the maximum before and after cTBS both with the cost about 0.3 in the bands above, which meant that the information transmission of functional brain network with this cost was highly efficient; 3) the clustering coefficient and path length after cTBS was significantly increased in delta, theta and beta bands. In conclusion, cTBS over PFC indeed enhanced the functional connectivity in the resting condition. In addition, the information transmission in the resting brain network was highly efficient with the cost about 0.3.Prefrontal cortex (PFC) plays an important role in the emotional processing as well as in the functional brain network. Hyperactivity in the right dorsolateral prefrontal cortex (DLPFC) would be found in anxious participants. However, it is still unclear what the role of PFC played in a resting functional network. Continuous theta burst transcranial magnetic stimulation (cTBS) is an effective tool to create virtual lesions on brain regions. In this paper, we applied cTBS over right prefrontal area, and investigated the effects of cTBS on the brain activity for functional connectivity by the method of graph theory. We recorded 64-channels EEG on thirteen healthy participants in the resting condition and emotional tasks before and after 40 s of cTBS. This work focused on the effect of cTBS on cortical activities in the resting condition by calculating the coherence between EEG channels and building functional networks before and after cTBS in the delta, theta, alpha and beta bands. Results revealed that 1) The functional connectivity after cTBS was significantly increased compared with that before cTBS in delta, theta, alpha and beta bands in the resting condition; 2) The efficiency-cost reached the maximum before and after cTBS both with the cost about 0.3 in the bands above, which meant that the information transmission of functional brain network with this cost was highly efficient; 3) the clustering coefficient and path length after cTBS was significantly increased in delta, theta and beta bands. In conclusion, cTBS over PFC indeed enhanced the functional connectivity in the resting condition. In addition, the information transmission in the resting brain network was highly efficient with the cost about 0.3.