The neural basis of early facial expression perception: neuromagnetic gamma-band studies in normal subjects and affective disorder patients

• Main Authors: Tai-Ying Liu, 劉玳縈
• Other Authors: Li-Fen Chen
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/37495844788692586975

博士 === 國立陽明大學 === 生物醫學資訊研究所 === 101 === The mood disorders are devastating psychiatric disorders in the 21 century with a lifetime prevalence estimate of 20.8%, and the two major categories of mood disorders are major depressive disorder (MDD) and bipolar disorder (BD). Cognitive dysfunctions and social problems usually occur in these patients and lead to heavy burdens and health-care costs for societies. The Diagnostic and Statistical Manual of Mental Disorder, Version V in 2013 included the basic and clinical neuroimaging research findings to lead to earlier and more accurate diagnosis. To clarify the differences of neural network during early emotion processing between the MDD and BD patients, this thesis uses a magnetoencephalography (MEG) with high spatiotemporal resolution to investigate the abnormalities of the brain functions and connectivity in these two patient groups during early facial expression perception (within 100 ms) and thus to facilitate diagnosis and treatment in the near future. The processing of facial emotion perception requires features (including facial expression, structure, and gender) to be integrated together and gamma oscillations have been shown as a potential mechanism for perceptual binding in previous studies. However, how fast the facial expression perception is processed and whether or not this early perception can convey sufficient emotional information still remain unclear. MEG with high temporal resolution and its spatial resolution being better than that of EEG can help to measure brain activation during early emotion processing (within 100 ms). The literature of early facial expression perception in humans was sparse so that two parts of the thesis include to investigate the early emotion processing in normal subjects and patients. We explored the early perceptual processing of emotions using gamma oscillations on MEG data in normal controls (NC) and affective disorder patients and compared the differences between NC and patients. The amygdala is proposed to serve as a key substrate for processing emotional faces. Patients with affective disorders show abnormal activity in the amygdala during facial emotion processing. In the first and second studies, we investigate that whether the temporal patterns of left and right amygdala activity in response to different facial expressions are distinct in early emotion perception (within 100 ms after stimulus onset).Which model, dual-route or many-roads, is more representative for each emotion? Our findings demonstrated that the thalamus responded at 35 ms and cortical responses in the occipital, temporal, parietal and frontal cortices occurred within 50 ms. Our data provide significant evidence that the left and right amygdala are involved in early perceptual processing of different emotions. The connectivity results support a "many-roads" model for processing various facial expressions (signaling from the thalamus, visual cortex, putamen, parahippocampus, and superior temporal sulcus to the amygdala). The finding of a conspicuous dual-route pathway in angry face processing indicates a survival advantage in detecting danger via a parallel network. The third study is to explore the distinct patterns of gamma activity and connectivity between the MDD and BD patients. The overall gamma activity in the whole brain within 300 milliseconds had no significant differences in patient groups but some regional gamma activity was significantly different in patient groups, compared to the NC group. The distinct alterations of gamma patterns between the BD and MDD patients implicate that their impairments of binding processes are located at different regions. The fourth study is to investigate abnormal regional activity of the MDD and BD patients in response to differential facial expressions during early perception and to combine these features from abnormal regions to differentiate these two patients and thus assist in diagnosis. The discriminant function of four variables, including gamma activation in the left superior medial frontal cortex (happy 35 ms), the right medial orbitofrontal cortex (happy 35 ms), the right anterior insula/inferior orbitofrontal cortex (sad 60 ms), and the right pre/postcentral cortex (sad 105 ms), accurately classified 89.6% of patients as unipolar/bipolar disorders. In conclusion, our findings imply that the cortex plays a more important role in emotion processing and are activated (within 50 ms) earlier than traditionally assumed (around 100 ms), including the occipital, temporal, parietal, and frontal cortices. Our data demonstrated different abnormal gamma activity of the MDD and BD patients during early facial expression perception. In the MDD patients, the abnormalities included altered activity in response to happy faces and to sad faces at very early stage in emotion-related regions (amygdala, anterior insula, and orbitofrontal cortex), which may be related to dysfunctions in perceptual binding of emotional features and negativity biases of top-down predictions. Increased occipital gamma activity of the BD patients indicates that they may have hyperactivity in perceptual binding of emotional features and tend to be oversensitive to facial features, especially for angry faces. Abnormal regional gamma activity can be a biomarker to differentiate BD patients from MDD patients to assist in diagnosis.