[Show abstract][Hide abstract] ABSTRACT: Behavioral studies suggest that humans evolve the capacity to cope with anxiety induced by the awareness of death's inevitability. However, the neurocognitive processes that underlie online death-related thoughts remain unclear. Our recent functional MRI study found that the processing of linguistic cues related to death was characterized by decreased neural activity in human insular cortex. The current study further investigated the time course of neural processing of death-related linguistic cues. We recorded event-related potentials (ERP) to death-related, life-related, negative-valence, and neutral-valence words in a modified Stroop task that required color naming of words. We found that the amplitude of an early frontal/central negativity at 84-120 ms (N1) decreased to death-related words but increased to life-related words relative to neutral-valence words. The N1 effect associated with death-related and life-related words was correlated respectively with individuals' pessimistic and optimistic attitudes toward life. Death-related words also increased the amplitude of a frontal/central positivity at 124-300 ms (P2) and of a frontal/central positivity at 300-500 ms (P3). However, the P2 and P3 modulations were observed for both death-related and negative-valence words but not for life-related words. The ERP results suggest an early inverse coding of linguistic cues related to life and death, which is followed by negative emotional responses to death-related information.
[Show abstract][Hide abstract] ABSTRACT: When making a difficult choice, people often justify the choice by increasing their liking for the chosen object and decreasing their liking for the rejected object. To uncover the neural signatures of choice justification, we used functional magnetic resonance imaging to monitor neural activity when subjects rated their preference for chosen and rejected musical CDs before and after they made their choices. We observed that the trial-by-trial attitude change (i.e., increase of preference for chosen items and decrease of preference for rejected items) was predicted by post-choice activity in the ventral medial prefrontal cortex (MPFC), right temporal-parietal junction, anterior insula, and bilateral cerebellum. Furthermore, individual difference in choice justification (i.e., increased preference for chosen items minus decreased preference for rejected items) was predicted by post-choice neural activity in the dorsal MPFC, left lateral prefrontal cortex, and right precentral cortex positively. In addition, interdependent self-construal was correlated with decreased activity in the ventral MPFC in the post-choice than pre-choice sessions. These findings suggest that both negative arousal/regulation and self-reflection are associated with choice justification. This provides evidence for the self-threat theory of choice justification.
[Show abstract][Hide abstract] ABSTRACT: Causal understanding of physical events is culturally universal. However, behavioral studies suggest that how we perceive causality is culturally sensitive, with East Asian culture emphasizing contextual factors and Western culture emphasizing dispositional factors guiding causal relationships. The present study investigated potential neural substrates of the cultural difference in causal attribution of physical events. Using functional magnetic resonance imaging, Experiment 1 scanned Chinese subjects during causality or motion direction judgments when viewing animations of object collisions and identified a causal-attribution related neural circuit consisting of the medial/lateral prefrontal cortex, left parietal/temporal cortex, and cerebellum. Moreover, by manipulating the task demand of causal inference and the complexity of contextual information in physical events, we showed that the medial prefrontal activity was modulated by the demand to infer causes of physical events whereas the left parietal activity was modulated by contextual complexity of physical events. Experiment 2 investigated cultural differences in the medial prefrontal and left parietal activity associated with causal attribution of physical events by scanning two independent groups of American and Chinese subjects. We found that, while the medial prefrontal activity involved in causality judgments was comparable in the two cultural groups, the left parietal activity associated with causality judgments was stronger in Chinese than in Americans regardless of whether the contextual information was attended. Our findings suggest that causal inference in the medial prefrontal cortex is universally implicated in causal reasoning whereas contextual processing in the left parietal cortex is sensitive to cultural differences in causality perception.
[Show abstract][Hide abstract] ABSTRACT: Consciousness of the finiteness of one's personal existence influences human thoughts and behaviors tremendously. However, the neural substrates underlying the processing of death-related information remain unclear. The current study addressed this issue by scanning 20 female adults, using functional magnetic resonance imaging, in a modified Stroop task that required naming colors of death-related, negative-valence, and neutral-valence words. We found that, while both death-related and negative-valence words increased activity in the precuneus/posterior cingulate and lateral frontal cortex relative to neutral-valence words, the neural correlate of the processing of death-related words was characterized by decreased activity in bilateral insula relative to both negative-valence and neutral-valence words. Moreover, the decreased activity in the left insula correlated with subjective ratings of death relevance of death-related words and the decreased activity in the right insula correlated with subjective ratings of arousal induced by death-related words. Our fMRI findings suggest that, while both death-related and negative-valence words are associated with enhanced arousal and emotion regulation, the processing of linguistic cues related to death is associated with modulations of the activity in the insula that mediates neural representation of the sentient self.
[Show abstract][Hide abstract] ABSTRACT: Temporal processing is of fundamental importance to the understanding of orders and durations of events in daily life. While recent research found that the perception of event durations is modulated by the visibility of perceived stimuli, it is still not known whether consciously and unconsciously perceived stimuli modulate temporal perception of a following stimulus in a similar vein. We investigated this using a temporal-comparison task that requires duration judgments of a standard stimulus and a probe. A prime prior to the standard stimulus reduced the subjective duration of the standard stimulus when observers were aware of the prime, and this effect changed with the temporal distance between the prime and standard. In contrast, a prime increased the subjective duration of the following standard stimulus when observers were unaware of the presence of the prime. Our findings indicate that a temporally neighbouring transient stimulus produces essentially different effects on temporal perception of following events when it is consciously and unconsciously perceived, leading to compression and expansion of subjective time, respectively.
[Show abstract][Hide abstract] ABSTRACT: Recent brain imaging studies indicate that empathy for pain relies upon both the affective and/or the sensorimotor nodes of the pain matrix, and empathic neural responses are modulated by stimulus reality, personal experience, and affective link with others. The current work investigated whether and how empathic neural responses are modulated by emotional contexts in which painful stimulations are perceived. Using functional magnetic resonance imaging (fMRI), we first showed that perceiving a painful stimulation (needle penetration) applied to a face with neutral expression induced activation in the anterior cingulate cortex (ACC) relative to nonpainful stimulation (Q-tip touch). However, when observation of the painful stimuli delivered to a neutral face was intermixed with observation of painful or happy faces, the ACC activity decreased while the activity in the face area of the secondary somatosensory cortex increased to the painful stimulation. Moreover, the secondary somatosensory activity associated with the painful stimulation decreased when the painful stimulation was applied to faces with happy and painful expressions. The findings suggest that observing painful stimuli in an emotional context weakens affective responses but increases sensory responses to perceived pain and implies possible interactions between the affective and sensory components of the pain matrix during empathy for pain.
Full-text · Article · Oct 2009 · Human Brain Mapping
[Show abstract][Hide abstract] ABSTRACT: The present study examined domain specific neural activities associated with the identification of environmental and personal risks. We recorded neural activities from subjects, using functional magnetic resonance imaging and event-related brain potential, when they identified risky and safe environmental and personal events. We found that, relative to the semantic control task, both environmental and personal risk identification tasks were associated with increased sustained activities in the medial frontal and supramarginal gyrus. Moreover, relative to the personal risk identification task, the environmental risk identification task resulted in greater transient activity in the posterior cingulate cortex and precuneus. ERPs recorded over the parietal area associated with the environmental risk identification task occurred earlier than that linked to the personal risk identification task. Our findings suggest that the extent of involvement and temporal courses of retrieval of emotional experiences may distinguish between the environmental and personal risk identification tasks.
Full-text · Article · Jun 2009 · Neuroscience Letters
[Show abstract][Hide abstract] ABSTRACT: Our recent functional MRI and event-related potential studies suggest that neural mechanisms underlying identifications of environmental and personal risks are characterized by distinct neural structures and time courses. The current work further investigated the role of non-phase locked activity in dissociation of the neural processes of environmental and personal risks. We recorded electroencephalogram (EEG) from healthy adults when they identified risky and safe environmental or personal events depicted in words or phrases. Event-related synchronization (ERS) and desynchronization (ERD) in association with risky and safe environmental and personal events were calculated using Morlet's wavelet analysis. We found that, relative to the identification of safe environmental events, the identification of risky environmental events induced increased theta band power at 260-380 ms over the frontal cortex and increased alpha band power after 700 ms with a wide scalp distribution. Moreover, theta band powers associated with the identification of risky environmental events correlated positively with subjective ratings of the risk degree of environmental events. In contrast, the identification of risky personal events was linked to decreased alpha band power at 740-900 ms with a wide scalp distribution compared with the identification of safe personal events. Our findings indicate that theta and alpha band neural oscillations are involved in differentiation between environmental and personal risks.
[Show abstract][Hide abstract] ABSTRACT: Psychometric studies of risk perception have categorized personal risks into social and physical domains. To investigate whether and how the human brain differentiates social and physical risks, we scanned human adults using functional magnetic resonance imaging when they identified potential risks involved in social and physical behaviors. We found that the identification of risky behaviors in both domains induced increased activations in the anterior medial prefrontal cortex (MPFC, BA9/10)/ventral anterior cingulate (ACC) and posterior cingulate (PCC) relative to identification of safe behaviors. However, social risks induced stronger anterior MPFC activation whereas physical risks were associated with stronger ventral ACC activity. In addition, anterior MPFC activity was negatively correlated with the rating scores of the degree of social risk whereas PCC activity was positively correlated with the rating scores of the degree of physical risk. Relative to an autobiographical control task, the social risk identification task induced stronger sustained activity in the left supplementary motor area/dorsal ACC and increased transient activity in bilateral posterior insula. The physical risk identification task, however, resulted in stronger sustained activity in the right cuneus/precuneus and increased transient activation in bilateral amygdala. Our results indicate the existence of distinct neural mechanisms underlying social and physical risk identifications and provide neural bases for the psychometric categorization of risks into different domains.
Preview · Article · Apr 2009 · Human Brain Mapping
[Show abstract][Hide abstract] ABSTRACT: Environmental risks threaten a large population and are more dreadful than personal risks that bring physical or health problems to individuals. To assess the neurocognitive processes involved in environmental risk identification, we recorded brain activities, using event-related potential (ERP) and functional magnetic resonance imaging (fMRI), from human adults while they identified risky and safe environmental and personal events depicted in words. We found that, relative to safe environmental events, the identification of risky environmental events induced larger amplitudes of an early positive ERP component at 180-260ms over the frontal area (P200) and of a late positive wave at 420-660ms over the central-parietal area (LPP). fMRI results showed that the identification of environmental risks was associated with increased activations in the ventral anterior cingulate cortex (vACC) and posterior cingulate cortex (PCC). The amplitudes of the LPP/P200 and the PCC activity positively correlated with subjective ratings of risk degree of and emotional responses to the risky environmental events. However, the identification of personal risks induced positive shift of ERPs at 280-320ms over the frontal and parietal areas and increased activity in the left inferior and medial prefrontal cortex. Our findings suggest that identification of dreadful environmental risks is subserved by an early detection in vACC and a late retrieval of emotional experiences in PCC.
[Show abstract][Hide abstract] ABSTRACT: We studied whether the posterior parietal cortex contributes both to focus attention on one level and to switch attention between global and local levels of compound letters across trials. After 1 Hz repeated transcranial magnetic stimulation was applied to the left, right posterior parietal cortex, and the precentral gyrus, participants identified global and local target letters. We found that repeated transcranial magnetic stimulation over the left posterior parietal cortex resulted in faster global than local responses but did not affect global-to-local interference and the level-repetition effect. The results suggest that the neural mechanism underlying focusing attention on one level of compound stimuli is distinct from that mediating switching attention between global and local levels across trials.
[Show abstract][Hide abstract] ABSTRACT: We sought to identify the neural substrates underlying perceptual grouping, and examined whether the grouping-related neural activities are modulated by task relevance and attention by recording high-density event-related potentials (ERPs). Participants were presented with stimulus arrays, in which local elements were either evenly distributed or grouped into rows or columns by proximity or similarity, and had to discriminate orientations of the perceptual groups, or to identify the colors of dots around stimulus displays or of the fixation cross. We found that proximity grouping was indexed by a positive activity over the medial occipital cortex with a peak latency of about 100 ms after stimulus onset (Pd100), whereas grouping by similarity of shape was reflected in a negative activity with longer latency over the occipito-temporal areas. Dipole modeling based on a realistic boundary element head model localized the Pd100 to the right calcarine cortex. Moreover, we showed that the grouping-related activities were weakened when stimulus arrays were of low task relevance and fell outside an attended area of field. The results suggest that human calcarine cortex is engaged in early grouping operations defined by proximity, reinforcing the previous fMRI findings. Moreover, our ERP results indicate that the neural bases underlying perceptual grouping in human visual cortex can be modulated by task relevance and attention as early as 100 ms after sensory stimulation. Hum Brain Mapp, 2005. (c) 2005 Wiley-Liss, Inc.
Full-text · Article · Nov 2005 · Human Brain Mapping