Neuropsychologia
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Brain imaging studies in humans have shown that face processing in several areas is modulated by the affective significance of faces, particularly with fearful expressions, but also with other social signals such gaze direction. Here we review haemodynamic and electrical neuroimaging results indicating that activity in the face-selective fusiform cortex may be enhanced by emotional (fearful) expressions, without explicit voluntary control, and presumably through direct feedback connections from the amygdala. fMRI studies show that these increased responses in fusiform cortex to fearful faces are abolished by amygdala damage in the ipsilateral hemisphere, despite preserved effects of voluntary attention on fusiform; whereas emotional increases can still arise despite deficits in attention or awareness following parietal damage, and appear relatively unaffected by pharmacological increases in cholinergic stimulation. Fear-related modulations of face processing driven by amygdala signals may implicate not only fusiform cortex, but also earlier visual areas in occipital cortex (e.g., V1) and other distant regions involved in social, cognitive, or somatic responses (e.g., superior temporal sulcus, cingulate, or parietal areas). ⋯ Altogether, these fMRI and ERP results demonstrate that emotion face perception is a complex process that cannot be related to a single neural event taking place in a single brain regions, but rather implicates an interactive network with distributed activity in time and space. Moreover, although traditional models in cognitive neuropsychology have often considered that facial expression and facial identity are processed along two separate pathways, evidence from fMRI and ERPs suggests instead that emotional processing can strongly affect brain systems responsible for face recognition and memory. The functional implications of these interactions remain to be fully explored, but might play an important role in the normal development of face processing skills and in some neuropsychiatric disorders.
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Comparative Study
Empathy examined through the neural mechanisms involved in imagining how I feel versus how you feel pain.
Perspective-taking is a stepping stone to human empathy. When empathizing with another individual, one can imagine how the other perceives the situation and feels as a result. To what extent does imagining the other differs from imagining oneself in similar painful situations? In this functional magnetic resonance imaging experiment, participants were shown pictures of people with their hands or feet in painful or non-painful situations and instructed to imagine and rate the level of pain perceived from different perspectives. ⋯ These results show the similarities between Self- and Other-pain representation, but most interestingly they also highlight some distinctiveness between these two representations, which is a crucial aspect of human empathy. It may be what allows us to distinguish empathic responses to others versus our own personal distress. These findings are consistent with the view that empathy does not involve a complete Self-Other merging.
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Comparative Study
How default is the default mode of brain function? Further evidence from intrinsic BOLD signal fluctuations.
The default mode of brain function hypothesis and the presence of spontaneous intrinsic low-frequency signal fluctuations during rest have recently attracted attention in the neuroscience community. In this study we asked two questions: First, is it possible to attenuate intrinsic activity in the self-referential, default mode of brain function by directing the brains resources to a goal-oriented and attention-demanding task? Second, what effect does a sustained attention-demanding overt task performance have on the two intrinsically active networks in the brain, those being the task-negative, default-mode and the anticorrelated, task-positive network? We used functional magnetic resonance imaging to monitor spontaneous intrinsic activity during rest and sustained performance of a sequential two-back working memory task. ⋯ Moreover, we show that the intrinsic activity in the task-positive network is reorganized in response to the working memory task. The results presented here complements earlier work that have shown that task-induced signal deactivations in the default-mode regions is modulated by cognitive load to also show that intrinsic, spontaneous signal fluctuations in the default-mode regions persist and reorganize in response to changes in external work load.
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Comparative Study
Role of the left inferior frontal gyrus in covert word retrieval: neural correlates of switching during verbal fluency.
Word retrieval ability is commonly assessed with a semantic verbal fluency task, in which subjects must produce a list of exemplars of a category (e.g., animals). The order in which exemplars are produced is not random; rather, subjects tend to produce "clusters" of semantically related items (e.g., cow, pig, sheep) and occasionally "switch" to other clusters (e.g., lion, tiger, bear). Patients with frontal lobe pathology (associated with focal lesions or Parkinson's disease) exhibit reduced output on semantic fluency tasks that has been characterized as a reduction in switching, in contrast to other impaired patient groups who produce normal switches but smaller clusters (e.g., [Troyer, A. ⋯ Proceedings of the National Academy of Sciences of the United States of America, 26, 14792-14797]. In the present study, we investigated the neural correlates of switching in the verbal fluency task, and in particular, the role of the LIFG in switching between semantic sub-categories. We observed greater activation in the LIFG during switching compared to free generation (Experiment 1) and self-reported clustering (Experiment 2), which is consistent with the hypothesis that the switching mechanism is subserved by the LIFG due to high semantic selection demands.
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Comparative Study
Impaired recognition of negative facial emotions in patients with frontotemporal dementia.
Patients with behavioral variant of frontotemporal dementia (FTD) have difficulties recognizing facial emotions, a deficit that may contribute to their impaired social skills. In three experiments, we investigated the FTD deficit in recognition of facial emotions, by comparing six patients with impaired social conduct, nine Alzheimer's patients, and 10 age-matched healthy adults. Experiment 1 revealed that FTD patients were impaired in the recognition of negative facial emotions. ⋯ Experiment 3 was a control study in which participants had to discriminate whether two faces were of the same sex. In this non-emotional processing task, both patient groups performed worse than normal participants, but FTD patients performed as well as Alzheimer's patients. We conclude that FTD patients are impaired in the recognition of negative facial emotions.