Neuropsychologia
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Comparative Study
Perception and production of facial and prosodic emotions by chronic CVA patients.
Variable etiology, limited testing of emotions and inclusion of patients in acute and chronic phases have made it difficult to specify the extent of right hemisphere involvement in the processing of emotional material. In addition, there is an absence of data concerning CVA patients' long-term abilities to process emotional information. Two groups of subjects with unilateral brain damage (15 RBD, 17 LBD), matched for chronicity (minimum 12 months post-CVA), etiology (ischemic CVA), duration of hospitalization and other variables, and an appropriate control group participated in two experiments to address these concerns. ⋯ LBD subjects performed as well as normal controls on almost all tasks. The RBD subjects were the only ones who showed relatively consistent impairment in the processing of both facial and prosodic emotional information. Taken together, these data strongly suggest that the right hemisphere is preferentially involved in processing emotional information in the chronic phase of brain damage.
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Social cognition, including complex social judgments and attitudes, is shaped by individual learning experiences, where affect often plays a critical role. Aversive classical conditioning-a form of associative learning involving a relationship between a neutral event (conditioned stimulus, CS) and an aversive event (unconditioned stimulus, US)-represents a well-controlled paradigm to study how the acquisition of socially relevant knowledge influences behavior and the brain. Unraveling the temporal unfolding of brain mechanisms involved appears critical for an initial understanding about how social cognition operates. ⋯ Tomographic source localization analyses revealed early activation modulated by the CS+ in the ventral visual pathway (e.g. fusiform gyrus, approximately 120 ms), right middle frontal gyrus (approximately 176 ms), and precuneus (approximately 240 ms). At approximately 120 ms, the CS- elicited increased activation in the left insula and left middle frontal gyrus. These findings not only confirm a critical role of prefrontal, insular, and precuneus regions in aversive conditioning, but they also suggest that biologically and socially salient information modulates activation at early stages of the information processing flow, and thus furnish initial insight about how affect and social judgments operate.
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Recently, there has been considerable debate regarding the involvement of the left and right prefrontal cortices in the encoding and retrieval of episodic memory. In a previous PET study, we found that the use of easily verbalisable material may lead to activation predominantly in the left lateral frontal cortex whilst the use of non-easily verbalisable material may lead to activation predominantly in the right lateral frontal cortex, in both cases irrespective of encoding and retrieval processes. In order to replicate and extend these findings, the same task was modified for use with fMRI. ⋯ To extend these findings further, the tasks used in the fMRI study were used to assess a group of patients with unilateral frontal lesions and a group of healthy control volunteers. The patients were significantly impaired compared to the healthy volunteers, although no significant differences were found in performance between the right- and left-sided lesioned patients. This result suggests that the memory-related asymmetries observed during functional neuroimaging studies may not be critical for task performance.
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Patients with visual form agnosia exhibit a profound impairment in shape perception (what an object is) coupled with intact visuomotor functions (how to act on an object), demonstrating a dissociation between visual perception and action. How can these patients act on objects that they cannot perceive? Although two explanations of this 'what-how' dissociation have been offered, each explanation has shortcomings. A 'pathway information' account of the 'what-how' dissociation is presented in this paper. ⋯ Following damage to an input layer common to the 'what' and 'where/how' pathways, the model performs object identification more poorly than spatial localization. Thus, the model offers a parsimonious explanation of differential 'what-how' performance in visual form agnosia. The simulation results are discussed in terms of their implications for visual form agnosia and other neuropsychological syndromes.
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Comparative Study Clinical Trial
Differences in visual attention and task interference between males and females reflect differences in brain laterality.
Two cognitive tasks (a letter memory task and a spatial memory task) designed to selectively activate the left or right hemisphere were combined with attentional probe tasks to measure how hemispheric activation affects attention to left and right hemifields. The probe task in Experiment 1 required the identification of digits in the left and right hemifield. During the letter task, male subjects identified more probes from the left hemifield than from the right. ⋯ These results indicate two separate effects of laterality in male subjects. The activation of one hemisphere produced more attention to the contralateral hemifield in Experiment 2, and the letter memory task interfered with the processing of other characters in the right visual field more than those in the left visual field in Experiment 1. Neither of these effects appeared in female subjects, corroborating earlier claims that female brains are less lateralized than male brains.