Neuropsychologia
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Performance on tests of odour discrimination, naming, and matching was compared in patients with four distinct forms of neurodegenerative disease: Alzheimer's disease (AD), semantic dementia (SD), frontotemporal dementia (FTD), and corticobasal degeneration (CBD). The SD patients were found to have a severe impairment of identification from olfaction despite having normal discrimination, consistent with the multimodal semantic impairment characteristic of this patient group. ⋯ The findings illustrate that breakdown in olfaction can occur at a perceptual or semantic level, analogous to the distinction between apperceptive and associative forms of deficit in the visual and auditory modalities. The findings add further insights into the nature of the semantic deficit in SD by exploring a hitherto neglected modality and may have relevance in explaining the altered eating habits commonly associated with SD.
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A defining characteristic of ideomotor apraxia is an inability to imitate meaningless gestures. This is widely interpreted as being due to difficulties in the formulation or execution of motor programs for complex action, but an alternative view is that there is a higher level cognitive problem in conceptualisation of the target posture. In a single case with inferior left parietal and temporal damage, severely impaired imitation was accompanied by preserved motor skill and spatial awareness but inability to make a conceptual match between the fingers of his own hand and an observed hand. ⋯ Knowledge of body structure seemed largely intact as he was only slightly inaccurate in showing correspondences between locations on drawings of a human figure and his own body, or a visually dissimilar figure. This indicated that difficulty on matching gestures was specific to representation of body posture rather than body structure, or that gesture imitation tasks place higher demand on a structural representation of the body. These data imply that for at least some cases of ideomotor apraxia, impaired gesture imitation is due to a deficit in representing the observed posture and is not a deficit in memory for action or of motor control.
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The spatiotemporal analysis of brain activation during the execution of conditional reasoning tasks (the four inference forms: Modus Ponens (MP), Modus Tollens (MT), affirming the consequent (AC), and denying the antecedent (DA)) and one baseline task (BS) was performed in 12 normal young adult participants using high-density event-related brain potentials (ERPs). Results showed that the early components elicited by the five task types were not significantly different. Reasoning tasks elicited a more negative EPR deflection (N600) than did the BS task in the time window of 500-700 ms after onset of the minor premise. ⋯ Following that period, a greater negativity in the reasoning tasks, in comparison to the BS task, developed between 1700 and 2000 ms poststimulus over the left fronto-central scalp regions. A generator of this effect was located in the right anterior cingulate cortex (BA 24) and was possibly related to cognitive control. The results indicate that the cingulate cortex was activated by conditional reasoning tasks with purely abstract materials and support the view that human reasoning is not a unified phenomenon but is content-sensitive.