1,720,975 research outputs found
Functional lateralization of feature specific processing in a phonetic classification task
No full textMethodological principles for optimising functional MRI experiments
No full textFunctional magnetic resonance imaging (fMRI) is one of the most common methods for localising neuronal activity in the brain. Even though the sensitivity of fMRI is comparatively low, the optimisation of certain experimental parameters allows obtaining reliable results. In this article, approaches for optimising the experimental design, imaging parameters and analytic strategies will be discussed. Clinical neuroscientists and interested physicians will receive practical rules of thumb for improving the efficiency of brain imaging experiments
Asymmetry of cortical activation during maximum and convenient tapping speed
No full textAn effect of finger tapping rate on the hemodynamic response in primary motor cortex and the cerebellum has been well established over the last years (the rate effect). The present study compares the magnitude of this effect when either the dominant or subdominant hand is used by right and left handers. In contrast to previous studies maximum and convenient tapping rate for both hands are used as tapping tasks. The results confirm "rate effects" for the primary motor cortex and the cerebellum. In addition, a "rate effect" was found for the cingulate motor area. A novel finding is that the cortical and cerebellar "rate effects" are similar for the subdominant and for the dominant hand even though tapping rates are lower for the subdominant hand. This result demonstrates that the subdominant motor cortex and neurally connected cerebellar areas operate at suboptimal control levels although maximum neurophysiological activation has been reached during the maximum tapping task. (C) 2004 Elsevier Ireland Ltd. All rights reserved
Evidence for rapid auditory perception as the foundation of speech processing: a sparse temporal sampling fMRI study
No full textWe examined the processing of verbal and nonverbal auditory stimuli using an event-related functional magnetic resonance imaging (fMRI) study to reveal the neural underpinnings of rapid temporal information processing and it's relevance during speech perception. In the context of a clustered sparse-temporal fMRI data collection eight right-handed native German speakers performed: (i) an auditory gap detection task; and (ii) a CV syllable discrimination task. A tone perception task served as a nontemporal control condition. Here we aimed to research to what extent the left hemisphere preferentially processes linguistically relevant temporal information available in speech and nonspeech stimuli. Furthermore, we sought to find out as to whether a left hemisphere's preference for linguistically relevant temporal information is specifically constrained to verbal utterances or if nonlinguistic temporal information may also activate these areas. We collected haemodynamic responses from three time points of acquisition (TPA) with varying temporal distance from stimulus onset to gain an insight on the time course of auditory processing. Results show exclusively left-sided activations of primary and secondary auditory cortex associated with the perception of rapid temporal information. Furthermore, the data shows an overlap of activations evoked by nonspeech sounds and speech stimuli within primary and secondary auditory cortex of the left hemisphere. The present data clearly support the assumption of a shared neural network for rapid temporal information processing within the auditory domain for both speech and nonspeech signals situated in left superior temporal areas
Stereoscopic presentation of the Shepard-Metzler figures in mental rotation tasks - Does the sex difference disappear?
No full textStereoscopic presentation of the Shepard-Metzler figures in mental rotation tasks - Does the sex difference disappear?
No full textStructural changes of the corpus callosum in mild cognitive impairment and Alzheimer's disease
No full textBackground: Although previous studies demonstrate significant atrophy of the corpus callosum (CC) in patients with Alzheimer's disease (AD), CC alterations in mild cognitive impairment have not been investigated yet. Methods: 21 subjects with mild cognitive impairment, 10 with AD and 21 healthy controls were investigated using magnetic resonance imaging. In the midsagittal slice the CC was traced manually. Additionally, voxel-based morphometry (VBM) was performed. Results: The CC was significantly smaller in patients with AD compared to healthy controls in both manual tracing and VBM. The atrophy was prominent in rostral parts of the CC. In subjects with mild cognitive impairment, the two rostral CC segments were smaller compared to controls when manually traced. In contrast, VBM revealed no significant difference between subjects with mild cognitive impairment and controls. Conclusion: Manual tracing was more sensitive in detecting discrete structural CC changes than VBM. Alterations of the CC in mild cognitive impairment rank in between normal aging and AD, supporting the hypothesis that mild cognitive impairment most often represents a preclinical stage of AD
Neural correlates of the interaction between transient and sustained processes: A mixed blocked/event-related fMRI study
No full textComplete understanding of the neural correlates of cognitive processes requires investigation of both event- and state-related correlates of cognitive performance as well as their interaction. Neuroimaging studies using blocked designs confound these two types of processes and studies using event-related designs focus exclusively on the detection of transient effects. Recent fMRI studies used mixed blocked/event-related designs and found that transient and sustained activity can be dissociated, but it is not yet known how event-related and state-related processing interact. Here we used a phonological categorization paradigm in a mixed blocked/event-related design to investigate where in the brain transient activity interacts with sustained activity. Task difficulty was parametrically manipulated based on individually determined categorization thresholds. We found an interaction effect of transient and sustained activity in the left precuneus. In this cortical structure transient activity increased with increasing task difficulty, while sustained neural activity decreased with increasing task difficulty. Our data suggest that sustained activity is enhanced during processing of an easy task, presumably because of ongoing internally cued endogenous processing, still allowing effortless processing of transient stimuli. During performance of a difficult task, sustained activity in the precuneus is reduced to provide resources for processing incoming stimuli. Processing of stimuli that are expected to be difficult elicits increased transient responses independent of the actual physical properties of the stimuli. In showing an interaction between transient and sustained activity in the precuneus, the present results accommodate seemingly diverging results from previous studies using event-related or blocked designs and expand the knowledge emerging from previous studies using mixed blocked/event-related designs
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
