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Peter H. Weiss
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Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2022) 34 (11): 2016–2027.
Published: 01 October 2022
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Recent evidence in healthy participants suggests that a motor subcomponent of working memory (mWM) may exist. We investigated whether this mWM is impaired in patients with a motor-dominant left hemisphere (LH) stroke and apraxia. Furthermore, we hypothesized that a deficient mWM contributes to deficits in motor cognition, that is, apraxia, in LH stroke. The study included 52 patients with LH stroke and 25 age-matched controls. Patients were classified into LH stroke patients with and without apraxia based on deficits in gesture imitation and object use. All participants were examined using the block span test (visuospatial WM), the digit span test (verbal WM), and a novel mWM task. In the latter, participants were presented with static pictures depicting three different actions: actions with objects, meaningless actions, and meaningful actions. In the mWM task, LH stroke patients with apraxia performed worse than age-matched controls. Notably, LH stroke patients with apraxia showed more pronounced mWM deficits than those without apraxia. These results remained significant even after controlling for visuospatial and verbal WM deficits. Regression analyses revealed that LH stroke patients' mWM deficits predicted deficits in imitation. Data provide neuropsychological evidence for a motor subsystem of WM and suggest that deficits in mWM contribute to the severity of apraxia in LH stroke patients.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2016) 28 (2): 223–236.
Published: 01 February 2016
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During rehabilitation after stroke motor sequence learning is of particular importance because considerable effort is devoted to (re)acquiring lost motor skills. Previous studies suggest that implicit motor sequence learning is preserved in stroke patients but were restricted to the spatial dimension, although the timing of single action components is as important as their spatial order. As the left parietal cortex is known to play a critical role in implicit timing and spatiotemporal integration, in this study we applied an adapted version of the SRT task designed to assess both spatial (different stimulus locations) and temporal (different response–stimulus intervals) aspects of motor learning to 24 right-handed patients with a single left-hemisphere (LH) stroke and 24 age-matched healthy controls. Implicit retrieval of sequence knowledge was tested both at Day 1 and after 24 hr (Day 2). Additionally, voxel-based lesion symptom mapping was used to investigate the neurobiological substrates of the behavioral effects. Although LH stroke patients showed a combined spatiotemporal learning effect that was comparable to that observed in controls, LH stroke patients did not show learning effects for the learning probes in which only one type of sequence information was maintained whereas the other one was randomized. Particularly on Day 2, patients showed significantly smaller learning scores for these two learning probes than controls. Voxel-based lesion symptom mapping analyses revealed for all learning probes that diminished learning scores on Day 2 were associated with lesions of the striatum. This might be attributed to its role in motor chunking and offline consolidation as group differences occurred on Day 2 only. The current results suggest that LH stroke patients rely on multimodal information (here: temporal and spatial information) when retrieving motor sequence knowledge and are very sensitive to any disruption of the learnt sequence information as they seem to build very rigid chunks preventing them from forming independent spatial and temporal sequence representations.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2014) 26 (8): 1871–1882.
Published: 01 August 2014
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A moon near to the horizon is perceived larger than a moon at the zenith, although—obviously—the moon does not change its size. In this study, the neural mechanisms underlying the “moon illusion” were investigated using a virtual 3-D environment and fMRI. Illusory perception of an increased moon size was associated with increased neural activity in ventral visual pathway areas including the lingual and fusiform gyri. The functional role of these areas was further explored in a second experiment. Left V3v was found to be involved in integrating retinal size and distance information, thus indicating that the brain regions that dynamically integrate retinal size and distance play a key role in generating the moon illusion.
Journal Articles
Neural Interaction between Spatial Domain and Spatial Reference Frame in Parietal–Occipital Junction
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2012) 24 (11): 2223–2236.
Published: 01 November 2012
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On the basis of double dissociations in clinical symptoms of patients with unilateral visuospatial neglect, neuropsychological research distinguishes between different spatial domains (near vs. far) and different spatial reference frames (egocentric vs. allocentric). In this fMRI study, we investigated the neural interaction between spatial domains and spatial reference frames by constructing a virtual three-dimensional world and asking participants to perform either allocentric or egocentric judgments on an object located in either near or far space. Our results suggest that the parietal–occipital junction (POJ) not only shows a preference for near-space processing but is also involved in the neural interaction between spatial domains and spatial reference frames. Two dissociable streams of visual processing exist in the human brain: a ventral perception-related stream and a dorsal action-related stream. Consistent with the perception–action model, both far-space processing and allocentric judgments draw upon the ventral stream whereas both near-space processing and egocentric judgments draw upon the dorsal stream. POJ showed higher neural activity during allocentric judgments (ventral) in near space (dorsal) and egocentric judgments (dorsal) in far space (ventral) as compared with egocentric judgments (dorsal) in near space (dorsal) and allocentric judgments (ventral) in far space (ventral). Because representations in the dorsal and ventral streams need to interact during allocentric judgments (ventral) in near space (dorsal) and egocentric judgments (dorsal) in far space (ventral), our results imply that POJ is involved in the neural interaction between the two streams. Further evidence for the suggested role of POJ as a neural interface between the dorsal and ventral streams is provided by functional connectivity analysis.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2009) 21 (10): 2019–2026.
Published: 01 October 2009
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In synesthesia, stimulation of one sensory modality leads to a percept in another nonstimulated modality, for example, graphemes trigger an additional color percept in grapheme–color synesthesia, which encompasses the variants letter–color and digit–color synesthesia. Until recently, it was assumed that synesthesia occurs strictly unidirectional: Although the perception of a letter induces a color percept in letter–color synesthetes, they typically do not report that colors trigger the percept of a letter. Recent data on number processing in synesthesia suggest, however, that colors can implicitly elicit numerical representations in digit–color synesthetes, thereby questioning unidirectional models of synesthesia. Using a word fragment completion paradigm in 10 letter–color synesthetes, we show here for the first time that colors can implicitly influence lexical search. Our data provide strong support for a bidirectional nature of grapheme–color synesthesia and, in general, may allude to the mechanisms of cross-modality interactions in the human brain.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2007) 19 (6): 1004–1012.
Published: 01 June 2007
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Impaired retrieval of conceptual knowledge for actions has been associated with lesions of left premotor, left parietal, and left middle temporal areas [Tranel, D., Kemmerer, D., Adolphs, R., Damasio, H., & Damasio, A. R. Neural correlates of conceptual knowledge for actions. Cognitive Neuropsychology , 409–432, 2003]. Here we aimed at characterizing the differential contribution of these areas to the retrieval of conceptual knowledge about actions. During functional magnetic resonance imaging (fMRI), different categories of pictograms (whole-body actions, manipulable and nonmanipulable objects) were presented to healthy subjects. fMRI data were analyzed using SPM2. A conjunction analysis of the neural activations elicited by all pictograms revealed ( p < .05, corrected) a bilateral inferior occipito-temporal neural network with strong activations in the right and left fusiform gyri. Action pictograms contrasted to object pictograms showed differential activation of area MT+, the inferior and superior parietal cortex, and the premotor cortex bilaterally. An analysis of psychophysiological interactions identified contribution-dependent changes in the neural responses when pictograms triggered the retrieval of conceptual action knowledge: Processing of action pictograms specifically enhanced the neural interaction between the right and left fusiform gyri, the right and left middle temporal cortices (MT+), and the left superior and inferior parietal cortex. These results complement and extend previous neuropsychological and neuroimaging studies by showing that knowledge about action concepts results from an increased coupling between areas concerned with semantic processing (fusiform gyrus), movement perception (MT+), and temporospatial movement control (left parietal cortex).
Journal Articles
Common and Differential Neural Mechanisms Supporting Imitation of Meaningful and Meaningless Actions
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2005) 17 (9): 1420–1431.
Published: 01 September 2005
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Neuropsychological studies indicate that, after brain damage, the ability to imitate meaningful or meaningless actions can be selectively impaired. However, the neural bases supporting the imitation of these two types of action are still poorly understood. Using PET, we investigated in 10 healthy individuals the neural mechanisms of imitating novel, meaningless actions and familiar, meaningful actions. Data were analyzed using SPM99. During imitation, a significant positive correlation (p < .05, corrected) of regional cerebral blood flow with the amount of meaningful actions was observed in the left inferior temporal gyrus only. In contrast, a significant positive correlation (p < .05, corrected) with the amount of meaningless movements was observed in the right parieto-occipital junction. The direct categorical comparison of imitating meaningful (100%) relative to meaningless (100%) actions showed differential increases in neural activity (p < .001, uncorrected) in the left inferior temporal gyrus, the left parahippocampal gyrus, and the left angular gyrus. The reverse categorical comparison of imitating meaningless (100%) relative to meaningful (100%) actions revealed differential increases in neural activity (p < .001, uncorrected) in the superior parietal cortex bilaterally, in the right parieto-occipital junction, in the right occipital-temporal junction (MT, V5), and in the left superior temporal gyrus. Increased neural activity common to imitation of meaningless and meaningful actions compared to action observation was observed in a network of areas known to be involved in imitation of actions including the primary sensorimotor cortex, the supplementary motor area, and the ventral premotor cortex. These results are compatible with the two-route model of action imitation which suggests that there are at least two mechanisms involved in imitation of actions: a direct mechanism transforming a novel action into a motor output, and a semantic mechanism, on the basis of stored memories, that allows reproductions of known actions. Our results indicate that, in addition to shared neural processes, the direct and the semantic mechanisms that underlie action imitation also draw upon differential neural mechanisms. The direct mechanism underlying imitation of meaningless actions differentially involves visuospatial transformation processes as evidenced by activation of areas belonging to the dorsal stream. In contrast, imitation of meaningful actions differentially involves semantic processing as evidenced by activation of areas belonging to the ventral stream.