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Purpose: To investigate the neural correlates associated with recovery from acute spatial neglect resulting from right hemispheric stroke. Methods: Four neglect patients were investigated both behaviourally and by fMRI at an acute (18 ± 5 days) and at a chronic stage (123 ± 18 days) post stroke. Results: At the second assessment all patients showed substantial behavioural improvements. These were associated with an increase of neural activity in the right middle frontal gyrus, right inferior parietal cortex, right inferior temporal gyrus/fusiform gyrus, left superior temporal gyrus/angular gyrus and left anterior cingulate gyrus. Decreased neural activity at the second assessment was found in the right parahippocampal gyrus and left fusiform gyrus. Conclusions: The pattern of neural reorganisation comprises areas of a right hemisphere fronto-parietal attentional network and corresponding left hemisphere areas suggesting a compensatory recruitment of analogous contralesional areas. Interestingly, a more complex pattern of neural changes was observed in the fusiform gyri which have previously been implicated in lateralised directed spatial attention. There was an increase in the right hemisphere and a decrease in the left hemisphere. This pattern of recovery is reminiscent of a "push-pull" pattern previously described for the dorsal parietal cortex by Corbetta et al. (2005) in the recovery from spatial neglect. [ABSTRACT FROM AUTHOR]

Abstract: It has been suggested that the processing of action-related words involves activation of the motor circuitry. Using fMRI (functional magnetic resonance imaging), the current study further explored the interaction between action and language by investigating whether the linguistic context, in which an action word occurs, modulates motor circuitry activity related to the processing of action words. To this end, we examined whether the presentation of hand action-related verbs as positive or negative imperatives, for example, “Do grasp” or “Don''t write,” modulates neural activity in the hand area of primary motor cortex (M1) or premotor cortex (Pm). Subjects (n = 19) were asked to read silently the imperative phrases, in which both meaningful action verbs and meaningless pseudo-verbs were presented, and to decide whether they made sense (lexical decision task). At the behavioral level, response times in the lexical decision task were significantly longer for negative, compared to positive, imperatives. At the neural level, activity was differentially decreased by action verbs presented as negative imperatives for the premotor and the primary motor cortex of both hemispheres. The data suggest that context (here: positive vs. negative imperatives), in which an action verb is encountered, modulates the neural activity within key areas of the motor system. The finding implies that motor simulation (or motor planning) rather than semantic processing per se may underlie previously observed motor system activation related to action verb processing. Furthermore, the current data suggest that negative imperatives may inhibit motor simulation or motor planning processes. [Copyright &y& Elsevier]

Introduction: Transcranial direct current stimulation (tDCS) non-invasively promotes recovery after stroke (Braun et al. Exp. Neurol. 2016; Hummel et al. Brain 2005). Stroke affects entire networks beyond the focal lesion, impacting post-stroke impairment (Blaschke et al. Stroke 2021). The thalamus constitutes a central hub due to its numerous functional connections but is also prone to secondary injury (Cao et al. Front. Neurol. 2020). Under the hypothesis that tDCS promotes recovery by supporting neuroprotection, we investigated the effects of tDCS on secondary thalamic neurodegeneration after stroke. Methods: Cortical stroke was induced in the sensory-motor cortex (photothrombosis model in mice). Starting three days after stroke, cathodal tDCS over the ipsilesional somatosensory cortex was performed daily for ten days (39.6 kC/m2), sham-stimulated mice served as control. Behavioral tests over time assessed functional recovery. Secondary degeneration of the ipsilesional thalamus was evaluated ex vivo 28 days after stroke. Using an atlas-based registration pipeline (Pallast et al. J. Neurosc. Methods 2019), the absolute number of GFAP+ astrocytes and relative number of ipsilesional NeuN+ neurons compared to the contralateral unaffected thalamus were evaluated. Lesion maps based on T2-weighted Magnetic Resonance Imaging (MRI) before tDCS were used for voxel-based lesion-symptom mapping (VBLSM) to evaluate the effect of the lesion location on remote neurodegeneration. Functional connectivity (FC) between the lesioned sensorimotor cortex and the ipsilesional thalamus was measured by resting-state functional MRI. Additionally, glucose metabolism after a likewise tDCS regimen in healthy mice was measured by positron emission tomography compared to sham stimulation. Results: Repetitive tDCS decreased the ipsilateral thalamic glucose metabolism in unlesioned animals, while accelerating motor recovery after stroke. Four weeks after cortical stroke, secondary glial scaring was found in the ipsilesional thalamus, most pronounced in the posterior (Po), ventral posterolateral (VPL), and ventral posteromedial (VPM) nucleus, its extent correlating to the cortical lesion size (R2=0.3, p<0.01). Neurodegeneration was associated with a lesion cluster (VSBLM, p<0.05) extending laterally and including the callosal white matter tracts as well as deeper primary somatosensory layers. A decrease in FC between the primary somatosensory area of the lower limb (SS-LL) and the thalamus correlated with secondary neurodegeneration (R2=0.25, p<0.01). Intriguingly, in contrast to glial scaring, tDCS reduced thalamic neurodegeneration by over 60% (p<0.05). Conclusion: Cortical stroke induced network changes and led to remote secondary structural impairment of the thalamus, depending on the affection of corticothalamic connections. TDCS mitigated this remote secondary neurodegeneration. Data suggest previously unknown effects of tDCS on remote brain regions after stroke. [ABSTRACT FROM AUTHOR]

Abstract: Research investigating risk perception suggests that not only the quantitative parameters used in technical risk assessment (i.e., frequency and severity of harm) but also ‘qualitative’ aspects such as the dread a hazard provokes or its controllability influence risk judgments. It remains to be elucidated, however, which neural mechanism underlie risk ratings in healthy subjects. Using fMRI to detect changes in neural activity we compared the neural activations elicited by risk ratings with those elicited by a letter detection task performed on the same stimuli. The latter task served to control for basic stimulus processing, response selection and button-pressing during task performance. Risk ratings differentially activated the medial prefrontal cortex, the inferior frontal gyrus, the cerebellum (P <0.05, FWE corrected, whole brain approach), and in an additional ROI analysis the amygdala (P <0.05, FWE corrected). Of these structures, particularly the amygdala and the prefrontal cortex have been previously associated with decisions about affective interference. Furthermore our data suggest both, similarities and differences between the neural correlates of risk ratings and risk taking as involved, for e.g., in gambling tasks. [Copyright &y& Elsevier]

Abstract: We used functional magnetic resonance imaging to explore the brain mechanisms of changing point of view (PoV) in a visuospatial memory task in 3D space. Eye movements were monitored and BOLD signal changes were measured while subjects were presented with 3D images of a virtual environment. Subjects were required to encode the position of a lamp in the environment and, after changing the PoV (angular difference varied from 0° to 180° in 45° steps), to decide whether the lamp position had been changed too or not. Performance data and a scan-path analysis based on eye movement support the use of landmarks in the environment for coding lamp position and increasing spatial updating costs with increasing changes of PoV indicating allocentric coding strategies during all conditions (0°- to 180°-condition). Subtraction analysis using SPM revealed that a parieto–temporo–frontal network including left medial temporal areas was activated during this 3D visuospatial task, independent of angular difference. The activity of the left parahippocampal area and the left lingual gyrus (but not the hippocampus) correlated with increasing changes of the PoV between encoding and retrieval, emphasizing their specific role in spatial scene memory and allocentric coding. The results suggest that these areas are involved in a continuous matching process between internal representations of the environment and the external status quo. In addition, hippocampal activation correlated with performance was found indicating successful recall of spatial information. Finally, in a prefrontal area comprising, the so-called “deep” frontal eye field, activation was correlated with the amount of saccadic eye movements confirming its role in oculomotor processes. [Copyright &y& Elsevier]

Abstract: This functional magnetic resonance imaging study investigates the effects of nicotine in a cued target detection task when changing cue reliability. Fifteen non-smoking volunteers were studied under placebo and nicotine (Nicorette® polacrilex gum 1 and 2 mg). Validly and invalidly cued trials were arranged in blocks with high, middle and low cue reliability. Two effects of nicotine were investigated: its influence on i) parietal cortex activity underlying the processing of invalid vs. valid trials (i.e. validity effect) and ii) neural activity in the context of low, middle and high informative value of the cue (i.e. cue reliability effect). Nicotine did not affect behavioral performance. However, nicotine reduced the difference in the blood oxygenation level dependent (BOLD) signal between invalid and valid trials in the right intraparietal sulcus. The reduction of parietal activity in invalid trials was smaller in the low cue reliability condition. The same posterior parietal region exhibited a nicotinic modulation of BOLD activity in valid trials which was dependent on cue reliability: Nicotine specifically enhanced the neural activity during valid trials in the context of low cue reliability, i.e. when subjects are already in a state of low certainty. We speculate that the right intraparietal sulcus might be part of two networks working in parallel: one responsible for reorienting attention and the other for the cholinergic modulation of cue reliability. By reducing the use of the cue, nicotine modulates parietal activity related to reorienting attention in conditions with higher cue certainty. On the other hand, nicotine increases parietal activity in states of low certainty. This enhanced activation might influence brain regions, such as the posterior cingulate, directly involved in the processing of cue reliability. [Copyright &y& Elsevier]

Abstract: The integration of spatial and temporal information is a prerequisite for skilled movements. Likewise, spatial and temporal information must be integrated to predict the potential collision (or otherwise) of two moving objects. In a previous blocked functional magnetic resonance imaging (fMRI) study [Neuroimage 20 (2003) S82] we showed that collision judgments (relative to size judgments) provoked a significant increase in neural activity in the left inferior parietal cortex (supramarginal gyrus). This result suggests that this region is involved in the integration of perceptual spatiotemporal information in addition to its known involvement in programming skilled actions. To further investigate the impact of the integration of temporal and spatial information on the left parietal cortex we conducted an event-related fMRI study in which we varied the difficulty of the collision (and the size) judgment tasks parametrically. Reaction times and error rates were used as behavioral measures of increasing task demands. There was a significant linear increase in reaction times and error rates during the collision and the size tasks over the four levels of task difficulty. A linear increase of the blood oxygen level-dependent signal in the left inferior parietal cortex was found only for the collision, not for the size, conditions. Neural activation in the left inferior parietal cortex thus paralleled the increasing demands on spatiotemporal integration. This result confirms that the left supramarginal gyrus integrates spatial and temporal information irrespective of motor demands. [Copyright &y& Elsevier]

Abstract: Using functional MRI, we characterized field sign maps of the occipital cortex and created three-dimensional maps of these areas. By averaging the individual maps into group maps, probability maps of functionally defined V1 or V2 were determined and compared to anatomical probability maps of Brodmann areas BA17 and BA18 derived from cytoarchitectonic analysis (Amunts, K., Malikovic, A., Mohlberg, H., Schormann, T., Zilles, K., 2000. Brodmann''s areas 17 and 18 brought into stereotaxic space—where and how variable? NeuroImage 11, 66–84). Comparison of areas BA17/V1 and BA18/V2 revealed good agreement of the anatomical and functional probability maps. Taking into account that our functional stimulation (due to constraints of the visual angle of stimulation achievable in the MR scanner) only identified parts of V1 and V2, for statistical evaluation of the spatial correlation of V1 and BA17, or V2 and BA18, respectively, the a priori measure κ was calculated testing the hypothesis that a region can only be part of functionally defined V1 or V2 if it is also in anatomically defined BA17 or BA18, respectively. κ = 1 means the hypothesis is fully true, κ = 0 means functionally and anatomically defined visual areas are independent. When applying this measure to the probability maps, κ was equal to 0.84 for both V1/BA17 and V2/BA18. The data thus show a good correspondence of functionally and anatomically derived segregations of early visual processing areas and serve as a basis for employing anatomical probability maps of V1 and V2 in group analyses to characterize functional activations of early visual processing areas. [Copyright &y& Elsevier]

Despite their crucial biological relevance, the neural structures differentially activated by the detection of optic flow towards the observer remain to be elucidated. Here, we deploy functional magnetic resonance imaging with normal volunteers to locate the areas differentially activated when motion towards the observer is detected. Motion towards the observer, compared with motion away, showed significant activations (P<0.05, corrected for multiple comparisons), as assessed using statistical parametric mapping, in the lateral inferior occipital cortex bilaterally and in right lateral superior occipital cortex. The areas implicated do not extend into area V5 or subdivisions thereof.Our data suggest that the representations of motion towards the observer implicate perceptual and attentional mechanisms acting at early stages of visual processing in extrastriate cortex. From the standpoint of efficient biological engineering, it makes sense that such crucially important functions as object motion towards the observer would be computed in early visual processing areas. Further studies will be required to determine the extent to which the effects we observed in lateral occipital cortex reflect differential attention to different types of motion, as contrasted with the derivation of explicit representations of motion towards the observer. [Copyright &y& Elsevier]