Pure apraxic agraphia: a disconnection syndrome after left subcortical stroke.
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Aged↗
Biomedical subjects
G R Fink
Publications and source records attributed to G R Fink.
Effects of nicotine on visuo-spatial selective attention as indexed by event-related potentials.
Nicotine has been shown to specifically reduce reaction times to invalidly cued targets in spatial cueing paradigms. In two experiments, we used event-related potentials to test whether the facilitative effect of nicotine upon the detection of invalidly cued targets is due to a modulation of perceptual processing, as indexed by early attention-related event-related potential components. Furthermore, we assessed whether the effect of nicotine on such unattended stimuli depends upon the use of exogenous or endogenous cues. In both experiments, the electroencephalogram was recorded while non-smokers completed discrimination tasks in Posner-type paradigms after chewing a nicotine polacrilex gum (Nicorette 2 mg) in one session and a placebo gum in another session. Nicotine reduced reaction times to invalidly cued targets when cueing was endogenous. In contrast, no differential effect of nicotine on reaction times was observed when exogenous cues were used. Electrophysiologically, we found a similar attentional modulation of the P1 and N1 components under placebo and nicotine but a differential modulation of later event-related potential components at a frontocentral site. The lack of a drug-dependent modulation of P1 and N1 in the presence of a behavioral effect suggests that the effect of nicotine in endogenous visuo-spatial cueing tasks is not due to an alteration of perceptual processes. Rather, the differential modulation of frontocentral event-related potentials suggests that nicotine acts at later stages of target processing.
Adult↗
The left parietal cortex and motor intention: an event-related functional magnetic resonance imaging study.
Traditionally the posterior parietal cortex was believed to be a sensory structure. More recently, however, its important role in sensory-motor integration has been recognized. One of its functions suggested in this context is the forming of intentions, i.e. high-level cognitive plans for movements. The selection and planning of a specific movement defines motor intention. In this study we used rapid event-related functional magnetic resonance imaging of healthy human subjects to investigate the involvement of posterior parietal cortex in motor intention in response to valid imperative cues. Subjects were provided with either neutral, motor or spatial cues. Neutral cues simply alerted, motor cues indicated which hand to use for response, and spatial cues indicated on which side the target would appear. Importantly, identical targets and responses followed these cues. Therefore any differential neural effects observed are independent from the actual movement performed. Differential blood oxygen level dependent signal changes for motor vs. neutral as well as motor vs. spatial cue trials were found in the left supramarginal gyrus, as hypothesized. The results demonstrate that neural activity in the left supramarginal gyrus underlies motor plans independent from the execution of the movement and thus extend previous neuropsychological and functional imaging data on the role of the left supramarginal gyrus in higher motor cognition.
Adult↗
The neural basis of perceptual hypothesis generation and testing.
Four-dot masking is a new form of visual masking that does not involve local contour interactions or spatial superimposition of the target stimulus and the mask (as, e.g., in pattern or metacontrast masking). Rather, the effective masking mechanism is based on object substitution. Object substitution masking occurs when low-level visual information representations are altered before target identification through iterative interaction with high-level visual processing stages has been completed. Interestingly, object substitution interacts with attention processes: Strong masking effects are observed when attentional orientation toward the target location is delayed. In contrast, no masking occurs when attention can be rapidly shifted to and engaged onto the target location. We investigated the neural basis of object substitution masking by studying the interaction of spatial attention and masking processes using functional magnetic resonance imaging. Behavioral data indicated a two-way interaction between the factors Spatial Attention (valid vs. invalid cueing) and Masking (four-dot vs. pattern masking). As expected, spatial attention improved performance more strongly during object substitution masking. Functional correlates of this interaction were found in the primary visual cortex, higher visual areas, and left intraparietal sulcus. A region-of-interest analysis in these areas revealed that the largest blood oxygenation level-dependent signal changes occurred during effective four-dot masking. In contrast, the weakest signal changes in these areas were observed when target visibility was highest. The data suggest that these areas represent an object substitution network dedicated to the generation and testing of a perceptual hypotheses as described by the object substitution theory of masking of Di-Lollo et al. [Competition for consciousness among visual events: The psychophysics of reentrant visual processes. Journal of Experimental Psychology: General, 129, 481-507, 2000].
Adult↗
Alertness-training in neglect: behavioral and imaging results.
PURPOSE: It has been proposed that the right hemisphere alerting network co-activates, either directly or via the brainstem, the spatial attention system in the parietal cortex. The observation that measures of impaired alertness and sustained attention can be used to predict the outcome of neglect might suggest such a relationship, too. The aim of the present study was to investigate the effects of alertness training on hemispatial neglect. METHOD: A three-week computerised alertness training was applied to patients with chronic (> 3 months) stable visuospatial hemineglect. Training effects were investigated both in a single case and in a group of 7 patients by means of neuropsychological tests and functional magnetic resonance imaging (fMRI). RESULTS: After the training, the patients showed a significant improvement in a neglect test battery above any natural fluctuation during a three-week baseline phase. Improvements in the neglect tasks were accompanied by an increase of both right and left hemisphere frontal, anterior cingulate and superior parietal activation, areas known to be associated with both alertness and spatial attention. Four weeks after the end of the training, the patients' neglect test performance had mostly returned to baseline. Despite decreases of activation in some of the initially reactivated areas, increases in neural activity bilaterally in frontal areas, in the right anterior cingulate cortex, the right angular gyrus and in the left temporoparietal cortex remained. An Optokinetic Stimulation Training (OKS) in a control group of another 7 neglect patients led to comparable behavioral results. After the training, however, there was a reactivation mainly in posterior parts of both hemispheres suggesting training specific functional reorganization. CONCLUSION: The limited stability of the behavioral and reactivation results over time demonstrates that a three-week alertness or OKS training alone does not result in long lasting behavioral improvements and stable reactivation patterns in every patient. We rather suggest that combining alertness and spatial attention oriented training procedures might lead to a more stable amelioration of neglect symptoms.
Adult↗
The modulatory effects of nicotine on parietal cortex activity in a cued target detection task depend on cue reliability.
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.
Adult↗
Impact of alertness training on spatial neglect: a behavioural and fMRI study.
The effects of a 3-week computerised alertness training on chronic (>3 months) visuospatial hemineglect were investigated prospectively in seven patients by means of neuropsychological tests and functional magnetic resonance imaging (fMRI). Following the alertness training, the group showed improved alertness and a significant improvement in the performance of a neglect test battery over and above any improvement during a 3-week baseline phase. Improvements in the neglect tasks were accompanied by an increase of right hemisphere neural activity in frontal cortex, anterior cingulate cortex, precuneus, cuneus and angular gyrus. These areas have previously been associated with alertness and spatial attention. A similar pattern of increased neural activity was found for the left hemisphere. Four weeks after the end of the training, the patients' neglect test performance had mostly returned to baseline, while the increases in neural activity bilaterally in frontal areas, in the right anterior cingulate cortex, the right angular gyrus and the left temporoparietal cortex remained. The data show that a 3-week computerised alertness training can improve performance both in alertness and neglect tests and that these behavioural improvements are associated with reactivation in areas associated with alerting and visuospatial attention. The limited stability of these effects over time suggests that a 3-week alertness training alone does not result in long lasting improvements in every patient, but refining the treatment protocol may lead to a more stable amelioration of neglect symptoms.
Adult↗
Linking retinotopic fMRI mapping and anatomical probability maps of human occipital areas V1 and V2.
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 kappa 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. kappa = 1 means the hypothesis is fully true, kappa = 0 means functionally and anatomically defined visual areas are independent. When applying this measure to the probability maps, kappa 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.
Adult↗
Difficulty of perceptual spatiotemporal integration modulates the neural activity of left inferior parietal cortex.
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.
Adult↗
On the benefits of not trying: brain activity and connectivity reflecting the interactions of explicit and implicit sequence learning.
Under certain circumstances, implicit, automatic learning may be attenuated by explicit memory processes. We explored the brain basis of this phenomenon in a functional magnetic resonance imaging (fMRI) study of motor sequence learning. Using a factorial design that crossed subjective intention to learn (explicit versus implicit) with sequence difficulty (a standard versus a more complex alternating sequence), we show that explicit attempts to learn the difficult sequence produce a failure of implicit learning and, in a follow-up behavioural experiment, that this failure represents a suppression of learning itself rather than of the expression of learning. This suppression is associated with sustained right frontal activation and attenuation of learning-related changes in the medial temporal lobe and the thalamus. Furthermore, this condition is characterized by a reversal of the fronto-thalamic connectivity observed with unimpaired implicit learning. The findings demonstrate a neural basis for a well-known behavioural effect: the deleterious impact of an explicit search upon implicit learning.
Adult↗
[Spatial neglect].
Unilateral spatial (hemi-)neglect or (hemi-)inattention are clinical terms used to describe a number of different clinical symptoms which have in common the patient's failure to attend to, respond adequately to, or orient voluntarily to people or objects in the contralesional space. Unilateral spatial neglect is most often observed following brain lesions affecting the right hemisphere, and in particular the right inferior parietal cortex (angular and supramarginal gyrus) and right temporoparietal junction. Importantly, the term hemineglect cannot be meaningfully used if the target behavior is explained by primary sensory or motor deficits only. Typically the patient's deficit is supramodal: patients with hemineglect fail to respond to novel or meaningful stimuli irrespective of whether they are presented in the visual, auditory, and somesthetic (somatosensory) domain. As adequate perception and spatial representation of both the body and the outside world are mandatory for almost all activities of daily living, hemineglect is known to limit the degree of active participation in rehabilitation programs and is thus commonly associated with poor functional recovery and less successful social reintegration. A number of new promising behavioral and pharmacological treatments may help to ameliorate neglect in the future.
Attention↗
A functional magnetic resonance imaging study of local/global processing with stimulus presentation in the peripheral visual hemifields.
When stimuli are presented in the left or right visual fields, hemispheric specialization for global and local processing in occipital areas is attenuated. Using functional magnetic resonance imaging, we investigated how this attenuation is compensated for when information must cross the corpus callosum to reach the areas specialized for global and local processing. We presented hierarchically nested letters (e.g. a large E made of smaller E's) to the right or the left visual hemifield while subjects fixated centrally. In half the trials, subjects indicated whether the global aspect and in the other half whether the local aspect of the stimulus matched a pre-specified target letter. Visual hemifield presentations showed the expected contralateral activations of occipital cortex. The main effects of locally or globally directed attention did not show any differential occipital activations, but the right anterior cingulate cortex was activated differentially during local processing. Region-of-interest-based analyses showed increased neural activity in left posterior occipital cortex during local processing when stimuli were presented in the left hemifield. During global processing with stimulus presentation to the right hemifield, the right posterior occipital cortex was activated. Activation of right anterior cingulate cortex during local processing is likely to reflect the suppression of global processing precedence in order to select correctly the local stimulus level. The activations in left (local) and right (global) occipital areas are likely to reflect the top-down augmentation of stimulus information that has been degraded by callosal crossing in order to access the hemisphere specialized for local or global processing.
Adult↗
Neural correlates of first-person perspective as one constituent of human self-consciousness.
Taking the first-person perspective (1PP) centered upon one's own body as opposed to the third-person perspective (3PP), which enables us to take the viewpoint of someone else, is constitutive for human self-consciousness. At the underlying representational or cognitive level, these operations are processed in an egocentric reference frame, where locations are represented centered around another person's (3PP) or one's own perspective (1PP). To study 3PP and 1PP, both operating in egocentric frames, a virtual scene with an avatar and red balls in a room was presented from different camera viewpoints to normal volunteers (n = 11) in a functional magnetic resonance imaging experiment. The task for the subjects was to count the objects as seen either from the avatar's perspective (3PP) or one's own perspective (1PP). The scene was presented either from a ground view (GV ) or an aerial view (AV ) to investigate the effect of view on perspective taking. The factors perspective (3PP vs. 1PP) and view (GV vs. AV ) were arranged in a two-factorial way. Reaction times were increased and percent correctness scores were decreased in 3PP as opposed to 1PP. To detect the neural mechanisms associated with perspective taking, functional magnetic resonance imaging was employed. Data were analyzed using SPM'99 in each subject and non-parametric statistics on the group level. Activations common to 3PP and 1PP (relative to baseline) were observed in a network of occipital, parietal, and prefrontal areas. Deactivations common to 3PP and 1PP (relative to baseline) were observed predominantly in mesial (i.e., parasagittal) cortical and lateral superior temporal areas bilaterally. Differential increases of neural activity were found in mesial superior parietal and right premotor cortex during 3PP (relative to 1PP), whereas differential increases during 1PP (relative to 3PP) were found in mesial prefrontal cortex, posterior cingulate cortex, and superior temporal cortex bilaterally. The data suggest that in addition to joint neural mechanisms, for example, due to visuospatial processing and decision making, 3PP and 1PP rely on differential neural processes. Mesial cortical areas are involved in decisional processes when the spatial task is solved from one's own viewpoint, whereas egocentric operations from another person's perspective differentially draw upon cortical areas known to be involved in spatial cognition.
Adult↗
Brain correlates of functional retrograde amnesia in three patients.
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Adult↗
Synchronization tomography: a method for three-dimensional localization of phase synchronized neuronal populations in the human brain using magnetoencephalography.
We present a noninvasive technique which allows the anatomical localization of phase synchronized neuronal populations in the human brain with magnetoencephalography. We study phase synchronization between the reconstructed current source density (CSD) of different brain areas as well as between the CSD and muscular activity. We asked four subjects to tap their fingers in synchrony with a rhythmic tone, and to continue tapping at the same rate after the tone was switched off. The phase synchronization behavior of brain areas relevant for movement coordination, inner voice, and time estimation changes drastically when the transition to internal pacing occurs, while their averaged amplitudes remain unchanged. Information of this kind cannot be derived with standard neuroimaging techniques like functional magnetic resonance imaging or positron emission tomography.
Brain↗
[Walter Poppelreuter (1886-1939). Remarks on the cover illustration].
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Germany↗
Ischemic brain tissue salvaged from infarction by the GP IIb/IIIa platelet antagonist tirofiban.
In an open pilot study, the authors tested whether the nonpeptide glycoprotein (GP) IIb/IIIa antagonist tirofiban, a highly effective and selective blocker of platelet aggregation, prevents the transition of ischemic brain tissue into the infarct proper as defined by MRI (perfusion-weighted/T2-weighted) in patients with acute ischemic stroke. The infarct volume (T2 lesion after 1 week) was smaller in treated patients (n = 10) compared with matched control subjects (n = 10; p = 0.029) with similar initial perfusion deficit (TTP-maps). The authors conclude that GP IIb/IIIa antagonists have therapeutic potential in acute stroke therapy.
Adult↗
[Hugo Karl Liepmann (1863-1925). Remarks regarding the title picture].
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Germany↗