Biomedical subjects

Silke Lux

Publications and source records attributed to Silke Lux.

6 recordsLinked to original sources

PubMed2006

Processing the spatial configuration of complex actions involves right posterior parietal cortex: An fMRI study with clinical implications.

The left hemispheric dominance for complex motor behavior is undisputed. Clinical observations of complex motor deficits in patients with right hemispheric lesions, however, suggest an additional contribution of the right hemisphere to higher motor control. We assessed, using functional MRI (fMRI), which brain regions are implicated in processing the spatial aspects of complex, object-related actions. Using a blocked, factorial design, 17 healthy volunteers were asked to detect either spatial or sequential errors (factor ERROR) in complex activities of daily living, presented as video sequences with the appropriate object(s) or as pantomimes (factor STIMULUS). Observing complex actions (irrespective of stimulus type) activated a bilateral frontoparietal network. Observing actions with objects (relative to pantomimes) differentially increased neural activity in the fusiform gyrus and inferior occipital cortex bilaterally. Observing pantomimes, i.e., the same actions but without any object, differentially activated right prefrontal cortex, anterior cingulate cortex, the precuneus, and left cerebellum. The left cingulate cortex was differentially activated when subjects assessed the sequencing of actions. By contrast, assessing the spatial configuration of complex actions differentially increased neural activity in right posterior parietal cortex. A significant interaction of ERROR and STIMULUS was revealed for the right inferior parietal cortex only. These findings suggest a specific role of the right hemisphere, especially of right posterior parietal cortex, in processing spatial aspects of complex actions and thus provide a physiological basis for the observed apraxic motor deficits in patients with right hemispheric damage.

Activities of Daily Living↗

PubMed2006

Sex differences in neural mechanisms underlying implicit symmetry processing.

Some species, including humans, prefer symmetrical to asymmetrical patterns. Preferences for symmetrical stimuli could have arisen in both sexes because specialized systems developed to detect and identify symmetrical stimuli, which are more likely to be figure than background. Females, it has been suggested, prefer symmetry because it may provide a cue to biological fitness when choosing a mate. Using functional magnetic resonance imaging, we found sex differences in neural activity when subjects distinguished figure from ground in abstract patterns whose component shapes differed in colour, brightness, and symmetry/asymmetry. Although no participant explicitly reported using symmetry as a decision criterion, women showed more neural activity than men in visual processing areas when the display contained a symmetrical shape. This enhanced activity in occipital cortex (middle and superior occipital gyrus) occurred bilaterally in women irrespective of whether they chose the symmetrical element in the display as the figure. Contrariwise, men showed a significant neural response in right temporal (superior temporal gyrus) and left parietal cortex (inferior parietal cortex/temporo-parietal junction) only when they chose a symmetrical element as the figure. The female brain thus appears to register symmetry automatically as a stimulus attribute, while the differential neurophysiological response of the male brain is dependent upon an explicit behavioural response to symmetry (choosing the symmetrical part of the display as figure), even if the criterion for choice (symmetry) is not reported verbally.

Adult↗

PubMed2006

Neural representations of self versus other: visual-spatial perspective taking and agency in a virtual ball-tossing game.

Human self-consciousness relies on the ability to distinguish between oneself and others. We sought to explore the neural correlates involved in self-other representations by investigating two critical processes: perspective taking and agency. Although recent research has shed light on the neural processes underlying these phenomena, little is known about how they overlap or interact at the neural level. In a two-factorial functional magnetic resonance imaging (fMRI) experiment, participants played a ball-tossing game with two virtual characters ("avatars"). During an active/agency (ACT) task, subjects threw a ball to one of the avatars by pressing a button. During a passive/nonagency (PAS) task, they indicated which of the other avatars threw the ball. Both tasks were performed from a first-person perspective (1PP), in which subjects interacted from their own perspective, and a third-person perspective (3PP), in which subjects interacted from the perspective of an avatar with another location in space. fMRI analyses revealed overlapping activity in medial prefrontal regions associated with representations of one's own perspective and actions (1PP and ACT), and overlapping activity in temporal-occipital, premotor, and inferior frontal, as well as posterior parietal regions associated with representation of others' perspectives and actions (3PP and PAS). These findings provide evidence for distinct neural substrates underlying representations of the self and others and provide support for the idea that the medial prefrontal cortex crucially contributes to a neural basis of the self. The lack of a statistically significant interaction suggests that perspective taking and agency represent independent constituents of self-consciousness.

Adult↗

PubMed2005

Directed and divided attention during hierarchical processing in patients with visuo-spatial neglect and matched healthy volunteers.

Hierarchically organized figures (for example, a large E made up of smaller N's) are frequently used to investigate directed and divided attention. Investigations of neurological and psychiatric patients, and also tachistoscopic and functional neuroimaging studies on healthy subjects, typically find the right hemisphere to be specialized for the processing of global stimuli and the left hemisphere to be specialized for the processing of local stimuli. In the current study, a group of 12 patients with visuo-spatial neglect (NP) after right hemisphere lesions and 12 age and sex-matched control subjects (CO) performed a directed and a divided attention task with hierarchically organized letters. As expected, faster reaction times were found for control subjects than for neglect patients, especially for the directed global attention task. Lower error rates were found for CO and NP for local than for global targets during the divided attention condition. Local on global interference was found for both groups in reaction times. These local processing advantages for older healthy adults have been reported previously. Additionally, an impairment in the divided attention task was found in both groups, but especially for global targets in NP. This impairment is consistent with other evidence of difficulty in disengaging attention shown by patients with visuo-spatial neglect.

Adult↗

PubMed2003

Chronic epilepsy and cognition: a longitudinal study in temporal lobe epilepsy.

It remains unclear whether uncontrolled epilepsy causes mental decline. This longitudinal study contrasts change of memory and nonmemory functions in 147 surgically and 102 medically treated patients with temporal lobe epilepsy. All participants were evaluated at baseline (T1) and after 2 to 10 years (T3). Surgical patients underwent additional testing 1 year postoperatively (T2). Data were analyzed on an individual and group level. Sixty-three percent of the surgical and 12% of the medically treated patients were seizure-free at T3. Fifty percent of the medically treated and 60% of the surgical patients showed significant memory decline at T3 with little change in nonmemory functions (difference not significant). Surgery anticipated the decline seen in the medically treated group and exceeded it when surgery was performed on the left, or if seizures continued postoperatively. Seizure-free surgical patients showed recovery of nonmemory functions at T2 (p < 0.001) and of memory functions at T3 (T3, p = 0.03). Multiple regression indicated retest interval, seizure control, and mental reserve capacity as predictors of performance changes. In addition, psychosocial outcome was better when seizures were controlled. In conclusion, chronic temporal lobe epilepsy is associated with progressive memory impairment. Surgery, particularly if unsuccessful, accelerates this decline. However, memory decline may be stopped and even reversed if seizures are fully controlled.

Adult↗

PubMed2003

Neural mechanisms associated with attention to temporal synchrony versus spatial orientation: an fMRI study.

Previous neuropsychological and functional imaging studies have suggested that the right hemisphere is crucially involved in spatial cognition. By contrast, much less is known about the putative left hemisphere specialization for aspects of temporal cognition. Accordingly, we studied with functional magnetic resonance imaging the neural mechanisms underlying attention to stimulus onset synchrony or orientational congruence with identical pairs of geometric figures. In each trial, two rhombuses were presented, each 4 degrees peripheral to a central fixation cross, in the left and right visual hemifields. In half of the trials, subjects were asked to judge and indicate via button presses whether the rhombuses appeared simultaneously. In the other half of the trials, subjects indicated whether the orientation of the rhombuses was the same (Factor 1, task, temporal synchrony, orientation). In half of the trials, subjects responded with their right hand and in the other half with their left hand (Factor 2, hand, right, left). Data were analyzed using SPM99 and a random-effects model. Attention to orientation differentially activated right temporo-occipital cortex. Attention to stimulus onset synchrony activated left anterior superior temporal gyrus, left inferior parietal cortex, left medial frontal gyrus, and right operculum. Activation of right temporo-occipital cortex for attention to stimulus orientation is in good agreement with previous functional neuroimaging studies of stimulus orientation. More importantly, activation of a predominantly left-hemispheric network with attention to stimulus onset synchrony extends the results of previous functional imaging, psychophysical, and neuropsychological studies of temporal processing.

Adult↗