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Biomedical subjects

Thomas Nyffeler

Publications and source records attributed to Thomas Nyffeler.

14 recordsLinked to original sources
PubMed2006

To look or not to look at threat? Scanpath differences within a group of spider phobics.

Predicting the behavior of phobic patients in a confrontational situation is challenging. While avoidance as a major clinical component of phobias suggests that patients orient away from threat, findings based on cognitive paradigms indicate an attentional bias towards threat. Here we present eye movement data from 21 spider phobics and 21 control subjects, based on 3 basic oculomotor tasks and a visual exploration task that included close-up views of spiders. Relative to the control group, patients showed accelerated reflexive saccades in one of the basic oculomotor tasks, while the fear-relevant exploration task evoked a general slowing in their scanning behavior and pronounced oculomotor avoidance. However, this avoidance strongly varied within the patient group and was not associated with the scores from spider avoidance-sensitive questionnaire scales. We suggest that variation of oculomotor avoidance between phobics reflects different strategies of how they cope with threat in confrontational situations.

Adult↗
PubMed2006

One-Hertz transcranial magnetic stimulation over the frontal eye field induces lasting inhibition of saccade triggering.

The aim of the study was to examine the effect of low-frequency repetitive transcranial magnetic stimulation on saccade triggering. In five participants, a train of 600 pulses with a frequency of 1 Hz was applied over the right frontal eye field and--as control condition--over the vertex. After repetitive transcranial magnetic stimulation application, oculomotor performance was evaluated with an overlap paradigm. The results show that the repetitive transcranial magnetic stimulation effect was specific for frontal eye field stimulation. Saccade latencies were found to be increased bilaterally for several minutes after the stimulation, and the time course of recovery was different for the ipsilateral and contralateral sides. The results are discussed in the light of possible local and remote repetitive transcranial magnetic stimulation effects on the oculomotor network.

Adult↗
PubMed2006

Cortical reorganization after brain damage: the oculomotor model.

Recovery from eye movement deficits after cortical lesions is amazingly rapid and almost complete, which is in sharp contrast to most other neurological deficits of cerebral lesions. The underlying mechanisms of this successful recovery remain uncertain. We had the rare opportunity to examine two patients with recovery from saccade deficits after a lesion restricted to the frontal eye field (FEF) by means of transcranial magnetic stimulation (TMS). The results provide direct evidence that recovery depended on the integrity of the oculomotor regions of the nonlesioned contralesional hemisphere, and that the compensatory network is task-specific.

Animals↗
PubMed2005

Examining the gateway to the limbic system with diffusion tensor imaging: the perforant pathway in dementia.

Current treatments for Alzheimer's disease (AD) are only able to slow the progression of mental deterioration, making early and reliable diagnosis an essential part of any promising therapeutic strategy. In the initial stages of AD, the first neuropathological alterations occur in the perforant pathway (PP), a large neuronal fiber tract located at the entrance to the limbic system. However, to date, there is no sensitive diagnostic tool for performing in vivo assessments of this structure. In the present bimodal magnetic resonance imaging (MRI) study, we examined 10 elderly controls, 10 subjects suffering from mild cognitive impairment (MCI), and 10 AD patients in order to evaluate the sensitivity of diffusion tensor imaging (DTI), a new MRI technique, for detecting changes in the PP. Furthermore, the diagnostic explanatory power of DTI data of the PP should be compared to high-resolution MRI volumetry and intervoxel coherences (COH) of the hippocampus and the entorhinal cortex, two limbic regions also involved in the pathophysiology of early AD. DTI revealed a marked decrease in COH values in the PP region of MCI (right side: 26%, left side: 29%, as compared to controls) and AD patients (right side: 37%, left side: 43%, as compared to controls). Reductions in COH values of the PP region were significantly correlated with cognitive impairment. DTI data of the PP zone were the only parameter differing significantly between control subjects and MCI patients, while the volumetric measures and the COH values of the hippocampus and the entorhinal cortex did not. DTI of medial temporal brain regions is a promising non-invasive tool for the in vivo diagnosis of the early/preclinical stages of AD.

Aged↗
PubMed2005

The influence of colour on oculomotor behaviour during image perception.

The aim of this study was to investigate how oculomotor behaviour depends on the availability of colour information in pictorial stimuli. Forty study participants viewed complex images in colour or grey-scale, while their eye movements were recorded. We found two major effects of colour. First, although colour increases the complexity of an image, fixations on colour images were shorter than on their grey-scale versions. This suggests that colour enhances discriminability and thus affects low-level perceptual processing. Second, colour decreases the similarity of spatial fixation patterns between participants. The role of colour on visual attention seems to be more important than previously assumed, in theoretical as well as methodological terms.

Adult↗
PubMed2005

Oculomotor behaviour in simultanagnosia: a longitudinal case study.

The aim of the present single case study was to investigate oculomotor recovery in a patient with simultanagnosia due to biparietal hypoxic lesions. Applying visual exploration as well as basic oculomotor tasks in three consecutive test sessions--i.e. 8 weeks, 14 weeks, and 37 weeks after brain damage had occurred--differential recovery was observed. While visual exploration remarkably improved, an impaired disengagement of attention persisted. The improvement of exploration behaviour is interpreted within an oculomotor network theory and implications for a deficit-specific recovery from simultanagnosia are discussed.

Agnosia↗
PubMed2005

Hypervigilance-avoidance pattern in spider phobia.

Cognitive-motivational theories of phobias propose that patients' behavior is characterized by a hypervigilance-avoidance pattern. This implies that phobics initially direct their attention towards fear-relevant stimuli, followed by avoidance that is thought to prevent objective evaluation and habituation. However, previous experiments with highly anxious individuals confirmed initial hypervigilance and yet failed to show subsequent avoidance. In the present study, we administered a visual task in spider phobics and controls, requiring participants to search for spiders. Analyzing eye movements during visual exploration allowed the examination of spatial as well as temporal aspects of phobic behavior. Confirming the hypervigilance-avoidance hypothesis as a whole, our results showed that, relative to controls, phobics detected spiders faster, fixated closer to spiders during the initial search phase and fixated further from spiders subsequently.

Adult↗
PubMed2005

Allocentric and egocentric spatial impairments in a case of topographical disorientation.

We describe a patient with a topographical disorientation after a stroke of the right mediotemporooccipital lobe including the parahippocampal cortex (PHC). Clinical observations and neuropsychological testing reveal an impairment of allocentric spatial representations as well as impairments of visuospatial learning and memory. These findings are in accordance with the well-known function of the PHC in topographical disorientation. As a new finding, results from oculomotor tasks show additional impairments of the egocentric spatial coordinate frame suggesting that in topographical disorientation due to a lesion of the right mediotemporooccipital lobe not only allocentric but also egocentric visuospatial functions are disturbed.

Aged↗
PubMed2005

The role of the human posterior parietal cortex in memory-guided saccade execution: a double-pulse transcranial magnetic stimulation study.

The present study investigated the role of the right posterior parietal cortex (PPC) in the triggering of memory-guided saccades by means of double-pulse transcranial magnetic stimulation (dTMS). Shortly before saccade onset, dTMS with different interstimulus intervals (ISI; 35, 50, 65 or 80 ms) was applied. For contralateral saccades, dTMS significantly decreased saccadic latency with an ISI of 80 ms and increased saccadic gain with an ISI of 65 and 80 ms. Together with the findings of a previous study during frontal eye field (FEF) stimulation the present results demonstrate similarities and differences between both regions in the execution of memory-guided saccades. Firstly, dTMS facilitates saccade triggering in both regions, but the timing is different. Secondly, dTMS over the PPC provokes a hypermetria of contralateral memory-guided saccades that was not observed during FEF stimulation. The results are discussed within the context of recent neurophysiological findings in monkeys.

Adult↗
PubMed2004

Residual oculomotor and exploratory deficits in patients with recovered hemineglect.

Several studies on hemineglect have reported that patients recover remarkably well when assessed with neuropsychological screening tests, however, they show deficits on novel or complex tasks. We investigated whether such deficits can be revealed with eye movement analysis, applying two basic oculomotor tasks as well as two exploratory tasks. Eye movements were recorded in eight hemineglect patients at least eleven months after right-hemisphere brain damage had occurred. Sixteen healthy volunteers participated in the control group. Regarding the basic oculomotor tasks, only the overlap task revealed residual deficits in patients, suggesting that a directional deficit in disengaging attention persisted during recovery. Further residual deficits were evident in the exploratory tasks. When everyday scenes were explored, patients showed a bias in early orienting towards the ipsilateral hemispace. In a search task, they demonstrated the same orienting bias as well as a non-directional deficit concerning search times. Moreover, patients preferentially fixated in the contralateral hemispace, but did not benefit from this asymmetry in terms of search times, i.e. they did not detect contralateral targets faster than ipsilateral ones. This suggests a dissociation between oculomotor processes and attentional ones. In conclusion, we have identified behavioural aspects that seem to recover slower than others. A disengagement deficit and biases in early orienting have been the most pronounced residual oculomotor deficits.

Adult↗
PubMed2004

Single-pulse transcranial magnetic stimulation over the frontal eye field can facilitate and inhibit saccade triggering.

The aim of this study was to investigate the effect of single-pulse transcranial magnetic stimulation on the triggering of saccades. The right frontal eye field was stimulated during modified gap and overlap paradigms with flashed presentation of the lateral visual target of 80 ms. In order to examine possible facilitating or inhibitory effects on saccade triggering, three different time intervals of stimulation were chosen, i.e. simultaneously with onset of the target, during the presentation and after target end. Stimulation applied simultaneously with target onset significantly decreased the latency of contralateral saccades in the gap but not in the overlap paradigm. Stimulation after target end significantly increased saccade latency for both sides in the gap paradigm and for the contralateral side in the overlap paradigm. Stimulation during presentation had no effect in either paradigm. The results show that, depending on the time interval and the paradigm tested, a facilitation or inhibition of saccade triggering can be achieved. The results are discussed in a context of two probable transcranial magnetic stimulation effects, a direct interference with the frontal eye field on the one hand and a remote interference with the superior colliculus on the other hand.

Adult↗
PubMed2003

Information processing in long delay memory-guided saccades: further insights from TMS.

The performance of memory-guided saccades with two different delays (3 s and 30 s of memorisation) was studied in eight subjects. Single pulse transcranial magnetic stimulation (TMS) was applied simultaneously over the left and right dorsolateral prefrontal cortex (DLPFC) 1 s after target presentation. In both delays, stimulation significantly increased the percentage of error in amplitude of memory-guided saccades. Furthermore, the interfering effect of TMS was significantly higher in the short delay compared to that of the long delay paradigm. The results are discussed in the context of a mixed model of spatial working memory control including two components: First, serial information processing with a predominant role of the DLPFC during the early period of memorisation and, second, parallel information processing, which is independent from the DLPFC, operating during longer delays.

Adult↗
PubMed2002

Time-dependent hierarchical organization of spatial working memory: a transcranial magnetic stimulation study.

The performance of memory-guided saccades with two different delays (3 and 30 s of memorization) was studied in seven healthy subjects. Double-pulse transcranial magnetic stimulation (dTMS) with an interstimulus interval of 100 ms was applied over the right dorsolateral prefrontal cortex (DLPFC) early (1 s after target presentation) and late (28 s after target presentation). Early stimulation significantly increased in both delays the percentage of error in amplitude (PEA) of contralateral memory-guided saccades compared to the control experiment without stimulation. dTMS applied late in the delay had no significant effect on PEA. Furthermore, we found a significantly smaller effect of early stimulation in the long-delay paradigm. These results suggest a time-dependent hierarchical organization of the spatial working memory with a functional dominance of DLPFC during the early memorization, independent from the memorization delay. For a long memorization delay, however, working memory seems to have an additional, DLPFC-independent component.

Adult↗