Biomedical subjects

Benno Koch

Publications and source records attributed to Benno Koch.

4 recordsLinked to original sources

PubMed2006

Altered processing of corollary discharge in thalamic lesion patients.

Accumulating evidence suggests that thalamic nuclei relay corollary discharge information of saccadic eye movements, enabling the visual system to update the representation of visual space. The present study aimed to explore the effect of thalamic lesions in humans on updating-related cortical processing. Event-related potentials were recorded while four patients with impairments in using corollary discharge information and 12 healthy control subjects performed a saccadic double-step task. In the experimental condition, which required the use of corollary discharge information, control subjects showed a pronounced positivity over the parietal cortex starting about 150 ms after first saccade onset, reflecting the updating process. In the patients, parietal processing related to updating was altered. Three patients showed evidence of reduced updating event-related potential effects, consistent with a unilateral deficit in using corollary discharge information. In two patients, the event-related potential topography differed significantly from the topography pattern observed in controls. Thalamic damage affects updating-related processing, presumably due to insufficient transfer of saccade-related information to parietal areas. This study thus provides further evidence for thalamic involvement in relaying corollary discharge information related to saccadic eye movements. Our data suggest that integration of corollary discharge and motor information occurs directly before the second saccade in a double-step task.

Adult↗

PubMed2005

Differential involvement of the cerebellum in biological and coherent motion perception.

Perception of biological motion (BM) is a fundamental property of the human visual system. It is as yet unclear which role the cerebellum plays with respect to the perceptual analysis of BM represented as point-light displays. Imaging studies investigating BM perception revealed inconsistent results concerning cerebellar contribution. The present study aimed to explore the role of the cerebellum in the perception of BM by testing the performance of BM perception in patients suffering from circumscribed cerebellar lesions and comparing their performance with an age-matched control group. Perceptual performance was investigated in an experimental task testing the threshold to detect BM masked by scrambled motion and a control task testing the detection of motion direction of coherent motion masked by random noise. Results show clear evidence for a differential contribution of the cerebellum to the perceptual analysis of coherent motion compared with BM. Whereas the ability to detect BM masked by scrambled motion was unaffected in the patient group, their ability to discriminate the direction of coherent motion in random noise was substantially affected. We conclude that intact cerebellar function is not a prerequisite for a preserved ability to detect BM. Because the dorsal motion pathway as well as the ventral form pathway contribute to the visual perception of BM, the question of whether cerebellar dysfunction affecting the dorsal pathway is compensated for by the unaffected ventral pathway or whether perceptual analysis of BM is performed completely without cerebellar contribution remains to be determined.

Adult↗

PubMed2004

Do normal D-dimer levels reliably exclude cerebral sinus thrombosis?

BACKGROUND AND PURPOSE: Cerebral sinus thrombosis (CST) needs to be considered in the differential diagnosis of all patients with acute headache. Early diagnosis is essential because early treatment may prevent morbidity and may even be life-saving. Definite exclusion, however, needs advanced neuroradiologic diagnostics, which are not readily available in many hospitals. Because measurement of D-dimers has been demonstrated to be helpful in excluding thromboembolic disease, our aim was to investigate whether D-dimers would be also sensitive enough to exclude CST. METHODS: We undertook a prospective multicenter study over a 2.5-year period including all patients who came to the emergency departments with symptoms suggestive of CST. All patients were diagnosed either by magnetic resonance venography, spiral computed tomography scan venography, or intra-arterial digital subtraction angiography. D-dimer levels were measured at admission and analyzed by the same method in all patients. RESULTS: A total of 343 patients were included. CST was diagnosed in 35 patients, of whom 34 had D-dimers above the cutoff value (>500 microg/L). From the 308 patients not having CST, D-dimers were elevated in 27. Sensitivity of D-dimers was 97.1%, with a negative predictive value of 99.6%. Specificity was 91.2%, with a positive predictive value of 55.7%. D-dimers were positively correlated with the extent of the thrombosis and negatively correlated with the duration of symptoms (Spearman rank correlation coefficients 0.76, -0.58, respectively). CONCLUSIONS: D-dimer measurement is useful in patients with suspected CST. Normal D-dimers make the presence of CST very unlikely.

Adult↗

PubMed2003

Involvement of the mediodorsal thalamic nucleus in mediating recollection and familiarity.

The mediodorsal (MD) thalamic nucleus is thought to play an important role in memory processes. Distinct hippocampal-thalamic-prefrontal connections have been described as the potential neural substrate for both, recollection and familiarity. The aim of this study was to investigate whether the MD is part of the circuits underlying these two memory components. We assessed the effects of ischemic thalamic lesions with or without MD involvement on performance in a word list discrimination task and standard tests of memory and executive function. Estimates of recollection and familiarity were derived using the dual-process signal-detection model (DPSD). The results revealed impairments in both, recollection and familiarity, after unilateral thalamic damage, with recollection being more affected than familiarity. There were no significant differences in the memory performance of patients with MD lesions compared to patients with ventrolateral-thalamic lesions except for familiarity estimates, which were lower for the latter group. Lesions involving the MD led to recollection deficits, although inspection of individual cases suggested a decrease in both memory components after damage in the medial part of this nucleus. Executive dysfunction was associated with lateral MD lesions and also ventrolateral-thalamic damage. The findings suggest that MD contributes to recollection, with some preliminary evidence of a contribution of the medial MD to familiarity. The small sample size does, however, not yet allow any clear conclusions in this regard. Since damage in the ventrolateral thalamus leads to memory and executive dysfunction, further research is needed to elucidate the role of this thalamic region in cognition.

Brain Ischemia↗