Biomedical subjects

Boris Suchan

Publications and source records attributed to Boris Suchan.

11 recordsLinked to original sources

PubMed2006

Dissociation of grey and white matter reduction in spinocerebellar ataxia type 3 and 6: a voxel-based morphometry study.

The aim of this study was to examine the different patterns of cerebellar and/or brainstem atrophy in spinocerebellar ataxia (SCA) type 3 and 6. Eighteen patients (SCA3 n=9, SCA6 n=9) and 15 healthy volunteers were studied. Voxel-based morphometry (VBM) was applied to segmented grey matter (GM) and white matter (WM) of high-resolution T1-weighted brain volumes of each group. We found reduction of grey matter in the pons as well as in the vermis in SCA3 as compared to control subjects. In SCA6 significant grey matter loss was found in hemispheric lobules bilaterally as well as in the vermis. White matter analysis revealed significant changes in SCA3, especially in the pons, in the white matter surrounding the dentate nucleus (DN) and in the cerebellar peduncles, whereas no significant white matter reduction was found in SCA6 patients. Our results demonstrate different patterns of grey and white matter affection detected by magnetic resonance imaging (MRI) in SCA3 and SCA6 patients, confirming the pathological concept of cortical cerebellar atrophy in SCA6. In contrast, SCA3 represents a form of ponto-cerebellar atrophy with predominant affection of pontine nuclei and fibre tracts.

Aged↗

PubMed2005

Cross-modal processing in auditory and visual working memory.

This study aimed to further explore processing of auditory and visual stimuli in working memory. Smith and Jonides (1997) [Smith, E.E., Jonides, J., 1997. Working memory: A view from neuroimaging. Cogn. Psychol. 33, 5-42] described a modified working memory model in which visual input is automatically transformed into a phonological code. To study this process, auditory and the corresponding visual stimuli were presented in a variant of the 2-back task which involved changes from the auditory to the visual modality and vice versa. Brain activation patterns underlying visual and auditory processing as well as transformation mechanisms were analyzed. Results yielded a significant activation in the left primary auditory cortex associated with transformation of visual into auditory information which reflects the matching and recoding of a stored item and its modality. This finding yields empirical evidence for a transformation of visual input into a phonological code, with the auditory cortex as the neural correlate of the recoding process in working memory.

Adult↗

PubMed2005

Visuo-verbal interactions in working memory: evidence from event-related potentials.

Working memory is thought to involve separate modality-specific storage systems. Interactions between these storage systems were investigated using a novel cross-modal 2-back paradigm. 2-back, 1-back and target items were presented either visually as a verbalizable linedrawing or auditorily as a digitized spoken word. ERPs for auditory targets were primarily modulated by the presentation modality of the 2-back item, whereas ERPs for visual targets were largely modulated by presentation modality of the 1-back item. Results indicate that verbalizable pictures are only partially transformed into a phonological code for rehearsal in working memory. Furthermore, results support the idea of a more stable and persistent auditory short-term store as opposed to a more transiently activated visual store for verbalizable material.

Acoustic Stimulation↗

PubMed2005

Structural encoding and recognition of biological motion: evidence from event-related potentials and source analysis.

In the present study, we investigated how different processing stages involved in the perceptual analysis of biological motion (BM) are reflected by modulations in event-related potentials (ERP) in order to elucidate the time course and location of neural processing of BM. Data analysis was carried out using conventional averaging techniques as well as source localization with low resolution brain electromagnetic tomography (LORETA). ERPs were recorded in response to point-light displays of a walking person, an inverted walking person and displays of scrambled motion. Analysis yielded a pronounced negativity with a peak at 180 ms after stimulus onset which was more pronounced for upright walkers than for inverted walkers and scrambled motion. A later negative component between 230 and 360 ms after stimulus onset had a larger amplitude for upright and inverted walkers as compared to scrambled walkers. In the later component, negativity was more pronounced in the right hemisphere revealing asymmetries in BM perception. LORETA analysis yielded evidence for sources specific to BM within the right fusiform gyrus and the right superior temporal gyrus for the second component, whereas sources for BM in the early component were located in areas associated with attentional aspects of visual processing. The early component might reflect the pop-out effect of a moving dot pattern representing the highly familiar form of a human figure, whereas the later component might be associated with the specific analysis of motion patterns providing biologically relevant information.

Adult↗

PubMed2005

Effect of working memory on evaluation-related frontocentral negativity.

Recent results suggest that a negative ERP potential emerges not only on error trials, but is also found after correct responses. There is broad evidence that this component is generated in the anterior cingulate cortex (ACC). The present study aimed to explore the influence of working memory demands on the evaluation process probably reflected by the negative potential. To this purpose, a modified continuous performance task (CPT) was used, with variations of the delay between cues and imperative stimuli. Data were analyzed using conventional averaging techniques as well as source localization with LORETA (low resolution brain electromagnetic tomography). Results suggest a significant effect of working memory delay on the amplitude of the post-response negative ERP component. Its source was located in the anterior cingulate cortex, with the exact location being dependent upon working memory demands. The results support the notion of a general response evaluation system reflected by a post-response negative component. The findings of a working memory dependent modification of this potential suggest a functional link between the medial frontal cortex and the lateral frontal regions primarily involved in working memory processing.

Adult↗

PubMed2005

Neuropsychological deficits after mechanical aortic valve replacement.

BACKGROUND AND AIM OF THE STUDY: Studies using transcranial Doppler monitoring have identified high-intensity transient signals (HITS) after mechanical valve replacement. Although cognitive dysfunction in relation to HITS was reported in some studies, the current data basis is inconsistent. The study aim was to investigate the long-term effects of HITS on cognitive function. METHODS: Forty patients who had undergone mechanical valve replacement (mean 5.3 years previously) participated in the study. HITS-measurements were performed on the day of neuropsychological assessment. Patients were allocated to HITS-high and HITS-low groups on the basis of the median HITS-rate. Both patient groups completed a neuropsychological test battery and were compared to healthy controls. RESULTS: Both patient groups showed verbal and visual memory deficits in comparison with controls. The HITS-high group scored lower on verbal memory compared to the HITS-low group. In addition, the HITS-high group showed executive deficits when compared to the HITS-low group and controls. The significant effects with respect to verbal memory and executive functions remained after extracorporeal circulation time differences were controlled for. CONCLUSION: The study results imply that heart valve replacement with mechanical prostheses may be associated with mild cognitive impairment. The differential impairment pattern of the high- and low-HITS groups further suggests that the number of HITS may be of critical importance. The observed memory impairments were consistent with the view that cognitive dysfunction after valve replacement may be due to temporal lobe dysfunction. However, future studies are required to investigate the association of number of HITS, cerebral changes and cognitive function in further detail.

Aged↗

PubMed2004

Effects of single pulse TMS on spatio-temporal integration in sequential isochronus movements.

This study was designed to investigate the effect of single pulse transcranial magnetic stimulation (TMS) on the isochronic performance of sequential movements which were recorded using a digitising pad. Magnetic stimulation was applied through an 8-shaped magnetic coil over primary motor and premotor cortex at a specific time point while executing the first of a three movement sequence. TMS applied to the premotor cortex showed an alteration effect on the first movement while stimulation of the primary motor cortex influenced the second movement in the sequence. Results suggest that the premotor cortex is involved in online monitoring and controlling of spatio-temporal features of trajectories while the motor cortex contributes to the execution of movements. Isochrony is maintained to a high degree under TMS which has been found in other studies to delay reaction times. The results show that although TMS has a significant influence on motor performance, isochrony is a robust component of motor programs, not readily to be disturbed.

Adult↗

PubMed2003

Apomorphine reduces BOLD signal in fMRI during voluntary movement in Parkinsonian patients.

Our group investigated modulatory effects of apomorphine on cerebral activation patterns during finger tapping movements in seven Parkinson's disease (PD) patients off medication. Cerebral activation was measured according to an established fMRI protocol. Apomorphine application disclosed a reduction of cerebral activation patterns to the contralateral precentral gyrus affecting both clinically affected and unaffected sides; tapping with the unaffected hand additionally revealed activation in the contralateral postcentral gyrus. These findings contradict those of similar functional imaging studies performed in PD to date, which variously found augmentation of cerebral activation patterns in Parkinsonian patients after dopaminergic stimulation. One conceivable explanation for our singular results would be preferred binding of apomorphine to presynaptic dopaminergic receptors, leading to inhibition of endogenous dopamine release and resultant diminished dopaminergic stimulation, reflected in diminished cerebral activation patterns. These findings warrant future consideration and further investigation of possible central inhibitory effects of dopaminergic therapy in functional imaging studies in PD.

Antiparkinson Agents↗

PubMed2002

Hemispheric dissociation of visual-pattern processing and visual rotation.

We aimed at investigating whether on-line and delayed visual pattern processing activated different areas in human prefrontal and parietal cortex. For this purpose we measured the regional cerebral blood flow (rCBF) during simultaneous and successive visual matrix processing in 10 right-handed subjects. Delayed matching to sample activated predominantly left hemispheric ventrolateral prefrontal cortex, Broca's area and parts of the parietal cortex. In contrast, visuospatial matrix rotation showed activation of the right dorsolateral prefrontal cortex and parietal lobe. The present results suggest a hemispheric dissociation of fronto-parietal circuits with a left dominance for visual pattern processing like storage and a right dominance for visuospatial processing.

Adult↗

PubMed2002

Neural correlates of visuospatial imagery.

We studied changes in regional cerebral blood flow (rCBF) in 10 healthy right-handed subjects during a visuospatial imagery task. The subject's task consisted of drawing imagined lines connecting encircled numbers in ascending order and estimating the number of lines crossing. Compared with a control task in which there were no crossed lines, there were significant rCBF increases in the cingulate gyrus, the adjacent superior frontal gyrus and in the left inferior parietal cortex. The rCBF changes of the latter area correlated with task performance time. Since these activation areas are close to those in imagery of movement trajectories, we concluded that they appear to be a subsystem for processing mental visuospatial images.

Adult↗

PubMedDate not supplied

Cortico-subcortical contributions to executive control.

The term "executive functions" refers to a range of cognitive processes, their common feature being the coordination of information processing and action control. Cortico-subcortical circuits which connect the prefrontal cortex (PFC), the basal ganglia and the cerebellum via the thalamus are believed to serve as neuroanatomical substrates of executive processing. This paper focuses on information processing related to executive functions by the PFC and related subcortical regions. Findings are mainly derived from neuropsychological investigations of brain-damaged patients but also from imaging studies in healthy subjects. There is evidence for subtle differences between these regions with respect to the cognitive mechanisms contributing to inhibition of habitual responses, task management/multitasking and set shifting, although the data base is sparse so far.

Basal Ganglia↗