Biomedical subjects

S Zysset

Publications and source records attributed to S Zysset.

9 recordsLinked to original sources

PubMed2006

The effects of insulin on the central nervous system--focus on appetite regulation.

Appetite and satiety are subject to complex regulation, with neuroendocrine mechanisms playing an important role. The central nervous system is attracting increasing attention as a target tissue for many hormones such as leptin, PYY3-36, ghrelin, glucagon-like-peptide 1 and many others. Among its many well-known functions, insulin is also a potent anorexigenic hormone, and insulin receptors are widely distributed throughout the central nervous system. One way to advance our understanding of central nervous regulation of hunger and satiety in humans is to develop suitable neuroimaging techniques for use in various clinical and experimental conditions. Several studies have been performed using functional magnetic resonance imaging and positron emission tomography to identify areas of the brain that are differentially activated by alteration of the feeding state. These preliminary data are taking shape as a complex neuronal network involving the hypothalamus, thalamus, limbic and paralimbic areas including the insular cortex and the anterior cingulate gyrus and the orbitofrontal cortex. Continuous efforts to understand hormonal effects on these pathways may advance our understanding of human obesity.

Animals↗

PubMed2001

Retrieval of long and short lists from long term memory: a functional magnetic resonance imaging study with human subjects.

Previous studies have shown that reaction time in an item-recognition task with both short and long lists is a quadratic function of list length. This suggests that either different memory retrieval processes are implied for short and long lists or an adaptive process is involved. An event-related functional magnetic resonance imaging study with nine subjects and list lengths varying between 3 and 18 words was conducted to identify the underlying neuronal structures of retrieval from long and short lists. For the retrieval and processing of word-lists a single fronto-parietal network, including premotor, left prefrontal, left precuneal and left parietal regions, was activated. With increasing list length, no additional regions became involved in retrieving information from long-term memory, suggesting that not necessarily different, but highly adaptive retrieval processes are involved.

Adult↗

PubMed2001

Color-word matching stroop task: separating interference and response conflict.

The Stroop interference task requires a person to respond to a specific dimension of a stimulus while suppressing a competing stimulus dimension. Previous PET and fMRI studies using the Color Stroop paradigm have shown increased activity in the "cognitive division" of the cingulate cortex. In our fMRI study with nine subjects, we used a Color-Word Matching Stroop task. A frontoparietal network, including structures in the lateral prefrontal cortex, the frontopolar region, the intraparietal sulcus, as well as the lateral occipitotemporal gyrus, was activated when contrasting the incongruent vs the neutral condition. However, no substantial activation in either the right or left hemisphere of the anterior cingulate cortex (ACC) was detected. In accordance with a series of recent articles, we argue that the ACC is not specifically involved in interference processes. The ACC seems rather involved in motor preparation processes which were controlled in the present Color-Word Matching Stroop task. We argue that the region around the banks of the inferior frontal sulcus is required to solve interference problems, a concept which can also be seen as a component of task set management.

Adult↗

PubMed2001

The inhibition of imitative response tendencies.

Recent neurocognitive studies show that perception and execution of actions are intimately linked. The mere observation of an action seems to evoke a tendency to execute that action. Since such imitative response tendencies are not adaptive in many everyday situations imitative response tendencies usually have to be inhibited. These inhibitory processes have never been investigated using brain imaging techniques. Former work on response inhibition and interference control has focused on paradigms such as the Stroop task or the go/no-go task. We have carried out an event-related functional magnetic resonance imaging study in order to investigate the cortical mechanisms underlying the inhibition of imitative responses. The experiment employs a simple response task in which subjects were instructed to execute predefined finger movements (tapping or lifting of the index finger) in response to an observed congruent or incongruent finger movement (tapping or lifting). A comparison of brain activation in incongruent and congruent trials revealed strong activation in the dorsolateral prefrontal cortex (middle frontal gyrus) and activation in the right frontopolar cortex and the right anterior parietal cortex, as well as in the precuneus. These results support the assumption of prefrontal involvement in response inhibition and extend this assumption to a "new" class of prepotent responses, namely, to imitative actions.

Adult↗

PubMed2001

Crossed nonaphasia in a dextral with left hemispheric lesions: a functional magnetic resonance imaging study of mirrored brain organization.

BACKGROUND: General conclusions concerning mechanisms of cerebral lateralization may be learned from the investigation of functional brain organization in patients with anomalous lateralization. CASE DESCRIPTION: The functional organization of language, attention, and motor performance was investigated in a 42-year-old patient with crossed nonaphasia by means of functional MRI. The strongly right-handed man experienced a left middle cerebral artery infarction documented by MRI without exhibition of aphasia. However, the left hemispheric stroke was accompanied by visuospatial impairment, right-sided slight sensory and motor paresis, and right homonymous hemianopia. No history of familial sinistrality or prior neurological illness was present. Functional MR language mapping revealed strong right hemispheric activation in inferior frontal and superior temporal cortices. Finger tapping with the right hand recruited ipsilateral premotor and motor areas as well as supplementary motor cortex. A Stroop task, usually strongly associated with left-sided inferior frontal activation in dextrals, resulted in strong right hemispheric frontal activation. CONCLUSIONS: From our data there is clear evidence that different modalities, such as language perception and production, attention, and motor performance, are processed exclusively by 1 hemisphere when atypical cerebral dominance is present.

Aphasia↗

PubMed2000

Dissociation of memory retrieval and search processes: an event-related fMRI study.

A cognitive task can often be subdivided into several subprocesses, which follow a specific temporal order. Here, we report an event-related functional magnetic resonance imaging (fMRI) experiment on memory search, in which the temporal onset of search in primary memory was varied relative to retrieval from secondary memory. Furthermore, previous behavioral studies demonstrated that search times in primary memory depend on the number of items in a memory set, whereas retrieval from secondary memory is a set-size independent process. We analyzed the dependency of the blood oxygenation level dependent (BOLD)-response on the temporal onset of memory search on the one hand and on memory set size on the other hand to differentiate the contribution of retrieval from secondary memory, maintenance in primary memory, item search in primary memory, and response-related processes. The timing of activation followed cue presentation bilaterally in the middle frontal gyri (Brodmann area (BA) 9,46) and the inferior parts of the precentral gyri (BA6). In all other regions of interest (ROI), supplementary motor area (SMA), posterior parietal cortex, antero-superior insula, and primary motor cortex, the onset of activation was delayed with delayed probe presentation, ruling out participation in retrieval from secondary memory. The amplitude of the BOLD-response increased with increasing memory set size in all ROI except primary motor cortex and left posterior parietal cortex. All areas with cue-associated BOLD onset, suggesting involvement in retrieval, showed prolonged BOLD activation, suggesting that they also support maintenance of the retrieved information.

Adult↗

PubMed2000

Nonlinear regression of functional MRI data: an item recognition task study.

A classical item-recognition task was used to examine human verbal working memory in an event-related functional MRI (fMRI) study. A highly flexible experimental design incorporated a broad variation of memory load and delay time. This design allows for only three or four repetitions per stimulus condition. In a first step, linear regression analysis was applied to locate functional activation in the fMRI data. As a second step, the time course of the hemodynamic response (HR) was analyzed using nonlinear regression, which served to quantify the dependency between HR shape properties and stimulation conditions in several regions-of-interest. On the basis of this study, a closer description of the frontoparietal network involved in verbal working memory was possible.

Adult↗

PubMed1999

Application of double voxel functional spectroscopy to event-related cognitive experiments.

The hemodynamic response to functional activation can be regarded as the convolution of the neuronal response with an unknown kernel. As such, it introduces an intrinsic blurring that limits the attainable temporal resolution of functional magnetic resonance (fMR) techniques. This study demonstrates that by measurement of displacements in activation onsets between different types of trial, it is nevertheless possible to obtain a subsecond temporal accuracy in fMR. A single trial stimulation paradigm was adopted: a simple search task embedded in a longer period of visual flicker stimulation that produced reliable activations in the primary visual cortex and supplementary motor area. Data were acquired from both of these regions using double voxel functional spectroscopy.

Evoked Potentials, Visual↗

PubMedDate not supplied

LIPSIA--a new software system for the evaluation of functional magnetic resonance images of the human brain.

This paper describes the non-commercial software system LIPSIA that was developed for the processing of functional magnetic resonance images (fMRI) of the human brain. The analysis of fMRI data comprises various aspects including filtering, spatial transformation, statistical evaluation as well as segmentation and visualization. In LIPSIA, particular emphasis was placed on the development of new visualization and segmentation techniques that support visualizations of individual brain anatomy so that experts can assess the exact location of activation patterns in individual brains. As the amount of data that must be handled is enormous, another important aspect in the development LIPSIA was the efficiency of the software implementation. Well established statistical techniques were used whenever possible.

Brain↗