Functional organization of the left inferior precentral sulcus: dissociating the inferior frontal eye field and the inferior frontal junction.

Two eye fields have been described in the human lateral frontal cortex: the frontal eye field (FEF) and the inferior frontal eye field (iFEF). The FEF has been extensively studied and has been found to lie at the ventral part of the superior precentral sulcus. Much less research, however, has focused on the iFEF. Recently, it was suggested that the iFEF is located at the dorsal part of the inferior precentral sulcus. A similar location was proposed for the inferior frontal junction area (IFJ), an area thought to be involved in cognitive control processes. The present study used fMRI to clarify the topographical and functional relationship of the iFEF and the IFJ in the left hemispheres of individual participants. The results show that both the iFEF and the IFJ are indeed located at the dorsal part of the inferior precentral sulcus. Nevertheless, the activations were spatially dissociable in every individual examined. The IFJ was located more towards the depth of the inferior precentral sulcus, close to the junction with the inferior frontal sulcus, whereas the iFEF assumed a more lateral, posterior and superior position. Furthermore, the results provided evidence for a functional double dissociation: the iFEF was activated only in a comparison of saccades vs. button presses, but not in a comparison of incongruent vs. congruent Stroop conditions, while the opposite pattern was found at the IFJ. These results provide evidence for a spatial and functional dissociation of two directly adjacent areas in the left posterior frontal lobe.

[Survey of risks related to static magnetic fields in ultra high field MRI]. / Bestandsaufnahme zu Risiken durch statische Magnetfelder im Zusammenhang mit der Ultrahochfeld-MRT.

In magnetic resonance imaging (MRI), substantial improvements with respect to sensitivity are expected due to the development of so-called ultra high field scanners, i. e., whole-body scanners with a magnetic field strength of 7 T or above. Users of this technology need to evaluate this benefit for potential risks since commercially available systems are not certified as a medical device for human use. This review provides a detailed survey of static field bioeffects related to the exposure of subjects being scanned, to occupational exposure, and to exposure of the general public under consideration of current standards and directives. According to present knowledge, it is not expected that exposure of human subjects to static magnetic fields of 7 T implies a specific risk of damage or disease provided that known contraindications are observed. The available database does not permit definition of exact thresholds for harmful effects. However, experience from previous application of ultra high field MRI indicates that transient phenomena, such as vertigo, nausea, metallic taste, or magneto-phosphenes, are more frequently observed. In particular, movements in the field or the gradient of the fringe field seem to lead to detectable effects. Besides such observations, there is a strong demand for systematic investigation of potential interaction mechanisms related to static field exposure during MRI examinations.

Selective visual dimension weighting deficit after left lateral frontopolar lesions.

The left lateral frontopolar (LFP) cortex showed dimension change-related activation in previous event-related functional magnetic resonance imaging studies of visual singleton feature search with non-brain-lesioned participants. Here, we tested the hypothesis that LFP actively supports changes of attention from the old to the new target-defining dimension in singleton feature search. Singleton detection was selectively slowed in this task when the target-defining dimension changed in patients with left LFP lesions, compared with patients with frontomedian lesions as well as with matched controls without brain lesions. We discuss a potential role of LFP in change detection when the optimal allocation of dimension-based attention is not clearly defined by the task.

Connectivity-Based Parcellation of Broca's Area.

It is generally agreed that the cerebral cortex can be segregated into structurally and functionally distinct areas. Anatomical subdivision of Broca's area has been achieved using different microanatomical criteria, such as cytoarchitecture and distribution of neuroreceptors. However, brain function also strongly depends upon anatomical connectivity, which therefore forms a sensible criterion for the functio-anatomical segregation of cortical areas. Diffusion-weighted magnetic resonance (MR) imaging offers the opportunity to apply this criterion in the individual living subject. Probabilistic tractographic methods provide excellent means to extract the connectivity signatures from diffusion-weighting MR data sets. The correlations among these signatures may then be used by an automatic clustering method to identify cortical regions with mutually distinct and internally coherent connectivity. We made use of this principle to parcellate Broca's area. As it turned out, 3 subregions are discernible that were identified as putative Brodmann area (BA) 44, BA45, and the deep frontal operculum. These results are discussed in the light of previous evidence from other methods in both human and nonhuman primates. We conclude that plausible results can be achieved by the proposed technique, which cannot be obtained by any other method in vivo. For the first time, there is a possibility to investigate the anatomical subdivision of Broca's area noninvasively in the individual living human subject.

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.

Cognitive priming in sung and instrumental music: activation of inferior frontal cortex.

Neural correlates of the processing of musical syntax-like structures have been investigated via expectancy violation due to musically unrelated (i.e., unexpected) events in musical contexts. Previous studies reported the implication of inferior frontal cortex in musical structure processing. However - due to the strong musical manipulations - activations might be explained by sensory deviance detection or repetition priming. Our present study investigated neural correlates of musical structure processing with subtle musical violations in a musical priming paradigm. Instrumental and sung sequences ended on related and less-related musical targets. The material controlled sensory priming components, and differences in target processing required listeners' knowledge on musical structures. Participants were scanned with functional Magnetic Resonance Imaging (fMRI) while performing speeded phoneme and timbre identification judgments on the targets. Behavioral results acquired in the scanner replicated the facilitation effect of related over less-related targets. The blood oxygen level-dependent (BOLD) signal linked to target processing revealed activation of right inferior frontal areas (i.e., inferior frontal gyrus, frontal operculum, anterior insula) that was stronger for less-related than for related targets, and this was independent of the material carrying the musical structures. This outcome points to the implication of inferior frontal cortex in the processing of syntactic relations also for musical material and to its role in the processing and integration of sequential information over time. In addition to inferior frontal activation, increased activation was observed in orbital gyrus, temporal areas (anterior superior temporal gyrus, posterior superior temporal gyrus and sulcus, posterior middle temporal gyrus) and supramarginal gyrus.

Clinical insights into paraneoplastic cerebellar degeneration.

Neuroimaging is usually unremarkable in paraneoplastic cerebellar degeneration (PCD), at least in the early stages of the disease. A patient with proven PCD is reported in whom it could be shown that cerebellar atrophy evolved very rapidly and was present in early imaging studies. Even with the use of the whole spectrum of modern diagnostic tools, the underlying malignancy can be difficult to diagnose. In addition to mammography, MRI is recommended in these cases and repeat FDG-PET may be necessary.

A construction of an averaged representation of human cortical gyri using non-linear principal component analysis.

Because of the complex shape of human cortical gyri and great variation between individuals, development of effective representation schemes which allow establishment of correspondence between individuals, extraction of average structure of a population, and co-registration has proved very difficult. We introduce an approach which extracts line representations of gyri at different depths from high resolution MRI, labels main gyri semi-automatically, and extracts a template from a population using non-linear principal component analysis. The method has been tested on data from 96 healthy human volunteers. The model captures the most salient shape features of all major cortical gyri, and can be used for inter-subject registration, for investigating regionalized inter-subject variability, and for inter-hemispheric comparisons.

Revisiting the role of Broca's area in sentence processing: syntactic integration versus syntactic working memory.

Most previous neuroimaging studies of sentence processing have associated Broca's area with syntactic processing; however, the exact nature of the processes subserved by this brain region is yet not well understood. Although some authors suggest that Brodmann area (BA) 44 of the left inferior frontal gyrus (i.e., Broca's area) is relevant for syntactic integration processes, others claim that it is associated with working memory mechanisms relevant for language processing. To dissociate these two possible functions, the present study investigated hemodynamic responses elicited while participants processed German indirect wh-questions. Activation increases were observed in left BA 44 together with superior temporal areas and right hemispheric homologues for sentences with noncanonical word order, in which a verb argument was dislocated from its canonical position over a relatively long distance. In these sentences, syntactic working memory load was assumed to be greatest. In contrast, no activation increase was elicited by object-initial as opposed to subject-initial sentences that did not differ with respect to working memory costs but with respect to syntactic integration costs. These data strongly suggest that Broca's area plays a critical role in syntactic working memory during online sentence comprehension.

Closed head injury and perceptual processing in dual-task situations.

Using a classical psychological refractory period (PRP) paradigm we investigated whether increased interference between dual-task input processes is one possible source of dual-task deficits in patients with closed-head injury (CHI). Patients and age-matched controls were asked to give speeded motor reactions to an auditory and a visual stimulus. The perceptual difficulty of the visual stimulus was manipulated by varying its intensity. The results of Experiment 1 showed that CHI patients suffer from increased interference between dual-task input processes, which is related to the salience of the visual stimulus. A second experiment indicated that this input interference may be specific to brain damage following CHI. It is not evident in other groups of neurological patients like Parkinson's disease patients. We conclude that the non-interfering processing of input stages in dual-tasks requires cognitive control. A decline in the control of input processes should be considered as one source of dual-task deficits in CHI patients.

Splenial lesions lead to supramodal target detection deficits.

Patients with lesions of the splenium showed higher validity effects of visuospatial cues than did patients with partial lesions of the corpus callosum anterior to the splenium and control participants. Many of the patients tested had also shown a left-ear suppression for consonant-vowel syllables in a previous dichotic listening study. The authors interpret these parallel findings as evidence for the disruption of signals that normally alert the individual to the presence of behaviorally relevant stimuli, possibly originating in the temporoparietal junction area. After splenial lesions, these signals may not reach the contralateral hemisphere, leading to supramodal deficits in target detection, especially under distracting conditions.

[Mrt-based morphometry. A current assessment]. / MRT-basierte Morphometrie Eine Bestandsaufnahme.

Morphometry offers new approaches for in vivo characterization of many neurologic and psychiatric pathologies. A survey of recent publications only hints at the attractiveness of magnetic resonance-based morphometry: published findings are heterogeneous, partly contradictory, and not always plausible in terms of known neuropathologic correlates. Hence, the sensitivity of the applied methods should be questioned. Three parameters affect the variance in morphometric findings: (1) knowledge about normal morphologic variability, (2) confounding physiologic parameters, and (3) methodologic misuse. Sound knowledge about the morphologic variability of the normal brain is vital for the assessment of volumetric findings. Large morphologic variability may also interfere with the precision of morphometric methods. The multitude of possible confounding physiologic parameters raises the necessity of precise subject control. Magnetic resonance scanning artefacts require rigid protocols, and application of the rather complex and sensitive methods demands profound insight into the techniques.

[Long-term life changes and stress sequelae for spouses of stroke patients]. / Langfristige Lebensveränderungen und Belastungsfolgen bei Ehepartnern von Schlaganfallpatienten.

OBJECTIVE: This study investigates the long-term effect of stroke on the quality of life and health of patients' spouses. METHOD: Twenty-six spouses of stroke patients were interviewed by means of standardized questionnaires and qualitative interviews. The study participants had been living with the consequences of stroke for 3 years on average when the interviews were carried out. RESULTS: A stroke is often followed by considerable changes in everyday life and by role shifts within the relationship. In particular, depressive and aggressive changes in the patient's behaviour are experienced as burdensome. In addition to impairments in quality of life, psychological and psychosomatic troubles can also from the burden experienced. Depressive symptoms are the main factor in these negative consequences: the more a patient is assessed as depressive, the more his/her spouse reports health problems and poor quality of life. DISCUSSION: Long-term changes in everyday life and partnership can bring about significant chronic burden for the spouses of stroke patients. Hence, offers of support and counseling are required not only in the acute and post-acute stages of stroke, but also after inpatient rehabilitation has ended.

Impaired hemodynamics and neural activation? A fMRI study of major cerebral artery stenosis.

Functional MRI motor mapping was performed in two women with unilateral high-grade stenosis of the middle cerebral artery (MCA) to determine the influence of impaired hemodynamics on the blood oxygenation level dependent (BOLD) response. In both patients no structural lesions were present in primary motor pathways. A redistribution of the motor network to the healthy hemisphere was the main indicator of chronic hemodynamic compromise.

Analyzing the neocortical fine-structure.

Cytoarchitectonic fields of the human neocortex are defined by characteristic variations in the composition of a general six-layer structure. It is commonly accepted that these fields correspond to functionally homogeneous entities. Diligent techniques were developed to characterize cytoarchitectonic fields by staining sections of post-mortem brains and subsequent statistical evaluation. Fields were found to show a considerable interindividual variability in extent and relation to macroscopic anatomical landmarks. With upcoming new high-resolution magnetic resonance imaging (MRI) protocols, it appears worthwhile to examine the feasibility of characterizing the neocortical fine-structure from anatomical MRI scans, thus, defining neocortical fields by in vivo techniques. A fixated brain hemisphere was scanned at a resolution of approximately 0.3 mm. After correcting for intensity inhomogeneities in the dataset, the cortex boundaries (the white/grey matter and grey matter/background interfaces) were determined as a triangular mesh. Radial intensity profiles following the shortest path through the cortex were computed and characterized by a sparse set of features. A statistical similarity measure between features of different regions was defined, and served to define the extent of Brodmann's Areas 4, 17, 44 and 45 in this dataset.

Intracerebral haemorrhage as a manifestation of Lyme neuroborreliosis?

Lyme Neuroborreliosis (LNB) has repeatedly been reported to cause cerebral vasculitis. However, there is no reliable information about the incidence of cerebral vessel affection. The majority of reports deal with ischaemic consequences, and there are a few reports of subarachnoid haemorrhage (SAH). We report a case of otherwise unexplained intracerebral haemorrhage (ICH) where clinical and laboratory tests have shown LNB. Late stage LNB might not only cause ischaemic, but haemorrhagic stroke as well.