Lesion-site affects grammatical gender assignment in German: perception and production data.

Two experiments investigated phonological, derivational-morphological and semantic aspects of grammatical gender assignment in a perception and a production task in German aphasic patients and age-matched controls. The agreement of a gender indicating adjective (feminine, masculine or neuter) and a noun was evaluated during perception in Experiment 1 (grammaticality judgment). In Experiment 2 the same participants had to produce the matching definite article to a noun. In the perception task patients with left frontal lesions (LF) made more errors during phonological gender assignment as compared to derivational-morphological and semantic gender assignment, while patients with lesions of the posterior superior temporal gyrus (pSTG) made more errors in derivational-morphological gender assignment as compared to phonological and semantic gender assignment. In the production task no differences between patient groups were found. These data support previous evidence that left frontal brain areas are critically involved in phonological processing. The pSTG on the other hand may be critically engaged in the integration of phonological and lexical information essential for phonological and derivational-morphological gender assignment.

Do quiescent arachnoid cysts alter CNS functional organization?: A fMRI and morphometric study.

OBJECTIVE: To investigate whether congenital and clinically quiescent arachnoid cysts (AC) in the left temporal fossa alter the functional organization of adjacent cortices. METHODS: fMRI mapping was applied in five right-handed asymptomatic patients to determine the functional organization of language. Moreover, morphometry was performed in each patient to gain the size of cortical surface areas and cortical thickness values in the neighboring brain adjacent to the AC and explicitly in the left opercular region. RESULTS: Four patients showed a clear left hemisphere language dominance regardless of the cyst size; a mixed laterality of language organization was found in the remaining patient. An interesting dissociation of morphometric data was assessed when comparing strongly language-related cortices in the inferior frontal gyrus with the entire neighboring cortices. Morphometry in the neighboring brain regions of the AC showed 1) overall reduced cortical surface areas and 2) a decrease in cortical thickness compared to the homologous right side. However, the surface area of the fronto-opercular region in the left inferior frontal gyrus-i.e., the pars triangularis and the pars opercularis-was larger on the left as compared to the right side. Both structures have earlier been identified to represent the morphologic substrate of language dominance in the left hemisphere. CONCLUSION: Arachnoid cysts do not disturb the normal asymmetry of hemisphere language organization despite delicate locations adjacent to the left inferior frontal gyrus.

Dynamic patterns make the premotor cortex interested in objects: influence of stimulus and task revealed by fMRI.

Research in monkey and man indicates that the ventrolateral premotor cortex (PMv) underlies not only the preparation of manual movements, but also the perceptual representation of pragmatic object properties. However, visual stimuli without any pragmatic meaning were recently found to elicit selective PMv responses if they were subjected to a perceivable pattern of change. We used functional magnetic resonance imaging (fMRI) to investigate if perceptual representations in the PMv might apply not only to pragmatic, but also to dynamic stimulus properties. To this end, a sequential figure matching task that required the processing of dynamic features was contrasted with a non-figure control task (Experiment 1) and an individual figure matching task (Experiment 2). In order to control for potential influences of stimulus properties that might be associated with pragmatic attributes, different types of abstract visual stimuli were employed. The experiments yielded two major findings: if their dynamic properties are attended, then abstract 2D visual figures are sufficient to trigger activation within premotor areas involved in hand-object interaction. Moreover, these premotor activations are independent from stimulus properties that might relate to pragmatic features. The results imply that the PMv is engaged in the processing of stimuli that are usually or actually embedded within either a pragmatic or a dynamic context.

Transient global ischemia specifically modulates visual P300 scalp distribution.

OBJECTIVE: Latency, amplitude, and scalp topography of the visual P300 component was examined in patients who had suffered from transient global ischemia (TGI) due to cardiac arrest and in age matched clinical and healthy controls in order to investigate the diagnostic value of this component. METHOD: Event-related potentials (ERPs) were recorded from 19 scalp electrodes in a visual oddball paradigm. RESULTS: Mean latency of the P300 component was prolonged in both patient groups. Changes in scalp distribution of the P300, however, appear to be specific to anoxic-ischemic encephalopathy. In particular, a selective reduction of the P300 amplitudes at posterior recording sites was observed in TGI patients. Moreover, examination of the auditory P300 in TGI patients revealed that this selective change seems to be restricted to the visual modality. CONCLUSION: The results are discussed with respect to selective vulnerability of brain tissue to hypoxic-ischemic injury. After TGI a modality-specific subset of P300 generators, probably located in the transitional parieto-occipital and extrastriate occipital cortex, appears to be affected. It is also noted, that the visual P300 component could serve as an additional marker of TGI especially in patients who do not show neuropathological changes in structural brain images.

Alignment of magnetic-resonance brain datasets with the stereotactical coordinate system.

Neuroanatomical and neurofunctional studies are often referenced to high-resolution magnetic-resonance brain datasets. For the analysis of the cortical surface, mapping of functional information on to the cortex or visualization, it is necessary to remove the outer surfaces of the brain. For intersubject comparison, it is useful to align the dataset with a coordinate system and introduce a spatial normalization. We describe an image processing chain that combines all of these steps in an interaction-free procedure. We report on a period of 2 years of routine application of this procedure, with >250 successfully processed datasets from healthy subjects and patients with various forms of brain damage.

Creative cognition and the brain: dissociations between frontal, parietal-temporal and basal ganglia groups.

The objective of the study was to investigate creativity in relation to brain function by assessing creative thinking in various neurological populations. Several measures were employed to assess different facets of creative thinking in clinical groups with frontal lobe, basal ganglia or parietal-temporal lesions relative to matched healthy control participants. The frontal group was subdivided into frontolateral, frontopolar and frontal-extensive groups. Hierarchical regression analyses were employed to assess the significance levels associated with the effects after accounting for IQ differences between the groups. Findings were only considered noteworthy if they at least suggested the presence of a strong trend and were accompanied by medium to large effect sizes. The parietal-temporal and frontolateral groups revealed poorer overall performance with the former demonstrating problems with fluency related measures, whereas the latter were also less proficient at producing original responses. In contrast, the basal ganglia and frontopolar groups demonstrated superior performance in the ability to overcome the constraints imposed by salient semantic distractors when generating creative responses. In summary, the dissociations in the findings reveal the selective involvement of different brain regions in diverse aspects of creativity. Lesion location posed selective limitations on the ability to generate original responses in different contexts, but not on the ability to generate relevant responses, which was compromised in most patient groups. The noteworthy findings from this exploratory study of enhanced performance in specific aspects of creative cognition following brain damage are discussed with reference to the generic idea that superior creative ability can result from altered brain function.

Neurovascular coupling is impaired in cerebral microangiopathy--An event-related Stroop study.

Small-vessel disease or cerebral microangiopathy is a common finding in elderly people leading finally to subcortical ischemic vascular dementia. Because cerebral microangiopathy impairs vascular reactivity and affects mainly the frontal lobes, we hypothesized that brain activation decreases during an event-related color-word matching Stroop task. 12 patients suffering from cerebral microangiopathy were compared with 12 age-matched controls. As an imaging method we applied functional near-infrared spectroscopy, because it is particularly sensitive to the microvasculature. The Stroop task led to activations in the lateral prefrontal cortex. Generally, the amplitude of the hemodynamic response was reduced in patients in tight correlation with behavioral slowing during the Stroop task and with neuropsychological deficits, namely attentional and executive dysfunction. Interestingly, patients showed an early deoxygenation of blood right after stimulation onset, and a delay of the hemodynamic response. Whereas the amplitude of the hemodynamic response is reduced in the frontal lobes also with normal aging, data suggest that impairments of neurovascular coupling are specific for cerebral microangiopathy. In summary, our findings indicate frontal dysfunction and impairments of neurovascular coupling in cerebral microangiopathy.

Towards a nosology for frontotemporal lobar degenerations-a meta-analysis involving 267 subjects.

Frontotemporal lobar degeneration is the second most common diagnosis of dementia in individuals younger than 65 years. We conducted a systematic and quantitative meta-analysis to examine neural correlates of frontotemporal lobar degeneration and its subtypes and to place the disease in a framework of cognitive neuropsychiatry. MedLine and Current Contents search engines were used to identify functional and anatomical imaging studies investigating frontotemporal lobar degeneration between 1980 and 2005. Studies were included, if they were peer-reviewed, applied internationally recognized diagnostic criteria, were original studies, and had results normalized to a stereotactic space. 19 studies were identified reporting either atrophy or decreases in glucose utilization. Finally, the analysis involved 267 subjects suffering from frontotemporal lobar degeneration and 351 control subjects. A quantitative meta-analysis was performed. Maxima of the studies resulted in activation likelihood estimates. The meta-analysis revealed specific neural networks for each of the three clinically defined subtypes of frontotemporal lobar degeneration, namely frontotemporal dementia, semantic dementia, and progressive non-fluent aphasia. Networks did not overlap as shown by a conjunction analysis, and they corresponded to clinical characteristics. The study relates the clinical features of each subtype of frontotemporal lobar degeneration specifically to its neural substrate. By 'triple dissociating' frontotemporal lobar degenerations into three clinicoanatomical prototypes, the study contributes to placing these disorders in cognitive neuropsychiatry and suggests a respective nosology.

Correlation of cognitive status, MRI- and SPECT-imaging in CADASIL patients.

Although there is evidence for correlations between disability and magnetic resonance imaging (MRI) total lesion volume in autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), the significance of structural MRI abnormalities for cognitive dysfunction remains controversial. We performed detailed neuropsychological testing, high resolution MRI, and Tc-99m-ethyl cysteinate-dimer SPECT in three CADASIL patients. MR-images were rated independently by two investigators for the presence of white matter lesions, lacunar infarcts, microbleeds, and ventricular enlargement. Cortical atrophy was quantified by the use of automatic morphometric assessment of the cortical thickness. In addition, laboratory and patients' history data were collected in order to assess the individual vascular risk factor profile. The differences in cognitive performance between the three patients are neither explained by structural-, or functional neuroimaging, nor by the patient-specific vascular risk factor profiles. The neuroradiologically least affected patient met criteria for dementia, whereas the most severely affected patient was in the best clinical and cognitive state. Conventional structural and functional neuroimaging is important for the diagnosis of CADASIL, but it is no sufficient surrogate marker for the associated cognitive decline. Detailed neuropsychological assessment seems to be more useful, particularly with respect to the implementation of reliable outcome parameters in possible therapeutic trials.

Clients' view of neuropsychological rehabilitation.

Postacute neuropsychological rehabilitation cannot be done successfully without the personal engagement of the brain-injured client. However, systematically collected data referring to clients' satisfaction with rehabilitation programmes are rare. In this study a structured interview was developed to assess various aspects of treatment evaluation by clients. In addition, handicap was judged by primary therapists. An aetiologically mixed sample of 130 mildly to moderately brain-injured clients undergoing a comprehensive neuropsychological rehabilitation programme was investigated. About two-thirds of the sample seemed content with the training programmes whereas a minority (13%) of mostly highly handicapped persons reported being largely discontented. In this respect no differences between cognitive, speech/language, and physical therapies were found. Even though many subjects were satisfied with the programme, a majority of clients desired a substantial amelioration in the future (80%), judged their life quality as reduced in comparison to the time preceding brain injury (77%), reported difficulties in accepting 'deficits' (52%), and were frightened of becoming dependent on others (52%).

Gender differences in the activation of inferior frontal cortex during emotional speech perception.

We investigated the brain regions that mediate the processing of emotional speech in men and women by presenting positive and negative words that were spoken with happy or angry prosody. Hence, emotional prosody and word valence were either congruous or incongruous. We assumed that an fRMI contrast between congruous and incongruous presentations would reveal the structures that mediate the interaction of emotional prosody and word valence. The left inferior frontal gyrus (IFG) was more strongly activated in incongruous as compared to congruous trials. This difference in IFG activity was significantly larger in women than in men. Moreover, the congruence effect was significant in women whereas it only appeared as a tendency in men. As the left IFG has been repeatedly implicated in semantic processing, these findings are taken as evidence that semantic processing in women is more susceptible to influences from emotional prosody than is semantic processing in men. Moreover, the present data suggest that the left IFG mediates increased semantic processing demands imposed by an incongruence between emotional prosody and word valence.

Event-related fMRI: comparison of conditions with varying BOLD overlap.

Recently, event-related fMRI-experiments have been reported in which subsequent trials were separated by only 2 sec or less. Because the BOLD response needs 10 sec and longer to return to baseline, the event-related signal in these experiments has to be extracted from the overlapping responses elicited by successive trials. Usually it is assumed that this convolved signal is a summation of the overlapping BOLD responses. We tested this assumption by comparing event-related signals in conditions with little and with substantial BOLD overlap in two fMRI experiments of a task-switching paradigm. We analyzed the difference in the activational time course elicited by a critical task and a baseline task when trials of both tasks were separated by intertrial intervals of 15 sec or when the critical trials were embedded in a stream of baseline trials with ISI = 1 sec. The change of the BOLD signal elicited by the critical trials showed a high correspondence between both experiments in five out of six cortical ROI. Our data support the view that BOLD overlap leads to largely linear signal changes. In the present study, task-related increases in the BOLD response were detected equally well with substantial BOLD overlap as with mostly nonoverlapping BOLD responses.

A new concept for EEG/MEG signal analysis: detection of interacting spatial modes.

We propose a new concept for analyzing EEG/MEG data. The concept is based on a projection of the spatiotemporal signal into the relevant phase space and the interpretation of the brain dynamics in terms of dynamical systems theory. The projection is obtained by a simultaneous determination of spatial modes and coefficients of differential equations. The resulting spatiotemporal model can be characterized by stationary points and corresponding potential field maps. Brain information processing can be interpreted by attraction and repulsion of spatial field distributions given by these stationary points. This allows an objective and quantitative characterization of the brain dynamics. We outline this concept and the underlying algorithm. Results of the application of this method to an event related potential (ERP) study of auditory memory processes are discussed.

Sequence learning in Parkinson's disease: the effect of spatial stimulus-response compatibility.

Patients with Parkinson's disease (PD) have repeatedly demonstrated reduced sequence-specific learning effects in serial reaction time tasks (SRTs). Previous research with PD patients has mainly employed the 'classical' SRT task, involving a spatially compatible assignment of stimuli and responses. From cognitive research, it is known that spatial compatibility triggers rapid, automatic responses in the direction of the stimulus. Automatic responding has shown to be disinhibited in PD patients and may therefore interfere with stimulus anticipation during the learning process. The aim of the present study was to test this hypothesis by investigating if reduced sequence-specific learning depends on spatial stimulus-response compatibility. PD patients and age-matched controls were examined either with an SRT variant involving central stimulus presentation, thereby preventing automatic linking of stimulus and response locations, or with a spatially compatible SRT task. Patients showed reduced sequence-specific learning effects only when the stimulus-response assignment was spatially compatible. This pattern of results confirms the hypothesis that sequence learning deficits in PD may result from a predominance of automatic response activation over learning-based stimulus anticipations during the learning phase.

Near-infrared spectroscopy can detect brain activity during a color-word matching Stroop task in an event-related design.

Brain activity can be monitored non-invasively by near-infrared spectroscopy (NIRS), which has several advantages in comparison with other imaging methods, such as flexibility, portability, low cost and biochemical specificity. Moreover, patients and children can be repetitively examined. Therefore, the objective of the study was to test the feasibility of NIRS for the event-related approach in functional brain activation studies with cognitive paradigms. Thus, changes in the concentration of oxy-, deoxy-, and total hemoglobin were measured by NIRS in 14 healthy subjects while performing a color-word matching Stroop task in an event-related design. The hemodynamic response (increase in the concentration of oxy-/total hemoglobin and decrease in the concentration of deoxy-hemoglobin) was stronger during incongruent compared to congruent and neutral trials of the Stroop task in the lateral prefrontal cortex bilaterally. This stronger hemodynamic response was interpreted as a stronger brain activation during incongruent trials of the Stroop task, due to interference. A new method for NIRS data evaluation that enables the analysis of the hemodynamic response to each single trial is introduced. Each hemodynamic response was characterized by the parameters gain, lag and dispersion of a Gaussian function fitted by nonlinear regression. Specific differences between the incongruent and neutral condition were found for gain and lag. Further, these parameters were correlated with the behavioral performance. In conclusion, brain activity may be studied by NIRS using cognitive stimuli in an event-related design. Hum. Brain Mapping 17:61-71, 2002.

Processing of temporal duration information in working memory after frontodorsal tumour excisions.

This study aimed to test the hypothesis that impairments of temporal duration processing after frontal lobe lesions reflect deficits in executive monitoring functions rather than a domain-specific deficit in the maintenance of duration information in working memory. Patients with frontodorsal lesions, clinical controls with post-central lesions, and healthy controls performed recognition and classification tasks, which should allow for testing maintenance and monitoring functions, respectively. Results showed mild non-selective impairments of the frontal patients on both temporal and spatial recognition tasks, but a marked selective degradation on temporal classification while performance on spatial classification was unimpaired. This suggests that maintenance of duration information in working memory after frontal lesions is basically preserved but that, depending on executive task characteristics, there is a specific deficit in the strategic organization of this type of information.