Th.J. Mueller

Loss of functional hemispheric asymmetry in Alzheimer's dementia assessed with near-infrared spectroscopy.

In a total of 10 patients with dementia of the Alzheimer-type (DAT) and in 10 healthy controls near-infrared spectroscopy (NIRS), a new non-invasive optical method, was used to measure the changes of concentrations of oxy- (O2HB) and deoxyhemoglobin (HHB) in left and right hemispheric prefrontal brain tissue areas during performance of the Verbal Fluency Test (VFT). On a neuropsychological level, the healthy subjects performed better in the VFT than patients with DAT. Statistical analysis of the relative concentrations of O2HB and HHB measured with NIRS during performance of the VFT revealed a significant interaction of the hemispheric effects with the diagnosis. A possible interpretation of this finding is that a good performance in the VFT relies on a predominantly left hemispheric activation observed in controls, whereas a low number of correct responses is associated with a loss of this asymmetric activation in patients with DAT. Although both, patients and controls, performed better in the category version of the VFT, the metabolic effects of this task were significantly less pronounced than in the letter version. This indicates that different energy demands, according to the type of access to the memory stores, may be interpreted as the result of a less energy-demanding access to categorically stored information and adds further evidence to the view that memory departments in humans are organized according to categorical principles.

Age-related changes in the brain electrical correlates of response control

OBJECTIVES Previously, a quantification method was validated which, on a single case basis, allows one to assess the NoGo-anteriorisation (NGA) of the positive area of long latency event-related potential (ERP) fields elicited by a cued continuous performance test (CPT). The NGA was shown to be associated with right frontal activity. The present study was conducted to investigate the influence of age and gender on this topographical index of cognitive response control. METHODS Thirty-seven healthy controls were investigated with 21-channel recordings during the execution of a cued CPT, and ERPs of the Go and NoGo condition were obtained. The location of the positive area centroids in a P300 range and the NGA were calculated and related to age and gender by means of correlation analysis and t tests. RESULTS The centroid locations of the brain electrical activity during the NoGo- and the Go-condition of the CPT, were both located in more anterior brain regions with increasing age (P<0.01 and P<0.1, respectively); the NGA, however, was not correlated with the subjects age. Latencies and amplitudes of the Go- and NoGo-centroids were not correlated with age. No gender differences were found. CONCLUSIONS The study showed that age is a source of variance for the positive area centroid locations in this Go-NoGo paradigm. The NGA, on the other hand, was robust to age and gender effects. The result is interpreted as a sign of an increasing contribution of frontal brain areas to cognitive response control during lifespan. The finding is consistent with the age-related topographical changes described in acoustic oddball-paradigms and, therefore, appears to be a general topographical ERP effect.

Distinct neurophysiological mechanisms for manic and cycloid psychoses: evidence from a P300 study on manic patients.

Pathologically asymmetrical P300 fields with right lateralized peaks were described in core schizophrenia as an expression of left‐temporal functional deficits, while higher than normal amplitudes were found in cycloid psychosis. This latter finding appeared to be specific for cycloid psychosis and was explained by a generalized cerebral hyperarousal. Based on some psychopathological analogies with cycloid psychosis, and on the comparable pharmacological treatment of the acute episodes, a group of 19 manic patients was investigated immediately after remission and clinical stabilization of an episode. Patients with psychotic features were excluded to avoid overlaps with cycloid psychosis. Patients showed normal P300 amplitudes and no pathological asymmetries of the field, but more posterior positive areas compared to age‐ and sex‐matched controls. This indicates that the neurophysiological changes underlying mania are different from both core schizophrenia and cycloid psychosis. Based on previous three‐dimensional source location studies, this finding indicates that disinhibition due to reduced frontal lobe activity, and not hyperarousal, is the basic functional mechanism of manic disorders.

Neurophysiological correlates of mental imagery in different sensory modalities

Mental Imagery is supposed to be a basic phenomenon of conscious mental operations, which is exerted in any sensory modality. The aim of the present study was to investigate neurophysiological correlates of mental imagery in the visual, the acoustic and tactile modality. For that purpose, word lists were created based on their power to evoke mental imagery in these modalities. Nine young healthy volunteers were included. Words were presented on a computer screen with 3-s intervals. Evoked electrical activity was recorded simultaneously with a 21-channel system. After inspection for artifacts and off-line averaging, further analysis was performed in a time range of 250-450 ms, corresponding to the P300 component. Within this range, six topographically stable segments were found. A repeated measures ANOVA was significant for the left-right directions of the positive and of the negative centroid, but not for the anterior-posterior directions. The posterior centroid was most right-located in the visual sensory modality and most left-located for tactile imagery; in the acoustic modality it had a midline-position. These differences in centroid locations during mental imagery in different sensory modalities can be explained by the underlying activity of different neural generator ensembles, possibly involving modality specific primary cortical areas.

Functional brain imaging (mapping of EEG) in relation to psychopathologic changes in schizophrenia

Our investigations turned to the EEG, which has the advantages of being noninvasive and of having extremely short analysis times. One aim of our study was to demonstrate that changes in psychopathology in schizophrenia can be demonstrated by electrophysiological methods such as EEG brain mapping

Differences of brain electrical microstates during modality-specific mental imagery

Mental imagery has been investigated mainly in the visual modality. However, imagery is practicable also in other sensory modalities, e.g. as acoustic or tactile sensations. In the present study, ten healthy subjects created mental pictures, sounds or tactile sensations based on words presented on a computer screen. Twenty-one channel (10-20 system, bandpass 0.3-70 Hz, A/D-rate 256 Hz) EEG-recordings were obtained. After careful artifact rejection, off-line averaging and a space-oriented segmentation of the evoked potentials was performed. Within the time interval from 250 to 450 ms post-stimulus, six topographically stable segments were found. In all segments, the orientation of the brain electrical fields differed significantly for the three imagery modalities (ANOVA, P < 0.05). In post-hoc tests, the posterior centroids of the first segment differed between visual/tactile and visual/acoustic (P < 0.02), and between acoustic/tactile ( P = 0.07). The results support the hypothesis that mental imagery in different sensory modalities involves topographically distinct neuronal cell ensembles. Normal planum temporale asymmetry in familial schizophrenia: a volumetric MRI study S. Frangou a, T. Sharma a, P. Barta b, G. Pearlson b, R.M. Murray a aDepartment of Psychological Medicine, Institute of Psychiatry, London, UK. bDepartment of Psychiatry and Behavioral Sciences, John Hopkins University, Baltimore, USA

Loss of functional hemispheric asymmetry in Alzheimer's dementia

In a total of 10 patients with dementia of the Alzheimer-type (DAT) and in 10 healthy controls near-infrared spectroscopy (NIRS), a new non-invasive optical method, was used to measure the changes of concentrations of oxy- (O2HB) and deoxyhemoglobin (HHB) in left and right hemispheric prefrontal brain tissue areas during performance of the Verbal Fluency Test (VFT). On a neuropsychological level, the healthy subjects performed better in the VFT than patients with DAT. Statistical analysis of the relative concentrations of O2HB and HHB measured with NIRS during performance of the VFT revealed a significant interaction of the hemispheric effects with the diagnosis. A possible interpretation of this finding is that a good performance in the VFT relies on a predominantly left hemispheric activation observed in controls, whereas a low number of correct responses is associated with a loss of this asymmetric activation in patients with DAT. Although both, patients and controls, performed better in the category version of the VFT, the metabolic effects of this task were significantly less pronounced than in the letter version. This indicates that different energy demands, according to the type of access to the memory stores, may be interpreted as the result of a less energy-demanding access to categorically stored information and adds further evidence to the view that memory departments in humans are organized according to categorical principles.