MRI-guided SPECT-measurements of medial temporal lobe blood flow in Alzheimer's disease

166

Abstracts / Psychiatry Research: Neuroimaging 68 (1997) 155-184

Both EEG and MEG can be considered as time-varying spatial patterns, sampled at a limited number of discrete locations. Using an appropriate interpolation, these patterns can be visualized, separately for each time point, as maps showing how the electrical potentials or the measured field components are distributed over the measurement surface. There is no doubt that different maps indicate that different generators are activated within the brain. However, the characterization of a brain state in terms of the activated sources represents a serious problem. Most studies up to now are based on discrete dipole models, especially single dipole models and multidipole models with simultaneous activation or not-simultaneous activation. However, results obtained with such models should be considered with care, especially if the number of channels is relatively small. The difficulties resulting from the non-uniqueness of the inverse problem are truly severe. However, a much different situation arises if the information content of EEG and MEG is considered in the context of other sources of information which are known a priori. A natural first step is the reduction of the source space. This can be done by assuming that the sources are located on the cortical surface, with an orientation perpendicular to the surface. Information about the cortical surface can easily be obtained by magnetic resonance imaging (MRI). The model of a single current dipole was replaced for that purpose by a dipole patch model. The idea underlying this model is that the source of the magnetic field corresponds to a uniformly activated patch of the cortical surface. Both the current dipole model and the dipole patch model were applied to somatosensory evoked fields (SEF). First results suggest that the dipole patch model is highly superior to the usual current dipole model, especially if a realistic volume conductor model is used rather than the present standard, the simple model of a homogeneous sphere. Cortical connections imaging A.M. Ivanitsky

Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences, Moscow, Russia To know not only 'where' but 'how' information is processed in the brain one needs to have the picture of cortical areas interaction, not available with the most brain imaging methods. Approaching the problem the method was elaborated, based on the idea that cortical connections were promoted with the neuronal oscillators synchronization, revealing particularly in the precise coincidence of the EEG and ERP spectral components in the interacting cortical areas. The method was applied for the study of the brain mechanisms in thinking operations. The main result was that the cortical connections at mental task solving converged to the particular cortical zones typical for e.g. abstract vs. imaginative thinking. These cortical areas were named the interaction foci. We hypothesize that these connections centers realize the function of the comparison and the synthesis of information coming to the focus resulting in decision making. The method was applied also to the mental pathology study.

Application of artificial neural networks to CNV data to investigate schizophrenia B.W. Jervis a. M.R. Saatchi a, S. Yu a, R.F. Harrison b, C.P. Lim b, S. Oke c

aSchool of Engineering, Sheffield Hallam University, UK. bDepartment of Automatic Control and Systems Engineering, University of Sheffield, UK. CTon Vale Hospital, Taunton, UK The results and usefulness of applying data extracted from the Contingent Negative Variation (CNV) response in the electroencephalogram (EEG) of schizophrenic patients and their age and sex matched normal control subjects to artificial neural networks in o r d e r to differentiate between schizophrenics and normals are presented. Schizophrenia is a condition associated with psychiatric symptoms including hallucinations, delusions, and thought disorder. MRI and neuropathological studies have shown that there are functional and anatomical defects in the brains of schizophrenics, and the CNVs of schizophrenics have been found to be altered. The CNVs of 20 schizophrenics, the severity of whose symptoms had been assessed, and their matched normal controls were recorded using vertex and pre-frontal electrodes. After pre-processing, features were extracted from the data preceding the imperative stimulus. The normalized features were used to train multilayer perceptrons (MLPs) and a fuzzy ARTMAP to differentiate between the schizophrenics and their controls. The results were assessed in terms of the standard medical statistics of sensitivity and specificity etc.. The vertex electrode was found to be the more accurate marker for schizophrenia. Because of the possible overlap of symptoms in the early stages between schizophrenia and Huntington's disease (HI)), it was established that the neural networks could be trained to distinguish between thc CNVs of schizophrenic and HD patients. Establishing the architectures and training MLPs is very time consuming. Good results were much more quickly obtained using the fuzzy ARTMAP which also solves the plasticity-stability problem. Another advantage of the fuzzy A R T M A P is that examples which do not belong to any known category may be assigned to a new cluster and be associated with an 'unknown' class. The difficulty of assessing the reliability of a classification by neural networks may pose a problem. However, this can be solved using a statistical analysis method such as predictive statistical diagnosis, which yields probabilities and atypicality indices provided the data are rendered normal, or principal components analysis. MRI-guided SPECT-measurements of medial temporal lobe blood flow in Alzheimer's disease P. Julin '~, L. Svensson b, O. Almkvist", K. Mfi.hrc ~:, LO. Wahlund ;~

aDepartment of Clinical Neuroscience, Geriatric Section, Karolinska Institute, Huddinge Univers'ity Ho.spital, Stockhohn, Sweden. Ho.wttal Phystcs, Karolinska Institute, Huddinge University Hospital Stockhohn, Sweden. CDiagnostic Radiology, Karolinska Institute, Haddhlge Univers'itv Hospital, Stockhohn, Sweden b

.

•

MRI-guided hippocampal/cerebellar CBF-ratios werc mcasurcd on images from eight healthy controls and one subjcc!

Abstracts / PsychiatnyResearch: Neuroimaging 68 (1997) 155-184 with AD at two different occasions to assess the reliability of alignment and ROl-definition. In two subjects external markers were used to assess the accuracy of the alignment procedure. The coefficient of error for hippocampal CBF-ratio was 3%. The S.D of marker displacement was 3.1 mm. Healthy controls had a mean hippocampal CBF ratio of 0.67_+ 0.05 and the AD subject had a clearly reduced hippocampal CBFratio of 0.55 ( - 2.6 S.D).

Semantic information processing: a functional MRI study T. Kammer, M.E. Bellemann, U. Kischka, G. Brix, S. Maier, M. Weisbrod, F. Gueckel, M. Spitzer

Section of Experimental Psychopathology, Psychiatric University Hospital Heidelberg, Germany Seventeen normal subjects read word pairs, successively projected on a screen visible from within a conventional 1.5-T MRI scanner. Decisions on semantic relatedne~ and reaction times (RTs) were monitored on-line. A color similarity task of psychometrically equivalent difficulty served as control activation condition. Activated areas were detected using a BOLD sequence and statistical comparisons on a pixel-to-pixel basis. Distinct activation patterns were found which reflected interindividual variability. The language paradigm activated left frontal and left insular areas when compared to the color task. A significant decline in RT data during processing of the language task was paralleled by a decline in the corresponding fMRI activation time-courses. In the color condition, no significant changes in RTs nor in brain activation profiles were found during stimulus presentation. The RT data are indicative of selective learning of the language task only which is mirrored by the fMRI activation time courses.

Event-related potentials and MRI findings in schizophrenia Y. Kawasaki, Y. Maeda, M. Higashima, T. Nagasawa, Y. Koshino

Department of Neurop.~chiatry, Kanazawa University School of Medicine, Japan Twenty-five right-handed male schizophrenic patients diagnosed by DSM-III-R underwent event-related potentials and magnetic resonance imaging scans. Principal component analysis was applied to reduce the problem of multiple comparisons. The factor score of the N100 amplitude correlated with the factor score of morphological changes in the right lateral and medial pre-frontal cortices (r = -0.521, P = 0.0076). The factor score of the P300 amplitude was well correlated with the factor score of volumetric changes in the medial temporal structures (r = 0.686, P = 0.0002), Subsequent individual analysis revealed that the highest correlation coefficient was obtained between reduced P300 amplitude at T5 scalp recording and volumetric reduction in the left anterior part of the medial temporal structure (r = 0.675, P = 0.0002). These findings suggest that the information processing dysfunction of schizophrenia is associated with a morphological abnormality in the brain.

167

fMRI correlates of abnormal sensori-motor integration D. Khorram-Sefat a, H. Hacker a, J. Frahm b

aDepartment of Neuroradiology, University Hospital Frankfurt/ Main, Germany. bBiomedizinische NMR Forschungs GmbH, G6ttingen, Germany Voluntary motor activity have been extensively studied with fMRl in healthy subjects. Modeling sensorimotor integration we investigated damages to the peripheral motor system and central disturbances. Recent fMRI sequence improvements have pointed out their different potentials for brain activation studies. To address the issue of somatotopical representation six amputees were investigated using high spatial resolution fMRl at 2T ( T R / T E = 63/30 ms, flip angle 10°, measuring time 6 s., 0.8 × 1.6 ram, 4-mm thickness) and correlational analysis of task related activation. Joint movements at the amputated side were expanded compared to the healthy arm. This might be a direct activation correlate of the phantom movement experience. To address psychomotor disturbances akinetic patients (n = 10) were chosen and investigated with multislice EPI (TR 1.8 ms, flip angle gO degree, matrix interpolation 128, 3, 13 × 3, 13 cm, 4-ram thickness, 15 slices, at 1.5 T.) with Z-statistics. We found a lack of SMA activation which might reflect the disorder of movement initiation m akinctic syndromes.

High resolution fMRI demonstrates expanded somatotopical cortical representation in congenital amputees D. Khorram-Sefat ~, M. Nitschke a, J. Frahm h

~Department of Neuroradiology, University Hospital Frankfitrt/ Main, Germany. ~Biomedizinische NMR Forschangs GmbH, G6ttingen, Germany Cortical activation during elbow stump, repetitive elbow and sequential finger oppositions were investigated in three congenital amputees. The goal of the study was to determine the somatotopical representation of upper limb movements. Functional imaging was performed at 2.0 T. using a Flash Sequence (Tr/TE 63/30, flip angle 10°, measuring time 6 s, 128 × 250 matrix, slice thickness 4 ram). Activated areas were delineated by correlation of the signal intensity time course on a pixel by pixel basis with an external reference box car wave form curve. In contrast to elbow movements of the intact side, stump movements elicited an expansion of activation area in M1 und S1 equally to the complex finger task. Furthermorc the SMA was activated during elbow stump but not elbow flexion-extension movements. These similarities of the amputated limb to finger movements activation might reflect the plastical changes due to increased fine control in early childhood.

fMRI correlates of music listening cortical-cerebellar activation pattern D. Khorram-Sefat ~', T. Dierks h, S. Herminghaus ~, H. Hacke¢'

aDepartment of Neuroradiology, University Hospital Frankfurt/ Main, Germany. bDepartment of Psychiatry I, University Hospital Frankfurt~Main. Germany