Functional cortical interaction patterns in visual perception and visuospatial problem solving

Metabolic thalamocortical correlations during a verbal learning task and their comparison with correlations among regional volumes

Methods based on the analysis of metabolic and volumetric interregional correlations have been used in neuroimaging research, yet metabolic and volumetric interregional correlations for identical regions of interest have never been compared in the same group of subjects. Magnetic resonance and [18F]-fluorodeoxyglucose positron emission tomography brain images were acquired in 59 healthy subject. Correlation matrices for relative glucose metabolic rates during a verbal learning task and for relative gray matter volumes were compiled between the manually traced mediodorsal, centromedian, and pulvinar nuclei of the thalamus and 39 cortical Brodmann's areas. Metabolic correlations between the cortex and these thalamic nuclei followed the known patterns of anatomical connectivity in non-human primates. Intercorrelations of the mediodorsal nucleus were widespread with the prefrontal cortex (9 out of 10 Brodmann's areas in the left hemisphere) and temporal lobe (10 out of 11 Brodmann's areas in the left hemisphere) while the pulvinar correlated only with the parietal and occipital cortical areas. Different correlation patterns were observed for the regional gray matter volumes whereby only the pulvinar yielded extensive cortical intercorrelations, primarily with the occipital, parietal, anterior cingulate, and orbitofrontal areas in the right hemisphere. Metabolic thalamocortical correlations were much more extensive for the mediodorsal and centromedian nuclei whereas structural correlations were more extensive for the pulvinar. Therefore, metabolic and volumetric correlational methods are sensitive to different aspects of interregional relations in the brain and their comparison in the same group of subjects may render complementary and only partially overlapping connectivity information.

Differential effects of Alzheimer's disease and Huntington's disease on the performance of mental rotation

The ability to spatially rotate a mental image was compared in patients with Alzheimer's disease (AD; n = 18) and patients with Huntington's disease (HD; n = 18). Compared to their respective age-matched normal control (NC) group, the speed, but not the accuracy, of mental rotation abnormally decreased with increasing angle of orientation for patients with HD. In contrast, the accuracy, but not the speed, of rotation abnormally decreased with increasing angle of orientation for patients with AD. Additional analyses showed that these unique patterns of performance were not attributable to different speed/accuracy trade-off sensitivities. This double dissociation suggests that the distinct brain regions affected in the two diseases differentially contribute to speed and accuracy of mental rotation. Specifically, the slowing exhibited by HD patients may be mediated by damage to the basal ganglia, whereas the spatial manipulation deficit of AD patients may reflect pathology in parietal and temporal lobe association cortices important for visuospatial processing.

Vascular dementia: a cognitive SPET-CBF activation study

OBJECTIVE

We investigated the pattern of regional cerebral blood flow (rCBF) responses to a cognitive task in vascular patients with and without dementia.

METHOD

We studied 8 controls and 18 vascular patients by quantitative rCBF assessed by (133)Xe inhalation method and SPET, both at rest and during a cognitive figure recognition task. Eight were mildly demented and 10 were nondemented vascular patients. According to their task performance, 12 patients were classified as 'good performers' (GPs) and 6 patients as 'poor performers' (PPs).

RESULTS

Vascular patients activated a larger number of brain areas than controls. No differences were observed between controls, nondemented and mildly demented patients in the pattern of rCBF activation. GPs presented a lower mean percentage of rCBF increase than either controls or PPs. GPs had lower values than PPs in the left temporal, parietal and occipital regions and in the right posterior cingulate and occipital regions.

CONCLUSIONS

These data suggest that vascular patients may functionally compensate for vascular damage by activating more brain areas than controls do and, consequently, by increasing the rate of regional activation.

Neural modeling and functional brain imaging: an overview

This article gives an overview of the different functional brain imaging methods, the kinds of questions these methods try to address and some of the questions associated with functional neuroimaging data for which neural modeling must be employed to provide reasonable answers.

Effect of non-steady-state perfusion on xenon-133 cerebral blood flow measurements: an analytical study

Activation studies employing the noninvasive xenon-133 technique are widely used to investigate the cerebral circulation. Typical examples are the investigation of hemispheral specialization of higher cortical function with cognitive activation or the assessment of the hemodynamic reserve in occlusive cerebrovascular disease by CO2 inhalation. Traditionally, in studies using this technique, there is the requirement of a circulatory steady state during the measurement. Due to limitations in the duration of the stimulus or habituation to the stimulus, the basic assumption is often violated. In this study we investigated with the aid of a computer model to what extent blood flow measurement results are affected by non-steady-state blood flow. The findings indicate that cortical activation need not extend throughout the whole measurement to be detectable. Maintenance of activation for at least 5 min is sufficient for a successful measurement. In addition, the results show that the activation should be fully established when the measurement starts to achieve maximal sensitivity. Delay in activating the circulation will result in attenuated responses, especially if the stimulus is delayed beyond 2 min.

Network analysis of brain cognitive function using metabolic and blood flow data

Functional neuroimaging has become a powerful tool for investigating the neurobiological foundations of cognition. An overview is presented of the two major strategies by which such data are currently analyzed. One strategy compares the pattern of activity between two (or more) tasks, looking for those brain areas that show significant changes. The second investigates the functional relationships between regional activities in an attempt to determine the systems-level neural networks mediating the tasks. Object and spatial visual processing tasks are used to illustrate each of these strategies.