An examination of regional cerebral blood flow during object naming tasks.

The purpose of this study was to examine regional cerebral blood flow using positron emission tomography (PET) during the performance of tasks related to visual confrontation naming. Ten healthy, young participants were scanned twice in each of 5 conditions; blood flow was measured using standard PET [15O]-water technology. Two major findings have replicated previous studies. First, the naming of visually presented objects, whether covert or overt, requires a region of the left inferior cortex including the fusiform gyrus. Second, during overt naming, there is an increase in activity in the inferior or frontal cortex and insula as a consequence of generating speech code. These data are consistent with other studies demonstrating the importance of the inferior temporal regions for semantic processing, and the frontal cortex for word form generation.

Regional cerebral blood flow during word and nonword reading.

The purpose of this study was to examine changes in regional cerebral blood flow (rCBF) using positron emission tomography (PET) during overt word and nonword reading tasks to determine structures involved in semantic processing. Ten young, healthy, right-handed subjects were scanned 12 times, twice in each of six specific conditions. Blood flow was measured by 15O-water using standard PET imaging technology. The rCBFs during different cognitive conditions were compared by using analysis of covariance (SPM94), which resulted in three-dimensional maps of those brain regions more active in one condition relative to another. When the subjects read aloud words with difficult or unusual grapheme-phoneme translations (i.e., third-order approximation to English or irregularly spelled real words), increases in activation were seen in the inferior frontal cortex. When subjects were reading aloud regular and irregular words (which had important semantic components relative to nonwords), activation of the fusiform gyrus was seen. These data are broadly consistent with brain regions generally associated with reading based on other neuropsychological paradigms, and they emphasize the multicomponent aspects of this complex cognitive process.

Functional connectivity in auditory-verbal short-term memory in Alzheimer's disease.

Alzheimer's disease (AD) patients show normal patterns of regional cerebral blood flow during performance of subspan verbal memory tasks, but appear to allocate new brain regions when performing supraspan recall tasks. To understand the relationships among these interconnected brain regions, their functional connectivity was considered using principal components analysis (PCA). AD patients and controls were scanned in four conditions: visual fixation only and visual fixation with one-word recall, three-word recall, and eight-word recall. When applied to the data from the three recall task conditions (i.e., eliminating fixation), PCA revealed a significant first component accounting for 75.8% of the variance in the control data and 66.8% of the variance in the patient data. The one-word recall condition had a high positive component score, and the eight-word condition a high negative score. The correlations of individual voxels on this factor (i.e., spatial modes) were very similar between the patients and the controls. The overall similarity in the results of the PCAs between the patients and the controls suggests that they have similar functional connectivity. This would suggest that, at least in the early course of the dementia, the functional CNS organization of verbal memory systems remains normal.