Human brain mapping under increasing cognitive complexity using regional cerebral blood flow measurements and positron emission tomography

test–retest reliability of functional MRI in a classification

Words in the brain’s language

Neuropsychological studies have demonstrated that the production of nouns and verbs can be dissociated in aphasia. These reports have been taken as evidence for separate representations of nouns and verbs in the human brain. We used whole-head magnetoencephalography to record cortical dynamics of action and object naming in 10 healthy adults and in 1 anomic patient with superior naming of verbs compared with nouns due to a left posterior parietal lesion. A single set of 100 line drawings was used for both action and object naming. In normal subjects, the activation sequences in action and object naming were essentially identical, advancing from the occipital to posterior temporoparietal and further to the left frontal cortex, without consistent involvement of the classical left inferior frontal (Broca) and temporal (Wernicke) language areas. In the anomic patient, pronounced differences between action and object naming emerged in the left hemisphere. The activation sequence was disrupted at the level of the damaged parietal cortex and did not reach the left frontal cortex even in the relatively easier action naming. The more severely impaired object naming was associated with exceptionally strong and early activation of the left inferior frontal cortex (Broca) and subsequent pronounced activation of the left middle temporal cortex, silent in action naming. Verb and noun retrieval thus utilized a spatiotemporally similar neuronal network in healthy individuals. A clear dissociation in cortical correlates of verb and noun retrieval only became evident in our anomic patient, in whom damage to the language network has resulted in disproportionately worse performance in object than action naming.

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The results from a single functional magnetic resonance imaging session are typically reported as indicative of the subject’s functional neuroanatomy. Underlying this interpretation is the implicit assumption that there are no responses specific to that particular session, i.e., that the potential variability of response between sessions is negligible. The present study sought to examine this assumption empirically. A total of 99 sessions, comprising 33 repeats of simple motor, visual, and cognitive paradigms, were collected over a period of 2 months on a single male subject. For each paradigm, the inclusion of session-by-condition interactions explained a significant amount of error variance (P < 0.05 corrected for multiple comparisons) over a model assuming a common activation magnitude across all sessions. However, many of those voxels displaying significant session-by-condition interactions were not seen in a multisession fixed-effects analysis of the same data set; i.e., they were not activated on average across all sessions. Most voxels that were both significantly variable and activated on average across all sessions did not survive a randomeffects analysis (modeling between-session variance). We interpret our results as demonstrating that correct inference about subject responses to activation tasks can be derived through the use of a statistical model which accounts for both within- and between-session variance, combined with an appropriately large session sample size. If researchers have access to only a single session from a single subject, erroneous conclusions are a possibility, in that responses specific to this single session may be claimed to be typical responses for this subject. © 2000 Academic Press