Atypical language dominance in the epilepsy group was associated with an earlier age of brain injury and with weaker right hand dominance. There was greater variability of language dominance in the epilepsy group, with 78% showing left hemisphere dominance, 16% showing a symmetric pattern and 6% showing right hemisphere dominance. None of the normal subjects had rightward dominance. Using a categorical dominance classification, 94% of the normal subjects were considered left hemisphere dominant and 6% had bilateral, roughly symmetric language representation. As expected, the majority of both groups showed left hemisphere dominance, although a continuum of activation asymmetry was evident, with nearly all subjects showing some degree of right hemisphere activation. Increases in blood oxygenation-dependent signal during a semantic language activation task relative to a non-linguistic, auditory discrimination task provided an index of language system lateralization. Language dominance and factors that influence language lateralization were investigated in right-handed, neurologically normal subjects ( n = 100) and right-handed epilepsy patients ( n = 50) using functional MRI. Such “event related” functional MRI should provide for fundamentally new ways to interrogate brain function, and allow for the direct comparison and ultimately integration of data acquired by using more traditional behavioral and electrophysiological methods.

Furthermore, because robust hemodynamic alterations are detectable after neuronal stimuli lasting only a few tens of milliseconds, a new class of task paradigms designed to measure regional responses to single sensory or cognitive events can now be studied. Today it is now possible to map changes in cerebrovascular parameters essentially in real time, conferring the ability to observe changes in brain state that occur over time periods of seconds. The advent of high-speed MRI methods, capable of imaging the entire brain with a temporal resolution of a few seconds, allows for brain mapping based on more transient aspects of the hemodynamic response. However, until recently, most studies have investigated equilibrium changes in blood flow measured over time periods upward of 1 min. Investigators have extensively exploited techniques such as positron emission tomography and MRI to map patterns of brain activity based on changes in cerebral hemodynamics. The past two decades have seen an enormous growth in the field of human brain mapping. (PsycINFO Database Record (c) 2012 APA, all rights reserved) What also continues to be clear, however, is that the gulf between technological know how and depth of understanding has never been wider. In spite of this, the book does demonstrate, unequivocally, that functional neuroimaging has had a dramatic impact on the study of human brain function. Physiologists, in particular, may find the title somewhat misleading 'Human Brain Function' focuses almost exclusively on the results of PET activation studies, while relevant electrophysiological studies are only given detailed consideration in one chapter on the visual system. This volume, by Frackowiak and colleagues from the Functional Imaging Laboratory in London, seeks to do that through a comprehensive overview of the group's own work in the field to date that is, mainly through the use of PET. It seems timely, therefore, to take stock and ask what has been learned from human brain imaging so far. Not only is MRI technology more widely available than PET, it is less invasive and can benefit from improved temporal and spatial resolution. A significant recent development in the rapidly evolving field of imaging technology has been the relative shift of emphasis from positron emission tomography (PET) activation studies to functional magnetic resonance imaging (MRI). Reviews the book, Human brain function by R.

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