1. ¹Human Cortical Physiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA
2. ²Department of Neurology, University of Münster, Münster, Germany
3. ³Department of Neurology II, University of Magdeburg, Magdeburg, Germany
4. ⁴Department of Psychiatry, University of Münster, Münster, Germany

Correspondence: Dr A Flöel, Human Cortical Physiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 10 Center Drive, Building 10, Bethesda, MD 20892-1430, USA. E-mail: floela@ninds.nih.gov or floeel@uni-muenster.de

^*Both these authors contributed equally to the present work and should therefore both be considered as first authors.

Received 21 September 2004; Revised 7 December 2004; Accepted 30 January 2005; Published online 6 April 2005.

Abstract

The right hemisphere is predominantly involved in tasks associated with spatial attention. However, left hemispheric dominance for spatial attention can be found in healthy individuals, and both spatial attention and language can be lateralized to the same hemisphere. Little is known about the underlying regional distribution of neural activation in these 'atypical' individuals. Previously a large number of healthy subjects were screened for hemispheric dominance of visuospatial attention and language, using functional Doppler ultrasonography. From this group, subjects were chosen who were 'atypical' for hemispheric dominance of visuospatial attention and language, and their pattern of brain activation was studied with functional magnetic resonance imaging during a task probing spatial attention. Right-handed subjects with the 'typical' pattern of brain organization served as control subjects. It was found that subjects with an inverted lateralization of language and spatial attention (language right, attention left) recruited left-hemispheric areas in the attention task, homotopic to those recruited by control subjects in the right hemisphere. Subjects with lateralization of both language and attention to the right hemisphere activated an attentional network in the right hemisphere that was comparable to control subjects. The present findings suggest that not the hemispheric side, but the intrahemispheric pattern of activation is the distinct feature for the neural processes underlying language and attention.