MULTIMODALATTENTION · Multimodal imaging of spatial attention networks in the human brain

Multimodal imaging of spatial attention networks in the human brain

A family of common and debilitating conditions occur more frequently with damage to the human right hemisphere (1-4). These disorders include neglect where patients typically show an inability to take into account information coming from the left side of space, ultimately resulting in a severe functional impairment in everyday activities, extinction and simultanagnosia (with bilateral lesions) where patients fail to perceive some stimuli when presented at the same time as others (5-7). From the perspective of cognitive neuroscience, these clinical symptoms are disorders of spatial attention. Hence neurologist and neuropsychologist consider the right hemisphere as dominant for spatial attention. Although there have been recent advances in our understanding of the neuroanatomical basis of spatial attention in man, many questions remain to be answered. One major problem is the difficulty in translating anatomical information derived from animal studies to humans. Although there is a long history of studies into the cortical areas serving attention and spatial awareness, until recently there has been no direct way of studying the connections between these cortical areas in man, details of the network being derived from axonal tracing studies in monkeys. This gap is frequently overlooked so that white matter pathways described only in animals are cited as if they also exist in the human. Hence, in a two year time of research, the MULTIMODALATTENTION study revealed: (i) that fronto- occipital and fronto-parietal pathways are dominant in the right hemisphere compared to the left, (ii) the fronto-parietal pathways anatomical organisation is similar to the monkey. Finally, in the last month of research, further investigations allowed us to report that (iii) a subcomponent of the fronto- parietal connection, the SLF II correlate with the neuropsychological assessments of visuo-spatial attention dominance in the right hemisphere and (iv) this dominance is due to a quicker visuo-spatial processing in the right compared to the left hemisphere. This group results has an impact on the human neuro-anatomical knowledge, bringing closer the knowledge of human and monkey's white matter anatomy and its function in the field of attention. Furthermore, the correlation between the lateralisation of the SLF II and the neuropsychological assessments of visuo-spatial attention dominance in the right hemisphere will allow us to perform classification of the participants in three groups, right dominant, left dominant and not lateralised brain for spatial attention. The behavioural effect of this classification will be important to study in visuo-spatial paradigm. Finally, this classification brings up interesting hypotheses on possible anatomical predictors of visuo-spatial disorders recovery that can be tested in patients with lesions of the superior longitudinal fasciculus. References (1) Gainotti, G., Messerli, P., Tissot, R., 1972. Qualitative analysis of unilateral spatial neglect in relation to laterality of cerebral lesions. J Neurol Neurosurg Psychiatry 35, 545-550. (2) Oxbury, J.M., Campbell, D.C., Oxbury, S.M., 1974. Unilateral spatial neglect and impairments of spatial analysis and visual perception. Brain 97, 551-564. (3) Weintraub, S., Mesulam, M.M., 1987. Right cerebral dominance in spatial attention. Further evidence based on ipsilateral neglect. Arch Neurol 44, 621-625. (4) Mesulam, M.M., 1999. Spatial attention and neglect: parietal, frontal and cingulate contributions to the mental representation and attentional targeting of salient extrapersonal events. Philos Trans R Soc Lond, B, Biol Sci 354, 1325-1346. (5) Bartolomeo, P., Chokron, S., 2001. Levels of impairment in unilateral neglect. Elsevier Science Publishers. (6) Mesulam, M.M., 1985. Principles of Behavioral Neurology. F.A. Davis, Philadelphia (PA).

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