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Krasnow Institute > Monday Seminars > Abstracts
Neurogenetics of Human Visual Attention Raja Parasuraman Director, Cognitive Science Laboratory, Catholic University of America The brain networks underlying human visual attention, and the neurochemical innervation of these networks, have become increasingly well specified in recent years. In this talk I present neuroimaging (PET, fMRI, ERP) evidence showing that tasks of shifting and scaling of attention to objects and locations in the visual environment provide "behavioral assays" of the integrity of a posterior parietal cortex system for spatial attention. These assays can then be combined with molecular genetic assays to examine the neurogenetics of human visual attention. The spatial attention system is strongly linked to nicotinic acetylcholine receptors (nAChRs), which regulate fast synaptic transmission in parietal cortex. Hence polymorphisms of nAChRs represent candidates for modulation of visuospatial attention. I present the results of studies in which tasks of cued spatial attention, cued visual search, and working memory were administered to large samples (N~100) of healthy adults genotyped for a T to C polymorphism in the CHRNA4 nicotinic receptor subunit gene. Increasing gene dose (0, 1, 2) of the C allele of the CHRNA4 gene was associated with increased reaction time (RT) benefits of valid cueing, reduced RT costs of invalid cues, and increased cue size benefits in visual search. However, individual differences in components of working memory were not associated with the CHRNA4 gene. Working memory has been linked to the brain dopaminergic system and to prefrontal cortical activation. We therefore examined the effects of variation in the dopamine beta hydroxylase (DBH) gene on performance of the same attention and working memory tasks. The D?H enzyme converts dopamine to norepinephrine. The DBH gene has several polymorphisms, one of which, a G to A substitution, affects plasma and CSF DBH enzyme levels . Increasing gene dose of the G allele of the DBH gene was associated with increased working memory accuracy at a high memory load. However, there was no consistent association between the DBH gene and individual differences in either the spatial attention or visual search tasks. Thus, a double dissociation was observed with visuospatial attention and visual search associated with CHRNA4 but not DBH and conversely, working memory with DBH but not with CHRNA4. I conclude that normal allelic variations in single neurotransmitter genes modulate individual differences in processing components of attention and working memory in healthy individuals. These genetic associations are consistent given the differential role of cholinergic parietal and dopaminergic prefrontal cortical activation in attention and working memory.
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