Dopamine asymmetries predict orienting bias in healthy individuals

Abstract

Pseudoneglect is traditionally viewed as reflecting right hemisphere specialization for processing spatial information, resulting in orienting toward the contralateral, left, hemispace. Recent evidence suggests that healthy individuals differ from each other in both direction and magnitude of orienting bias, and moreover, the bias displayed by a person is consistent across time, suggesting that it may represent a trait of the individual. Animal studies reveal consistent orienting bias within an individual, which reflects asymmetry in dopaminergic brain systems. We measured basal D2-like receptor binding using positron emission tomography and the high-affinity ligand [F-18]fallypride, to test the hypothesis that asymmetry in dopaminergic neurotransmission in healthy humans modulates the orienting bias in humans. As predicted, we found that individual differences in the direction and magnitude of the orienting bias were strongly associated with the pattern of asymmetric binding of dopamine (DA) D2 receptors in the striatum, as well as clusters in the frontal and temporal cortex. These findings show for the first time that orienting bias reflects individual differences in the lateralization of DA systems in the healthy human brain.

Keywords: PET; asymmetry; dopamine; individual differences; spatial attention.

Figure 1.

Association between asymmetric D2 receptor binding in the striatum and orienting bias asymmetry index. Positive orienting bias score denotes rightward bias whereas negative bias score indicates leftward bias. Positive D2 binding values indicate relatively higher binding in the left hemisphere, compared with the corresponding cluster in the right hemisphere. Top panel: Clusters (MNI coordinates of peak voxel) in the left hemisphere, where higher D2 binding was associated with rightward orienting bias. Bottom panel: Scatter plots showing the cross-subject correlation between D2 binding asymmetry and orienting bias asymmetry score, separately for the putamen and caudate clusters. Binding asymmetry values are based on the peak voxel within each cluster. For illustrative purposes, the correlation is shown using the nonranked data.

Figure 2.

Association between asymmetric D2 binding in frontal and temporal cortical regions, and orienting bias. See Figure 1 for details.