Subcortical Contributions to Behavioural Asymmetries: Insights from the Hemispheric Laterality of Basal Ganglia and Thalamus

The size difference between the left and right putamen—a deep brain structure involved in movement and learning—predicts which way a person will bias their attention on a simple visual test. This research addresses a gap in understanding how brain asymmetries below the cortex contribute to behavioural biases. Most studies of hemispheric laterality focus on the cortex, but the basal ganglia and thalamus also show structural asymmetries whose functional significance remains unclear. By linking a specific subcortical volume difference to performance on a line bisection task—where people mark the centre of a horizontal line—the work provides a concrete, measurable connection between brain structure and a basic attentional bias. This is fundamental science. It does not have an immediate practical application. However, similar discoveries about subcortical asymmetries have informed models of spatial neglect after stroke, where patients ignore one side of space. A deeper understanding of how the putamen and thalamus shape attention could eventually refine diagnostic tools for neurological conditions or improve the design of cognitive tests used in clinical assessments. For now, the value lies in mapping the neural architecture that underpins a simple, everyday asymmetry in how we perceive the world.