Time to get deep

Abstract

Asymmetries in the size of structures deep below the cortex explain how alpha oscillations in the brain respond to shifts in attention.

Keywords: alpha; hemispheric asymmetry; human; neuroscience; oscillations; spatial attention; subcortical structures.

Figure 1.. Alpha wave modulation during a spatial attention task.

The brains of two individuals are shown schematically from the back, with subcortical structures (thalamus, caudate nucleus and globus pallidus) highlighted in different colors. Note that for individual A, the thalamus (yellow) in the left hemisphere is slightly smaller than the thalamus in the right hemisphere. There are also asymmetries in the sizes of the caudate nucleus (purple) and globus pallidus (brown), and also for all three structures in individual B. MEG sensors (black squares) attached to the posterior cortex record alpha waves as the individuals shift their attention to the left or right side of their visual field. For both individuals, shifting attention to the left leads to increased alpha waves in the left hemisphere (blue lines), and shifting attention to the right leads to increased alpha waves in the right hemisphere (red lines). The extent of this modulation of the alpha waves is related to the size of various subcortical structures: a larger thalamus on one side of the brain – the right hemisphere of individual A, the left hemisphere of individual B – correlates with a stronger alpha modulation in the opposite hemisphere. Conversely, a larger caudate nucleus or globus pallidus correlates with stronger alpha modulation in the same hemisphere.