Updated: Jul 28, 2022
Thalamic pacemakers produce the alpha rhythm through bidirectional connections with the cortex. Graphic © SciePro/Shutterstock.com.
When we are inattentive, thalamic pacemakers generate the alpha rhythm. When we need to focus attention, we activate the brainstem noradrenergic locus coeruleus. Graphic © Vasilisa Tsoy/Shutterstock.com.
Increased norepinephrine release by this 15-mm network focuses attention and abolishes alpha oscillations. This phenomenon is called alpha blocking. The locus coeruleus enhances the brain's sensory information processing by suppressing thalamic alpha generators. Movie © John S. Anderson. The recording begins with eyes open. The eyes-closed condition starts at 14’01” and clearly shows increased 8-12 Hz voltage (posterior dominant rhythm or PDR) in occipital and parietal locations in the line tracing and topographic maps to the right of the tracing.
The eyes open again at 14’31”, and alpha attenuates (alpha blocking). This shows the posterior dominant rhythm (generally known as "alpha") appearing in the eyes-closed condition when visual sensory input is stopped. The attenuation or blocking of this rhythm as sensory input returns in the eyes-open condition.
Although researchers cannot noninvasively monitor locus coeruleus activity in human participants, it is correlated with pupil dilation. In human studies, the greater the alpha blocking response and pupil dilation, the better the performance on demanding attention tasks (Dahl et al., 2020; Dahl et al., 2022). Graphic © sruilk/Shutterstock.com.
The alpha rhythm is not a cause but a sign that incoming stimulation is too weak to overcome inhibition by the reticular nucleus. EEG activity is not causal and reflects network activity that has already occurred. Summary Norepinephrine release by the locus coeruleus when we focus attention produces alpha blocking. This phenomenon is associated with pupil dilation. Learn More
References Dahl, M. J., Mather, M., Sander, M. C., & Werkle-Bergner, M. (2020). Noradrenergic responsiveness supports selective attention across the adult lifespan. J Neurosci, 40(22), 4372-4390. https://doi.org/10.1016/j.tics.2021.10.009
Dahl, M. J., Mather, M., & Werkle-Bergner, M. (2022). Noradrenergic modulation of rhythmic neural activity shapes selective attention. Trends in Cognitive Sciences, 26(1), 38-52. https://doi.org/10.1016/j.tics.2021.10.009