Keynote Series: Mac Shine — From specificity to flexibility and everything in between: The segregation and integration of brain function
By Lavinia Uscatescu
It is morning, and our alarm clock goes off. We get out of bed and begin the chain of habitual behaviors that form our morning routine. Before long, we are ready to leave our home and start a new workday. We step outside and close the door behind us. As we leave the comfort of our home, get into our car, and start driving to work, the predictability of our environment diminishes. While driving, we perform a masterful blend of well-learned and spontaneous behaviors, as we switch lanes, take turns, and adapt to the behavior of the other drivers alongside us. Our brain performs impressive acrobatics of information processing to enable this seamless switching between habitual and novel behaviors.
Without the right balance between brain function specialization and flexibility, our everyday behavior would not go as smoothly. Specialized brain functions enable habitual behaviors, such as recognizing the red traffic light, remembering that it means we should stop the car, and consequently pushing the brake pedal. These illustrate the brain’s ability to segregate information based on the activity of specialized cortical areas (i.e., areas on the surface of the brain). These specialized areas do not work in isolation, however: communication between distinct functional brain regions enables a broad and flexible repertoire of cognitive processes. This illustrates the brain’s ability to integrate diverse types of information across various specialized modules. Given that the brain’s communication pathways—the white matter tracts—are relatively fixed structural features, how is the brain able to optimize the balance between information segregation and integration?
This is what Dr. Brandon Munn, working in the research group led by Dr. James (Mac) Shine at the Brain and Mind Centre of the University of Sydney, Australia, set out to find out. In one of their most recent papers, published in Nature Communications, they analyzed spontaneous signals from resting state functional magnetic resonance imaging (rs-fMRI) from adult human participants, with a focus on two subcortical (i.e., below the surface) brain areas: the locus coeruleus and the basal nucleus of Mynert (BNM). The locus coeruleus uses a neurotransmitter called noradrenaline, while the BNM uses acetylcholine to support arousal, vigilance, exploratory behaviors, and attentional focus. Although similar in function, these subcortical brain structures act differently, with the locus coeruleus sending diffuse signals towards cortical areas, while the BNM targets specific brain areas.
The authors have therefore hypothesized that the complementary activity of the locus coeruleus and the BNM form the basis of the brain’s flexible switch between information segregation and integration. What is more, the authors verified this hypothesis by including participants who were expert meditators, therefore being adept at controlling their level of arousal and awareness. The authors were thus able to show that the synergistic activity of the locus coeruleus and the BNM enables the shift between different awareness and arousal states, hence supporting the dynamic shift between segregation and integration brain processes.
So the next time you start a new workday, think about how amazing your brain is and how easily you navigate between the routine and the unexpected! The perfect blend between the specificity and flexibility your brain is able to deploy is nothing short of a scientific enigma. But thanks to Dr. Munn, Dr. Shine, and their collaborators, we are now closer to solving it.
Original Research:
Munn, B. R., Müller, E. J., Wainstein, G., & Shine, J. M. (2021). The ascending arousal system shapes neural dynamics to mediate awareness of cognitive states. Nature Communications, 12(1). https://doi.org/10.1038/s41467-021-26268-x
If you’d like to learn more about Dr. Shine’s research, check out our interview with him here.