The brain’s action network

As a complex system, the brain always operates as a functional whole, with multiple brain networks collectively facilitating the interaction between the intrinsic system and the external environment. On one hand, in the resting state without specific tasks, the brain maintains organized intrinsic neural activity and synchronizes the functions of different regions within the networks. Previous neuroimaging studies have identified a set of brain regions that exhibit relatively high energy consumption in the resting state and consistently show non-task-dependent negative activation in response to various task stimuli. The neural activities in these brain regions are highly synchronized, forming a functional network known as the default network (DN). On the other hand, when the brain is engaged in high-load, goal-oriented external tasks, it exhibits cognitive characteristics such as high arousal levels, focused attention, and the generation of action plans. The latest neuroimaging research has revealed that in this task-action state, there is also a set of brain regions that show non-task-dependent positive activation in response to various task stimuli, forming a functional network termed the action network (AN). From the perspective of working mechanism, the DN and the AN are complementary and constitute the “yin” and “yang” poles of the brain’s complex dynamical system. The discovery of the AN not only deepens and completes our understanding of the brain’s working principles but also provides a new perspective for the study of brain disease mechanisms and the development of brain-inspired intelligence. This paper first reviews the naming process of the DN and explores the naming of the AN. It then summarizes the discovery process and neuroimaging evidence of the AN, analyzes its anatomical composition and functional characteristics, and proposes a three-dimensional hierarchical view of the AN’s anatomical structure from a clinical perspective (cortex-basal ganglia/thalamus-cerebellum). It is suggested that future research should integrate considerations from the three dimensions of cortex, basal ganglia/thalamus, and cerebellum to provide a systematic framework for clinical and basic research in neuroscience. Thirdly, the paper elaborates on the theoretical insight into the functional opposition and unity of the AN and the DN, emphasizing the need for future in-depth studies on the network neuroscience laws of the AN’s anatomy and function, its development and evolution across the entire life span, and the innovation of multi-level, interdisciplinary scientific paradigms to reveal the cross-scale neurophysiological mechanisms underlying its neuroimaging findings. Finally, the paper looks forward to the important scientific significance and application value of the brain’s AN for brain science and brain-inspired research.