Brain-body physiology: Local, reflex, and central communication

Figures

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  Figure 1.. Overview of hierarchical loops of brain-body communication The nervous system communicates with every physiological system in the body through multiple interconnected levels. These levels form control loops, with higher levels regulating lower ones to achieve adaptive bodily control. Top: central, adaptive regulation, and immunoception involve higher-order brain structures integrating interoceptive information with external sensory data, past experiences, motivational drives, and emotions to form a complex representation. This integration allows adaptive modulation of the internal physiological state, including of the immune system, across different contexts and timescales, enabling prospective and goal-directed regulation of physiology. This regulation includes adjusting the homeostatic set points and modulating body phyisiology directly and indirectly through adjustments in motivation and behavior. Adaptive control is guided by cortical regions (darker blue) such as the aIC, ACC, vmPFC, and OFC, while subcortical regions (lighter blue) like the CeA, BNST, hypothalamus, VS, PAG, and PBN implement the integrated adjustments in physiology, motivation, and behavior. Middle:…

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  Figure 2.. Peripheral anatomy facilitating brain-body communication Left: Internal sensory information reaches the brain through major humoral and neuronal pathways (afferent pathways). Right:The autonomic nervous system is broadly divided into two main programs: the sympathetic and parasympathetic systems (efferent pathways). All these pathways are present bilaterally in the body and are illustrated according to human anatomy. Left panel illustrates the afferent pathways, composed of vagal (left) and spinal (right) afferents. Vagal afferents are pseudounipolar sensory neurons in the nodose or jugular ganglia (vagal ganglion in figure). These sensory neurons send a peripheral branch to innervate organs and a central branch to the brainstem. Nodose neurons synapse in the NTS and sometimes in the AP, while jugular neurons synapse in the SPV. This internal sensory information is then transmitted from these brainstem sites to higher-order neurons. Spinal afferents are pseudounipolar neurons in the dorsal root ganglia (DRGs). DRG neurons extend a peripheral branch to innervate organs and a central branch to the dorsal horn of the spinal cord, and occasionally to the DCN in the brainstem. This…

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  Figure 3.. Reflexive control of inflammation Reflex circuits play a critical role in maintaining homeostasis. During inflammation, these circuits can be engaged by peripheral signals such as cytokines. Brainstem areas including the NTS, AP, and DMV are activated by these signals to reduce inflammation or mediate behaviors. (The anti-inflammatory reflex, which ultimately reduces inflammation, consists of splenic projecting postganglionic neurons from the DMV that secrete NE, which acts on B2AR on T cells. These T cells then secrete ACh, which helps to reduce inflammation.45 Similar circuits can be deliberately engaged to reduce inflammation by electrostimulation. For example, stimulating the acupuncture point ST36 activates the DMV, which projects to the adrenal gland.46 Here, neuropeptide Y (NPY)+ chromaffin cells secrete ACh, reducing inflammation. CG, celiac ganglion; NE, norepinephrine; B2AR, β2-adrenergic receptors.

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  Figure 4.. Central networks of bodily physiology and immunoception Information from the periphery, including immune signals, is relayed to the brain through vagal and spinal afferents. These pathways converge in the NTS and PBN, ascend via the thalamus (e.g., ventromedial and ventroposterior lateral nuclei), and reach cortical areas such as the posterior IC, ACC, S1, and S2.55 Humoral information detected by CVOs (e.g., IL-6) is also transmitted through neural pathways to higher brain regions. Visceromotor cortices, including the aIC, ACC, vmPFC, and OFC, mediate the contextual and adaptive regulation of physiology, initiating coordinated responses across physiological systems and behavior. These responses are recruited by interconnected subcortical structures, with the hypothalamus (e.g., PVN and LHA) playing a crucial role in sensing physiological needs and mediating homeostatic control by engaging autonomic, neuroendocrine, immune, and motivated behavioral responses as needed. The CeA and BNST are involved in processing emotions and stress and in recruiting the physiological responses associated with their expression. Additional regions contributing to adaptive physiological changes…