Resources:Electrical stimulation of cranial nerves in cognition and disease
| Title | Electrical stimulation of cranial nerves in cognition and disease |
| Authors | Devin Adair · Dennis Truong · Zeinab Esmaeilpour · Nigel Gebodh · Helen Borges · Libby Ho · J. Douglas Bremner · Bashar W. Badran · Vitaly Napadow · Vincent P. Clark · Marom Bikson |
| Source | Document |
| Original | https://www.brainstimjrnl.com/action/showPdf?pii=S1935-861X%2820%2930041-3 |
| Date | 18 July 2019 |
| Journal | Brain Stimulation |
| DOI | 10.1016/j.brs.2020.02.019 |
| PUBMED | https://pubmed.ncbi.nlm.nih.gov/32289703/ |
| License | CC BY |
| This resource has been identified as a Free Scientific Resource, this is why Masticationpedia presents it here as a mean of gratitude toward the Authors, with appreciation for their choice of releasing it open to anyone's access | |
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Electrical stimulation of cranial nerves in cognition and disease
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Free resource by Devin Adair · Dennis Truong · Zeinab Esmaeilpour · Nigel Gebodh · Helen Borges · Libby Ho · J. Douglas Bremner · Bashar W. Badran · Vitaly Napadow · Vincent P. Clark · Marom Bikson
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Abstract
The cranial nerves are the pathways through which environmental information (sensation) is directly communicated to the brain, leading to perception, and giving rise to higher cognition. Because cranial nerves determine and modulate brain function, invasive and non-invasive cranial nerve electrical stimulation methods have applications in the clinical, behavioral, and cognitive domains. Among other neuromodulation approaches such as peripheral, transcranial and deep brain stimulation, cranial nerve stimulation is unique in allowing axon pathway-specific engagement of brain circuits, including thalamo-cortical networks. In this review we amalgamate relevant knowledge of 1) cranial nerve anatomy and biophysics; 2) evidence of the modulatory effects of cranial nerves on cognition; 3) clinical and behavioral outcomes of cranial nerve stimulation; and 4) biomarkers of nerve target engagement including physiology, electroencephalography, neuroimaging, and behavioral metrics. Existing non-invasive stimulation methods cannot feasibly activate the axons of only individual cranial nerves. Even with invasive stimulation methods, selective targeting of one nerve fiber type requires nuance since each nerve is composed of functionally distinct axon-types that differentially branch and can anastomose onto other nerves. None-the-less, precisely controlling stimulation parameters can aid in affecting distinct sets of axons, thus supporting specific actions on cognition and behavior. To this end, a rubric for reproducible dose-response stimulation parameters is defined here. Given that afferent cranial nerve axons project directly to the brain, targeting structures (e.g. thalamus, cortex) that are critical nodes in higher order brain networks, potent effects on cognition are plausible. We propose an intervention design framework based on driving cranial nerve pathways in targeted brain circuits, which are in turn linked to specific higher cognitive processes. State-of-the-art current flow models that are used to explain and design cranial-nerve-activating stimulation technology require multi-scale detail that includes: gross anatomy;skull foramina and superficial tissue layers; and precise nerve morphology. Detailed simulations also predict that some non-invasive electrical or magnetic stimulation approaches that do not intend to modulate cranial nerves per se, such as transcranial direct current stimulation (tDCS) and transcranialmagnetic stimulation (TMS), may also modulate activity of specific cranial nerves. Much prior cranial nerve stimulation work was conceptually limited to the production of sensory perception, with individual titration of intensity based on the level of perception and tolerability. However, disregarding sensory emulation allows consideration of temporal stimulation patterns (axon recruitment) that modulate the tone of cortical networks independent of sensory cortices, without necessarily titrating perception. For example, leveraging the role of the thalamus as a gatekeeper for information to the cerebral cortex, preventing or enhancing the passage of specific information depending on the behavioral state. We show that properly parameterized computational models at multiple scales are needed to rationally optimize neuromodulation that target sets of cranial nerves, determining which and how specific brain circuitries are modulated, which can in turn influence cognition in a designed manner.
©2020 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Introduction
Cognition is conceptualized as the processing of information acquired through the senses. The central nervous system (CNS; nerves within the brain and spine) integrates and responds to signals transmitted by the peripheral nervous system (PNS; nerves outside the brain and spine), whose primary function is to connect the CNS with the rest of the body and the environment [[1] ]. The cranial nerves are a specialized part of the PNS that emerge directly from the brain rather than through the spine and include both afferents and efferents. Afferent cranial nerve axons convey sensory information —sight, hearing, taste (gustation), touch (heat, pressure, pain, proprioception), smell (olfaction), interoception (input from the gut and internal organs), and equilibrium— to the brain. Efferent cranial nerves’ axons regulate muscles (smooth, skeletal, and cardiac) and glands (either directly or through a postganglionic axon; Table 1). In contrast to other peripheral nerves that first route through the spinal cord, cranial nerves project directly through the skull into the brain, which makes them a special target for neuromodulation. For each cranial nerve, there is a portion that is relatively accessible (extra-cranial), and each nerve is intimately linked to perception and regulation of CNS function, including established “bottom-up” functions in cognition and clinical disorders [2, 3, 4].
Table 1
Summary of cranial nerve modality, conduction direction and function. The modality describes the type of information each nerve conducts. Classic modality are the designations given by anatomists; SVA – special visceral afferent; SSA – special sensory afferent; GSA – general sensory afferent; SVE – special visceral efferent; GVE –general visceral efferent; GSE – general sensory efferent, A– Afferent, E − Efferent. Cranial nerves that contain at least one major afferent branch — characterized fully in this review — are bolded.