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Resources:Electrical stimulation of cranial nerves in cognition and disease (view source)
Revision as of 19:14, 23 March 2021
, 4 years ago→Table 1
<small>''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 a major afferent branch — characterized fully in this review — are bolded.''</small>
<small>''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 a major afferent branch — characterized fully in this review — are bolded.''</small>
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Here we develop a formalism to design cranial nerve stimulation by leveraging insight from modern biomedical engineering and neuroscience (i.e. biomarkers) – in order to target specific cognitive constructs and behaviors that may be linked to neuropsychiatric disorders. We focus mainly on nerves that contain a major sensory (or afferent) component, however in some cases it can be challenging to disambiguate the cognitive effects of cranial nerves stimulation on afferents vs. efferents (see sec.5). Our overall approach is to focus on each afferent cranial nerve that modulates a specific brain circuit -- including those circuits involved in lower and higher-level processes - providing a rational basis to target specific cognitive functions by optimized cranial nerve stimulation. Indeed, while transcranial approaches (e.g. TMS and tDCS) or some invasive approaches (e.g. certain forms of DBS) inevitably stimulate a complex constellation of neurons, cranial nerve stimulation allows (with limitations discussed) activation of targeted pathways into the CNS using minimally or non-invasive technology.
There is a large body of literature on the modulation of cranial nerves by electrical stimulation for both therapeutic and experimental applications; however, these studies are variable in methodology and conclusions. The clinical neuroanatomy of each cranial nerve have been explored [[5]], but nuance continues to emerge in anatomy and function [[6],[7]
]. Some of the earliest applications of electrical stimulation to cranial nerves were to treat neurological disorders such as seizures [[8],[9]] and sensory dysfunctions [e.g., vision loss, equilibrium damage; 10, 11]. Subsequent inclusion of broader clinical indications — including neuropsychiatric disorders -- have furthered knowledge of how activity of early sensory systems through cranial nerves can influence higher cognitive processes [12, 13, 14]. This improved understanding has driven the expansion of devices geared towards a variety of applications including treatment of specific disorders as well as enhancement of cognitive and other functions [15, 16, 17].
Neuroimaging and neurophysiological techniques can further characterize the response of cranial nerve activation, and potentially act as biomarkers of target engagement. For example, electrically induced evoked potentials (EPs) measured using electroencephalography (EEG) can be used to monitor a variety of nerve functions [[22]]. Auditory and visual EPs measured with electroencephalography (EEG) are used for a variety of diagnostic purposes in neurology to validate electrical stimulation of cranial nerves and as an adjunctive tool in neurosurgery [[23],[24]] The use of EEG measurement of EPs has been used to validate non-invasive electrical stimulation of cranial nerves as well [25, 26, 27].
Functional magnetic resonance imaging (fMRI), magnetoencephalography (MEG) and positron emission tomography (PET) can be used to examine both subcortical and cortical activation induced by targeted cranial nerve electrical stimulation [28, 29, 30, 31, 32]. Potential biomarkers can be developed through neural signatures evoked by electrically stimulating cranial nerve(s), in both healthy and dysfunctional subjects [[2],[33]], but only if they are distinct and reliable. Examples of the electrically evoked potentials and induced network effects explored as measures of cranial nerve function are summarized in Table 2 and expanded on for each nerve in the text.
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