Abstract
It is known that sensory signals sustain the background discharge of the ascending reticular activating system (ARAS) which includes the noradrenergic locus coeruleus (LC) neurons and controls the level of attention and alertness. Moreover, LC neurons influence brain metabolic activity, gene expression and brain inflammatory processes. As a consequence of the sensory control of ARAS/LC, stimulation of a sensory channel may potential influence neuronal activity and trophic state all over the brain, supporting cognitive functions and exerting a neuroprotective action. On the other hand, an imbalance of the same input on the two sides may lead to an asymmetric hemispheric excitability, leading to an impairment in cognitive functions. Among the inputs that may drive LC neurons and ARAS, those arising from the trigeminal region, from visceral organs and, possibly, from the vestibular system seem to be particularly relevant in regulating their activity. The trigeminal, visceral and vestibular control of ARAS/LC activity may explain why these input signals: (1) affect sensorimotor and cognitive functions which are not directly related to their specific informational content; and (2) are effective in relieving the symptoms of some brain pathologies, thus prompting peripheral activation of these input systems as a complementary approach for the treatment of cognitive impairments and neurodegenerative disorders.
Highlights
The reticular formation (RF), a network of scattered cells that extends from the medulla to the hypothalamus and connects to most of brain structures, sustains nervous functions which are of crucial importance for body homeostasis and proper interaction with the environment, such as breathing, blood circulation (Guyenet, 2006, 2014), body (Luccarini et al, 1990; Pompeiano et al, 1991; Schepens and Drew, 2006; Takakusaki et al, 2016), head (Quessy and Freedman, 2004) and eye (Sparks et al, 2002) voluntary and reflex movements
The first pattern leads to an electroencephalographic (EEG) activity characterized by high amplitude and predominant low frequency components, typical of drowsiness and slow wave sleep, the second to a low amplitude, high frequency EEG pattern characteristic of wakefulness, and present in the desynchronized sleep (Steriade et al, 1993; Steriade, 1995)
The ascending reticular activating system (ARAS) extended up to the rostral region described by von Economo (1930) at the level of the junction between midbrain and thalamus, whose lesion leads to a persistent sleep in lethargic encephalitis
Summary
The reticular formation (RF), a network of scattered cells that extends from the medulla to the hypothalamus and connects to most of brain structures, sustains nervous functions which are of crucial importance for body homeostasis and proper interaction with the environment, such as breathing, blood circulation (Guyenet, 2006, 2014), body (Luccarini et al, 1990; Pompeiano et al, 1991; Schepens and Drew, 2006; Takakusaki et al, 2016), head (Quessy and Freedman, 2004) and eye (Sparks et al, 2002) voluntary and reflex movements. The histaminergic neurons in the tuberomammillary nucleus (TMN) of the posterior hypothalamic region, the peptidergic neurons in the lateral hypothalamus (LH) and the dopaminergic neurons in the mesencephalon and serotoninergic neurons in raphe nuclei (Jones, 2003; Saper et al, 2005) can be considered as ARAS components, the precise action of the raphe neurons on cortical arousal has been questioned (Monti, 2011). These specific ARAS components regulate arousal through their. Among the different ARAS components, the LC has attracted a large amount of investigations, which, on top of elucidating the LC effects on neuronal activity and brain networks signaling, have disclosed neurobiological LC actions that may have a deep impact on the brain dynamics, both in health and disease
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