Ascending Reticular Activating System Research Articles

Altered functional connectivity of the ascending reticular activating system in obstructive sleep apnea

Repeated arousals during sleep in obstructive sleep apnea (OSA) may lead to altered functional connectivity (FC) of the ascending reticular activating system (ARAS). We evaluated resting-state FC between eight ARAS nuclei and 105 cortical/subcortical regions in OSA patients and healthy controls. Fifty patients with moderate to severe OSA and 20 controls underwent overnight polysomnography and resting-state functional magnetic resonance imaging. Seed-to-voxel analysis of ARAS–cortex FC was compared between OSA patients and controls. The ARAS nuclei included the locus coeruleus (LC), laterodorsal tegmental nucleus (LDTg), and ventral tegmental area (VTA). FC values of three ARAS nuclei (the LC, LDTg, and VTA) significantly differed between the groups. FC of the LC with the precuneus, posterior cingulate gyrus, and right lateral occipital cortex (LOC) was stronger in OSA patients than controls. FC between the LDTg and right LOC was stronger in OSA patients than controls, but FC between the VTA and right LOC was weaker. Average LC–cortex FC values positively correlated with the arousal, apnea, and apnea–hypopnea index in OSA patients. Alterations in ARAS–cortex FC were observed in OSA patients. The strength of LC–cortex noradrenergic FC was related to arousal or OSA severity in patients.

0510 Altered functional connectivity of the ascending reticular activating system in obstructive sleep apnea

Abstract Introduction Recurrent arousals in obstructive sleep apnea (OSA) may lead to alteration in functional connection involving in the ascending reticular activating system (ARAS). We aimed to evaluate resting-state functional connectivity (FC) between eight ARAS nuclei and 105 cortical/subcortical regions in OSA patients and matched controls. Methods Total of 50 patients with moderate to severe OSA and 20 controls without OSA underwent overnight polysomnography (PSG) and resting-state functional magnetic resonance imaging in the following morning. Seed to voxel analysis of ARAS-cortical FC was compared between the patients and controls. The ARAS nuclei included dorsal and median raphe nucleus, locus coeruleus (LC), laterodorsal tegmental nucleus (LDTg), pedunculopontine tegmental nucleus, pontine nucleus oralis, parabrachial complex, and ventral tegmental area (VTA). Correlations between average FC values of significant clusters and PSG parameters were calculated in the patients. Results FC values in the three of the ARAS nuclei (LC, LDTg, and VTA) were significantly different between the group. The FC value between the LC and the precuneus cortex, posterior cingulate gyrus, and right lateral occipital cortex (LOC) was increased in OSA patients compared to the controls. The FC value between the LDTg and right LOC was enhanced, but the FC one between the VTA and right LOC was reduced in the patients. The average LC-cortical FC values positively correlated with the arousal index(r=0.282, p=0.047), apnea index(r=0.325, p=0.021), or apnea-hypopnea index (r=0.302, p=0.033) in OSA patients. Conclusion The results of this study support alteration in ARAS-cortical FC in OSA patients. Degree of the noradrenergic LC-cortical FC may be related to arousal or OSA severity in the patients. Support (if any)

Chewing and Cognitive Improvement: The Side Matters.

Chewing improves cognitive performance, which is impaired in subjects showing an asymmetry in electromyographic (EMG) masseter activity during clenching. In these subjects, the simultaneous presence of an asymmetry in pupil size (anisocoria) at rest indicates an imbalance in Ascending Reticular Activating System (ARAS) influencing arousal and pupil size. The aim of the present study was to verify whether a trigeminal EMG asymmetry may bias the stimulating effect of chewing on cognition. Cognitive performance and pupil size at rest were recorded before and after 1 min of unilateral chewing in 20 subjects with anisocoria, showing an EMG asymmetry during clenching. Unilateral chewing stimulated performance mainly when it occurred on the side of lower EMG activity (and smaller pupil size). Following chewing on the hypotonic side, changes in cognitive performance were negatively and positively correlated with those in anisocoria and pupil size, respectively. We propose that, following chewing on the hypotonic side, the arousing effects of trigeminal stimulation on performance are enhanced by a rebalancing of ARAS structures. At variance, following chewing on the hypertonic side, the arousing effect of trigeminal stimulation could be partially or completely prevented by the simultaneous increase in ARAS imbalance.

Difference in the ascending reticular activating system between vegetative and minimally conscious states following traumatic brain injury.

ObjectivesWe investigated differences in the ascending reticular activating system (ARAS) between vegetative state (VS) and minimally conscious state (MCS) in patients with traumatic brain injury (TBI) by using diffusion tensor tractography.MethodsWe recruited TBI patients and normal subjects. We reconstructed the lower ARAS and five parts of upper ARAS [prefrontal cortex (PFC), premotor cortex, primary motor cortex, primary somatosensory cortex, and posterior parietal cortex].ResultsSignificant differences were observed in the fractional anisotropy (FA) and fiber number (FN) values of the five parts of upper ARAS between the VS and control groups and between the MCS and control groups (P < 0.05), but no differences were detected in the lower ARAS (P > 0.05). The FA and FN values of the PFC in the upper ARAS were significantly different between the VS and MCS groups (P < 0.05). No other significant differences in FA and FN values were detected among the other segments of the upper ARAS or in the lower ARAS (P > 0.05).ConclusionThe results indicate that the prefrontal portion of the upper ARAS is the critical area for distinguishing between VS and MCS in patients with TBI.

Cannabidiol has a unique effect on global brain activity: a pharmacological, functional MRI study in awake mice

BackgroundThe phytocannabinoid cannabidiol (CBD) exhibits anxiolytic activity and has been promoted as a potential treatment for post-traumatic stress disorders. How does CBD interact with the brain to alter behavior? We hypothesized that CBD would produce a dose-dependent reduction in brain activity and functional coupling in neural circuitry associated with fear and defense.MethodsDuring the scanning session awake mice were given vehicle or CBD (3, 10, or 30 mg/kg I.P.) and imaged for 10 min post treatment. Mice were also treated with the 10 mg/kg dose of CBD and imaged 1 h later for resting state BOLD functional connectivity (rsFC). Imaging data were registered to a 3D MRI mouse atlas providing site-specific information on 138 different brain areas. Blood samples were collected for CBD measurements.ResultsCBD produced a dose-dependent polarization of activation along the rostral-caudal axis of the brain. The olfactory bulb and prefrontal cortex showed an increase in positive BOLD whereas the brainstem and cerebellum showed a decrease in BOLD signal. This negative BOLD affected many areas connected to the ascending reticular activating system (ARAS). The ARAS was decoupled to much of the brain but was hyperconnected to the olfactory system and prefrontal cortex.ConclusionThe CBD-induced decrease in ARAS activity is consistent with an emerging literature suggesting that CBD reduces autonomic arousal under conditions of emotional and physical stress.

Hypersomnia in stroke ischemic

ObjectiveHypersomnia/excessive daytime sleepiness post-stroke is a condition of prolonged daytime napping and nighttime sleep following a cerebrovascular accident. The incidence of sleep disorders occurs in more than 40% in the chronic phase and 70% in the acute phase. The incidence of hypersomnia increases in the first month after stroke. MethodsBased on observations by Von Economo found that symptoms of excessive sleepiness are often found in individuals with lesions in the junction area between the posterior hypothalamus and mesencephalon. Drowsiness can be caused by the presence of a direct lesion in the Reticular formation, which located in the midline region of the diencephalic structure caused by the involvement of the fibers tract, which builds Ascending Reticular Activating System (ARAS). ARAS is a central nervous system that has functions as a promotor of the sleep-wake process. There have been few cases of the mesencephalon and cerebellar infarction that affect the ARAS, which causes excessive drowsiness and hypersomnia. ResultsThis case will present a patient with ischemic stroke in the mesencephalon and cerebellar regions that affect the ARAS, thus providing symptoms of excessive drowsiness, nystagmus, multiple cranial nerve palsy and spastic hemiparesis due to the presence of several atherosclerotic plaques in the posterior circulations. This study used the Epworth Sleepiness Scale questionnaire to establish a diagnosis of hypersomnia. The administration of therapy depends on the underlying cause.

Functional connectivity disturbances of ascending reticular activating system and posterior thalamus in juvenile myoclonic epilepsy in relation with photosensitivity: A resting-state fMRI study

ObjectiveJuvenile myoclonic epilepsy (JME) is typified by the occurrence of myoclonic seizures after awakening, though another common trait is myoclonic seizures triggered by photic stimulation. We aimed to investigate the functional connectivity (FC) of nuclei in the ascending reticular activating system (ARAS), thalamus and visual cortex in JME with and without photosensitivity. MethodsWe examined 29 patients with JME (16 photosensitive (PS), 13 non- photosensitive-(NPS)) and 28 healthy controls (HCs) using resting-state functional magnetic resonance imaging (rs-fMRI). Seed-to-voxel FC analyses were performed using 25 seeds, including the thalamus, visual cortex, and ARAS nuclei. ResultsMesencephalic reticular formation seed revealed significant hyperconnectivity between the bilateral paracingulate gyrus and anterior cingulate cortex in JME group, and in both JME-PS and JME-NPS subgroups compared to HCs (pFWE-corr < 0.001; pFWE-corr < 0.001; pFWE-corr = 0.002, respectively). Locus coeruleus seed displayed significant hyperconnectivity with the bilateral lingual gyri, intracalcarine cortices, occipital poles and left occipital fusiform gyrus in JME-PS group compared to HCs (pFWE-corr <0.001). Additionally, locus coeruleus seed showed significant hyperconnectivity in JME-PS group compared to JME-NPS group with a cluster corresponding to the bilateral lingual gyri and right intracalcarine cortex (pFWE-corr < 0.001). Lastly, the right posterior nuclei of thalamus revealed significant hyperconnectivity with the right superior lateral occipital cortex in JME-PS group compared to HCs (pFWE-corr < 0.002). ConclusionsIn JME, altered functional connectivity of the arousal networks might contribute to the understanding of myoclonia after awakening, whereas increased connectivity of posterior thalamus might explain photosensitivity.

Electroencephalographic findings in Bickerstaff’s brainstem encephalitis: A possible reflection of the dysfunction of the ascending reticular activating system

ObjectivesBickerstaff’s brainstem encephalitis (BBE) is a rare post-infectious inflammatory disease, which causes impaired consciousness by the dysfunction of the ascending reticular activating system (ARAS). We aimed to clarify EEG changes possibly caused by the dysfunction of the ARAS in BBE. MethodsWe retrospectively investigated 15 EEGs from 5 patients with definite BBE (i.e., the positivity for serum IgG anti-GQ1b antibodies was mandatory for the diagnosis) admitted to our hospital from January 2014 through December 2019, particularly focusing on whether N1 and N2 sleep patterns were maintained. ResultsAll of the 10 EEGs recorded when patients had consciousness disturbance were abnormal. Stereotypical EEG changes correlating with their level of consciousness were identified: poorly organized posterior dominant rhythms with maintenance of sleep patterns in patients with mild consciousness disturbance (n = 5); predominant N1 and/or N2 sleep patterns even with external stimuli, including spindle coma pattern, in patients with moderate consciousness disturbance (“unarousable sleep-like” EEG) (n = 4); and generalized slow waves without N1 and N2 sleep patterns in patients with severe consciousness disturbance (n = 1). Among 5 patients, 3 (60%) had “unarousable sleep-like” EEG in their clinical course. ConclusionsPatients with BBE showed stereotypical EEG changes correlating with their level of consciousness, mostly with maintenance of N1 and N2 sleep patterns, and often exhibited characteristic “unarousable sleep-like” EEG. SignificanceThis study revealed characteristic EEG changes possibly caused by the dysfunction of the ARAS, which can be a diagnostic clue for BBE.

The relationship between consciousness and the ascending reticular activating system in patients with traumatic brain injury

BackgroundWe investigated the relationship between consciousness and the ascending reticular activating system (ARAS) by using diffusion tensor tractography (DTT) in patients with traumatic brain injury (TBI).MethodsTwenty-six patients with TBI and 13 healthy control subjects were recruited for this study. Glasgow Coma Scale (GCS) scores were used for evaluation of subject consciousness state at the chronic stage of TBI (at DTT scanning), According to the GCS score, the patient group was divided into two subgroups: A (14 patients;impaired consciousness: GCS score < 15, and B (12 patients;intact consciousness;GCS score = 15). Fractional anisotropy (FA) and tract volume (TV) values were assessed in the lower dorsal and upper ARAS.ResultsThe FA values of the lower dorsal ARAS and the upper ARAS in patient subgroup A were significantly lower than those in patient subgroup B and the control group(p < 0.05). However, the FA and TV values for the lower dorsal ARAS and the upper ARAS were not significantly different between patient subgroup B and the control group(p > 0.05). The FA value of the lower dorsal ARAS(r = 0.473,p < 0.05) and the TV of upper ARAS(r = 0.484,p < 0.05) had moderate positive correlations with the GCS score. The FA value of the upper ARAS had a strong positive correlation with the GCS score of the patient group(r = 0.780,p < 0.05).ConclusionsWe detected a close relationship between consciousness at the chronic stage of TBI and injuries of the lower dorsal and upper ARAS (especially, the upper ARAS) in patients who showed impaired consciousness at the onset of TBI. We believe that our results can be useful during the development of therapeutic strategies for patients with impaired consciousness following TBI.Trial registrationYUMC 2019–06–032-003. Retrospectively registered 06 Jun 2020.

Encephalitis lethargica epidemic milestones in early sleep neurobiology researches

Around 100 years ago, the outbreak of peculiar encephalitis promoted knowledge advancement regarding sleep and psychomotricity control. This epidemic is believed to have disappeared ten years after it started, and it remained from 1916 to 1927. Since then, only a few sporadic cases have been reported, but previously, they happened in occasional and epidemics forms. Two pioneers in describing the cases were Jean-René Cruchet and his collaborators, and Constantin Von Economo. The firsts described diffuse symptomatology, “sub-acute encephalomyelitis.” However, the reports by the Austrian aristocrat had a localized aspect which was admitted by him as a new disease, “Encephalitis lethargica” (EL). In his suppositions, based on clinical and anatomopathological material analysis, von Economo found distinct centers for sleep, in the rostral hypothalamus, and wakefulness, posterior hypothalamus. He plays an essential role in new achievements about EL and sleep neurobiology comprehension.These basic structural sleep-arousal regulatory neural systems had a lasting impact on contemporary sleep research, unfolded initially mainly by Frédéric Bremer, Giuseppe Moruzzi, and Horace Winchell Magoun, based on a passive theory of sleep induction. The lasts arrived at the conception of “diffuse” and “unspecific” ascending reticular activating system (ARAS) of the brain stem. This notion was unfolding until the idea of various interconnected “waking centers” and “sleep centers” levels, and also, active sleep induction.

Brainstem Functional Connectivity Disturbances in Epilepsy may Recover After Successful Surgery.

Focal seizures in temporal lobe epilepsy (TLE) are associated with widespread brain network perturbations and neurocognitive problems. To determine whether brainstem connectivity disturbances improve with successful epilepsy surgery, as recent work has demonstrated decreased brainstem connectivity in TLE that is related to disease severity and neurocognitive profile. We evaluated 15 adult TLE patients before and after (>1 yr; mean, 3.4 yr) surgery, and 15 matched control subjects using magnetic resonance imaging to measure functional and structural connectivity of ascending reticular activating system (ARAS) structures, including cuneiform/subcuneiform nuclei (CSC), pedunculopontine nucleus (PPN), and ventral tegmental area (VTA). TLE patients who achieved long-term postoperative seizure freedom (10 of 15) demonstrated increases in functional connectivity between ARAS structures and fronto-parietal-insular neocortex compared to preoperative baseline (P=.01, Kruskal-Wallis), with postoperative connectivity patterns resembling controls' connectivity. No functional connectivity changes were detected in 5 patients with persistent seizures after surgery (P=.9, Kruskal-Wallis). Among seizure-free postoperative patients, larger increases in CSC, PPN, and VTA functional connectivity were observed in individuals with more frequent seizures before surgery (P<.05 for each, Spearman's rho). Larger postoperative increases in PPN functional connectivity were seen in patients with lower baseline verbal IQ (P=.03, Spearman's rho) or verbal memory (P=.04, Mann-Whitney U). No changes in ARAS structural connectivity were detected after successful surgery. ARAS functional connectivity disturbances are present in TLE but may recover after successful epilepsy surgery. Larger increases in postoperative connectivity may be seen in individuals with more severe disease at baseline.

Effect of repetitive transcranial magnetic stimulation on the ascending reticular activating system in a patient with disorder of consciousness: a case report

BackgroundWe report on a stroke patient with disorder of consciousness (DOC) who underwent repetitive transcranial magnetic stimulation (rTMS) and showed recovery of an injured upper ascending reticular activating system (ARAS) injury, which was demonstrated by using serial diffusion tensor tractography (DTT).Case presentationA 45-year-old male patient was diagnosed as subarachnoid and intracerebral hemorrhages in the left fronto-parieto-temporal lobes. At 5 months after onset, the patient exhibited a persistent vegetative state, with a Coma Recovery Scale-Revised (CRS-R) score of 4. He underwent comprehensive rehabilitative therapy that included drugs for recovery of impaired consciousness and rTMS of the right dorsolateral prefrontal lobe. He recovered to a minimally conscious state (CRS-R: 13) at 7 months after onset and was transferred to a local rehabilitation hospital where he underwent similar rehabilitation but without rTMS. At 9 months after onset, his CRS-R score remained at 13. He was then readmitted to our hospital and underwent rehabilitation with rTMS until 10 months after onset. His CRS-R remained at 13, but his higher cognition had improved. The tract volume (TV) of the neural tract in the right prefrontal lobe in the upper ARAS on the 7-month DTT was higher than that on the 5-month DTT. However, compared to the 7-month DTT, the right prefrontal lobe TV was lower on the 9-month DTT. On the 10-month DTT, the TV of that neural tract had again increased.ConclusionsIncreases in neural TV in the right prefrontal lobe of the upper ARAS that were associated with the periods of rTMS application were demonstrated in a stroke patient with DOC.

Neurophysiology and Treatment of Disorders of Consciousness Induced by Traumatic Brain Injury: Orexin Signaling as a Potential Therapeutic Target.

Traumatic brain injury (TBI) can cause disorders of consciousness (DOC) by impairing the neuronal circuits of the ascending reticular activating system (ARAS) structures, including the hypothalamus, which are responsible for the maintenance of the wakefulness and awareness. However, the effectiveness of drugs targeting ARAS activation is still inadequate, and novel therapeutic modalities are urgently needed. The goal of this work is to describe the neural loops of wakefulness, and explain how these elements participate in DOC, with emphasis on the identification of potential new therapeutic options for DOC induced by TBI. Hypothalamus has been identified as a sleep/wake center, and its anterior and posterior regions have diverse roles in the regulation of the sleep/wake function. In particular, the posterior hypothalamus (PH) possesses several types of neurons, including the orexin neurons in the lateral hypothalamus (LH) with widespread projections to other wakefulness-related regions of the brain. Orexins have been known to affect feeding and appetite, and recently their profound effect on sleep disorders and DOC has been identified. Orexin antagonists are used for the treatment of insomnia, and orexin agonists can be used for narcolepsy. Additionally, several studies demonstrated that the agonists of orexin might be effective in the treatment of DOC, providing novel therapeutic opportunities in this field. The hypothalamic-centered orexin has been adopted as the point of entry into the system of consciousness control, and modulators of orexin signaling opened several therapeutic opportunities for the treatment of DOC.

Assessing Pupil-linked Changes in Locus Coeruleus-mediated Arousal Elicited by Trigeminal Stimulation.

Current scientific literature provides evidence that trigeminal sensorimotor activity associated with chewing may affect arousal, attention, and cognitive performance. These effects may be due to widespread connections of the trigeminal system to the ascending reticular activating system (ARAS), to which noradrenergic neurons of the locus coeruleus (LC) belongs. LC neurons contain projections to the whole brain, and it is known that their discharge co-varies with pupil size. LC activation is necessary for eliciting task-related mydriasis. If chewing effects on cognitive performance are mediated by the LC, it is reasonable to expect that changes in cognitive performance are correlated to changes in task-related mydriasis. Two novel protocols are presented here to verify this hypothesis and document that chewing effects are not attributable to aspecific motor activation. In both protocols, performance and pupil size changes observed during specific tasks are recorded before, soon after, and half an hour following a 2 min period of either: a) no activity, b) rhythmic, bilateral handgrip, c) bilateral chewing of soft pellet, and d) bilateral chewing of hard pellet. The first protocol measures level of performance in spotting target numbers displayed within numeric matrices. Since pupil size recordings are recorded by an appropriate pupillometer that impedes vision to ensure constant illumination levels, task-related mydriasis is evaluated during a haptic task. Results from this protocol reveal that 1) chewing-induced changes in performance and task-related mydriasis are correlated and 2) neither performance nor mydriasis are enhanced by handgrip. In the second protocol, use of a wearable pupillometer allows measurement of pupil size changes and performance during the same task, thus allowing even stronger evidence to be obtained regarding LC involvement in the trigeminal effects on cognitive activity. Both protocols have been run in the historical office of Prof. Giuseppe Moruzzi, the discoverer of ARAS, at the University of Pisa.

Thalamic Arousal Network Disturbances in Temporal Lobe Epilepsy and Improvement After Surgery

Abstract INTRODUCTION The effects of temporal lobe epilepsy (TLE) on subcortical arousal structures remain incompletely understood. Here we evaluate thalamic arousal network functional connectivity in TLE and examine changes after epilepsy surgery. METHODS We examined 26 adult TLE patients and 26 matched control participants and used resting-state functional magnetic resonance imaging (fMRI) to measure functional connectivity between the thalamus (entire thalamus and 19 bilateral thalamic nuclei) and both neocortex and brainstem ascending reticular activating system (ARAS) nuclei. Postoperative imaging was completed for 19 patients &gt; 1 yr after surgery and compared to preoperative baseline. RESULTS Before surgery, TLE patients demonstrated abnormal thalamo-occipital functional connectivity, losing the normal negative fMRI correlation between the intralaminar central lateral (CL) nucleus and medial occipital lobe seen in controls (P &lt; .001, paired t-test). Patients also had abnormal connectivity between ARAS and CL, lower ipsilateral intrathalamic connectivity, and smaller ipsilateral thalamic volume compared to controls (P &lt; .05 for each, paired t-tests). Abnormal brainstem-thalamic connectivity was associated with impaired visuospatial attention (? = −0.50, P = .02, Spearman's rho), while lower intrathalamic connectivity and volume were related to higher frequency of consciousness-sparing seizures (P &lt; .02, Spearman's rho). After epilepsy surgery, patients with improved seizures showed partial recovery of thalamo-occipital and brainstem-thalamic connectivity, with values more closely resembling controls (P &lt; .01 for each, ANOVA). CONCLUSION Overall, TLE patients demonstrate impaired connectivity in thalamic arousal networks that may be involved in visuospatial attention, but these disturbances may partially recover after successful epilepsy surgery. Thalamic arousal network dysfunction may contribute to morbidity in TLE.

Relationship Between Impaired Consciousness and Injury of Ascending Reticular Activating System in Patients With Intracerebral Hemorrhage.

Background and Purpose- We investigated the relationship between impaired consciousness and ascending reticular activating system (ARAS) characteristics on diffusion tensor tractography during the early stage of spontaneous intracerebral hemorrhage confined to a unilateral supratentorial area. Methods- A total of 29 consecutive patients with impaired consciousness (the patient group A), 31 age- and sex-matched patients without impaired consciousness (the patient group B), and 20 age- and sex-matched healthy control subjects were recruited. The Glasgow Coma Scale was used to evaluate patients' conscious state in the early stage of intracerebral hemorrhage (within 30 days after onset). Three parts of the ARAS (lower dorsal, lower ventral, and upper) were reconstructed, and fractional anisotropy and tract volume values were determined. Results- The tract volume value of the lower dorsal ARAS in the patient group A was significantly lower than those of the patient group B and control group in the affected hemisphere (P<0.05). Among the diffusion tensor tractography parameters, only the tract volume of the lower dorsal ARAS in the affected hemispheres of the patient group A had a moderate positive correlation with Glasgow Coma Scale score (r=0.456; P<0.05). Conclusions- Impaired consciousness during the early stage of intracerebral hemorrhage was closely related to injury of the lower dorsal ARAS in the affected hemisphere. Clinical Trial Registration- URL: http://www.e-irb.com/index.jsp. Unique identifier: 2015-07-064.

Thalamic arousal network disturbances in temporal lobe epilepsy and improvement after surgery

ObjectiveThe effects of temporal lobe epilepsy (TLE) on subcortical arousal structures remain incompletely understood. Here, we evaluate thalamic arousal network functional connectivity in TLE and examine changes after epilepsy surgery.MethodsWe...

Difference in the Ascending Reticular Activating System Injury Between Mild Traumatic Brain Injury and Cerebral Concussion.

IntroductionWe investigated differences in the ascending reticular activating system (ARAS) injuries between patients with mild traumatic brain injury (mTBI) and cerebral concussion by using diffusion tensor tractography (DTT).MethodsThirty-one patients with mTBI, 29 patients with concussion, and 30 control subjects were recruited. We used DTT to reconstruct the lower ventral and dorsal ARAS, and the upper ARAS. The fractional anisotropy (FA) value and the fiber number (FN) of the lower ventral and dorsal ARAS, and the upper ARAS were determined.ResultsSignificant differences were observed in the FA values of the lower ventral and dorsal ARAS on both sides between the mTBI and control groups and between the concussion and control groups (p < 0.05). The FN value was significantly different in the lower ventral ARAS on both sides between the concussion and control groups and between the mTBI and concussion groups (p < 0.05).ConclusionBoth the mTBI and concussion patients suffered injuries in the lower ventral and dorsal ARAS, with the concussion patients exhibiting more severe injury in the ventral ARAS than that in the mTBI patients. These results suggest that the terms mTBI and concussion should be used differentially, even though they have used interchangeably for a long time.

The Ascending Reticular Activating System.

Discovery of the ascending reticular activating system (ARAS) can be attributed to work done in research neuroscientist Horace Magoun's laboratory. Before this finding, most scientists would focus on the diencephalon (and anterior midbrain) but not more caudally. Stimulation of the medial bulbar reticular formation in the pontine and midbrain tegmentum resulted disappearance of synchronized discharge and low-voltage fast activity. The effects were mediated by a thalamic projection system. This finding was a dramatic departure from the early philosophers' ascription of the awake soul to the ventricles (Galen), lumbosacral cord (Plato), pineal gland (Descartes), and even from more modern nineteenth- and twentieth-century hypotheses that the corpus striatum or periaqueductal gray matter housed the "seat of awareness." Magoun and his collaborators closed in on its true location in the cephalic brainstem-clinicians and neuropathologists would soon follow.

Recovery of consciousness after a brainstem cavernous malformation hemorrhage: A descriptive study of preserved reticular activating system with tractography

The aim of this study is to describe the imaging features, the relevant anatomy, and the fractional anisotropy (FA) values in diffusion tensor tractography (DTT) of the ascending reticular activating system (ARAS) fiber tracts in 2 patients who recovered from initial altered consciousness after presenting with a brainstem cavernous malformation (BSCM) hemorrhage. A DTT was performed in 2 patients with impaired consciousness after a brainstem cavernous malformation hemorrhage. A 1.5 T scanner was used to obtain the axial tensors. Post-processing was performed and the mean FA values were recorded. The FA maps were used to seed the following regions of interest: the ventromedial midbrain, the anterior thalamus bilaterally, and the hypothalamus bilaterally. The first case presented with posterior displacement of the dorsal raphè fiber tracts, with preservation of all the ascending reticular activating fiber tracts and spontaneous recovery of consciousness after 20 days. The second case presented with no destruction but also had posterior displacement of the inferior dorsal raphè fiber tracts, with recovery of consciousness 1 month after resection surgery. Described in this study are affected fibers of the ARAS, as well as the FA value abnormalities in 2 patients, with recovery of a transient disorder of consciousness after a BSCM hemorrhage.