Lower Ascending Reticular Activating System Research Articles

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.

Impaired consciousness caused by injury of the lower ascending reticular activating system: evaluation by diffusion tensor tractography.

A 34-year-old male patient underwent conservative management for traumatic hemorrhage in the right frontal lobe (Figure 1A). The patient lost consciousness for approximately 4 weeks and experienced post-traumatic amnesia continuously from the time of the accident. The patient's Glasgow Coma Scale score (Teasdale et al., 1974) was 6 when he arrived at the hospital. At 5 weeks after onset, he was transferred to the rehabilitation department to undergo rehabilitation. Brain MRI showed malactic lesions in both the frontal lobes and right thalamus (Figure 1B). The patient exhibited impaired consciousness, with a Glasgow Coma Scale score of 9 and Coma Recovery Scale-Revised score of 8 (Giacino et al., 2004). Figure 1 Brain CT images, magnetic resonance images and diffusion tensor tractography (DTT) images of a 34-year-old male patient with traumatic brain injury. Diffusion tensor tractography (DTT) data were obtained at 6 weeks after onset using a 6-channel head coil on a 1.5 T Philips Gyroscan Intera (Philips, Best, the Netherlands) with single-shot echo-planar imaging. Imaging parameters were as follows: acquisition matrix = 96 × 96; reconstructed matrix = 192 × 192; field of view = 240 × 240 mm2; repetition time = 10,726 ms; echo time = 76 ms; parallel imaging reduction factor (SENSE factor) = 2; EPI factor = 49; b = 1,000 s/mm2; number of excitations = 1; and a slice thickness of 2.5 mm. FACT algorithm was used for fiber tracking. For ascending reticular activating system (ARAS) analysis, the seed region of interest (ROI) was given on the pontine reticular formation. According to previous reports (Yeo et al., 2013; Jang et al., 2014), the target ROI was placed on the thalamic intralaminar nuclei to analyze the connectivity of the intralaminar nuclei. The patient showed intact neural connectivity between the thalamic intralaminar nuclei the frontal lobe. However, the left lower ARAS between pontine reticular formation and thalamic intralaminar nuclei was thinner than the right lower one of the same patient and those in five age-matched healthy control subjects (Figure 1C). In this study, we evaluated the ARAS in a patient with severe traumatic brain injury through two portions: First, three-dimensional reconstruction at the lower ARAS between the pontine reticular formation and the thalamic intralaminar nuclei, second, neural connectivity of the upper ARAS between the thalamic intralaminar nuclei and the cerebral cortex. Our results showed that the left lower ARAS was thinner than that of the right side of the patient and those of normal subjects. These findings appear to suggest an injury of the left lower ARAS. This injury was attributed to traumatic axonal injury because the conventional brain MRI of the patient was normal in the left thalamus and brainstem. Before analysis of the ARAS, we assumed that the main lesion would be located in the right ARAS and left upper ARAS because the brain MRI showed malactic lesions in both frontal lobes and the right thalamus. The main lesion site was detected in the left lower ARAS between the thalamic reticular formation and the thalamic intralaminar nuclei (Edlow et al., 2013; Jang et al., 2015a, b). Our results suggest that analysis of the ARAS using DTT would be useful for elucidating the cause of impaired consciousness. However, limitation of DTT with 1.5 T MRI should be considered, because a higher tesla MRI such as 3.0 T, can show better resolution and identify small tract more precisely. This work was supported by the National Research Foundation (NRF) of Korea Grant funded by the Korean Government (MSIP), No. 2015R1A2A2A01004073.