Midbrain injury in patients with subarachnoid hemorrhage: a diffusion tensor imaging study

We investigated the characteristics of midbrain injuries in patients with spontaneous subarachnoid hemorrhage (SAH) by using diffusion tensor imaging (DTI). Twenty-seven patients with SAH and 25 healthy control subjects were recruited for this study. Fractional anisotropy (FA) and mean diffusivity (MD) data were obtained for four regions of the midbrain (the anterior ventral midbrain, posterior ventral midbrain, tegmentum area, and tectum) in 27 hemispheres that did not show any pathology other than SAH. The mean FA and MD values of the four regions of the midbrain (anterior ventral midbrain, posterior ventral midbrain, tegmentum, and tectum) of the patient group were significantly lower and higher than those of the control group, respectively (p < 0.05). The mean FA values of the patient group were significantly different among the anterior ventral midbrain, posterior ventral midbrain, tegmentum, and tectum regions (ANOVA; F = 3.22, p < 0.05). Post hoc testing showed that the mean FA value of the anterior ventral midbrain was significantly lower than those of the posterior ventral midbrain, tegmentum, and tectum (p < 0.05); in contrast, there were no differences in mean FA values of the posterior ventral midbrain, tegmentum, and tectum (p > 0.05). However, differences were not observed among four regions of the midbrain (anterior ventral midbrain, posterior ventral midbrain, tegmentum, and tectum) in the mean MD values. We detected evidence of neural injury in all four regions of the midbrain of patients with SAH, and the anterior ventral midbrain was the most severely injured among four regions of the midbrain. Our results suggest that a pathophysiological mechanism of these neural injuries might be related to the occurrence of a subarachnoid hematoma.

Midbrain Injury in Patients With Subarachnoid Hemorrhage: A Diffusion Tensor Imaging Study

We investigated the characteristics of midbrain injuries in patients with spontaneous subarachnoid hemorrhage (SAH) by using diffusion tensor imaging (DTI). Twenty-seven patients with SAH and 25 healthy control subjects were recruited for this study. Fractional anisotropy (FA) data were obtained for four regions of the midbrain (the anterior ventral midbrain, posterior ventral midbrain, tegmentum area, and tectum) in 27 hemispheres that did not show any pathology other than SAH. The mean FA values of the four regions of the midbrain (anterior ventral midbrain, posterior ventral midbrain, tegmentum, and tectum) of the patient group were significantly lower than those of the control group (p < 0.05). The mean FA values of the patient group were significantly different among the anterior ventral midbrain, posterior ventral midbrain, tegmentum, and tectum regions (ANOVA; F = 3.22, p < 0.05). Post hoc testing showed that the mean FA value of the anterior ventral midbrain was significantly lower than those of the posterior ventral midbrain, tegmentum, and tectum (p < 0.05); in contrast, there were no differences in mean FA values of the posterior ventral midbrain, tegmentum, and tectum (p > 0.05). We detected evidence of neural injury in all four regions of the midbrain of patients with SAH, and the anterior ventral midbrain was the most severely injured among four regions of the midbrain. Our results suggest that a pathophysiological mechanism of these neural injuries might be related to the occurrence of a subarachnoid hematoma.

Cerebellar projections to the macaque midbrain tegmentum: Possible near response connections

Since most gaze shifts are to targets that lie at a different distance from the viewer than the current target, gaze changes commonly require a change in the angle between the eyes. As part of this response, lens curvature must also be adjusted with respect to target distance by the ciliary muscle. It has been suggested that projections by the cerebellar fastigial and posterior interposed nuclei to the supraoculomotor area (SOA), which lies immediately dorsal to the oculomotor nucleus and contains near response neurons, support this behavior. However, the SOA also contains motoneurons that supply multiply innervated muscle fibers (MIFs) and the dendrites of levator palpebrae superioris motoneurons. To better determine the targets of the fastigial nucleus in the SOA, we placed an anterograde tracer into this cerebellar nucleus in Macaca fascicularis monkeys and a retrograde tracer into their contralateral medial rectus, superior rectus, and levator palpebrae muscles. We only observed close associations between anterogradely labeled boutons and the dendrites of medial rectus MIF and levator palpebrae motoneurons. However, relatively few of these associations were present, suggesting these are not the main cerebellar targets. In contrast, labeled boutons in SOA, and in the adjacent central mesencephalic reticular formation (cMRF), densely innervated a subpopulation of neurons. Based on their location, these cells may represent premotor near response neurons that supply medial rectus and preganglionic Edinger–Westphal motoneurons. We also identified lens accommodation-related cerebellar afferent neurons via retrograde trans-synaptic transport of the N2c rabies virus from the ciliary muscle. They were found bilaterally in the fastigial and posterior interposed nuclei, in a distribution which mirrored that of neurons retrogradely labeled from the SOA and cMRF. Our results suggest these cerebellar neurons coordinate elements of the near response during symmetric vergence and disjunctive saccades by targeting cMRF and SOA premotor neurons.

Categorical signaling of the strongest stimulus by an inhibitory midbrain nucleus

ABSTRACTThe isthmi pars magnocellularis (Imc), a group of inhibitory neurons in the vertebrate midbrain tegmentum, orchestrates stimulus competition and spatial selection in the optic tectum (OT). Here, we investigate the properties of relative-strength dependent competitive interactions within the barn owl Imc. Imc neurons exhibit switch-like as well as gradual response profiles as a function of relative stimulus strength, do so for competing stimuli both within and across sensory modalities, and signal the strongest stimulus in a dynamically flexible manner. Notably, Imc signals the strongest stimulus more categorically (with greater precision), and earlier than the OT. Paired recordings at spatially aligned Imc and OT sites reveal that although some properties of stimulus competition are correlated, others are set independently. Our results demonstrate that the Imc is itself an active site of competition, and may be the first site in the midbrain selection network at which stimulus competition is resolved.

Spatial Dependence of Stimulus Competition in the Avian Nucleus Isthmi Pars Magnocellularis

The nucleus isthmi pars magnocellularis (Imc) is a group of specialized inhibitory neurons in the midbrain tegmentum, thought to be conserved across vertebrate classes. Past anatomical work in reptiles has suggested a role for it in stimulus selection, which has been supported by recent studies in avians. Additionally, focal inactivation of Imc neurons is known to abolish all competitive interactions in the optic tectum (OT; SC in mammals), a midbrain sensorimotor hub that is critical for the control of spatial attention, thereby revealing a key role for Imc in stimulus selection. However, the functional properties of Imc neurons are not well understood. Here, with electrophysiological experiments in the barn owl Imc, we show that Imc neurons themselves exhibit signatures of stimulus competition. Distant competing stimuli outside the spatial receptive field (RF) suppressed powerfully, and divisively, the responses of Imc neurons to stimuli inside the RF, and did so from all tested locations along the elevation as well as azimuth. Notably, this held true even for locations encoded by the opposite side of the brain from the one containing the recording site. This global divisive inhibition operated independently of the sensory modality of the competing stimulus. Thus, the Imc not only supplies inhibition to the OT to support competition there, but may itself be an active site of stimulus competition. These results from experiments in the barn owl shed light on the functional properties of a vital node in the vertebrate midbrain selection network.

DEEP BRAIN STIMULATION IN INTRACTABLE SHORT-LASTING UNILATERAL NEURALGIFORM HEADACHE ATTACKS: A MULTICASE SERIES

IntroductionSUNCT and SUNA are primary headache conditions characterized by short lasting attacks of unilateral pain accompanied by autonomic features. Neuroimaging studies have suggested a role of the posterior hypothalamus in its pathogenesis.AimPrevious case reports on deep brain stimulation (DBS) of the midbrain tegmentum (just posterior to the hypothalamus) for SUNCT/SUNA are limited to a total of three patients. We present clinical data on eight new patients treated with DBS.MethodEight patients underwent midbrain tegmentum DBS with an MRI-guided and verified approach. The target lay between the mammillothalamic tract and the anteromedial quadrant of the red nucleus. Headache diaries were used to monitor response.ResultsThe median follow up period was 20 months. Median improvement in attack frequency was 70%. Seven patients obtained a 30% or more reduction in attack frequency at final follow up. At final follow up, one patient had the stimulator off. Seven out of eight patients would opt to have the stimulator again and all would recommend to others.ConclusionMidbrain tegmentum DBS may be a useful treatment in intractable SUNCT. It should be reserved only for patients failing all other medical and surgical treatment options.