Cortical Responses to Vagus Nerve Stimulation Are Modulated by Brain State in Nonhuman Primates.

Vagus nerve stimulation (VNS) has been tested as therapy for several brain disorders and as a means to modulate cortical excitability and brain plasticity. Cortical effects of VNS, manifesting as vagal-evoked potentials (VEPs), are thought to arise from activation of ascending cholinergic and noradrenergic systems. However, it is unknown whether those effects are modulated by brain state at the time of stimulation. In 2 freely behaving macaque monkeys, we delivered short trains of 5 pulses to the left cervical vagus nerve at different frequencies (5-300 Hz) while recording local field potentials (LFPs) from sites in contralateral prefrontal, sensorimotor and parietal cortical areas. Brain states were inferred from spectral components of LFPs and the presence of overt movement: active awake, resting awake, REM sleep and NREM sleep. VNS elicited VEPs in all sampled cortical areas. VEPs comprised early (<70 ms), intermediate (70-250 ms) and late (>250 ms) components. The magnitude of the intermediate and late components was largest during NREM sleep and smallest during wakefulness, whereas that of the early component was not modulated by brain state. VEPs during NREM were larger for stimuli delivered at the depolarized phase of ongoing delta oscillations. Higher pulsing frequencies generated larger VEPs. These short VNS trains did not affect brain state transitions during wakefulness or sleep. Our findings suggest that ongoing brain state modulates the evoked effects of VNS on cortical activity. This has implications for the role of ongoing cortical activity and brain state in shaping cortical responses to peripheral stimuli, for the modulation of vagal interoceptive signaling by cortical activity, and for the dose calibration of VNS therapies.

Symptomatic spinal cord compression from an intradural arachnoid cyst with associated syrinx in a child: case report.

Symptomatic intradural extramedullary arachnoid cysts in children are rare, and of the previously reported pediatric cases in the current literature, none to our knowledge were associated with a spinal cord syrinx. We describe an 8-year-old child who presented with paraparesis and regression of bowel and bladder control. An intradural extramedullary arachnoid cyst was identified on preoperative magnetic resonance imaging, with an associated spinal cord syrinx. We describe the preoperative imaging, surgical management, and clinical course of this patient, who had improvement in his paraparesis. This paper reviews relevant pediatric literature and the etiology of arachnoid cysts and associated spinal cord syrinx formation.

Intrafascicular peripheral nerve stimulation produces fine functional hand movements in primates.

Restoring dexterous hand control is critical for people with paralysis. Approaches based on surface or intramuscular stimulation provide limited finger control, generate insufficient force to recover functional movements, and require numerous electrodes. Here, we show that intrafascicular peripheral electrodes could produce functional grasps and sustained forces in three monkeys. We designed an intrafascicular implantable electrode targeting the motor fibers of the median and radial nerves. Our interface selectively and reliably activated extrinsic and intrinsic hand muscles, generating multiple functional grips, hand opening, and sustained contraction forces for up to 2 months. We extended those results to a behaving monkey with transient hand paralysis and used intracortical signals to control simple stimulation protocols that enabled this animal to perform a functional grasping task. Our findings show that just two intrafascicular electrodes can generate a rich portfolio of dexterous and functional hand movements with important implications for clinical applicability.

Sequential activation of premotor, primary somatosensory and primary motor areas in humans during cued finger movements.

OBJECTIVE: Human voluntary movements are a final product of complex interactions between multiple sensory, cognitive and motor areas of central nervous system. The objective was to investigate temporal sequence of activation of premotor (PM), primary motor (M1) and somatosensory (S1) areas during cued finger movements. METHODS: Electrocorticography (ECoG) was used to measure activation timing in human PM, S1, and M1 neurons in preparation for finger movements in 5 subjects with subdural grids for seizure localization. Cortical activation was determined by the onset of high gamma (HG) oscillation (70-150Hz). The three cortical regions were mapped anatomically using a common brain atlas and confirmed independently with direct electrical cortical stimulation, somatosensory evoked potentials and detection of HG response to tactile stimulation. Subjects were given visual cues to flex each finger or pinch the thumb and index finger. Movements were captured with a dataglove and time-locked with ECoG. A windowed covariance metric was used to identify the rising slope of HG power between two electrodes and compute time lag. Statistical constraints were applied to the time estimates to combat the noise. Rank sum testing was used to verify the sequential activation of cortical regions across 5 subjects. RESULTS: In all 5 subjects, HG activation in PM preceded S1 by an average of 53±13ms (P=0.03), PM preceded M1 by 180±40ms (P=0.001) and S1 activation preceded M1 by 136±40ms (P=0.04). CONCLUSIONS: Sequential HG activation of PM, S1 and M1 regions in preparation for movements is reported. Activity in S1 prior to any overt body movements supports the notion that these neurons may encode sensory information in anticipation of movements, i.e., an efference copy. Our analysis suggests that S1 modulation likely originates from PM. SIGNIFICANCE: First electrophysiological evidence of efference copy in humans.

Ultrasound stylet for non-image-guided ventricular catheterization.

OBJECT Urgent ventriculostomy placement can be a lifesaving procedure in the setting of hydrocephalus or elevated intracranial pressure. While external ventricular drain (EVD) insertion is common, there remains a high rate of suboptimal drain placement. Here, the authors seek to demonstrate the feasibility of an ultrasound-based guidance system that can be inserted into an existing EVD catheter to provide a linear ultrasound trace that guides the user toward the ventricle. METHODS The ultrasound stylet was constructed as a thin metal tube, with dimensions equivalent to standard catheter stylets, bearing a single-element, ceramic ultrasound transducer at the tip. Ultrasound backscatter signals from the porcine ventricle were processed by custom electronics to offer real-time information about ventricular location relative to the catheter. Data collected from the prototype device were compared with reference measurements obtained using standard clinical ultrasound imaging. RESULTS A study of porcine ventricular catheterization using the experimental device yielded a high rate of successful catheter placement after a single pass (10 of 12 trials), despite the small size of pig ventricles and the lack of prior instruction on porcine ventricular architecture. A characteristic double-peak signal was identified, which originated from ultrasound reflections off of the near and far ventricular walls. Ventricular dimensions, as obtained from the width between peaks, were in agreement with standard ultrasound reference measurements (p < 0.05). Furthermore, linear ultrasound backscatter data permitted in situ measurement of the stylet distance to the ventricular wall (p < 0.05), which assisted in catheter guidance. CONCLUSIONS The authors have demonstrated the ability of the prototype ultrasound stylet to guide ventricular access in the porcine brain. The alternative design of the device makes it potentially easy to integrate into the standard workflow for bedside EVD placement. The availability of a fast, easy-to-use, inexpensive guidance system can play a role in reducing the complication rate for EVD placement.

Two patients with primary sellar leiomyomas, a rare entity.

Leiomyomas are benign smooth muscle tumors commonly found in the genitourinary or gastrointestinal tracts. Rarely, they present as primary intracranial extra-axial brain tumors. Most of these lesions have been described in immunocompromised patients, but have been found very rarely in the immunocompetent patient. We present two patients with sporadic sellar leiomyomas. The first patient is a 25-year-old woman who presented with a 2-year history of amenorrhea and a heterogeneous lesion. The second is a 53-year-old man who presented with headaches and progressive panhypopituitarism, and a large cystic lesion expanding the sella. In both patients, transnasal transphenoidal surgery was performed for resection of the tumor. We review the intraoperative findings, neuropathology and immunohistochemistry and the clinical follow-up. A literature search, which revealed only two prior reported cases of sporadic sellar leiomyomas, and subsequent review led us to conclude that the natural history of sellar leiomyomas relates to the immune status of the patient and that these tumors may cause pituitary dysfunction through infiltration of the gland, mass effect and compression, or even potentially as a byproduct of prolactin secretion intrinsic to the tumor itself. Complete surgical resection of these infiltrating tumors may not be advisable when pituitary function is intact. Long-term endocrine follow-up in these patients is advised.

The "triple-overlay" technique for percutaneous diagnosis and treatment of lesions of the head and neck: combined three-dimensional guidance with magnetic resonance imaging, cone-beam computed tomography, and fluoroscopy.

OBJECTIVE: Accurate image guidance is an essential component of percutaneous procedures in the head and neck. The combination of preprocedural magnetic resonance imaging (MRI) with cone-beam computed tomography (CBCT) and real-time fluoroscopy (the "triple-overlay" technique) could be useful in image-guided targeting of lesions in the head and neck. METHODS: Three patients underwent percutaneous diagnostic or therapeutic procedures of head and neck lesions (mean, 2.3 ± 2.4 cm). One patient presented for biopsy of a small lesion in the infratemporal fossa only visible on MRI, one presented for preoperative embolization of a nasal tumor, and one presented for sclerotherapy of a parotid hemangioma. Preprocedural MRI for each case was merged with CBCT to create a three-dimensional volume for procedural planning. This was then combined with real-time fluoroscopy to create a triple-overlay for needle trajectory and real-time guidance. RESULTS: The registration of MRI, CBCT, and fluoroscopy was successful for all three procedures, allowing 3D manipulation of the combined images. Percutaneous procedures were successful in all patients without complications. CONCLUSIONS: The combination of MRI, CBCT, and real-time fluoroscopy provides detailed anatomical information for 3D image-guided percutaneous procedures of the head and neck, especially for small lesions or lesions with features visible only by MRI.