Real-time navigation guidance with intraoperative CT imaging for pedicle screw placement using an augmented reality head-mounted display: a proof-of-concept study.

OBJECTIVE: Augmented reality (AR) has the potential to improve the accuracy and efficiency of instrumentation placement in spinal fusion surgery, increasing patient safety and outcomes, optimizing ergonomics in the surgical suite, and ultimately lowering procedural costs. The authors sought to describe the use of a commercial prototype Spine AR platform (SpineAR) that provides a commercial AR head-mounted display (ARHMD) user interface for navigation-guided spine surgery incorporating real-time navigation images from intraoperative imaging with a 3D-reconstructed model in the surgeon's field of view, and to assess screw placement accuracy via this method. METHODS: Pedicle screw placement accuracy was assessed and compared with literature-reported data of the freehand (FH) technique. Accuracy with SpineAR was also compared between participants of varying spine surgical experience. Eleven operators without prior experience with AR-assisted pedicle screw placement took part in the study: 5 attending neurosurgeons and 6 trainees (1 neurosurgical fellow, 1 senior orthopedic resident, 3 neurosurgical residents, and 1 medical student). Commercially available 3D-printed lumbar spine models were utilized as surrogates of human anatomy. Among the operators, a total of 192 screws were instrumented bilaterally from L2-5 using SpineAR in 24 lumbar spine models. All but one trainee also inserted 8 screws using the FH method. In addition to accuracy scoring using the Gertzbein-Robbins grading scale, axial trajectory was assessed, and user feedback on experience with SpineAR was collected. RESULTS: Based on the Gertzbein-Robbins grading scale, the overall screw placement accuracy using SpineAR among all users was 98.4% (192 screws). Accuracy for attendings and trainees was 99.1% (112 screws) and 97.5% (80 screws), respectively. Accuracy rates were higher compared with literature-reported lumbar screw placement accuracy using FH for attendings (99.1% vs 94.32%; p = 0.0212) and all users (98.4% vs 94.32%; p = 0.0099). The percentage of total inserted screws with a minimum of 5° medial angulation was 100%. No differences were observed between attendings and trainees or between the two methods. User feedback on SpineAR was generally positive. CONCLUSIONS: Screw placement was feasible and accurate using SpineAR, an ARHMD platform with real-time navigation guidance that provided a favorable surgeon-user experience.

Motor preparatory activity in posterior parietal cortex is modulated by subjective absolute value.

For optimal response selection, the consequences associated with behavioral success or failure must be appraised. To determine how monetary consequences influence the neural representations of motor preparation, human brain activity was scanned with fMRI while subjects performed a complex spatial visuomotor task. At the beginning of each trial, reward context cues indicated the potential gain and loss imposed for correct or incorrect trial completion. FMRI-activity in canonical reward structures reflected the expected value related to the context. In contrast, motor preparatory activity in posterior parietal and premotor cortex peaked in high "absolute value" (high gain or loss) conditions: being highest for large gains in subjects who believed they performed well while being highest for large losses in those who believed they performed poorly. These results suggest that the neural activity preceding goal-directed actions incorporates the absolute value of that action, predicated upon subjective, rather than objective, estimates of one's performance.

Space representation for eye movements is more contralateral in monkeys than in humans.

Contralateral hemispheric representation of sensory inputs (the right visual hemifield in the left hemisphere and vice versa) is a fundamental feature of primate sensorimotor organization, in particular the visuomotor system. However, many higher-order cognitive functions in humans show an asymmetric hemispheric lateralization--e.g., right brain specialization for spatial processing--necessitating a convergence of information from both hemifields. Electrophysiological studies in monkeys and functional imaging in humans have investigated space and action representations at different stages of visuospatial processing, but the transition from contralateral to unified global spatial encoding and the relationship between these encoding schemes and functional lateralization are not fully understood. Moreover, the integration of data across monkeys and humans and elucidation of interspecies homologies is hindered, because divergent findings may reflect actual species differences or arise from discrepancies in techniques and measured signals (electrophysiology vs. imaging). Here, we directly compared spatial cue and memory representations for action planning in monkeys and humans using event-related functional MRI during a working-memory oculomotor task. In monkeys, cue and memory-delay period activity in the frontal, parietal, and temporal regions was strongly contralateral. In putative human functional homologs, the contralaterality was significantly weaker, and the asymmetry between the hemispheres was stronger. These results suggest an inverse relationship between contralaterality and lateralization and elucidate similarities and differences in human and macaque cortical circuits subserving spatial awareness and oculomotor goal-directed actions.

Intracranial lymphoma in human immunodeficiency virus-infected patients: A diagnostic dilemma?

Primary central nervous system (CNS) lymphoma is an aggressive malignancy which constitutes one of the acquired immunodeficiency syndrome -defining illnesses. Early diagnosis and timely management can increase the chances of cure. Although many times the diagnosis is straightforward, we present a case of primary CNS lymphoma in a human immunodeficiency virus--positive individual which posed as a major diagnostic dilemma with initially normal imaging findings. A 42-year-old male presented with unremitting fever and a perianal ulcer for 3 months. A battery of diagnostic tests were negative, including a positron emission tomography-computed tomography scan and a magnetic resonance imaging brain. With unresolving symptoms and a high index of suspicion as he developed dizziness and loss of balance, the same were repeated which confirmed a space-occupying lesion in the cerebellum. Although treatment was instituted, the patient did not recover and died in the 4th month of treatment.

Understanding drug resistance patterns across different classes of antiretrovirals used in HIV-1-infected treatment-Naïve and experienced patients in Mumbai, India.

Background: The aim of this study is to find out the proportion of treatment-naïve (Tn) and treatment-experienced (Te) patients experiencing HIV drug resistance (DR) to different classes of antiretrovirals (ARVs) being used for HIV treatment and their in class DR correlation. Methods: A cross-sectional study was done on 109 HIV patients enrolled at a private hospital in Thane, India, from 2014 to 2019. All patients were tested for CD4 count, viral load, and resistance to ARVs. Results: Sixty-six patients were Tn and 43 patients were Te. Among Tn and Te patients, the percentage of high-level resistance (HLR) for nonnucleoside reverse transcriptase inhibitors (NNRTI) was 4.55% and 37.8%, respectively, for nucleoside reverse transcriptase inhibitors (NRTI) was 0.43% and 36.4%, respectively. No HLR was observed for protease inhibitors (PIs) among Tn patients, while Te patients showed 2.62% HLR. Tn and Te patients showed high susceptibility for Darunavir (98.48% and 95.34%, respectively) followed by Atazanavir and Lopinavir (96.96%, each and 90.69%, each). Tn patients showed HLR for Lamivudine and Emtricitabine (1.52%, each). Integrase Strand Transfer Inhibitors were susceptible (100%) in both Tn and Te patients. A positive correlation was observed for within class across ARVs. Conclusion: An increased incidence of HLR was observed for NNRTI as compared to NRTI while PIs and integrase strand transfer inhibitors (INSTIs) demonstrated no HLR in either group of patients. When selecting a regimen for Tn patients consisting of NRTIs + NNRTIs genotypic DR test is essential. While with PIs or INSTIs its optional. Among Te patients, DR testing is recommended for all classes of drugs.

Human posterior parietal cortex plans where to reach and what to avoid.

In this time-resolved functional magnetic resonance imaging (fMRI) study, we aimed to trace the neuronal correlates of covert planning processes that precede visually guided motor behavior. Specifically, we asked whether human posterior parietal cortex has prospective planning activity that can be distinguished from activity related to retrospective visual memory and attention. Although various electrophysiological studies in monkeys have demonstrated such motor planning at the level of parietal neurons, comparatively little support is provided by recent human imaging experiments. Rather, a majority of experiments highlights a role of human posterior parietal cortex in visual working memory and attention. We thus sought to establish a clear separation of visual memory and attention from processes related to the planning of goal-directed motor behaviors. To this end, we compared delayed-response tasks with identical mnemonic and attentional demands but varying degrees of motor planning. Subjects memorized multiple target locations, and in a random subset of trials targets additionally instructed (1) desired goals or (2) undesired goals for upcoming finger reaches. Compared with the memory/attention-only conditions, both latter situations led to a specific increase of preparatory fMRI activity in posterior parietal and dorsal premotor cortex. Thus, posterior parietal cortex has prospective plans for upcoming behaviors while considering both types of targets relevant for action: those to be acquired and those to be avoided.

Schwannomas of the Frontal Sinus: Cases and Review of the Literature.

BACKGROUND: Although schwannomas are commonly found in the head and neck region, sinonasal tract involvement is extremely rare, estimated as <4%. The presence of these lesions in the frontal sinus is even less common. CASE DESCRIPTION: Two patients presented with schwannomas originating in the frontal sinus with variable degrees of extension. These patients underwent resection of the tumors via an endoscopic or combined approach. The histologic diagnosis confirmed schwannoma in both cases. CONCLUSIONS: Although these lesions have traditionally been approached through larger craniotomies and open procedures, we describe less invasive approaches for these rare frontal sinus schwannomas and demonstrate them as a valid alternative with minimal morbidity for patients.

What do we perceive in a glance of a real-world scene?

What do we see when we glance at a natural scene and how does it change as the glance becomes longer? We asked naive subjects to report in a free-form format what they saw when looking at briefly presented real-life photographs. Our subjects received no specific information as to the content of each stimulus. Thus, our paradigm differs from previous studies where subjects were cued before a picture was presented and/or were probed with multiple-choice questions. In the first stage, 90 novel grayscale photographs were foveally shown to a group of 22 native-English-speaking subjects. The presentation time was chosen at random from a set of seven possible times (from 27 to 500 ms). A perceptual mask followed each photograph immediately. After each presentation, subjects reported what they had just seen as completely and truthfully as possible. In the second stage, another group of naive individuals was instructed to score each of the descriptions produced by the subjects in the first stage. Individual scores were assigned to more than a hundred different attributes. We show that within a single glance, much object- and scene-level information is perceived by human subjects. The richness of our perception, though, seems asymmetrical. Subjects tend to have a propensity toward perceiving natural scenes as being outdoor rather than indoor. The reporting of sensory- or feature-level information of a scene (such as shading and shape) consistently precedes the reporting of the semantic-level information. But once subjects recognize more semantic-level components of a scene, there is little evidence suggesting any bias toward either scene-level or object-level recognition.

Manipulating stored phonological input during verbal working memory.

Verbal working memory (vWM) involves storing and manipulating information in phonological sensory input. An influential theory of vWM proposes that manipulation is carried out by a central executive while storage is performed by two interacting systems: a phonological input buffer that captures sound-based information and an articulatory rehearsal system that controls speech motor output. Whether, when and how neural activity in the brain encodes these components remains unknown. Here we read out the contents of vWM from neural activity in human subjects as they manipulated stored speech sounds. As predicted, we identified storage systems that contained both phonological sensory and articulatory motor representations. Unexpectedly, however, we found that manipulation did not involve a single central executive but rather involved two systems with distinct contributions to successful manipulation. We propose, therefore, that multiple subsystems comprise the central executive needed to manipulate stored phonological input for articulatory motor output in vWM.

Components of bottom-up gaze allocation in natural images.

Recent research [Parkhurst, D., Law, K., & Niebur, E., 2002. Modeling the role of salience in the allocation of overt visual attention. Vision Research 42 (1) (2002) 107-123] showed that a model of bottom-up visual attention can account in part for the spatial locations fixated by humans while free-viewing complex natural and artificial scenes. That study used a definition of salience based on local detectors with coarse global surround inhibition. Here, we use a similar framework to investigate the roles of several types of non-linear interactions known to exist in visual cortex, and of eccentricity-dependent processing. For each of these, we added a component to the salience model, including richer interactions among orientation-tuned units, both at spatial short range (for clutter reduction) and long range (for contour facilitation), and a detailed model of eccentricity-dependent changes in visual processing. Subjects free-viewed naturalistic and artificial images while their eye movements were recorded, and the resulting fixation locations were compared with the models' predicted salience maps. We found that the proposed interactions indeed play a significant role in the spatiotemporal deployment of attention in natural scenes; about half of the observed inter-subject variance can be explained by these different models. This suggests that attentional guidance does not depend solely on local visual features, but must also include the effects of interactions among features. As models of these interactions become more accurate in predicting behaviorally-relevant salient locations, they become useful to a range of applications in computer vision and human-machine interface design.