Contralateral Occipital Research Articles

Reorganization of Oscillatory Activity in Human Parietal Cortex during Spatial Updating

Single-neuron recordings have shown that the posterior parietal cortex (PPC) processes spatial information in many frames of reference, including gaze-centered, head-centered, body-centered, and intermediate coding frames. At the population level, rhythmic neuronal synchronization may provide a mechanism by which PPC could selectively emphasize the task-relevant reference frame in spatial processing. Using magnetoencephalography, we tested this hypothesis by studying the modulations in oscillatory activity in a spatial updating task. Human subjects had to remember the location of a target, briefly flashed left or right of central fixation. Next, they refixated and then, after a further memory delay, made a saccade to the memorized target location. We observed gamma-band (>40 Hz) synchronization and alpha-band (8-12 Hz) desychronization in contralateral occipital and parietal areas, both showing updating in a gaze-centered reference frame but with fast and slow time courses, respectively. Furthermore, after updating, ipsilateral areas showed less alpha desynchronization when they had been contralateral to the target before updating. Taken together, our results suggest that power in the gamma band is instantly reorganized to encode task-relevant visuomotor space in a gaze-centered reference frame, while power in the alpha band reflects a regulatory mechanism actively facilitating the gating of the saccade target and inhibiting the original stimulus representation.

Sonographic Evaluation of the Greater Occipital Nerve in Unilateral Occipital Neuralgia

Occipital neuralgia is a headache that may result from greater occipital nerve entrapment. Entrapped peripheral nerves typically have an increase in cross-sectional area. The purpose of this study was to measure the cross-sectional area and circumference of symptomatic and asymptomatic greater occipital nerves in patients with unilateral occipital neuralgia and to correlate the greater occipital nerve cross-sectional area with headache severity, sex, and body mass index. Both symptomatic and contralateral asymptomatic greater occipital nerve cross-sectional areas and circumferences were measured by a single examiner using sonography in 17 patients. The Wilcoxon signed rank test and Spearman rank order correlation coefficient were used to analyze the data. Significant differences between the cross-sectional areas and circumferences of the symptomatic and asymptomatic greater occipital nerves were noted (P < .001). No difference existed in cross-sectional area (P = .40) or circumference (P = .10) measurements of the nerves between male and female patients. A significant correlation existed between the body mass index and symptomatic (r = 0.424; P = .045) and asymptomatic (r = 0.443; P = .037) cross-sectional areas. There was no correlation shown between the cross-sectional area of the symptomatic nerve and the severity of Headache Impact Test 6 scores (r = -0.342; P = .179). We report sonographic evidence showing an increased cross-sectional area and circumference of the symptomatic greater occipital nerve in patients with unilateral occipital neuralgia.

Subarachnoid Hemorrhage Caused by Ruptured Intracranial Fusiform Aneurysm Associated With Microscopic Polyangiitis

A 44-year-old woman with microscopic polyangiitis (MPA) presented with a ruptured cerebral aneurysm. She was admitted to our hospital for further examination of progressive renal failure. She was found lying on the ward floor. Computed tomography showed subarachnoid hemorrhage, and digital subtraction angiography revealed a saccular-like aneurysm arising from the right distal posterior inferior cerebellar artery (PICA) at the non-branching site. We performed neck clipping of the right distal PICA aneurysm, which recurred 5 days after the operation. Second angiography demonstrated a right distal PICA aneurysm just above the site of the clip. Therefore, we performed trapping of the affected lesion with emergent bypass of the contralateral occipital artery to the ipsilateral PICA. Her postoperative course was uneventful until she coughed up blood and had gross hematuria 3 days after the second surgery. Histological examination of a renal biopsy specimen revealed crescentic glomerulonephritis. MPA was diagnosed on the basis of the cardinal symptoms, including progressive glomerular nephritis and the lung abnormality, as well as the presence of myeloperoxidase-antineutrophil cytoplasmic antibodies. After intensive treatment, she was discharged for rehabilitation without neurological deficit. MPA commonly affects small-sized vessels mainly in the kidneys and lungs and may lead to crescentic glomerulonephritis and pulmonary hemorrhage. MPA is rarely associated with aneurysms of medium-sized muscular vessels. Cerebral aneurysm is extremely rare in patients with MPA, but rupture of an intracranial fusiform aneurysm can be lethal, so screening of the intracranial vessels should be performed by magnetic resonance imaging in patients with MPA.

Right-and-left visual field stimulation: A frequency and space mixed coding method for SSVEP based brain-computer interface

On the condition of using limited frequencies, fewer targets could be presented in brain-computer interface (BCI) based on steady-state visual evoked potentials (SSVEP). This paper proposes a novel coding method for SSVEP that, through a combination of frequency and spatial information, could increase the number of targets. Each target was composed of two flickers placed in the right-and-left visual fields. Given the role of the optic chiasm in the vision pathway, the two frequency components could be projected to contralateral occipital regions. Canonical correlation analysis (CCA) was utilized to detect the frequency components from the right or left visual cortex. Asymmetric index as a supplementary feature was also computed. Linear discriminant analysis (LDA) was used for target recognition. The attractive feature of this method is that it would substantially increase the number of targets. If the number of frequency was N, the method could present N times more targets than conventional SSVEP-based BCIs.

Effects of subjective preference of colors on attention-related occipital theta oscillations

Human daily behaviors are often affected by subjective preferences. Studies have shown that physical responses are affected by unconscious preferences before conscious decision making. Accordingly, attention-related neural activities could be influenced by unconscious preferences. However, few neurological data exist on the relationship between visual attention and subjective preference. To address this issue, we focused on lateralization during visual attention and investigated the effects of subjective color preferences on visual attention-related brain activities. We recorded electroencephalograph (EEG) data during a preference judgment task that required 19 participants to choose their preferred color from 2 colors simultaneously presented to the right and left hemifields. In addition, to identify oscillatory activity during visual attention, we conducted a control experiment in which the participants focused on either the right or the left color without stating their preference. The EEG results showed enhanced theta (4-6 Hz) and decreased alpha (10-12 Hz) activities in the right and left occipital electrodes when the participants focused on the color in the opposite hemifield. Occipital theta synchronizations also increased contralaterally to the hemifield to which the preferred color was presented, whereas the alpha desynchronizations showed no lateralization. The contralateral occipital theta activity lasted longer than the ipsilateral occipital theta activity. Interestingly, theta lateralization was observed even when the preferred color was presented to the unattended side in the control experiment, revealing the strength of the preference-related theta-modulation effect irrespective of visual attention. These results indicate that subjective preferences modulate visual attention-related brain activities.

Exploring steady‐state visual evoked potentials as an index for intermodal and crossmodal spatial attention

The present study used steady-state visual evoked potentials (SSVEPs) recorded in parallel to a task-relevant auditory/visual stimulation to study the process of intermodal and crossmodal spatial attention on visual processing. SSVEPs were elicited by task-irrelevant 10/15Hz pattern-reversing checkerboards. The participants were asked to respond to deviant transient stimuli of the attended side in the attended modality only. A phase-locking index (PLI) method was employed to characterize SSVEPs. Both unimodal and crossmodal spatial attention resulted in an increase of PLI values over contralateral occipital brain regions. Intermodal attention effects were observed as an increase of the PLI over the same brain areas when the auditory rather than the visual modality was attended. These findings support recent hypotheses that the phase resetting of the brain activity in early sensory cortices is an essential mechanism of multisensory interaction.

Occipitofrontal Switching for Simultaneous Correction of Synostotic Frontal and Occipital Plagiocephaly: A Novel Surgical Technique

Plagiocephaly has traditionally been corrected by unilateral or bilateral frontal bone advancement or rotation using bone-molding forceps and distraction devices. Complete symmetrical correction of deformed frontal bones is considered almost impossible because the curvature of each frontal bone varies. We evaluated the feasibility of measuring the optimal curvature of frontal and occipital bones using a plaster skull model and applying these measurements to "switch" them for simultaneous correction of frontal and occipital plagiocephaly. A 2-year-old girl suffering from unifrontal flattening visited our clinic. Unilateral coronal synostosis was observed. The 3-D rapid prototype model and skull replica method using thin paper clay were used for preplanned virtual surgery. The triangular bone was harvested from the contralateral bulging side of the occipital bone ("occipitofrontal switching") for the best optimal curvature in the affected frontal bone. Another triangular bone was harvested from the ipsilateral flattened side of the frontal bone, and bones were switched with each other. Further bending of the frontal or occipital segment was not necessary for optimal curvature. Symmetrical correction was made by switching the triangular bone of the frontal area with that of the contralateral occipital area. Revision has not been necessary, and infection was not observed at 1-year follow-up. Our novel technique of preplanning surgery using a 3-D plaster model for simultaneous correction of frontal and occipital plagiocephaly is effective and time-saving.

Backward masked fearful faces enhance contralateral occipital cortical activity for visual targets within the spotlight of attention

Spatial attention has been argued to be adaptive by enhancing the processing of visual stimuli within the 'spotlight of attention'. We previously reported that crude threat cues (backward masked fearful faces) facilitate spatial attention through a network of brain regions consisting of the amygdala, anterior cingulate and contralateral visual cortex. However, results from previous functional magnetic resonance imaging (fMRI) dot-probe studies have been inconclusive regarding a fearful face-elicited contralateral modulation of visual targets. Here, we tested the hypothesis that the capture of spatial attention by crude threat cues would facilitate processing of subsequently presented visual stimuli within the masked fearful face-elicited 'spotlight of attention' in the contralateral visual cortex. Participants performed a backward masked fearful face dot-probe task while brain activity was measured with fMRI. Masked fearful face left visual field trials enhanced activity for spatially congruent targets in the right superior occipital gyrus, fusiform gyrus and lateral occipital complex, while masked fearful face right visual field trials enhanced activity in the left middle occipital gyrus. These data indicate that crude threat elicited spatial attention enhances the processing of subsequent visual stimuli in contralateral occipital cortex, which may occur by lowering neural activation thresholds in this retinotopic location.

Group‐specific regional white matter abnormality revealed in diffusion tensor imaging of medial temporal lobe epilepsy without hippocampal sclerosis

In comparison to temporal lobe epilepsy (TLE) patients with hippocampal sclerosis (TLE-HS), TLE patients without HS (TLE-NH) have a similar clinical course but may result in worse surgical outcome. We investigated whether the clinical features related to the lack of HS in TLE patients (TLE-NH) can be explained by water diffusion abnormalities throughout diffusion tensor imaging (DTI) by voxel-based analysis. Nineteen patients with TLE-HS (left/right TLE 12:7), 18 patients with TLE-NH (left/right TLE 10:8), and 20 controls were included in the study. By statistical parametric mapping (SPM2), the diffusion properties specific to disease characteristics (TLE-HS vs. TLE-NH) were analyzed. In TLE-HS, we found the areas of increased mean diffusivity (MD) in their ipsilateral temporal and extratemporal areas including the hippocampus, parahippocampal, and frontoparietal regions. Left TLE-HS showed a characteristic MD increase in the ipsilateral posterior cingulum, isthmus of corpus callosum, and contralateral occipital and temporal regions, which was not observed in right TLE-HS group. In left TLE-NH, two regions of increased MD were observed in the ipsilateral posterior fornix (within fusiform gyrus) and posterior cingulum. Right TLE-NH did not show any increased MD. In left TLE-NH, we could find the water diffusion change along the posterior cingulum, which was quite different from the extensive abnormality from TLE-HS. In addition, there was a lesion-side-specific distribution (left predominant) of pathology in mesial TLE. This provides a possibility that TLE-NH is a heterogeneous or entity different from TLE-HS.

Studying the Role of Human Parietal Cortex in Visuospatial Attention with Concurrent TMS-fMRI

Combining transcranial magnetic stimulation (TMS) with concurrent functional magnetic resonance imaging (fMRI) allows study of how local brain stimulation may causally affect activity in remote brain regions. Here, we applied bursts of high- or low-intensity TMS over right posterior parietal cortex, during a task requiring sustained covert visuospatial attention to either the left or right hemifield, or in a neutral control condition, while recording blood oxygenation-level–dependent signal with a posterior MR surface coil. As expected, the active attention conditions activated components of the well-described “attention network,” as compared with the neutral baseline. Also as expected, when comparing left minus right attention, or vice versa, contralateral occipital visual cortex was activated. The critical new finding was that the impact of high- minus low-intensity parietal TMS upon these visual regions depended on the currently attended side. High- minus low-intensity parietal TMS increased the difference between contralateral versus ipsilateral attention in right extrastriate visual cortex. A related albeit less pronounced pattern was found for left extrastriate visual cortex. Our results confirm that right human parietal cortex can exert attention-dependent influences on occipital visual cortex and provide a proof of concept for the use of concurrent TMS–fMRI in studying how remote influences can vary in a purely top–down manner with attentional demands.

Neuronal oscillatory correlates of stimulus-response (in)congruency

Transforming sensory input into motor output is an important function of the brain and involves various brain regions. Stimulus response (SR) congruency tasks can be used to probe these regions. Traditionally, electroencephalography (EEG) has been used to measure sensor level lateralized evoked potentials in the time domain, to study the neural correlates of sensorimotor transformations. We used magnetoencephalography (MEG) in combination with a modified Simon task to explore the oscillatory components related to the processing of SR-(in)congruencies. MEG allows for whole head coverage and source analysis, reducing the need to combine left and right recording sites. Moreover, evidence is increasing that oscillations are crucial for information processing within and between regions. 19 Subjects performed a two choice response task. In a given trial, one out of two lateralized visual stimuli reflected the required response side. Differences in oscillatory activity between SR-congruent and SR-incongruent trials were assessed at the source level using beamformers, and the results for the two response sides were combined. We found SR congruency effects in several brain regions. Specifically, we observed a more profound event related desynchronization (ERD) in visual and parietal regions (α-band) and sensorimotor regions (β-band) contralateral to the response side in the congruent condition, and a less profound ERD in ipsilateral sites. High frequency power was increased in contralateral temporo occipital, parietal and sensorimotor regions in the congruent condition, and decreased in homologous ipsilateral sites. These findings extend earlier reports and show a hemisphere specific increase in activity, not only in visual regions processing the target stimulus, but also in ipsilateral executive regions in the incongruent condition. The latter finding may reflect activity to suppress an automated response to spatially congruent SR-pairs. Event abstract at: Biomag 2010 - 17th International Conference on Biomagnetism Conference, 28 March - 01 April 2010, Dubrovnik, Croatia.

Incidence of Otitis Media in Children With Deformational Plagiocephaly

In the past decade, deformational plagiocephaly has seen a staggering increase attributed to the Back to Sleep Campaign of April 1992. With this increase, the possible clinical associations need to be fully understood. The anatomic changes seen include ipsilateral occipital flattening, ipsilateral frontal bossing, ipsilateral anterior ear displacement, contralateral occipital bossing, and contralateral frontal flattening [J Craniofac Surg 2004;15:368-372, erratum in J Craniofac Surg 2004;15:705; Fig. l]. Children with deformational plagiocephaly can have malpositioned ears affecting normal drainage of the eustachian tube as it shifts with this deformity. The eustachian tube plays an important role in draining the middle ear. As evidenced by children with cleft palates, structural differences in the anatomy of the middle ear and eustachian tube can result in an increased susceptibility to otitis media. An institutional review board-approved retrospective study was conducted on all patients whose conditions were diagnosed as deformational plagiocephaly from a cleft and craniofacial deformities clinic for a 2-year period. Parents of patients self-reported the number of ear infections on a questionnaire. The questionnaire results were compared to age-matched patient data available from the Center for Disease Control. There were 1259 patients who fit the inclusion criteria for the questionnaire part of the study, and of these, 634 (50.4%) reported at least 1 ear infection by 1 year of age. In addition to the questionnaire, a subset of infants with deformational plagiocephaly up to 1 year of age were administered a tympanogram, to assess the state of the middle ear. There were 124 patients who fit the inclusion criteria for the tympanometry part of the study, and of these 121 had an abnormal tympanogram at 1 or more clinic visits. The questionnaire did not show deformational plagiocephaly to be a significant risk factor for otitis media in our patient population; however, a trend directly correlating otitis media and the severity level of deformational plagiocephaly was observed. Although this trend lacked statistical significance, further studies should explore these differences. Tympanogrametry showed a marked percentage of infants with deformational plagiocephaly to have eustachian tube dysfunction. Future studies will focus on the significance of these findings.

Gaussian source model based iterative algorithm for EEG source imaging

Estimation of the neural active sources from the scalp electroencephalogram (EEG) is an ill-posed inverse problem. In this paper, we propose a new source model: Gaussian distributed Source Model (GSM), to model the activations in brain. GSM may imitate an Isolated Source Model (ISM) or a Distributed Source Model (DSM) by adopting different supporting range parameter of the Gaussian function. Using GSM, an iterative Gaussian source Imaging Algorithm (GIA) is developed to detect the EEG sources. As GIA dynamically reduces the solution space, the solution may gradually converge to a desired distribution. A comparative evaluation among LORETA, FOCUSS and GIA was conducted for both isolated point sources and distributed sources, the results demonstrate that GIA is more flexible and efficient for various actual sources configurations. Finally, GSM was applied to real recordings obtained from a visual spatial attention task; the corresponding source activation areas of the early component are localized in contralateral occipital cortices, consistent with the retinotopic organization of early visual spatial attention effects.

Isolating event-related potential components associated with voluntary control of visuo-spatial attention

Attention-directing cues presented at fixation evoke several lateralized event-related potential (ERP) components prior to the onset of visual targets. These components have been associated with the control of visuo-spatial attention, but the neuro-cognitive operations and neural generators of the components are still largely unknown. Here, we isolated cue-elicited ERP activity in different ways to home in on different neuro-cognitive operations and to gain a better understanding about the possible neuroanatomical sources of the cue-elicited ERP activities. To isolate lateralized cue-ERP activity, we compared shift-left and shift-right cue ERPs to shift-up cue ERPs. To measure all of the ERP activity related to attentional control, including spatially nonspecific activity that is removed in the process of isolating lateralized cue-ERP components, we compared shift-cue ERPs to neutral-cue (i.e., no-shift) ERPs. Isolated lateralized-ERP activity was seen in the contralateral–occipital lobe in the early phase of the cue-target interval and in the ipsilateral–occipital lobe in the late phase. The later, ipsilateral activity indicates that the late directing attention positivity (LDAP) reflected processing of the to-be-ignored location. The neutral-cue isolation revealed a shift-related positivity over posterior scalp regions and a shift-related negativity over more anterior scalp regions. The spatio-temporal sequence of shift-related activity observed on the scalp, together with estimates of distributed source activity underlying the shift-related ERP components, indicated that frontal and parietal regions of cortex participated in the control of attention and led to pre-target biasing in visual cortical areas.

Processing of multisensory spatial congruency can be dissociated from working memory and visuo‐spatial attention

Tactile stimuli at the same location as a visual target can increase activity in the contralateral occipital cortex compared with spatially incongruent bimodal stimulation. Does this cross-modal congruency effect in the visual cortex depend on available cognitive resources? Visual attention and working memory can modulate responses to visual stimuli in the occipital cortex, with attenuation in conditions of high-attentional or low-memory load. Here, we asked if these two cognitive factors affect multisensory processing in the visual cortex. Using functional magnetic resonance imaging in humans, we manipulated the load of working memory or visuo-spatial attention. Concurrently with these primary tasks we presented same-side (congruent) or opposite-side (incongruent) visuo-tactile stimuli. Both experiments revealed enhancement of brain activity for congruent vs incongruent bimodal stimulation in the contralateral occipital cortex. Critically, these cross-modal effects occurred irrespective of the level of load. We conclude that processing of visuo-tactile spatial congruency in the visual cortex does not depend on available visuo-spatial and memory resources.

Happy and fearful emotion in cues and targets modulate event-related potential indices of gaze-directed attentional orienting.

The goal of the present study was to characterize the effects of valence in facial cues and object targets on event-related potential (ERPs) indices of gaze-directed orienting. Participants were shown faces at fixation that concurrently displayed dynamic gaze shifts and expression changes from neutral to fearful or happy emotions. Emotionally-salient target objects subsequently appeared in the periphery and were spatially congruent or incongruent with the gaze direction. ERPs were time-locked to target presentation. Three sequential ERP components were modulated by happy emotion, indicating a progression from an expression effect to a gaze-by-expression interaction to a target emotion effect. These effects included larger P1 amplitude over contralateral occipital sites for targets following happy faces, larger centrally distributed N1 amplitude for targets following happy faces with leftward gaze, and faster P3 latency for positive targets. In addition, parietally distributed P3 amplitude was reduced for validly cued targets following fearful expressions. Results are consistent with accounts of attentional broadening and motivational approach by happy emotion, and facilitation of spatially directed attention in the presence of fearful cues. The findings have implications for understanding how socioemotional signals in faces interact with each other and with emotional features of objects in the environment to alter attentional processes.

Diagnosis and Treatment Algorithm in Cases of Head Deformity

Purpose: To demonstrate the diagnostic and therapeutic approach to infants with head deformities since a variety of treatments including physiotherapy, dynamic orthotic cranioplasty (DOC), and surgical remodeling have to be clearly differentiated. Method: One hundred twenty-six nonsyndromal infants presenting with abnormal head shape were clinically evaluated. Signs leading to the clinical diagnosis of deformational plagiocephaly included ipsilateral occipital flattening, contralateral occipital or ispilateral frontal bossing, or ear displacement. Contrarily, a synostotic plagiocephaly was considered in cases of ipsilateral occipital flattening with compensatory ipsilateral mastoid and contralateral parietal bossing. In all cases sonography of the cranial sutures was performed as first-line imaging modality. Only patients with uncertain sonographic findings or signs of premature synostosis underwent x-ray or CT imaging. Treatment modalities were DOC and surgical remodeling. Results: Interosseous hypoechogenic tissues between hyperechogenic bony plates comparable to normal cranial sutures were found in nonsynostotic sutures. In synostotic sutures hyperechogenic bony bridging and osseous ridging with a thin layer of periosteum was seen. Synostotic and nonsynostotic sutures could reliably be distinguished sonographically. The correct diagnoses already confirmed by sonography led to DOC treatment in nonsynostotic plagiocephaly (N = 100) and to surgical correction in true craniosynostoses (n = 26). Conclusion: The sonographic findings led to a change of the diagnostic algorithm in infant head deformity in our clinic. X-ray or CT imaging is only performed in doubtful sonographic findings for further diagnostic security. Ultrasound examination consistently leads the way to treatment with DOC or to a surgical approach. Since ultrasound examinations turned out to be as effective as CT imaging in diagnosing suture fusion or nonsynostotic plagiocephaly, and CT imaging does not add any morphological information, it remains controversial whether CT reconstruction is necessary in planning surgery of solitary affected sutures. Due to radiation doses, CT imaging should be restricted to the infants with complex or multiple suture synostosis. Furthermore, since treatments vary from physiotherapy, DOC, to craniofacial remodeling, due to the lack of objective and noninvasive assessing methods treatment guidelines become highly necessary.

Homeostatically regulated spontaneous neuronal discharges protect developing cerebral cortex networks from becoming hyperactive following prolonged blockade of excitatory synaptic receptors

In order to further examine the role of spontaneous action potential (SAP) discharges in neocortical development, amino-acid-mediated synaptic transmission was selectively blocked in an improved organotypic neocortex culture preparation. Contralateral occipital cortex slices from neonatal rats were co-cultured for several weeks in a ventricle-to-ventricle orientation known to greatly enhance cyto-morphological and electrophysiological maturation. Such preparations are highly resistant to attempts to suppress neuronal firing by blocking ionotropic glutamate receptors: not only can kainate receptors partly substitute for NMDA- and AMPA-mediated neurotransmission when these receptors are pharmacologically blocked, but (muscarinic) cholinergic receptors also begin to drive SAP activity when the kainate receptors, too, are chronically blocked. Only tetrodotoxin proved able to eliminate SAPs altogether in these co-cultures, while GABAergic receptor blockade (using bicucculine) led to persistent epileptiform discharges. Treatment effects were assayed upon transfer to control medium by means of a quantitative analysis of spontaneously occurring polyneuronal spike trains. Total suppression of action potentials for several weeks (by tetrodotoxin treatment) led, as in earlier experiments, to strongly intensified burst firing upon transfer to control medium. Chronic glutamate receptor blocked cultures, on the other hand, showed only minor deviations from control firing levels and patterns when assayed in normal medium. Protection against the development of hyperactivity despite partial blockade of synaptic transmission was roughly proportional to the degree to which spontaneous firing during the treatment period approximated normal SAP levels. This homeostatic response to chronically reduced excitatory drive thus differs from earlier results using isolated organotypic cortex cultures, in which the restoration of SAP activity failed to prevent the development of network hyperactivity. Chronic bicucculine treatment, in contrast, had little or no homeostatic effect on SAP firing patterns; on the contrary, opposite to earlier findings using isolated occipital cortex explants, paroxysmal discharges persisted even after transfer to control medium.

Posterior Interhemispheric Approach: Surgical Technique, Application to Vascular Lesions, and Benefits of Gravity Retraction

To review an experience with the posterior interhemispheric approach applied to vascular lesions in the posterior midline, to examine the effects of patient position and gravity retraction of the occipital lobe, and to identify circumstances requiring increased exposure by sectioning the falx and tentorium. During a 6.5-year period, 46 posterior interhemispheric approaches were performed to treat 28 arteriovenous malformations, 10 dural arteriovenous fistulae, seven cavernous malformations, and one posterior cerebral artery aneurysm. Twenty-three patients were positioned prone and 23 patient were positioned laterally. A standard posterior interhemispheric approach was used in 38 patients, and the occipital bitranstentorial/falcine approach was used in seven patients. A contralateral occipital transfalcine approach was used with one thalamic cavernous malformation. All lesions were resected completely and/or obliterated angiographically, with good neurological outcomes in 83% of patients and no operative mortality. Blood loss was lower, operative durations were shorter, postoperative cerebral edema was decreased, and visual outcomes were improved in patients positioned laterally. The posterior interhemispheric approach, without additional dural cuts, is appropriate for most vascular lesions in the posterior midline. Gravity retracts the occipital lobes when patients are positioned laterally, enhancing operative exposure and reducing morbidity. Extension of the posterior interhemispheric approach to a transtentorial or transfalcine approach is required for falcotentorial dural arteriovenous fistulae and vein of Galen arteriovenous malformations, but is not usually necessary with cavernous malformations or other arteriovenous malformations.

Pain activates cortical areas in the preterm newborn brain

To study the patterns of supraspinal pain processing in neonates, we hypothesized that acute pain causes haemodynamic changes associated with activation of the primary somatosensory cortex. Forty preterm neonates at 28–36 weeks of gestation (mean = 32.0) and at 25–42 h (mean = 30.7) of age were studied following standardized tactile (skin disinfection) and painful (venipuncture) stimuli. Changes in regional cerebral haemodynamics were monitored by near infrared spectroscopy (NIRS) over both somatosensory cortices in 29 newborns, and over the contralateral somatosensory and occipital areas in 11 newborns. Heart rate (HR) and peripheral oxygen saturation (SaO 2) were recorded simultaneously with NIRS parameters: oxygenated [HbO 2], deoxygenated, and total hemoglobin. Tactile stimulation produced no changes in HR or SaO 2. HR increased in the first 20 s ( p < 0.001), while SaO 2 decreased during the 40 s after venipuncture ( p < 0.0001). Following tactile or painful stimulation, [HbO 2] increased bilaterally regardless of which hand was stimulated ( p < 0.0001). Pain-induced [HbO 2] increases in the contralateral somatosensory cortex ( p < 0.05) were not mirrored in the occipital cortex ( p > 0.1). Pain-related [HbO 2] increases were more pronounced in male neonates ( p < 0.05 on left, p < 0.001 on right), inversely correlated with gestational age ( r = −0.53 on left, p < 0.01; r = −0.42 on right, p < 0.05) and directly correlated with postnatal age ( r = 0.75 on left, p < 0.0001; r = 0.67 on right, p < 0.0001). Painful and tactile stimuli elicit specific haemodynamic responses in the somatosensory cortex, implying conscious sensory perception in preterm neonates. Somatosensory cortical activation occurs bilaterally following unilateral stimulation and these changes are more pronounced in male neonates or preterm neonates at lower gestational ages.