Interhemispheric Research Articles

Interhemispheric axonal sprouting occurs after pial removal in mice.

White matter lacks the kind of plasticity that is present in the cortex, and subcortical injuries often result in permanent neurological deficits. Because cortical regions share common subcortical nuclei, creating new intergyral connections may allow for the bypass of subcortical damage. In this manuscript, a surgical interhemispheric bridge is created in mice, providing a model for an intercortical transpial bypass. To model this bypass, a midline craniotomy followed by interhemispheric (IH) pial removal was performed in C57BL/6 mice, allowing for the juxtaposition of the right and left prefrontal cortices. Adeno-associated virus (AAV) expressing tdTomato under a neuronal-specific promoter were injected into the right hemisphere. Animals were sacrificed two and four weeks after surgery, and axonal sprouting and glial changes were assessed in the "bypass" (BP) operation and sham surgery. Surgery did not result in any clear functional impairments. Removing the pia resulted in the formation of a physical connection between the hemispheres and the loss of the normal pial IH barrier. Cortical layer I became thinner with neuronal bodies in closer proximity than in the sham group. New interhemispheric axonal crossings were visible at two and four weeks in the BP group but not in the sham mice. These findings constitute the first step in the development of a cortico-cortico transpial bypass, allowing us to test a new way to surgically restore neurological function.

Examining the Inter Hemispheric Transfer Time Test: A new computerized cognitive test to incorporate into therapeutic strategy for patients with brain metastases? A pilot study

ObjectiveTo evaluate the computerized Inter Hemispheric Transfer Time Test (IHTTT), a cognitive test designed for the detection of information processing speed impairment in patients undergoing stereotactic radiation therapy for brain metastases. MethodsInclusion criteria: age ≥18 years, brain metastases treated by stereotactic radiotherapy (SRT) with dose schedule: 33 Gy in 3 fractions, solid tumour, ≥70 Karnofsky Performance Status, Mini-Mental State Evaluation (MMSE) ≥ 24, no history of stroke brain injury. Twenty-nine patients were recruited from June 2014 to April 2015. All recruited patients were administered Frontal Assessment Battery at Bedside (FAB), IHTTT and QLQ-C30 quality of life questionnaire before SRT, at one-month, six-month and one-year follow-up. The primary endpoint was Interhemispheric Transfer Index (IHTI). Secondary endpoints included Interhemispheric Transfer Time (IHTT), MMSE, FAB, and quality of life. ResultsA significant evolution of cognitive function over time was assessed by the IHTTT: IHTT = 720 ± 27 ms at baseline, 728 ± 20 at one month, 736 ± 36 at 6 months, 799 ± 111 at one-year follow-up (p = 0.0010); IHTI = 13.1 ± 31.4, 11.5 ± 24.3, 50.6 ± 57.9, 91.0 ± 59.4 (p < 0.0001). There was also a significant evolution over time for MMSE (p = 0.014) but neither for FAB score nor the quality of life scores. IHTI was strongly related to progression-free survival (p = 0.0091). ConclusionOur results suggest that IHTTT is able to detect the evolution of cognitive function over time. IHTTT could be an interesting sensitive cognitive test to include in evaluation of patients with brain metastases irradiated by SRT.

Unprecedented strength of Hadley circulation in 2015–2016 impacts on CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; interhemispheric difference

Abstract. The extreme El Niño of 2015 and 2016 coincided with record global warming and unprecedented strength of the Hadley circulation with significant impact on mean interhemispheric (IH) transport of CO2. The relative roles of eddy transport and mean advective transport on interannual differences in CO2 concentration between Mauna Loa and Cape Grim (Cmlo−cgo), from 1992 through to 2016, are explored. Eddy transport processes occur mainly in boreal winter–spring when Cmlo−cgo is large; an important component is due to Rossby wave generation by the Himalayas and propagation through the equatorial Pacific westerly duct generating and transmitting turbulent kinetic energy. Mean transport occurs mainly in boreal summer–autumn and varies with the strength of the Hadley circulation. The timing of annual changes in Cmlo−cgo is found to coincide well with dynamical indices that we introduce to characterize the transport. During the unrivalled 2009–2010 step in Cmlo−cgo, the effects of the eddy and mean transport were reinforced. In contrast, for the 2015 to 2016 change in Cmlo−cgo, the mean transport counteracts the eddy transport and the record strength of the Hadley circulation determines the annual IH CO2 difference. The interaction of increasing global warming and extreme El Niños may have important implications for altering the balance between eddy and mean IH CO2 transfer. The effects of interannual changes in mean and eddy transport on interhemispheric gradients in other trace gases are also examined.

T121. Effect of electroconvulsive therapy and repetitive transcranial magnetic stimulation on corticol excitability in patients with major depression

Repetitive transcranial magnetic stimulation (rTMS) can enhance or depress cortical excitability depending on stimulation frequency and intensity. These features of rTMS may be related to its antidepressant action that has been recently demonstrated. Changes in cortical excitability may also play an important role in the mechanisms of action of other antidepressant treatments, electroconvulsive therapy (ECT) in particular. Twenty-two patients with MD were randomized to receive either ECT + rTMS or ECT + sham rTMS in a double blind design. ECT was given twice weekly and 12 rTMS was applied throughout 3 weeks. rTMS was administered to the right prefrontal cortex with a circular coil. 900 stimuli in each session were delivered at a rate of 1 Hz and at an intensity of 110% of the resting motor threshold (rMT). Severity of depression was assessed by the Hamilton Depression Rating Scale (HDRS). The rMT and the size of motor evoked potential (MEP) were assessed before and after ECT. The MEP/M-wave area ratio was then calculated by dividing the MEP area by the maximal M-wave area obtained after electrical stimulation of the median nerve. For assessment of changes in the intra-cortical inhibition (ICI) and intra-cortical facilitation (ICF), the standard paired-pulse TMS paradigm was used at baseline and after the last ECT. The inter-hemispheric (IHR) ratio was calculated as Rt/Lt for each MEP parameter. 19 out of the 22 patients showed a marked clinical improvement treatments. The left aMT was significantly decreased following 6 ECTs. This was associated with significant change of the rMT inter-hemispheric ratio towards a relative decrease of the left hemisphere rMT indicating enhancement of the excitability in the left hemisphere. Only those patients who improved following ECT or ECT + TMS, had a significant increase of the MEP/M-wave area ratio in the left hemisphere but not in the right hemisphere. Each ECT caused an increase of MEP size in the left hemisphere. The cumulative effect of ECT on the left hemisphere MEP size was significant after 3 ECTs. Paired-pulse TMS paradigm revealed a significant reduction of the intracortical inhibition only in the left hemisphere in patients who clinically improved ECT causes a relative decrease of motor thresholds to TMS in the left hemisphere. The antidepressant effect of ECT is associated with an increase of the MEP size and reduction of the intracortical inhibition in the left hemisphere. These findings suggest that enhancement of left hemispheric excitability may be related to therapeutic effect of ECT. Similar results were obtained in patients who improved in response to antidepressant medication or rTMS. Taken together, this may suggest that an increase of left hemispheric excitability is shared by different antidepressant treatments and might be related to their therapeutic effect. rTMS as applied in our study does not seem to have an additive effect on cortical excitability and does not enhance the therapeutic effect of ECT.

Anterior Midline Skull Base Meningiomas: Interhemispheric Approach versus the Different Classical Surgical Approaches—Clinical Outcomes

Backgrounds: Different surgical approaches have been used to remove anterior skull base meningiomas (ASBMs) such as olfactory groove (OG) and tuberculum sellae (TS) meningiomas. These tumors are traditionally resected through pterional (PT), lateral supraorbital (LS) approaches. The endonasal endoscopic (EE) approach has gained some attention in recent years. The interhemispheric (IH) approach represents another option that has been rarely described and even more rarely compared with other approaches.

Olfaction preservation after removal of large tuberculum sellae meningiomas via a superior interhemispheric approach. A quantitative and qualitative study

IntroductionWe present a prospective series of tuberculum sellae meningioma (TSM) resected via a superior interhemispheric (IH) approach in 10 patients who preoperatively and postoperatively underwent extensive olfaction testing using a standardised test battery. Patients and methodsThis prospective longitudinal study evaluated the olfactory function after TSM resection. The resection was performed via a superior interhemispheric (IH) approach. The quantitative and qualitative analyses of the olfactory function were assessed with the Biolfa® olfactory test (at 6 months). ResultsBetween November 2009 and April 2012, 10 consecutive patients with symptomatic TSM and preserved olfactory function were operated via a superior IH approach. For the self-evaluation criteria of the olfactory function, the mean preoperative visual analog scale score was 8.8. The mean preoperative total quantitative (/27) scored 18.2±6.3 for this cohort of 10 patients. In the postoperative period, the mean total score decreased non-significantly to 15.8±8.8 (Wilcoxon test, P=0.085). The mean preoperative qualitative score (/8) was 5.5±1.7 and in the postoperative period decreased, non-significantly, to 4.7±2.6 (Wilcoxon test, P=0.12). The olfactory function was quantitatively and qualitatively preserved in 6 patients (60%), but a postoperative deterioration occurred in 2 (20%) and an anosmia in 2 (20%). Size and invasive characteristics of the meningioma determined the post-surgical deterioration. ConclusionOlfaction is an important factor of emotional and social life, which needs to be integrated into the challenge regarding the resection of TSM. The risks of nerve damage are reviewed.

A greater involvement of posterior brain areas in interhemispheric transfer in autism: fMRI, DWI and behavioral evidences.

A small corpus callosum (CC) is one of the most replicated neurobiological findings in autism spectrum (AS). However, its effect on interhemispheric (IH) communication is unknown. We combined structural (CC area and DWI), functional (task-related fMRI activation and connectivity analyses) as well as behavioral (Poffenberger and Purdue tasks) measures to investigate IH integration in adult AS individuals of typical intelligence. Despite similar behavioral IH transfer time and performances in bimanual tasks, the CC sub-regions connecting frontal and parietal cortical areas were smaller in AS than in non-AS individuals, while those connecting visual regions were similar. The activation of visual areas was lower in AS than in non-AS individuals during the presentation of visual stimuli. Behavioral IH performances were related to the properties of CC subregions connecting motor areas in non-AS individuals, but to the properties of posterior CC regions in AS individuals. Furthermore, there was greater functional connectivity between visual areas in the AS than in the non-AS group. Levels of connectivity were also stronger in visual than in motor regions in the autistic subjects, while the opposite was true for the non-autistic group. Thus, visual IH transfer plays an important role in visuo-motor tasks in AS individuals. These findings extend the well established enhanced role of perception in autistic cognition to visuo-motor IH information transfer.

Prefrontal-Parietal Correlation during Performance of a Visuospatial Working Memory Task in Children, Adolescents and Young Adults

Development of the prefrontal cortex and its connectivity with different cortical areas has strong implications for the improvement of working memory. The aim of this research was to characterize the interhemispheric (INTER) prefrontal and hemispheric (INTRA) frontopolar-dorsolateral prefrontal and dorsolateral prefrontal-parietal correlation (r) in children, adolescents and adults during performance of a visuospatial working memory task (VSWM). INTERr and INTRAr of 36 different aged male participants (11 - 13, 18 - 20 and 26 - 30 years old) were calculated during performance of the Corsi Block-Tapping task, which assessed VSWM. On this task, children showed lower correct responses than adolescents and adults. Adults also showed lower total execution times than children and adolescents, with a more efficient performance. On the EEGs, the older groups showed both higher interfrontal correlations and left and right prefronto-parietal correlations than children. According to our results, the progressive efficiency in VSWM is related to differences in EEG patterns among children, adolescents and adults.

Broca's area damage is necessary but not sufficient to induce after-effects of cathodal tDCS on the unaffected hemisphere in post-stroke aphasia.

The inter-individual variability of behavioral effects after tDCS applied to the unaffected right hemisphere in stroke may be related to factors such as the lesion location. We investigated the effect of left Broca's area (BA) damage on picture naming in aphasic patients after cathodal tDCS applied over the right BA. We conducted a study using pre-interventional diffusion and resting state functional MRI (rsfMRI) and two cross-over tDCS sessions (TYPE: sham and cathodal) over the right homologous BA in aphasic stroke patients with ischemic lesions involving the left BA (BA+) or other left brain areas (BA-). Picture naming accuracy was assessed after each session. Inter-hemispheric (IH) functional balance was investigated via rsfMRI connectivity maps using the right BA as a seed. Probabilistic tractography was used to study the integrity of language white matter pathways. tDCS had different effects on picture naming accuracy in BA+ and BA- patients (TYPE×GROUP interaction, F(1,19): 4.6, P: 0.04). All BA- patients except one did not respond to tDCS and demonstrated normal IH balance between the right and left BA when compared to healthy subjects. BA+ patients were improved by tDCS in 36% and had decreased level of functional IH balance. Improvement in picture naming after cathodal tDCS was associated with the integrity of the arcuate fasciculus in BA+ patients. Behavioral effects of cathodal tDCS on the unaffected right hemisphere differ depending on whether BA and the arcuate fasciculus are damaged. Therefore, IH imbalance could be a direct consequence of anatomical lesions.

TransCom model simulations of CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; and related species: linking transport, surface flux and chemical loss with CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; variability in the troposphere and lower stratosphere

Abstract. A chemistry-transport model (CTM) intercomparison experiment (TransCom-CH4) has been designed to investigate the roles of surface emissions, transport and chemical loss in simulating the global methane distribution. Model simulations were conducted using twelve models and four model variants and results were archived for the period of 1990–2007. All but one model transports were driven by reanalysis products from 3 different meteorological agencies. The transport and removal of CH4 in six different emission scenarios were simulated, with net global emissions of 513 ± 9 and 514 ± 14 Tg CH4 yr−1 for the 1990s and 2000s, respectively. Additionally, sulfur hexafluoride (SF6) was simulated to check the interhemispheric transport, radon (222Rn) to check the subgrid scale transport, and methyl chloroform (CH3CCl3) to check the chemical removal by the tropospheric hydroxyl radical (OH). The results are compared to monthly or annual mean time series of CH4, SF6 and CH3CCl3 measurements from 8 selected background sites, and to satellite observations of CH4 in the upper troposphere and stratosphere. Most models adequately capture the vertical gradients in the stratosphere, the average long-term trends, seasonal cycles, interannual variations (IAVs) and interhemispheric (IH) gradients at the surface sites for SF6, CH3CCl3 and CH4. The vertical gradients of all tracers between the surface and the upper troposphere are consistent within the models, revealing vertical transport differences between models. An average IH exchange time of 1.39 ± 0.18 yr is derived from SF6 time series. Sensitivity simulations suggest that the estimated trends in exchange time, over the period of 1996–2007, are caused by a change of SF6 emissions towards the tropics. Using six sets of emission scenarios, we show that the decadal average CH4 growth rate likely reached equilibrium in the early 2000s due to the flattening of anthropogenic emission growth since the late 1990s. Up to 60% of the IAVs in the observed CH4 concentrations can be explained by accounting for the IAVs in emissions, from biomass burning and wetlands, as well as meteorology in the forward models. The modeled CH4 budget is shown to depend strongly on the troposphere-stratosphere exchange rate and thus on the model's vertical grid structure and circulation in the lower stratosphere. The 15-model median CH4 and CH3CCl3 atmospheric lifetimes are estimated to be 9.99 ± 0.08 and 4.61 ± 0.13 yr, respectively, with little IAV due to transport and temperature.

Superior interhemispheric approach for midline meningioma from the anterior cranial base

Background For suprasellar meningioma, the fronto-basal exposure is considered the standard approach. The superior interhemispheric (IH) approach is less described in the literature. Objective To assess the surgical complications, functional outcome (visual, olfaction), morbidity and mortality rates and late recurrence, after resection by superior IH approach of midline skull base meningioma. Methods Between 1998 and 2008, 52 consecutive patients with midline meningioma on the anterior portion of the skull base (mean age: 63.8 ± 13.1; sex ratio F/M: 3.7) were operated on via the superior IH approach. After a mean follow-up of 56.9 ± 32.9 months, an independent neurosurgeon proposed a prospective examination of functional outcome to each patient, as well as a visual and olfactory function assessment. Results Fifty-two patients were divided into a group with olfactory groove meningioma ( n = 34) and another with tuberculum sellae meningioma ( n = 18). The outcome was characterized by postoperative complications in 13 patients (25%), mortality rate in two (3.8%) and long-term morbidity at in 17 (37%) of 50 surviving patients. Based on multivariate analysis, no prognosis factor was significant as regards the favorable outcome. The mean postoperative KPS score (86.6 ± 9.4) was significantly improved. However, dysexecutive syndrome was observed in four patients (8%), hyposmia-anosmia in 34 (68%) and visual acuity deteriorated in one (2%). Conclusion The superior IH approach could be considered a safe anteriorly orientated midline approach for removal OGM and TSM meningioma.

A misleading distal anterior cerebral artery aneurysm

Background:Aneurysmal rupture causing pure acute subdural hematoma (aSDH) is rare. In the four previously reported cases of distal anterior cerebral artery (ACA) aneurysm resulting in pure aSDH, blood distribution in the interhemispheric (IH) space has systematically incriminated the distal ACA as the source of rupture. We present a misleading case of a distal ACA rupture resulting in convexity aSDH with minimal IH blood.Case Description:A 51-year-old patient presented in coma with decerebrate posturing and a blown left pupil from a left convexity acute hemispheric subdural hematoma. She underwent urgent left craniectomy and subdural hematoma evacuation. Given the absence of identifiable etiology, including trauma, we performed an immediate postoperative Computed tomography-angiography (CTA) in order to rule out an underlying cause. The CTA revealed an aneurysm originating from the callosomarginal artery branch of the ACA. Although the minimal amount of IH blood and the remote distance of convexity blood from the aneurysm suggested that it may be a fortuitous finding, we considered the possibility that the two might be related. The patient underwent surgical aneurysm clipping, confirming that it had ruptured and allowing complete aneurysm obliteration. Following the procedure, the patient’s neurological and functional status gradually improved.Conclusion:Ruptured distal ACA aneurysms may present with convexity isolated aSDH with minimal IH blood. Quantity and distribution of isolated aSDH can be misleading and is not always a reliable predictor of aneurysm location. Misinterpretation of the aneurysm as an incidental finding would lead to improper management with potentially serious consequences.

前交通動脈動脈りゅうの手術手技 穿通枝温存 前交通動脈りゅうの解剖学的特徴をもとにした手術法の選択と手術手技

Neurosurgeons have 2 established approaches for the anterior communicating artery aneurysm (ACoAn): pterional (PT) and interhemispheric (IH). To elucidate which approach best suits various types of ACoAn, we studied angiograms from 202 consecutive operated cases. ACoAn can be classified into 4 groups by the direction of neck protrusion: anterior/inferior (AI: 43%), superior (SUP: 23%), posterior/superior (POST: 2%) and lateral (LAT: 32%). The LAT type is a peculiar aneurysm defined as protruding its neck and the dome sideways contralateral to the dominant A1. It is hard to recognize this type well on lateral projection angiogram because its neck and the dome are superimposed on the A1-A2 corner that the aneurysm arises from. In LAT, the dominant A1 is overwhelmingly on the left side (73.8%), while in the other types, the left A1 predominance is not observed (the left A1 dominant in 31.4%, the right A1 dominant in 32.8% and epui-A1 in 35.8%). Ninety percent of AI were operated on by PT. For the SUP type, both PT (48%) and IH (41%) were employed, depending on the size and shape of the dome and height of the neck from the frontal base. The LAT and POST type were clipped safely by IH (75.4 and 75.0%, respectively). Though LAT can be clipped by PT from the side of the neck protrusion getting over the dome (16%), this is apparently more difficult and risky than by IH. We present typical cases operated on both by PT or IH in each ACoAn type with annotations concerning surgical indications and techniques.

高位前交通動脈りゅうに対する安全なクリッピング手術 穿通枝およびＨｅｕｂｎｅｒ’ｓ ａｒｔｅｒｙの温存法

We studied how to minimize the brain retraction and preserve the hypothalamic (hA) and Heubner's artery (HA) in clipping surgeries for high-positioned Acom aneurysms with the pterional (PT), orbitocranial (OC), and interhemispheric (IH) approaches using cadavers and in clinical cases. With the PT approach, excessive retraction of the frontal lobe was required to access Acom aneurysms located higher than 10 mm from the anterior clinoid process. Untethering of the frontal lobe (wide split of the sylvian and IH fissure, opening of the basal cisterns and division of the thick arachnoid fibers from the optic nerves and chiasma, etc.) and a gyrus rectus (GR) resection minimized brain retraction and exposed the Acom complex up to 13 mm high. Subpial GR resection was required to avoid injury of Heubner's artery (HA).Long and excessive retraction of the frontal lobe including the A1 and HA should be avoided to prevent subsequent brain infarction. The OC approach offered much wider and better exposure of Acom aneurysms up to 15 mm high. Sacrifice of the olfactory nerve, if possible, offered access to Acom aneurysms higher than 15 mm even with the PT and OC approaches. The IH approach, preferable for high-located and superiorly-posteriorly projecting Acom aneurysms, could not always offer visual access to the hA running behind the aneurysmal dome. In one such case, the hA could be prepared by placing a small rubber sheat between the aneurysmal dome and the hA.In safe clipping surgeries for high-located aneurysms, the best surgical approach should be selected according to the aneurysmal height and fundus projection, and great care should be taken during surgery to minimize brain retraction and to prepare the hA, HA, and A1 perforators.

Effect of spatial ability and sex inter- and intrahemispheric correlation of EEG activity

Inter- and intrahemispheric correlation of the EEG activity at rest was computed in two groups of men and women, between 17 and 21 years old, with extreme degrees of spatial ability (SA) evaluated by the Spatial Relations Subtest of the Differential Aptitudes Test (DAT). Interhemispheric (INTERr) and intrahemispheric (INTRAr) EEG correlations were computed by means of Pearson productmoment coefficients for 5 EEG bands after digitally filtering with an FFT. Women showed significantly higher INTERr of alpha1 between left and right centrals, lower IINTRAr between right frontal and right central regions and lower INTRAr within the left than in the right hemisphere. High SA subjects showed lower INTERr between left and right frontal derivations and higher INTRAr between frontal and parietal and between central and parietal regions of both hemispheres. Sex interacted with SA in INTRAr of alpha between right frontal and right temporal regions with high SA women showing lower INTRAr than low SA women and than men. The present results indicate a different inter- and intrahemispheric functional organization in men and women and in subjects with high and low spatial ability.

破裂前交通動脈瘤に対するpterional approachとinterhemispheric approachの比較

From 1990 to 1993, 56 cases of ruptured anterior communicating artery aneurysms were operated on in an acute stage through the Pterional (PT) approach or the Interhemispheric (IH) approach. In this series, the PT approach was used in 33 cases (PT group), and the IH approach in 23 cases (IH group). We evaluated the surgical complications of these 2 surgical groups retrospectively.Injury of perforating artery occurred more often in the PT group, and was caused mainly by improper brain retraction or temporary occlusion of the parent artery. In most of these cases, the aneurysms projected laterally or superiorly and the operation was carried out at the side of the A2 running anteriorly.On the other hand, symptomatic vasospasm was observed more frequently in the IH group. In these cases, the methods for prevention of symptomatic vasospasm were insufficient.These results indicate that in the PT approach, it is very important to assess the projection of aneurysm, and the anatomical relationship between the aneurysm and the surrounding vascular structure preoperatively, and to decide the approach side in consideration of the posteriority of the A2 segment. While, in the IH approach, great care should be taken to prevent vasospasm.

破裂前交通動脈瘤に対する手術法の検討II: 血管写上の特徴と手術法の選択について

In this paper, operative indications, especially as regards the selection of surgical approach for anterior communicating artery aneurysms (ACAA) are discussed with precise and detailed analyses of angiographical anatomy of the aneurysm and the surrounding arteries in 120 surgical cases.Aneurysms originating in the anterior communicating artery itself were much less frequently observed (18.3%), and the majority have their origins on the A1-A2 junction (81.7%). Fifty percent of the A1 segments of the anterior cerebral arteries were dominant on the left side. The right-dominant and the equi-A, type comprised 25% each. In 60% of the cases, the left A2 was anterior to the right one, in 25% vice versa and only in 15% both A, were running in parallel. These inequalities of the arteries surrounding the ACAA seemingly affect the incidence of aneurysmal type. That is, about one third (31.7%) of the ACAA projected laterally from the origin on the A1-A2 junction, and for this lateral-type aneurysm the most suitable surgical approach is the interhemispheric (IH), among numbers of access methods.The location of the neck of the aneurysm, the direction of its dome and the side of the dominant A1 segment of the anterior cerebral artery are important factors in deciding what type of surgical approach is to be done. Though the anteriority of the A, segment is a factor that cannot be disregarded in the pterional (PT) approach, the authors believe that it is not essential in considering the IH approach because this approach can be used for any type of ACAA. At the same time, surgeons should not stick to a single method, especially in the acute stage of subarachnoid hemorrhage because, in this situation, they must try to accomplish the operation as safely, quickly and, of course, completely as possible. In the authors' series, the pterional approach was used in 66 cases (55.0%), the interhemispheric approach in 47 (39.2%), and the bilateral subfrontal and trans-hematoma access were chosen for 4 and 3 cases respectively. And there were 11 cases in which the IH approach with an additional PT approach was used for securing the Al segment which was hidden behind the dome of the aneurysm from the IH surgical view and/or for removal of diffuse and thick subarachnoid clots.

Homotopic and nonhomotopic interhemispheric cortical projections in the squirrel monkey

Electrophysiological studies of interhemispheric (IH) connections in the squirrel monkey revealed IH projections from the postcentral forelimb, hind limb, and trunk areas of primary somatosensory cortex (SM I) to frontal lobe polysensory areas of motor and premotor cortex (areas 4 and 6), to SM I trunk area, and to the postcentral dimple of parietal lobe. Anatomical studies in the squirrel monkey also demonstrated the projections to contralateral SM I and to other ipsilateral and contralateral areas, but not to the contralateral frontal lobe. The failure of the anatomical technique to demonstrate the frontal lobe IH projections emphasizes the role of electrophysiological studies in supplementing anatomical studies of cortico-cortical projections. The electrophysiological studies demonstrated, in addition, that visual cortex of the squirrel monkey has IH projections to areas 4 and 6 of frontal lobe as well astto nonstriateaareas of occipital lobe. By combinations of cortical ablations and cuts of the corpus callosum it was determined that the projection from SM I to contralateral frontal lobe probably involves a slowly conducting fiber system running rostrally from SM I in white matter, then crossing in the rostral corpus callosum. The precentral corpus callosum does not appear to be essential for the occipitofrontal projection.