Callosal lesions and behavior: history and modern concepts

Cognitive and behavioral impact of antiseizure medications, neuromodulation, ketogenic diet, and surgery in Lennox-Gastaut syndrome: A comprehensive review

Lennox-Gastaut syndrome (LGS) is a severe developmental and epileptic encephalopathy marked by drug-resistant seizures and profound cognitive and behavioral impairments, with nearly 95% of individuals affected by moderate to severe intellectual disability. This review comprehensively explores the cognitive and behavioral impacts of current treatment options for LGS, including antiseizure medications (ASMs), neuromodulation strategies, the ketogenic diet, and surgical interventions. Given the limited availability of LGS-specific data for several ASMs, the evidence base is supplemented with findings from general epilepsy populations and individuals with epilepsy and intellectual disabilities. The evidence reveals that ASMs exert varied cognitive and behavioral effects in LGS. Medications such as valproate, lamotrigine, cannabidiol, fenfluramine, levetiracetam, brivaracetam, felbamate, and rufinamide generally support cognitive stability, while topiramate and zonisamide are associated with cognitive challenges. Behavioral outcomes also vary: stability is observed with valproate, lamotrigine, rufinamide, cannabidiol, and fenfluramine, whereas medications like levetiracetam, perampanel, brivaracetam, clobazam, and zonisamide can increase aggression or irritability. Nonpharmacological therapies, particularly when they reduce seizure frequency, typically provide greater cognitive and behavioral stability, with some offering improvement. Early intervention-especially through surgical options-appears most beneficial for preserving cognitive function. Additionally, therapies such as the ketogenic diet and neuromodulation may provide independent cognitive benefits beyond seizure control. This review emphasizes the importance of personalized treatment strategies, integrating cognitive and behavioral evaluations in therapy selection. Key components include baseline cognitive and behavioral assessments, followed by regular follow-up evaluations, particularly after therapy changes. Consideration of minimizing ASM polytherapy, careful evaluation of drug-drug interactions, pharmacogenomic implications, and the need for therapeutic drug monitoring in cases of cognitive adverse effects is essential. Future research should focus on developing assessment tools tailored to the unique needs of individuals with LGS, utilizing connectivity measures to assess intervention impacts, and advancing precision therapeutics to improve cognitive and behavioral outcomes.

A rare case of simultaneous occurrence of non-arteritic anterior ischemic optic neuropathy and corpus callosum ischemia

PURPOSE

To report a case of non-arteritic anterior ischemic optic neuropathy (NAION) in an elderly patient with ischemia of the left splenium of the corpus callosum, providing details of the diagnostic work-up and subsequent follow-up.

METHODS SECTION

Case report.

RESULTS

A pseudophakic 80 years-old woman referred complaining sudden visual impairment in the left eye (LE) in concomitance with episode of hypertensive crisis. Fundus examination showed diffuse swelling of optic disc associated with flame peripapillary hemorrhages in LE and small crowded disc in right eye (RE). A superior altitudinal defect with arcuate defect including the blind spot were detected at the visual field in the LE. The patient was diagnosed with NAION. Five days later the patient complained a further vision loss and a pathological area within the left splenium of corpus callosum, consistent ischemia, was depicted at magnetic resonance imaging of brain. Corpus callosum infarction was completely asymptomatic and neurological evaluation was normal. At 45 days follow-up fundus examination showed white ischemic nerve while visual field was irreversibly constricted with tubular defect in LE.

CONCLUSION

In case of NAION linked with corpus callosum ischemia multimodal imaging and systemic work-up play a pivotal role for an early diagnosis.

Case report: Symmetrical and increased lateral sway-based walking training for patients with corpus callosum infarction: a case series

Introduction

Corpus callosum injury is a rare type of injury that occurs after a stroke and can cause lower limb dysfunction and a decrease in activities of daily living ability. Furthermore, there are no studies that focus on the progress in rehabilitation of the lower limb dysfunction caused by infarction in the corpus callosum and the effective treatment plans for this condition. We aimed to present a report of two patients with lower limb dysfunction caused by corpus callosum infarction after a stroke and a walking training method.

Methods

We implemented a walking training method that prioritizes bilateral symmetry and increases lateral swaying before the patients established sitting/standing balance. The plan is a rapid and effective method for improving walking dysfunction caused by corpus callosum infarction.

Case characteristics

Following sudden corpus callosum infarction, both patients experienced a significant reduction in lower limb motor function scores and exhibited evident gait disorders. Scale evaluations confirmed that walking training based on symmetrical and increased lateral sway for patients with lower limb motor dysfunction after corpus callosum infarction led to significant symptom improvement.

Conclusion

We report two cases of sudden motor dysfunction in patients with corpus callosum infarction. Symmetrical and increased lateral sway-based walking training resulted in substantial symptom improvement, as confirmed by scale assessments.

Diffusion Restriction in the Splenium: A Comparative Study of Cytotoxic Lesions of the Corpus Callosum (CLOCCs) versus Lesions of Vascular Etiology

Cytotoxic lesions of the corpus callosum (CLOCCs) have broad differential diagnoses. Differentiating these lesions from lesions of vascular etiology is of high clinical significance. We compared the clinical and radiological characteristics and outcomes between vascular splenial lesions and CLOCCs in a retrospective cohort study. We examined the clinical and radiologic characteristics and outcomes in 155 patients with diffusion restriction in the splenium of the corpus callosum. Patients with lesions attributed to a vascular etiology (N = 124) were older (64.1 vs. 34.6 years old, p < 0.001) and had >1 vascular risk factor (91.1% vs. 45.2%, p < 0.001), higher LDL and A1c levels, and echocardiographic abnormalities (all p ≤ 0.05). CLOCCs (N = 31) more commonly had midline splenial involvement (p < 0.001) with only splenial diffusion restriction (p < 0.001), whereas vascular etiology lesions were more likely to have multifocal areas of diffusion restriction (p = 0.002). The rate of in-hospital mortality was significantly higher in patients with vascular etiology lesions (p = 0.04). Across vascular etiology lesions, cardio-embolism was the most frequent stroke mechanism (29.8%). Our study shows that corpus callosum diffusion restricted lesions of vascular etiology and CLOCCs are associated with different baseline, clinical, and radiological characteristics and outcomes. Accurately differentiating these lesions is important for appropriate treatment and secondary prevention.

Long-term follow-up seizure outcomes after corpus callosotomy: A systematic review with meta-analysis

BACKGROUND

Corpus callosotomy (CC) is appropriate for patients with seizures of a bilateral or diffuse origin, or those with seizures of a unilateral origin with rapid spread to the contralateral cerebral hemisphere. The efficiency of CC in patients with drug-resistant epilepsy is a long-term concern because most articles reporting the surgical results of CC arise from small case series, and the durations of follow-up vary.

METHODS

PubMed, Embase, Cochrane Library, and Web of Science were searched to identify papers published before November 8, 2021. The systematic review was completed following PRISMA guidelines. Outcomes were analyzed by meta-analysis of the proportions.

RESULTS

A total of 1644 patients with drug-resistant epilepsy (49 retrospective or prospective case series studies) underwent CC, and the follow-up time of all patients was at least 1 year. The rate of complete seizure freedom (SF) was 12.38% (95% confidence interval [CI], 8.17%-17.21%). Meanwhile, the rate of complete SF from drop attacks was 61.86% (95% CI, 51.87%-71.41%). The rates of complete SF after total corpus callosotomy (TCC) and anterior corpus callosotomy (ACC) were 11.41% (95% CI, 5.33%-18.91%) and 6.75% (95% CI, 2.76%-11.85%), respectively. Additionally, the rate of complete SF from drop attacks after TCC was significantly higher than that after ACC (71.52%, 95% CI, 54.22%-86.35% vs. 57.11%, 95% CI, 42.17%-71.49%). The quality of evidence for the three outcomes by GRADE assessment was low to moderate.

CONCLUSION

There was no significant difference in the rate of complete SF between TCC and ACC. TCC had a significantly higher rate of complete SF from drop attacks than did ACC. Furthermore, CC for the treatment of drug-resistant epilepsy remains an important problem for further investigation because there are no universally accepted standardized guidelines for the extent of CC and its benefit to patients. In future research, we will focus on this issue.

Thyroid storm complicated by corpus callosum infarction in a young patient: A case report and literature review

RATIONALE

Thyroid storm (TS) is a rare life-threatening hypermetabolic thyrotoxicosis with an incidence of 0.57-0.76/100,000. The coexistence of TS and acute cerebral infarction is rare. Previous studies have shown that hyperthyroidism complicated by cerebral infarction mainly occurs in the intracranial basal ganglia; however, there are no reports of corpus callosum infarction. We report a case of TS complicated by cerebral infarction of the corpus callosum at our hospital.

PATIENT CONCERNS

A 31-year-old male patient with a history of hyperthyroidism was admitted to the hospital because of fatigue, palpitations, fever, and profuse sweating accompanied by a mild decrease in the muscle strength of the left limb. Diagnosis of a TS was confirmed by the laboratory test results. The patient's clinical symptoms gradually improved after treatment. However, his left limb muscle strength progressively decreased, and the bilateral pathological signs were positive at the same time. Magnetic resonance imaging (MRI) of the head revealed acute cerebral infarction of the corpus callosum and pons.

DIAGNOSIS

The diagnosis was thyroid strom with acute cerebral infarction of the corpus callosum and pons and severe stenosis or occlusion of the basilar artery.

INTERVENTIONS

The patient was given 300 mg hydrocortisone intravenously per day, propylthiouracil tablets of 200 mg 3 times a day by nasal feeding, and 20 mg propranolol three times a day by nasal feeding. Aspirin and clopidogrel were administered to prevent platelet aggregation, and atorvastatin calcium was administered to lower lipid levels to stabilize plaques.

OUTCOMES

The patient's left limb muscle strength recovered to grade 4+, and he could walk beside the bed with support. Simultaneously, thyroid function was better than before.

LESSONS

Careful physical examination should be performed in patients with thyroid storm, and head imaging examination should be improved for the early detection of cerebral infarction.

White matter abnormalities in first-episode patients with depersonalization/derealization disorder: A tract-based spatial statistics study

BACKGROUND

Neuroimaging studies on depersonalization / derealization disorder (DPD) have revealed that there are structural and functional alterations across numerous brain regions. However, to date, the exact white matter abnormalities that are associated with different clinical symptoms and cognitive impairments in first-episode, drug-naïve patients with DPD remain unclear.

METHODS

Overall, 25 first-episode, drug-naïve patients with DPD and 23 healthy controls were recruited and underwent DTI scans. The tract-based spatial statistics analysis was conducted in order to determine white matter microstructural changes between the two groups. Correlation analysis was conducted between the fractional anisotropy (FA) of abnormal WM fibers and the total score of the 30-item Cambridge Depersonalization Scale (CDS-30), cognitive assessments.

RESULTS

Patients with DPD demonstrated higher FA in the right corpus callosum (CC), and posterior corona radiate (CR), compared to healthy controls. The FA in the right CC demonstrated a positive correlation with total score of CDS-30, numbing, unreality of self, perceptual alterations, and temporal disintegration, respectively. FA in the right CR region indicated a positive correlation with the total score of CDS-30, unreality of self, perceptual alterations, and temporal disintegration, respectively. Furthermore, FA in the right CR region was found to be negatively correlated with the Continuous Performance Test and the Stroop color-word test.

CONCLUSION

The altered white matter microstructure and cognitive impairments of medication naïve DPD patients were observed. Abnormalities in the integrity of CC and CR were associated with severity of symptoms and cognitive impairments, which may provide a potential biomarker for clinical studies on DPD.

Corpus Callosum Swelling after Resection of Intraventricular Central Neurocytoma

Corpus callosum swelling has been reported to occur after ventriculoperitoneal shunting for long-standing hydrocephalus. This report presents a case of corpus callosum swelling after intraventricular tumor resection. A 34-year-old woman presented with a headache that worsened over 1 month. Magnetic resonance (MR) images revealed a mass lesion in the left lateral ventricle and obstructive hydrocephalus. She underwent subtotal resection with a transcallosal approach. After tumor resection, she had long-lasting status epilepticus followed by consciousness disturbance. T2-weighted MR images obtained 8 hr after the operation showed a hyperintense area in the corpus callosum. The patient then presented with bilateral dilated pupils 14 hr after the operation due to acute hydrocephalus and tension pneumocephalus. An emergent re-craniotomy was performed and a ventricular drain was placed. The patient recovered consciousness 3 days after the operation. However, she experienced progressive corpus callosum swelling 25 days after the operation, which improved since then. Approximately 4 months after the operation, she returned to her usual workplace with no neurocognitive functional decline. Two years later, she was doing well with no radiological abnormal findings except corpus callosum thinning. Thus, corpus callosum swelling can develop not only after shunting for chronic hydrocephalus but also after intraventricular tumor resection. It occurred relatively acutely and there was no decline in intelligence after long-term follow-up. This case suggests that corpus callosum swelling after intraventricular tumor resection is a rare but noteworthy complication that can improve without intervention.

Reversible splenial lesion syndrome with mental disorders as only manifestation

Background

Reversible splenial lesion syndrome (RESLES) was reported to be associated with variable entities. However, much less is known about the cases in which the mental disorders act as the only manifestation.

Method

Total ten patients of RESLES were obtained in this retrospective study from Shenzhen Kangning Hospital. T1-fluid attenuated inversion recovery (T1-FLAIR), T2-weighted images, T2-FLAIR, diffusion-weighted images and apparent diffusion coefficient map were performed on all the patients. Clinical manifestations, laboratory examination results, magnetic resonance imaging (MRI) findings, treatments and outcomes were analyzed.

Result

All patients showed different mental disorders as the only manifestation. There were two cases of alcohol abuse, one of Asperger’s syndrome with malnutrition, one of infection and one of invasive pituitary adenoma. The other cases were diagnosis as major depressive disorder, dissociative and conversion disorders, undifferentiated somatoform disorder, unspecified psychosis and bipolar disorder, respectively. Three patients were completely recovered while the clinical symptoms of rest seven patients partially recovered at the follow-up three months later. Oval-shaped lesion centered on the splenial of corpus callosum (SCC) was observed in all patients using MRI. The lesions of SCC of all patients were completely resolved within five weeks.

Conclusions

We found that RESLES might only showed mental symptoms. On the one hand, for the patients with acute mental disorders, clinicians should be alert to the possibility of RESLES caused by physical disease. On the other hand, we suggest that mental disorder might be a precipitating factor of RESLES.

Music Playing and Interhemispheric Communication: Older Professional Musicians Outperform Age-Matched Non-Musicians in Fingertip Cross-Localization Test

OBJECTIVE

Numerous investigations have documented that age-related changes in the integrity of the corpus callosum are associated with age-related decline in the interhemispheric transfer of information. Conversely, there is accumulating evidence for more efficient white matter organization of the corpus callosum in individuals with extensive musical training. However, the relationship between making music and accuracy in interhemispheric transfer remains poorly explored.

METHODS

To test the hypothesis that musicians show enhanced functional connectivity between the two hemispheres, 65 professional musicians (aged 56-90 years) and 65 age- and sex-matched non-musicians performed the fingertip cross-localization test. In this task, subjects must respond to a tactile stimulus presented to one hand using the ipsilateral (intra-hemispheric test) or contralateral (inter-hemispheric test) hand. Because the transfer of information from one hemisphere to another may imply a loss of accuracy, the value of the difference between the intrahemispheric and interhemispheric tests can be utilized as a reliable measure of the effectiveness of hemispheric interactions.

RESULTS

Older professional musicians show significantly greater accuracy in tactile interhemispheric transfer than non-musicians who suffer from age-related decline.

CONCLUSIONS

Musicians have more efficient interhemispheric communication than age-matched non-musicians. This finding is in keeping with studies showing that individuals with extensive musical training have a larger corpus callosum. The results are discussed in relation to relevant data suggesting that music positively influences aging brain plasticity.

The Evolution of Corpus Callosotomy for Epilepsy Management

Corpus callosotomy, first used in the management of epilepsy by William P. van Wagenen in 1940, was for years a contentious procedure. Two decades later, Nobel Laureate Roger W. Sperry's split-brain studies inspired surgeons to reexamine the role of corpus callosotomy in the control of epileptic seizures. In 1962, Joseph Bogen and Philip Vogel performed complete corpus callosotomies in patients with a history of generalized seizures. The identification of a set of postsurgical disconnection symptoms and other neurologic deficits begged the improvement of the surgical technique. Modifications to the operation, including anterior callosotomy, posterior callosotomy, partial callosotomy, staged callosotomy, microsurgical techniques, and radiosurgical techniques, continue to refine the procedure.

Clinical Features, Etiology, and 6-Month Prognosis of Isolated Corpus Callosum Infarction

As the largest subcortical commissural fiber, the corpus callosum plays an important role in cerebral functions and has abundant blood supply from bilateral circulation. Isolated corpus callosum infarction (ICCI) may have specific characteristics. The aim of the study is to evaluate the clinical features, etiology, and 6-month prognosis of ICCI. Consecutive patients with acute ICCI treated at the China-Japan Friendship Hospital between June 2012 and June 2016 were retrospectively assessed for clinical and imaging findings. These cases were compared with patients suffering from other isolated supratentorial subcortical infarctions, matched for age, sex, and infarction size (n=60; control group). ICCI etiology and 6-month prognosis were further analyzed. ICCI cases accounted for 2.9% (33/1125) of all acute ischemic strokes and 30 patients were included. Most patients (n=28, 93.3%) presented nonspecific clinical symptoms, and only two (6.7%) with diffuse infarction developed callosal disconnection syndrome (CDS). The splenium was the most frequent site (37.5%). Large artery atherosclerosis (LAA) (n=16, 53.3%) was the most common etiology. Only four (13.3%) patients developed transient ischemic attacks (n=1, 3.3%) or cerebral infarction (n=3, 10%) during the 6-month follow-up. The frequency of good prognosis (modified Rankin score of 1-2 and without cardiovascular events) was higher in patients with ICCI compared with controls (P=0.024). Poor prognosis was associated with multiple cerebrovascular stenosis, diffuse/large infarction, and diabetes (all P<0.05). ICCI is a rare stroke type, frequently involving the splenium; its common etiology is likely LAA. Most patients show nonspecific symptoms, with only a few developing CDS. ICCI generally shows favorable short-term outcome.

Defining the Normal Dorsal Contour of the Corpus Callosum with Time

BACKGROUND AND PURPOSE

Morphological changes of the corpus callosum have been associated with a large number of congenital neurocognitive and psychiatric disorders. Focal defects or notches of the dorsal surface of the corpus callosum have not been well characterized. Our purpose was the following; 1) to characterize the dorsal contour of the corpus callosum during the life span, 2) to characterize the relationship of contour deviations to neighboring vessels, and 3) to determine whether contour deviations are congenital or acquired.

MATERIALS AND METHODS

We retrospectively reviewed normal sagittal T1-weighted brain MR images. A "notch" was defined as a concavity in the dorsal surface at least 1 mm in depth. The corpus callosum was considered to be "undulating" if there were >2 notches, including an anterior and posterior notch. The presence of a pericallosal artery and its relationship to a notch were assessed.

RESULTS

We reviewed 1639 MR imaging studies, spanning 0-89 years of age. A total of 1102 notches were identified in 823 studies; 344 (31%) were anterior, 660 (60%) were posterior, and 98 (9%), undulating. There was a positive correlation between the prevalence (P < .001) and depth (P = .028) of an anterior notch and age and a negative correlation between the prevalence of a posterior notch and age (P < .001). There was no difference between patient sex and corpus callosum notching (P = .884). Of the 823 studies with notches, 490 (60%) were associated with a pericallosal artery (P < .001).

CONCLUSIONS

The prevalence and depth of notches in the anterior corpus callosum increase significantly with age; this finding suggests that most notches are acquired. There is a significant positive association between the presence of a corpus callosum notch and adjacent pericallosal arteries, suggesting that this may play a role in notch formation.

Anesthetic Management in Corpus Callosum Agenesis

Corpus callosum agenesis develops when the band which connects the two hemispheres of the brain does not occur in utero. It is associated with prenatal infections, genetic factors, toxic exposures, metabolic disorders, and chromosome errors. Mostly seen clinical features are macrocephaly, microcephaly, seizures, motor retardation, hypotonia, eye anomalies, and facial dysmorphisms. Here, we report a case of corpus callosum agenesis syndrome undergoing upper endoscopy under deep sedation with dexmedetomidine. The main anesthetic concerns are difficulty in airway, respiratory problems, gastric reflux, and interaction of the seizures therapy with general anesthetics.

Diagonistic Apraxia: A Unique Case of Corpus Callosal Disconnection Syndrome and Neuromyelitis Optica Spectrum Disorder

Diagonistic apraxia is a corpus callosal disconnection syndrome. Callosal lesions in Neuromyelitis optica spectrum disorder (NMOSD) have been reported, but callosal disconnection syndrome are rare. A 48-year-old woman was treated for fever and a cough before hospitalization. Her fever abated immediately, but she had balance problems in walking and standing. She also had slurred speech. On neurological examination, she had diagonistic apraxia. Her left hand moved in an uncoordinated way when she moved her right hand: changing her clothes for example or using a knife and fork. She had to instruct her left hand to stop. She had dysarthria and her gait was wide-based. She also had many callosal disconnection syndrome symptoms such as alexia of left visual field, left ear extinction, crossed optic ataxia. Using FLAIR and DWI MRI, a mixture of low and high signals, a so-called “marbled pattern,” was seen in the corpus callosum. Since the patient was positive for anti-aquaporin-4 antibody, she was diagnosed with NMOSD. After two courses of steroid pulse therapy, the symptoms improved. Here we report diagonistic apraxia and other symptoms of callosal disconnection syndrome in anti-AQP4-positive NMOSD.

Corpus callosum infarction with cognitive dysfunction: two case reports and literature review

INTRODUCTION

The incidence of corpus callosum infarction is low, and sudden cognitive dysfunction caused by corpus callosum infarction is very rare. We report two cases of acute corpus callosum infarction with sudden cognitive impairment, and the related basis, clinical manifestations, diagnosis, differential diagnosis, treatment, and prognosis of this disease are reviewed.

CASES PRESENTATION

The two patients had sudden and severe memory impairment and spatial orientation disorder. Their cognitive function scores were significantly lower, and their MRI demonstrated clear corpus callosum infarction. Through treatment, the symptoms improved significantly.

DISCUSSION

This paper reports two cases with corpus callosum infarction with sudden cognitive impairment, and its relevant background is also reviewed, which will help doctors with the classification diagnosis of cerebral infarction and understanding of corpus callosum infarction.

White matter microstructure in a genetically defined group at increased risk of autism symptoms, and a comparison with idiopathic autism: an exploratory study

Klinefelter syndrome (47,XXY) is associated with physical, behavioral, and cognitive consequences. Deviations in brain structure and function have been reported, but structural characteristics of white matter have barely been assessed. This exploratory diffusion tensor imaging study assessed white matter microstructure in boys with 47,XXY compared with non-clinical, male controls. Additionally, both similarities and differences between 47,XXY and autism spectrum disorders (ASD) have been reported in cognition, behavior and neural architecture. To further investigate these brain-behavior pathways, white matter microstructure in boys with 47,XXY was compared to that of boys with ASD. Fractional anisotropy (FA), radial diffusivity (Dr), axial diffusivity (Da), and mean diffusivity (MD) were assessed in 47,XXY (n = 9), ASD (n = 18), and controls (n = 14), using tract-based spatial statistics. Compared with controls, boys with 47,XXY have reduced FA, coupled with reduced Da, in the corpus callosum. Boys with 47,XXY also have reduced Dr. in the left anterior corona radiata and sagittal striatum compared with controls. Compared with boys with ASD, boys with 47,XXY show reduced Da in the right inferior fronto-occipital fasciculus. Although this study is preliminary considering the small sample size, reduced white matter integrity in the corpus callosum may be a contributing factor in the cognitive and behavioral problems associated with 47,XXY. In addition, the differences in white matter microstructure between 47,XXY and ASD may be important for our understanding of the mechanisms that are fundamental to behavioral outcome in social dysfunction, and may be targeted through intervention.

Diffuse corpus callosum infarction - Rare vascular entity with differing etiology

INTRODUCTION

Infarctions of the corpus callosum are rare vascular events. It is relatively immune to vascular insult because of its rich vascular supply from anterior and posterior circulations of brain.

OBJECTIVE

Report of 3 patients with largely diffuse acute corpus callosum infarction.

METHODS

3 patients with largely diffuse acute corpus callosum infarction were studied and each of these 3 patients had 3 different aetiologies.

RESULTS

The 3 different aetiologies of largely diffuse acute corpus callosum infarction were cardioembolism, tuberculous arteritis and takayasu arteritis.

CONCLUSION

Diffuse corpus callosum infarcts are rare events. This case series narrates the three different aetiologies of diffuse acute corpus callosum infarction which is a rare vascular event.

Infarction of the corpus callosum: a retrospective clinical investigation

Objectives

The aim of this study was to investigate patients with ischemic infarctions in the territory of the corpus callosum to advance our understanding of this rare stroke subtype by providing comprehensive descriptive and epidemiological data.

Methods

From January 1, 2010 to June 30, 2014, all cases of acute ischemic stroke diagnosed by clinical manifestation and diffusion weighted imaging in Dalian Municipal Central Hospital were investigated. The patients presenting with corpus callosum infarctions were selected and further allocated into genu and/or body and splenium infarction groups. Proportion, lesion patterns, clinical features, risk factors and etiology of corpus callosum infarction were analyzed.

Results

Out of 1,629 cases, 59 patients (3.6%) with corpus callosum infarctions were identified by diffusion weighted imaging, including 7 patients who had ischemic lesions restricted to the corpus callosum territory. Thirty six patients had lesions in the splenium (61.0%). Corpus callosum infarction patients suffered from a broad spectrum of symptoms including weakness and/or numbness of the limbs, clumsy speech, and vertigo, which could not be explained by lesions in corpus callosum. A classical callosal disconnection syndrome was found in 2 out of all patients with corpus callosum infarctions. Statistical differences in the risk factor and infarct pattern between the genu and/or body group and splenium group were revealed.

Conclusion

Corpus callosum infarction and the callosal disconnection syndrome were generally rare. The most susceptible location of ischemic corpus callosum lesion was the splenium. Splenium infarctions were often associated with bilateral cerebral hemisphere involvement (46.2%). The genu and/or body infarctions were associated with atherosclerosis. The most common cause of corpus callosum infarction probably was embolism.

Bright splenium of a psychotic mind

A twenty-one-year old primigravida presented two weeks postpartum with new onset of behavioral alteration and irrelevant talking without fever, headache, or seizures. Magnetic resonance imaging (MRI) of brain showed a lesion with diffusion restriction in splenium of corpus callosum. A possibility of postpartum psychosis was considered after ruling out various etiologies for splenium hyperintense lesion. Near complete resolution of symptoms was noted after initiation of antipsychotic medications. Literature has described multiple etiologies for lesions involving splenium of corpus callosum on brain imaging. We present this case as a unique clinical presentation of splenial pathology in the form of postpartum psychosis.

Arterial vascularization patterns of the splenium: An anatomical study

The aim of this study was to provide detailed information about the arterial vascularization of the splenium of the corpus callosum (CC). The splenium is unique in that it is part of the largest commissural tract in the brain and a region in which pathologies are seen frequently. An exact description of the arterial vascularization of this part of the CC remains under debate. Thirty adult human brains (60 hemispheres) were obtained from routine autopsies. Cerebral arteries were separately cannulated and injected with colored latex. Then, the brains were fixed in formaldehyde, and dissections were performed using a surgical microscope. The diameter of the arterial branches supplying the splenium of the CC at their origin was investigated, and the vascularization patterns of these branches were observed. Vascular supply to the splenium was provided by the anterior pericallosal artery (40%) from the anterior circulation and by the posterior pericallosal artery (88%) and posterior accessory pericallosal artery (50%) from the posterior circulation. The vascularization pattern of the splenium differs in each hemisphere and is usually supplied by multiple branches. The arterial vascularization of the splenium of the CC was studied comprehensively considering the ongoing debate and the inadequacy of the studies on this issue currently available in the literature. This anatomical knowledge is essential during the treatment of pathologies in this region and especially for splenial arteriovenous malformations.

Cavernous angioma of the corpus callosum presenting with acute psychosis

Psychiatric symptoms may occasionally be related to anatomic alterations of brain structures. Particularly, corpus callosum lesions seem to play a role in the change of patients' behavior. We present a case of a sudden psychotic attack presumably due to a hemorrhagic cavernous angioma of the corpus callosum, which was surgically removed with complete resolution of symptoms. Although a developmental defect like agenesis or lipoma is present in the majority of these cases, a growing lesion of the corpus callosum can rarely be the primary cause. Since it is potentially possible to cure these patients, clinicians should be aware of this association.

Neuroimaging evidence of major morpho-anatomical and functional abnormalities in the BTBR T+TF/J mouse model of autism

BTBR T+tf/J (BTBR) mice display prominent behavioural deficits analogous to the defining symptoms of autism, a feature that has prompted a widespread use of the model in preclinical autism research. Because neuro-behavioural traits are described with respect to reference populations, multiple investigators have examined and described the behaviour of BTBR mice against that exhibited by C57BL/6J (B6), a mouse line characterised by high sociability and low self-grooming. In an attempt to probe the translational relevance of this comparison for autism research, we used Magnetic Resonance Imaging (MRI) to map in both strain multiple morpho-anatomical and functional neuroimaging readouts that have been extensively used in patient populations. Diffusion tensor tractography confirmed previous reports of callosal agenesis and lack of hippocampal commissure in BTBR mice, and revealed a concomitant rostro-caudal reorganisation of major cortical white matter bundles. Intact inter-hemispheric tracts were found in the anterior commissure, ventro-medial thalamus, and in a strain-specific white matter formation located above the third ventricle. BTBR also exhibited decreased fronto-cortical, occipital and thalamic gray matter volume and widespread reductions in cortical thickness with respect to control B6 mice. Foci of increased gray matter volume and thickness were observed in the medial prefrontal and insular cortex. Mapping of resting-state brain activity using cerebral blood volume weighted fMRI revealed reduced cortico-thalamic function together with foci of increased activity in the hypothalamus and dorsal hippocampus of BTBR mice. Collectively, our results show pronounced functional and structural abnormalities in the brain of BTBR mice with respect to control B6 mice. The large and widespread white and gray matter abnormalities observed do not appear to be representative of the neuroanatomical alterations typically observed in autistic patients. The presence of reduced fronto-cortical metabolism is of potential translational relevance, as this feature recapitulates previously-reported clinical observations.

Spinal commissural connections to motoneurons controlling the primate hand and wrist

Left-right coordination is essential for locomotor movements and is partly mediated by spinal commissural systems. Such coordination is also essential for reaching and manipulation in primates, but the role of spinal commissural systems here has not been studied. We investigated commissural connectivity to motoneurons innervating forelimb muscles using intracellular recordings in acutely anesthetized macaque monkeys. In 57 of 81 motoneurons, synaptic responses (52 of 57 excitatory) were evoked after contralateral intraspinal microstimulation in the gray matter (cISMS; 300 μA maximum current intensity). Some responses (15 of 57) occurred at latencies compatible with a monosynaptic linkage, including in motoneurons projecting to intrinsic hand muscles (9 cells). Three pieces of evidence suggest that these effects reflected the action of commissural interneurons. In two cells, preceding cISMS with stimulation of the contralateral medial brainstem descending pathways facilitated the motoneuron responses, suggesting that cISMS acted on cell bodies whose excitability was increased by descending inputs. Pairing cISMS with stimulation of the contralateral corticospinal tract yielded no evidence of response occlusion in 16 cells tested, suggesting that the effects were not merely axon reflexes generated by stimulation of corticospinal axon branches, which cross the midline. Finally, stimulation of contralateral peripheral nerves evoked responses in 28 of 52 motoneurons (7 of 9 projecting to the hand). Our results demonstrate the existence of commissural neurons with access to spinal motoneurons in primate cervical spinal cord that receive inputs from the periphery as well as descending pathways. Most importantly, commissural neurons also innervate motoneurons of intrinsic hand muscles.

Neuroleptic treatments and overflow movements in schizophrenia: are they independent?

Neurological soft signs (NSS) are minor neurological abnormalities that can be revealed by a clinical examination focused on sensory and motor information processing. NSS include overflow movements (OMs), which are defined as involuntary movements that may accompany the production of voluntary movements. OM is generally considered to be a characteristic feature of schizophrenia. White matter abnormalities might be involved in the pathogenesis of OMs. Dopamine receptors play a role in oligodendrocytes development. There is a direct link between antipsychotic agents that bind to dopamine receptors on oligodendrocytes and the development of oligodendrocytes and myelin formation. In this paper, we review the current knowledge of the effects of antipsychotic agents on NSS in schizophrenic patients. As a result of this critical review we hypothesize that the neuroleptic actions described in this paper could explain why antipsychotic agents have no effect on the resolution of NSS in patients with schizophrenia.

Ventral and dorsal visual streams in posterior cortical atrophy: a DT MRI study

Using diffusion tensor magnetic resonance imaging tractography, ventral (inferior longitudinal fasciculus) and fronto-occipital (inferior fronto-occipital fasciculus) and dorsal (fronto-parietal superior longitudinal fasciculus) visual pathways were assessed in 7 patients with posterior cortical atrophy (PCA), showing either predominantly ventral or additional dorsal cognitive deficits. Corpus callosum and corticospinal tracts were also studied. Gray and white matter atrophy was assessed using voxel-based morphometry. In all PCA patients, abnormal diffusivity indexes were found in bilateral inferior longitudinal fasciculus and inferior fronto-occipital fasciculus, with a left-side predominance. Patients also had mild microstructural damage to the corpus callosum. The 2 patients with more dorsal symptoms also showed right fronto-parietal superior longitudinal fasciculus abnormalities. Corticospinal tracts were normal, bilaterally. When studied separately, patients with ventral clinical impairment showed a pattern of atrophy mainly located in the ventral occipitotemporal regions, bilaterally; patients with both ventral and dorsal clinical deficits showed additional atrophy of the bilateral inferior parietal lobe. Magnetic resonance imaging patterns of abnormalities mirror closely the clinical phenotypes and could provide reliable ante mortem markers of tissue damage in PCA.

Correlation between cognitive function and the association fibers in patients with Alzheimer's disease using diffusion tensor imaging

White matter (WM) changes, along with well-characterized cortical abnormalities, occur in patients with Alzheimer's disease (AD). We investigated the integrity of WM tracts within association fibers by the use of fractional anisotropy (FA), and the relationship between FA values and cognitive function in patients with AD. Neuropsychological examination and conventional MRI, as well as diffusion tensor imaging, (DTI) were conducted on 12 patients with mild to moderate AD and 18 cognitively healthy volunteers. DTI was performed to measure FA in the bilateral inferior fronto-occipital fasciculus (IFOF) and the superior longitudinal fasciculus (SLF). Mini-Mental State Examination (MMSE) scores and Montreal Cognitive Assessment (MoCA) values were used to evaluate cognitive function and the Clinical Dementia Rating (CDR) scale was used as a staging tool for dementia severity. FA measures were analyzed and correlated with neuropsychological data. No patient showed any WM tract abnormality on either T1-weighted or T2-weighted MRI. However, the FA values in the bilateral IFOF and SLF and the MoCA scores in patients with AD were significantly decreased (p<0.05) compared to the controls. Furthermore, the decreased FA values in the SLF were positively correlated with cognitive function (MMSE scores - right: r=0.672, p=0.033, left: r=0.919, p<0.01; MoCA values - right: r=0.747, p=0.013, left: r=0.679, p=0.031). Our findings confirmed that the loss of integrity of microstructural WM connectivity has a role in the cognitive decline of patients with AD. The data also suggest that the FA values of the SLF may be used as a clinical marker of cognitive function.

Corpus callosum in aging and neurodegenerative diseases

SUMMARY The corpus callosum (CC) is a major white matter bundle that connects primarily homologous areas of the cortex. The structure may be involved in interhemispheric communication and enable the lateralization of certain cerebral functions. Despite its possible role as the main conduit for interhemispheric communication, interest from researchers has, at times, been sparse. Renewed interest has led to research that has shown that the CC may play a role in both cognitive aging and neurodegenerative diseases including Alzheimer´s disease and frontotemporal dementia. Studies employing structural MRI and diffusion-weighted MRI have found distinct subregional patterns of callosal atrophy in aging, Alzheimer´s disease and frontotemporal dementia. Furthermore, imaging studies may help to elucidate the underlying pathological mechanisms of callosal atrophy. The present review aims to provide an overview of the current knowledge of the structure and function of the CC and its role in aging and neurodegenerative disease.

Inhibition by 5-HT of the synaptic responses evoked by callosal fibers on cortical neurons in the mouse

We have studied the modulation by 5-HT of the synaptic excitatory responses evoked by callosal fibers on cortical pyramidal neurons. We have used a mouse brain slice preparation that preserves the callosal fibers and allows their selective activation. EPSCs evoked by callosal stimulation (ccEPSCs) were recorded with patch electrodes from pyramidal neurons identified visually. We observed that 5-HT (10-40 μM) inhibited the ccEPSCs peak amplitude in 64% of the neurons; 5-HT had no effect in the remaining neurons. 5-HT also increased the frequency and amplitude of spontaneous EPSCs. This inhibition was accompanied with an increase in the coefficient of variation of the fluctuations of the ccEPSCs amplitude and with an increase in the ratio of the amplitudes of paired ccEPSCs. Agonists of 5-HT receptor subtypes 5-HT(1A) (8-OH-DPAT) and 5-HT(2A) (DOI) mimicked the effect of 5-HT; also, the effect of 8-OH-DPAT and DOI was blocked in the presence of specific blockers of 5-HT(1A) (WAY 100135) and 5-HT(2A) (MDL 11,939) receptors. Application of 5-HT did not change the amplitude of currents evoked by direct application of glutamate to neurons in which 5-HT decreased the amplitude of ccEPSC. The effects of 5-HT on ccEPSCs and on the synaptic currents evoked by intracortical stimulation were not correlated; this suggests that the effect of 5-HT was specific to particular synaptic inputs to a neuron. These results demonstrate the presynaptic modulation of the callosal synaptic responses by 5-HT and the implication of 5-HT(1A) and 5-HT(2A) receptors in this effect.

Cuprizone demyelination of the corpus callosum in mice correlates with altered social interaction and impaired bilateral sensorimotor coordination

For studies of remyelination in demyelinating diseases, the cuprizone model of CC (corpus callosum) demyelination has experimental advantages that include overall size, proximity to neural stem cells of the subventricular zone, and correlation with a lesion predilection site in multiple sclerosis. In addition, cuprizone treatment can be ended to allow more direct analysis of remyelination than with viral or autoimmune models. However, CC demyelination lacks a useful functional correlate in rodents for longitudinal analysis throughout the course of demyelination and remyelination. In the present study, we tested two distinct behavioural measurements in mice fed 0.2% cuprizone. Running on a 'complex' wheel with varied rung intervals requires integration between cerebral hemispheres for rapid bilateral sensorimotor coordination. Maximum running velocity on the 'complex' wheel decreased during acute (6 week) and chronic (12 week) cuprizone demyelination. Running velocity on the complex wheel distinguished treated (for 6 weeks) from non-treated mice, even after a 6-week recovery period for spontaneous remyelination. A second behavioural assessment was a resident-intruder test of social interaction. The frequency of interactive behaviours increased among resident mice after acute or chronic demyelination. Differences in both sensorimotor coordination and social interaction correlated with demonstrated CC demyelination. The wheel assay is applicable for longitudinal studies. The resident-intruder assay provides a complementary assessment of a distinct modality at a specific time point. These behavioural measurements are sufficiently robust for small cohorts as a non-invasive assessment of demyelination to facilitate analysis of subsequent remyelination. These measurements may also identify CC involvement in other mouse models of central nervous system injuries and disorders.

Postnatal lesion evidence against a primary role for the corpus callosum in mouse sociability

The BTBR T+tf/J (BTBR) strain is an inbred strain of mice that displays prominent social deficits and repetitive behaviors analogous to the defining symptoms of autism, along with complete congenital agenesis of the corpus callosum (CC). The BTBR strain is genetically distant from the widely used C57BL/6J (B6) strain, which exhibits high levels of sociability, a low level of repetitive behaviors, and an intact CC. Emerging evidence implicates compromised interhemispherical connectivity in some cases of autism. We investigated the hypothesis that the disconnection of CC fiber tracts contributes to behavioral traits in mice that are relevant to the behavioral symptoms of autism. Surgical lesion of the CC in B6 mice at postnatal day 7 had no effect on juvenile play and adult social approaches, and did not elevate repetitive self-grooming. In addition, LP/J, the strain that is genetically closest to the BTBR strain but has an intact CC, displayed juvenile play deficits and repetitive self-grooming similar to those seen in BTBR mice. These corroborative results offer evidence against the hypothesis that the CC disconnection is a primary cause of low sociability and a high level of repetitive behaviors in inbred mice. Our findings indicate that genes mediating other aspects of neurodevelopment, including those whose mutations underlie more subtle disruptions in white matter pathways and connectivity, are more likely to contribute to the aberrant behavioral phenotypes in the BTBR mouse model of autism.

Selective reduction of Von Economo neuron number in agenesis of the corpus callosum

Von Economo neurons (VENs) are large spindle-shaped neurons localized to anterior cingulate cortex (ACC) and fronto-insular cortex (FI). VENs appear late in development in humans, are a recent phylogenetic specialization, and are selectively destroyed in frontotemporal dementia, a disease which profoundly disrupts social functioning and self-awareness. Agenesis of the corpus callosum (AgCC) is a congenital disorder that can have significant effects on social and emotional behaviors, including alexithymia, difficulty intuiting the emotional states of others, and deficits in self- and social-awareness that can impair humor, comprehension of non-literal or affective language, and social judgment. To test the hypothesis that VEN number is selectively reduced in AgCC, we used stereology to obtain unbiased estimates of total neuron number and VEN number in postmortem brain specimens of four normal adult controls, two adults with isolated callosal dysgenesis, and one adult whose corpus callosum and ACC were severely atrophied due to a non-fatal cerebral arterial infarction. The partial agenesis case had approximately half as many VENs as did the four normal controls, both in ACC and FI. In the complete agenesis case the VENs were almost entirely absent. The percentage of neurons in FI that are VENs was reduced in callosal agenesis, but was actually slightly above normal in the stroke patient. These results indicate that the VEN population is selectively reduced in AgCC, but that the VENs do not depend on having an intact corpus callosum. We conclude that in agenesis of the corpus callosum the reduction in the number of VENs is not the direct result of the failure of this structure to develop, but may instead be another consequence of the genetic disruption that caused the agenesis. The reduction of the VEN population could help to explain some of the social and emotional deficits that are seen in this disorder.

Callosal branches of the anterior cerebral artery: an anatomical report

Although the morphology of the corpus callosum is well defined, the arterial supply of this structure has not been comprehensively studied. To elucidate this further, 40 cerebral hemispheres from 30 adult cadaveric brains were obtained. The anterior cerebral arteries were cannulated and injected with red latex. The following were observed and documented: (1) the number, diameter, and course of the arteries supplying the corpus callosum; (2) the territories vascularized by these arteries; (3) any variations of the callosal arteries. Short callosal arteries were present in 58 hemispheres (96.6%) and supplied the superficial surface of the corpus callosum along its midline and were a primary arterial source to this structure. Long callosal arteries were found in 28 hemispheres (46.6%) and contributed to the pial plexus. The cingulocallosal arteries were present in all hemispheres and supplied the corpus callosum, cingulate gyrus, and also contributed to the pericallosal pial plexus. The recurrent cingulocallosal arteries were present in 17 hemispheres (28.3%) and also contributed to the pericallosal pial plexus. The median callosal artery, an anatomical variation, was present in 10 brains (33.3%). This vessel supplied the corpus callosum and the cingulate gyrus. The aim of the present study was to provide a detailed description of the arteries supplying the corpus callosum for those who encounter these vessels radiologically or surgically.

Loss of resting interhemispheric functional connectivity after complete section of the corpus callosum

Slow (<0.1 Hz), spontaneous fluctuations in the functional magnetic resonance imaging blood oxygen level-dependent (BOLD) signal have been shown to exhibit phase coherence within functionally related areas of the brain. Surprisingly, this phenomenon appears to transcend levels of consciousness. The genesis of coherent BOLD fluctuations remains to be fully explained. We present a resting state functional connectivity study of a 6-year-old child with a radiologically normal brain imaged both before and after complete section of the corpus callosum for the treatment of intractable epilepsy. Postoperatively, there was a striking loss of interhemispheric BOLD correlations with preserved intrahemispheric correlations. These unique data provide important insights into the relationship between connectional anatomy and functional organization of the human brain. Such observations have the potential to increase our understanding of large-scale brain systems in health and disease as well as improve the treatment of neurologic disorders.

Limbic leukotomy for intractable major affective disorders: a 7-year follow-up study using nine comprehensive psychiatric test evaluations

Surgical treatment of psychiatric disease can be effective for some patients with severe, intractable disorders. However, few long-term studies using comprehensive psychiatric test evaluation of patients who have undergone surgery have been carried out. Stereotactic limbic leukotomy (subcaudate tractotomy and cingulotomy) was performed via radiofrequency thermocoagulation on 16 patients with intractable major affective disorders (bipolar). Patients were followed for 7 years, and nine complete psychiatric test evaluations were conducted before and after the procedure. Clinical outcomes were evaluated using the Current Global Psychiatric-Social Status Scale (CGPSS). In the 7-year follow-up, mean scores on the Hamilton Depression Rating Scale and the Beck Depression Inventory declined significantly from 42+/-5.76 to 20+/-11.98 (p<0.01) and from 32+/-9.13 to 19 +/- 14.29 (p<0.05), respectively. Also, mean scores on the Hamilton Anxiety Rating Scale and Negative Symptom Scale declined significantly from 104+/-53.62 to 57+/-36.41 (p<0.01) and from 57+/-15.38 to 33+/-18.8 (p<0.05), respectively. There were no statistical differences before and after surgery for Young's Mania Rating Scale, p>0.1. Using the CGPSS, 68.8% of patients had a marked response (CGPSS of >or=3), 18.9% of patients had a possible response (CGPSS of 2), and 12.6% did not improve or became worse (CGPSS of 0 or 1). There was no surgical mortality and only three patients experienced temporary minor complications. Based on these nine comprehensive psychiatric test evaluations, limbic leukotomy is an effective procedure for long-term treatment of severe, intractable major affective disorders, with no significant side effects. The results of the psychiatric tests carried out during the 7 years of follow-up were constant and stable. The current findings demonstrate that depression, anxiety, and negative symptoms are significantly reduced by limbic leukotomy, but mania and active symptoms are not. Surgical intervention remains an important therapeutic option for the treatment of major affective disorders, and is probably underused.

Different contributions of the corpus callosum and cerebellum to motor coordination in monkey

We investigated the different contribution of the corpus callosum (CC) and cerebellum to motor control in two macaque monkeys trained to perform a precision grip task with one or both hands. Recordings were made from antidromically identified CC cells and nearby unidentified neurons (UIDs) in the hand representation of the supplementary motor area (SMA) and compared with cells from the deep cerebellar nuclei (DCN). All cells showed their greatest modulation in activity (rate change locked to particular task event) during the movement epochs of the task (CC, 21.3 +/- 22.2; UIDs, 36.2 +/- 30.1 spike/s for contralateral trials; DCN, 63 +/- 56.4 for ipsilateral trials; mean +/- SD). Surprisingly, CC cells fired at very low basal rates compared with UIDs (3.9 +/- 4.9 vs. 10 +/- 9.1 spike/s) or DCN neurons (50.8 +/- 23.8 spike/s). However, SMA cells had the greatest rate modulation to baseline ratio (CC: 12.1 +/- 13.7; UID: 5.3 +/- 5.4; DCN: 1.7 +/- 2.0). This would allow them to code the timing of a behavioral event with better fidelity than DCN cells. A multivariate regression analysis between cell firing and EMG measured cells' representation of moment-by-moment modulations in muscle activity. CC neurons coded these real-time behavioral parameters significantly less well than the other cells types, using both linear and nonlinear models. Basal firing rate substantially constrains cell function. CC cells with low basal rates have restricted dynamic range for coding continuous parameters, but efficiently code the time of discrete behavioral events. DCN neurons with higher basal rates are better suited to control continuously variable parameters of movement.

The effects of age and attention on motor overflow production—A review

Motor overflow refers to overt involuntary movement, or covert muscle activity, that sometimes co-occurs with voluntary movement. Various clinical populations exhibit overflow. Motor overflow is also present in healthy children and the elderly, although in young adults, overt overflow is considered abnormal unless elicited under conditions of extreme force or muscle fatigue. Current theories of overflow imply that the corpus callosum may mediate production of this phenomenon. However, given that the corpus callosum is a conduit enabling the transfer of cortical information, surprisingly few studies have considered the cortical or subcortical structures underlying overflow. This review considers the developmental trend of motor overflow production, specifically in the upper-limbs, and the mechanisms thought to underlie this age-related phenomenon. Potential neurological correlates of motor overflow will be discussed in conjunction with higher order attentional processes which also regulate motor overflow production. Future research investigating the impact of attentional processes on overflow production may be particularly valuable for designing rehabilitation strategies for patients experiencing induced pathological overflow or conversely, to develop techniques to encourage the recovery of movement function in individuals with paretic limbs.

Functional anatomy of interhemispheric cortical connections in the human brain

Interhemsipheric interaction between the human cerebral hemispheres is served by abundant white-matter fibres in the human corpus callosum (CC). Damage to these fibres has notable behavioural and cognitive sequelae that depend on the exact location of the fibre loss. Until now, correlations between fibre loss and neurological disorders have been limited to post-mortem studies. Here we used probabilistic diffusion magnetic resonance imaging tractography to produce a two-dimensional map of the CC in the mid-sagittal plane. We observed an antero-posterior topography of interhemispheric tracts within the CC, consistent with our current neuroanatomical understanding of post-mortem studies in human. Callosal tract to the left and right hemispheres had comparable volume. Gender, a factor that is often reported to affect CC shape and geometry, also had no effect on the volume of the tracts. Our map showed high consistency across individuals. We propose that this map might be useful in the study of the effects of damage to human CC in neurodegenerative and cognitive disorders.

Association, commissural, and projection pathways and their functional deficit reported in literature

This study demonstrates normal white matter structures of the supratentorial system revealed by diffusion tensor imaging. Their anatomic connections and functional significance are discussed in the context of the lesion-induced deficits reported in the literature, which may not fully represent the lesion-induced effects on the white matter function and may not be entirely specific to the tract discussed. Nevertheless, understanding the most common effects of lesions on the functional connectivity provides a framework that we can use in advanced neuroimaging studies, like diffusion tensor imaging, functional magnetic resonance imaging, and positron emission tomography, and in our daily clinical practice.

Frontal connections and cognitive changes in normal aging rhesus monkeys: a DTI study

Recent anatomical studies have found that cortical neurons are mainly preserved during the aging process while myelin damage and even axonal loss is prominent throughout the forebrain. We used diffusion tensor imaging (DT-MRI) to evaluate the hypothesis that during the process of normal aging, white matter changes preferentially affect the integrity of long corticocortical association fiber tracts, specifically the superior longitudinal fasciculus II and the cingulum bundle. This would disrupt communication between the frontal lobes and other forebrain regions leading to cognitive impairments. We analyzed DT-MRI datasets from seven young and seven elderly behaviorally characterized rhesus monkeys, creating fractional anisotropy (FA) maps of the brain. Significant age-related reductions in mean FA values were found for the superior longitudinal fasciculus II and the cingulum bundle, as well as the anterior corpus callosum. Comparison of these FA reductions with behavioral measures demonstrated a statistically significant linear relationship between regional FA and performance on a test of executive function. These findings support the hypothesis that alterations to the integrity of these long association pathways connecting the frontal lobe with other forebrain regions contribute to cognitive impairments in normal aging. To our knowledge this is the first investigation reporting such alterations in the aging monkey.

GABAergic and pyramidal neurons of deep cortical layers directly receive and differently integrate callosal input

We studied the involvement of deep cortical layer neurons in processing callosal information in the rat. We observed with electron microscopy that both parvalbumin (PV)-labeled profiles and unlabeled dendritic spines of deep cortical layer neurons receive synapses from the contralateral hemisphere. Stimulation of callosal fibers elicited monosynaptic excitatory postsynaptic currents in both layer VI pyramidal neurons and gamma-aminobutyric acidergic (GABAergic) interneurons immunopositive for the vesicular GABA transporter and PV. Pyramidal cells had intrinsic electrophysiological properties and synaptic responses with slow kinetics and a robust N-metyhl-D-aspartate (NMDA) component. In contrast, GABAergic interneurons had intrinsic membrane properties and synaptic responses with faster kinetics and a less pronounced NMDA component. Consistent with these results, the temporal integration of callosal input was effective over a significantly longer time window in pyramidal neurons compared with GABAergic interneurons. Interestingly, callosal stimulation did not evoke feedforward inhibition in all GABAergic interneurons and in the majority of pyramidal neurons tested. Furthermore, retrogradely labeled layer VI pyramidal neurons of the contralateral cortex responded monosynaptically to callosal stimulation, suggesting interconnectivity between callosally projecting neurons. The data show that pyramidal neurons and GABAergic interneurons of deep cortical layers receive interhemispheric information directly and have properties supporting their distinct roles.

Free radical-mediated damage to barrier function is not associated with altered brain morphology in high-altitude headache

The present study combined molecular and neuroimaging techniques to examine if free radical-mediated damage to barrier function in hypoxia would result in extracellular edema, raise intracranial pressure (ICP) and account for the neurological symptoms typical of high-altitude headache (HAH) also known as acute mountain sickness (AMS). Twenty-two subjects were randomly exposed for 18 h to 12% (hypoxia) and 21% oxygen (O2 (normoxia)) for collection of venous blood (0 h, 8 h, 15 h, 18 h) and CSF (18 h) after lumbar puncture (LP). Electron paramagnetic resonance (EPR) spectroscopy identified a clear increase in the blood and CSF concentration of O2 and carbon-centered free radicals (P<0.05 versus normoxia) subsequently identified as lipid-derived alkoxyl (LO*) and alkyl (LC*) species. Magnetic resonance imaging (MRI) demonstrated a mild increase in brain volume (7.0+/-4.8 mL or 0.6%+/-0.4%, P<0.05 versus normoxia) that resolved within 6 h of normoxic recovery. However, there was no detectable evidence for gross barrier dysfunction, elevated lumbar pressures, T2 prolongation or associated neuronal and astroglial damage. Clinical AMS was diagnosed in 50% of subjects during the hypoxic trial and corresponding headache scores were markedly elevated (P<0.05 versus non-AMS). A greater increase in brain volume was observed, though this was slight, independent of oxidative stress, barrier dysfunction, raised lumbar pressure, vascular damage and measurable evidence of cerebral edema and only apparent in the most severe of cases. These findings suggest that free-radical-mediated vasogenic edema is not an important pathophysiological event that contributes to the mild brain swelling observed in HAH.

Increased seizure susceptibility and cortical malformation in beta-catenin mutant mice

Beta-catenin has been implicated in epilepsy because of its altered post seizure expression and the role of Wnt2 signaling in autism. To determine beta-catenin's role in seizure susceptibility, we injected penetylenetetrazol intraperitoneally in beta-catenin cerebral cortex- and hippocampus-specific knockout mice. We then analyzed the latency, number, and duration of four phases of seizure behaviors: (I) non-seizure activity, (II) myoclonic jerks, (III) generalized clonic seizures, and (IV) tonic seizures. The latencies to both death and Phase IV were significantly reduced in mutant mice. Mutant mice also spent significantly more time in Phases III and IV and showed significantly less time in the non-convulsive state (Phase I). Nissl and gold chloride staining indicated that the knockout mice had underdeveloped cortices, lacked a corpus callosum, and were missing hippocampal structures. This suggests that dysfunction of beta-catenin-mediated signaling pathways in mice leads to cortical malformation and increased seizure susceptibility.