Microsurgical anatomy of the anterior cerebral artery and the arterial supply of the cingulate gyrus.

PURPOSE: The cingulate gyrus is a potential surgical area to treat tumours, psychiatric diseases, intractable pain and vascular malformations. The aim of the study was to define the topographic anatomy and arterial supply of the cingulate gyrus located on the medial surface of the cerebral hemisphere. METHODS: We studied thirty-six hemispheres, each hemisected in the midsagittal plane. The vertical thickness of the cingulate gyrus was measured at the anterior commissure (AC), posterior commissure (PC), and genu levels of the corpus callosum. The branches of the anterior and posterior cerebral arteries supplying each zone were noted separately. The arterial pathways were transformed to digital data in AutoCAD to identify the condensation and reduction areas. RESULTS: The mean AC-PC distance was 27.17 ± 1.63 mm. The thinnest region was the genu level of the corpus callosum (10.29 mm). The superior internal parietal artery (SIPA), inferior internal parietal artery (IIPA) and pericallosal artery (PrCA) supplied all zones of the cingulate gyrus. The anterior zone received the greatest supply. The arterial condensation and reduction areas on both sides of cingulate gyrus and its x, y, and z coordinates specified. CONCLUSIONS: The target cingulotomy (TC) area was determined for anterior cingulotomy. The properties of the TC area are that the thinnest region of the cingulate gyrus is supplied relatively less than other areas and is close to the anterior cingulotomy areas in the literature. The arterial reduction area (ARA) was found to be suitable for corpus callosotomy in terms of avoiding haemorrhage.

Transient Receptor Potential Melastatin 3 Is Functionally Expressed in Oligodendrocyte Precursor Cells and Is Upregulated in Ischemic Demyelinated Lesions.

Oligodendrocyte precursor cells (OPCs) are glial cells that differentiate into oligodendrocytes and myelinate axons. The number of OPCs is reportedly increased in brain lesions in some demyelinating diseases and during ischemia; however, these cells also secrete cytokines and elicit both protective and deleterious effects in response to brain injury. The mechanism regulating the behaviors of OPCs in physiological and pathological conditions must be elucidated to control these cells and to treat demyelinating diseases. Here, we focused on transient receptor potential melastatin 3 (TRPM3), a Ca2+-permeable channel that is activated by the neurosteroid pregnenolone sulfate (PS) and body temperature. Trpm3+/Pdgfra+ OPCs were detected in the cerebral cortex (CTX) and corpus callosum (CC) of P4 and adult rats by in situ hybridization. Trpm3 expression was detected in primary cultured rat OPCs and was increased by treatment with tumor necrosis factor α (TNFα). Application of PS (30-100 µM) increased the Ca2+ concentration in OPCs and this effect was inhibited by co-treatment with the TRP channel blocker Gd3+ (100 µM) or the TRPM3 inhibitor isosakuranetin (10 µM). Stimulation of TRPM3 with PS (50 µM) did not affect the differentiation or migration of OPCs. The number of Trpm3+ OPCs was markedly increased in demyelinated lesions in an endothelin-1 (ET-1)-induced ischemic rat model. In conclusion, TRPM3 is functionally expressed in OPCs in vivo and in vitro and is upregulated in inflammatory conditions such as ischemic insults and TNFα treatment, implying that TRPM3 is involved in the regulation of specific behaviors of OPCs in pathological conditions.

Callosal Diffusion-Restriction in Patients with Intracranial Hemorrhage.

OBJECTIVE: We aim to report the incidence and clinical characteristics of patients who were found to have diffusion restricting lesions of the corpus callosum (CC) on Diffusion-weighted imaging (DWI) on magnetic resonance imaging (MRI) following intracranial hemorrhage (ICH). DESIGN/METHODS: A retrospective cross-sectional analysis was performed of medical records of all adult patients admitted to a single tertiary center with a primary diagnosis of ICH and received nicardipine infusion over a 2-year period. Patients without MRI brain available or patients who underwent digital subtraction angiography (DSA) prior to MRI were excluded. ICH and intraventricular hemorrhage (IVH) volumes and scores were calculated. MRI brain scans were evaluated for presence and locations of DWI lesions. RESULTS: Among 162 patients who met inclusion criteria, 6 patients (4%, median age 53, range 37-71, 100% male, 33% white) were found to have DWI lesions in the CC with a median ICH volume of 17ml (range 1-105ml). The ICH locations were lobar (n=3), deep (n=2) and cerebellum (n=1). All patients (100%) had intraventricular hemorrhage (IVH) with median IVH volume of 25ml (range 2.7-55ml). Four patients were on levetiracetam. No identifiable infections or metabolic abnormalities were found among these patients. All but one patient had normal DSA. Follow up MRI was only available in one patient and showed no reversibility at 14 days. CONCLUSION: Although rare, diffusion restricting corpus callosum lesions can be seen in patients with ICH, especially in patients with IVH. The etiology and clinical significance of these lesions remains unknown and warrant further research.

Mapping the principal gradient onto the corpus callosum.

Gradients capture some of the variance of the resting-state functional magnetic resonance imaging (rsfMRI) signal. Amongst these, the principal gradient depicts a functional processing hierarchy that spans from sensory-motor cortices to regions of the default-mode network. While the cortex has been well characterised in terms of gradients little is known about its underlying white matter. For instance, comprehensive mapping of the principal gradient on the largest white matter tract, the corpus callosum, is still missing. Here, we mapped the principal gradient onto the midsection of the corpus callosum using the 7T human connectome project dataset. We further explored how quantitative measures and variability in callosal midsection connectivity relate to the principal gradient values. In so doing, we demonstrated that the extreme values of the principal gradient are located within the callosal genu and the posterior body, have lower connectivity variability but a larger spatial extent along the midsection of the corpus callosum than mid-range values. Our results shed light on the relationship between the brain's functional hierarchy and the corpus callosum. We further speculate about how these results may bridge the gap between functional hierarchy, brain asymmetries, and evolution.

Full recovery of Akinetic Mutism after corpus callosum infarction in post subarachnoid hemorrhage of ruptured distal anterior cerebral artery aneurysm.

The authors report a previously healthy 23-year-old male patient who presented with subarachnoid hemorrhage and was found to have a ruptured right distal anterior cerebral artery aneurysm. He was treated by endovascular coiling technique, which was uneventful perioperatively. After a few days of mechanical ventilation and upon extubation, he expressed symptoms of apathy, drowsiness, lack of motivation, and lack of spontaneous motor function consistent with akinetic mutism. The magnetic resonance imaging of the brain revealed infarction of the whole body of corpus callosum. He remained in akinetic mutism status for twenty-one days before he started to show improvement until he fully recovered in 3 months. The authors report a unique finding where akinetic mutism resulted from infarction of the corpus callosum rather than medial frontal lobe (cingulate gyrus).

The goblet sign in the amnestic syndrome of the subcallosal artery infarct.

We here describe an acute-onset amnesic syndrome with evidence of an embolic infarction in the distribution of the subcallosal artery, a proximal branch of the anterior communicating artery. The infarction involved the corpus callosum genu and both fornices, giving a peculiar image on MRI that resembled a goblet. Although infrequent, the subcallosal artery infarction should be considered in the differential diagnosis of patients with an acute amnestic syndrome. We propose "the goblet sign" for the peculiar diffusion-weighted MRI image of the brain in this syndrome.

Is the presence of corpus callosum predictable in the first trimester?

Corpus callosum agenesis (CCA) is a clinical condition accompanied by various aneuploidy and genetic syndromes. We identified the development of the corpus callosum (CC) in 278 patients before 18 weeks of gestational age by visualising the pericallosal artery (PCA) in the callosal sulcus and changes in the lengths and ratios of the midbrain (MB) and falx (F), which suggested elevation of the third ventricle and thalamus due to CCA in the first trimester. We succeeded in visualising the path of the PCA in 273 patients. As expected, we observed an increase in the lengths of the MB and F throughout the pregnancies. The MB:F ratio was 0.5-0.6, and it was independent of gestational age. In all 278 patients, the MB:F ratio was <0.6 (95th percentile = 0.79). We observed the presence of the CC during anatomical screening at gestational weeks 18-24. Visualisation of the PCA path (98% sensitivity) and calculation of the MB:F ratio <95th percentile (0.79-100% sensitivity) had very high sensitivity that indirectly confirmed the presence of the CC in the first trimester of pregnancy. Impact statement What is already known on this subject: After reading the articles for detecting the absence of corpus callosum (CC) at first trimester with midbrain (MB) and falx (F) measurement by Lachmann et al. ( 2013 ) and visualising pericallosal artery (PCA) as an indirect sign of CC agenesis by Pati et al. ( 2012 ), we aimed to have a look for our records visualising PCA in callosal sulcus and measure MB-F, as well as their ratios for an indirect sign of 'presence' of CC at first trimester. What the results of this study add: In recent literature, it is not possible to find many articles suggesting the presence of CC between 11 and 13 weeks of gestation. Díaz-Guerrero et al. ( 2013 ) and Pati et al. ( 2012 ) has researched visualising PCA path. Lachmann et al. ( 2013 ) reported an article for MB and F measurements in early suspicion of CC agenesis. Our study will be the first article in visualising PCA path and measuring MB-F lengths as well as their ratios for 'presence' of CC with high sensitivity rates (98% and 100%). What are the implications of these findings for clinical practice and/or further research: This study encourages clinicians visualising PCA path and measure MB-F lengths when they will try to visualise repetitive times and see how it is an easy procedure when you get used to it.

Critical Illness-Associated Cerebral Microbleeds.

BACKGROUND AND PURPOSE: Cerebral microbleeds (petechial hemorrhages) are a well-known consequence of cerebral amyloid angiopathy and chronic hypertension among other causes. We report 12 patients with a clinically and radiologically distinct microbleed phenomenon in the cerebral white matter. METHODS: These patients were assessed at the University Health Network (Toronto, Canada) between 2004 and 2014. RESULTS: Median age was 40 years (range, 27-63 years), and 7 out of 12 patients were women. All patients had brain magnetic resonance imaging during or immediately after an intensive care unit admission. All patients had respiratory failure, 11 out of 12 received mechanical ventilation, and 3 out of 12 received extracorporeal life support. Magnetic resonance imaging in all 12 patients showed extensive microbleeds, diffusely involving the juxtacortical white matter and corpus callosum but sparing the cortex, deep and periventricular white matter, basal ganglia, and thalami. Several patients also had internal capsule or posterior fossa involvement. CONCLUSIONS: We have described a distinct microbleed phenomenon in the cerebral white matter of patients with critical illness. The specific cause of the microbleeds is unclear, but the pathogenesis may involve hypoxemia as the microbleeds are similar to those described with high-altitude exposure.

Induction of Genes Expressed in Endothelial Cells of the Corpus Callosum in the Chronic Cerebral Hypoperfusion Rat Model.

BACKGROUND: Cerebrovascular white matter lesions (WMLs) are associated with cognitive impairment in patients with subcortical vascular dementia. We performed a comprehensive gene expression analysis to elucidate genes associated with WML development in a chronic cerebral hypoperfusion rat model. METHODS: Brains of rats with bilateral carotid ligation (2VO, n = 10) and sham-operated rats (n = 5-10/group) were removed on days 1, 7, or 28 after surgery. Total RNA isolated from the corpus callosum was evaluated by microarray analysis and quantitative reverse transcription-polymerase chain reaction. RESULTS: On days 7 and 28, WMLs exhibited histologic changes. On day 7, 16 genes were differentially expressed between groups. mRNA levels of Ptprb, Kcnj8, Crispld2, Bcl6b, and Gja5 were differentially expressed in 2VO rats on day 7, but then returned to normal, whereas mRNA levels of Vwf and Trappc6a were upregulated after day 7. Immunohistochemistry showed that GJA5 and vWF were detected in endothelial cells, KCNJ8 in endothelial cells and astrocytes, CRISPLD2 in neurons and astrocytes, and TRAPPC6A in neurons. CONCLUSION: Our findings indicate novel genes that may be associated with WML development in the chronic cerebral hypoperfusion rat model, and suggest an important role of neurovascular dysfunction in the pathophysiology.

Median pericallosal artery with double proximal origin: case report and clinical consideration.

A 76-year-old male patient underwent magnetic resonance angiography of the head and neck vessels due to a recent incident of transitory ischemic attack. Cerebral angiogram uncovered the double proximal origin of the median unpaired pericallosal artery from the duplicated anterior communicating complex. The vessel curved around the corpus callosum and irrigated the paracentral lobule and the medial parietal cortical areas. The main trunks of the anterior cerebral arteries showed a branching pattern of the marginal callosal arteries, supplying orbital and frontal territories. The pre-communicating segment of the left anterior cerebral artery was identified as hypoplastic. The co-existence of the duplicated anterior communicating artery, with the medial pericallosal artery ascending from it, represents a potential danger for both open and endovascular surgery on the anterior circle of Willis as the deep half of this complex is obscured from the surgeon's eyes. Thorough interpretation of preoperative radiographic images and understanding of the developmental mechanisms of such variability are vital. The described branching arrangement of the anterior communicative region and possible mechanisms of migration with following fusion of the pericallosal arteries are discussed in this paper.

[GENERAL PRINCIPLE OF THE CORPUS CALLOSUM INTERNAL STRUCTURE IN ADULT HUMAN].

The structure of the corpus callosum is a certain form of order of the nerve fibers, glial cells and blood microvessels and it is actually unexplored. We set the goal to understand the general constructive principle of the myeloarchitectonics of human corpus callosum. We used whole mounts of the corpus callosum (5 men and 5 women aged from 36 to 60 years) after their two-week fixation in 10% formalin solution. The next stage was to dissect plate sections of the corpus callosum brainstem in two mutually perpendicular planes. Some of them were subjected to impregnation in 1% osmium tetroxide solution, according to the method adopted in transmission electron microscopy. To prepare these plate sections of the corpus callosum for further study in the light microscope we used the method of plastination in epoxy resin. After complete polymerization plastinated mounts were used for making slices. For further research at high magnification light microscopy they were thinned up to 0.3 mm thickness and were subjected to coloration using 1% solution of methylene blue on 1% borax solution. They were studied using a binocular microscope МБС-9 and microscope "Konus" equipped with digital camera. It was found that the human corpus callosum consists of a number of transversely oriented bands of nerve fibers (commissural cords). Each of them consists of a tightly appressed stratified sections, fascicular rations, which are separated by interstitial layers. In turn, these interfascicular layers give short lateral spurs that divide fascicular rations into individual segments - subfascicular rations. Multiple cells containing interfascicular oligodendrocytes associated with individual subfascicular sets of nerve tracts are dispersed in the cluster order among myelinated nerve fibers of fascicular rations. Fundamentally important point is that the interstitial layers in the corpus callosum as a whole form a complex three-dimensional network structure which is subordinated to the nature of branching of blood microcirculation vessels of capillary type, being simultaneously the reticular system, performing extravascular circulation of fluid containing dissolved nutrients.

Apoptosis signal-regulating kinase 1 is a novel target molecule for cognitive impairment induced by chronic cerebral hypoperfusion.

OBJECTIVE: There are currently no specific strategies for the treatment or prevention of vascular dementia. White matter lesions, a common pathology in cerebral small vessel disease, are a major cause of vascular dementia. We investigated whether apoptosis signal-regulating kinase 1 (ASK1) might be a key molecule in cerebral hypoperfusion, associated with blood-brain barrier breakdown and white matter lesions. APPROACH AND RESULTS: A mouse model of cognitive impairment was developed by inducing chronic cerebral hypoperfusion in white matter including the corpus callosum via bilateral common carotid artery stenosis (BCAS) surgery. BCAS-induced white matter lesions caused cognitive decline in C57BL/6J (wild-type) mice but not in ASK1-deficient (ASK1(-/-)) mice. Phosphorylated ASK1 increased in wild-type mouse brains, and phosphorylated p38 and tumor necrosis factor-α expression increased in corpus callosum cerebral endothelial cells after BCAS in wild-type mice but not in ASK1(-/-) mice. BCAS decreased claudin-5 expression and disrupted blood-brain barrier in the corpus callosum of wild-type but not ASK1(-/-) mice. Cerebral nitrotyrosine was increased in wild-type and ASK1(-/-) BCAS mice. Cerebral phosphorylated ASK1 did not increase in wild-type mice treated with NADPH-oxidase inhibitor. A p38 inhibitor and NADPH-oxidase inhibitor mimicked the protective effect of ASK1 deficiency against cognitive impairment. Specific ASK1 inhibitor prevented cognitive decline in BCAS mice. In vitro oxygen-glucose deprivation and tumor necrosis factor-α stimulation caused the disruption of endothelial tight junctions from wild-type mice but not ASK1(-/-) mice. CONCLUSIONS: Oxidative stress-ASK1-p38 cascade plays a role in the pathogenesis of cognitive impairment, through blood-brain barrier breakdown via the disruption of endothelial tight junctions. ASK1 might be a promising therapeutic target for chronic cerebral hypoperfusion-induced cognitive impairment.

Subcallosal artery stroke: infarction of the fornix and the genu of the corpus callosum. The importance of the anterior communicating artery complex. Case series and review of the literature.

INTRODUCTION: Despite the variable anatomy of the anterior communicating artery (AcoA) complex, three main perforating branches can be typically identified the largest of which being the subcallosal artery (ScA). We present a case series of infarction in the vascular territory of the ScA to highlight the anatomy, the clinical symptomatology, and the presumed pathophysiology as it pertains to endovascular and surgical management of vascular pathology in this region. METHODS: In this retrospective multicenter case series study of patients who were diagnosed with symptomatic ScA stroke, we analyzed all available clinical records, MRI, and angiographic details. Additionally, a review of the literature is provided. RESULTS: We identified five different cases of ScA stroke, leading to a subsequent infarction of the fornix and the genu of the corpus callosum. The presumed pathophysiology in non-iatrogenic cases is microangiopathy, rather than embolic events; iatrogenic SCA occlusion can present after both surgical and endovascular treatment of AcoA aneurysms that may occur with or without occlusion of the AcoA. CONCLUSION: Stroke in the vascular territory of the ScA leads to a characteristic imaging and clinical pattern. Ischemia involves the anterior columns of the fornix and the genu of the corpus callosum, and patients present with a Korsakoff's syndrome including disturbances of short-term memory and cognitive changes. We conclude that despite its small size, the ScA is an important artery to watch out for during surgical or endovascular treatment of AcoA aneurysms.

Normal Doppler Reference Values of the Pericallosal Artery.

PURPOSE: To provide the normal reference values of the Doppler flow of the pericallosal artery in relation to gestational age from 18 to 41 weeks of gestation. MATERIALS AND METHODS: The pericallosal artery (PCA) was studied in 466 normal pregnancies. The pulsed Doppler evaluation of the pericallosal artery was done in A3 and A4 segments, and records from PI, RI and Vmax were studied. RESULTS: The resistance index of the pericallosal artery in A3/A4 segments exhibits a plateau from 18 to 31 weeks of gestation. After 31 weeks, a marked decrease becomes apparent. The pulsatility index of the pericallosal artery in A3/A4 segments shows a plateau until 36 weeks of gestation. During the final weeks of gestation, there is a decrease in the pulsatility index. Vmax exhibits a plateau for the maximal flow velocity in A3/A4 segments of the pericallosal artery from 18 to 28 weeks of gestation. After 28 weeks of gestation, there is a slight increase in Vmax. CONCLUSION: Normal reference values of the pericallosal artery might have an impact on clinical judgment during adaptive hemodynamic changes and regarding the progression of the fetal deterioration occurring in the presence of fetal hypoxia.

Demonstration of the Pericallosal Artery at 11-13 Weeks of Gestation Using 3D Ultrasound.

OBJECTIVE: To assess the sonographic visualization of the pericallosal arteries in normal fetuses at 11-13 weeks of gestation using 3D ultrasound. METHODS: We prospectively enrolled women with a singleton pregnancy undergoing ultrasound at 11-13 weeks of gestation. A 3D volume with high-definition power Doppler was acquired starting from the sagittal view of the fetal head and stored in the spatiotemporal image correlation mode. The images of the pericallosal arteries were assigned a score of 0 (no visualization), 1 (visualization of the origin) or 2 (visualization of the whole course). A follow-up scan was performed in all cases at 20 weeks of gestation to assess the presence of the corpus callosum. RESULTS: 70 patients were included and the pericallosal arteries were sonographically detectable in all cases. Image scores of 1 and 2 were obtained in 8 and 62 cases, respectively. The whole length of the vessel was between 3.5 and 4.5 mm. The vast majority of those with a score of 2 were beyond 12 completed weeks of gestation. All fetuses showed a normal corpus callosum at midtrimester and no abnormal brain findings after birth. CONCLUSIONS: The pericallosal arteries are sonographically visible since the first trimester in 3D ultrasound scans of fetuses found to have a normal corpus callosum at follow-up.

Interhemispheric functional connectivity following prenatal or perinatal brain injury predicts receptive language outcome.

Early brain injury alters both structural and functional connectivity between the cerebral hemispheres. Despite increasing knowledge on the individual hemispheric contributions to recovery from such injury, we know very little about how their interactions affect this process. In the present study, we related interhemispheric structural and functional connectivity to receptive language outcome following early left hemisphere stroke. We used functional magnetic resonance imaging to study 14 people with neonatal brain injury, and 25 age-matched controls during passive story comprehension. With respect to structural connectivity, we found that increased volume of the corpus callosum predicted good receptive language outcome, but that this is not specific to people with injury. In contrast, we found that increased posterior superior temporal gyrus interhemispheric functional connectivity during story comprehension predicted better receptive language performance in people with early brain injury, but worse performance in typical controls. This suggests that interhemispheric functional connectivity is one potential compensatory mechanism following early injury. Further, this pattern of results suggests refinement of the prevailing notion that better language outcome following early left hemisphere injury relies on the contribution of the contralesional hemisphere (i.e., the "right-hemisphere-take-over" theory). This pattern of results was also regionally specific; connectivity of the angular gyrus predicted poorer performance in both groups, independent of brain injury. These results present a complex picture of recovery, and in some cases, such recovery relies on increased cooperation between the injured hemisphere and homologous regions in the contralesional hemisphere, but in other cases, the opposite appears to hold.

Prenatal demonstration of normal variants of the pericallosal artery by 3D ultrasound.

PURPOSE: To demonstrate the different normal variants of the fetal pericallosal artery (PCA) with the different branching forms of callosomarginal artery (CMA) by three-dimensional glass body-rendering. MATERIALS AND METHODS: With the use of the glass body mode (grey scale ultrasound and color or power Doppler), 3-D ultrasound permits precise imaging of the fetal pericallosal artery, an important anatomic landmark of the corpus callosum. This rendering mode enabled us for the first time to demonstrate sonographically the origin, course and branching pattern of the pericallosal artery with the callosomarginal artery. RESULTS: In 452 fetus between 18 and 41 weeks of gestation 5 variants of branching of the fetal A. callosomarginalis from the pericallosal artery were found using three-dimensional ultrasonography. The CMA was absent in 36.06 % of the 452 fetal brains studied. In 63.94 % the CMA was present and arose from four different segments of the anterior cerebral artery (ACA) from the A3 segment in 59.17 %, from the A2 segment in 20.7 %, from the A4 segment in 13.15 % and from the A1 segment in 7.61 % of the cases. CONCLUSIONS: The use of 3-D power Doppler sonoangiography enables the precise demonstration of the normal variants of the fetal pericallosal artery with different origins of the callosomarginal artery. The knowledge of normal variants helps to detect pathological forms of the pericallosal artery.

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.

The architecture of cross-hemispheric communication in the aging brain: linking behavior to functional and structural connectivity.

Contralateral recruitment remains a controversial phenomenon in both the clinical and normative populations. To investigate the neural correlates of this phenomenon, we explored the tendency for older adults to recruit prefrontal cortex (PFC) regions contralateral to those most active in younger adults. Participants were scanned with diffusion tensor imaging and functional magnetic rresonance imaging during a lateralized word matching task (unilateral vs. bilateral). Cross-hemispheric communication was measured behaviorally as greater accuracy for bilateral than unilateral trials (bilateral processing advantage [BPA]) and at the neural level by functional and structural connectivity between contralateral PFC. Compared with the young, older adults exhibited 1) greater BPAs in the behavioral task, 2) greater compensatory activity in contralateral PFC during the bilateral condition, 3) greater functional connectivity between contralateral PFC during bilateral trials, and 4) a positive correlation between fractional anisotropy in the corpus callosum and both the BPA and the functional connectivity between contralateral PFC, indicating that older adults' ability to distribute processing across hemispheres is constrained by white matter integrity. These results clarify how older adults' ability to recruit extra regions in response to the demands of aging is mediated by existing structural architecture, and how this architecture engenders corresponding functional changes that allow subjects to meet those task demands.

Distinctive neural processes during learning in autism.

This functional magnetic resonance imaging study compared the neural activation patterns of 18 high-functioning individuals with autism and 18 IQ-matched neurotypical control participants as they learned to perform a social judgment task. Participants learned to identify liars among pairs of computer-animated avatars uttering the same sentence but with different facial and vocal expressions, namely those that have previously been associated with lying versus truth-telling. Despite showing a behavioral learning effect similar to the control group, the autism group did not show the same pattern of decreased activation in cortical association areas as they learned the task. Furthermore, the autism group showed a significantly smaller increase in interregion synchronization of activation (functional connectivity) with learning than did the control group. Finally, the autism group had decreased structural connectivity as measured by corpus callosum size, and this measure was reliably related to functional connectivity measures. The findings suggest that cortical underconnectivity in autism may constrain the ability of the brain to rapidly adapt during learning.