Mammillothalamic tract in human brain: Diffusion tensor tractography study

In vivo probabilistic atlas of white matter tracts of the human subthalamic area combining track density imaging and optimized diffusion tractography

The human subthalamic area is a region of high anatomical complexity, tightly packed with tiny fiber bundles. Some of them, including the pallidothalamic, cerebello-thalamic, and mammillothalamic tracts, are relevant targets in functional neurosurgery for various brain diseases. Diffusion-weighted imaging-based tractography has been suggested as a useful tool to map white matter pathways in the human brain in vivo and non-invasively, though the reconstruction of these specific fiber bundles is challenging due to their small dimensions and complex anatomy. To the best of our knowledge, a population-based, in vivo probabilistic atlas of subthalamic white matter tracts is still missing. In the present work, we devised an optimized tractography protocol for reproducible reconstruction of the tracts of subthalamic area in a large data sample from the Human Connectome Project repository. First, we leveraged the super-resolution properties and high anatomical detail provided by short tracks track-density imaging (stTDI) to identify the white matter bundles of the subthalamic area on a group-level template. Tracts identification on the stTDI template was also aided by visualization of histological sections of human specimens. Then, we employed this anatomical information to drive tractography at the subject-level, optimizing tracking parameters to maximize between-subject and within-subject similarities as well as anatomical accuracy. Finally, we gathered subject level tracts reconstructed with optimized tractography into a large-scale, normative population atlas. We suggest that this atlas could be useful in both clinical anatomy and functional neurosurgery settings, to improve our understanding of the complex morphology of this important brain region.

Autonomic disorders in Parkinson disease: Disrupted hypothalamic connectivity as revealed from resting-state functional magnetic resonance imaging

Converging evidence from diverse methodologies implicate the hypothalamus in the pathophysiology of Parkinson's disease (PD). Pathology in the hypothalamus and in hypothalamic pathways has been linked primarily to autonomic dysfunction, routinely experienced by individuals with PD throughout the course of the disease, sometimes predating onset of motor symptoms. Postmortem and molecular imaging studies have delineated pathologic changes in the hypothalamus and demonstrated alterations in neurotransmitter systems within this structure and associated pathways, which track the progression of the disease. More recently, functional interactions between the hypothalamus, thalamus, and striatum, as assessed using resting-state functional magnetic resonance imaging, were shown to be reduced in PD patients with high in comparison to those with low autonomic symptom burden. These functional changes may relate to micro- and macrostructural alterations which are also observed in PD. An examination of the hypothalamus and hypothalamic pathways can also shed light on atypical parkinsonian disorders and their distinct pathophysiologic characteristics relative to idiopathic PD. Altogether, the current state of knowledge on the involvement of the hypothalamus in PD is profound, yet emerging methodological advances are likely to move our understanding of hypothalamic pathology in PD significantly forward.

Variability Between Direct and Indirect Targeting of the Anterior Nucleus of the Thalamus

BACKGROUND

Preoperative thalamic targeting methods have historically relied on indirect targeting techniques that do not fully account for variances in anatomy or for thalamic atrophy in epilepsy. We aimed to address variability noted between traditional indirect targeting and direct targeting methods for the anterior nucleus of the thalamus (ANT).

METHODS

Fifteen consecutive patients undergoing ANT deep brain stimulator placement were evaluated (30 thalamic nuclei). Direct ANT targeting was performed using a fast gray matter acquisition T1 inversion recovery sequence and compared with standard stereotactic coordinates. Thalamic volumes were calculated for each patient, and degree of thalamic volume loss was assessed compared with matched control subjects. Vertex analysis was performed to assess shape changes in the thalamus compared with age- and sex-matched subjects.

RESULTS

There was significant variation between direct and indirect targets in the y-axis and z-axis on both sides. On the left, the direct target was located at y = 2 ± 1.3 mm and z = 9.3 ± 1.8 mm (both P = 0.02). On the right, the direct target was located at y = 2.9 ± 1.8 mm and z = 9.2 ± 2 mm (both P ≤ 0.0003). There was no significant difference in the x-coordinate on either side (P > 0.5). Additionally, there was a correlation between thalamic volume and difference between direct and indirect targets in the y-axis and the z-axis.

CONCLUSIONS

We showed a significant difference in direct and indirect targeting in the y-axis and z-axis when targeting the ANT for deep brain stimulation for epilepsy. This difference is correlated to thalamic volume, with a larger difference noted in patients with thalamic atrophy.

The mammillothalamic tracts: Age-related conspicuity and normative morphometry on brain magnetic resonance imaging

The mammillothalamic tract (MTT, bundle of Vicq d'Azyr) is a white-matter projection from each mammillary body to the anterior nucleus of the thalamus (ANT). Deep brain stimulation of the MTTs or ANTs is a treatment option for medically refractory focal epilepsy. Since the ANTs may be atrophied in epilepsy, targeting of the MTT terminations could be used as a proxy for ANT locations. However, MTT conspicuity and morphometry on MRI have not been evaluated to date. We investigated normative age- and sex-related MRI morphometrics of the MTTs in healthy individuals. We retrospectively analyzed magnified axial T2-weighted images of 80 subjects for bilateral MTT conspicuity, diameters, areas, shapes, precise locations, and symmetry. We statistically tested the effects of independent variables (sex and MTT side) on measured dependent variables using two-way ANOVA; and performed linear regressions with age as the independent variable for each of the dependent variables. Subjects were F:M = 44:36, with mean age 45.3 years. Only one (0.63%) MTT was inconspicuous. Mean MTT diameter was 1.8 mm, area was 2.0 mm² , and distance from third ventricle was 3.1 mm. MTTs were mostly bilaterally symmetrical in shape, equally round, or ovoid. The right MTT diameter was larger than the left, and males had larger MTT areas than females. We found no statistical difference between MTT diameters and areas in young, middle-aged, and older adults. We report normative axial MRI morphometrics of the MTTs to guide neuromodulation treatments. Future detailed analyses will determine if the MTTs atrophy in proportion to the ANTs in refractory epilepsy.

Reduced Interhemispheric White Matter Asymmetries in Medial Temporal Lobe Epilepsy With Hippocampal Sclerosis

Mesial temporal lobe epilepsy (MTLE), one of the most common types of refractory focal epilepsy, has shown white matter abnormalities both within and beyond the temporal lobe. In particular, the white matter abnormalities in the ipsilateral hemisphere are more obvious than those in the contralateral hemisphere in MTLE, that is, the abnormalities present asymmetrical characteristics. However, very few studies have characterized the white matter microstructure asymmetry in MTLE patients specifically. Thus, we performed diffusion tensor imaging (DTI) to investigate the white matter microstructure asymmetries of patients with MTLE with unilateral hippocampal sclerosis (MTLE-HS). We enrolled 25 MTLE-HS (left MTLE-HS group, n = 13; right MTLE-HS group, n = 12) and 26 healthy controls (HC). DTI data were analyzed by tract-based spatial statistics (TBSS) to test the hemispheric differences across the entire white matter skeleton. We also conducted a two-sample paired t-test for 21 paired region of interests (ROIs) parceled on the basis of the ICBM-DTI-81 white-matter label atlas of bilateral hemispheres to test the hemispheric differences. An asymmetry index (AI) was calculated to further quantify the differences between the left and right paired-ROIs. It was found that the asymmetries of white matter skeletons were significantly lower in the MTLE-HS groups than in the HC group. In particular, the asymmetry traits were moderately reduced in the RMTLE-HS group and obviously reduced in the LMTLE-HS group. In addition, AI was significantly different in the RMTLE-HS group from the LMTLE-HS or HC group in the limbic system and superior longitudinal fasciculus (SLF). The current study found that the interhemispheric white matter asymmetries were significantly reduced in the MTLE-HS groups than in the HC group. The interhemispheric white matter asymmetries are distinctly affected in left and right MTLE-HS groups. The differences in AI among RMTLE-HS, LMTLE-HS, and HC involved the limbic system and SLF, which may have some pragmatic implications for the diagnosis of MTLE and differentiating LMTLE-HS from RMTLE-HS.

Awakening Neuropsychiatric Research Into the Stria Medullaris: Development of a Diffusion-Weighted Imaging Tractography Protocol of This Key Limbic Structure

The Stria medullaris (SM) Thalami is a discrete white matter tract that directly connects frontolimbic areas to the habenula, allowing the forebrain to influence midbrain monoaminergic output. Habenular dysfunction has been shown in various neuropsychiatric conditions. However, there exists a paucity of research into the habenula’s principal afferent tract, the SM. Diffusion-weighted tractography may provide insights into the properties of the SM in vivo, opening up investigation of this tract in conditions of monoamine dysregulation such as depression, schizophrenia, addiction and pain. We present a reliable method for reconstructing the SM using diffusion-weighted imaging, and examine the effects of age and gender on tract diffusion metrics. We also investigate reproducibility of the method through inter-rater comparisons. In consultation with neuroanatomists, a Boolean logic gate protocol was developed for use in ExploreDTI to extract the SM from constrained spherical deconvolution based whole brain tractography. Particular emphasis was placed on the reproducibility of the tract, attention to crossing white matter tract proximity and anatomical consistency of anterior and posterior boundaries. The anterior commissure, pineal gland and mid point of the thalamus were defined as anatomical fixed points used for reconstruction. Fifty subjects were scanned using High Angular Resolution Diffusion Imaging (HARDI; 61 directions, b-value 1500 mm³). Following constrained spherical deconvolution whole brain tractography, two independent raters isolated the SM. Each output was checked, examined and cleaned for extraneous streamlines inconsistent with known anatomy of the tract by the rater and a neuroanatomist. A second neuroanatomist assessed tracts for face validity. The SM was reconstructed with excellent inter-rater reliability for dimensions and diffusion metrics. Gender had no effect on the dimensions or diffusion metrics, however radial diffusivity (RD) showed a positive correlation with age. Reliable identification and quantification of diffusion metrics of the SM invites further exploration of this key habenula linked structure in neuropsychiatric disorders such as depression, anxiety, chronic pain and addiction. The accurate anatomical localization of the SM may also aid preoperative stereotactic localization of the tract for deep brain stimulation (DBS) treatment.

Diffusion tensor tractography of the mammillothalamic tract in the human brain using a high spatial resolution DTI technique

The mammillary bodies as part of the hypothalamic nuclei are in the central limbic circuitry of the human brain. The mammillary bodies are shown to be directly or indirectly connected to the amygdala, hippocampus, and thalami as the major gray matter structures of the human limbic system. Although it is not primarily considered as part of the human limbic system, the thalamus is shown to be involved in many limbic functions of the human brain. The major direct connection of the thalami with the hypothalamic nuclei is known to be through the mammillothalamic tract. Given the crucial role of the mammillothalamic tracts in memory functions, diffusion tensor imaging may be helpful in better visualizing the surgical anatomy of this pathway noninvasively. This study aimed to investigate the utility of high spatial resolution diffusion tensor tractography for mapping the trajectory of the mammillothalamic tract in the human brain. Fifteen healthy adults were studied after obtaining written informed consent. We used high spatial resolution diffusion tensor imaging data at 3.0 T. We delineated, for the first time, the detailed trajectory of the mammillothalamic tract of the human brain using deterministic diffusion tensor tractography.

Significant Injury of the Mammillothalamic Tract without Injury of the Corticospinal Tract After Aneurysmal Subarachnoid Hemorrhage: A Retrospective Diffusion Tensor Imaging Study

OBJECTIVE

Little is known about the pathophysiologic mechanisms of white matter injury after aneurysmal subarachnoid hemorrhage (aSAH). The purpose of this study is to investigate whether the mammillothalamic tract (MTT) or corticospinal tract (CST) is more affected by aSAH in the same patients with good outcome (Grade 5 on Glasgow Outcome Scale at 3 months) using diffusion tensor imaging (DTI).

METHODS

Between June 2013 and September 2016, 21 patients with aSAH with good outcome and 21 sex- and age-matched normal healthy control participants were recruited. DTI was obtained at 8.92 ± 2.4 weeks after onset. Moreover, reconstruction of the CST and the MTT was completed with DTI-studio software. Apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values were measured. In addition, the motricity index and Mini-Mental State Examination scores were obtained.

RESULTS

There was no statistically significant difference detected in the ADC and FA values of the CST between the patient and control groups (P > 0.05). On the contrary, there was a statistically significant difference in ADC and FA values of the MTT between the patient and control groups (P < 0.05). In addition, in the patient group, no correlation (P > 0.05) was observed between motricity index scores and DTI parameters (ADC and FA), whereas the Mini-Mental State Examination showed a positive correlation with FA (r = 0.591, P = 0.029) without correlation to ADC (r = 0.142, P = 0.628).

CONCLUSIONS

Patients with good outcomes (Grade 5 on Glasgow Outcome Scale at 3 months) after aSAH appeared to suffer an injury of the MTT without an associated injury of the CST compared with the control group. This injury showed a correlation with cognitive dysfunction.

Mammillothalamic and Mammillotegmental Tracts as New Targets for Dementia and Epilepsy Treatment

BACKGROUND

Recently, neuromodulation through deep brain stimulation (DBS) has appeared as a new surgical procedure in the treatment of some types of dementia and epilepsy. The mammillothalamic and mammillotegmental tracts are involved among the new targets. To our knowledge, a review article focused specifically on these mammillary body efferents is lacking in the medical literature. Their contribution to memory is, regrettably, often overlooked.

METHODS

A review of the relevant literature was conducted.

RESULTS

There is evidence that mammillary bodies can contribute to memory independently from hippocampal formation, but the mechanism is not yet known. Recent studies in animals have provided evidence for the specific roles of these mammillary body efferents in regulating memory independently. In animal studies, it has been shown that the disruption of the mammillothalamic tract inhibits seizures and that electrical stimulation of the mammillary body or mammillothalamic tract raises the seizure threshold. In humans, DBS targeting the mammillary body through the mammillothalamic tract or the stimulation of the anterior thalamic nucleus, especially in the areas closely related to the mammillothalamic tract, has been found effective in patients with medically refractory epilepsy. Nonetheless, little knowledge exists on the functional anatomy of the mammillary body efferents, and their role in the exact mechanism of epileptogenic activity and in the memory function of the human brain.

CONCLUSIONS

A comprehensive knowledge of the white matter anatomy of the mammillothalamic and mammillotegmental tracts is crucial since they have emerged as new DBS targets in the treatment of various disorders including dementia and epilepsy.

Hippocampal - diencephalic - cingulate networks for memory and emotion: An anatomical guide

This review brings together current knowledge from tract tracing studies to update and reconsider those limbic connections initially highlighted by Papez (1937) for their presumed role in emotion. These connections link hippocampal and parahippocampal regions with the mammillary bodies, the anterior thalamic nuclei, and the cingulate gyrus, all structures now strongly implicated in memory functions. An additional goal of this review is to describe the routes taken by the various connections within this network. The original descriptions of these limbic connections saw their interconnecting pathways forming a serial circuit that began and finished in the hippocampal formation. It is now clear that, with the exception of the mammillary bodies, these various sites are multiply interconnected with each other, including many reciprocal connections. In addition, these same connections are topographically organised, creating further subsystems. This complex pattern of connectivity helps to explain the difficulty of interpreting the functional outcome of damage to any individual site within the network. For these same reasons, Papez' initial concept of a loop beginning and ending in the hippocampal formation needs to be seen as a much more complex system of hippocampal-diencephalic-cingulate connections. The functions of these multiple interactions might be better viewed as principally providing efferent information from the posterior medial temporal lobe. Both a subcortical diencephalic route (via the fornix) and a cortical cingulate route (via retrosplenial cortex) can be distinguished. These routes provide indirect pathways for hippocampal interactions with prefrontal cortex, with the preponderance of both sets of connections arising from the more posterior hippocampal regions. These multi-stage connections complement the direct hippocampal projections to prefrontal cortex, which principally arise from the anterior hippocampus, thereby creating longitudinal functional differences along the anterior-posterior plane of the hippocampus.

Neural injury of the Papez circuit following hypoxic-ischemic brain injury: A case report

INTRODUCTION

Hypoxic-ischemic brain injury (HI-BI), a result of oxygen deprivation of the brain, is accompanied by memory impairment. In this study, we report on a patient with neural injury of the Papez circuit following HI-BI, demonstrated by diffusion tensor tractography (DTT).

CLINICAL FINDINGS/PATIENT CONCERNS

A 48-year-old male patient suffered spontaneous cardiopulmonary arrest and underwent cardiopulmonary resuscitation for approximately 20 minutes with the concomitant oxygen deprivation leading to HI-BI. The patient showed severe memory impairment at 10 weeks after onset: a Mini-Mental State Examination score of 11 (full score: 30, cut-off score < 24), and examination using the memory function test was not possible due to severe cognitive deficit.

OUTCOMES

On 10-week DTT, discontinuation of the fornical column was observed in both hemispheres and thinning of the thalamocingulate tract was observed in the right hemisphere and nonreconstruction in the left hemisphere.

CONCLUSION

Using DTT, neural injury of the Papez circuit was demonstrated in a patient with memory impairment following HI-BI. These results suggest that analysis of the Papez circuit using DTT could provide beneficial information by detecting injury of the Papez circuit that cannot be detected on conventional brain MRI in patients with HI-BI.

Injury of the Thalamocingulate Tract in the Papez Circuit in Patients with Mild Traumatic Brain Injury

The thalamocingulate tract between the anterior thalamic nuclei and the cingulate gyrus is a part of the Papez circuit. Using diffusion tensor tractography, injury of the thalamocingulate tract was investigated in patients with mild traumatic brain injury. Two patients (patient 1: a 58-yr-old woman and patient 2: a 49-yr-old man) with head trauma resulting from a car accident were enrolled. They were classified as mild traumatic brain injury and no specific lesion was observed on brain magnetic resonance imaging. These patients complained of memory impairment after head trauma. The entire Papez circuits, including thalamocingulate tract, fornix, mammillothalamic tract, and cingulum, were reconstructed in both hemispheres except for the left thalamocingulate tract: patient 1, it was thinner and discontinued compared with the right thalamocingulate tract; and patient 2, it was not reconstructed. The injury of the left thalamocingulate tract appeared to be related to the memory impairment in these patients.

Limbic pathway lesions in patients with multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) is a well-known demyelinating disease to cause cognitive dysfunction. The limbic system, relevant to memory, can be easily overlooked in conventional magnetic resonance imaging (MRI).

PURPOSE

To investigate the distribution and frequency of demyelinating lesions affecting white matter connections of the limbic system based on localization with diffusion tensor imaging (DTI)-derived fractional anisotropy (FA) color maps compared to three-dimensional T2-weighted (T2W) and FLAIR volumes in MS patients.

MATERIAL AND METHODS

One hundred and fifty patients with a known diagnosis of MS were identified for this Health Insurance Portability and Accountability (HIPAA)-compliant retrospective cross-sectional study. DTI-derived FA color maps, co-registered to T2W and FLAIR images, were analyzed for lesions affecting the three white matter tracts of the limbic system including cingulum, fornix, and mammilothalamic tracts by two investigators. The approximate location of the lesions on FLAIR was always confirmed on the co-registered DTI-derived FA color maps.

RESULTS

Of the 150 patients analyzed, 14.6% had cingulum lesions, 2.6% had fornix lesions, and 2.6% had mammilothalamic tract lesions; 21.3% of patients had at least one of the three tracts affected.

CONCLUSION

A relatively high frequency of lesions involving the limbic tracts may explain memory deficits and emotional dysfunction commonly experienced by patients with MS. The combined information from T2W, FLAIR, and DTI-derived FA color map allowed for more accurate localization of lesions affecting the major white matter tracts of the limbic system.

Accelerated forgetting of contextual details due to focal medio-dorsal thalamic lesion

Effects of thalamic nuclei damage and related white matter tracts on memory performance are still debated. This is particularly evident for the medio-dorsal thalamus which has been less clear in predicting amnesia than anterior thalamus changes. The current study addresses this issue by assessing 7 thalamic stroke patients with consistent unilateral lesions focal to the left medio-dorsal nuclei for immediate and delayed memory performance on standard visual and verbal tests of anterograde memory, and over the long-term (>24 h) on an object-location associative memory task. Thalamic patients showed selective impairment to delayed recall, but intact recognition memory. Patients also showed accelerated forgetting of contextual details after a 24 h delay, compared to controls. Importantly, the mammillothalamic tract was intact in all patients, which suggests a role for the medio-dorsal nuclei in recall and early consolidation memory processes.

Injury of the mammillothalamic tract in patients with subarachnoid haemorrhage: a retrospective diffusion tensor imaging study

OBJECTIVE

Few studies have reported on injury of the mammillothalamic tract (MTT) in patients with stroke. However, no study in patients with subarachnoid haemorrhage (SAH) has been reported. Using diffusion tensor tractography, we attempted to investigate injury of the MTT in patients with SAH.

METHODS

We recruited 16 patients with SAH and 15 control participants. DTI was obtained at 5.7±1.5 weeks after onset and reconstruction of the MTT was performed using the probabilistic tractography method. The fractional anisotropy (FA) value and tract number of the MTT and the Mini-Mental State Examination (MMSE) score were determined. Values of FA and tract volume showing a decrement of more than two SDs that of normal control were defined as abnormal.

RESULTS

The FA value and tract volume in the patient group were significantly lower than those in the control group (p<0.05). In addition, MMSE showed strong (r=0.67, p=0.005) positive correlation with tract volume without correlation with FA. In the individual analysis, 16 MTTs of 32 MTTs in 16 patients showed abnormalities of the MTT in terms of the FA value, the tract volume or the presence of a reconstructed MTT. As a result, 10 (62.5%) of 16 patients showed abnormality of the MTT in at least one hemisphere.

CONCLUSIONS

We found that patients with SAH showed injury of the MTT and this injury showed correlation with cognitive dysfunction.

Thalamocortical connections between the mediodorsal nucleus of the thalamus and prefrontal cortex in the human brain: a diffusion tensor tractographic study

PURPOSE

The elucidation of thalamocortical connections between the mediodorsal nucleus (MD) of thalamus and the prefrontal cortex (PFC) is important in the clinical fields of neurorehabilitation and psychiatry. However, little is known about these connections in human brain. We attempted to identify and investigate the anatomical characteristics of the thalamocortical connection between MD and PFC in human brain using diffusion tensor tractography (DTT).

MATERIALS AND METHODS

Thirty-two healthy volunteers were recruited for this study. Diffusion tensor images were scanned using a 1.5-T. A seed region of interest was placed at the MD of the thalamus on coronal images, and target regions of interest were placed on the dorsolateral prefrontal cortex (DLPFC), the ventrolateral prefrontal cortex (VLPFC), and the orbitofrontal cortex (OFC), respectively. The three thalamocortical connections found were reconstructed using Functional Magnetic Resonance Imaging of the Brain (FMRIB) software.

RESULTS

The three thalamocortical connections were arranged in subcortical white matter in the following order from upper to lower levels: the DLPFC, the VLPFC, and the OFC. In terms of fractional anisotropy and mean diffusivity values, no significant differences were observed between the DLPFC, VLPFC and OFC (p>0.05). In contrast, the OFC tract volume was higher than those of the DLPFC and the VLPFC (p<0.05).

CONCLUSION

Three thalamocortical connections were reconstructed between MD and PFCs in human brain using DTT. We believe that the results of this study would be helpful to clinicians in treating frontal network syndrome and psychiatric diseases.

Injury of the mammillothalamic tract in patients with thalamic hemorrhage

Objective: Injury of the mammillothalamic tract (MTT) has been suggested as one of the plausible pathogenic mechanisms of memory impairment in patients with thalamic hemorrhage; however, it has not been clearly demonstrated so far. We attempted to investigate whether injury of the MTT documented by diffusion tensor tractography following thalamic hemorrhage correlates with cognitive impairment.

Methods: We recruited 22 patients with a thalamic hemorrhage and 20 control subjects. MTTs were reconstructed using the probabilistic tractography method. Patients were classified into two subgroups: reconstructed group, patients whose MTT was reconstructed in the affected hemisphere, and non-reconstructed group, patients whose MTT was not reconstructed.

Results: Mammillothalamic tract was reconstructed in 5 (22.7%, reconstructed group) patients in the affected hemisphere and was not reconstructed in the remaining 17 patients (77.3%, non-reconstructed group). In addition, the MTT was not reconstructed even in the unaffected hemisphere in four patients (23.5%) in non-reconstructed group. Fractional anisotropy and mean diffusivity values of the affected hemisphere in reconstructed group also did not show significant differences from those in the unaffected hemisphere of reconstructed group and the control group (p > 0.05). However, the tract volume of the affected hemisphere in reconstructed group was significantly lower than that of the unaffected hemisphere in reconstructed group and the control group (p < 0.05).

Conclusion: A large portion of patients with thalamic hemorrhage appeared to suffer severe injury of the ipsilesional MTT (77.3%) and 18.2% of them appeared to suffer severe injury even in the contralesional MTT. In addition, the remaining 22.7% of patients who had preserved integrity of the ipsilesional MTT appeared to suffer partial injury of the ipsilesional MTT.

Deficits in episodic memory retrieval reveal impaired default mode network connectivity in amnestic mild cognitive impairment

Amnestic mild cognitive impairment (aMCI) is believed to represent a transitional stage between normal healthy ageing and the development of dementia. In particular, aMCI patients have been shown to have higher annual transition rates to Alzheimer's Disease (AD) than individuals without cognitive impairment. Despite intensifying interest investigating the neuroanatomical basis of this transition, there remain a number of questions regarding the pathophysiological process underlying aMCI itself. A number of recent studies in aMCI have shown specific impairments in connectivity within the default mode network (DMN), which is a group of regions strongly related to episodic memory capacities. However to date, no study has investigated the integrity of the DMN between patients with aMCI and those with a non-amnestic pattern of MCI (naMCI), who have cognitive impairment, but intact memory storage systems. In this study, we contrasted the DMN connectivity in 24 aMCI and 33 naMCI patients using seed-based resting state fMRI. The two groups showed no statistical difference in their DMN intra-connectivity. However when connectivity was analysed according to performance on measures of episodic memory retrieval, the two groups were separable, with aMCI patients demonstrating impaired functional connectivity between the hippocampal formation and the posterior cingulate cortex. We provide evidence that this lack of connectivity is driven by impaired communication from the posterior cingulate hub and does not simply represent hippocampal atrophy, suggesting that posterior cingulate degeneration is the driving force behind impaired DMN connectivity in aMCI.

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First trial to explore Default Mode Network (DMN) connectivity between MCI and naMCI

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Amnestic and nonamnestic MCI groups show similar overall DMN intra-connectivity.

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aMCI patients have connectivity deficits related to impaired memory retention.

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Impaired DMN connectivity is driven by deficits in posterior cingulate cortex.

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Alzheimer’s disease pathology likely evolves from PCC to hippocampus

Thalamocortical tract between anterior thalamic nuclei and cingulate gyrus in the human brain: diffusion tensor tractography study

Most portions of the Papez circuit have been identified by diffusion tensor tractography (DTT). However, no DTT study on the proportion of the Papez circuit between the anterior thalamic nuclei and cingulate gyrus has been reported. We attempted to reconstruct the thalamocortical tract between the anterior thalamic nuclei and cingulate gyrus using DTT. All the reconstructed thalamocortical tracts originated from the anterior thalamic nuclei, ascended through the genu of the internal capsule, the anterior limb of the internal capsule, and the white matter around the anterior horn of the lateral ventricle in the anterior and lateral direction, and then terminated at the anterior cingulate gyrus. In terms of FA, MD, and tract volume, no significant differences were observed between hemispheres (p > 0.05). We reconstructed the thalamocortical tract between the anterior thalamic nucleus and cingulate gyrus in the human brain using DTT. We believe that the methodology and results of this study will be helpful to researchers investigating the Papez circuit.

The anatomical characteristics of the stria terminalis in the human brain: a diffusion tensor tractography study

The stria terminalis (ST) connects the amygdale (AM) with the hypothalamus, anterior commissure, preoptic area, and septal region. Many animal studies have reported on the anatomy and function of the ST; in contrast, little is known about its anatomy and function in the human brain. In the current study, we attempted to investigate the anatomical characteristics of the ST in the normal human brain, using diffusion tensor tractography. We recruited 30 healthy volunteers for this study. Diffusion tensor images were scanned using 1.5-T, and the ST was obtained using FMRIB software. Values of fractional anisotropy, mean diffusivity, and tract volume of the ST were measured. STs passed from the AM to the anterior hypothalamus, through the region, around to the anterior margin of the temporal horn of the lateral ventricle, over the posterior and superior margin of the thalamus, behind the anterior commissure. No differences according to the side of the hemisphere and sex in terms of fractional anisotropy, mean diffusivity, and tract volume of the ST (P<0.05) were observed. We identified the ST and observed the anatomical characteristics of the ST in the normal human brain. We believe that the methodology and results reported here would be helpful to researchers and clinicians in this field.