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

Deep brain stimulation for chronic refractory cluster headache: A case series about long-term outcomes and connectivity analysis

OBJECTIVE

The aim of this study was to provide long-term clinical results-including "sweet spot" identification and connectomic imaging analysis-in a series of patients treated with deep brain stimulation for refractory chronic cluster headache.

BACKGROUND

Deep brain stimulation is a relatively recent indication for the treatment of refractory chronic cluster headache. This indication has generated substantial debate in recent years due to uncertainty surrounding the mechanism of action and the lack of long-term efficacy data.

METHODS

Case retrospective series of adult patients diagnosed with refractory chronic cluster headache and treated with deep brain stimulation. Demographic and clinical data were registered preoperatively and at 3, 6, 12, and 24 months. The primary endpoint was reduction in headache load, a composite score of frequency, severity, and duration of each attack. Imaging analyses (sweet spot and connectomic analyses) were performed to identify the brain regions most closely correlated with the reduction in headache load and to identify the structural networks involved. Treatment response was categorized according to the reduction in headache load, as follows: poor (<30% reduction), partial (30-50%), or high (>50%).

RESULTS

A total of 14 patients were included, with a mean (standard deviation [SD]) age of 42.4 (10.7) years and mean (SD) headache duration of 8.0 (5.8) years. Headache load scores decreased significantly from baseline to Month 24: mean (SD) 424.2 (325.9) versus 135.9 (155.7) (p = 0.001). In most patients (eight patients [58.0%]), headache load scores decreased by 50% after treatment. The other six patients showed either a partial (three [21.0%]) or poor (three [21.0%]) response. The optimized sweet spot was the lateral ventral tegmental area ((Montreal Neurological Institute) MNI coordinates of the center of mass: x = ± 9.0 mm, y = -10.6 mm, z = -3.5 mm). The connectomic analysis pointed to the probable implication of corticorubral tracts.

CONCLUSION

These findings suggest that a substantial proportion of patients with refractory chronic cluster headache obtain significant long-term clinical benefits from deep brain stimulation. Good responders were characterized by a robust improvement in headache load within 3-6 months after surgery. The lateral ventral tegmental area was identified as the best target for this indication, with the likely participation of corticorubral tracts.

Advancing thalamic neuromodulation in epilepsy: Bridging adult data to pediatric care

Thalamic neuromodulation has emerged as a treatment option for drug-resistant epilepsy (DRE) with widespread and/or undefined epileptogenic networks. While deep brain stimulation (DBS) and responsive neurostimulation (RNS) depth electrodes offer means for electrical stimulation of the thalamus in adult patients with DRE, the application of thalamic neuromodulation in pediatric epilepsy remains limited. To address this gap, the Neuromodulation Expert Collaborative was established within the Pediatric Epilepsy Research Consortium (PERC) Epilepsy Surgery Special Interest Group. In this expert review, existing evidence and recommendations for thalamic neuromodulation modalities using DBS and RNS are summarized, with a focus on the anterior (ANT), centromedian(CMN), and pulvinar nuclei of the thalamus. To-date, only DBS of the ANT is FDA approved for treatment of DRE in adult patients based on the results of the pivotal SANTE (Stimulation of the Anterior Nucleus of Thalamus for Epilepsy) study. Evidence for other thalamic neurmodulation indications and targets is less abundant. Despite the lack of evidence, positive responses to thalamic stimulation in adults with DRE have led to its off-label use in pediatric patients. Although caution is warranted due to differences between pediatric and adult epilepsy, the efficacy and safety of pediatric neuromodulation appear comparable to that in adults. Indeed, CMN stimulation is increasingly accepted for generalized and diffuse onset epilepsies, with recent completion of one randomized trial. There is also growing interest in using pulvinar stimulation for temporal plus and posterior quadrant epilepsies with one ongoing clinical trial in Europe. The future of thalamic neuromodulation holds promise for revolutionizing the treatment landscape of childhood epilepsy. Ongoing research, technological advancements, and collaborative efforts are poised to refine and improve thalamic neuromodulation strategies, ultimately enhancing the quality of life for children with DRE.

Neural substrates of the interaction between effort-expenditure reward decision-making and outcome anticipation

OBJECTIVE

Reward anticipation is important for future decision-making, possibly due to re-evaluation of prior decisions. However, the exact relationship between reward anticipation and prior effort-expenditure decision-making, and its neural substrates are unknown.

METHOD

Thirty-three healthy participants underwent fMRI scanning while performing the Effort-based Pleasure Experience Task (E-pet). Participants were required to make effort-expenditure decisions and anticipate the reward.

RESULTS

We found that stronger anticipatory activation at the posterior cingulate cortex was correlated with slower reaction time while making decisions with a high-probability of reward. Moreover, the substantia nigra was significantly activated in the prior decision-making phase, and involved in reward-anticipation in view of its strengthened functional connectivity with the mammillary body and the putamen in trial conditions with a high probability of reward.

CONCLUSIONS

These findings support the role of reward anticipation in re-evaluating decisions based on the brain-behaviour correlation. Moreover, the study revealed the neural interaction between reward anticipation and decision-making.

Targeting papez circuit for cognitive dysfunction- insights into deep brain stimulation for Alzheimer's disease

Hippocampus is the most widely studied brain area coupled with impairment of memory in a variety of neurological diseases and Alzheimer's disease (AD). The limbic structures within the Papez circuit have been linked to various aspects of cognition. Unfortunately, the brain regions that include this memory circuit are often ignored in terms of understanding cognitive decline in these diseases. To properly comprehend where cognition problems originate, it is crucial to clarify any aberrant contributions from all components of a specific circuit -on both a local and a global level. The pharmacological treatments currently available are not long lasting. Deep Brain Stimulation (DBS) emerged as a new powerful therapeutic approach for alleviation of the cognitive dysfunctions. Metabolic, functional, electrophysiological, and imaging studies helped to find out the crucial nodes that can be accessible for DBS. Targeting these nodes within the memory circuit produced significant improvement in learning and memory by disrupting abnormal circuit activity and restoring the physiological network. Here, we provide an overview of the neuroanatomy of the circuit of Papez along with the mechanisms and various deep brain stimulation targets of the circuit structures which could be significant for improving cognitive dysfunctions in AD.

Do the mammillary bodies atrophy with aging? A magnetic resonance imaging study

PURPOSE

This retrospective study aimed to explore age-related atrophy of the mammillary bodies (MBs) based on their temporal change using magnetic resonance imaging (MRI).

MATERIALS AND METHODS

The study included 30 adult outpatients who presented to the hospital and were followed for more than 100 months with annual MRIs. The bi-ventricular width (BVW), third ventricle width (TVW), and bi-mammillary dimension (BMD) were measured on axial T2-weighted imaging and analyzed.

RESULTS

The 30 patients comprised 1 in their 40s, 5 in their 50s, 6 in their 60s, 11 in their 70s, 5 in their 80s, and 2 in their 90s. The MBs were consistently detected with left-to-right symmetry. The mean BVW was 32 ± 2.2 mm on the initial (BVW1) and 32 ± 2.4 mm on the last (BVW2) MRI. The mean TVW was 7.0 ± 2.3 mm on the initial (TVW1) and 7.6 ± 2.7 mm on the last (TVW2) MRI. Furthermore, the mean BMD was 9.9 ± 1.3 mm on the initial (BMD1) and 10 ± 1.3 mm on the last (BMD2) MRI. Statistically, no age ranges had a large dimension for BVW1, BVW2, TVW1, TVW2, BMD1, or BMD2. Changes between TVW1 and TVW2 were significantly different in the patients in their 80s; changes between BMD1 and BMD2 were not different for any age range or between sexes.

CONCLUSIONS

Aging alone does not seem to promote MB atrophy. In healthy brains, the MBs may be stationary structures throughout life.

Neuromodulation of the anterior thalamus: Current approaches and opportunities for the future

The role of thalamocortical circuits in memory has driven a recent burst of scholarship, especially in animal models. Investigating this circuitry in humans is more challenging. And yet, the development of new recording and stimulation technologies deployed for clinical indications has created novel opportunities for data collection to elucidate the cognitive roles of thalamic structures. These technologies include stereoelectroencephalography (SEEG), deep brain stimulation (DBS), and responsive neurostimulation (RNS), all of which have been applied to memory-related thalamic regions, specifically for seizure localization and treatment. This review seeks to summarize the existing applications of neuromodulation of the anterior thalamic nuclei (ANT) and highlight several devices and their capabilities that can allow cognitive researchers to design experiments to assay its functionality. Our goal is to introduce to investigators, who may not be familiar with these clinical devices, the capabilities, and limitations of these tools for understanding the neurophysiology of the ANT as it pertains to memory and other behaviors. We also briefly cover the targeting of other thalamic regions including the centromedian (CM) nucleus, dorsomedial (DM) nucleus, and pulvinar, with associated potential avenues of experimentation.

Selective surgical mamillo-thalamic tract disconnection in hypothalamic hamartoma results in complete disappearance of gelastic seizures

Hypothalamic hamartoma is a less common condition characterized by the several types of epileptic seizures including the gelastic type. It is reported that gelastic seizures are resistant to medical treatment with anticonvulsants, while stereotactic thermocoagulation or Gamma Knife radiosurgery are effective for seizure control. Here, we report an individual case where direct surgical resection disconnecting hypothalamic hamartoma from mammillothalamic tract resulted in complete disappearance of gelastic seizures without deterioration of cognitive function. A 6-year-old boy developed gelastic seizures at the age of 2 and suffered from precocious puberty. Anticonvulsants including carbamazepine and zonisamide failed to control seizures. The patient underwent direct division of the mammillothalmic tract by removal of hypothalamic hamartoma partially via anterior interhemispheric approach. It was observed that gelastic seizures disappeared completely after the surgical treatment without any endocrine and cognitive dysfunction for a follow-up period of 14 years. The mammillothalamic tract which connects anterior nucleus of thalamus and mammillary bodies plays a key role in gelastic seizures related to hypothalamic hamartoma. In this case, we disconnected the hamartoma specifically from the mammillary bodies and not from the rest of hypothalamus. Effectively, it enabled permanent control of seizures. This result shows that fibers connecting other hypothalamic structures and the dorsomedial nucleus of thalamus are not involved in gelastic seizure propagation from the hypothalamic hamartoma. When surgical treatment of hypothalamic hamartomas is performed it has high morbidity associated with hypothalamic disorders. Therefore, disconnection between hypothalamic hamartoma and mammillary bodies presents a possibility of reducing hypothalamic damage. Surgical disconnection between hamartoma and mammillothalamic tract carries minimal hypothalamic injury risk and our results suggest that it has the potential of seizure control for intractable gelastic seizures with less complications.

Mammillary Body Atrophy in Temporal Lobe Epilepsy With Hippocampal Sclerosis

BACKGROUND AND PURPOSE

We aimed to determine 1) the frequency of mammillary body (MB) atrophy in patients with temporal lobe epilepsy (TLE) and hippocampal sclerosis (HS), 2) the clinical significance of MB atrophy, and 3) the association between MB atrophy and volume changes in other subcortical limbic structures.

METHODS

We enrolled 69 patients with pathologically confirmed TLE with HS, who underwent a standard anterior temporal lobectomy, as well as 40 healthy controls. We used the FreeSurfer deep-learning tool of U-Net to obtain the volumes of the subcortical limbic structures, including the MB, hypothalamus, basal forebrain, septal nuclei, fornix, and nucleus accumbens. MB atrophy was considered to be present when the MB volume was decreased relative to the healthy controls.

RESULTS

MB atrophy was present in 18 (26.1%) of the 69 patients with TLE and HS. Among the clinical characteristics, the mean age at seizure onset was higher (25.5 vs. 15.9 years, p=0.027) and the median duration of epilepsy was shorter (149 vs. 295 months, p=0.003) in patients with than without MB atrophy. The basal forebrain (0.0185% vs. 0.0221%, p=0.004) and septal nuclei (0.0062% vs. 0.0075%, p=0.003) in the ipsilateral hemisphere of HS were smaller in the patients with MB atrophy.

CONCLUSIONS

We observed ipsilateral MB atrophy in about one-quarter of patients with TLE and HS. The severity of subcortical limbic structure abnormalities was greater in patients without MB atrophy. These findings suggest that MB atrophy in TLE with HS is not rare, but it has little clinical significance.

MRI-Visible Anatomy of the Basal Ganglia and Thalamus

Conventional MR imaging does not discriminate basal ganglia and thalamic internal anatomy well. Radiology reports describe anatomic locations but not specific functional structures. Functional neurosurgery uses indirect targeting based on commissural coordinates or atlases that do not fully account for individual variability. We describe innovative MR imaging sequences that improve the visualization of normal anatomy in this complex brain region and may increase our understanding of basal ganglia and thalamic function. Better visualization also may improve treatments for movement disorders and other emerging functional neurosurgery targets. We aim to provide an accessible review of the most clinically-relevant neuroanatomy within the thalamus and basal ganglia.

Cavernous malformations of the hypothalamus: a single-institution series of 12 cases and review of the literature

OBJECTIVE

There remains a paucity of literature on hypothalamic cavernous malformations (HCMs). Here, the authors present the largest series of HCMs to date and review the literature to gain additional insight into this rare disease subset.

METHODS

A prospectively managed database was retrospectively reviewed for patients diagnosed with symptomatic HCM and treated surgically between 1987 and 2019. Data gathered included demographics, presenting signs, radiological measurements, surgical approach, and postoperative events. Functional outcome was measured using the modified Rankin Scale (mRS) and Glasgow Outcome Scale-Extended (GOSE) pre- and postoperatively. A PRISMA guideline systematic review of HCM in the literature was performed.

RESULTS

Our cohort study consisted of 12 patients with symptomatic, and radiographically confirmed, HCM treated with microsurgery by the senior author (G.K.S.). An additional 16 surgically or conservatively managed patients were also identified from the literature, and the authors analyzed the data of all 28 patients (with 54% of patients being male; mean age 39 ± 16 years, range 10-68 years). Patients harboring HCMs most commonly presented with headache (16/28, 57%), short-term memory impairment (11/28, 39%), and gait disturbance (8/28, 32%). Radiographically, lesions most commonly involved the mammillary region (18/23, 78%), the tuberal/infundibulum region (13/23, 57%), and the preoptic/lamina terminalis region (12/23, 52%), with a mean diameter of 2.5 ± 1.4 cm (range 0.8-7 cm) at presentation. Acute hemorrhage was identified in 96% (23/24) of patients on presentation, with 96% (23/24) intraparenchymal and 29% (7/24) intraventricular. Of 24 patients who were managed surgically, gross-total resection (GTR) was achieved in 88% (21/24) of cases. There were no reports of perioperative infarction or mortality. With a mean follow-up period of 41 months (range 0.5-309 months), 77% (20/26) of patients experienced functional improvement, while 12% (3/26) had no change, and 12% (3/26) experienced increased disability. In our cohort of 12 patients, 83% (10/12) continued to report symptoms at the last follow-up (mean 4.8 years, range 0.1-25.7 years). However, there was a significant improvement in mRS score noted after surgery (mean 1.4 vs 3.1, p = 0.0026) and a trend toward improvement in GOSE score (mean 6.3 vs 5.1, p = 0.09).

CONCLUSIONS

Hemorrhage from HCMs can cause a symptomatic mass effect on adjacent eloquent structures. While patients are unlikely to be deficit free following surgery, GTR allows for functional improvement and reduces recurrent hemorrhage rates. Microsurgery remains a viable option for symptomatic HCMs in experienced hands.

In Vivo Super-Resolution Track-Density Imaging for Thalamic Nuclei Identification

The development of novel techniques for the in vivo, non-invasive visualization and identification of thalamic nuclei has represented a major challenge for human neuroimaging research in the last decades. Thalamic nuclei have important implications in various key aspects of brain physiology and many of them show selective alterations in various neurologic and psychiatric disorders. In addition, both surgical stimulation and ablation of specific thalamic nuclei have been proven to be useful for the treatment of different neuropsychiatric diseases. The present work aimed at describing a novel protocol for histologically guided delineation of thalamic nuclei based on short-tracks track-density imaging (stTDI), which is an advanced imaging technique exploiting high angular resolution diffusion tractography to obtain super-resolved white matter maps. We demonstrated that this approach can identify up to 13 distinct thalamic nuclei bilaterally with very high inter-subject (ICC: 0.996, 95% CI: 0.993-0.998) and inter-rater (ICC:0.981; 95% CI:0.963-0.989) reliability, and that both subject-based and group-level thalamic parcellation show a fair share of similarity to a recent standard-space histological thalamic atlas. Finally, we showed that stTDI-derived thalamic maps can be successfully employed to study structural and functional connectivity of the thalamus and may have potential implications both for basic and translational research, as well as for presurgical planning purposes.

Seizure Frequency Is Associated with Effective Connectivity of the Hippocampal-Diencephalic-Cingulate in Epilepsy with Unilateral Mesial Temporal Sclerosis

Background: Temporal lobe epilepsy (TLE) with mesial temporal sclerosis (MTS) is a common intractable epilepsy. To seek neural correlates of seizure recurrence, this study investigated aberrant intrinsic effective connectivity (iEC) in TLE with unilateral MTS and their associations with seizure frequency. Methods: Thirty patients with unilateral MTS (left/right MTS = 14/16) and 37 age-matched healthy controls underwent resting-state functional magnetic resonance imaging (rsfMRI) on a 3-Tesla magnetic resonance imaging (MRI) system. The structural equation modeling was employed to estimate the iEC of the three candidate epilepsy models, including the Papez circuit, hippocampal-diencephalic-cingulate (HDC) model, and simplified HDC model. After comparing the performance of model fitting, the best model was selected to compare iEC among the study groups. The linear regression analysis was performed to associate abnormal iEC with seizure frequency. Results: The simplified HDC model was the best model to estimate iEC across the three study groups (p < 0.05), and it composed of the 26 interconnected pathway between the mesial temporal lobe, thalamus, and cingulate cortices. The linear regression analysis revealed a significant relationship between the shared iEC alterations in both patient groups and seizure frequency (adjusted-R² = 0.350; p = 0.037), including the three paths of mammillary body (MB) → bilateral anterior thalamic nuclei (left: standardized β-value = 0.580, p = 0.013; right: standardized β-value = -0.711, p = 0.006) and right hippocampus → MB (standardized β-value = 0.541, p = 0.045). Conclusions: Our findings provide new insights into neurophysiological significance relevant to seizure recurrence. Aberrant iEC on the neural paths connected to the MB can be a potential imaging marker, aiding the therapeutic management in TLE with unilateral MTS. Impact statement Within the simplified hippocampal-diencephalic-cingulate model, we identified that altered intrinsic effective connectivity (iEC) on the three paths connecting to the mammillary body was common in temporal lobe epilepsy (TLE) with left and right mesial temporal sclerosis (MTS) and was associated with seizure frequency. Therefore, these common iEC alterations could be a potential imaging marker, aiding the therapeutic management in patients with TLE with unilateral MTS.

Anatomy and cytoarchitectonics of the human hypothalamus

Due to the complexity of hypothalamic functions, the organization of the hypothalamus is extremely intricate. This relatively small brain area contains several nuclei, most of them are ill-defined regions without distinct boundaries; these nuclei are often connected with each other and other distant brain regions with similarly indistinct pathways. These hypothalamic centers control numerous key physiological functions including reproduction, growth, food intake, circadian rhythm, behavior, and autonomic balance via neural and endocrine signals. To understand the morphology of the hypothalamus is therefore extremely important, though it remains a stupendous task due to the complex organization of neuronal networks formed by the various neurotransmitter and neuromodulator systems.

The contribution of mamillary body damage to Wernicke's encephalopathy and Korsakoff's syndrome

Histopathological alterations of the mamillary bodies are the most conspicuous and the most consistent neuropathological features of several disorders that occur after severe thiamine deficiency, such as Wernicke's encephalopathy and Korsakoff's syndrome. Moreover, they are among the few abnormalities that are visible to the naked eye in these disorders. With a lifetime prevalence of approximately 1.3%, Wernicke's encephalopathy is by far the most frequent cause of damage to the mamillary bodies in humans. Still, there is a persisting uncertainty with regard to the development and the clinical consequences of this damage, because it is virtually impossible to study in isolation. As a rule, it always occurs alongside neuropathology in other subcortical gray matter structures, notably the medial thalamus. Converging evidence from other pathologies and animal experiments is needed to assess the clinical impact of mamillary body damage and to determine which functions can be attributed to these structures in healthy subjects. In this chapter, we describe the history and the current state of knowledge with regard to thiamine deficiency disorders and the contribution of mamillary body damage to their clinical presentations.

Assessing the connectional anatomy of superior and lateral surgical approaches for medial temporal lobe epilepsy

The most common approaches in the treatment of epilepsy, the trans-sylvian selective amygdalohippocampectomy (SAH) and the anterior temporal lobe resection (ATLR) reach the medial temporal lobe through different surgical routes. Our aim was to delineate the white matter (WM) fiber tracts at risk in relation to trans-sylvian SAH and ATLR by defining each fascicle en route to medial temporal lobe during each approach. ATLR and trans-sylvian SAH were performedand related WM tracts en route to medial temporal region were presented in relation to the relevant approaches and surrounding neurovascular structures. The WM tracts most likely to be disrupted during trans-sylvian SAH along the roof of the temporal horn were the UF - and less commonly IFOF - at the layer of the external capsule, anterior commissure, anterior bend of optic radiations, and sublenticular internal capsule. Amygdaloid projections to the claustrum, putamen and globus pallidus, the tail of caudate and the peduncle of the lentiform nucleus were also in close proximity to the resection cavity. Fiber tracts most likely to be impaired during ATLR included the UF, ILF, IFOF, anterior commissure, optic radiations, and, less likely, the vertical ventral segment of the arcuate fascicle. Both ATLR and trans-sylvian SAH carry the risk of injury to WM pathways, which may result in unpredictable functional loss. A detailed 3-D knowledge of the related connectional anatomy will help subside neurocognitive, neuroophtalmologic, neurolinguistic complications of epilepsy surgery, providing an opportunity to tailor the surgery according to patient's unique connectional and functional anatomy.

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.

An improved neuroanatomical model of the default-mode network reconciles previous neuroimaging and neuropathological findings

The brain is constituted of multiple networks of functionally correlated brain areas, out of which the default-mode network (DMN) is the largest. Most existing research into the DMN has taken a corticocentric approach. Despite its resemblance with the unitary model of the limbic system, the contribution of subcortical structures to the DMN may be underappreciated. Here, we propose a more comprehensive neuroanatomical model of the DMN including subcortical structures such as the basal forebrain, cholinergic nuclei, anterior and mediodorsal thalamic nuclei. Additionally, tractography of diffusion-weighted imaging was employed to explore the structural connectivity, which revealed that the thalamus and basal forebrain are of central importance for the functioning of the DMN. The contribution of these neurochemically diverse brain nuclei reconciles previous neuroimaging with neuropathological findings in diseased brains and offers the potential for identifying a conserved homologue of the DMN in other mammalian species.

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.