Mapping the trajectory of the amygdalothalamic tract in the human brain

The anterior perforated substance (APS) revisited: Commented anatomical and imagenological views

INTRODUCTION

Since 2002, when we published our article about the anterior perforated substance (APS), the knowledge about the region has grown enormously.

OBJECTIVE

To make a better description of the anatomy of the zone with new dissection material added to the previous, to sustain the anatomical analysis of the MRI employing the SPACE sequence, interacting with our imagenology colleagues. Especially, we aim to identify and topographically localize by MRI the principal structures in APS-substantia innominata (SI).

METHOD

The presentation follows various steps: (1) location and boundaries of the zone and its neighboring areas; (2) schematic description of the region with simple outlines; (3) cursory revision of the SI and its three systems; (4) serial images of the dissections of the zone and its vessels, illustrated and completed when possible, by MRI images of a voluntary experimental subject (ES).

RESULTS

With this method, we could expose most of the structures of the region anatomically and imagenologically.

DISCUSSION

The zone can be approached for dissection with magnification and the habitual microsurgical instruments with satisfactory results. We think that fibers in this region should be followed by other anatomical methods in addition to tractography. The principal structures of ventral striopallidum and extended amygdala (EA) can be identified with the SPACE sequence. The amygdala and the basal ganglion of Meynert (BGM) are easily confused because of their similar signal. Anatomical clues can orient the clinician about the different clusters of the BGM in MRI.

CONCLUSIONS

The dissection requires a previous knowledge of the zone and a good amount of patience. The APS is a little space where concentrate essential vessels for the telencephalon, "en passage" or perforating, and neural structures of relevant functional import. From anatomical and MRI points of view, both neural and vascular structures follow a harmonious and topographically describable plan. The SPACE MRI sequence has proved to be a useful tool for identifying different structures in this area as the striatopallidal and EA. Anatomical knowledge of the fibers helps in the search of clusters of the basal ganglion.

Unfolding the direct connectivity of the occipital cortex with the hypothalamic, septal and BNST nuclei of the human brain

The hypothalamus plays essential roles in the human brain by regulating feeding, fear, aggression, reproductive behaviors, and autonomic activities. The septal nuclei and the bed nucleus of stria terminalis (BNST) are also known to be involved in control of autonomic, motivational, learning, emotional and associative processes in the human brain. Multiple animal dissection studies have revealed direct connectivity between central limbic gray matter nuclei and occipital cortex, particularly from the hypothalamic, septal and BNST nuclei. However, the detailed anatomy of this connectivity in the human brain has yet to be determined. The primary objective of this study was to explore the utility of high spatial and high angular resolution diffusion weighted tractography techniques for mapping the connectivity pathways between the occipital cortex and central limbic gray matter nuclei in the human brain. We studied 30 healthy adult human brains, delineated, and reconstructed the trajectory of the occipito-hypothalamic/septal/BNST for the first time in the human brain.

The Cortico-Limbo-Thalamo-Cortical Circuits: An Update to the Original Papez Circuit of the Human Limbic System

The Papez circuit, first proposed by James Papez in 1937, is a circuit believed to control memory and emotions, composed of the cingulate cortex, entorhinal cortex, parahippocampal gyrus, hippocampus, hypothalamus, and thalamus. Pursuant to James Papez, Paul Yakovlev and Paul MacLean incorporated the prefrontal/orbitofrontal cortex, septum, amygdalae, and anterior temporal lobes into the limbic system. Over the past few years, diffusion-weighted tractography techniques revealed additional limbic fiber connectivity, which incorporates multiple circuits to the already known complex limbic network. In the current review, we aimed to comprehensively summarize the anatomy of the limbic system and elaborate on the anatomical connectivity of the limbic circuits based on the published literature as an update to the original Papez circuit.

The ansa peduncularis in the human brain: A tractography and fiber dissection study

INTRODUCTION

The ansa peduncularis is a composite of white matter fiber bundles closely packed together that sweeps around the cerebral peduncle. The exact components of the ansa peduncularis and their anatomical trajectories are still not established firmly in the literature.

OBJECTIVE

The aim of this study was to examine the topographical anatomy of the ansa peduncularis and its subcomponents using the fiber dissection and tractography techniques.

METHODS

Ten formalin-fixed brains were prepared according to Klingler's method and dissected by the fiber dissection technique from the lateral, medial and inferior surfaces. The ansa peduncularis was also traced using high definition fiber tracking (HDFT) from the MRI data of twenty healthy adults and a 1021-subject template from the Human Connectome Project.

RESULTS

The ventral amygdalofugal pathway system includes white matter fiber bundles with a topographically close relation as they sweep around the cerebral peduncle and contribute to form the ansa peduncularis: amygdaloseptal fibers connect the amygdala and anterior temporal cortex to the septal region and amygdalohypothalamic fibers project from the amygdala to the hypothalamus. Additionally, from the amygdala and anterior temporal cortex, amygdalothalamic fibers project to the medial thalamic region. The ansa lenticularis, which connects the globus pallidus to the thalamus, was not shown in our study.

CONCLUSION

The study demonstrated the trajectory of the ansa peduncularis and its subcomponents, based on fiber dissection and tractography, improving our understanding of human brain anatomical connectivity.

A direct visuosensory cortical connectivity of the human limbic system. Dissecting the trajectory of the parieto-occipito-hypothalamic tract in the human brain using diffusion weighted tractography

The human hypothalamus is at the center of the human limbic system anatomically and physiologically. The hypothalamus plays pivotal roles in controlling autonomic responses and instinctive behaviors such as regulating fear, aggression, learning, feeding behavior, circadian rhythm, and reproductive activities. The detailed anatomy of the pathways responsible for mediating these responses, however, is yet to be determined. The inhibitory effect of the cerebral cortex on the hypothalamus in many autonomic responses, suggests the presence of direct connection between the cortex and hypothalamic nuclei. While, there is ample information to support the cortico-hypothalamic association between the prefrontal cortex and hypothalamic nuclei, the information regarding a direct posterior cortico-hypothalamic alliance is scant. The visuosensory information may be crucial for the limbic system to regulate some of the important limbic functions. Multiple dissection animal studies revealed direct posterior cortical connectivity with the hypothalamic nuclei. However, a direct cortico-hypothalamic connectivity from the parieto-occipital cortices has not been revealed in the human brain yet. Diffusion weighted imaging (DWI) may be helpful in better visualizing the anatomy of this direct posterior cortico-limbic connectivity noninvasively in the human brain. We studied 30 healthy human subjects. Using a high-spatial and high angular resolution diffusion weighted tractography technique, for the first time, we were able to delineate and reconstruct the trajectory of the parieto-occipito-hypothalamic tract.

Papez Circuit Observed by in vivo Human Brain With 7.0T MRI Super-Resolution Track Density Imaging and Track Tracing

The Papez circuit has been considered as an important anatomical substrate involved in emotional experience. However, the circuit remains difficult to elucidate in the human brain due to the resolution limit of current neuroimaging modalities. In this article, for the first time, we report the direct visualization of the Papez circuit with 7-Tesla super-resolution magnetic resonance tractography. Two healthy, young male subjects (aged 30 and 35 years) were recruited as volunteers following the guidelines of the institutional review board (IRB). Track density imaging (TDI) generation with track tracing was performed using MRtrix software package. With these tools, we were able to visualize the entire Papez circuit. We believe this is the first study to visualize the complete loop of the Papez circuit, including the perforant path (PP), thalamocortical fibers of the anterior nucleus (AN), and mammillothalamic tract (MTT), which were hitherto difficult to visualize by conventional imaging techniques.

Yakovlev's Basolateral Limbic Circuit in Multiple Sclerosis Related Cognitive Impairment

BACKGROUND AND PURPOSE

In 1948, Paul Yakovlev described an additional limbic circuit located basolateral to James Papez's circuit (1937) and included orbitofrontal cortex, amygdala, and dorsomedial nucleus of thalamus. This circuit is shown to be an important component of subcortical cognitive abilities. We aimed to demonstrate this circuit in a multiple sclerosis (MS) cohort using diffusion tensor imaging (DTI) and evaluate its role in MS-related cognitive impairment (CI).

METHODS

We enrolled cognitively intact (n = 10) and impaired (n = 36) MS patients who underwent a comprehensive cognitive assessment; the minimal assessment of cognitive function in MS (MACFIMS) and structural magnetic resonance imaging. Correlation analyses between volumetric and DTI-derived values of the orbitofrontothalamic (OFT), amygdalothalamic tracts (ATTs), and dorsomedial nucleus of thalamus and CI index derived from MACFIMS were computed after adjustment for age, education, and lesion load.

RESULTS

We observed a consistent trend between CI index and bilateral dorsomedial nucleus' mean diffusivity (MD) (r = .316; P = .02), left OFT Fractional anisotropy (FA) (r = -.302; P = .02), MD (r = .380; .006), and radial diffusivities (RDs) (r = .432; P = .002), also with right ATT FA (r = -.475; P = .0006) and left ATT FA ( = -.487; P = .0005). After Bonferroni correction, correlations of left OFT RD and right and left ATT FA with CI were found to be significant.

CONCLUSIONS

Our study provides in vivo DTI delineation of Yakovlev's historical basolateral limbic circuit and establishes a role in MS-related CI. These findings may potentially pave the way for future clinical studies using targeted invasive and noninvasive neurostimulation modalities for CI in MS.