Amnesia following damage to the mammillary bodies

Papillary Craniopharyngioma: An Integrative and Comprehensive Review

Papillary craniopharyngioma (PCP) is a rare type of tumor, comprising ∼20% of all craniopharyngioma (CP) cases. It is now recognized as a separate pathological entity from the adamantinomatous type. PCPs are benign tumors, classified as World Health Organization grade 1, characterized by nonkeratinizing squamous epithelium. They typically grow as solid and round papillomatous masses or as unilocular cysts with a cauliflower-like excrescence. PCPs primarily occur in adults (95%), with increased frequency in males (60%), and predominantly affect the hypothalamus. Over 80% of these tumors are located in the third ventricle, expanding either above an anatomically intact infundibulum (strictly third ventricle tumors) or within the infundibulo-tuberal region of the third ventricle floor. Clinical manifestations commonly include visual deficits and a wide range of psychiatric disturbances (45% of patients), such as memory deficits and odd behavior. Magnetic resonance imaging can identify up to 50% of PCPs by the presence of a basal duct-like recess. Surgical management is challenging, requiring complex approaches to the third ventricle and posing significant risk of hypothalamic injury. The endoscopic endonasal approach allows radical tumor resection and yields more favorable patient outcomes. Of intriguing pathogenesis, over 90% of PCPs harbor the somatic BRAFV600E mutation, which activates the mitogen-activated protein kinase signaling pathway. A phase 2 clinical trial has demonstrated that PCPs respond well to proto-oncogene B-Raf/MAPK/ERK kinase inhibitors. This comprehensive review synthesizes information from a cohort of 560 well-described PCPs and 99 large CP series including PCP cases published from 1856 to 2023 and represents the most extensive collection of knowledge on PCPs to date.

A Case With Bilateral Hippocampal Infarction Resembling Transient Global Amnesia

Transient global amnesia (TGA) is a benign and transient condition with a sudden short-term amnesia. One of the conditions resembling TGA is hippocampal infarction, which requires relapse prevention treatments. In this report, we present a case with bilateral hippocampal infarction in whom distinguishing these two conditions was difficult for up to 1 week from the onset. A 60-year-old female visited our hospital with sudden onset retrograde and anterograde amnesia. Thin-slice magnetic resonance imaging (MRI) with 2-mm thickness revealed hyperintense signals on diffusion-weighted imaging (DWI) with signal loss on apparent diffusion coefficient (ADC) on both sides of the hippocampus. MRI with 5-mm thickness on day 7 revealed persistent restricted diffusion on both sides, one of which was still with decreased ADC values. Based on this finding, the diagnosis of bilateral hippocampal infarction was reached, and the relapse-preventive antiplatelet was continued. This case implied the potential difficulty of distinguishing cases with TGA and those with hippocampal infarction based on MRI findings within the first several days after onset. Thin-slice brain MRI, careful search of potential cardiovascular risks, and follow-up MRI ≥ 7 days after onset will be helpful to reach a correct diagnosis in cases with sudden amnesia.

Converging diencephalic and hippocampal supports for episodic memory

To understand the neural basis of episodic memory it is necessary to appreciate the significance of the fornix. This pathway creates a direct link between those temporal lobe and medial diencephalic sites responsible for anterograde amnesia. A collaboration with Andrew Mayes made it possible to recruit and scan 38 patients with colloid cysts in the third ventricle, a condition associated with variable fornix damage. Complete fornix loss was seen in three patients, who suffered chronic long-term memory problems. Volumetric analyses involving all 38 patients then revealed a highly consistent relationship between mammillary body volume and the recall of episodic memory. That relationship was not seen for working memory or tests of recognition memory. Three different methods all supported a dissociation between recollective-based recognition (impaired) and familiarity-based recognition (spared). This dissociation helped to show how the mammillary body-anterior thalamic nuclei axis, as well as the hippocampus, is vital for episodic memory yet is not required for familiarity-based recognition. These findings set the scene for a reformulation of temporal lobe and diencephalic amnesia. In this revised model, these two regions converge on overlapping cortical areas, including retrosplenial cortex. The united actions of the hippocampal formation and the anterior thalamic nuclei on these cortical areas enable episodic memory encoding and consolidation, impacting on subsequent recall.

Improving Amnesia Diagnostic Accuracy with RAVLT Single Scores and Composite Indices: Italian Normative Data

Objective

The Rey Auditory Verbal Learning Test (RAVLT) is a widely used verbal memory measure that provides scores for different aspects of memory. It involves repeated auditory presentation and recall of a 15-item word list (List A) followed by presentation and recall of a distractor list (List B) and then un-cued immediate and delayed recalls (at 15 min and 1 week) of List A as well as recognition testing. Aims of this study are to provide Italian normative data for certain RAVLT Scores and Composite Indices to improve the diagnostic accuracy of the test in clinical settings and to provide further evidence on how RAVLT can differentiate different amnesia profiles due to focal lesions.

Methods

We enrolled 440 healthy participants and RAVLT Single Scores and Composite Indices have been analyzed by means of multiple regression to verify the influence of age, education, and gender.

Results

We computed the best linear models with RAVLT Single Scores and Composite Indices, as dependent variables, and the most suitable transformation of independent variables. By reversing the signs of the regression coefficients, the adjustment factors for each level of age and, if needed, education and gender have been computed and the adjusted scores have been standardized into Equivalent Scores.

Conclusion

Using these standardized measures, we differentiate three profiles of amnesia due to selective hippocampal sclerosis with severe encoding deficit, fornix lesions with source memory problems, and temporal lobe epilepsy with consolidation failure.

The Mammillary Bodies: A Review of Causes of Injury in Infants and Children

Despite their small size, the mammillary bodies play an important role in supporting recollective memory. However, they have typically been overlooked when assessing neurologic conditions that present with memory impairment. While there is increasing evidence of mammillary body involvement in a wide range of neurologic disorders in adults, very little attention has been given to infants and children. Literature searches of PubMed and EMBASE were performed to identify articles that describe mammillary body pathology on brain MR imaging in children. Mammillary body pathology is present in the pediatric population in several conditions, indicated by signal change and/or atrophy on MR imaging. The main causes of mammillary body pathology are thiamine deficiency, hypoxia-ischemia, direct damage due to masses or hydrocephalus, or deafferentation resulting from pathology within the wider Papez circuit. Optimizing scanning protocols and assessing mammillary body status as a standard procedure are critical, given their role in memory processes.

Going round in circles-The Papez circuit in Alzheimer's disease

The hippocampus is regarded as the pivotal structure for episodic memory symptoms associated with Alzheimer's disease (AD) pathophysiology. However, what is often overlooked is that the hippocampus is 'only' one part of a network of memory critical regions, the Papez circuit. Other Papez circuit regions are often regarded as less relevant for AD as they are thought to sit 'downstream' of the hippocampus. However, this notion is oversimplistic, and increasing evidence suggests that other Papez regions might be affected before or concurrently with the hippocampus. In addition, AD research has mostly focused on episodic memory deficits, whereas spatial navigation processes are also subserved by the Papez circuit with increasing evidence supporting its valuable potential as a diagnostic measure of incipient AD pathophysiology. In the current review, we take a step forward analysing recent evidence on the structural and functional integrity of the Papez circuit across AD disease stages. Specifically, we will review the integrity of specific Papez regions from at-genetic-risk (APOE4 carriers), to mild cognitive impairment (MCI), to dementia stage of sporadic AD and autosomal dominant AD (ADAD). We related those changes to episodic memory and spatial navigation/orientation deficits in AD. Finally, we provide an overview of how the Papez circuit is affected in AD diseases and their specific symptomology contributions. This overview strengthened the need for moving away from a hippocampal-centric view to a network approach on how the whole Papez circuit is affected in AD and contributes to its symptomology, informing future research and clinical approaches.

Beyond the bipolar disorder diagnosis: Hypothalamus and its network damage in determining neuropsychiatric and Korsakoff-like memory disorders

Craniopharyngiomas (CP's) are hypothalamic tumors often associated with psychological disorders. Nevertheless, its diagnosis is still challenging when psychiatric disorders are not associated with any other neurological symptoms. This single-case study describes a patient with a history of bipolar disorder before a diagnosis of a large CP arising the sellar and suprasellar region was posed. At the time of the present study the patient showed emotional/behavioral disorders and Korsakoff-like amnesia, that completely recovered after surgical resection of the tumor. This is one of those few cases described in literature, who presented cognitive/behavioral disorders because the compression of the diencephalic structures due to CP mass effect. This case offers further evidence on the functional neuroanatomy of the hypothalamus and its pathways.

Time to put the mammillothalamic pathway into context

The medial diencephalon, in particular the mammillary bodies and anterior thalamic nuclei, has long been linked to memory and amnesia. The mammillary bodies provide a dense input into the anterior thalamic nuclei, via the mammillothalamic tract. In both animal models, and in patients, lesions of the mammillary bodies, mammillothalamic tract and anterior thalamic nuclei all produce severe impairments in temporal and contextual memory, yet it is uncertain why these regions are critical. Mounting evidence from electrophysiological and neural imaging studies suggests that mammillothalamic projections exercise considerable distal influence over thalamo-cortical and hippocampo-cortical interactions. Here, we outline how damage to the mammillary body-anterior thalamic axis, in both patients and animal models, disrupts behavioural performance on tasks that relate to contextual ("where") and temporal ("when") processing. Focusing on the medial mammillary nuclei as a possible 'theta-generator' (through their interconnections with the ventral tegmental nucleus of Gudden) we discuss how the mammillary body-anterior thalamic pathway may contribute to the mechanisms via which the hippocampus and neocortex encode representations of experience.

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.

Craniopharyngiomas primarily affecting the hypothalamus

The concept of craniopharyngiomas (CPs) primarily affecting the hypothalamus, or "hypothalamic CPs" (Hy-CPs), refers, in a restrictive sense, to the subgroup of CPs originally developing within the neural tissue of the infundibulum and tuber cinereum, the components of the third ventricle floor. This subgroup, also known as infundibulo-tuberal CPs, largely occupies the third ventricle and comprises up to 40% of this pathological entity. The small subgroup of strictly intraventricular CPs (5%), lesions wholly developed within the third ventricle above an anatomically intact third ventricle floor, can also be included within the Hy-CP category. The remaining types of sellar and/or suprasellar CPs may compress or invade the hypothalamic region during their growth but will not be considered in this review. Hy-CPs predominantly affect adults, causing a wide range of symptoms derived from hypothalamic dysfunction, such as adiposogenital dystrophy (Babinski-Fröhlich's syndrome), diabetes insipidus (DI), abnormal diurnal somnolence, and a complex set of cognitive (dementia-like, Korsakoff-like), emotional (rage, apathy, depression), and behavioral (autism-like, psychotic-like) disturbances. Accordingly, Hy-CPs represent a neurobiological model of psychiatric disorders caused by a lesion restricted to the hypothalamus. The vast majority (90%) of squamous-papillary CPs belong to the Hy-CP category. Pathologically, most Hy-CPs present extensive and strong adhesions to the surrounding hypothalamus, usually formed of a thick band of gliotic tissue encircling the central portion of the tumor ("ring-like" attachment) or its entire boundary ("circumferential" attachment). CPs with these severe adhesion types associate high surgical risk, with morbidity and mortality rates three times higher than those for sellar/suprasellar CPs. Consequently, radical surgical removal of Hy-CPs cannot be generally recommended. Rather, Hy-CPs should be accurately classified according to an individualized surgery-risk stratification scheme considering patient age, CP topography, presence of hypothalamic symptoms, tumor size, and, most importantly, the CP-hypothalamus adhesion pattern.

Four patients with infarction in key areas of the Papez circuit, with anterograde amnesia as the main manifestation

The Papez circuit is an important brain structure that is closely associated with learning and memory. In this report, we present four patients with anterograde amnesia as the main manifestation induced by Papez circuit infarction. In addition, we review the distribution of the responsible arteries in key and rare regions to investigate the pathogenesis of these infarctions.

Ultra-High-Resolution Imaging of Amygdala Subnuclei Structural Connectivity in Major Depressive Disorder

BACKGROUND

Major depressive disorder (MDD) is an increasingly common and disabling illness. As the amygdala has been reported to have pathological involvement in mood disorders, we aimed to investigate for the first time potential changes to structural connectivity of individual amygdala subnuclei in MDD using ultra-high-field 7T diffusion magnetic resonance imaging.

METHODS

Twenty-four patients with MDD (11 women) and 24 age-matched healthy control participants (7 women) underwent diffusion-weighted imaging with a 1.05-mm isotropic resolution at 7T. Amygdala nuclei regions of interest were obtained through automated segmentation of 0.69-mm resolution T1-weighted images and 0.35-mm resolution T2-weighted images. Probabilistic tractography was performed on all subjects, with random seeding at each amygdala nucleus.

RESULTS

The right lateral, basal, central, and centrocortical amygdala nuclei exhibited significantly increased connection density to the rest of the brain, whereas the left medial nucleus demonstrated significantly lower connection density (false discovery rate p < .05). Increased connection density in the right lateral and basal nuclei was driven by the stria terminalis, and the significant difference in the right central nucleus was driven by the uncinate fasciculus. Decreased connection density at the left medial nucleus did not appear to be driven by any individual white matter tract.

CONCLUSIONS

By exploiting ultra-high-resolution magnetic resonance imaging, structural hyperconnectivity was demonstrated involving the amygdaloid nuclei in the right hemisphere in MDD. To a lesser extent, impairment of subnuclei connectivity was shown in the left hemisphere.

Preoperative Assessment of Craniopharyngioma Adherence: Magnetic Resonance Imaging Findings Correlated with the Severity of Tumor Attachment to the Hypothalamus

BACKGROUND AND OBJECTIVE

Craniopharyngioma (CP) adherence represents a heterogeneous pathologic feature that critically influences the potentially safe and radical resection. The aim of this study was to define the magnetic resonance imaging (MRI) predictors of CP adherence severity.

METHODS

This study retrospectively investigated a cohort of 200 surgically treated CPs with their corresponding preoperative conventional MRI scans. MRI findings related to the distortions of anatomic structures along the sella turcica-third ventricle axis caused by CPs, in addition to the tumor's shape and calcifications, were analyzed and correlated with the definitive type of CP adherence observed during the surgical procedures.

RESULTS

CP adherence is defined by 3 components, as follows: 1) the specific structures attached to the tumor, 2) the adhesion's extent, and 3) its strength. Combination of these 3 components determines 5 hierarchical levels of adherence severity with gradually increasing surgical risk of hypothalamic injury. Multivariate analysis identified 4 radiologic variables that allowed a correct overall prediction of the levels of CP adherence severity in 81.5% of cases: 1) the position of the hypothalamus in relation to the tumor-the most discriminant factor; 2) the type of pituitary stalk distortion; 3) the tumor shape; and 4) the presence of calcifications. A binary logistic regression model including the first 3 radiologic variables correctly identified the CPs showing the highest level of adherence severity (severe/critical) in almost 90% of cases.

CONCLUSIONS

A position of the hypothalamus around the middle portion of the tumor, an amputated or infiltrated appearance of the pituitary stalk, and the elliptical shape of the tumor are reliable predictors of strong and extensive CP adhesions to the hypothalamus.

Hypothalamic tumors impact gray and white matter volumes in fronto-limbic brain areas

Patients with hypothalamic involvement of a sellar/parasellar tumor often suffer from cognitive and social-emotional deficits that a lesion in the hypothalamus cannot fully explain. It is conceivable that these deficits are partly due to distal changes in hypothalamic networks, evolving secondary to a focal lesion. Focusing on childhood-onset craniopharyngioma patients, we aimed at investigating the impact of hypothalamic lesions on gray and white matter areas densely connected to the hypothalamus, and to relate structural changes to neuropsychological deficits frequently observed in patients. We performed a voxel-based morphometric analysis based on data of 11 childhood-onset craniopharyngioma patients with hypothalamic tumor involvement, and 18 healthy controls (median age: 17.2 and 17.4 yrs.). Whole-brain analyses were used to test for volumetric differences between the groups (T-tests) and subsequent regression analyses were used to correlate neuropsychological performance with gray and white matter volumes within the patient group. Patients compared to controls had significantly reduced gray matter volumes in areas of the anterior and posterior limbic subsystems which are densely connected with the hypothalamus. In addition, a reduction in white matter volumes was observed in tracts connecting the hypothalamus to other limbic areas. Worse long-term memory retrieval was correlated with smaller gray matter volumes in the posterior cingulate cortex. Our data provide the first evidence that hypothalamic tumor involvement impacts gray and white matter volumes in limbic areas, outside the area of tumor growth. Notably, the functional range of the two limbic subsystems affected, strikingly parallels the two major domains of psychological complaints in patients i.e., deficits in episodic memory and in socio-emotional functioning. We suggest that focal hypothalamic lesions may trigger distal changes in connected brain areas, which then contribute to the impairments in cognitive, social and emotional performance often observable in patients, and not explicable by a hypothalamic lesion alone.

Mammillary Bodies in Alzheimer's Disease: A Golgi and Electron Microscope Study

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, characterized by irreversible memory decline, concerning no rarely spatial memory and orientation, alterations of the mood and personality, gradual loss of motor skills, and substantial loss of capacities obtained by previous long education. We attempted to describe the morphological findings of the mammillary bodies in early cases of AD. Samples were processed for electron microscopy and silver impregnation techniques. The nuclei of the mammillary bodies demonstrated a substantial decrease in the neuronal population and marked abbreviation of dendritic arbors. Decrease in spine density and morphological abnormalities of dendritic spines was also seen. Synaptic alterations were prominent. Alzheimer's pathology, such as deposits of amyloid-β peptide and neurofibrillary degeneration, was minimal. Electron microscopy revealed mitochondrial alterations and fragmentation of Golgi apparatus, associated frequently with synaptic pathology.

Revealing the ventral amygdalofugal pathway of the human limbic system using high spatial resolution diffusion tensor tractography

The amygdala is known to have a role in core processes regulated by the limbic system such as motivation, memory, emotion, social behavior, self-awareness as well as certain primitive instincts. Several functional studies have investigated some of these brain tasks of the human limbic system. However, the underlying neuronal fiber connectivity of the amygdalo-diencephalon, as part of the limbic system, has not been delineated separately by prior diffusion-weighted imaging studies. The ability to trace the underlying fiber connections individually will be helpful in understanding the neurophysiology of these tracts in different functions. To date, few diffusion-weighted studies have focused on the amygdala, yet the fine connections of the amygdala, hypothalamus, septum or other adjacent limbic structures have yet to be elucidated by diffusion-weighted tractography studies. We therefore aimed to further investigate these fine neuronal connections using fiber tractography and high spatial resolution diffusion tensor imaging on 3T on 15 healthy right-handed male human subjects (age range 24-37 years). The ventral amygdalofugal pathway, anterior commissure and stria terminalis are the three main efferent pathways of the amygdala. We delineated the detailed trajectories of the ventral amygdalofugal tract, anterior commissure and their connections bilaterally in 15 normal adult human brains. Using a high-resolution diffusion tensor tractography technique, for the first time, we were able to demonstrate the trajectory of amygdalofugal tract and its connections to the hypothalamic and septal nuclei. We further revealed, for the first time, the close relationship of the amygdalofugal tract and anterior commissure with the fornix, stria terminalis and uncinate fasciculus bilaterally in 15 healthy adult human brains.

Homing in on consciousness in the nervous system: An action-based synthesis

What is the primary function of consciousness in the nervous system? The answer to this question remains enigmatic, not so much because of a lack of relevant data, but because of the lack of a conceptual framework with which to interpret the data. To this end, we have developed Passive Frame Theory, an internally coherent framework that, from an action-based perspective, synthesizes empirically supported hypotheses from diverse fields of investigation. The theory proposes that the primary function of consciousness is well-circumscribed, serving the somatic nervous system. For this system, consciousness serves as a frame that constrains and directs skeletal muscle output, thereby yielding adaptive behavior. The mechanism by which consciousness achieves this is more counterintuitive, passive, and "low level" than the kinds of functions that theorists have previously attributed to consciousness. Passive frame theory begins to illuminate (a) what consciousness contributes to nervous function, (b) how consciousness achieves this function, and (c) the neuroanatomical substrates of conscious processes. Our untraditional, action-based perspective focuses on olfaction instead of on vision and is descriptive (describing the products of nature as they evolved to be) rather than normative (construing processes in terms of how they should function). Passive frame theory begins to isolate the neuroanatomical, cognitive-mechanistic, and representational (e.g., conscious contents) processes associated with consciousness.

Displacement of mammillary bodies by craniopharyngiomas involving the third ventricle: surgical-MRI correlation and use in topographical diagnosis

OBJECT

Accurate diagnosis of the topographical relationships of craniopharyngiomas (CPs) involving the third ventricle and/or hypothalamus remains a challenging issue that critically influences the prediction of risks associated with their radical surgical removal. This study evaluates the diagnostic accuracy of MRI to define the precise topographical relationships between intraventricular CPs, the third ventricle, and the hypothalamus.

METHODS

An extensive retrospective review of well-described CPs reported in the MRI era between 1990 and 2009 yielded 875 lesions largely or wholly involving the third ventricle. Craniopharyngiomas with midsagittal and coronal preoperative and postoperative MRI studies, in addition to detailed descriptions of clinical and surgical findings, were selected from this database (n = 130). The position of the CP and the morphological distortions caused by the tumor on the sella turcica, suprasellar cistern, optic chiasm, pituitary stalk, and third ventricle floor, including the infundibulum, tuber cinereum, and mammillary bodies (MBs), were analyzed on both preoperative and postoperative MRI studies. These changes were correlated with the definitive CP topography and type of third ventricle involvement by the lesion, as confirmed surgically.

RESULTS

The mammillary body angle (MBA) is the angle formed by the intersection of a plane tangential to the base of the MBs and a plane parallel to the floor of the fourth ventricle in midsagittal MRI studies. Measurement of the MBA represented a reliable neuroradiological sign that could be used to discriminate the type of intraventricular involvement by the CP in 83% of cases in this series (n = 109). An acute MBA (< 60°) was indicative of a primary tuberal-intraventricular topography, whereas an obtuse MBA (> 90°) denoted a primary suprasellar CP position, causing either an invagination of the third ventricle (pseudointraventricular lesion) or its invasion (secondarily intraventricular lesion; p < 0.01). A multivariate model including a combination of 5 variables (the MBA, position of the hypothalamus, presence of hydrocephalus, psychiatric symptoms, and patient age) allowed an accurate definition of the CP topography preoperatively in 74%-90% of lesions, depending on the specific type of relationship between the tumor and third ventricle.

CONCLUSIONS

The type of mammillary body displacement caused by CPs represents a valuable clue for ascertaining the topographical relationships between these lesions and the third ventricle on preoperative MRI studies. The MBA provides a useful sign to preoperatively differentiate a primary intraventricular CP originating at the infundibulotuberal area from a primary suprasellar CP, which either invaginated or secondarily invaded the third ventricle.

Memory loss in Alzheimer's disease: implications for development of therapeutics

Alzheimer's disease (AD) is a progressive neurodegenerative disease marked by a constellation of cognitive disturbances, the earliest and most prominent being impaired episodic memory. Episodic memory refers to the memory system that allows an individual to consciously retrieve a previously experienced item or episode of life. Many recent studies have focused on characterizing how AD pathology impacts particular aspects of episodic memory and underlying mental and neural processes. This review summarizes the findings of those studies and discusses the effects of current and promising treatments for AD on episodic memory. The goal of this review is to raise awareness of the strides that cognitive neuroscientists have made in understanding intact and dysfunctional memory. Knowledge of the specific memorial processes that are impaired in AD may be of great value to basic scientists developing novel therapies and to clinical researchers assessing the efficacy of those therapies.

Mammillary bodies and fornix fibers are injured in heart failure

Cognitive abnormalities, including memory deficits, are common in heart failure (HF). Brain structures, including the hippocampus, fornix, and thalamus participate in memory processing, and most show structural injury and functional deficits in HF. The mammillary bodies and fornix play essential roles in spatial and working memory processing, interact with other structures, and may also be injured in HF. We assessed mammillary body volumes and cross-sectional fornix areas in 17 HF and 50 control subjects using high-resolution T1-weighted magnetic resonance images. Mammillary body volumes and fornix cross-sectional areas were significantly reduced bilaterally in HF, and these differences remained after controlling age, gender, and intracranial volume. Mammillary body and fornix injury may contribute to the compromised spatial and working memory deficits in HF. Pathological processes eliciting the damage may include injury accompanying hypoxic/ischemic processes in pathologic HF perfusion and breathing, and thiamine deficiency accompanying diuretic use and nutritional mal-absorption in the condition.

EPS Mid-Career Award 2006. Understanding anterograde amnesia: disconnections and hidden lesions

Three emerging strands of evidence are helping to resolve the causes of the anterograde amnesia associated with damage to the diencephalon. First, new anatomical studies have refined our understanding of the links between diencephalic and temporal brain regions associated with amnesia. These studies direct attention to the limited numbers of routes linking the two regions. Second, neuropsychological studies of patients with colloid cysts confirm the importance of at least one of these routes, the fornix, for episodic memory. By combining these anatomical and neuropsychological data strong evidence emerges for the view that damage to hippocampal-mammillary body-anterior thalamic interactions is sufficient to induce amnesia. A third development is the possibility that the retrosplenial cortex provides an integrating link in this functional system. Furthermore, recent evidence indicates that the retrosplenial cortex may suffer "covert" pathology (i.e., it is functionally lesioned) following damage to the anterior thalamic nuclei or hippocampus. This shared indirect "lesion" effect on the retrosplenial cortex not only broadens our concept of the neural basis of amnesia but may also help to explain the many similarities between temporal lobe and diencephalic amnesia.

Widespread cognitive impairment in psychogenic anterograde amnesia

A 34-year-old man without a past history of any psychiatric or neurological disorder developed severe anterograde amnesia following a psychological trauma. Initial assessment of neuropsychological functions 3 months after the psychological trauma indicated severe memory deficits for acquiring new information in both verbal and visual modalities with widespread cognitive deficits in attention, executive functions, and intellectual ability. Importantly, working and remote memory were intact. The case illustrates that psychogenic anterograde amnesia might be associated with a wider range of cognitive deficits. Possible neurobiological explanations are discussed to explain large cognitive impairments associated with anterograde psychogenic amnesia.

Distinct, parallel pathways link the medial mammillary bodies to the anterior thalamus in macaque monkeys

Mammillary body neurons projecting to the thalamus were identified by injecting retrograde tracers into the medial thalamus of macaque monkeys. The source of the thalamic projections from the medial mammillary nucleus showed strikingly different patterns of organization depending on the site of the injection within the two anterior thalamic nuclei, anterior medialis and anterior ventralis. These data reveal at least two distinct modes by which the primate medial mammillary bodies can regulate anterior thalamic function. Projections to the thalamic nucleus anterior medialis arise mainly from the pars lateralis of the medial mammillary nucleus. A particularly dense source is the dorsal cap in the posterior half of the pars lateralis, a subregion that has not previously been distinguished. In contrast, neurons spread evenly across the medial mammillary nucleus gave rise to projections more laterally in the anterior thalamic nuclei. A third pattern of medial mammillary neurons appeared to provide the source of projections to the rostral midline thalamic nuclei. In contrast, the labeled cells in the lateral mammillary nucleus were evenly spread across that nucleus, irrespective of injection site. In addition to the established projection to anterior dorsalis, the lateral mammillary nucleus appears to project lightly to a number of other thalamic nuclei, including lateralis dorsalis, anterior medialis, anterior ventralis, and the rostral midline nuclei, e.g. nucleus reuniens. These anatomical findings not only reveal novel ways of grouping the neurons within the medial mammillary nucleus, but also indicate that the mammillothalamic connections support cognition in multiple ways.

Selective anterograde amnesia with thalamus and hippocampal lesions in neuro-Behcet's disease

Anterograde amnesia and minimal retrograde amnesia with thalamic and hippocampal lesions in neuro-Behcet's disease is rare. A 50-year-old man presented with forgetfulness and severe memory disturbance after suffering multiple oral and genital aphthous ulcers with erythema nodosum. A neurological examination and a neuropsychological assessment revealed prominent anterograde memory impairment without focal neurological deficits. On brain MRI there were high signal intensity lesions involving right anterior thalamus, left posterior basal ganglia, and left hippocampus. This is a quite selective anterogrde memory deficit in a case of neuro-Behcet's disease caused by parenchymal lesions in the thalamus and hippocampus.

Severe Amnesic Syndrome and Collecting Behavior After Surgery for Craniopharyngioma

Significant neuropsychologic sequelae were induced by total removal of craniopharyngioma via a frontobasal interhemispheric approach. A 50-year-old right-handed man developed severe amnesic syndrome and collecting behavior after total removal of a craniopharyngioma. He had very poor results on tests of learning, recall, and recognition for both verbal and nonverbal tasks. Magnetic resonance imaging revealed damage to the bilateral mammillary bodies and fornices, and N-isopropyl-p-[23I]iodoamphetamine single photon emission computed tomography showed decreased cerebral blood flow in the bilateral frontal lobes, predominantly in the right, and regions around the third ventricle. The present case suggests that damage to the brain structures surrounding the third ventricle associated with surgery for craniopharyngioma may result in amnesic syndrome and collecting behavior. Generally, the frontobasal interhemispheric approach is the optimum choice for the removal of craniopharyngioma without significant sequelae related to the surgical method, but the risk of neuropsychologic disturbances must be kept in mind.

Astroglial distribution and sexual differences in neural metabolism in mammillary bodies

The sexual differences in cerebral nuclei are produced by the organizational and the activational function of gonadal hormones. The different performances by male and female rats in memory tasks requiring use of the mammillary bodies (MBs), could be due to structural and functional sexual dimorphic differences. Our work quantifies the number of glial fibrillary acidic protein immunoreactive (GFAP-IR) astrocytes, and neuronal metabolic activity measured by the cytochrome oxidase (CO) histochemistry in the MBs in rats of both sexes. We find that there is no difference in astroglial number in the medial mammillary nucleus (MMN) and in the lateral mammillary nucleus (LMN) of males, females in estrus and diestrus adult rats. However, we do find statistically significant differences between the sexes in the neuronal oxidative metabolism influenced by the estrous cycle. We, therefore, conclude that there are functional and not structural sex differences in the MBs.

Involvement of the mammillary bodies in spatial working memory revealed by cytochrome oxidase activity

In view of the inconclusive findings relating the nuclei of the mammillary bodies (MB) with spatial memory, we evaluated the oxidative metabolic activity of the medial and lateral nuclei of the mammillary bodies (MB) after training young rats (30 days) of both sexes in the Morris water maze. Different groups were trained in spatial working (WM) or reference memory (RM) tasks, respectively. The corresponding naïve groups swam for the same amount of time as the trained groups but without the escape platform. Control groups were added that had not been manipulated in any way. No sex-related differences were detected in the working memory task although males exhibited better reference memory than females. Cytochrome oxidase (CO) activity, an endogenous metabolic marker for neuronal activity, was measured in all the groups. CO activity increased significantly in both MB nuclei of male and female rats only in the spatial working memory group. In addition, high CO activity in the lateral nucleus of the MB was linearly correlated with lower escape latencies in both sexes after training in the working memory task. No CO activity changes were found in the basolateral amygdala (BL) in any of the experimental groups. This nucleus was used as a control brain region because of its participation in emotional behavior. The results suggest a specific role of the MB nuclei in spatial working memory in both sexes.

Changes in metabolic activity and estrogen receptors in the human medial mamillary nucleus: relation to sex, aging and Alzheimer's disease

The medial mamillary nucleus (MMN) is situated caudally in the human hypothalamus and is involved in memory processes. In search for putative sites of action in estrogen replacement therapy on memory both in aging and Alzheimer's disease (AD), we aimed at determining whether changes would occur in estrogen receptors (ER) or metabolic activity in the MMN neurons under these conditions in a sex-dependent way. The Golgi apparatus (GA) and cell size, that were previously shown to be good measures of changes in neuronal metabolic activity, were measured in the MMN of 10 young (20-50 years old), 11 elderly (56-76 years old) control men and women and 11 AD patients (54-78 years old). In addition, we investigated whether estrogen receptor alpha or beta (ERalpha or ERbeta) immunoreactivity was altered in the MMN in aging or AD. There were no sex- or AD-related differences in the GA or cell size in the MMN. Both the GA and cell size of the MMN neurons were found to be increased in postmenopausal compared to young control women accompanied by a decrease in the amount of nuclear ERbeta. The percentage of nuclear ERalpha-positive MMN neurons was markedly enhanced in AD patients compared to controls and most prominently in AD men. In AD patients the proportion of nuclear ERalpha-positive neurons was positively correlated to the Braak stages that indicate the progression of the disease. No differences in the proportion of ERbeta-positive neurons were observed between AD and control patients. We propose that estrogens play an inhibitory role with respect to the metabolic activity of human MMN, which is mediated via ERbeta. This inhibitory effect is diminished in postmenopausal women. The role of the enhanced nuclear ERalpha staining in AD, that was also found in other brain areas, remains to be elucidated.

Evidence of a spatial encoding deficit in rats with lesions of the mammillary bodies or mammillothalamic tract

The present study sought to identify the role of the mammillary bodies and their projections to the anterior thalamic nuclei for spatial memory. Rats with either selective, neurotoxic mammillary body lesions or discrete mammillothalamic tract lesions were tested on various spatial working memory tasks. Tests using the T-maze, radial-arm maze, and water maze were manipulated to compare three possible theories of mammillary body function by increasing proactive interference, increasing retention interval, and taxing the rapid processing of novel spatial stimuli. On T-maze alternation and radial-arm maze tasks, both lesion groups were initially impaired but seemed to recover. Transfer tests revealed, however, a more permanent change in performance, suggesting a failure to use distal (allocentric) cues. Consistent with this, both groups were also impaired at matching-to-place in the water maze and showed little improvement with practice. Nevertheless, once the lesion groups had been trained on a task, they were not affected differentially either by an increase of proactive interference or by retention intervals of up to 30 min. Although both mammillary body and mammillothalamic tract lesions resulted in similar impairments, the mammillothalamic tract group was the more affected when acquiring new spatial information. Together, these results suggest that mammillary body damage causes an encoding deficit when learning new spatial tasks, resulting in a suboptimal mode of performance, which may reflect a loss of directional heading information.

Estrogen receptor-alpha distribution in the human hypothalamus in relation to sex and endocrine status

The present study reports the first systematic rostrocaudal distribution of estrogen receptor-alpha immunoreactivity (ERalpha-ir) in the human hypothalamus and its adjacent areas in young adults. Postmortem material taken from 10 subjects (five male and five female), between 20 and 39 years of age, was investigated. In addition, three age-matched subjects with abnormal levels of estrogens were studied: a castrated, estrogen-treated 50-year-old male-to-female transsexual (T1), a 31-year-old man with an estrogen-producing tumor (S2), and an ovariectomized 46-year-old woman (S8). A strong sex difference, with more nuclear ERalpha-ir in women, was observed rostrally in the diagonal band of Broca and caudally in the medial mamillary nucleus. Less robust sex differences were observed in other brain areas, with more intense nuclear ERalpha-ir in men, e.g., in the sexually dimorphic nucleus of the medial preoptic area, paraventricular nucleus, and lateral hypothalamic area, whereas women had more nuclear ERalpha-ir in the suprachiasmatic nucleus and ventromedial nucleus. No nuclear sex differences in ERalpha were found, e.g., in the central part of the bed nucleus of the stria terminalis. In addition to nuclear staining, ERalpha-ir appeared to be sex-dependently present in the cytoplasm of neurons and was observed in astrocytes, plexus choroideus, and other non-neuronal cells. ERalpha-ir in T1, S2, and S8 suggested that most of the observed sex differences in ERalpha-ir are "activational" (e.g., ventromedial nucleus/medial mamillary nucleus) rather than "organizational." Species similarities and differences in ERalpha-ir distribution and possible functional implications are discussed.

Akinetic mutism caused by bilateral infiltration of the fornix in a patient with astrocytoma

In a 59-year-old female patient, a World Health Organization (WHO) grade II astrocytoma had been diagnosed 16 years ago, which finally progressed into WHO grade III. Several right frontal neurosurgical resections, local radiation and a local radioimplant had been applied. Despite this long record, she was reported alert with a Karnofsky index of 90% until admission. Within a few weeks she rapidly developed akinetic mutism. Upon admission, computed tomography (CT) scan showed a large cystic right frontal defect and a suggested small tumor recurrence. White matter of the frontal lobe appeared to be translucent and compatible with previous radiation. The severe mental changes were initially attributed to a delayed radiation encephalopathy. Neuropathologically, the white matter of the frontal lobe showed mild elevated cell density consistent with gliosis; however, a tumor recurrence invading the tip of the corpus callosum and invading the entire length both fornices appeared. From the neuropathological findings of massive local tumor recurrence in both fornices, together with the acute clinical onset, it seems unlikely that the sequel of radiotherapy caused akinetic mutism, but the symmetric and severe involvement of the limbic system. We conclude that the rapid progression from a state of alertness to a full clinical picture of akinetic mutism was because of infiltration of both fornices.

Theta-rhythmically firing neurons in the anterior thalamus: implications for mnemonic functions of Papez's circuit

In 1937 Papez described an anatomical circuit (or loop) beginning and ending in the hippocampal formation that he proposed subserved emotional experience (Papez, 1937). Specifically, the projections of the circuit were as follows: hippocampal formation--> mammillary bodies--> anterior thalamus--> cingulate cortex--> parahippocampal gyrus--> hippocampal formation. Although the circuit has been refined based on subsequent anatomical findings (Amaral and Witter, 1995; Shibata, 1992; Van Groen and Wyss, 1995), the major links of the circuit unquestionably represent a prominent system of connections in the mammalian brain. Hence, the enduring nature of 'Papez's circuit'. Unlike, however, its persistence as anatomical entity, the proposed functional role for the circuit has been less resilient. The early notion that Papez's circuit subserves emotional experience/expression has been abandoned (LeDoux, 1993) and replaced by the proposal that it is primarily involved in mnemonic functions (Aggleton and Brown, 1999). Lesions of each of the major components of the circuit have been shown to disrupt memory (Aggleton and Brown, 1999; Sutherland et al., 1988; Sziklas and Petrides, 1993). The mammillary bodies represent a major output from the hippocampus in Papez's circuit (Amaral and Witter, 1995). It has recently been shown that cells of mammillary body fire rhythmically in bursts synchronous with the theta rhythm of the hippocampus (Bland et al., 1995; Kirk et al., 1996; Kocsis and Vertes, 1994, 1997) and that this rhythmical activity is dependent upon the action of the hippocampus on the mammillary bodies (Bland et al., 1995; Kirk et al., 1996). It is well established that the mammillary bodies project massively to the anterior thalamus (Shibata, 1992), which taken together with the demonstration that mammillary body cells fire synchronously with theta, suggests that the mammillary bodies may act on the anterior thalamus, possibly in the manner that the hippocampus acts on the mammillary bodies, to rhythmically activate cells of the anterior thalamus at theta frequency. We demonstrated that approximately 75% of cells of the anterior ventral nucleus of the thalamus fire rhythmically synchronous with the hippocampal theta rhythm and the activity of 46% of these anterior ventral neurons was highly correlated with theta. These findings, together with demonstration of theta-rhythmically firing cells in other structures of Papez's circuit, indicate that a theta-rhythmic signal may resonate throughout Papez's circuit, possibly involved in the control of mnemonic functions of the circuit.

Severe Amnesia in Epilepsy: Causes, Anatomopsychological Considerations, and Treatment

Severe amnesia in epileptic patients is a catastrophic condition that may be due to different etiologies. Because of the striking findings and thorough neuropsychological studies of Patient H.M., the literature has focused on postsurgical occurrence of such memory impairment, with much less emphasis on other causes. Here we summarize, for comparison, the history of H.M. We report five patients with pronounced memory loss who had extensive neuropsychological and electroencephalographic testing. MRI was also performed in four of the patients, MRI volumetric measurements of amygdala and hippocampal formation in three, and measurements of entorhinal cortex in two. The amnesia occurred after head trauma in one patient, following encephalitis in one, after partial status epilepticus in two, and after unilateral surgical resection in a woman with bilateral lesions. On the basis of these studies it was impossible to distinguish the role of recurrent temporal lobe epileptic seizures as distinct from underlying lesions in the genesis and course of the memory loss. We review here the anatomical substrate, neuropsychological, and other investigations and the etiological factors leading to the amnesia in these patients, together with current concepts regarding possible causes of such severe memory dysfunction. In patients with this degree of severity of memory deficit, temporal resection in an attempt to control seizures did not lead to a measurable increase in memory problems. It also, however, did not bring about worthwhile improvement in seizure control.

Unbiased estimation of the total number of nervous cells and volume of medial mammillary nucleus in humans

In this study, we demonstrate that aging does not provoke any changes in neuronal number or in the glial cells of the medial mammillary nucleus (MMN) in humans. Three age groups were used: young (age 17-35), adult (age 50-57), and aged (age 70-88). Furthermore, no age-dependent volumetric changes were observed in the MMN. All the estimations were performed with stereological methods: an optical fractionator and Cavalier's principle. The total number of neurons cells was estimated using an optical fractionator and amounted to 32x10(3) in the young group, 24x103 in the adult group, and 29x103 in the aged group. The number of glial cells was 164x10(3), 187x103, 185x103, respectively. Thus, all three age groups had a neuron/glial ratio of about 1:5, 1:8, and 1:6, respectively. The MMN volume was estimated using the Cavalier's principle. The total volume was 6.98 mm3 in the young group, 6.66 mm3 in the adult group, and 6.80 mm3 in the aged group. We have demonstrated that neither the total number of neurons and glial cells nor the volume of MMN are affected by age.

Effects of mammillary body lesions on spatial reference and working memory tasks

This work examines the effects of electrolytic mammillary body (MB) lesions on the performance of rats in different spatial memory tasks in the Morris water maze. The first experiment assessed the effect of MB lesion on performance in a spatial reference memory task (place learning with multiple trials). The second experiment examined the effect of a lesion in this nucleus on performance in a spatial working memory task (single-trial place learning). The results show that lesion of the MB impairs the animals performance in spatial working memory tasks but does not impair acquisition in spatial reference memory tasks (place learning, transfer task, reversal task) or in a visual-cued task. However, the deficit in the spatial working memory task does not appear to vary with the delay between acquisition and retention trials (30 s and 5 min). Our results demonstrate a clear role of the mammillary bodies in the processing of spatial information in a working memory task. Lesion of the MB impairs performance in a working memory task but does not affect reference memory processes.

Functional anatomy of long-term memory

Memory in the brain is organized into multiple memory systems that perform different memory functions and have different neurologic substrates. Declarative memory involves conscious memory for facts and events. The medial temporal lobe and structures in the diencephalon are essential in the establishment of new declarative memories, and these memory traces are finally stored in domain-specific regions of the cerebral cortex. The frontal lobe and basal ganglia are important in some forms of declarative memory that require reasoning about the contents of memory. Nondeclarative forms of memory (including skill learning, repetition priming, and classical conditioning) do not involve conscious recollection and are measured through changes in the way in which tasks are performed. These forms of memory rely upon the cerebral cortex, basal ganglia, and cerebellum.