Volumetric MRI of the limbic system: anatomic determinants

Reduced mammillary body volume in individuals with a schizophrenia diagnosis: an analysis of the COBRE data set

While the frontal cortices and medial temporal lobe are well associated with schizophrenia, the involvement of wider limbic areas is less clear. The mammillary bodies are important for both complex memory formation and anxiety and are implicated in several neurological disorders that present with memory impairments. However, little is known about their role in schizophrenia. Post-mortem studies have reported a loss of neurons in the mammillary bodies but there are also reports of increased mammillary body volume. The findings from in vivo MRI studies have also been mixed, but studies have typically only involved small sample sizes. To address this, we acquired mammillary body volumes from the open-source COBRE dataset, where we were able to manually measure the mammillary bodies in 72 individuals with a schizophrenia diagnosis and 74 controls. Participant age ranged from 18 to 65. We found the mammillary bodies to be smaller in the patient group, across both hemispheres, after accounting for the effects of total brain volume and gender. Hippocampal volumes, but not subiculum or total grey matter volumes, were also significantly lower in patients. Given the importance of the mammillary bodies for both memory and anxiety, this atrophy could contribute to the symptomology in schizophrenia.

Atrophy of the ipsilateral mammillary body in unilateral hippocampal sclerosis shown by thin-slice-reconstructed volumetric analysis

PURPOSE

Conventional volumetric analysis could not detect ipsilateral atrophy of the mammillary body in patients with unilateral hippocampal sclerosis. By using thin-slice-reconstructed volumetric analysis, we investigated whether the mammillary body volume is smaller on the hippocampal sclerosis side than in healthy subjects or the non-hippocampal sclerosis side.

METHODS

This retrospective study included 45 patients with unilateral hippocampal sclerosis and 30 healthy subjects. Three-dimensional T1WI of 1 mm thicknesses were oversampled to a thickness of 0.2 mm (thin-slice-reconstructed images), and the mammillary bodies were segmented manually to determine mammillary body volume on each side. Mammillary body volumes on the hippocampal sclerosis side were compared with those in healthy subjects or the non-hippocampal sclerosis side.

RESULTS

In patients with right hippocampal sclerosis, right mammillary body volume was both significantly smaller than that in healthy subjects (30.3 ± 10.3 vs. 43.3 ± 8.07 mm³, P < 0.001) and significantly smaller than the left mammillary body volume in each patient (30.3 ± 10.3 vs. 41.4 ± 10.1 mm³, P < 0.001). Similarly, in patients with left hippocampal sclerosis, left mammillary body volume was both significantly smaller than that in healthy subjects (37.7 ± 11.2 vs. 47.0 ± 8.65 mm³, P < 0.001) and significantly smaller than right mammillary body volume in each patient (37.7 ± 11.2 vs. 42.5 ± 7.78 mm³, P = 0.044).

CONCLUSIONS

In this study, thin-slice-reconstructed volumetric analysis showed that, in patients with unilateral hippocampal sclerosis, mammillary body volume on the hippocampal sclerosis side is smaller than that in healthy subjects and the non-hippocampal sclerosis side.

Neuroanatomical Correlates of Hierarchical Personality Traits in Chimpanzees: Associations with Limbic Structures

A converging literature has revealed the existence of a set of largely consistent, hierarchically organized personality traits, that is broader traits are able to be differentiated into more fine-grained traits, in both humans and chimpanzees. Despite recent work suggesting a neural basis to personality in chimpanzees, little is known with regard to the involvement of limbic structures (i.e., amygdala and hippocampus), which are thought to play important roles in emotion. Using saved maximum likelihood estimated exploratory factor scores (two to five factors) in the context of a series of path analyses, the current study examined associations among personality dimensions across various levels of the personality hierarchy and individual variability of amygdala and hippocampal grey matter (GM) volume in a sample of captive chimpanzees (N=191). Whereas results revealed no association between personality dimensions and amygdala volume, a more nuanced series of associations emerged between hippocampal GM volume and personality dimensions at various levels of the hierarchy. Hippocampal GM volume associated most notably with Alpha (a dimension reflecting a tendency to behave in an undercontrolled and agonistic way) at the most basic two-factor level of the hierarchy; associated positively with Disinhibition at the next level of the hierarchy (“Big Three”); and finally, associated positively with Impulsivity at the most fine-grained level (“five-factor model”) of the hierarchy. Findings underscore the importance of the hippocampus in the neurobiological foundation of personality, with support for its regulatory role of emotion. Further, results suggest the importance of the distinction between structure and function, particularly with regard to the amygdala.

The fornix in mild cognitive impairment and Alzheimer's disease

The fornix is an integral white matter bundle located in the medial diencephalon and is part of the limbic structures. It serves a vital role in memory functions and as such has become the subject of recent research emphasis in Alzheimer's disease (AD) and mild cognitive impairment (MCI). As the characteristic pathological processes of AD progress, structural and functional changes to the medial temporal lobes and other regions become evident years before clinical symptoms are present. Though gray matter atrophy has been the most studied, degradation of white matter structures especially the fornix may precede these and has become detectable with use of diffusion tensor imaging (DTI) and other complimentary imaging techniques. Recent research utilizing DTI measurement of the fornix has shown good discriminability of diagnostic groups, particularly early and preclinical, as well as predictive power for incident MCI and AD. Stimulating and modulating fornix function by the way of DBS has been an exciting new area as pharmacological therapeutics has been slow to develop.

Quantitative ventricular neuroendoscopy performed on the third ventriculostomy: anatomic study

BACKGROUND

One of the key elements for a successful endoscopic intervention in the ventricular system is the ability to recognize the anatomic structures and use them as a reference.

OBJECTIVE

To measure the choroid plexus with endoscopy in the interventricular foramen, together with the structures on the third ventricle floor, and to compare these variables.

METHODS

An observational prospective study was carried out on 37 brains of cadavers for which the cause of death was assessed at the Death Check Unit of the University of São Paulo in April 2008. This study was done on adults of both sexes with a rigid neuroendoscope. Endoscopic images were recorded, submitted for correction of distortion, and then measured.

RESULTS

The measurements of the choroid plexus in the interventricular foramen, laterolateral distance of mammillary bodies, distance from the infundibular recess to the mammillary bodies, and area of the triangle in the tuber cinereum were 1.71 ± 0.77 mm, 2.23 ± 0.74 mm, 3.22 ± 0.82 mm, and 3.69 ± 2.09 mm, respectively. The ventricle floor was opaque in 84% of cases. The internal distance of mammillary bodies was absent in 89%. Associations between the translucent floor of the third ventricle and laterolateral distance of mammillary bodies, internal distance of mammillary bodies, and age were identified.

CONCLUSION

Before this research, there was no record of the measurements of the choroid plexus in the interventricular foramen. The remaining variables of the present study show a greater number in normal brains compared with others.

Brain hemispheric structural efficiency and interconnectivity rightward asymmetry in human and nonhuman primates

Evidence for interregional structural asymmetries has been previously reported for brain anatomic regions supporting well-described functional lateralization. Here, we aimed to investigate whether the two brain hemispheres demonstrate dissimilar general structural attributes implying different principles on information flow management. Common left hemisphere/right hemisphere structural network properties are estimated and compared for right-handed healthy human subjects and a nonhuman primate, by means of 3 different diffusion-weighted magnetic resonance imaging fiber tractography algorithms and a graph theory framework. In both the human and the nonhuman primate, the data support the conclusion that, in terms of the graph framework, the right hemisphere is significantly more efficient and interconnected than the left hemisphere, whereas the left hemisphere presents more central or indispensable regions for the whole-brain structural network than the right hemisphere. From our point of view, in terms of functional principles, this pattern could be related with the fact that the left hemisphere has a leading role for highly demanding specific process, such as language and motor actions, which may require dedicated specialized networks, whereas the right hemisphere has a leading role for more general process, such as integration tasks, which may require a more general level of interconnection.

Fornix microstructure correlates with recollection but not familiarity memory

The fornix is the main tract between the medial temporal lobe (MTL) and medial diencephalon, both of which are critical for episodic memory. The precise involvement of the fornix in memory, however, has been difficult to ascertain since damage to this tract in human amnesics is invariably accompanied by atrophy to surrounding structures. We used diffusion-weighted imaging to investigate whether individual differences in fornix white matter microstructure in neurologically healthy participants were related to differences in memory as assessed by two recognition tasks. Higher microstructural integrity in the fornix tail was found to be associated with significantly better recollection memory. In contrast, there was no significant correlation between fornix microstructure and familiarity memory or performance on two non-mnemonic tasks. Our findings support the idea that there are distinct MTL-diencephalon pathways that subserve differing memory processes.

The frequency and extent of mammillary body atrophy associated with surgical removal of a colloid cyst

BACKGROUND AND PURPOSE

Patients who have had a colloid cyst removed from the third ventricle sometimes experience some difficulty with day-to-day memory. This study provided quantitative MR imaging volume measures of 1 structure potentially responsible for mnemonic problems, the mammillary bodies. Additional volume estimates in structures connected to the mammillary bodies sought to determine the specificity of any atrophy.

MATERIALS AND METHODS

Volume estimates of the mammillary bodies were performed on 38 patients after surgical removal of colloid cysts and 20 control subjects by the application of stereologic volume-estimation techniques. For the mammillary body measures, 2 groups of MR images were assessed (0.8- and 1.0-mm section thickness) to compare the sensitivity of each imaging sequence for detecting any atrophy. Other structures associated with memory processes, such as the hippocampus and fornix, were also assessed quantitatively to determine whether there was a correlation between mammillary body damage and atrophy in connecting structures.

RESULTS

Our investigations established the superiority of 0.8-mm-volume scans over standard isotropic 1.0-mm-thick-volume scans for mammillary body assessments. Comparisons with 20 age-matched controls revealed that patients with colloid cysts frequently showed significant mammillary body atrophy (mean volume of colloid cysts, 0.037 cm(3) right and 0.038 cm(3) left; control subjects, 0.069 cm(3) right and 0.067 cm(3) left). In fact, every patient had a mammillary body volume below the control mean, and the majority of patients had a volume decrease of >1 SD (82% right, 74% left). Mammillary body volumes correlated with fornix volumes in the same patient group.

CONCLUSIONS

Our results reveal the frequent presence of mammillary body atrophy in patients with surgical removal of colloid cysts and indicate that this atrophy is partly due to a loss of temporal lobe projections in the fornix.

A voxel-based diffusion tensor imaging study of temporal white matter in patients with schizophrenia

Diffusion tensor imaging (DTI) is a relatively new technique used to detect changes in the anisotropic diffusion of white matter. The study of the disruption of brain connectivity may increase our understanding of cognitive deficits associated with schizophrenia. Here we analysed DTI data in 25 patients with DSM-IV schizophrenia and 24 healthy controls. Two complementary measures, fractional anisotropy (FA) and the apparent diffusion coefficient (ADC), were considered and analysed using voxel-based morphometry. Declarative memory functions were also investigated and their associations with DTI data were analysed. FA was significantly reduced, and the ADC increased in the left sub-gyral white matter of the temporal lobe, which involves the posterior part of the fornix. In the schizophrenic group, females had lower FA than males in the genu of the corpus callosum. Memory functions correlate with FA values. These data provide further evidence for the disruption of white matter connectivity in the left medial temporal lobe, and for its contribution to the declarative memory deficit in schizophrenia.

A preliminary study, using electron and light-microscopic methods, of axon numbers in the fornix in autopsies of patients with temporal lobe epilepsy

Our objective was to show morphological changes of the fornix in autopsies of patients with temporal lobe epilepsy, which may potentially serve for post-mortem diagnosis. Epileptic and non-epileptic autopsy brains were obtained from the council of forensic medicine between the years 2005 and 2007. In both non-epileptic and epileptic autopsies the mean cross-sectional areas and fiber densities of the right and left fornices were calculated and analyzed. The numbers of myelinated and unmyelinated fibers, and the total number of fibers forming each fornix were counted. The total number of fibers in the right fornix was always greater than in the left fornix, in both epileptic and non-epileptic autopsies. The mean total number of fornix fibers was significantly reduced in epileptics compared with non-epileptics, in both the right (p = 0.043) and left (p = 0.043) sides. The electron-microscopic sections showed that myelinated axons outnumbered unmyelinated axons in both epileptic and non-epileptic autopsies. However, the reduction in the number of unmyelinated fibers was only statistically significant for the right fornix in right epileptic autopsies (p = 0.021). Although the reduction in the number of myelinated fibers was not statistically significant, electron-microscopic evaluations showed myelin degeneration of the myelinated fibers in the right fornix of the right temporal lobe in epileptic autopsies. In conclusion, our results suggest that unmyelinated fiber loss is functionally important, and may have functional consequences of diagnostic value.

The volumes of the fornix in schizophrenia and affective disorders: a post-mortem study

Structural and functional pathology of limbic structures including the hippocampus are frequently replicated in schizophrenia. Although the fornix is the main afferent system of the hippocampus to the septal nuclei and the hypothalamus (especially the mammillary bodies), relatively few studies have investigated structural changes of the fornix in schizophrenia. We measured the volume of the fornix in post-mortem brains in 19 patients with schizophrenia, 9 patients with bipolar disorder, 7 patients with unipolar depression, and 14 control subjects by planimetry of serial sections. The volumes, the mean cross-sectional areas, and the anterior to posterior distances of the fornix did not differ among patients with schizophrenia, bipolar disorder, unipolar depression, and control subjects. No lateralization existed between the right and the left fornices in among patients in the diagnostic groups and the control subjects. The fornix does not show morphometrical abnormalities in patients with schizophrenia, bipolar disorder and unipolar depression compared with control subjects, which might indicate that the fornix is not a primary focus of structural changes in these diseases.

Rey Osterrieth complex figure test spatial and figural scoring: relations to seizure focus and hippocampal pathology in patients with temporal lobe epilepsy

The purpose of the study was to compare figural and spatial memory in patients with left (LTLE, n=56) and right (RTLE, n=48) temporal lobe epilepsy using J.I. Breier and colleagues' (J Int Neuropsychol Soc 1996;2:535-40) figural/spatial scoring method for the Rey Osterrieth Complex Figure Test (RCFT). The study also examined the association between figural and spatial components of the RCFT, temporal lobe laterality, and hippocampal structure (MRI hippocampal volumes and neuropathology ratings). Neither immediate or delayed trial figural and spatial memory scores were associated with seizure laterality or hippocampal pathology ratings. Immediate and delayed recall scores were not associated with right hippocampal volume. However, modestly positive correlations were found between left hippocampal volume and RCFT delayed recall scores. Similar to recent work (A.C. Kneebone et al., J Int Neuropsychol Soc 2007;13:664-71), stronger associations were related to left temporal lobe function. This study provides further evidence for the lack of sensitivity of the RCFT as a surrogate measure of right temporal lobe memory function.

A disproportionate role for the fornix and mammillary bodies in recall versus recognition memory

Uncovering the functional relationship between temporal lobe amnesia and diencephalic amnesia depends on determining the role of the fornix, the major interlinking fiber tract. In this study relating fornix volume with memory, we made magnetic resonance imaging-based volume estimates of 13 brain structures in 38 individuals with surgically removed colloid cysts. Fornix status was assessed directly by overall volume and indirectly by mammillary body volume (which atrophies after fornix damage). Mammillary body volume significantly correlated with 13 out of 14 tests of episodic memory recall, but correlated poorly with recognition memory. Furthermore, as the volumes of the left fornix and the left mammillary bodies decreased, the difference between recall and recognition scores increased. No other structure was consistently associated with memory. These findings support models of diencephalic memory mechanisms that require hippocampal inputs for recall, but not for key elements of recognition.

Hippocampus and amygdala volumes in a random community-based sample of 60-64 year olds and their relationship to cognition

Reduced volumes of the hippocampus (HC) and amygdala (AG) are potential biomarkers for Alzheimer's disease (AD) and other neuropsychiatric disorders. Published studies on HC and AG volumes suffer from methodological limitations, and a valid and reliable normative database does not exist. This study aimed to establish a database of HC and AG volumes from a large community sample of participants 60-64 years old and relate them to cognition. A total of 452 randomly selected participants (from 622 approached) were retained in the study (238 males, 214 females), and all received brain MRI scans, as well as cognitive and physical assessments. HC and AG volumes were estimated from manual tracings on T1-weighted images, and intracranial volume (ICV) was obtained from an automated program. In both sexes, right hippocampi were larger than left, while left amygdala were larger than right. The only correlation to remain significant after normalization was left HC volume and percent retention of a word list in females. This study provides a HC and AG volumetrics database and describes its relationship with cognitive performance in a representative sample using a standard methodology that will be a reference for future studies. It will therefore have clinical applicability in early AD and other disorders.

Prevalence of asymmetry of mamillary body and fornix size on MR imaging

BACKGROUND AND PURPOSE

Mamillary body and fornix asymmetry are frequent findings on MR imaging of the brain. We sought to determine the prevalence of asymmetry of the fornix and mamillary body on MR imaging in patients with or without seizures.

MATERIALS AND METHODS

MR images were retrospectively evaluated for asymmetry of the mamillary body and fornix in 178 patients who had a history of seizures, of whom 35 had suspected mesial temporal sclerosis (MTS). Additionally, 353 patients who had no limbic system pathology were reviewed. All patients were examined with spin-echo MR imaging, consisting of contiguous axial and/or coronal fluid-attenuated inversion recovery (FLAIR), T2-weighted, and sagittal T1-weighted imaging. Additionally, the patients with seizures had oblique coronal 3-mm T2-weighted, FLAIR, and 1.5-mm magnetization-preparation rapid gradient echo scanning through their temporal lobes.

RESULTS

In the patients who had no limbic system pathology or seizure history, 6.5% (23/353) had MR imaging evidence of asymmetric mamillary bodies and 7.9% (28/353) had asymmetric fornix size. Asymmetry of the mamillary body and fornix size was found in 37.1% (13/35) and 34.3% (12/35), respectively, of subjects with suggested hippocampal sclerosis. The prevalence of asymmetry of the mamillary body and fornix was statistically significantly higher in the patients with MTS (chi(2) test, P <.0001).

CONCLUSION

Although asymmetry of the mamillary bodies and fornices is highly associated with MTS, this could also be seen as a normal variation or congenital abnormality.

The fornix and mammillary bodies in older adults with Alzheimer's disease, mild cognitive impairment, and cognitive complaints: a volumetric MRI study

The fornix and mammillary bodies are important limbic structures that have not been systematically investigated in the earliest stages of preclinical dementia. The present study examined volumetric changes in the fornix and mammillary bodies and improved previously established tracing guidelines to increase reliability and provide more comprehensive measurements. Volumetric measurements were made in euthymic older adults, including 16 patients with mild Alzheimer's disease (AD), 20 patients with amnestic mild cognitive impairment (MCI), 20 individuals with cognitive complaints (CC) but normal neuropsychological test performance, and 20 demographically matched healthy controls (HC). Structural magnetic resonance imaging included a T1-weighted 1.5-mm coronal volume, acquired on a GE 1.5T LX scanner. After adjustment for total intracranial volume (ICV), significant volume reductions were observed in the fornix and mammillary bodies in patients with AD as compared with HC, CC, and MCI participants. No volume differences were seen between the HC, CC, and MCI groups. Study findings are consistent with previous research showing volume decreases of the fornix and mammillary bodies in AD, and provide new data on the relative preservation of these structures in preclinical disease stages. Results suggest that atrophy of the fornix and mammillary bodies becomes apparent at the point of conversion from MCI to AD. Longitudinal assessments are needed to delineate the time course and extent of the observed volumetric changes.

Hemispheric asymmetry of sulcus-function correspondence: quantization and developmental implications

Spatial covariances between the geometric centers of human occipital sulci and visual functional areas were calculated to reduce the spatial variance of functional-area locations between subjects. Seven visual areas in each occipital hemisphere were retinotopically mapped, using horizontal- and vertical-meridian stimuli and (15)O PET in 11 subjects. Sulcal locations were determined using anatomic brain models derived from high-resolution MRI images. Location variability for sulci and functional areas was similar in magnitude, with average standard deviations of (2.7x, 5.3y, 5.7z) mm and (4.3x, 5.4y, 5.3z) mm, respectively. Sulcal locations were predictive of functional-area locations (i.e., significant spatial covariance) in the minority of structure-function pairings tested (25 of 168). Location variability was reduced by an average of 27% for functional areas showing significant covariation with sulcal features. Early-developing sulci were stronger predictors of functional-area location than late-developing sulci. Sulcus-function covariance was stronger in the left occipital lobe than in the right occipital lobe. Notably, the left calcarine fissure demonstrated powerful covariances with functional areas in both hemispheres, suggesting that it serves as a developmental "anchor" for functional areas in the occipital cortex. These findings support the hypothesis that hemispheric lateralization of function is reflected in the strength of correspondence between cortical surface anatomy and function.

Sex and symmetry differences in hippocampal volumetrics: before and beyond the opening of the crus of the fornix

Published normative volumetrics of the hippocampus (HC) vary substantially. While the protocol suggested by Watson et al. (Neurology 42 (1992) 1743-1750; Arch Neurology 54 (1997) 1521-1531) is the most frequently adhered to, this leaves the posterior section of the HC tail unmeasured, which has been estimated to be in the order of 2-4 mm, representing 5-10% of total HC volume. The objective of the current study was to compare HC volumes according to the method of Watson et al. (Neurology 42 (1992) 1743-1750; Arch Neurology 54 (1997) 1521-1531) against those measured to include the posterior tail section. From a random community sample of 60-64 yr old individuals, 478 subjects underwent magnetic resonance imaging brain scans. Of these, 452 scans (238 males and 214 females) were adequate for hippocampal measurement. The scans comprised whole brain T1- weighted and T2-weighted FLAIR images. One hundred and fifty scans were randomly selected for the measurement of HC volumes beyond the opening of the crus of the fornix by manual tracings on T1-weighted images by a trained operator. Intracranial volume (ICV) and total brain volume (TBV) were measured using an automated program. We found that the posterior HC tail extended for a mean of just over 5 mm and comprised 11% of total HC volume. Males had significantly larger raw HC volumes, and while normalization with ICV or TBV reversed this pattern, it was significant only when the posterior HC tail was included in the measurement. In conclusion, this study showed that including the posterior part of the tail can influence the results of HC measurement. An argument is presented that accurate HC volumes should include the entire HC and not exclude the tail.

Topographic anatomy of the fornix as a guide for the transcallosal-interforniceal approach with a special emphasis on sex differences

The topographic anatomy and morphometry of the fornix is important for standardizing the transcallosal-interforniceal approach and avoiding memory disturbances. The detailed morphometry of the fornix was investigated with a special emphasis on sex differences using midsagittal magnetic resonance imaging of 80 males and 102 females. Various parameters of the fornix, including the length of the upper and lower fornices, the curvature of the upper and lower fornices, and the insertion point of the fornix to corpus callosum, were investigated. The thickness of the fornix at the attachment point to the anterior commissure, the maximum distance to the upper and lower surfaces of the fornix, and the curvature of the upper and lower fornices showed sex differences (p < 0.5). The upper insertion point of the fornix to the corpus callosum was more frontal in females, but the functional relevance of these differences need further investigation.

Predicting memory performance in normal ageing using different measures of hippocampal size

A number of different methods have been employed to correct hippocampal volumes for individual variation in head size. Researchers have previously used qualitative visual inspection to gauge hippocampal atrophy. The purpose of this study was to determine the best measure(s) of hippocampal size for predicting memory functioning in 102 community-dwelling individuals over 80 years of age. Hippocampal size was estimated using magnetic resonance imaging (MRI) volumetry and qualitative visual assessment. Right and left hippocampal volumes were adjusted by three different estimates of head size: total intracranial volume (TICV), whole-brain volume including ventricles (WB+V) and a more refined measure of whole-brain volume with ventricles extracted (WB). We compared the relative efficacy of these three volumetric adjustment methods and visual ratings of hippocampal size in predicting memory performance using linear regression. All four measures of hippocampal size were significant predictors of memory performance. TICV-adjusted volumes performed most poorly in accounting for variance in memory scores. Hippocampal volumes adjusted by either measure of whole-brain volume performed equally well, although qualitative visual ratings of the hippocampus were at least as effective as the volumetric measures in predicting memory performance in community-dwelling individuals in the ninth or tenth decade of life.

Emotional context during encoding of neutral items modulates brain activation not only during encoding but also during recognition

In general, encoding of neutral material includes the context in which the respective material is learned. The effect of emotional context on successfully encoded neutral material has been investigated only recently in few studies, but the main underlying mechanisms are still fairly unknown. In the present study, we investigated the effect of positive and negative emotional context on encoding and later recognition of neutral items. We could demonstrate that brain activation not only during encoding but also during recognition of neutral items depended on the emotional valence of the encoding context. Whereas activation of medial temporal lobe structures during encoding specifically predicted subsequent memory when learning appears in a positive emotional context, activation of the anterior temporal cortex in a region with afferent input to the amygdala predicted memory for material learned in negative context. Recognition of items encoded in positive emotional context revealed activation of hippocampal and medial prefrontal regions, recognition of items encoded in negative emotional context revealed activation of the caudate nucleus. We assume that our findings reflect the recruitment of different brain circuits depending on the emotional context during learning.

MR-based in vivo hippocampal volumetrics: 2. Findings in neuropsychiatric disorders

Magnetic resonance imaging (MRI) has opened a new window to the brain. Measuring hippocampal volume with MRI has provided important information about several neuropsychiatric disorders. We reviewed the literature and selected all English-language, human subject, data-driven papers on hippocampal volumetry, yielding a database of 423 records. Smaller hippocampal volumes have been reported in epilepsy, Alzheimer's disease, dementia, mild cognitive impairment, the aged, traumatic brain injury, cardiac arrest, Parkinson's disease, Huntington's disease, Cushing's disease, herpes simplex encephalitis, Turner's syndrome, Down's syndrome, survivors of low birth weight, schizophrenia, major depression, posttraumatic stress disorder, chronic alcoholism, borderline personality disorder, obsessive-compulsive disorder, and antisocial personality disorder. Significantly larger hippocampal volumes have been correlated with autism and children with fragile X syndrome. Preservation of hippocampal volume has been reported in congenital hyperplasia, children with fetal alcohol syndrome, anorexia nervosa, attention-deficit and hyperactivity disorder, bipolar disorder, and panic disorder. Possible mechanisms of hippocampal volume loss in neuropsychiatric disorders are discussed.

Asymmetries in the hippocampus and amygdala of chimpanzees (Pan troglodytes)

Magnetic resonance imaging was used to measure the hippocampal and amygdalar volumes of 60 chimpanzees (Pan troglodytes). An asymmetry quotient (AQ) was then used to calculate the asymmetry for each of the structures. A one-sample t test indicated that there was a population-level right hemisphere asymmetry for the hippocampus. There was no significant population-level asymmetry for the amygdala. An analysis of variance using sex and rearing history as between-group variables showed no significant main effects or interaction effects on the AQ scores; however, males were more strongly lateralized than females. Several of these findings are consistent with results found in the human literature.

Confirmatory Factor Analysis of the California Verbal Learning Test in Patients With Epilepsy: Relationship to Clinical and Neuropathological Markers of Temporal Lobe Epilepsy

Latent constructs involved in California Verbal Learning Test (D. C. Delis, J. H. Kramer, E. Kaplan, & B. A. Ober, 1987) performance were examined using confirmatory factor analysis in 388 epilepsy surgery candidates. Eight factor models were compared. A single-factor model was examined, along with 7 models accommodating constructs of auditory attention, inaccurate recall, and delayed recall in different combinations. The retained model consisted of 3 correlated factors: Auditory Attention. Verbal Learning, and Inaccurate Recall. Validity of this factor structure was examined in a subsample of patients with left and right temporal lobe epilepsy. All 3 factors were related to seizure focus and magnetic resonance imaging hippocampal volume. Only Verbal Learning was related to hippocampal neuropathology, supporting the distinction between learning and attention in the factor structure.

Amygdalar atrophy in panic disorder patients detected by volumetric magnetic resonance imaging

It has been suggested that the pathophysiology of panic disorder (PD) may involve abnormalities in several brain structures, including the amygdala. To date, however, no study has used quantitative structural neuroimaging techniques to examine amygdalar anatomy in this disorder. Volumetric magnetic resonance imaging (MRI) studies of the amygdalas, hippocampi, and temporal lobes were conducted in 12 drug-free, symptomatic PD patients (six females and six males), and 12 case-matched healthy comparison subjects. Volumetric MRI data were normalized for brain size. PD patients were found to have smaller left-sided and right-sided amygdalar volumes than controls. No differences were found in either hippocampi or temporal lobes. These findings provide new evidence of changes in amygdalar structure in PD and warrant further anatomical and MRI brain studies of patients with this disorder.

Anterior hippocampal volume reduction in male patients with schizophrenia

Quantitative high resolution magnetic resonance imaging (MRI) was utilized to measure anterior, posterior, and total hippocampal volumes in 27 male patients with chronic schizophrenia and 24 male controls. To optimize measurement techniques, hippocampal volumes were: (1) acquired with 1.4-mm slices; (2) excluded with the amygdala; (3) normalized for position; and (4) corrected for total intracranial volume (ICV). The results of a linear mixed effects regression analysis, which made it possible to analyze total anterior and total posterior hippocampal volumes separately, indicated that the anterior hippocampus was significantly smaller in the schizophrenic group relative to the control group. There were no significant group differences with respect to posterior hippocampal volumes, and no significant correlations between hippocampal volumes and illness duration. A significant lateralized asymmetry was also noted in both groups with the right hippocampal volume being larger than the left. These preliminary findings support a significant anterior hippocampal volume reduction in men with schizophrenia as well as a similar hippocampal volume asymmetry in both male controls and schizophrenics.

The human amygdala and the emotional evaluation of sensory stimuli

A wealth of animal data implicates the amygdala in aspects of emotional processing. In recent years, functional neuroimaging and neuropsychological studies have begun to refine our understanding of the functions of the amygdala in humans. This literature offers insights into the types of stimuli that engage the amygdala and the functional consequences that result from this engagement. Specific conclusions and hypotheses include: (1) the amygdala activates during exposure to aversive stimuli from multiple sensory modalities; (2) the amygdala responds to positively valenced stimuli, but these responses are less consistent than those induced by aversive stimuli; (3) amygdala responses are modulated by the arousal level, hedonic strength or current motivational value of stimuli; (4) amygdala responses are subject to rapid habituation; (5) the temporal characteristics of amygdala responses vary across stimulus categories and subject populations; (6) emotionally valenced stimuli need not reach conscious awareness to engage amygdala processing; (7) conscious hedonic appraisals do not require amygdala activation; (8) activation of the amygdala is associated with modulation of motor readiness, autonomic functions, and cognitive processes including attention and memory; (9) amygdala activations do not conform to traditional models of the lateralization of emotion; and (10) the extent and laterality of amygdala activations are related to factors including psychiatric status, gender and personality. The strengths and weakness of these hypotheses and conclusions are discussed with reference to the animal literature.

The human amygdala: a systematic review and meta-analysis of volumetric magnetic resonance imaging

The structure and function of the human amygdala is attracting increasing attention in the scientific literature, particularly since the advent of high resolution magnetic resonance imaging (MRI). We carried out a systematic review of the published literature reporting left and right amygdala volumes from MRI in non-clinical subjects. Our aim was to estimate the normal range of the volume of the amygdala and to account for heterogeneity of the measures. The factors we considered included the detail given regarding various subject factors, the plane of scan acquisition, slice thickness and contiguity, magnet strength, positional and volume correction, and the reliability of measurement. Thirty-nine studies with 51 data sets fulfilled selection criteria. The mean+/-95% confidence interval for the left amygdala volume was 1726.7 mm(3)+/-35.1, and right was 1691.7 mm(3)+/-37.2. The left-right difference did not reach statistical significance. The overall range of reported volumes was 1050 mm(3) to 3880 mm(3). The amygdala is significantly larger in men and shows an inverse correlation with age. The main methodological factor found to influence amygdala measurement was anatomical definition. Studies using 'Watson's criteria' (Neurology 42 (1992) 1743) produced significantly larger volumes than the remainder. An index of study quality revealed an inverse relationship with volume-the higher the quality the smaller the volume. This reflected such factors as slice thickness, correction for brain volume, positional correction and number of subjects. We conclude by putting forward a detailed operationalized anatomical delineation of the amygdala, based on Watson's criteria. This work should guide future research in obtaining accurate and reliable amygdala volume measures which in turn will aid comparisons with clinical groups and the specification of structural-functional relationships.

Relationships among hippocampal volumetry, proton magnetic resonance spectroscopy, and verbal memory in temporal lobe epilepsy

PURPOSE

To examine the relationship between hippocampal volumes, 1H magnetic resonance spectroscopy (MRS)-identified hippocampal metabolic function, and verbal memory in patients with unilateral mesial temporal lobe epilepsy (MTLE).

METHODS

Hippocampal volumes, 1H MRS-derived hippocampal creatine to N-acetylaspartate (Cr/NAA), and verbal memory assessment were obtained preoperatively in 22 patients (six right, 16 left) with EEG-defined unilateral MTLE.

RESULTS

Left hippocampal volume correlated significantly with left hippocampal Cr/NAA (r=-0.549, p < 0.01), whereas right volume correlated significantly with right Cr/NAA (r=-0.478, p < 0.05). Verbal memory correlated significantly with left hippocampal Cr/NAA (r=-0.594, p < 0.01), but not with left hippocampal volume or right hippocampal measures.

CONCLUSIONS

Hippocampal volumes and 1H MRS-derived metabolite ratios are statistically related, but share only a small percentage of variance, suggesting separate but related pathophysiologic processes. Left hippocampal Cr/NAA appears to be more sensitive to verbal memory function than volumes.

Neonatal novelty exposure modulates hippocampal volumetric asymmetry in the rat

Early life environmental manipulations have been shown to affect hippocampal-dependent learning, hippocampal volume and cerebral lateralization. In this study, we investigated the effects of neonatal stimulation on hippocampal volumetric asymmetry. Long-Evans hooded rats were exposed to a novel non-home environment 3 min daily for the first 3 weeks of life. Histological measures of the left and right hippocampus were made at 8 months of age. We found that neonatal novelty exposure resulted in a long-lasting change in hippocampal volumetric asymmetry. Specifically, this brief and transient early life stimulation increased the right hippocampal volumetric dominance at mid-adulthood.

Verbal retention lateralizes patients with unilateral temporal lobe epilepsy and bilateral hippocampal atrophy

PURPOSE

To examine the lateralization utility of preoperative verbal retention in patients with and without bilateral hippocampal atrophy.

METHODS

The sample consisted of 74 patients with EEG-defined unilateral temporal lobe epilepsy (TLE) who had also undergone volumetric magnetic resonance imaging (MRI). Verbal retention was operationalized by the Logical Memory percentage retention subtest (LM%) of the Wechsler Memory Scale. Patients were divided into groups with (a) bilaterally normal hippocampal volumes, (b) unilateral atrophy, or (c) bilateral atrophy. Two different thresholds (empirically derived vs. normative) were used to lateralize on the basis of LM%. LM% lateralization was then examined by group using chi2, sensitivity, positive predictive values, and odds ratios. Analyses were also conducted separately in the subset of patients who were seizure free after surgery.

RESULTS

Mean LM% performance was significantly lower in patients with left versus right TLE in the subset with bilateral hippocampal atrophy (p = 0.018), but not in patients with a normal MRI (p = 0.918) or unilateral atrophy (p = 0.087). The odds of a correct lateralization by LM% increased from 1.67 in patients with normal MRI to 36.11 in patients with bilateral hippocampal atrophy. The power of a right and left lateralization prediction by LM% was 100% and 75%, respectively, in patients with bilateral hippocampal atrophy. Similar results were obtained when analysis was restricted to patients who were seizure free after surgery.

CONCLUSIONS

Preoperative verbal retention as measured by LM% may provide meaningful lateralization information in patients who are difficult to lateralize via MRI.

Hippocampal volume discriminates between normal cognition; questionable and mild dementia in the elderly

The sensitivity of MRI volumetric measures to detect cognitive dysfunction is examined in 39 participants of an epidemiological field study (age 75-85, MMSE 19-30). According to Clinical dementia rating (CDR), 17 subjects had normal cognition (CDR 0), 12 had questionable (CDR 0.5) and 10 mild dementia (CDR 1). Discriminant analysis based on four hippocampal measures resulted in a correct classification of 76.9% of all subjects. Left-sided and posterior hippocampal measures were more responsible for group discrimination than right-sided and anterior measures. In CDR 0.5, a significant hippocampal volume reduction of 14.3% vs.11.3% (left vs. right) relative to normal was found. The right hippocampus was significantly greater than the left in CDR 0 and CDR 0.5, but not in CDR 1. The magnitude of non-directional hippocampal asymmetry increased with decreasing cognitive state. We conclude that hippocampal atrophy is sensitive to detect cognitive dysfunction and subjects at risk for Alzheimer's disease in the elderly population.

Evidence of a smaller left hippocampus and left temporal horn in both patients with first episode schizophrenia and normal control subjects

Findings from cerebral magnetic resonance imaging (MRI) studies in schizophrenia indicating temporal lobe involvement have been inconsistent and controversial. In a prospective study, we quantified the volumes of temporal lobe structures in 20 male patients with first episode schizophrenia (FES; mean+/-S.D.=27.4+/-4. 8 years) and 20 healthy age-matched male control subjects (27.7+/-3. 1 years). Measurements were performed on contiguous 2.2-mm coronal MRI slices, which included, as well as the temporal lobe, the amygdala, the hippocampal formation, and the temporal horn of the lateral ventricle. The definition of the borders of the structures relied on measurement guidelines derived from mutual comparisons of MRI and histological data. The definition of the hippocampus-amygdala interface was also validated in a correlated triplanar display. We did not detect any significant volume reductions of the measured structures in the FES group, as compared with healthy control subjects, on either side. Comparisons within groups, however, revealed that in both the patients and the healthy volunteers the hippocampal formations showed a significant right-sided bias (+9%, P=0.004, in the FES group; +12%, P=0.0003 in the control subjects). A significant volume difference in favor of the right hemisphere was also observed in the temporal horns of the lateral ventricles (+17%, P=0.02 in the patients with FES; +34%, P=0. 003, in the control group). There was only a nonsignificant trend for a larger temporal horn on the left side in patients with schizophrenia as compared with the control subjects. Our findings do not indicate a loss or reversal of the normal volume asymmetry pattern in the FES group.

Lateralization of temporal lobe epilepsy (TLE) and discrimination of TLE from extra-TLE using pattern analysis of magnetic resonance spectroscopic and volumetric data

PURPOSE

To examine whether or not pattern analysis of magnetic resonance volumetric (MRVol) and proton magnetic resonance spectroscopic imaging (1H-MRSI) data would enable (a) the accurate lateralization of temporal lobe epilepsy (TLE) and (b) the discrimination of TLE from extratemporal epilepsy (E-TLE).

METHODS

For lateralization analysis, we used data from 150 nonforeign tissue lesional TLE patients [88 left-sided (L-TLE), 46 right-sided (R-TLE), and 16 bilateral (Bi-TLE)]. For the discrimination of TLE from E-TLE, we used data from 174 patients (145 with unilateral TLE, 14 with unilateral E-TLE, and 15 with widespread epileptogenic zones involving both the TL and extra-TL regions-multilobar epilepsy). A series of "leave-one-out" cross-validated linear discriminant analyses were performed using the MRVol and 1H-MRSI data sets to lateralize TLE and discriminate it from E-TLE.

RESULTS

Lateralization: The leave-one-out linear discriminant analyses were able to correctly lateralize (with a posterior probability >0.50) 120 (90%) of the 134 L-TLE and R-TLE patients. Imposing higher posterior probability (>0.95) increased accuracy of lateralization to 98%, with only two discordant cases who underwent surgery on the side of electroencephalogram, and both had bad outcome. Discrimination: the leave-one-out linear discriminant analyses were able to correctly classify (with a posterior probability >0.50) 142 (89%) of the 159 TLE and E-TLE patients. Accuracy increased slightly as higher posterior probability cutoffs were imposed, with fewer patients being classified.

CONCLUSIONS

Pattern analysis of 1H-MRSI and MRVol data can accurately lateralize TLE. Discriminating TLE from E-TLE was less accurate, probably due to the presence of temporal lobe damage in some patients with E-TLE reflecting dual pathology.

Gender, Memory, and Hippocampal Volumes: Relationships in Temporal Lobe Epilepsy

Previous research has suggested bilateral hippocampal support for verbal memory in women with early left-hemisphere injury and that women experience better verbal memory outcome following anterior temporal lobectomy (ATL). The present study investigated two issues: (1) Do women have better verbal memory outcome following ATL compared with men? (2) Are verbal memory abilities differentially supported by the right and left hippocampus in males and females? Verbal memory performance [Wechsler Memory Scale: Logical Memory (LM) savings score] was assessed in 70 patients who underwent ATL. MRI volumetric measurements of the left and right hippocampus were performed. No LM savings score difference was found between groups preoperatively although a statistically significant gender effect (P < 0.04) was found for postoperative LM savings scores. Females displayed better postoperative memory performance, regardless of side of surgery. Preoperative verbal memory performance was not associated with right or left hippocampal volumes in either left or right ATL females, although the right hippocampus was positively associated with memory performance for left ATL males. Hippocampal volumes were not associated with postoperative LM savings scores for any group. Results suggest that prose recall was only modestly influenced by gender and that bilateral hippocampal support for prose recall was not present in our female patients.

Hippocampal asymmetries and white matter abnormalities on MRI in benign childhood epilepsy with centrotemporal spikes

PURPOSE

To look for brain abnormalities by using magnetic resonance imaging (MRI) in patients with benign childhood epilepsy with centrotemporal spikes (BCECTS), which is the most common epilepsy syndrome in children.

METHODS

Eighteen children, aged 6-12 years, with typical BCECTS were examined with MRI, six of them twice.

RESULTS

Some hippocampal abnormality was found in six (33%) of the children, all with the syndrome's typical electroencephalogram (EEG) pattern ipsilaterally. Hippocampal size asymmetry was found in five (28%) children (right side < left in two and left < right in three), and high signal intensities on T2-weighted images were found in three (17%). Two children also had other abnormalities; one had a heterotopic nodule near the contralateral frontal horn, and one had an Arnold-Chiari malformation. The hippocampal asymmetry remained unchanged in three of the children who were reexamined after 2 years. High signal intensities on T2-weighted images were seen beneath the cortex-white matter junction in the frontal and temporal lobes of five (28%) children, one of whom also had a hippocampal asymmetry. MRIs were normal in eight (44%) children.

CONCLUSION

For the first time, hippocampal asymmetries and white-matter abnormalities have been detectable on the MRIs of children with typical BCECTS. The etiology of the former is unclear, whereas the latter may be a result of a maturational delay involving a defective myelination. Long-term follow-up studies are needed to evaluate the relation between these findings and the clinical course of BCECTS.