Loss of nonphosphorylated neurofilament immunoreactivity in temporal cortical areas in Alzheimer's disease

The distribution of immunoreactive neurons with nonphosphorylated neurofilament protein (SMI32) was studied in temporal cortical areas in normal subjects and in patients with Alzheimer's disease (AD). SMI32 immunopositive neurons were localized mainly in cortical layers II, III, V and VI, and were medium to large-sized pyramidal neurons. Patients with AD had prominent degeneration of SMI32 positive neurons in layers III and V of Brodmann areas 38, 36, 35 and 20; in layers II and IV of the entorhinal cortex (Brodmann area 28); and hippocampal neurons. Neurofibrillary tangles (NFTs) were stained with Thioflavin-S and with an antibody (AT8) against hyperphosphorylated tau. The NFT distribution was compared to that of the neuronal cytoskeletal marker SMI32 in these temporal cortical regions. The results showed that the loss of SMI32 immunoreactivity in temporal cortical regions of AD brain is paralleled by an increase in NFTs and AT8 immunoreactivity in neurons. The SMI32 immunoreactivity was drastically reduced in the cortical layers where tangle-bearing neurons are localized. A strong SMI32 immunoreactivity was observed in numerous neurons containing NFTs by double-immunolabeling with SMI32 and AT8. However, few neurons were labeled by AT8 and SMI32. These results suggest that the development of NFTs in some neurons results from some alteration in SMI32 expression, but does not account for all, particularly, early NFT-related changes. Also, there is a clear correlation of NFTs with selective population of pyramidal neurons in the temporal cortical areas and these pyramidal cells are specifically prone to formation of paired helical filaments. Furthermore, these pyramidal neurons might represent a significant portion of the neurons of origin of long corticocortical connection, and consequently contribute to the destruction of memory-related input to the hippocampal formation.

Modular and laminar pathology of Brodmann's area 37 in Alzheimer's disease

Previous studies suggested a relationship between severity of symptoms and the degree of neurofibrillary tangles (NFTs) clustering in different areas of the cortex in Alzheimer's disease (AD). The posterior inferior temporal cortex or Brodmann's area (BA 37) is involved in object naming and recognition memory. But the cellular architecture and connectivity and the NFT pathology of this cortex in AD received inadequate attention. In this report, we describe the laminar distribution and topography of NFT pathology of BA 37 in brains of AD patients by using Thionin staining for Nissl substance, Thioflavin-S staining for NFTs, and phosphorylated tau (AT8) immunohistochemistry. NFTs mostly occurred in cortical layers II, III, V and VI in the area 37 of AD brain. Moreover, NFTs appeared like a patch or in cluster pattern along the cortical layers III and V and within the columns of pyramidal cell layers. The abnormal, intensely labeled AT8 immunoreactive cells were clustered mainly in layers III and V. Based on previously published clinical correlations between cognitive abnormalities in AD and the patterns of laminar distributed NFT cluster pathology in other areas of the brain, we conclude that a similar NFT pathology that severely affected BA 37, may indicate disruption of some forms of naming and object recognition-related circuits in human AD.

Posterior parahippocampal gyrus pathology in Alzheimer's disease

The posterior parahippocampal gyrus (PPHG) of the non-human primate brain has a distinct dual role in cortical neural systems. On the one hand, it is a critical link in providing the entorhinal cortex and hippocampal formation with cortical input, while on the other hand it receives output from these structures and projects widely by disseminating the medial temporal lobe output to the cortex. Layer III of TF and TH areas largely mediate the former (input) while layer V mediates the latter (output). We have examined areas TF and TH in the normal human brain and in Alzheimer's disease (AD) using pathological stains (Nissl, Thioflavin S) and phenotype specific stains non-phosphorylated neurofilament protein (SMI32) and parvalbumin (PV). Seven clinically and pathologically confirmed AD cases have been studied along with six age-compatible normal cases. Our observations reveal that neurofibrillary tangles (NFTs) heavily invest the area TF and TH neurons that form layers III and V. In both cortical areas, the large pyramids that form layer V contain a greater number of NFTs. These changes, and possibly, pyramidal cell loss, greatly alter the cytoarchitectural picture and diminish SMI32 staining patterns. Layer III of area TH loses the majority of SMI32 immunoreactivity, whereas this change is more conspicuous in layer V of area TF. PV-staining in both areas is largely unaffected. Normal cases contained no evidence of pathology or altered cytoarchitecture. These observations reveal a further disruption of memory-related temporal neural systems in AD where pathology selectively alters both the input to the hippocampal formation and its output to the cortex.

Prefrontal cortex in humans and apes: a comparative study of area 10

Area 10 is one of the cortical areas of the frontal lobe involved in higher cognitive functions such as the undertaking of initiatives and the planning of future actions. It is known to form the frontal pole of the macaque and human brain, but its presence and organization in the great and lesser apes remain unclear. It is here documented that area 10 also forms the frontal pole of chimpanzee, bonobo, orangutan, and gibbon brains. Imaging techniques and stereological tools are used to characterize this area across species and provide preliminary estimates of its absolute and relative size. Area 10 has similar cytoarchitectonic features in the hominoid brain, but aspects of its organization vary slightly across species, including the relative width of its cortical layers and the space available for connections. The cortex forming the frontal pole of the gorilla appears highly specialized, while area 10 in the gibbon occupies only the orbital sector of the frontal pole. Area 10 in the human brain is larger relative to the rest of the brain than it is in the apes, and its supragranular layers have more space available for connections with other higher-order association areas. This suggests that the neural substrates supporting cognitive functions associated with this part of the cortex enlarged and became specialized during hominid evolution.

The selective vulnerability of brainstem nuclei to Alzheimer's disease

In a study of thioflavin S-stained serial sections from the entire brainstem, we found that the inferior and superior colliculi and the autonomic, monoaminergic, cholinergic, and classical reticular nuclei were affected with varying degrees of severity and frequencies in 32 patients with Alzheimer's disease, whereas no changes were seen in the brainstems of 26 control subjects. The majority of the affected nuclei in patients with Alzheimer's disease exhibit either neurofibrillary tangles or senile plaques, and only a few display both. However, when sections were immunostained with the antibodies 10D5 and AT8 or ALZ50, both beta-amyloid and hyperphosphorylated epitopes of tau protein were found to be present in various concentrations in all the affected nuclei. Our findings suggest that each brainstem nucleus has a distinct vulnerability to Alzheimer's disease-related pathological changes. Given that each nucleus has idiosyncratic neuroanatomical connections and prevailing neurochemical characteristics, the heterogeneous collection of brainstem nuclei can be considered a suitable anatomical ground for further investigation of selective vulnerability in Alzheimer's disease. The finding of severe pathological changes in some brainstem nuclei also raises the possibility that the dysfunction of these nuclei may contribute to the cognitive defects and increased rates of morbidity and mortality in patients with Alzheimer's disease.

Selective pathological changes of the periaqueductal gray matter in Alzheimer's disease

The periaqueductal gray matter (PAG) is a major neuroanatomical component of the brainstem and has pivotal roles in autonomic functions, behavior, and cognition, most notably in the processing of emotions and feelings. In a study of 32 brains obtained from patients with Alzheimer's disease (AD), thioflavin S-stained sections from the PAG contained major pathological changes in 81% of cases. These changes were absent in all 26 control brains (13 from normal subjects and 13 from non-AD patients). In the AD cases, both sides of the PAG were affected symmetrically; in 72%, there were only senile plaques, but there were both senile plaques and neurofibrillary tangles in 9%. Using immunohistochemical methods with 10D5, ALZ-50, and AT8 antibodies, we also established the presence of beta-amyloid peptide and abnormally phosphorylated tau protein in the PAG. Furthermore, we found that the type and density of pathological changes were expressed differently in different PAG regions and correlated with gender and the duration of dementia. These findings constitute a first step in documenting the selective changes of PAG in AD. The compartmentalized pattern of AD changes in PAG also reveals for the first time the columnar organization of PAG in human subjects.

The parahippocampal gyrus in Alzheimer's disease. Clinical and preclinical neuroanatomical correlates

The human parahippocampal gyrus forms a large part of the limbic lobe along the ventromedial part of the temporal cortical mantle. It is a variable and complicated cortex in terms of structure, and the latter is aggravated further by interfaces with the anterior insula anteriorly and the cingulate gyrus and occipital lobe posteriorly. Additional complications relate to its lateral border with the temporal cortex and especially the sulcal configurations that define this junction. The rhinal sulcus, which separates parahippocampal and temporal cortices in other species, including the anthropoid apes, is either lacking or rudimentary in the human brain. Thus, defining this junction requires cytoarchitectural examination and precludes the use of mere inspection of sulcal existing patterns. The cortical areas that form the parahippocampal gyrus are vulnerable to pathological changes in Alzheimer's disease (AD), and its entorhinal and perirhinal subdivisions are both the most heavily damaged cortical areas and the focus for disease onset. The neurons that acquire neurofibrillary tangles (NFTs) occupy the junction of the isocortical mantle with the limbic cortical mantle, but share, or partially share, a vulnerability phenotype with large neurons in both domains. The differential expression of this phenotype across time creates the false impression of NFT spread in cross-sectional comparisons of AD brains. The questions of what this phenotype is and why it is expressed first in the perirhinal and entorhinal cortices of the parahippocampal gyrus are the central molecular biological/neuroanatomical questions in understanding the etiology of AD.

Orbitofrontal cortex pathology in Alzheimer's disease

The orbitofrontal cortex has been examined in Alzheimer's disease (AD) from the viewpoint of neurofibrillary tangle (NFT) pathology, its laminar distribution and topography. NFT pathology in the orbitofrontal cortex is extensive in AD. In cases with extensive cortical pathology, NFTs extend from the pole of the frontal lobe to the orbitoinsular junction. In lesser affected cases, the anterior granular part of the orbital cortex is less invested by NFTs. Layers III and V contain the greatest density of NFTs and these are most dense in the dysgranular areas, posterior to the transverse orbital sulcus. Posterior and medial orbitofrontal areas, forming area 13 and the posterior tip of the paraolfactory gyrus, are the most severely damaged, as are the smaller agranular fields that surround the olfactory tract and cortex. The widespread orbitofrontal damage in AD affecting projection neurons suggests that this pathology may contribute heavily to the many non-memory-related behavior changes observed in this disorder.

Localization of area prostriata and its projection to the cingulate motor cortex in the rhesus monkey

Area prostriata is a poorly understood cortical area located in the anterior portion of the calcarine sulcus. It has attracted interest as a separate visual area and progenitor for the cortex of this modality. In this report we describe a direct projection from area prostriata to the rostral cingulate motor cortex (M3) that forms the fundus and lower bank of the anterior part of the cingulate sulcus. Injections of retrograde tracers in M3 resulted in labeled neurons in layers III, V and VI of prostriate cortex. However, injections of anterograde tracers in M3 did not demonstrate axon terminals in area prostriata. This connection was organized topographically such that the rostral part of M3 received input from the dorsal region of prostriate cortex, whereas middle and caudal levels of M3 received input from more ventral locations. Injections of retrograde and anterograde tracers in the caudal cingulate motor cortex (M4) did not produce labeling in prostriate cortex. Cytoarchitectural analysis confirmed the identity of area prostriata and further clarified its extent and borders with the parasubiculum of the hippocampal formation rostrally, and V1 of the visual cortex caudally. This linkage between cortex bordering V1 and cortex giving rise to a component of the corticofacial and corticospinal pathways demonstrates a more direct visuomotor route than visual association projections coursing laterally.

Ventromedial temporal lobe pathology in dementia, brain trauma, and schizophrenia

The ventromedial temporal area contains numerous anatomical structures collectively or selectively involved in a wide range of neurological and psychiatric disorders. Collective involvement is exemplified best by Alzheimer's disease where a host of anatomical structures and a host of cognitive and behavioral changes are manifested. Selective disease of the amygdala can yield deficits in the ability to judge and evaluate emotional expressions. While memory functions are nearly synonymous with the concept of ventromedial temporal area, they overshadow other functions associated with the diverse anatomical structures in this part of the brain. For example, it could be argued that in addition to output directed toward the hippocampal formation, the output of the ventromedial temporal area is equally strong to the ventral striatopallidal system of the basal forebrain. Denervation of these structures could be associated with the behavioral changes that occur in tandem with the memory-related changes of ventromedial temporal lobe pathology. Here we explore the anatomical and pathological correlate associated with ventromedial temporal area pathology and consider how these may impact on ventral striatopallidal conceptualizations. We conclude that ventromedial temporal area pathology deprives the basal forebrain of multimodal association information from the endstages of corticocortical sensory processing. This endstage information carries with it an analysis of real-time sensory awareness, historical-time or past sensory experiences, and decisions from hippocampal output structures regarding relevancy and novelty. In this sense, basal forebrain structures are in a unique position to regulate behavioral responses to a wide range of stimuli and to organize appropriate emotional, motor, autonomic, and endocrine responses to them.

Some temporal and parietal cortical connections converge in CA1 of the primate hippocampus

Large sectors of polymodal cortex project to the hippocampal formation via convergent input to the entorhinal cortex. The present study reports an additional access route, whereby several cortical areas project directly to CA1. These are parietal areas 7a and 7b, area TF medial to the occipitotemporal sulcus (OTS), and a restricted area in the lateral bank of the OTS that may be part of ventromedial area TE. These particular cortical areas are implicated in visuospatial processes; and their projection to and convergence within CA1 may be significant for the elaboration of 'view fields', for the postulated role of the hippocampal formation in topographic learning and memory, or for the snapshot identification of objects in the setting of complex visuospatial relationships. Convergence of vestibular and visual inputs (from areas 7b and 7a respectively) would support previous physiological findings that hippocampal neurons respond to combinations of whole-body motion and a view of the environment. The direct corticohippocampal connections are widely divergent, especially those from the temporal areas, which extend over much of the anteroposterior axis of the hippocampal main body. Divergent connections potentially influence large populations of CA1 pyramidal neurons, consistent with the suggestion that these neurons are involved in conjunctive coding. The same region of ventromedial TE, besides the direct connections to CA1, also gives rise to direct projections to area V1, and may correspond to a functionally specialized subdivision, perhaps part of VTF.

Severe pathological changes of parabrachial nucleus in Alzheimer's disease

In the first of a series of studies aimed at mapping brain stem pathological changes in patients with Alzheimer's disease (AD), we report a new finding regarding the parabrachial nucleus (PBN), a unit of paramount importance in the relay and integration of visceral and nociceptive information as well as in homeostatic control. The brains of 20 patients with AD were surveyed. The PBN contained pervasive neuropathological changes in 100% of the brains from those with early-onset dementia and in 80% from those with late-onset dementia. These changes were entirely absent in all 10 normal controls. The pathological changes of PBN, would cause autonomic dysfunction in patients with AD and perhaps contribute to the disproportionate mortality encountered in these patients.

Multivariate analysis of laminar patterns of neurodegeneration in posterior cingulate cortex in Alzheimer's disease

Posterior cingulate cortex is the site of earliest reductions in glucose metabolism and qualitatively different laminar patterns of neurodegeneration in Alzheimer's disease (AD). This study used multivariate analyses of area 23 in 72 cases of definite AD to assess relationships between laminar patterns of neurodegeneration, neurofibrillary tangle (NFT) and senile plaque (SP) densities, age of disease onset and duration, and apolipoprotein E (ApoE) genotype. No age-related changes in neurons occurred over four decades in 17 controls and regression analysis of all AD cases showed no relationships between neuron, SP, and tau-immunoreactive NFT densities. Principal components analysis of neurons in layers III-Va and eigenvector projections showed five subgroups. The subgroups were independent because each had a full range of disease durations and qualitatively different laminar patterns in degeneration suggested disease subtypes (ST). Cases with most severe neuron losses (STSevere) had an early onset, most SP, and highest proportion of ApoE epsilon4 homozygotes. Changes in the distribution of NFT were similar over disease course in two subtypes and NFT did not account for most neurodegeneration. In STII-V with moderate neuron loss in most layers, cases with no NFT had a disease duration of 3.5 +/- 0.9 years (mean +/- SEM), those with most in layers IIIc or Va had a duration of 7.3 +/- 1 years, and those with most in layers II-IIIab had a duration of 12.1 +/- 1 years. In STSevere, cases with highest NFT densities in layers II-IIIab also were late stage. Finally, epsilon4 homozygotes were most frequent in STSevere, but four statistical tests showed that this risk is not directly involved in neurodegeneration. In conclusion, multivariate pattern recognition shows that AD is composed of independent neuropathological subtypes and NFT in area 23 do not account for most neuron losses.

Limbic frontal cortex in hominoids: a comparative study of area 13

The limbic frontal cortex forms part of the neural substrate responsible for emotional reactions to social stimuli. Area 13 is one of the cortical areas long known to be part of the posterior orbitofrontal cortex in several monkey species, such as the macaque. Its presence nevertheless in the human brain has been unclear, and the cortex of the frontal lobe of the great and lesser apes remains largely unknown. In this study area 13 was identified in human, chimpanzee, bonobo, gorilla, orangutan, and gibbon brains, and cortical maps were generated on the basis of its cytoarchitecture. Imaging techniques were used to characterize and quantify the microstructural organization of the area, and stereological tools were applied for estimates of the volume of area 13 in all species. Area 13 is conservative in its structure, and features such as size of cortical layers, density of neurons, and space available for connections are similar across hominoids with only subtle differences present. In contrast to the homogeneity found in its organization, variation is present in the relative size of this cortical area (as a percentage of total brain volume). The human and the bonobo include a complex orbitofrontal cortex and a relatively smaller area 13. On the contrary the orangutan stands out by having a shorter orbitofrontal region and a more expanded area 13. Differences in the organization and size of individual cortical areas involved in emotional reactions and social behavior can be related to behavioral specializations of each hominoid and to the evolution of emotions in hominids.

Convergence of limbic input to the cingulate motor cortex in the rhesus monkey

Limbic system influences on motor behavior seem widespread, and could range from the initiation of action to the motivational pace of motor output. Motor abnormalities are also a common feature of psychiatric illness. Several subcortical limbic-motor entry points have been defined in recent years, but cortical entry points are understood poorly, despite the fact that a part of the limbic lobe, the cingulate motor cortex (area 24c or M3, and area 23c or M4), contributes axons to the corticospinal pathway. Using retrograde and anterograde tracers in rhesus monkeys, we investigated the ipsilateral limbic input to area 24c and adjacent area 23c. Limbic cortical input to areas 24c and 23c arise from cingulate areas 24a, 24b, 23a, 23b, and 32, retrosplenial areas 30 and 29, and temporal areas 35, TF and TH. Areas 24c and 23c were also interconnected strongly. The dysgranular part of the orbitofrontal cortex and insula projects primarily to area 24c while the granular part of the orbitofrontal cortex and insula projects primarily to area 23c. Afferents from cingulate area 25, the retrocalcarine cortex, temporal pole, entorhinal cortex, parasubiculum, and the medial part of area TH target primarily or only area 24c. Our findings indicate that a variety of telencephalic limbic afferents converge on cortex lining the lower bank and fundus of the anterior part of the cingulate sulcus. Because it is known that this cortex gives rise to axons ending in the spinal cord, facial nucleus, pontine gray, red nucleus, putamen, and primary and supplementary motor cortices, we suggest that the cingulate motor cortex forms a strategic cortical entry point for limbic influence on the voluntary motor system.

Autosomal dominant dementia with widespread neurofibrillary tangles

Several familial dementing conditions with atypical features have been characterized, but only rarely is the neuropathology dominated solely by neurofibrillary lesions. We present a Midwestern American pedigree spanning four generations in which 15 individuals were affected by early-onset dementia with long disease duration, with an autosomal dominant inheritance pattern, and with tau-rich neurofibrillary pathology found in the brain post mortem. The average age at presentation was 55 years with gradual onset and progression of memory loss and personality change. After 30 years' disease duration, the proband's neuropathologic examination demonstrated abundant intraneuronal neurofibrillary tangles (NFTs) involving the hippocampus, pallidum, subthalamic nucleus, substantia nigra, pons, and medulla. Only sparse neocortical tangles were present and amyloid plaques were absent. The tangles were recognized by antibodies specific for phosphorylation-independent (Tau-2, T46, 133, and Alz-50) and phosphorylation-dependent epitopes (AT8, T3P, PHF-1, 12E8, AT6, AT18, AT30) in tau proteins. Electron microscopy of NFTs in the dentate gyrus and midbrain demonstrated paired helical filaments. Although the clinical phenotype resembles Alzheimer's disease, and the neuropathologic phenotype resembles progressive supranuclear palsy, an alternative consideration is that this familial disorder may be a new or distinct disease entity.

Ventromedial temporal lobe anatomy, with comments on Alzheimer's disease and temporal injury

The ventromedial temporal area has a complicated topography and neuroanatomy that has yielded secrets only grudgingly. The major features of surface topography are reviewed here as well as recent neuroanatomical findings that establish the ventromedial temporal area as both a recipient of cortical input and the origin for widespread output back to the cortex. The devastating involvement of all ventromedial temporal areas in Alzheimer's disease is highlighted, and comments are offered on the tentorium cerebelli and on mechanical injury to the area.

The evolution of the frontal lobes: a volumetric analysis based on three-dimensional reconstructions of magnetic resonance scans of human and ape brains

Scenarios regarding the evolution of cognitive function in hominids depend largely on our understanding of the organization of the frontal lobes in extant humans and apes. The frontal lobe is involved in functions such as creative thinking, planning of future actions, decision making, artistic expression, aspects of emotional behavior, as well as working memory, language and motor control. It is often claimed that the frontal lobe is disproportionately larger in humans than in other species, but conflicting reports exist on this issue. The brain of the apes in particular remains largely unknown. In this report we measure the volume of the frontal lobe as a whole and of its main sectors (including cortex and immediately underlying white matter) in living humans, and in post-mortem brains of the chimpanzee, gorilla, orang-utan, gibbon and the macaque using three-dimensional reconstructions of magnetic resonance (MR) scans of the brain. On the basis of these data we suggest that although the absolute volume of the brain and the frontal lobe is largest in humans, the relative size of the frontal lobe is similar across hominoids, and that humans do not have a larger frontal lobe than expected from a primate brain of the human size. We also report that the relative size of the sectors of the frontal lobe (dorsal, mesial, orbital) is similar across the primate species studied. Our conclusions are preliminary, because the size of our sample, although larger than in previous studies, still remains small. With this caveat we conclude that the overall volume of the frontal lobe in hominids enlarged in absolute size along with the rest of the brain, but did not become relatively larger after the split of the human line from the ancestral African hominoid stock. Aspects other than relative volume of the frontal lobe have to be responsible for the cognitive specializations of the hominids.

The autonomic-related cortex: pathology in Alzheimer's disease

Alzheimer's disease (AD) causes progressive deterioration of cognition and behavior. Memory dysfunction is the hallmark, but there are also changes in behavior, emotion and autonomic functions, which cannot be explained simply as a consequence of memory impairment. These observations suggest that the natural disease process of AD involves not only memory-related neural structures, but also specific neural systems related to other behaviors, emotion and autonomic functions. Since recent evidence has indicated a primary role for ventromedial frontal (VMF) cortex in such functions, we examined laminar distribution of neurofibrillary tangles and Alz 50 immunoreactive neurons in subdivisions of VMF cortex in 20 AD patients and seven age-matched controls. The densities of pathological changes were: (i) highest in the posteromedial mesocortical regions, particularly Brodmann's area 25 (A25), posterior orbitofrontal cortex (POF) and anterior insula (AI); (ii) of comparable severity between posteromedial mesocortical regions and most temporal cortices, excluding only the entorhinal cortex and temporal pole; and (iii) located predominantly in layer III and especially layer V. Further analysis demonstrated selective pathology in layer V of A25, POF and AI that would disrupt direct cortico-autonomic projections. This is the first study to detail severe AD pathology in these autonomic-related cortices, which could contribute to the behavioral changes, emotional disturbance and autonomic dysregulation that often accompany AD.

Contingent vulnerability of entorhinal parvalbumin-containing neurons in Alzheimer's disease

Calcium-binding proteins containing local circuit neurons are distributed ubiquitously in the human cerebral cortex where they colocalize with a subpopulation of cells that contain GABA. Several reports using a variety of pathological models, including Alzheimer's disease (AD), have suggested that cells containing calcium-binding proteins are resistant to pathological insults. In this report, we test the hypothesis that AD pathology can differentially affect parvalbumin-containing cells depending on their location in the entorhinal cortex and the state of projection neurons with which they are associated. Using cases with different quantities of AD pathology, we determined the density of immunostaining for parvalbumin in the entorhinal cortex, and we correlated this with the concomitant pathological lesions in the various layers of this cortex. Our results show a clear decrease in parvalbumin immunostaining in some parts of the entorhinal cortex when AD neuropathological markers are present. As the density of pathological markers in the entorhinal cortex becomes greater and more widespread, there is a decrease of parvalbumin immunostaining in additional layers, although in all cases, some cells persist. Parvalbumin-containing neurons are clearly vulnerable in AD, but not because of neurofibrillary tangle formation. Instead, they are rendered vulnerable only after substantial loss of projection neurons; only then do they, too, become part of the lesion.

Distinctive forms of partial retrograde amnesia after asymmetric temporal lobe lesions: possible role of the occipitotemporal gyri in memory

We tested the hypothesis that partial forms of retrograde amnesia were associated with highly asymmetric lesions to the inferior and anterior-medial temporal lobe. Postencephalitic subjects EK and DR were both impaired on standardized retrograde memory tests, but showed strikingly different profiles in cognitive tasks of name stem completion, name:face matching, temporal ordering, forced choice recognition, and occupational judgments of famous names and faces from the past 3 decades. EK sustained left inferior and anterior-medial temporal lobe lesion with a small right temporal polar lesion, and showed near-complete loss of retrieval, knowledge, and familiarity associated with famous names but minimal deficiencies with famous faces. DR sustained right inferior and anterior-medial temporal lobe lesion and showed a milder retrograde loss limited to utilizing famous face prompts in name stem completion, name:face matching, occupational judgments, and forced choice recognition. These impairments were also different from the memory retrieval deficit, but intact recognition shown by a case of ruptured anterior communicating artery aneurysm with presumed basal forebrain damage. We hypothesize that EK's extensive loss of famous name knowledge was related to left inferior temporal lobe damage, particularly in the lateral and medial occipitotemporal gyri. This region in the left temporal lobe may serve as a critical processing area for retrograde memory that permits activation of established semantic, temporal, and visual (i.e., facial) associations biographically dependent on the category of proper names. On the basis of connectional anatomy patterns in the nonhuman primate, this region receives extensive hippocampal output and is interconnected with the temporal polar region and cortical association areas, which have been implicated in retrieval and storage aspects of retrograde memory. In the right hemisphere, the occipitotemporal gyri may serve an important role in famous face processing as part of a bilateral neural network.

Entorhinal cortex modules of the human brain

Much is known about modular organization in the cerebral cortex, but this knowledge is skewed markedly toward primary sensory areas, and in fact, it has been difficult to demonstrate elsewhere. In this report, we test the hypothesis that a unique form of modules exists in the entorhinal area of the human cortex (Brodmann's area 28). We examined this issue using classic cyto- and myeloarchitectonic stains, immunolabeling for various neurochemicals, and histochemistry for certain enzymes. The findings reveal that the entorhinal cortex in the human is formed by a mosaic of cellular aggregates whose most conspicuous elements are the cell islands of layer II and myelinated fibers around the cell islands, the disposition of glutamic acid decarboxylase-positive neurons and processes, cytochrome oxidase staining, and the pattern of cholinergic afferent fibers. The neuropathology of Alzheimer's disease cases highlights the modules, but inversely so, by destroying their features. The findings are of interest because 1) anatomically defined modules are shown to be present in areas other than the sensory and motor cortices, 2) the modules are morphological entities likely to reflect functions of the entorhinal cortex, and 3) the destruction of entorhinal cortex modules may account disproportionately for the severity of memory impairments in Alzheimer's disease.

Anatomy of the medial temporal lobe

The medial temporal lobe concept is an example of neurojargon rich in clinical and behavioral meaning, but sparse in neuroanatomical meaning except for topography. Like the concept of anterior speech area, many know roughly where it is located and what its functional correlates are, but not a lot else. At least three anatomical entities qualify as components of the medial temporal lobe. These include the amygdaloid body, the hippocampal formation, and the parahippocampal cortices that cover them superficially and are visible on the external surface of the hemisphere. For the greater part of this century, topographical observations, dissection, and descriptive data from passive staining methods have formed the principal source of information about the anatomy of the medial temporal lobe. However, in the past two decades much new information has emerged from experimental neuroanatomical studies in nonhuman primates and from neuropathological studies in humans. With magnetic resonance imaging (MRI), previous neuroanatomical detail, which earlier may have seemed like descriptive minutia, has now come alive and assumed substantial relevance in neurological and psychiatric diagnosis. Some of the emerging concepts as they relate to the neuroanatomy of the primate brain are highlighted and summarized here.

Direct temporal-occipital feedback connections to striate cortex (V1) in the macaque monkey

Although there have been reports of sparse projections from temporal areas TE, TF, and even TH to area V1, it is generally believed that cortical afferents to V1 originate exclusively from prestriate areas. Injections of anterograde tracers in anterior occipital and temporal areas, however, consistently produce labeled terminals in area V1. In order to confirm these results and display the full range of foci projecting to V1, we injected V1 in two monkeys with the retrograde tracer fast blue. Feedback connections were found, as expected, from several prestriate areas (V2, V3, V4, and MT). These originate from neurons in layers 3A and 6. Connections were also found from several more distal regions, namely, areas TEO, TE, TF, TH, and from cortex in the occipitotemporal and superior temporal (STS) sulci. Filled neurons occurred in two small foci in the caudal intraparietal sulcus. These more distal feedback connections tend to originate only from layer 6. An additional injection of the retrograde tracer diamidino yellow in area V2 of one animal revealed a similarly widespread network of feedback connections. In some areas (in the STS and in TEO), 10-15% of fluorescent neurons were double-labeled. These results indicate that feedback connections to early visual cortex derive from a widespread network of areas, including limbic-associated cortices. These connectional patterns testify to the massive recursiveness of anatomical pathways. As there are no reports of projections from V1 to anterior temporal cortices, our results also indicate that some cortical feedback connections may not be strictly reciprocal.

Neuropathologic changes of the temporal pole in Alzheimer's disease and Pick's disease

OBJECTIVE

To describe the pattern of neuropathologic changes in temporal polar cortex in Alzheimer's disease (AD) in comparison with changes in Pick's disease (PD) and normal elderly cytoarchitecture.

DESIGN

Examination of degenerative changes, neurofibrillary tangles, and senile plaques in the temporal poles of 10 patients with AD, three patients with PD, and five age-compatible control subjects, by means of thionein and thioflavine S stains and Alz-50 and ubiquitin immunocytochemistry.

SUBJECTS

All patients had a documented history of dementia and AD or PD confirmed on neuropathologic examination. Control subjects were without a history of cognitive impairment or evident neuropathologic changes.

OUTCOME MEASURES

Cytoarchitecture, neuronal loss, neurofibrillary tangles, senile plaques, and Pick bodies.

RESULTS

All patients with AD showed atrophy of the temporal pole and marked neuronal loss, especially in layers III and V and, to a lesser degree, in layers II and VI. Heavy accumulation of neurofibrillary tangles was found in layers II, III, V, and VI. Patients with PD showed extensive neuron loss throughout, although this appeared to be most prominent in layer III.

CONCLUSIONS

Both AD and PD pathologic changes severely affect the layers of the temporal pole that mediate widespread reciprocal connections with temporal and frontal cortices and limbic cortical and subcortical structures. Neural systems that interconnect temporal polar cortex with sensory association areas and memory-related limbic structures are, therefore, disrupted, and it is likely that these lesions play a role in the multifaceted cognitive and behavioral changes of AD and PD.

Frontal granular cortex input to the cingulate (M3), supplementary (M2) and primary (M1) motor cortices in the rhesus monkey

Although frontal lobe interconnections of the primary (area 4 or M1) and supplementary (area 6m or M2) motor cortices are well understood, how frontal granular (or prefrontal) cortex influences these and other motor cortices is not. Using fluorescent dyes in rhesus monkeys, we investigated the distribution of frontal lobe inputs to M1, M2, and the cingulate motor cortex (area 24c or M3, and area 23c). M1 received input from M2, lateral area 6, areas 4C and PrCO, and granular area 12. M2 received input from these same areas as well as M1; granular areas 45, 8, 9, and 46; and the lateral part of the orbitofrontal cortex. Input from the ventral part of lateral area 6, area PrCO, and frontal granular cortex targeted only the ventral portion of M1, and primarily the rostral portion of M2. In contrast, M3 and area 23c received input from M1, M2; lateral area 6 and area 4C; granular areas 8, 12, 9, 46, 10, and 32; as well as orbitofrontal cortex. Only M3 received input from the ventral part of lateral area 6 and areas PrCO, 45, 12vl, and the posterior part of the orbitofrontal cortex. This diversity of frontal lobe inputs, and the heavy component of prefrontal input to the cingulate motor cortex, suggests a hierarchy among the motor cortices studied. M1 receives the least diverse frontal lobe input, and its origin is largely from other agranular motor areas. M2 receives more diverse input, arising primarily from agranular motor and prefrontal association cortices. M3 and area 23c receive both diverse and widespread frontal lobe input, which includes agranular motor, prefrontal association, and frontal limbic cortices. These connectivity patterns suggest that frontal association and frontal limbic areas have direct and preferential access to that part of the corticospinal projection which arises from the cingulate motor cortex.

Some modular features of temporal cortex in humans as revealed by pathological changes in Alzheimer's disease

The concept of cortical modularity has surfaced as a generic term that alludes to any grouping or periodicity within the cerebral cortex relating to its neurons and their processes, and the enzymes, transmitters, and metabolic markers associated with them. Some of the best examples of anatomical modularity have been described in primary sensory areas such as the visual and somatosensory koniocortices. Functional examples of modularity abound in these same areas but may or may not have known morphological and chemical correlates. We depart from the traditional methods of cortical neuroanatomical analysis in this report and describe instead pathological alterations in the cortex in Alzheimer's disease. In particular, we focus on the cortex of the hippocampal formation and entorhinal, perirhinal, and anterior inferior temporal cortex and report findings that point toward a modular distribution of pathological changes unique to each of these cortical types. We argue that changes in modular organization as seen in Alzheimer's disease are in all likelihood germane to the abnormal function of each cortical area. These changes at the modular level may lie at the heart of the devastating behavioral breakdown in this illness, which can be severe even with limited pathology.

The modern concept of association cortex

Although enormous amounts of new neuroanatomical, neurophysiological and neurobehavioral data have been gathered on the association cortices in the past decade, it seems more permissible now than ever to use this functionally loaded concept. Its generality helps enormously, but the modern recognition of multiple interactive neural systems all contributing to cognition has diffused previous concerns relating to strict localization.

Cingulate input to the primary and supplementary motor cortices in the rhesus monkey: evidence for somatotopy in areas 24c and 23c

We examined the distribution of cingulate projections to the somatotopically related parts of the primary (M1) and supplementary (M2) motor cortices of the monkey by using fluorescent dyes. Labeled neurons were found in layers 3, 5 and 6 of areas 24c and 23c and were heaviest following injections placed in M2. Projections to analogous somatotopic areas in M1 and M2 arose from similar cingulate regions. In area 24c, neurons projecting to the face area of M1 and M2 were located anteriorly, those to the hindlimb were located posteriorly, and neurons projecting to the forelimb area of M1 and M2 were located in between. In area 23c, neurons projecting to the forelimb area of M1 and M2 were located anteriorly and those to the hindlimb area of M1 and M2 were located posteriorly. The face area of M1 and M2 was not found to receive afferents from area 23c. In contrast to this discreteness, cingulate projections to Woolsey's axial representation of M1 were diffuse. The results support the presence of a separate and somatotopically organized cingulate motor cortex in area 24c. This is predicated on the facts that: (1) small injections of retrograde tracers placed in analogous somatotopic parts of M1 and M2 resulted in similar patterns of labeling within the electrophysiologically "excitable" portion of the anterior cingulate cortex, and (2) this organized topography infers somatotopy. Our data fail to support a somatotopically organized cingulate motor area in area 23c if the criterion of all body parts is demanded. By virtue of its anatomical location and its connectional relation to the spinal cord and isocortical motor fields on the one hand and to the limbic cortex on the other, area 24c may be considered as M3 and provide limbic influences at several levels of motor control.

Alteration in the pattern of nerve terminal protein immunoreactivity in the perforant pathway in Alzheimer's disease and in rats after entorhinal lesions

Neurons in layer II of the entorhinal cortex consistently develop neurofibrillary tangles in Alzheimer's disease (AD). Experimental neuroanatomical studies have shown that these neurons give rise to the perforant pathway, a major excitatory projection to the hippocampal formation, which terminates in a discrete pattern in the outer portion of the molecular layer of the dentate gyrus. The distribution of two nerve terminal associated proteins, synaptophysin and NT75, was studied in the molecular layer of the dentate gyrus in AD and control cases to determine whether Alzheimer neuronal pathology is associated with loss of synaptic markers. In parallel studies, the effect of ablation of the entorhinal cortex in rats was evaluated. In AD as compared to controls, a decrease in synaptophysin immunostaining was evident in the terminal zone of the perforant pathway. NT75 nerve terminal immunostaining was too weak to interpret in the human hippocampal formation. Both synaptophysin and NT75 immunoreactivity were found in association with some neuritic plaques. In rats, entorhinal lesions resulted in diminished immunoreactivity for both synaptophysin and NT75 in the perforant pathway terminal zone. These results suggest that nerve terminal protein loss is a concomitant feature of neuronal pathology in AD.

Computer-aided two-dimensional high-resolution axon tracing: an application using the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHAL)

A computer-aided method for mapping the spatial distribution of axons labeled with the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHAL) has been devised. The method is based upon a histochemical charting system that controls a motorized microscope stage. The Computerized Charting System (CCS) does not require a camera lucida and can be installed on a common laboratory computer with minimal specialized hardware. The system provides features for storing, manipulating, and plotting the data, and recording the location of photographic images. The CCS has been used in our laboratory for: (1) the analysis of retrograde and anterograde neuroanatomical tract tracing using horseradish peroxidase, fluorescent dyes, PHAL, and 3H-labeled amino acids; (2) mapping the distribution of cells identified by immunohistochemistry; (3) mapping the distribution of silver grain-positive cells using in situ hybridization; (4) mapping the spatial distribution of neurofibrillary tangles and neuritic plaques in Alzheimer's disease; and (5) mapping the pattern of congophilic angiopathy in human brain. With the addition of high-resolution tracing features, the CCS provides a cost-effective and comprehensive alternative to the tedious and often inaccurate X-Y recording techniques used routinely in neuroanatomy and neuropathology.

Quantitative assessment of ALZ-50 immunoreactivity in Alzheimer's disease

A quantitative assay for ALZ-50 immunoreactivity was evaluated in samples of superior temporal gyrus taken at autopsy from 13 Alzheimer patients and 11 controls. The assayable immunoreactivity appears to be stable for at least 24 hours postmortem but was lost with formalin fixation. The mean value of the Alzheimer patients was tenfold higher than that of the controls (P less than .002). The values of four Alzheimer samples overlapped with the low levels seen in controls, but no controls had elevated levels. In this sample population, therefore, the assay had a sensitivity of 69% and specificity of 100%.

The axonal origin of a subpopulation of dystrophic neurites in Alzheimer's disease

Dystrophic neurites are observed characteristically in Alzheimer's disease (AD). They are thought to arise from sprouting dendrites and contribute to dementia because of their abnormal growth and close association with neurofibrillary tangles and neuritic plaques. In the present study, dystrophic neurites are demonstrated in the thalamic reticular nucleus in AD in the context of a normal neural and glial architecture. They do not collocalize with somata and dendrites identified by simultaneous labeling with the microtubule-associated protein MAP2, suggesting that they are derived from axons. Throughout the brain, dystrophic neurites may well be comprised of a heterogeneous population of both dendrites and axon terminals and preterminals. While many recent studies have focused upon the dendritic origin of dystrophic neurites, these results emphasize that the interconnectivity of certain brain regions may be compromised by cytoskeletal changes occurring in neurons and their axons in AD.

Entorhinal cortex pathology in Alzheimer's disease

The anatomical distribution of pathological changes in Alzheimer's disease, although highly selective for only certain brain areas, can be widespread at the endstage of the illness and can affect many neural systems. Propriety for onset among these is a question of importance for clues to the etiology of the disease, but one that is formidable without an experimental animal model. The entorhinal cortex (Brodmann's area 28) of the ventromedial temporal lobe is an invariant focus of pathology in all cases of Alzheimer's disease with selective changes that alter some layers more than others. The authors' findings reveal that it is the most heavily damaged cortex in Alzheimer's disease. Neuroanatomical studies in higher mammals reveal that the entorhinal cortex gives rise to axons that interconnect the hippocampal formation bidirectionally with the rest of the cortex. Their destruction in Alzheimer's disease could play a prominent role in the memory deficits that herald the onset of Alzheimer's disease and that characterize it throughout its course.

The topographical and neuroanatomical distribution of neurofibrillary tangles and neuritic plaques in the cerebral cortex of patients with Alzheimer's disease

The distribution of neurofibrillary tangles (NFTs) and neuritic plaques (NPs) was mapped in 39 cortical areas of 11 brains of patients with Alzheimer's disease (AD). Whole hemisphere blocks were embedded in polyethylene glycol (Carbowax), sectioned coronally, and stained with thioflavin S and thionin. The densities of NFTs and NPs were assessed using a numerical rating scale for each area. Scores were grouped by type of cortex and by lobe for statistical analysis. Highly significant differences were obtained. For example, limbic periallocortex and allocortex had more NFTs than any other type of cortex. In descending order, the density of NFTs was as follows: periallocortex (area 28) greater than allocortex (subiculum/CA1 zones of hippocampal formation, area 51) greater than corticoid areas (accessory basal nucleus of amygdala, nucleus basalis of Meynert) greater than proisocortex (areas 11, 12, 24, 23, anterior insula, 38, 35) greater than nonprimary association cortex (32, 46, superior temporal sulcus, 40, 39, posterior parahippocampal cortex, 37, 36) greater than primary sensory association cortex (7, 18, 19, 22, 21, 20) greater than agranular cortex (44-5, 8, 6, 4) greater than primary sensory cortex (41-2, 3-1-2, 17). The laminar distribution of NFTs tended to be selective, involving primarily layers III and V of association areas and layers II and IV of limbic periallocortex. There were far more NFTs in both limbic and temporal lobes than in frontal, parietal, and occipital lobes. In general, NPs were more evenly distributed throughout the cortex, with the exceptions of limbic periallocortex and allocortex, which had notably fewer NPs than other cortical areas. Temporal and occipital lobes had the highest NP densities, limbic and frontal lobes had the lowest, and parietal lobe was intermediate. No significant left-right hemispheric differences for NFT or NP densities were found across the population, and there was no relationship between duration of illness and densities of NFTs or NPs. The regional and laminar distribution of NFTs (and, to a lesser degree, that of NPs) suggests a consistent pattern of vulnerability within the cerebral cortices that seems correlated to the hierarchies of cortico-cortical connections. The higher-order association cortices, especially those in the anterior and ventromedial sectors of temporal lobe, are the most vulnerable, while other cortices appear less vulnerable to a degree commensurate with their connectional "distance" (i.e., synapses removed) from the limbic areas.

Fields of origin and pathways of the interhemispheric commissures in the temporal lobe of macaques

The interhemispheric connections of the cortical areas of the temporal lobe and some neighboring regions were investigated in monkeys (Macaca mulatta and Macaca fascicularis) by anterograde autoradiographic tracing, following injection of radioactively labeled amino acids. The results revealed that the interhemispheric projections of the temporal lobe course through three interhemispheric commissures on their way to the opposite hemisphere. The anterior commissure receives fibers from virtually the entire temporal lobe, including the temporal pole, superior and inferior temporal gyri, and parahippocampal gyrus. Moreover, area 13 of the orbitofrontal cortex, the frontal and temporal subdivisions of the prepiriform cortex, and the cortical and deep nuclei of the amygdala also contribute fibers to the anterior commissure. The heaviest projections arise in the rostral third of the temporal isocortex. These projections become progressively lighter from more caudal regions. By contrast, the corpus callosum receives fibers from the caudal two-thirds of the temporal lobe, including the temporal pole, superior and inferior temporal gyri, and parahippocampal gyrus. The heaviest projections arise in the caudal third of the temporal lobe and cross primarily in the caudal third of the corpus callosum, including the splenium. Progressively lighter projections arise more rostrally. Fibers from proisocortical and isocortical areas of the posterior parahippocampal gyrus cross in the ventralmost part of the splenium (inferior forceps), whereas cortical areas lateral to the occipitotemporal sulcus give rise to fibers that cross in the caudal part of the body of the corpus callosum and dorsal splenium. The dorsal hippocampal commissure receives fibers exclusively from the parahippocampal gyrus. The fibers of the corpus callosum, hippocampal commissure, and, to a lesser extent, the anterior commissure are intimately associated with the ventricular system as they course through the white matter of the temporal lobe. The fields of origin of the anterior commissure and corpus callosum overlap extensively over the caudal two-thirds of the temporal lobe. The posterior parahippocampal gyrus is unique in that it gives rise to fibers that cross in all three commissures.

Memory-related neural systems in Alzheimer's disease: an anatomic study

In the primate brain, there are strong connections among the entorhinal cortex, the hippocampal formation, and the amygdala, 3 structures of the ventromedial temporal lobe that are related to memory function. Because memory impairment is a central feature of Alzheimer's disease, we examined the probable cells of origin and terminal zones of these connections in the brains of humans affected by the disease, using thioflavine S, Alz-50, and anti-A4 amyloid protein immunocytochemistry. Specific cytoarchitectural areas and lamina that give rise to projections from the entorhinal cortex, the hippocampal formation, and the amygdala consistently contained neurofibrillary tangles. The terminal zones of many of these projections contained neuritic plaques, Alz-50-positive neuritic alterations, and A4 deposition. Other cytoarchitectural areas and lamina, sometimes immediately adjacent, were consistently spared from these Alzheimer changes. This pattern of Alzheimer-related alterations would disrupt projections among the entorhinal cortex, hippocampal formation, and amygdala at multiple sites, and also disrupt projections between these structures and cortical and subcortical targets. In functional terms, this pattern of structural damage is likely to be as devastating as bilateral destruction of the ventromedial temporal lobe, and thus contribute substantially to the memory disorder seen in this condition.

Laminar distribution of neuron degeneration in posterior cingulate cortex in Alzheimer's disease

The laminar distribution of neuron losses in posterior cingulate cortex were evaluated in 25 clinically and neuropathologically diagnosed cases of dementia of the Alzheimer type (DAT). The layer of maximal neuron loss in area 23a for each DAT case was determined by comparison with mean neuron densities for each layer of 17 neurologically intact control cases. The DAT cases were separated into five classes: class 1, 12% of all DAT cases, no or less than 40% neuron loss in any layer; class 2, 24%, maximal neuron losses in layers II or III; class 3, 28%, losses mainly in layer IV; class 4, 12%, losses mainly in layers V or VI; class 5, 24%, severe losses in all layers. An analysis of large and small neurons showed that in class 2 there was an equal loss of both in layer IIIa--b, in class 3 mostly small neurons were lost in layer IV, in class 4 mostly large neurons were lost in layers III, IV and V, while in class 5 there was no selectivity. The age of disease onset and length of the disease were the same for all classes, although classes 4 and 5 tended to have an earlier onset. No measures of thioflavin S-stained neuritic plaque (NP) or neurofibrillary tangle (NFT) density discriminated among these classes. In 64% of all DAT cases there was a progressive shift in NFT from ventral area 30 where most were in layer II to areas 23a--b where there was a balance between those in superficial and deep layers to dorsal area 23c where most were in layers V and VI.(ABSTRACT TRUNCATED AT 250 WORDS)

Alz-50 immunoreactivity in the thalamic reticular nucleus in Alzheimer's disease

Examination of the thalamic reticular nucleus (Rt) with the monoclonal antibody Alz-50 in brains of Alzheimer's disease patients reveals dense extracellular and terminal-like immunoreactivity in the absence of neurofibrillary tangles or neuritic plaques. Similar terminal-like immunoreactivity is not present in other thalamic nuclei of AD brains or in the brains of controls. Based on (1) an immunocytochemical and histopathological analysis of areas known to project to the Rt, (2) that Alz-50 immunocytochemistry reveals immunoreactive neurons, neurofibrillary tangles and neuritic plaques, and (3) evidence that Alz-50 immunoreactivity can be demonstrated in the terminal fields of immunoreactive neurons, the terminal-like immunoreactivity in the Rt probably corresponds to altered preterminal axons and terminals from degenerating basal forebrain neurons. Given the presumed physiological role of the Rt, these selective lesions could alter thalamocortical processing and contribute to the cognitive impairment in Alzheimer's disease.

Progressive aphasia in a patient with Pick's disease: a neuropsychological, radiologic, and anatomic study

Although Pick's disease is generally considered as a dementia characterized by signs of frontal lobe dysfunction, it can present with selective language defects rather than with cognitive decline. In this study, we report prospective and serial clinical, neuropsychological, and neuroradiologic observations in a 59-year-old man whose prominent disturbance was in the retrieval and learning of names denoting concrete entities and actions. Postmortem study confirmed the diagnosis of Pick's disease and revealed that neuronal loss and gliosis were most prominent in left anterior temporal cortices. The findings are in keeping with evidence that the left anterior temporal cortices and interconnected hippocampal system are critically involved in the learning and retrieval of verbal lexical items. The evidence from this patient, along with similar evidence from the literature we reviewed, suggests that when patients present with a progressive aphasia characterized by anomia, Pick's disease should be considered as the probable diagnosis.

Diencephalic amnesia

The anatomical basis and cognitive profile of diencephalic amnesia remain unclear. We report a two-part study. First, we studied 4 patients with bilateral medial thalamic infarctions using magnetic resonance imaging and comprehensive neuropsychological testing. All patients were followed for more than 1 year. Using a stereotactic method, we plotted the lesions in an atlas delineating the probable structure involved. Secondly, in 2 monkeys, using autoradiography, we traced the pathway from the amygdala to the dorsomedial nucleus, paying particular attention to the intrathalamic course of the amygdalothalamic projections. Our findings were (1) patients develop amnesia when infarctions are located anteriorly; (2) in patients with amnesia, the lesions can be small and strategically located, probably interfering with both hippocampal-related neural structures such as the mamillothalamic tract, and amygdala-related neural structures such as the ventroamygdalofugal pathway; and (3) a specific component of the latter is situated lateral but immediately adjacent to the mamillothalamic tract in the monkey, enabling both structures to be damaged bilaterally by small mirror image lesions. The amnesia is characterized by deficits in anterograde verbal and visual learning and in retrograde amnesia, but motor learning is preserved. We raise the possibility that bilateral diencephalic lesions may interfere particularly with temporal aspects of memory.

Pathological alterations in the amygdala in Alzheimer's disease

The amygdala is severely and consistently affected by pathology in Alzheimer's disease. The distribution of Thioflavin S-stained neurofibrillary tangles and neuritic plaques was examined in the various nuclei that form the amygdala in 20 cases of clinically diagnosed Alzheimer's disease and five non-demented control cases. Large numbers of neurofibrillary tangles and neuritic plaques were observed in the accessory basal and cortical nuclei and the cortical transition area, while there was lesser involvement of the mediobasal nucleus. The medial, lateral, laterobasal and central nuclei were relatively spared. The distribution of neurofibrillary tangles and neuritic plaques was compared with neuroanatomic connections known from non-human primate experimental studies. This comparison suggests that (1) nuclei receiving and giving rise to hippocampal projections are consistently affected by neuropathological alterations in Alzheimer's disease; (2) the nuclei which receive strong cholinergic projections from the nucleus basalis of Meynert (e.g. laterobasal nucleus) have, in general, relatively few neuritic plaques; and (3) nuclei which receive olfactory projections are not uniformly affected, the cortical nucleus being heavily affected but the medial nucleus consistently spared.

Hippocampal formation: anatomy and the patterns of pathology in Alzheimer's disease

Anatomical studies of the primate brain have shown that the subicular and CA1 allocortices give rise to hippocampal efferents that course to numerous telencephalic and diencephalic targets including other parts of the cortex. The hippocampal formation is damaged heavily in Alzheimer's disease, and is a focal point for pathology. We examined the anteroposterior extent of the hippocampal formation in 52 cases of Alzheimer's disease, 6 cases of other types of dementia and 10 age-compatible controls, to determine the patterns of pathology. We have observed that only certain subfields of the hippocampal formation are affected by cell loss, neurofibrillary tangles and neuritic plaques, while adjacent, anatomically distinct subfields are relatively spared. The portions of the hippocampal formation most crucial for both cortical and subcortical efferent projections are severely affected by Alzheimer pathological changes. Most notable are neurofibrillary tangles in the subicular and CA1 subfields. Layer IV of entorhinal cortex, specifically affected by neurofibrillary tangles. Hippocampal input is also compromised. For example, layer II of entorhinal cortex, which gives rise to perforant pathway hippocampal afferents, also undergoes severe neurofibrillary changes. Neuritic plaques appear in a distinct layer in the terminal zone of the perforant pathway, which carries the majority of corticohippocampal afferents. Plaques are also common in a zone that receives serotoninergic projections from the raphe complex, thus compromising another hippocampal afferent. In sum, these changes disrupt intrinsic and extrinsic hippocampal circuitry at multiple levels, and the pathological dissection deprives the hippocampal formation of many of its efferent and afferent connections with cortical and subcortical structures important in memory-related neural systems. These changes likely contribute to the memory impairment that characterizes Alzheimer's disease and the devastating intellectual decline that ensues.

A4 amyloid protein immunoreactivity is present in Alzheimer's disease neurofibrillary tangles

Neurofibrillary tangles and neuritic plaques are the neuropathological hallmarks of Alzheimer's disease. The latter consist of a core of A4 amyloid protein. We now report that some neurofibrillary tangles ('tombstone tangles') are also A4 immunoreactive. This observation is consistent with the hypothesis that A4 amyloid accumulation is a component of both neurofibrillary tangles and neuritic plaques.

A graphics-oriented personal computer-based microscope charting system for neuroanatomical and neurochemical studies

This report describes a computerized microscope charting system based on the IBM personal computer or compatible. Stepping motors are used to control the movement of the microscope stage and to encode its position by hand manipulation of a joystick. Tissue section contours and the location of cells labeled with various compounds are stored by the computer, plotted at any magnification and manipulated into composites created from several charted sections. The system has many advantages: (1) it is based on an industry standardized computer that is affordable and familiar; (2) compact and commercially available stepping motor microprocessors control the stage movement. These controllers increase reliability, simplify implementation, and increase efficiency by relieving the computer of time consuming control tasks; (3) the system has an interactive graphics interface allowing the operator to view the image during data collection. Regions of the graphics display can be enlarged during the charting process to provide higher resolution and increased accuracy; (4) finally, the digitized data are stored at 0.5 micron resolution and can be routed directly to a multi-pen plotter or exported to a computer-aided design (CAD) program to generate a publication-quality montage composed of several computerized chartings. The system provides a useful tool for the acquisition and qualitative analysis of data representing stained cells or chemical markers in tissue. The modular design, together with data storage at high resolution, allows for potential analytical enhancements involving planimetric, stereologic and 3-D serial section reconstruction.

Alz-50 immunoreactivity in the neonatal rat: changes in development and co-distribution with MAP-2 immunoreactivity

Alz-50 is a monoclonal antibody that recognizes pathological alterations in Alzheimer's disease. It has recently been noted also to mark some subplate neurons in human infants under the age of 2 years. We now report that Alz-50 recognizes many neurons in the normal neonatal rat in a pattern that changes with development. Immunoreactivity decreases substantially in intensity as the rat matures. This immunoreactivity co-distributes with microtubule-associated protein-2 (MAP-2) immunoreactivity in terms of topography, cellular localization and changes over the developmental time-course. This observation raises the possibility of exploring cytologic triggers that may lead to re-expression of Alz-50 immunoreactivity in aging and in pathological conditions.