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

Temporal lobe contusions on computed tomography are associated with impaired 6-month functional recovery after mild traumatic brain injury: a TRACK-TBI study

INTRODUCTION

Mild traumatic brain injury (MTBI) can cause persistent functional deficits and healthcare burden. Understanding the association between intracranial contusions and outcome may aid in MTBI treatment and prognosis.

METHODS

MTBI patients with Glasgow Coma Scale 13-15 and 6-month outcomes [Glasgow Outcome Scale-Extended (GOSE)], without polytrauma from the prospective TRACK-TBI Pilot study were analyzed. Intracranial contusions on computed tomography (CT) were coded by location. Multivariable regression evaluated associations between intracranial injury type (temporal contusion [TC], frontal contusion, extraaxial [epidural/subdural/subarachnoid], other-intraaxial [intracerebral/intraventricular hemorrhage, axonal injury]) and GOSE. Odds ratios (OR) are reported.

RESULTS

Overall, 260 MTBI subjects were aged 44.4 ± 18.1-years; 67.7% were male. Ninety-seven subjects were CT-positive and 46 had contusions (41.3%-frontal, 30.4%-temporal, 21.7%-frontal + temporal, 2.2% each-parietal/occipital/brainstem); 95.7% had concurrent extraaxial hemorrhage. Mortality was 0% at discharge and 2.3% by 6-months. GOSE distribution was 2.3%-death, 1.5%-severe disability, 27.7%-moderate disability, 68.5%-good recovery. Forty-six percent of TC-positive subjects suffered moderate disability or worse (GOSE ≤6) and 41.7% were unable to return to baseline work capacity (RTBWC), compared to 29.1%/20.4% for CT-negative and 26.1%/20.9% for CT-positive subjects without TC. On multivariable regression, TC associated with OR = 3.33 (95% CI [1.16-9.60], p = 0.026) for GOSE ≤6, and OR = 4.48 ([1.49-13.51], p = 0.008) for inability to RTBWC.

CONCLUSIONS

Parenchymal contusions in MTBI are often accompanied by extraaxial hemorrhage. TCs may be associated with 6-month functional impairment. Their presence on imaging should alert the clinician to the need for heightened surveillance of sequelae complicating RTBWC, with low threshold for referral to services.

A small molecule p75(NTR) ligand protects neurogenesis after traumatic brain injury

The p75 neurotrophin receptor (p75(NTR)) influences the proliferation, survival, and differentiation of neuronal precursors and its expression is induced in injured brain, where it regulates cell survival. Here, we test the hypotheses that pharmacologic modulation of p75(NTR) signaling will promote neural progenitor survival and proliferation, and improve outcomes of traumatic brain injury (TBI). LM11A-31, an orally available, blood-brain barrier-permeant small-molecule p75(NTR) signaling modulator, significantly increased proliferation and survival, and decreased JNK phosphorylation, in hippocampal neural stem/progenitor cells in culture expressing wild-type p75(NTR), but had no effect on cells expressing a mutant neurotrophin-unresponsive form of the receptor. The compound also enhanced the production of mature neurons from adult hippocampal neural progenitors in vitro. In vivo, intranasal administration of LM11A-31 decreased postinjury hippocampal and cortical neuronal death, neural progenitor cell death, gliogenesis, and microglial activation, and enhanced long-term hippocampal neurogenesis and reversed spatial memory impairments. LM11A-31 diminished the postinjury increase of SOX2-expressing early progenitor cells, but protected and increased the proliferation of endogenous polysialylated-neural cell adhesion molecule positive intermediate progenitors, and restored the long-term production of mature granule neurons. These findings suggest that modulation of p75(NTR) actions using small molecules such as LM11A-31 may constitute a potent therapeutic strategy for TBI.

Memory and cognition in preclinical dementia: what we know and what we do not know

This overview focuses on the cognitive transition between normal aging and dementia. Numerous studies indicate that individuals who will go on to develop dementia show cognitive deficits many years before the time at which a clinical diagnosis could be rendered. The degree of preclinical impairment is remarkably similar for tasks assessing episodic memory, executive functioning, and perceptual speed, consistent with the view that multiple brain alterations occur prior to clinical disease onset. Although most research in this area has dealt with Alzheimer disease (AD), several recent reports indicate that the pattern of preclinical impairment is very similar in the second largest dementia disorder, vascular dementia (VaD). This is important because currently the possibility for interventions to postpone disease onset is greater in VaD than in AD. Despite pronounced preclinical cognitive deficits in dementia, the performance distributions between cases and controls are largely overlapping, hampering the ability to identify high-risk individuals. To alleviate this problem, future research should evaluate hybrid models for the prediction of dementia. In such models, multiple indicators of cognitive functioning should be included along with markers from other domains that have been linked to subsequent dementia (such as brain imaging, genetics, and lifestyle variables). To the extent that these categories of variables add unique variance, classification accuracy will increase and the overlap in performance scores between incident cases and controls will decrease, thereby enhancing clinical usefulness. This approach would also facilitate the examination of interactive effects among classes of preclinical markers.

Neuropsychology and clinical neuroscience of persistent post-concussive syndrome

On the mild end of the acquired brain injury spectrum, the terms concussion and mild traumatic brain injury (mTBI) have been used interchangeably, where persistent post-concussive syndrome (PPCS) has been a label given when symptoms persist for more than three months post-concussion. Whereas a brief history of concussion research is overviewed, the focus of this review is on the current status of PPCS as a clinical entity from the perspective of recent advances in the biomechanical modeling of concussion in human and animal studies, particularly directed at a better understanding of the neuropathology associated with concussion. These studies implicate common regions of injury, including the upper brainstem, base of the frontal lobe, hypothalamic-pituitary axis, medial temporal lobe, fornix, and corpus callosum. Limitations of current neuropsychological techniques for the clinical assessment of memory and executive function are explored and recommendations for improved research designs offered, that may enhance the study of long-term neuropsychological sequelae of concussion.

Animal models of post-traumatic epilepsy

Epilepsy is a major unfavorable long-term consequence of traumatic brain injury (TBI). Moreover, TBI is one of the most important predisposing factors for the development of epilepsy, particularly in young adults. Understanding the molecular and cellular cascades that lead to the development of post-traumatic epilepsy (PTE) is key for preventing its development or modifying the disease process in such a way that epilepsy, if it develops, is milder and easier-to-treat. Tissue from TBI patients undergoing epileptogenesis is not available for such studies, which underscores the importance of developing clinically relevant animal models of PTE. The goal of this review is to (1) provide a description of PTE in humans, which is critical for the development of clinically relevant models of PTE, (2) review the characteristics of currently available PTE models, and (3) provide suggestions for the development of future models of PTE based on our current understanding of the mechanisms of TBI and epilepsy. The development of clinically relevant models of PTE is critical to advance our understanding of the mechanisms of post-traumatic epileptogenesis and epilepsy, as well as for producing breakthroughs in the development and testing of novel antiepileptogenic treatments.

Patterns of prospective and retrospective memory impairment in preclinical Alzheimer's disease

Forty-six preclinical Alzheimer's disease (AD) participants and 188 nondemented control persons from the Kungsholmen Project (L. Bäckman et al., 2004) were compared on prospective memory (ProM) and retrospective memory (RetM) tasks 3 years before dementia diagnosis. The preclinical AD participants showed deficits in both ProM and RetM. Most interestingly, logistic regression analyses revealed that ProM made an independent contribution to the prediction of AD over and above that of RetM. This finding suggests that ProM and RetM tap partly different cognitive operations. Furthermore, within the ProM task, both the retrospective and prospective components were similarly impaired in preclinical AD. Within RetM, the preclinical AD participants were impaired on indices of encoding, storage (forgetting), and retrieval of information. Hence, the findings indicate a rather global episodic memory impairment in preclinical AD that cuts across type of memory assessed (ProM and RetM) as well as across different components of both the ProM and RetM tasks.

Anatomy of the Anterior Temporal Lobe and the Frontotemporal Region Demonstrated by Fiber Dissection

OBJECTIVE:

The white matter structure of the anterior temporal lobe and the frontotemporal region is complex and not well appreciated from the available neurosurgical literature. The fiber dissection method is an excellent means of attaining a thorough knowledge of the three-dimensional structure of the white matter tracts. This study was performed to demonstrate the usefulness of the dissection technique in understanding the white matter anatomy and the effects of current surgical approaches on the subcortical structure of the region.

METHODS:

Seventeen brain specimens obtained at routine autopsy were dissected by use of Klingler's fiber dissection technique after preparation by fixation and freezing. The dissections were performed with an operating microscope and followed a stepwise pattern of progressive white matter dissection.

RESULTS:

The dissection is described in an orderly fashion showing the white matter tracts of the anterior temporal lobe and the frontotemporal region. An insight is gained into the three-dimensional course of the anterior loop of the optic radiation, the temporal stem, the anterior commissure, and the ansa peduncularis.

CONCLUSION:

The anterior temporal lobe and the frontotemporal region contain several important white matter tracts that can be uniquely understood by performing a white matter dissection of the region. Surgical procedures on the anterior temporal lobe differ substantially as to their repercussions on the subcortical white matter tract anatomy, as shown by the findings in this study.

The hippocampus in schizophrenia: a review of the neuropathological evidence and its pathophysiological implications

This paper puts the case for the hippocampus as being central to the neuropathology and pathophysiology of schizophrenia. The evidence comes from a range of approaches, both in vivo (neuropsychology, structural and functional imaging) and post mortem (histology, morphometry, gene expression, and neurochemistry). Neuropathologically, the main positive findings concern neuronal morphology, organisation, and presynaptic and dendritic parameters. The results are together suggestive of an altered synaptic circuitry or "wiring" within the hippocampus and its extrinsic connections, especially with the prefrontal cortex. These changes plausibly represent the anatomical component of the aberrant functional connectivity that underlies schizophrenia. Glutamatergic pathways are prominently but not exclusively affected. Changes appear somewhat greater in the left hippocampus than the right, and CA1 is relatively uninvolved compared to other subfields. Hippocampal pathology in schizophrenia may be due to genetic factors, aberrant neurodevelopment, and/or abnormal neural plasticity; it is not due to any recognised neurodegenerative process. Hippocampal involvement is likely to be associated with the neuropsychological impairments of schizophrenia rather than with its psychotic symptoms.

Stability of the preclinical episodic memory deficit in Alzheimer's disease

We sought to determine the course of the preclinical episodic memory deficit in Alzheimer's disease. Using data from a population-based study, we compared persons who developed Alzheimer's disease n = 15) with persons who were non-demented n = 105) 6 and 3 years prior to the diagnosis of dementia. Participants were tested on tasks assessing episodic memory free recall and recognition of words) and short-term memory digit span). The incident Alzheimer's disease cases performed more poorly than their non-demented counterparts both 3 and 6 years before diagnosis on recall and recognition. There were no group differences in either forward or backward digit span. The selective impairment of episodic memory before the diagnosis of Alzheimer's disease is consistent with the view that early changes in the hippocampal complex play an important role in the memory deficit in preclinical Alzheimer's disease. On both preclinical measurement occasions, recall and recognition made independent contributions to group classification in logistic regression analyses. However, there was no evidence for accelerated decline of episodic memory in the incident Alzheimer's disease group from 6 to 3 years before diagnosis. These results indicate that Alzheimer's disease is characterized by a long preclinical period during which episodic memory deficits are detectable. The magnitude of these deficits appears to be quite stable, at least up to 3 years before diagnosis. This may reflect the fact that those biological events that eventually result in clinically diagnosed Alzheimer's disease e.g. the appearance of amyloid plaques and neurofibrillary tangles) accumulate at a relatively slow rate.

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.

Two-phase computational model training long-term memories in the entorhinal-hippocampal region

The computational model described here is driven by the hypothesis that a major function of the entorhinal cortex (EC)-hippocampal system is to alter synaptic connections in the neocortex. It is based on the following postulates: (1) The EC compares the difference between neocortical representations (primary input) and feedback information conveyed by the hippocampus (the "reconstructed input"). The difference between the primary input and the reconstructed input (termed "error") initiates plastic changes in the hippocampal networks (error compensation). (2) Comparison of the primary input and reconstructed input requires that these representations are available simultaneously in the EC network. We suggest that compensation of time delays is achieved by predictive structures, such as the CA3 recurrent network and EC-CA1 connections. (3) Alteration of intrahippocampal connections gives rise to a new hippocampal output. The hippocampus generates separated (independent) outputs, which, in turn, train long-term memory traces in the EC (independent components, IC). The ICs of the long-term memory trace are generated in a two-step manner, the operations of which we attribute to the activities of the CA3 (whitening) and CA1 (separation) fields. (4) The different hippocampal fields can perform both nonlinear and linear operations, albeit at different times (theta and sharp phases). We suggest that long-term memory is represented in a distributed and hierarchical reconstruction network, which is under the supervision of the hippocampal output. Several of these model predictions can be tested experimentally.