Diaschisis and neurobehavior

Crossed Cerebellar Diaschisis in Alzheimer's Disease Detected by Arterial Spin-labelling Perfusion MRI

BACKGROUND

Crossed cerebellar diaschisis (CCD) is a phenomenon with depressed metabolism and hypoperfusion in the cerebellum. Using arterial spin-labelling perfusion weighted magnetic resonance imaging (ASL PWI), we investigated the frequency of CCD in patients with Alzheimer's disease (AD) and differences between patients with and without CCD.

PATIENTS AND METHODS

In patients with AD who underwent a standardized magnetic resonance imaging including ASL PWI cerebral blood flow was evaluated in the cerebellum, and brain segmentation/volumetry was performed using mdbrain (mediaire GmbH, Berlin, Germany) and FSL FIRST (Functional Magnetic Resonance Imaging of the Brain Software Library).

RESULTS

In total, 65 patients were included, and 22 (33.8%) patients were assessed as being CCD-positive. Patients with CCD had a significantly smaller whole brain volume (862.8±49.9 vs. 893.7±62.7 ml, p=0.049) as well as white matter volume (352.9±28.0 vs. 374.3±30.7, p=0.008) in comparison to patients without CCD.

CONCLUSION

It was possible to detect CCD by ASL PWI in approximately one-third of patients with AD and was associated with smaller whole brain and white matter volume.

Stem Cell Repair of the Microvascular Damage in Stroke

Stroke is a life-threatening disease that leads to mortality, with survivors subjected to long-term disability. Microvascular damage is implicated as a key pathological feature, as well as a therapeutic target for stroke. In this review, we present evidence detailing subacute diaschisis in a focal ischemic stroke rat model with a focus on blood–brain barrier (BBB) integrity and related pathogenic processes in contralateral brain areas. Additionally, we discuss BBB competence in chronic diaschisis in a similar rat stroke model, highlighting the pathological changes in contralateral brain areas that indicate progressive morphological brain disturbances overtime after stroke onset. With diaschisis closely approximating stroke onset and progression, it stands as a treatment of interest for stroke. Indeed, the use of stem cell transplantation for the repair of microvascular damage has been investigated, demonstrating that bone marrow stem cells intravenously transplanted into rats 48 h post-stroke survive and integrate into the microvasculature. Ultrastructural analysis of transplanted stroke brains reveals that microvessels display a near-normal morphology of endothelial cells and their mitochondria. Cell-based therapeutics represent a new mechanism in BBB and microvascular repair for stroke.

Serial MR Imaging of Adult-Onset Rasmussen's Encephalitis

A 52-year-old woman was referred for a progressive neurological condition which started a year before with continuous irregular twitching of the right facial and arm muscles as well as the tongue and palate, followed by progressive dysphagia, right hemiparesis, ataxia, dysphasia and dysarthria. Though magnetic resonance imaging (MRI) at clinical presentation and a year after were both normal (Figure A1), Rasmussen's encephalitis (RE) was strongly suspected and treatment with corticosteroids and immunoglobulins were begun. A third MRI, two years after onset, revealed mild T2 hyperintense subcortical white matter changes over the left perisylvian region (Figure A) which confirmed our initial suspicion of RE as she now met clinical, electrophysiological and morphological criterias for RE. While waiting for a cerebral biopsy after unsatisfactory response from antiepileptic drugs, corticosteroids and immunoglobulins, her condition markedly worsened less than three years after onset with the sudden occurrence of status epilepticus requiring intubation and continuous infusions of midazolam and propofol.

Metabolite changes in the ipsilateral and contralateral cerebral hemispheres in rats with middle cerebral artery occlusion

Cerebral ischemia not only causes pathological changes in the ischemic areas but also induces a series of secondary changes in more distal brain regions (such as the contralateral cerebral hemisphere). The impact of supratentorial lesions, which are the most common type of lesion, on the contralateral cerebellum has been studied in patients by positron emission tomography, single photon emission computed tomography, magnetic resonance imaging and diffusion tensor imaging. In the present study, we investigated metabolite changes in the contralateral cerebral hemisphere after supratentorial unilateral ischemia using nuclear magnetic resonance spectroscopy-based metabonomics. The permanent middle cerebral artery occlusion model of ischemic stroke was established in rats. Rats were randomly divided into the middle cerebral artery occlusion 1-, 3-, 9- and 24-hour groups and the sham group. 1H nuclear magnetic resonance spectroscopy was used to detect metabolites in the left and right cerebral hemispheres. Compared with the sham group, the concentrations of lactate, alanine, γ-aminobutyric acid, choline and glycine in the ischemic cerebral hemisphere were increased in the acute stage, while the concentrations of N-acetyl aspartate, creatinine, glutamate and aspartate were decreased. This demonstrates that there is an upregulation of anaerobic glycolysis (shown by the increase in lactate), a perturbation of choline metabolism (suggested by the increase in choline), neuronal cell damage (shown by the decrease in N-acetyl aspartate) and neurotransmitter imbalance (evidenced by the increase in γ-aminobutyric acid and glycine and by the decrease in glutamate and aspartate) in the acute stage of cerebral ischemia. In the contralateral hemisphere, the concentrations of lactate, alanine, glycine, choline and aspartate were increased, while the concentrations of γ-aminobutyric acid, glutamate and creatinine were decreased. This suggests that there is a difference in the metabolite changes induced by ischemic injury in the contralateral and ipsilateral cerebral hemispheres. Our findings demonstrate the presence of characteristic changes in metabolites in the contralateral hemisphere and suggest that they are most likely caused by metabolic changes in the ischemic hemisphere.

Enhancing Recovery after Stroke with Noradrenergic Pharmacotherapy: A New Frontier?

Despite much progress in stroke prevention and acute intervention, recovery and rehabilitation have traditionally received relatively little scientific attention. There is now increasing interest in the development of stroke recovery drugs and innovative rehabilitation techniques to promote functional recovery after completed stroke. Experimental work over the past two decades indicates that pharmacologic intervention to enhance recovery may be possible in the subacute stage, days to weeks poststroke, after irreversible injury has occurred. This paper discusses the concept of “rehabilitation pharmacology” and reviews the growing literature from animal studies and pilot clinical trials on noradrenergic pharmacotherapy, a new experimental strategy in stroke rehabilitation. Amphetamine, a monoamine agonist that increases brain norepinephrine levels, is the most extensively studied drug shown to promote recovery of function in animal models of focal brain injury. Further research is needed to investigate the mechanisms and clinical efficacy of amphetamine and other novel therapeutic interventions on the recovery process.

Blood-Spinal Cord Barrier Alterations in Subacute and Chronic Stages of a Rat Model of Focal Cerebral Ischemia

We previously demonstrated blood-brain barrier impairment in remote contralateral brain areas in rats at 7 and 30 days after transient middle cerebral artery occlusion (tMCAO), indicating ischemic diaschisis. Here, we focused on effects of subacute and chronic focal cerebral ischemia on the blood-spinal cord barrier (BSCB). We observed BSCB damage on both sides of the cervical spinal cord in rats at 7 and 30 days post-tMCAO. Major BSCB ultrastructural changes in spinal cord gray and white matter included vacuolated endothelial cells containing autophagosomes, pericyte degeneration with enlarged mitochondria, astrocyte end-feet degeneration and perivascular edema; damaged motor neurons, swollen axons with unraveled myelin in ascending and descending tracts and astrogliosis were also observed. Evans Blue dye extravasation was maximal at 7 days. There was immunofluorescence evidence of reduction of microvascular expression of tight junction occludin, upregulation of Beclin-1 and LC3B immunoreactivities at 7 days and a reduction of the latter at 30 days post-ischemia. These novel pathological alterations on the cervical spinal cord microvasculature in rats after tMCAO suggest pervasive and long-lasting BSCB damage after focal cerebral ischemia, and that spinal cord ischemic diaschisis should be considered in the pathophysiology and therapeutic approaches in patients with ischemic cerebral infarction.

A unified 3D default space consciousness model combining neurological and physiological processes that underlie conscious experience

The Global Workspace Theory and Information Integration Theory are two of the most currently accepted consciousness models; however, these models do not address many aspects of conscious experience. We compare these models to our previously proposed consciousness model in which the thalamus fills-in processed sensory information from corticothalamic feedback loops within a proposed 3D default space, resulting in the recreation of the internal and external worlds within the mind. This 3D default space is composed of all cells of the body, which communicate via gap junctions and electrical potentials to create this unified space. We use 3D illustrations to explain how both visual and non-visual sensory information may be filled-in within this dynamic space, creating a unified seamless conscious experience. This neural sensory memory space is likely generated by baseline neural oscillatory activity from the default mode network, other salient networks, brainstem, and reticular activating system.

Blood-brain barrier alterations provide evidence of subacute diaschisis in an ischemic stroke rat model

BACKGROUND

Comprehensive stroke studies reveal diaschisis, a loss of function due to pathological deficits in brain areas remote from initial ischemic lesion. However, blood-brain barrier (BBB) competence in subacute diaschisis is uncertain. The present study investigated subacute diaschisis in a focal ischemic stroke rat model. Specific focuses were BBB integrity and related pathogenic processes in contralateral brain areas.

METHODOLOGY/PRINCIPAL FINDINGS

In ipsilateral hemisphere 7 days after transient middle cerebral artery occlusion (tMCAO), significant BBB alterations characterized by large Evans Blue (EB) parenchymal extravasation, autophagosome accumulation, increased reactive astrocytes and activated microglia, demyelinization, and neuronal damage were detected in the striatum, motor and somatosensory cortices. Vascular damage identified by ultrastuctural and immunohistochemical analyses also occurred in the contralateral hemisphere. In contralateral striatum and motor cortex, major ultrastructural BBB changes included: swollen and vacuolated endothelial cells containing numerous autophagosomes, pericyte degeneration, and perivascular edema. Additionally, prominent EB extravasation, increased endothelial autophagosome formation, rampant astrogliosis, activated microglia, widespread neuronal pyknosis and decreased myelin were observed in contralateral striatum, and motor and somatosensory cortices.

CONCLUSIONS/SIGNIFICANCE

These results demonstrate focal ischemic stroke-induced pathological disturbances in ipsilateral, as well as in contralateral brain areas, which were shown to be closely associated with BBB breakdown in remote brain microvessels and endothelial autophagosome accumulation. This microvascular damage in subacute phase likely revealed ischemic diaschisis and should be considered in development of treatment strategies for stroke.

Functional Connectivity in the Normal and Injured Brain

The brain is neither uniform nor composed of similar modules but is rather a mosaic of different and highly interconnected regions. Accordingly, knowledge of functional connectivity between brain regions is crucial to understanding perception, cognition, and behavior. Functional connectivity methods estimate similarities between activity recorded in different regions of the brain. They are often applied to resting state activity, thus providing measures that are by nature task independent. The spatial patterns revealed by functional connectivity are not only shaped by the underlying anatomical structure of the brain but also partially depend on the history of task-driven coactivations. Inter-subject differences in functional connectivity may, at least to some degree, underlie variability observed in task performance across healthy subjects and in behavioral impairments in neurological patients. In this respect, recent studies have demonstrated that behavioral deficits in patients with brain injury are not only due to local tissue damage but also due to altered functional connectivity among structurally intact regions connected to the damaged site. Studies based on functional connectivity have the potential to advance basic understanding of how brain lesions induce neuropsychological syndromes. Furthermore, they may eventually suggest improved rehabilitation strategies for patients with brain injury, through the design of individualized treatment and recovery protocols.

Restorative neurology: consideration of the new anatomy and physiology of the injured nervous system

The adult human nervous system is an incredibly complex set of thousands to tens of thousands of connections between a hundred billion neurons that develops via an intricate spatial-temporal process and is shaped by experience. In addition, any one anatomical arrangement of neural circuits is usually capable of multiple physiological states. Following neurological injury, a new anatomy, and consequently a new spectrum of physiology, emerges within this nervous system with its mix of both injured and uninjured parts. It is this new combination of neural components that determines the extent to which natural functional recovery can occur and the extent to which clinical interventions can further that recovery. Detecting the new anatomy and physiology of the injured human nervous system is difficult but not impossible and some methods can track over time changes in neural structure or, more often, functions that correlate with neurological improvement. The goal of restorative neurology is to make best use of this new anatomy and physiology to facilitate neurological recovery. While we are still learning about how neurorehabilitation interventions generate functional recovery, we can begin to test hypothesis regarding the underlying mechanisms of neural plasticity and attempt to augment those processes.

Central thalamic contributions to arousal regulation and neurological disorders of consciousness

This review focuses on the contributions of the central thalamus to normal mechanisms of arousal regulation and to neurological disorders of consciousness. Forebrain arousal is regulated by ascending influences from brainstem/basal forebrain neuronal populations ("arousal systems") and control signals descending from frontal cortical systems. These subcortical and cortical systems have converging projections to the central thalamus that emphasize their role in maintaining organized behavior during wakefulness. Central thalamic neurons appear to be specialized both anatomically and physiologically to support distributed network activity that maintains neuronal firing patterns across long-range cortico-cortical pathways and within cortico-striatopallidal-thalamocortical loop connections. Recruitment of central thalamic neurons occurs in response to increasing cognitive demand, stress, fatigue, and other perturbations that reduce behavioral performance. In addition, the central thalamus receives projections from brainstem pathways evolved to rapidly generate brief shifts of arousal associated with the appearance of salient stimuli across different sensory modalities. Through activation of the central thalamus, neurons across the cerebral cortex and striatum can be depolarized and their activity patterns selectively gated by descending or ascending signals related to premotor attention and alerting stimuli. Direct injury to the central thalamus or prominent deafferentation of these neurons as a result of complex, multifocal, brain insults are both associated with severe impairment of forebrain functional integration and arousal regulation. Interventions targeting neurons within the central thalamus may lead to rational therapeutic approaches to the treatment of impaired arousal regulation following nonprogressive brain injuries. A model accounting for present therapeutic strategies is proposed.

Neurology of affective prosody and its functional-anatomic organization in right hemisphere

Unlike the aphasic syndromes, the organization of affective prosody in brain has remained controversial because affective-prosodic deficits may occur after left or right brain damage. However, different patterns of deficits are observed following left and right brain damage that suggest affective prosody is a dominant and lateralized function of the right hemisphere. Using the Aprosodia Battery, which was developed to differentiate left and right hemisphere patterns of affective-prosodic deficits, functional-anatomic evidence is presented in patients with focal ischemic strokes to support the concepts that (1) affective prosody is a dominant and lateralized function of the right hemisphere, (2) the intrahemispheric organization of affective prosody in the right hemisphere, with the partial exception of Repetition, is analogous to the organization of propositional language in the left hemisphere and (3) the aprosodic syndromes are cortically based as part of evolutionary adaptations underlying human language and communication.

Functional neuroimaging applications for assessment and rehabilitation planning in patients with disorders of consciousness

OBJECTIVE

To describe the theoretic framework, design, and potential clinical applications of functional neuroimaging protocols in patients with disorders of consciousness.

DATA SOURCES

Recent published literature and authors' own work.

STUDY SELECTION

Studies using functional neuroimaging techniques to investigate cognitive processing in patients diagnosed with vegetative and minimally conscious state.

DATA EXTRACTION

Not applicable.

DATA SYNTHESIS

Positron-emission tomography activation studies suggest that the vegetative state represents a global disconnection syndrome in which higher order association cortices are functionally disconnected from primary cortical areas. In contrast, patterns of activation in functional magnetic resonance imaging studies of patients in the minimally conscious state show preservation of large-scale cortical networks associated with language and visual processing.

CONCLUSIONS

Novel applications of functional neuroimaging in patients with disorders of consciousness may aid in differential diagnosis, prognostic assessment and identification of pathophysiologic mechanisms. Improvements in patient characterization may, in turn, provide new opportunities for restoration of function through interventional neuromodulation.

Measurements and models of cerebral function in the severely injured brain

We review the emerging applications of functional and structural neuroimaging techniques for the assessment of patients with disorders of consciousness. Measurements of brain function from patients in the vegetative state (VS) and minimally conscious state (MCS) are compared, and a conceptual organization is developed that suggests models of brain mechanisms associated with different functional levels of recovery. We emphasize developing strategies to place complex brain injuries on a more equal footing using global and regional quantification of resting or activated brain activity using functional imaging techniques alongside more detailed structural assessments of neuronal integrity and axonal connectivity now available. Preliminary studies from several investigative groups suggest that some MCS patients may harbor a functional reserve in the form of recruitable cerebral networks. These findings support developing systematic characterizations of the severely injured brain and suggest that some patients may benefit from improved diagnostic assessments.

Brain plasticity: From pathophysiological mechanisms to therapeutic applications

Cerebral plasticity, which is the dynamic potential of the brain to reorganize itself during ontogeny, learning, or following damage, has been widely studied in the last decade, in vitro, in animals, and also in humans since the development of functional neuroimaging. In the first part of this review, the main hypotheses about the pathophysiological mechanisms underlying plasticity are presented. At a microscopic level, modulations of synaptic efficacy, unmasking of latent connections, phenotypic modifications and neurogenesis have been identified. At a macroscopic level, diaschisis, functional redundancies, sensory substitution and morphological changes have been described. In the second part, the behavioral consequences of such cerebral phenomena in physiology, namely the "natural" plasticity, are analyzed in humans. The review concludes on the therapeutic implications provided by a better understanding of these mechanisms of brain reshaping. Indeed, this plastic potential might be 'guided' in neurological diseases, using rehabilitation, pharmacological drugs, transcranial magnetic stimulation, neurosurgical methods, and even new techniques of brain-computer interface - in order to improve the quality of life of patients with damaged nervous systems.

Towards an understanding of cognitive function in Friedreich ataxia

There is limited documentation regarding cognitive function in individuals with Friedreich ataxia (FRDA), possibly because FRDA is widely held to predominantly affect the spinal cord, peripheral sensory nerves and cerebellum and not to affect cognition. Traditionally, the cerebellum has been thought to coordinate voluntary movement and motor tone, posture and gait. However, recent studies have implicated the cerebellum in a range of cognitive functions including executive function, visuospatial organisation and memory. We review the available data on cognitive function and neuroimaging in FRDA and the role of the cerebellum in cognitive function. We conclude with recommendations for future research including correlating cognitive function in individuals with FRDA with possible determinants of disease severity, such as age of onset and the causative genetic mutation.

New concepts in surgery of WHO grade II gliomas: functional brain mapping, connectionism and plasticity – a review

Despite a recent literature supporting the impact of surgery on the natural history of low-grade glioma (LGG), the indications of resection still remain a matter of debate, especially because of the frequent location of these tumors within eloquent brain areas - thus with a risk to induce a permanent postoperative deficit. Therefore, since the antagonist nature of this surgery is to perform the most extensive glioma removal possible, while preserving the function and the quality of life, new concepts were recently applied to LGG resection in order to optimize the benefit/risk ratio of the surgery.First, due to the development of functional mapping methods, namely perioperative neurofunctional imaging and intrasurgical direct electrical stimulation, the study of cortical functional organization is currently possible for each patient - in addition to an extensive neuropsychological assessment. Such knowledge is essential because of the inter-individual anatomo-functional variability, increased in tumors due to cerebral plasticity phenomena. Thus, brain mapping enables to envision and perform a resection according to individual functional boundaries.Second, since LGG invades not only cortical but also subcortical structures, and shows an infiltrative progression along the white matter tracts, new techniques of anatomical tracking and functional mapping of the subcortical white matter pathways were also used with the goal to study the individual effective connectivity - which needs imperatively to be preserved during the resection.Third, the better understanding of brain plasticity mechanisms, induced both by the slow-growing LGG and by the surgery itself, were equally studied in each patient and applied to the surgical strategy by incorporating individual dynamic potential of reorganization into the operative planning. The integration of these new concepts of individual functional mapping, connectivity and plastic potential to the surgery of LGG has allowed an extent of surgical indications, an optimization of the quality of resection (neuro-oncological benefit), and a minimization of the risk of sequelae (benefit on the quality of life). In addition, such a strategy has also fundamental applications, since it represents a new door to the connectionism and cerebral plasticity.

Reduced regional cerebral blood flow in SPG4-linked hereditary spastic paraplegia

Hereditary spastic paraplegia (HSP) linked to the spastic gait gene 4 (SPG4) is controversial, as the "pure" form traditionally has been considered confined to the long axons of the spinal cord. However, recent immunolabeling experiments have demonstrated extensive Spastin expression in the cortex and striatum. This could indicate a more widespread neuropathology from mutations in the SPG4 gene than previously assumed. The aim of this study was therefore to ascertain the extent of cerebral involvement in SPG4 linked HSP by neuropsychological examination and measurement of the regional cerebral blood flow (rCBF) as an indirect marker of regional neuronal activity. Eighteen SPG4 patients and 18 matched control subjects were studied. Resting state rCBF was measured using Positron Emission Tomography (PET) and the (15)O-labelled water bolus technique and relative group differences were explored using Statistical Parametric Mapping (SPM 99). Neuropsychological assessment was performed using established and nationally validated tests (RH Basic Battery). Compared to healthy controls, the patient group had significantly decreased rCBF in the left fronto-temporal cortex (P<0.05), and more extensive changes were observed in a separate analysis of the most disabled individuals. The neuropsychological assessment revealed only significantly impaired recognition memory for faces. In summary, the findings support cerebral pathology in SPG4-linked HSP, although the decreased rCBF in fronto-temporal cortex was not associated with severe cognitive impairment.

Lessons from brain mapping in surgery for low-grade glioma: insights into associations between tumour and brain plasticity

Surgical treatment of low-grade gliomas (LGGs) aims to maximise the amount of tumour tissue resected, while minimising the risk of functional sequelae. In this review I address the issue of how to reconcile these two conflicting goals. First, I review the natural history of LGG-growth, invasion, and anaplastic transformation. Second, I discuss the contribution of new techniques, such as functional mapping, to our understanding of brain reorganisation in response to progressive growth of LGG. Third, I consider the clinical implications of interactions between tumour progression and brain plasticity. In particular, I show how longitudinal studies (preoperative, intraoperative, and postoperative) could allow us to optimise the surgical risk-to-benefit ratios. I will also discuss controversial issues such as defining surgical indications for LGGs, predicting the risk of postoperative deficit, aspects of operative surgical neuro-oncology (eg, preoperative planning and preservation of functional areas and tracts), and postoperative functional recovery.

Neuroanatomic deficits in congenital central hypoventilation syndrome

Congenital Central Hypoventilation Syndrome (CCHS) patients exhibit compromised autonomic regulation, reduced breathing drive during sleep, diminished ventilatory responses to chemoreceptor stimulation, and diminished air hunger perception. The syndrome provides an opportunity to partition neural processes regulating breathing and cardiovascular action. No obvious lesions appear with conventional magnetic resonance imaging; however, T2 relaxometry procedures can detect reduced cell or fiber density or diminished myelination not found with routine evaluation. High-resolution T1, proton density, and T2-weighted brain images were collected from 12 patients and 28 age- and gender-matched controls. Voxel-by-voxel T2 maps were generated from the proton density and T2-weighted images and evaluated by voxel-based-relaxometry procedures. Normalized and smoothed T2 maps were compared between groups using analysis of covariance at each voxel, with age and ventricle size included as covariates. Patients showed damaged or maldeveloped tissue, principally right-sided, including white matter from the level of the anterior cingulate cortex caudally to the level of the posterior cingulate and laterally to the posterior superior temporal cortex. Portions of the posterior, mid, and anterior cingulate, as well as the internal capsule, putamen, and globus pallidus and basal forebrain extending to the anterior and medial thalamus were affected. Deficits in the cingulum bundle and mid-hippocampus and ventral prefrontal cortex appeared, as well as the right cerebellar cortex and deep nuclei. Neuroanatomic deficiencies in limbic structures suggest a structural basis for reduced air hunger perception, thermoregulatory and autonomic deficiencies in the syndrome, while cerebellar deficits may also contribute to breathing and cardiovascular dysregulation.

Modeling the minimally conscious state: measurements of brain function and therapeutic possibilities

The minimally conscious state (MCS) defines a functional level of recovery following severe brain injuries. Patients in MCS demonstrate unequivocal evidence of response to their environment yet fail to recover the ability to communicate. Drawing on recent functional brain-imaging studies, pathological data, and neurophysiological investigations, models of brain function in MCS are proposed. MCS models are compared and contrasted with models of the vegetative state (VS), a condition characterized by wakeful appearance and unconsciousness. VS reflects a total loss of cognitive function and failure to recover basic aspects of the normal physiologic brain state associated with wakefulness. MCS may represent a recovery of the minimal dynamic architecture required to organize behavioral sets and respond to sensory stimuli. Several pathophysiological mechanisms that might limit further recovery in MCS patients are considered. Implications for future research directions and possible therapeutic strategies are reviewed.

Cognitive deficits in adult patients with brain tumours

Cognitive function, with survival and response on brain imaging, is increasingly regarded as an important outcome measure in patients with brain tumours. This measure provides us with information on a patient's clinical situation and adverse treatment effects. Radiotherapy has been regarded as the main cause of cognitive decline in these patients, because children with brain tumours can develop intellectual deterioration caused by radiotherapy. In long-term surviving patients, radiotherapy may indeed lead to cognitive deficits, or even dementia. Recent studies, however, have made clear that focal radiotherapy in patients with glioma is not the main reason for cognitive deficits. The tumour itself and other medical treatments contribute largely to the cognitive deficits. Cognitive function is now also recognised as an independent prognostic factor in the survival of glioma patients. Additionally, cognitive deterioration can be the first indicator of progressive disease after treatment.

Permanent or transitory effects on neurocognitive components of the CNV complex induced by brain dysfunctions, lesions and ablations in humans

Since the mid-1960s, essentially using electrophysiological methods, our research group has examined the effects of different brain diseases in humans, both on first- and second-order conditioned responses and on some types of neurocognitive potentials of the CNV complex. This didactic lecture will focus on our various attempts to identify and understand the neuroanatomical and neurophysiological substrates involved in cognitive information processing followed by the conception and execution of sensory-motor and behavioural responses evoked by significant acoustic stimuli, in both pathological situations and normal control subjects. Great interest was, e.g. aroused in the early 1970s by the rare, fortunately unrepeatable, opportunity of examining the CNV patterns in various psychiatric patients treated with psychosurgical Freeman-Watts bilateral prefrontal 'radical' lobotomy, also with repeated recordings (The Responsive Brain (1976) 158; Multidisciplinary Perspectives in Event-Related Brain-Potentials Research (1978) 376) or bimedial bifrontal cingulotomy (Multidisciplinary Perspectives in Event-Related Brain Potential Research (1978) 383). In the same period, investigations into CNV activity recorded in patients submitted to complete callosotomy ('split brain': Attention and Performance, vol. IV (1972) 221; Electroenceph. Clin. Neurophysiol. Suppl. 33 (1973) 161) were also begun and were continued into the 1980s, also with regard to other types of ERP (Brain 111 (1988) 553; J. Cog. Neurosci. 2 (1990) 258). All these data furnished unique information about the sub-second dynamics of unilateral or bihemispheric cortico-cortical and cortico-subcortical interconnections in humans. In recent years, with a classic method of analysis based on sequential scalp-topographic bidimensional neuroelectric mapping and 21/19 electrodes connected to three different references, and binaural/monaural clicks as warning signals (S1), we have repeatedly examined the CNV activity of 11 selected patients submitted to complete ablation of the damaged cortical areas, with uni- or bilateral lesions restricted to the prefrontal or associative parieto-temporal areas. We have always used the standard CNV paradigm (S1-S2 motor-response) which evokes a complex of neurocognitive potentials, including the P300 from S1, which are well-known, since they are certainly among the most studied ERPs in the various ages and races of normal subjects, psychiatric patients and subjects with different brain diseases. The most important results have been, (1) In normal subjects the MRI and the latency differences of CNV component measurements along the bidirectional pathways functionally interconnecting ipsilateral distant associative cortical areas (e.g. the arcuate-superior longitudinal complex bundle) were accounted for by the transcortical conduction time, which varies in our scalp recordings from 1 cm/0.74 to 1.28 ms ( approximately 9.8 m/s). (2) Constantly, no true auditory S1-elicited N1a, b, c, P2, N2, P300 components or CNV slow waves (O- and E-wave) were recordable over the whole of the ablated cortical areas, but only clearly identifiable volume-conducted EP/ERPs generated in other hemispheric structures. (3) The post-S1 ERP/CNV complexes on the intact hemisphere were found to be within the normal limits. (4) Effects of severe disruption on the S1 ERP/CNV complexes evocable on the site and on remote ipsilateral apparently normal anatomo-functionally interconnected brain regions were observed in 5 patients, 4 of whom had extensive frontocortical ablations. In two of the latter the distant disruptive action on the CNV components over the neuroradiologically normal ipsilateral two-way connected post-rolandic sensory and association areas was seen to be partially reversible, showing aspects of a probable slowly evolving diaschisis-like effect. Similar deactivation of some ERP components was observed in reverse on the ipsilateral dorsolateral frontocortical region in the fifth patient with a large parieto-temporal cortex ablation. These data require confirmahese data require confirmation, and when this phenomenon is observable, it must be appropriately monitored with different methods of functional neuroimaging. This will serve not only for medical and neuropsychophysiological diagnosis purposes, but also particularly for a correct and really useful planning of neuro-rehabilitation activities in selected cases.

Prolonged cortical relay time of long latency reflex and central motor conduction in patients with spinocerebellar ataxia type 6

OBJECTIVE

Spinocerebellar ataxia type 6 (SCA6) is a neurodegenerative disorder characterized by a slowly progressive ataxia and dysarthria. Anatomically. SCA6 was said to affect only the cerebellum. However, ithasbeen argued that SCA6 may involve widespread regions of the brain. This study was designed to investigate the electrophysiological functions of the central nervous system in patients affected with SCA6.

METHODS

Nine patients with SCA6 and 10 normal, age-matched control subjects were included in the study. The motor evoked potentials, somatosensory evoked potentials, and long latency reflex (LLR) of the hand muscle were measured to evaluate the functions of the central nervous system.

RESULTS

Significantly delayed LLR, as well as prolonged cortical relay time (CRT) and central motor conduction time (CMCT) of the hand muscle, were noted in the patients with SCA6.

CONCLUSIONS

The prolongation of CMCT andCRT suggested that SCA6 disturbed the functions of the corticospinal tract and the transcortical polysynaptic pathways from the sensory to motorcortices. It seems likely that the CNS dysfunction caused by SCA6 is not limited to the structures that are anatomically abnormal. Furthermore, the prolongation of CMCT alone does not seem to suffice to differentiate between various types of autosomal dominant cerebellar ataxias. Molecular analysis is indispensable for the diagnosis of different genetic types of SCA.

Frontal and parieto-temporal cortical ablations and diaschisis-like effects on auditory neurocognitive potentials evocable from apparently intact ipsilateral association areas in humans: five case reports

The aim of this study was to investigate the effects of disruption on the warning auditory S1-elicited ERP and CNV complexes recordable on the site and on remote ipsilateral apparently normal anatomo-functionally interconnected brain regions. These effects in some cases showed aspects of a probable diaschisis-like phenomenon, due to resections of extensive frontal association cortex or of primary and secondary sensory parieto-temporal areas damaged by differing pathological processes. Using a standard CNV paradigm, 21/19 EEG electrodes connected with three different references, and scalp-topographic bidimensional mapping analysis, the S1 auditory binaural/monaural clicks N1a,b,c, P2, N2, P3 and CNV waves were recorded in 10 normal subjects and 11 patients. Nine of the latter had been submitted to unilateral frontal dorsolateral cortex ablation, one to bihemispheric dorsomedial cortex ablation, and one to unilateral ablation of sensory parieto-temporal cortex and underlying white matter, verified through CT/MRI examinations. No true S1ERP/CNV components were recordable over the ablated cortical areas, whereas normal ERP/CNV complexes were observable on the intact hemispheres. In five patients, four of whom with frontocortical ablations, the S1 ERP/CNV complexes appeared severely diminished or disrupted, in two cases in a slow, partially-reversible manner, also in the neuroradiologically normal ipsilateral functionally-connected post-rolandic sensory and association areas. Similar deactivation of some ERP components was observed in reverse on the unilateral dorsolateral frontocortical region in the fifth patient with parieto-temporal cortex ablation. Even when they are partially reversible, these ipsilateral remote ERP changes in apparently intact brain regions, due to ablations of functionally-interconnected cortical formations, probably reflect cortical deactivation or simply dysfacilitation deriving from functional unilateral diaschisis. If these changes are instead irreversible they may probably be interpreted as transneuronal degeneration phenomena, though they are not at present easy to document either neuroradiologically or electroclinically.

Post-traumatic amnesia after closed head injury: a review of the literature and some suggestions for further research

Post-traumatic amnesia (PTA) is a transient sequela of closed head injury (CHI). The term PTA has been in clinical use for over half a century, and generally refers to the subacute phase of recovery immediately after unconsciousness following CHI. The duration of PTA predicts functional outcome after CHI, but its pathophysiological mechanism is not known. This paper compares current methods of determining the duration of PTA, summarizes reports on neuropsychological deficits in PTA, reviews available data that allow inferences about its mechanism, and suggests methods for further exploration of its pathophysiology.

Functional differentiation of multiple perilesional zones after focal cerebral ischemia

Transient and permanent focal cerebral ischemia results in a series of typical pathophysiologic events. These consequences evolve in time and space and are not limited to the lesion itself, but they can be observed in perilesional (penumbra) and widespread ipsi- and sometimes contralateral remote areas (diaschisis). The extent of these areas is variable depending on factors such as the type of ischemia, the model, and the functional modality investigated. This review describes some typical alterations attributable to focal cerebral ischemia using the following classification scheme to separate different lesioned and perilesional areas: (1) The lesion core is the brain area with irreversible ischemic damage. (2) The penumbra is a brain region that suffers from ischemia, but in which the ischemic damage is potentially, or at least partially, reversible. (3) Remote brain areas are brain areas that are not directly affected by ischemia. With respect to the etiology, several broad categories of remote changes may be differentiated: (3a) remote changes caused by brain edema; (3b) remote changes caused by waves of spreading depression; (3c) remote changes in projection areas; and (3d) remote changes because of reactive plasticity and systemic effects. The various perilesional areas are not necessarily homogeneous; but a broad differentiation of separate topographic perilesional areas according to their functional state and sequelae allows segregation into several signaling cascades, and may help to understand the functional consequences and adaptive processes after focal brain ischemia.

Proton magnetic resonance spectroscopic imaging studies in patients with newly diagnosed partial epilepsy

PURPOSE

To assess whether the N-acetyl aspartate (NAA) to creatine ratio (NAA/Cr) is abnormally low at the onset of epilepsy and whether successful treatment of seizures with antiepileptic drugs is sufficient for normalization of NAA/Cr.

PATIENTS AND METHODS

Proton magnetic resonance spectroscopic imaging (1H-MRSI) was used to measure NAA/Cr in temporal lobes of eight patients with newly diagnosed epilepsy before or soon after starting medication. Six patients had follow-up 1H-MRSI examinations 7 months later. Clinical pattern of the seizures and the EEG findings suggested partial seizures in all and TLE in five patients. None of the patients had lesional epilepsy according to magnetic resonance imaging.

RESULTS

Initial 1H-MRSI of the temporal lobes showed significantly low NAA/Cr values in five of eight patients. Five of six patients who had follow-up 1H-MRSI were seizure-free after using medication; the remaining patient did not take medication and continued to experience occasional auras. Wilcoxon rank sign comparison of NAA/Cr on initial 1H-MRSI examination and follow-up 1H-MRSIs showed no significant difference (Z = 135, p = 0.893, 2-tailed) for five seizure-free patients.

CONCLUSIONS

Neuronal dysfunction is present at an early stage of the epileptic process. NAA/Cr recovery in seizure-free patients controlled with antiepileptic drugs is less evident, compared with successful surgical treatment. Thus, absence of seizures is not necessarily coupled with NAA/Cr improvement and observed variable response warrants further investigation.