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PubMed1999

Review neuroimaging in amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a chronic degenerative disorder of unknown etiology affecting the motor system. Conventional and non-conventional neuroimaging techniques can provide essential help both to increase the confidence in ALS diagnosis and to assess the disease evolution. Signal abnormalities at the level of the motor cortex and the corticospinal tract on conventional T2-weighted magnetic resonance (MR) images are a potentially useful marker of ALS pathology. However, the prognostic value of these conventional MR abnormalities is still hampered by their low pathological specificity. Non-conventional MR techniques with a higher pathological specificity, such as MR spectroscopy, magnetization transfer imaging and diffusion-weighted imaging, seem to have some potential not only for ALS diagnosis, but also for monitoring disease evolution either naturally or when modified by experimental treatments.

Amyotrophic Lateral Sclerosis↗

PubMed1996

Neuroimaging Findings in Anxiety Disorders.

Individuals with severe anxiety have long sought a physical basis for their symptoms. There is increasing evidence to suggest brain abnormalities as the primary mechanism responsible for pathological anxiety, particularly panic disorder. However, older-generation brain imaging techniques, capable of assessing brain structure, have not identified consistent anatomical differences or structural abnormalities by which to explain the symptoms. In this regard, the development of modern functional imaging techniques that can specifically assess regional brain blood flow, metabolic status, or chemical composition are beginning to elucidate underlying brain mechanisms which may be responsible for "state" or situational-specific anxiety and "trait" or pathological anxiety. The intent of this article is to provide a review of neuroimaging studies undertaken to investigate state anxiety or specific anxiety disorders. The focus of this article is on studies that have used newer brain imaging techniques capable of assessing brain functionality, such as single photon emission computerized tomography, positron emission tomography, or magnetic resonance spectroscopy (MRS), in relationship to specific anxiety disorders. We have undertaken studies of panic disorder using MRS to investigate acute panic precipitated by physiological or chemical challanges, such as intravenous sodium lactate infusion, while measuring brain metabolic responses. These studies are presented in detail as a model of how these newer functional imaging modalities can be applied as a tool to begin to unravel the underlying pathophysiological processes responsible for production of panic. It is anticipated that future application of these newer functional imaging techniques will allow both the determination of a brain mechanism(s) responsible for pathological anxiety and advance our understanding of mechanisms responsible for effective treatments.

Journal Article↗

PubMed1997

Neuroimaging in Closed Head Injury.

Closed head injury can be associated with significant neurologic dysfunction. Neuroimaging in this condition consists of conventional techniques such as computed tomography (CT) and magnetic resonance imaging (MR), and functional imaging studies such as single photon emission computerized tomography (SPECT) and positron emission tomography (PET). Whereas CT and MR are sufficient to show the acute concomitants of head trauma such as extra-axial hematomas, contusions, and shear injury, functional brain imaging has been shown to play an important role in management of victims of closed head injury, particularly in the chronic stages. Detection of changes in regional cerebral blood flow associated with brain injury have been found to correlate better with neurological status and prognosis than abnormalities seen by CT or MRI.

Journal Article↗

PubMed2003

Neuroimaging in cerebrovascular disorders: measurement of cerebral physiology after stroke and assessment of stroke recovery.

Nuclear medicine imaging can play an important role in the diagnosis of stroke risk, the differential diagnosis of vascular and parenchymal cerebral abnormalities, and the understanding and management of poststroke recovery. Radionuclide brain-imaging methods can assess hemodynamic, vascular, and metabolic status before and after stroke. Several techniques, including vasodilatory stress imaging with regional cerebral blood flow (rCBF) single-photon emission computed tomography (SPECT), oxygen extraction methods with positron emission tomography (PET), and spectroscopic imaging with magnetic resonance spectroscopic imaging, offer ways to distinguish vascular from parenchymal dysfunction and to determine whether any observed abnormalities in cerebral blood flow are primary or secondary disease manifestations. The value of radionuclide imaging in assessing the efficacy of several interventional surgical procedures is presented. Data from several imaging modalities bearing on the controversial issue of luxury perfusion and reperfusion injury are analyzed, including some of the discrepancies between animal and human clinical data. Imaging evidence for white matter disease and microangiopathy is analyzed, including a quantitative rCBF pattern analysis that distinguishes between typical Alzheimer's disease and microangiopathy by using multivariate analysis of variance curve profile analysis, which shows results of significant differences in the circumferential cortical blood flow profiles at P =.01. Microangiopathy showed rCBF reduction in the frontal and frontotemporal regions as compared with the more typical reduction in posterior temporal-parietal rCBF diminution characteristic of Alzheimer's disease. Several functional neuroimaging approaches to the study of cerebral poststroke reorganization are analyzed in the context of 2 major models of recovery: the resolution of diaschisis and reorganization in spared brain. Research on these issues is presented with SPECT, PET, magnetic resonance imaging, and magnetic resonance spectroscopy. Data show how standard structural magnetic resonance imaging, (99m)Tc hexamethylpropylene amine oxime SPECT, PET imaging, and magnetic resonance spectroscopy can be used to identify the extent of permanent damage versus penumbral and remote effects of a stroke. The results of the analysis of the pure-diaschisis model show a high correlation between the rCBF brain SPECT defect volume in the cortex and the magnetic resonance spectroscopic imaging (MRSI) change in the white matter. There is a statistically significant positive correlation between the 2 (P <.01; r(2) = 0.94). The increased creatine/N-acetyl aspartate and reduced rCBF are proposed to be due to an increase in the white matter creatine component due to diaschisis and the repair mechanisms associated with increased astrocytosis, in addition to a reduction of N-acetyl aspartate in diaschitic white matter. Xenon-133 dynamic SPECT is shown to be a quantitative and sensitive measure of cerebrovascular status and hemodynamic constraints in both spared and affected brain, providing evidence for reorganization and cerebral plasticity. Fluorine-18 PET and (31)P spectroscopic imaging data show reorganizational changes in the contralesional hemisphere after stroke. The phosphocreatine-adenosine triphosphate ratio in the contralesional hemisphere was 38% +/- 17% higher than in the ipsilateral hemisphere. The phosphocreatine-adenosine triphosphate ratio was highly correlated (r = 0.88, P <.05) with increasing (18)F-fluorodeoxyglucose uptake. These results showed that there is a parallel change in glucose metabolism and high-energy phosphate metabolism associated with poststroke recovery that is proposed to be due to cerebral reorganization in the contralateral premotor cortex. The value of these results on rehabilitation strategy, including possible criteria for the use of facilitatory versus compensatory approaches, is analyzed.

Aged↗

PubMed2001

Pituitary tumours in adolescence: clinical behaviour and neuroimaging features of seven cases.

The clinicopathologic features of seven paediatric patients with pituitary adenomas (2 male, 5 female; mean age 14.3 years) were reviewed. There were three non-functioning adenomas, three prolactinomas, and one growth hormone producing adenoma. Five patients presented with visual field deficits, and six patients had endocrine symptoms, which included menstrual irregularities in all female patients, pubertal delay in two females, and growth delay and gigantism in one case each. On neuroimaging studies, five adenomas showed parasellar extension, while the remaining two prolactinomas were intrasellar microadenomas. While two patients with prolactinomas received good results with bromocriptine treatment alone, the remaining five patients underwent either craniotomy or transsphenoidal surgery. Postoperatively, visual disturbances improved markedly in all patients. Two patients also received replacement hormonal therapy. While six patients have been stable for 3.6 years on average, one non-functioning tumour recurred 2 years after the initial transcranial subtotal resection of the tumour. Although there are still many unknowns concerning the biology and optimal treatments for paediatric pituitary adenomas, many of them are assumed to be relatively rapidly growing tumours, while others merely have an earlier tumour genesis than in adults.

Adolescent↗

PubMed2002

Tumours around the foramen of Monro: clinical and neuroimaging features and their differential diagnosis.

The clinical and neuroimaging features of 20 patients with lateral ventricular tumours located around the foramen of Monro were reviewed retrospectively with special emphasis on the differential diagnoses. Histologic types were: eight neurocytomas, four subependymal giant cell astrocytomas (SGCAs), three subependymomas, two fibrillary astrocytomas, and one each of pilocytic astrocytoma, malignant astrocytoma and malignant teratoma. The mean age of the patients with neurocytoma was 29.6 years, with SGCA 13.3 years and with subependymoma 55.3 years. All tumours appeared nodular in shape, and on computed tomography (CT) neurocytomas were either isodense or highdense with the brain, while all subependymomas and SGCAs were lowdense. Calcification was observed in two SGCAs, and one neurocytoma. Five neurocytomas and all four SGCAs showed mild to moderate contrast enhancement, while all three subependymomas showed either no, or scarce, enhancement. Magnetic resonance imaging (MRI) studies were available in 10 patients, with the signal characteristics of four neurocytomas and three SGCAs being nonspecific, while two subependymomas were both hypointense on T1-weighted images and hyperintense on T2-weighted images. Thus important features for differential diagnosis included age of the patient and density on precontrast CT. In this series, either an extensive excision of the tumour or a partial removal, thus relieving the obstruction of the foramina of Monro, usually provided long term survival, with 18 patients surviving a mean of 10.8 years.

Adolescent↗

PubMed1999

A topological hypothesis for the functional connections of the cortex. A principle of the cortical graphs' based on the neuroimaging.

Combined EEG and PET techniques show three activation levels of the cortex: deep sleep, relaxed state and alert. We propose, correspondingly, that a cortical module can be in one of three equivalent states: inactivated, pre-activated, and activated. Neuroimaging techniques can show activated cortical regions in detail. However, the functional connections (FCs) among them are not shown in the image. They can be found by EEG-coherence functions. This can be seen as a 'three-level- cortical graph'. A cortical graph is a mathematical representation where the cortical units (modules or regions) are represented by points (nodes) and the FCs are represented by lines between these points. At the upper level, activated modules can establish FCs implying high electrical coherence (they are the winners of a competitive process between preactivated modules at the middle level). We propose that, during alert state, the activated nodes and the dynamic switching among them always form connected graphs. It means that, for any possible configuration, there always exists a path (direct or indirect) between any couple of nodes. We base our view on (1) analysis of simple tasks by PET; (2) the existence of coordinated behavior in normal subjects; (3) cortical topologies previously proposed; and (4) computer simulations of cortico-cortical connections. We also suggest that disengaged (nonconnected) cortical graphs, produce 'functional disconnection syndromes' which cause some symptoms in schizophrenia, and Alzheimer disease.

Cerebral Cortex↗

PubMed2003

Stereotactic biopsy in the era of advanced neuroimaging. Does the minimal therapeutic gain justify its current wide use?

OBJECTIVE: This study reviewed the contribution of stereotactic brain biopsy in the management and final outcome of a series of patients with presumed inoperable lesions. PATIENTS AND METHODS: Sixty-nine consecutive patients underwent a CT-guided lesion biopsy (n = 67) or abscess/cyst aspiration (n = 2) using the Cosman-Roberts-Wells (CRW) frame. RESULTS: A definitive specific diagnosis was made in 53 of 67 patients (79 %). The remaining procedures did not provide a diagnosis because of failure to obtain appropriate specimen (11 patients), findings consistent with non-specific inflammation (2 patients) or uneventful surgical complication requiring termination of the procedure (1 patient). A total of 55 patients (80 %) died due to the malignant nature of the lesion, most within six months after the biopsy. The preoperative imaging diagnosis was consistent with the histological diagnosis in 60 patients (87 % accuracy). The perioperative morbidity and mortality were nil and most of the patients were discharged within twenty-four hours. CONCLUSIONS: The stereotactic biopsy did not alter either the therapeutic management or the mortality due to the natural course of the lesion. These findings indicate that the current principle of mandatory histological diagnosis in virtually all non-resectable brain lesions should be re-evaluated taking into account parameters such as: age, medical/neurological status, neuroimaging characteristics, patients' best interest and health care financial shortages.

Adolescent↗

PubMed2005

[Neuroimaging findings in posttraumatic stress disorder: review of the literature].

The knowledge about the development and maintenance of the posttraumatic stress disorder (PTSD) has increased significantly in the past 10 years with important insights coming from imaging studies. Through these insights PTSD has changed from "traumatic neurosis" to a biologically based psychological disorder. This paper summarises the recent literature on morphological, functional and metabolic neuroimaging on PTSD. Of special interest are four brain areas, the hyperactive amygdala, the hippocampus with volume reduction as well as the cingulate gyrus and orbitofrontal cortical regions, which may not be able to inhibit the hyperactive amygdala to trauma related stimuli. Based on these imaging data the current understanding of the pathophysiology of PTSD as well as present methodological limitations of imaging methods will be discussed.

Brain↗

PubMed2006

[Management of incidental findings in neuroimaging in diagnosis and pathophysiological research].

Structural, quantitative and functional neuroimaging has contributed greatly to the advancement in clinical diagnosis and research into pathophysiology of psychiatric disorders. In diagnostic investigations, the frequency of "incidental" findings, i. e. potentially pathological findings, which are unexpected with regards to the primary diagnostic question and which cannot be related to the presenting clinical symptomatology, amounts up to 30 %. Approximately 2 - 5 % of these unexpected findings have immediate clinical consequences. The analysis of incidental findings in the context of clinical diagnostic procedures allows to extrapolate on their prevalence in experimental studies, because here, such findings are not systematically documented. Several medical, ethical and legal problems arise related to the detection, evaluation and documentation of incidental findings in clinical experimental studies. These problems and resulting obligations will be discussed and solutions with respect to the management of incident findings will be proposed.

Biomedical Research↗

PubMed2006

[The neurobiological dimension of meditation--results from neuroimaging studies].

Meditation in general can be understood as a state of complete and unintentional silent and motionless concentration on an activity, an item or an idea. Subjectively, meditative experience is said to be fundamentally different from "normal" mental states and is characterized by terms like timelessness, boundlessness and lack of self-experience. In recent years, several fMRI- and PET-studies about meditation which are presented in this paper have been published. Due to different methods, especially different meditation types, the results are hardly comparable. Nevertheless, the data suggest the hypothesis of a "special" neural activity during meditative states being different from that during calm alertness. Main findings were increased activation in frontal, prefrontal and cingulate areas which may represent the mental state of altered self-experience. In the present studies, a considerable lack of scientific standards has to be stated making it of just casuistic value. Today's improved neurobiological examination methods - especially neuroimaging techniques - may contribute to enlighten the phenomenon of qualitatively different states of consciousness.

Humans↗

PubMed1993

Electroencephalographic and neuroimaging findings in neonates undergoing extracorporeal membrane oxygenation.

Electroencephalograms (EEGs) were recorded on 36 infants who were treated with arteriovenous extracorporeal membrane oxygenation (ECMO) between 1986 and 1989. Twelve of 36 infants had EEGs prior to and during ECMO. Twenty-one infants who met ECMO criteria but were treated with mechanical ventilation only served as a comparison (COMP) group. Electrographic seizures occurred in 7 of the 36 (19%) ECMO patients and in 3 of the 21 (14%) COMP patients. Five of 7 ECMO infants had electrographic status epilepticus. Three infants developed electrographic seizures during ECMO in association with an acute cerebral injury. These patients did not have significant hemispheric predominance in the origin of electrographic seizures (2 right, 3 left and 2 bilateral). Repetitive or periodic discharges (RPD) with frequencies between 0.5 and 5 Hz were seen after starting therapy in 23 of the 36 (64%) ECMO patients and 15 of the 21 (71%) of the COMP group. Only in the ECMO patients did RPD arise significantly more frequently from the right hemisphere (13 right, 4 left and 6 bilateral; p = 0.015). Neuroimaging studies showed evidence of ischemic lesion in 8 of the 36 (22%) ECMO patients with significantly right-sided predominance (5 right, 1 left and 2 bilateral; p = .05). Cerebellar hemorrhages occurred in 3 ECMO patients. Ischemic lesions occurred in 3 of the 21 (14%) COMP patients, all occurring on the left side. In the ECMO group, severe outcome or death was significantly associated with the presence of electrographic seizures, status epilepticus, and suppression-burst pattern (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Brain Injuries↗

PubMed1998

The neural development and organization of letter recognition: evidence from functional neuroimaging, computational modeling, and behavioral studies.

Although much of the brain's functional organization is genetically predetermined, it appears that some noninnate functions can come to depend on dedicated and segregated neural tissue. In this paper, we describe a series of experiments that have investigated the neural development and organization of one such noninnate function: letter recognition. Functional neuroimaging demonstrates that letter and digit recognition depend on different neural substrates in some literate adults. How could the processing of two stimulus categories that are distinguished solely by cultural conventions become segregated in the brain? One possibility is that correlation-based learning in the brain leads to a spatial organization in cortex that reflects the temporal and spatial clustering of letters with letters in the environment. Simulations confirm that environmental co-occurrence does indeed lead to spatial localization in a neural network that uses correlation-based learning. Furthermore, behavioral studies confirm one critical prediction of this co-occurrence hypothesis, namely, that subjects exposed to a visual environment in which letters and digits occur together rather than separately (postal workers who process letters and digits together in Canadian postal codes) do indeed show less behavioral evidence for segregated letter and digit processing.

Adult↗

PubMed1998

Components of verbal working memory: evidence from neuroimaging.

We review research on the neural bases of verbal working memory, focusing on human neuroimaging studies. We first consider experiments that indicate that verbal working memory is composed of multiple components. One component involves the subvocal rehearsal of phonological information and is neurally implemented by left-hemisphere speech areas, including Broca's area, the premotor area, and the supplementary motor area. Other components of verbal working memory may be devoted to pure storage and to executive processing of the contents of memory. These studies rest on a subtraction logic, in which two tasks are imaged, differing only in that one task presumably has an extra process, and the difference image is taken to reflect that process. We then review studies that show that the previous results can be obtained with experimental methods other than subtraction. We focus on the method of parametric variation, in which a parameter that presumably reflects a single process is varied. In the last section, we consider the distinction between working memory tasks that require only storage of information vs. those that require that the stored items be processed in some way. These experiments provide some support for the hypothesis that, when a task requires processing the contents of working memory, the dorsolateral prefrontal cortex is disproportionately activated.

Brain↗

PubMed2001

Neuroimaging evidence implicating cerebellum in the experience of hypercapnia and hunger for air.

Recent neuroimaging and neurological data implicate cerebellum in nonmotor sensory, cognitive, vegetative, and affective functions. The present study assessed cerebellar responses when the urge to breathe is stimulated by inhaled CO(2). Ventilation changes follow arterial blood partial pressure CO(2) changes sensed by the medullary ventral respiratory group (VRG) and hypothalamus, entraining changes in midbrain, pons, thalamus, limbic, paralimbic, and insular regions. Nearly all these areas are known to connect anatomically with the cerebellum. Using positron emission tomography, we measured regional brain blood flow during acute CO(2)-induced breathlessness in humans. Separable physiological and subjective effects (air hunger) were assessed by comparisons with various respiratory control conditions. The conjoint physiological effects of hypercapnia and the consequent air hunger produced strong bilateral, near-midline activations of the cerebellum in anterior quadrangular, central, and lingula lobules, and in many areas of posterior quadrangular, tonsil, biventer, declive, and inferior semilunar lobules. The primal emotion of air hunger, dissociated from hypercapnia, activated midline regions of the central lobule. The distributed activity across the cerebellum is similar to that for thirst, hunger, and their satiation. Four possible interpretations of cerebellar function(s) here are that: it subserves implicit intentions to access air; it provides predictive internal models about the consequences of CO(2) inhalation; it modulates emotional responses; and that while some cerebellar regions monitor sensory acquisition in the VRG (CO(2) concentration), others influence VRG to adjust respiratory rate to optimize partial pressure CO(2), and others still monitor and optimize the acquisition of other sensory data in service of air hunger aroused vigilance.

Adult↗

PubMed2001

Advances in functional neuroimaging methodology for the study of brain systems underlying human neuropsychological function and dysfunction.

Functional neuroimaging allows the non-invasive identification of distributed patterns of human brain activity associated with perceptual, congnitive, emotional and behavioral processes, in health and disease. Work in this field is methodologically intensive, requiring an interdisciplinary team of scientists to develop and apply rapidly advancing techniques. Here we focus upon the principles and methods of functional imaging, from hypothesis generation and study design, to subject recruitment and clinical characterization, neuropsychological paradigm development, image acquisition, image processing and statistical analysis, and data interpretation. The strengths and limitations of the various techniques are discussed, with an emphasis on positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), which have proven to be powerful tools for human brain mapping. The integration of these techniques with electroencephalography (EEG) and magnetoencephalography (MEG), which provide greater temporal information, is outlined. An understanding of such methodological issues is a necessary prerequisite to the development of new imaging methods with improved capabilities, to the careful application of existing methods to neuropsychological problems, and to the critical examination of planned or published studies.

Brain↗

PubMed2001

Functional neuroimaging and episodic memory: a perspective.

One area of research that has significantly benefited from the recent development of functional neuroimaging techniques is the study of memory. In this review we explore what has been learned about the neural basis of normal memory function using these techniques. We focus on episodic memory, which is characterized by the ability to consciously recollect memories for facts or events. We highlight three neuroanatomical regions that have been linked to episodic memory: The hippocampal complex, the prefrontal cortex and the amygdala. For each of these regions, we discuss the behavioral methods of assessment and specific episodic memory processes, particularly encoding and retrieval. Finally, we briefly comment on the potential clinical applications for this research and other memory systems.

Amygdala↗

PubMed2001

Functional neuroimaging of human central auditory processing in normal subjects and patients with neurological and neuropsychiatric disorders.

Auditory sensory processing in the human cerebral cortex is disturbed in several neurological and neuropsychiatric disorders, ranging from devastating perceptual deficits in neuropsychological syndromes such as cortical deafness and auditory agnosia to the problem of involuntary hallucinatory perception in schizophrenia. With modern non-invasive functional imaging techniques (e.g., PET, fMRI, and MEG), the normal auditory cortical functional anatomy can now be studied in humans in vivo, as well as its disruption in pathological conditions. This article will summarize current knowledge on human central auditory perception in health and disease, with an emphasis on recent functional neuroimaging studies, in the context of clinical and basic neuroscientific knowledge. New strategies include a focus on the role of other, non-temporal brain areas for auditory processing, particularly in the frontal lobes, and the combined use of techniques offering both precise spatial and temporal resolution. One step towards this goal has been the recent development of a silent, event-related fMRI scanning technique.

Auditory Perception↗