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PubMed2001

Frontal lobes and human memory: insights from functional neuroimaging.

The new functional neuroimaging techniques, PET and functional MRI (fMRI), offer sufficient experimental flexibility and spatial resolution to explore the functional neuroanatomical bases of different memory stages and processes. They have had a particular impact on our understanding of the role of the frontal cortex in memory processing. We review the insights that have been gained, and attempt a synthesis of the findings from functional imaging studies of working memory, encoding in episodic memory and retrieval from episodic memory. Though these different aspects of memory have usually been studied in isolation, we suggest that there is sufficient convergence with respect to frontal activations to make such a synthesis worthwhile. We concentrate in particular on three regions of the lateral frontal cortex--ventrolateral, dorsolateral and anterior--that are consistently activated in these studies, and attribute these activations to the updating/maintenance of information, the selection/manipulation/monitoring of that information, and the selection of processes/subgoals, respectively. We also acknowledge a number of empirical inconsistencies associated with this synthesis, and suggest possible reasons for these. More generally, we predict that the resolution of questions concerning the functional neuroanatomical subdivisions of the frontal cortex will ultimately depend on a fuller cognitive psychological fractionation of memory control processes, an enterprise that will be guided and tested by experimentation. We expect that the neuroimaging techniques will provide an important part of this enterprise.

Animals↗

PubMed1993

Neuroimaging in schizophrenia research.

Neuroimaging has advanced the study of brain structure and function in schizophrenia. Magnetic resonance imaging provides measures of whole brain and regional anatomy and cerebrospinal fluid volume. Functional methods have included the Xenon-133 technique for measuring cerebral blood flow (CBF); positron emission tomography for assessing metabolism, CBF, and neuroreceptor functioning; and single photon emission computed tomography for studying CBF and neuroreceptors. Despite heterogeneity of patient samples, and studies which differed in the methodologies applied, there is converging evidence implicating three brain systems: frontal, temporolimbic, and basal ganglia. Current emphasis is aimed at probing specific regions across imaging modalities. Now these findings and research paradigms in neuroimaging must be integrated with phenomenological, neurobehavioral, and neuropathological investigations. The application of this technology is already helping to elucidate the neurobiology of schizophrenia, and further important advances can be anticipated.

Brain↗

PubMed1999

Neuroimaging in pediatric traumatic head injury: diagnostic considerations and relationships to neurobehavioral outcome.

Contemporary neuorimaging techniques in child traumatic brain injury are reviewed, with an emphasis on computerized tomography (CT) and magnetic resonance (MR) imaging. A brief overview of MR spectroscopy (MRS), functional MR imaging (fMRI), single-photon emission computed tomography (SPECT), and magnetoencephalography (MEG) is also provided because these techniques will likely constitute important neuroimaging techniques of the future. Numerous figures are provided to illustrate the multifaceted manner in which traumatic deficits can be imaged and the role of neuroimaging information as it relates to TBI outcome.

Acute Disease↗

PubMed2002

Educational neuroimaging: a proposed neuropsychological application of near-infrared spectroscopy (nIRS).

OBJECTIVE: To provide a description of an emerging neuroimaging methodology, near-infrared spectroscopy (nIRS), and a potential educational application of the unique aspects of this technology. SUMMARY: nIRS is documented for its potential as a personal, portable, brain imaging system that may prove useful for cerebral monitoring in applied settings such as home, school, and work. The basis of nIRS brain imaging is reviewed, with summary descriptions of optical and neurovascular issues as well as a brief comparison to other brain imaging methodologies. Recent developments in nIRS technology are discussed, including ongoing validation efforts and potential applications for neuropsychologists. We describe one potential application of nIRS (i.e., educational neuroimaging) as an illustration of the use of nIRS technology and the potential expansion of the neuropsychologist's role in the educational setting. CONCLUSION: nIRS holds the potential of opening new clinical questions and opportunities for neuropsychologists, and may provide a low-cost means of repeatable, neurovascular monitoring in nonmedical settings.

Brain Injuries↗

PubMedDate not supplied

Incoherence of neuroimaging studies of attention deficit/hyperactivity disorder.

Neuroimaging studies have been conducted with increasing frequency in recent years in attempts to identify structural and functional abnormalities in the brains of persons with attention deficit/hyperactivity disorder. Although the results of these studies are frequently cited in support of a biologic etiology for this disorder, inconsistencies among studies raise questions about the reliability of the findings. The present review shows that no specific abnormality in brain structure or function has been convincingly demonstrated by neuroimaging studies. Implications regarding stimulant treatment for attention deficit/hyperactivity disorder are discussed.

Animals↗

PubMed1995

Neuroimaging in child and adolescent neuropsychiatric disorders.

OBJECTIVE: To review the major findings and pathophysiological implications of imaging studies of neuropsychiatric disorders that onset in childhood or adolescence. METHOD: More than 200 neuroimaging studies were selected for review from Medline searches if the studies concerned developmental neuropsychiatric disorders such as autism, fragile X syndrome, Down syndrome, schizophrenia, obsessive-compulsive disorder, Tourette's syndrome, attention-deficit hyperactivity disorder, and dyslexia. RESULTS: Disordered central nervous system development may produce evidence of cortical neuronal migration abnormalities in autism, smaller cortical structures in Down syndrome, frontal lobe deficits and larger basal ganglia in schizophrenia, hypoplastic basal ganglia in Tourette's syndrome, aberrancies of the planum temporale in dyslexia, and hypoplastic cerebellar structures in numerous developmental disorders. Normal cerebral asymmetries appear to be disrupted in a number of disorders, including schizophrenia, Tourette's syndrome, attention deficit disorder, and dyslexia. CONCLUSIONS: Neuroimaging data regarding pathological central nervous system development in childhood are still sparse, and many of the findings in developmental disorders of childhood onset concern the study of adult subjects with those disorders. Nevertheless, imaging modalities previously used only in adults are with increasing frequency being applied to the study of children, which will likely continue to contribute to the understanding of pathological brain structure and function throughout childhood and to the improved treatment of these disorders.

Adolescent↗

PubMed2000

Neurodevelopmental and neuroimaging correlates in nonsyndromal microcephalic children.

This descriptive study examined the relationship between head size, developmental functioning, and neuroimaging findings in children with absolute microcephaly. Subjects, aged 1 to 48 months, were assigned to one of two groups based on occipitofrontal head circumference (OFC). Group A included subjects with an OFC of 2 to 2.99 standard deviations below the mean, and Group B included subjects with an OFC of 3 or more standard deviations below the mean. Brain scan findings for 62% of the subjects were abnormal. Findings included cerebral atrophy, cortical dysplasia, myelination delay, and white matter hypoplasia. Mean scores for developmental measures in Groups A and B were less than 70. Mean developmental scores in the normal imaging group were 70 or greater, whereas developmental scores in the abnormal imaging group were 52 or less. Forty-three percent of the subjects in Group A and 80% of those in Group B had abnormal findings from imaging studies (p = .0394). Subjects with one or more brain abnormalities determined on the basis of magnetic resonance images or computed tomographic scans had significantly lower scores in all developmental areas (p < .05). The authors concluded that abnormal brain images seem to be a better reflection of developmental performance than the degree of microcephaly. J Dev Behav Pediatr 21:12-18, 2000. Index terms: microcephaly, neuroimaging, neurodevelopment.

Anthropometry↗

PubMed1995

A comparison of neuroimaging modalities for diagnosing dementia.

Advances in neuroimaging have permitted knowledge of brain structures and physiology that were unknown 20 years ago and are playing an increasingly important role in the diagnosis of dementia. This article provides information on the types of brain scans, usual indications, risks, costs, and preparation of patients undergoing neuroimaging for the diagnosis of dementia. Each of the major imaging modalities is discussed from the perspective of what it uniquely offers to the diagnostic process. In general, the information gained from anatomic imaging complements that obtained from functional studies. In early stages of dementia, anatomic scans may appear normal while significant abnormalities are evident in functional images. This review familiarizes clinicians with these major developments to prepare them to educate and communicate with patients and their families.

Brain↗

PubMed2000

Chloral hydrate versus midazolam for sedation of children for neuroimaging: a randomized clinical trial.

OBJECTIVE: The comparative safety and efficacy of chloral hydrate and midazolam for sedation of children has not been adequately studied. METHODS: In a double-blind randomized trial, at a single university hospital, we enrolled 40 children, ages 2 months to 8 years, in an out-patient neuroimaging study. Children judged to require sedation were enrolled during a 14-month period ending August 1995. They received identically appearing liquids of equal volume of either chloral hydrate (75 mg/kg, maximum 2 g) or midazolam (0.5 mg/kg, maximum 10 mg) by mouth. Children were monitored for changes in arterial blood pressure, oxygen saturation, pulse, respiration and anxiety. Efficacy was judged by evaluating the child's ability to complete the intended scan. Supplemental dosing was administered to children who were judged inadequately sedated 30 minutes after the initial medication. RESULTS: Interim analysis demonstrated a significant sedation failure rate. Of 40 enrolled children, 33 completed the protocol. Efficacy was significantly improved for the chloral hydrate group for both ability to perform the scan, chloral hydrate = 11/11 (100%, 95% CI = 72-100) vs. midazolam = 11/22 (50%, 95% CI = 29-71), and the need for supplementary dosing, chloral hydrate = 1/11 (9%, 95% CI = 0-26) vs midazolam = 12/22 (55%, 95% CI = 34-76), P<0.05. Mean duration of sedation was not significantly different. No physiological deterioration occurred and no oxygen administration was required. CONCLUSIONS: We conclude that, in these doses, oral chloral hydrate may provide more effective sedation than midazolam for brief neuroimaging studies in young children.

Anxiety↗

PubMed1998

Diagnostic problems in multiple sclerosis: overreliance on neuroimaging.

Atypical manifestations of multiple sclerosis (MS) can mislead the physician into misdiagnosis. The correct diagnosis of MS depends on a combination of clinical and laboratory evidence. The introduction of newer neuroimaging studies has decreased the proportion of overdiagnoses of MS. Overreliance on either clinical or laboratory (currently neuroimaging) data can lead to underdiagnosis. The physician should consider the possibility of an atypical clinical presentation of MS in the differential diagnosis of patients with disease of the central nervous system.

Adult↗

PubMed1994

Contributions of neuroimaging to diagnosis and monitoring of multiple sclerosis.

Recent advances in magnetic resonance neuroimaging have resulted in an increased ability to distinguish acute, potentially reversible lesions from chronic, irreversible lesions in multiple sclerosis. Refinements of magnetic resonance imaging techniques, such as fluid-attenuated inversion recovery, diffusion imaging, and magnetization transfer imaging, as well as magnetic resonance spectroscopic imaging, are providing increased sensitivity and allowing detection of changes in multiple sclerosis white matter that appears normal on standard spin-echo magnetic resonance images. Increased neuroimaging specificity and sensitivity enhance the ability to diagnose, monitor, and understand the progression of multiple sclerosis. Magnetic resonance spectroscopy and magnetic resonance spectroscopic imaging detect metabolites in vivo and have even greater potential for elucidating the biochemical pathology of demyelination in multiple sclerosis.

Brain↗

PubMed2000

Contribution of neuroimaging in the diagnosis of Alzheimer's disease and other dementias.

This paper reviews the use of neuroimaging in the diagnosis of dementia, especially Alzheimer's disease. Computed tomography is still used to determine reversible causes of dementia; however, without clinical symptoms these causes are hard to find and computed tomography scanning is only cost-effective in a defined group of patients. Using magnetic resonance imaging, atrophy of the medial temporal lobe can be assessed volumetrically and visually, with a high correlation between the two methods. Medial temporal lobe atrophy is highly predictive of Alzheimer's disease, and correlates with neuropsychological performance and postmortem histologically measured volume. Cerebral volume changes over time seem to differentiate Alzheimer's disease and mild cognitive impairment progressing to Alzheimer's disease from controls with high accuracy. Studies of the corpus callosum in dementia indicate a cortico-cortical disconnection caused by atrophy. Of the new techniques, functional magnetic resonance imaging seems the most promising. This technique can possibly play a role in predicting Alzheimer's disease in patients with mild cognitive impairment. The use of single-photon emission computed tomography and positron emission tomography in (early) differential diagnoses seems limited. Lower regional cerebral blood flow is related to the severity of dementia and survival. Iodine-123 iodobenzamide single-photon emission computed tomography in dementia with Lewy bodies seems promising. Current and future positron emission tomography studies concentrate on memory function and receptor imaging. The focus in neuroimaging, especially magnetic resonance imaging, has shifted to early diagnosis and monitoring of the disease course, with a special interest in predicting dementia in patients with mild cognitive impairment.

Alzheimer Disease↗

PubMed2005

Neuroimaging of rodent and primate models of alcoholism: initial reports from the integrative neuroscience initiative on alcoholism.

Neuroimaging of animal models of alcoholism offers a unique path for translational research to the human condition. Animal models permit manipulation of variables that are uncontrollable in clinical, human investigation. This symposium, which took place at the annual meeting of the Research Society on Alcoholism in Vancouver, British Columbia, Canada, on June 29th, 2004, presented initial findings based on neuroimaging studies from the two centers of the Integrative Neuroscience Initiative on Alcoholism funded by the National Institute on Alcohol Abuse and Alcoholism. Effects of alcohol exposure were assessed with in vitro glucose metabolic imaging of rat brain, in vitro receptor imaging of monkey brain, in vivo magnetic resonance imaging of monkey brain, and in vivo magnetic resonance spectroscopic quantification of alcohol metabolism kinetics in rat brain.

Alcoholism↗

PubMed2004

Update on neuroimaging in infectious central nervous system disease.

PURPOSE OF REVIEW: Neuroimaging constitutes an important component in the diagnosis of the underlying infectious agents in central nervous system infection. This review summarizes progress in the neuroimaging of infectious central nervous system disease since January 2003. It focuses on imaging of viral encephalitis, including that caused by exotic and emerging viruses, and on imaging in immunodeficient patients. RECENT FINDINGS: Diffusion-weighted imaging has been shown to be superior to conventional magnetic resonance imaging for the detection of early signal abnormalities in herpes simplex virus encephalitis but also in enterovirus 71 encephalitis and in West Nile encephalitis. Several studies defined the pattern of magnetic resonance imaging signal changes in endemic diseases such as West Nile encephalitis, Murray Valley encephalitis, enterovirus 71 encephalitis and Japanese encephalitis, but also in encephalitides due to ubiquitous viruses such as measles virus and Lyssavirus (rabies). In patients with HIV infection, apparent diffusion coefficient ratios obtained by diffusion-weighted imaging were significantly greater in lesions due to Toxoplasma encephalitis than in primary central nervous system lymphomas. SUMMARY: The diagnosis of unclear infectious central nervous system diseases remains a challenge. More recent magnetic resonance imaging techniques, such as diffusion-weighted imaging and magnetic resonance spectroscopy, provide additional helpful information. However, the mainstay of diagnosis remains the detection of viral DNA or serological markers of specific infectious agents within the cerebrospinal fluid.

Brain↗

PubMed2006

The neural bases of prosopagnosia and pure alexia: recent insights from functional neuroimaging.

PURPOSE OF REVIEW: To discuss whether recent functional neuroimaging results can account for clinical phenomenology in visual associative agnosias. RECENT FINDINGS: Functional neuroimaging studies in healthy human subjects have identified only two regions of ventral occipitotemporal cortex that invariantly respond to individual faces and visual words, respectively. The signature of face identity coding in the fusiform neural response was shown to be missing in a patient with prosopagnosia. Another case study established that a surgical lesion close to the region sensitive to visual words can result in pure alexia. SUMMARY: Evidence is increasing that functional specialization for processing face identity and visual word forms is restricted to two specialized sensory modules in the occipitotemporal cortex. A structural or functional lesion to face-sensitive and word-sensitive regions in the ventral occipitotemporal cortex can provide the most parsimonious account for the clinical syndromes of prosopagnosia and agnosic alexia. This review suggests that functional specialization should be considered in terms of whether exclusively one brain region (instead of many) underpins a defined function and not as whether this brain region underpins exclusively one cognitive function. Such functional specialization seems to exist for at least two higher-order visual perceptual functions, face and word identification.

Dyslexia↗

PubMed1999

Functional neuroimaging in psychiatry.

Functional neuroimaging is one of the most powerful means available for investigating the pathophysiology of psychiatric disorders. In this review, we shall focus on the different ways that it can be employed to this end, describing the major findings in the field in the context of different methodological approaches. We will also discuss practical issues that are particular to studying psychiatric disorders and the potential contribution of functional neuroimaging to future psychiatric research.

Brain↗

PubMed2006

The impact of the 1991 Gulf War on the mind and brain: findings from neuropsychological and neuroimaging research.

Many veterans of the 1991 Gulf War (GW) have complained of somatic and cognitive symptoms that may be neurological in nature. However, whether or not changes in brain function are associated with GW service continues to be debated. Studies of GW veterans using objective, performance-based neuropsychological measures have yielded inconsistent findings, with those indicating deficits among GW veterans typically revealing only relatively mild levels of neuropsychological impairment. Further, performances on objective neuropsychological tasks show little correspondence to subjective perceptions of cognitive functioning. Although preliminary magnetic resonance spectroscopy (MRS) studies demonstrate reduced N-acetylaspartate-to-creatine (NAA/Cr) ratio in select brain regions among GW veterans who report health concerns, this work requires further replication with larger, more representative samples. There is no evidence from neuroimaging studies of a non-specific effect of GW service or of changes in brain structure or function related to health status when conventional radiological methods are used. Owing to the paucity of objective exposure, baseline health data, and the now significant time elapsed since the GW, aetiological issues may never be fully resolved. Therefore, research addressing clinical management of GW veterans with neuropsychological dysfunction and neuroimaging abnormalities may prove more fruitful than exclusive focus on aetiology.

Brain↗

PubMed2003

Mixtures of general linear models for functional neuroimaging.

We set out a new general framework for making inferences from neuroimaging data, which includes a standard approach to neuroimaging analysis, statistical parametric mapping (SPM), as a special case. The model offers numerous conceptual and statistical advantages that derive from analyzing data at the "cluster level" rather than the "voxel level" and from explicit modeling of the shape and position of clusters of activation. This provides a natural and principled way to pool data from nearby voxels for parameter and variance-component estimation. The model can also be viewed as performing a spatio-temporal cluster analysis. The parameters of the model are estimated using an expectation maximization (EM) algorithm.

Acoustic Stimulation↗