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Results for “Brain Mapping”

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At least 811 records · Page 45Linked to original sources

PubMed1994

[Study of topographic mapping of the auditory middle latency response in the guinea pigs].

Topographic mapping techniques were applied to study the auditory middle latency response (MLR) in 10 awake guinea pigs. Fourteen holes (1mm in diameter) were drilled through the skull regions and epidural electrodes were fixed on the skull with the dental cement, then auditory MLR were recorded with 13 electrodes, and MLR brain maps were obtained with a concerto system. Our result supports the hypothesis of multiple MLR generators. The main components are wave A, wave B and wave C. The foci localise the temporal lobe contralateral to the stimulated ear. The other components are wave M- and wave M+. The foci localise parietal and occipital lobes. Each wave responds differently to procaine. The result suggests that wave A, wave M- and wave M+ are generated from the subcortex, while wave B, wave C generated from the cortex.

Acoustic Stimulation↗

PubMed1996

A stereotaxic atlas of the basal ganglia in macaques.

Maps of the striatum, pallidum and subthalamic nucleus were established in two macaque species (Macaca mulatta and Macaca fascicularis) in stereotaxic coordinates. The cartographic method relied on the use of intracerebral, ventricular landmarks (CA: anterior commissure and CP: posterior commissure). The basal ganglia outlines, first drawn in transverse sections perpendicular to the CA-CP plane, were reconstructed on the horizontal and midsagittal planes. Maps from several individuals were superimposed and statistical variations studied. The results confirm that the length between the two CA and CP points is statistically greater (7%) in the Macaca mulatta than Macaca fascicularis but reveal considerable inter-individual differences. The closer a given nucleus is from a ventricular reference point, the more stable its outline. Superimpositions led to a statistical determination of the stereotaxic coordinates required to reach a given target center. Comparison of the lateralities with those measured in six previously published atlases indicates that the brain mapped by Snider and Lee [17] is the smallest and that mapped by Olszewski [8] is the largest.

Animals↗

PubMed2003

On the synchronization of transcranial magnetic stimulation and functional echo-planar imaging.

PURPOSE: To minimize artifacts in echo-planar imaging (EPI) of human brain function introduced by simultaneous transcranial magnetic stimulation (TMS). MATERIALS AND METHODS: Distortions due to TMS pulses (0.25 msec, 2.0 T) were studied at 2.0 T before and during EPI. RESULTS: Best results were obtained if both the EPI section orientation and the frequency-encoding gradient were parallel to the plane of the TMS coil. Under these conditions, a TMS pulse caused image distortions when preceding the EPI sequence by less than 100 msec. Recordings with a magnetic field gradient pick-up coil revealed transient magnetic fields after TMS, which are generated by eddy currents in the TMS coil. TMS during image acquisition completely spoiled all transverse magnetizations and induced disturbances ranging from image corruption to mild image blurring, depending on the affected low and high spatial frequencies. Simultaneous TMS and radio-frequency (RF) excitation gave rise to T1-dependent signal changes that lasted for several seconds and yielded pronounced false-positive activations during functional brain mapping. CONCLUSION: To ensure reliable and robust combinations, TMS should be applied at least 100 msec before EPI while completely avoiding any pulses during imaging.

Artifacts↗

PubMed1999

Cognitive N140 electrogenesis and concomitant 40 Hz synchronization in mid-dorsolateral prefrontal cortex (area 46) identified in non-averaged human brain potentials.

The mid-dorsolateral prefrontal area 46 has working memory functions for putting current cognitive processing into context and for updating relevant information on a trial-by-trial basis. Using non-averaged human brain responses to a target finger stimulus attended by the subject, we identified the cognitive prefrontal N140 electrogenesis with the Z method which numerically assesses the detailed consistency between scalp topographies of any single response and a grand average template. The cognitive N140 was present between 100 and 180 ms at the scalp contralateral to the attended target finger stimulus. Control responses to physically identical finger stimuli that were ignored by the subject did not elicit a prefrontal N140. In brain mapping the N140 focus was located 30-80 mm from scalp midline, and 50-60 mm in front of the vertex (Cz) coronal plane of the head. The data were consistent with recently disclosed anatomical locations of area 46 and they further document its interindividual variations in brain-to-scalp relationship. N140, is thought to manifest cortico-cortical activation from the posterior parietal area 7b which generates the cognitive P100 electrogenesis that precedes N140 in the target response. At the prefrontal site, the non-averaged EEG showed desynchronized 40 Hz oscillations, but these became transiently phase-locked in conjunction with the cognitive N140 excitatory effect. This seems in line with the Traub model suggesting that excitation of certain cortical inhibitory interneurons generates doublet firings which will pace the spiking of pyramidal neurons so as to promote synchronization at about 40 Hz. These results complement our recent finding that P300 inhibition conversely disrupts on-going 40 Hz phase-locking ('binding'). Considering the marked trial-to-trial variations in timing of the cortical cognitive processes, such physiological relationships between target response components and 40 Hz dynamics could only be uncovered by studying non-averaged single responses.

Adult↗

PubMed2001

[New functional cerebral cartography: studies of plasticity of the human brain].

The non-invasive brain scanning techniques, introduced a quarter of a century ago, have become crucial for diagnosis in clinical neurology. They have also been used to investigate brain function and have provided information about normal activity and pathogenesis. They have been used to investigate functional specialisation in the brain and how specialised areas communicate to generate complex integrated functions such as speech, memory, the emotions and so on. Brain plasticity is a generic term that has now come to be used to signify any changes in brain structure or function. The phenomenon is poorly understood, and yet clinical neurologists are aware that spontaneous recovery from brain lesions is not uncommon. An improved understanding of the mechanisms of recovery may generate new therapeutic strategies and indicate ways of modulating mechanisms that promote plastic compensation for loss of function. The main methods used to investigate these issues are positron emission tomography and magnetic resonance imaging (MRI). The techniques of functional brain mapping and computational morphometrics depend on high performance scanners and a validated set of analytic statistical procedures that generate reproducible data and meaningful inferences from them. The motor system presents a good paradigm to illustrate advances made by scanning towards an understanding of plasticity at the level of brain areas. The normal motor system is organised in a nested hierarchy. Recovery from paralysis caused by internal capsule strokes involves functional reorganisation manifesting as changed patterns of activity in the component brain areas of the normal motor system. The pattern of plastic modification depends in part on patterns of residual or disturbed connectivity after brain injury. Therapeutic manipulations in patients with Parkinson's disease using deep brain stimulation, dopaminergic agents or foetal mesencephalic transplantation provide a means to examine mechanisms underpinning plastic change. Other models of plastic change, such as normal visuospatial learning or re-establishing speech comprehension after cochlear implantation in the deaf illustrate how patterns of brain function adapt over time. Limitations of the scanning techniques and prospects for the future are discussed in relation to new developments in the neuroimaging field.

Brain↗

PubMed2002

EEG mapping in patients with restless legs syndrome as compared with normal controls.

Restless legs syndrome (RLS) is a sensorimotor movement and sleep disorder with a high prevalence. While the sleep disturbance due to RLS has been studied quite well polysomnographically, little is known about the electrophysiological function during daytime. The aim of the present study was to investigate the diurnal quantitative EEG and clinical symptomatology in 33 drug-free RLS patients as compared with age- and sex-matched normal controls. Investigations comprised brain mapping of the vigilance-controlled EEG as well as completion of the Zung Self-Rating Depression Scale, the Zung Self-Rating Anxiety Scale, the Quality of Life Index, the Pittsburgh Sleep Quality Index and the Epworth Sleepiness Scale for evaluation of clinical symptomatology. Statistical analysis demonstrated an increase in absolute delta and absolute and relative alpha-2 power, a decrease in absolute and relative alpha-1 power, an acceleration of the dominant frequency and the alpha centroid, and a slowing of the delta/theta centroid, as well as a non-significant attenuation in total power. These findings are characteristic of dissociated vigilance changes described in depression. Indeed, RLS patients demonstrated significantly higher depression and anxiety scores, lower quality of life and deteriorated sleep quality. The score of the Epworth Sleepiness Scale was not elevated, in contrast to the increased daytime sleepiness observed in other highly prevalent organic sleep disorders (e.g. sleep apnea). In conclusion, daytime EEG mapping revealed neurophysiological correlates of depression in RLS, which was confirmed by self-ratings at the symptomatological level.

Adult↗

PubMed2002

Functional brain reorganization for hand movement in patients with multiple sclerosis: defining distinct effects of injury and disability.

Previous work has demonstrated potentially adaptive cortical plasticity that increases with brain injury in patients with multiple sclerosis. However, animal studies showing use-dependent changes in motor cortex organization suggest that functional changes also may occur in response to disability. We therefore wished to test whether brain injury and disability lead to distinguishable patterns of activation with hand movement in patients with multiple sclerosis. By employing a passive as well as an active movement task, we also wished to test whether these changes were independent of voluntary recruitment and thus more likely to reflect true functional reorganization. Fourteen patients [Extended Disability Status Score (EDSS) 0-7.5] with relapsing-remitting multiple sclerosis were selected on the basis of pathology load and hand functional impairment for three study groups: group 1, low diffuse central brain injury (DCBI) as assessed from relative N-acetylaspartate concentration (a marker of axonal integrity) and normal hand function (n = 6); group 2, greater DCBI and normal hand function (n = 4); and group 3, greater DCBI and impaired hand function (n = 4). Functional MRI (fMRI) was used to map brain activation with a four-finger and both one-finger passive and active flexion-extension movement tasks for the three groups. Considering all the patients, we found increased activity in ipsilateral premotor and ipsilateral motor cortex (IMC) and in the ipsilateral inferior parietal lobule with increasing global disability (as assessed from the EDSS score). These changes appear to define true functional reorganization, as fMRI activations in IMC (r = 0.87, P < 0.001) and in the contralateral motor cortex (r = 0.67, P < 0.007) were highly correlated between active and passive single finger movements. We attempted to disambiguate any distinct effects of disability and brain injury by direct contrasts between patients differing predominantly in one or the other. To make these contrasts as powerful as possible, we used impairment of finger tapping as a measure of disability specific to the hand tested. A direct contrast of patients matched for DCBI, but differing in hand disability (group 3 - group 2) showed greater bilateral primary and secondary somatosensory cortex activation with greater disability alone. A contrast matched for hand disability, but differing in DCBI (group 2 - group 1) showed a different pattern of changes with relative ipsilateral premotor cortex and bilateral supplementary motor area activity. We conclude that the pattern of brain activity with finger movements changes both with increasing DCBI and with hand disability in patients with multiple sclerosis, and that these changes are distinct. Those related directly to disability may reflect responses to altered patterns of use. As injury- and disability-related activation changes are found even with passive finger movements, they may reflect true brain reorganization.

Analysis of Variance↗

PubMedDate not supplied

Nasopharyngeal recordings of somatosensory evoked potentials document the medullary origin of the N18 far-field.

Because the nasopharyngeal electrode provides non-invasive access to the ventral brain-stem at the medullo-pontine level we used it for recording somatosensory evoked potentials (SEPs) to median nerve stimulation (non-cephalic reference). After the P9 and P11 far-fields, the nasopharyngeal SEPs disclosed a negative-going component which was interpreted as the near-field equivalent of the P14 scalp far-field generated in the caudal part of the medial lemniscus. Nasopharyngeal SEPs also revealed a large N18 with voltage and features strikingly similar to those of the scalp-recorded N18 far-field. These results suggest that N18 is generated in the medulla and not more rostrally in the brain-stem. The use of a nasopharyngeal electrode as reference for topographic brain mapping is discussed. The paper documents the feasibility and relevance of nasopharyngeal recordings for non-invasive analysis of short-latency SEPs.

Adult↗

PubMed1995

Hyperkinetic motor behaviors contralateral to hemiplegia in acute stroke.

Motor behaviors on the 'good side' of the body, i.e. ipsilateral to the hemispheric lesion, have not been studied systematically. We assessed motor behaviors in 20 consecutive patients during the acute phase (first 1-2 weeks) of a hemispheric stroke with hemiparesis. The behaviors were essentially rotations of the head, neck, eyes and trunk, orofaciopharyngeal or limb stereotypes, compulsive manipulation of the surroundings, or passive mobilization of the paralyzed arm or leg. These behaviors were found only with large infarcts in the territory of the internal carotid artery, middle cerebral artery and/or the anterior cerebral artery (ACA). All but two ACA infarcts involved the internal capsule and basal ganglia. The severity of the motor deficit and the presence of aphasia, neglect, or sensory loss were significantly correlated with the motor behaviors. Although the understanding of these behaviors remains unclear, we suggest that they may represent the clinical expression of early plastic changes of brain maps and circuits after an acute lesion; this is probably an active process induced by disinhibition, in order to establish new compensatory pathways.

Acute Disease↗

PubMed1996

Non-invasive functional mapping of the human motor cortex using near-infrared spectroscopy.

We applied non-invasive multisite near-infrared spectroscopy (NIRS) to assess oxygenation changes during performance of a sequential finger opposition task in five healthy human adults. Oxygenation response was localized anatomically using three-dimensional high-resolution magnetic resonance imaging (3D MRI). NIRS measurements showed a localized increase in [oxy-Hb] and a decrease in [deoxy-Hb] in all subjects. The largest response was obtained when the measurement position was over the primary motor and sensory cortex hand area. Interestingly, changes in [deoxy-Hb] seemed to be more localized than changes in [oxy-Hb]. We conclude that this simple, non-invasive and flexible optical bedside method may be used for functional brain mapping.

Adult↗

PubMed1999

Usefulness of motor functional MRI correlated to cortical mapping in Rolandic low-grade astrocytomas.

The indications for surgery of slow growing tumours like low grade astrocytomas in eloquent areas are difficult. The timing and the benefit/risk ratio of the surgery must be evaluated, taking into account the potential post operative deficit. The purpose of this study was: a) to validate the data obtained with functional MRI (FMRI) by direct cortical stimulation in patients who are candidate for surgery; b) to demonstrate the usefulness of FMRI coupled with cortical brain mapping and 3D reconstructions of the surfaces of the brain in low grade astrocytoma. FMRI of the hand-motor cortex was performed in 8 patients with low grade astrocytomas. They subsequently underwent direct cortical mapping to correlate the results of FMRI and resective surgery sparing the functional area. In the 8 cases, the results of direct cortical mapping in the precentral region matched accurately those obtained from FMRI. When surgical resection of low grade astrocytoma in the motor areas is considered, FMRI used with intra-operative cortical mapping can help the surgeon to spare functional areas during tumour removal.

Adult↗

PubMed1995

Neural pattern formation via a competitive Hebbian mechanism.

In this contribution we investigate a simple pattern formation process [9,10] based on Hebbian learning and competitive interactions within cortex. This process generates spatial representations of afferent (sensory) information which strongly resemble patterns of response properties of neurons commonly called brain maps. For one of the most thoroughly studied phenomena in cortical development, the formation of topographic maps, orientation and ocular dominance columns in macaque striate cortex, the process, for example, generates the observed patterns of receptive field properties including the recently described correlations between orientation preference and ocular dominance. Competitive Hebbian learning has not only proven to be a useful concept in the understanding of development and plasticity in several brain areas, but the underlying principles have have been successfully applied to problems in machine learning [22]. The model's universality, simplicity, predictive power, and usefulness warrants a closer investigation.

Animals↗

PubMed1998

Calibrated functional MRI: mapping the dynamics of oxidative metabolism.

MRI was extended to the measurement of changes in oxidative metabolism in the normal human during functionally induced changes in cellular activity. A noninvasive MRI method that is model-independent calibrates the blood oxygen level dependent (BOLD) signal of functional MRI (fMRI) against perfusion-sensitive MRI, using carbon dioxide breathing as a physiological reference standard. This calibration procedure provides a regional measurement of the expected sensitivity of the fMRI BOLD signal to changes in the cellular activity of the brain. Maps of the BOLD signal calibration factor showed regional heterogeneity, indicating that the magnitude of functionally induced changes in the BOLD signal will be dependent on both the local change in blood flow and the local baseline physiology of the cerebral cortex. BOLD signal magnitude is shown to be reduced by 32% from its expected level by the action of oxygen metabolism. The calibrated fMRI technique was applied to stimulation of the human visual cortex with an alternating radial checkerboard pattern. With this stimulus oxygen consumption increased 16% whereas blood flow increased 45%. Although this result is consistent with previous findings of a significant difference between the increase in blood flow and oxygen consumption, it does indicate clearly that oxidative metabolism is a significant component of the metabolic response of the brain to functionally induced changes in cellular activity.

Brain↗

PubMed2002

Assessment of neuroprotective ability of a spin trap, alpha-phenyl-N-tert-butylnitrone, against malonate-induced ischemic injury of rat brain by apparent water diffusion coefficient mapping.

Ischemic brain injury induced by injection of 3-micromol malonate into the left striatum of male Sprague-Dawley rats was examined by apparent water diffusion coefficient (ADC) mapping of magnetic resonance imaging. The region surrounding the injection core was imaged as a hypointense area in ADC mapping and ADC values in the regions were significantly decreased 3 and 6 h after ischemia. Significant reduction of the hypointense area and the recovery of ADC values were observed in rats to which alpha-phenyl-N-tert-butylnitrone (PBN) was intraperitoneally administered 1 h before ischemia. Since ADC mapping has been reported to be a suitable method for evaluating the extent and the degree of cytotoxic edema in the early period after the onset of ischemia, the present results prove that PBN is able to prevent early ischemic insults such as cytotoxic edema.

Animals↗

PubMed2000

Comparison of rhyming and word generation with FMRI.

Functional magnetic resonance imaging (FMRI) has been successfully used to non-invasively map language function, but has several disadvantages. These include severe motion sensitivity, which limits overt verbal responses in behavioral paradigms, such as word generation. The lack of overt responses prevents behavioral validation, making data interpretation difficult. Our objective was to compare the FMRI activation patterns of a novel silent rhyme determination task requiring a non-verbal response, to covert word generation from visually presented letters. Five strongly right-handed subjects performed both tasks during multi-slice coronal echo-planar T2*-weighted FMRI. Single subject activation maps were generated for each task by correlation analysis of single pixel time series to a boxcar reference function. These maps for the two tasks were separately interpolated to 256(3), transformed into Talairach space, summed, and thresholded at t>6. Combined activation maps from both tasks showed similar robust perisylvian language area activation, including inferior frontal gyrus, posterior superior temporal lobe, and fusiform gyrus. Subjects performed well on the rhyming task, which activated left hemisphere cortical regions more selectively than the word generation task. The rhyming task showed less activation than the word generation task in areas typically not considered specifically related to language function, such as the dorsolateral prefrontal cortex and anterior cingulate. The rhyming task is a useful tool for brain mapping and clinical applications, potentially more specific to cortical language areas than verbal fluency.

Adult↗

PubMed1998

Functional MRI studies of word-stem completion: reliability across laboratories and comparison to blood flow imaging with PET.

Functional magnetic resonance imaging (fMRI) based on blood oxygen level-dependent (BOLD) contrast has become an increasingly popular technique for mapping the brain. The relationship between BOLD-fMRI imaging and imaging of blood flow activation with positron emission tomography (PET) remains unclear. Moreover, BOLD imaging strategies and analysis procedures vary widely across laboratories. To examine the relationship between these different methods, we compared brain activation maps of a word-stem completion task obtained both using PET and using fMRI across two separate institutions (Washington University and Massachusetts General Hospital) with different acquisitions (gradient-refocused echo and asymmetric spin echo) and different analysis techniques. Overall, activation maps were highly similar across both fMRI methods and PET. A set of activated brain areas, in consistent locations in Talairach atlas space, were identified across all three studies, including visual striate and extrastriate, left prefrontal, supplementary motor area (SMA), and right cerebellar areas. Decreases in activation were also consistently observed in medial parietal, posterior insular, and medial inferior frontal areas. Some differences were noted that may be related to the silent performance of the task with fMRI. The largely consistent results suggest that comparisons can be made appropriately across imaging modalities and laboratory methods. A further implication of the consistencies, which extended to both increases and decreases in signal, is that the underlying brain physiology leading to BOLD contrast may be more similar to blood flow than originally appreciated.

Adult↗

PubMedDate not supplied

Technology in the assessment of learning disability.

Recent neuroradiologic and brain imaging technologies, along with methods for displaying electrophysiologic data, have promulgated active exploration in the assessment of learning disability with attempts to improve diagnostic precision and elucidate the neurobiological substrates of learning disorders. The following article reviews these techniques and explores the research that has been conducted in this area over the past two decades. Initial investigations attempted to elucidate irregularities or abnormalities of brain morphology in individuals with learning disability utilizing computerized tomography (CT). The current standard for structural imaging of the brain is magnetic resonance (MR) imaging, which has allowed for greater specificity in identifying brain abnormalities. More recently, functional magnetic resonance imaging (fMRI) has been postulated as holding some promise in distinguishing anatomic/function differences in LD. Electrophysiological (EEG) and metabolic imaging techniques offer methods by which human brain activity can be studied during cognitive processes. Computerized EEG studies including evoked potentials (EP) or event-related potentials (ERP), spectral EEG analysis, and topographic EEG brain mapping have also identified a number of brain irregularities in individuals with learning disabilities, though no consistent exemplars have emerged. Studies with positron emission tomography (PET) and single photon emission computerized tomography (SPECT) have also demonstrated a number of abnormalities and inconsistencies in individuals with learning disabilities, but, again, no systematic research has demonstrated specific diagnostic abnormalities. Though inroads and some consistent patterns have begun to emerge in the assessment of learning disability with the preceding technologies, a number of challenges persist with neuroimaging and neurophysiological and metabolic imaging techniques. To date, no diagnostic conclusions have been drawn utilizing these methods in the assessment of the neurobiologic basis to LD.

Brain↗

PubMed1999

[Pathogenetic mechanisms and clinical peculiarities of trigeminal facial pain].

316 patients with extracranial, intracranial and intracerebral lesions of the trigeminal system were examined. Together with a neurologic observation, the examination included registration of trigeminal somatosensory, acoustic brain stem and visual evoked potentials as well as electroencephalography (including brain mapping) and magnetic resonance tomography of the brain. Etiologic factors, location of the damage and systemic pathogenetic mechanisms characteristic for the main types of both paroxysmal and nonparoxysmal facial pain were established. Peculiarities of the manifestations of trigeminal neuralgia, neuropathy and differential facial pain are discussed. A comparative analysis of peculiarities of an algesic syndrome in three forms of verified radiculopathies conditioned by the lesion of trigeminal, glossopharyngeal and cerebrospinal nerves was performed. An original classification of trigeminal facial pain is proposed.

Facial Pain↗