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PubMedDate not supplied

[Brain mapping of middle latency auditory potentials in normal subjects].

The MLRs of 20 normal hearing adults were recorded by cerebral mapping. In regard to the Pa and Na waves, it is suggested that two different generation sites exist because of the different spatio-temporal distribution of the waves over the scalp. It is demonstrated that amplitudes measured by the "grand average" technique are constantly lower than those obtained with the manual determination, and they conclude that manual determination represents the most reliable method in order to calculate waves amplitude. Finally, it is suggested that, due to the different generation sites for Pa and Na waves and to the uneven distribution of the Na wave over the scalp, Pa amplitude should be measured from the baseline and not from the Na negative deflection. Moreover, in 14 cases, when one ear was stimulated the Pa wave obtained at most recording points was significantly larger than the one recorded contralaterally.

Acoustic Impedance Tests↗
PubMed2001

Phonological aspects of word recognition as revealed by high-resolution spatio-temporal brain mapping.

We describe, for the first time, the use of high-resolution event-related brain potentials (hrERP) to identify the spatio-temporal characteristics of neural systems involved in phonological analysis. Subjects studied a visual word/non-word that was followed by the brief presentation of a prime letter (e.g. House, M) with the instruction to anticipate the word/non-word formed by replacing the word's first letter with the prime letter. After the prime letter, an auditory target word/non-word was presented that either matched/mismatched expectations (e.g., Mouse/Barn). ERPs were recorded to the onset of the auditory targets and scalp topographical maps were derived for the phonological mismatch negativity (PMN). The PMN reflected phonological analysis and examination of the peak topography revealed that the response was characterized by a prominent frontal, right-asymmetrical distribution. Spatial de-blurring (using current source density maps) indicated that the PMN scalp topography resulted primarily from an active left anterior source. The current results provide the initial evidence for the localization of the intra-cranial generator(s) involved in phonological analysis.

Acoustic Stimulation↗
PubMed2005

Brain maps, great and small: lessons from comparative studies of primate visual cortical organization.

In this paper, we review evidence from comparative studies of primate cortical organization, highlighting recent findings and hypotheses that may help us to understand the rules governing evolutionary changes of the cortical map and the process of formation of areas during development. We argue that clear unequivocal views of cortical areas and their homologies are more likely to emerge for "core" fields, including the primary sensory areas, which are specified early in development by precise molecular identification steps. In primates, the middle temporal area is probably one of these primordial cortical fields. Areas that form at progressively later stages of development correspond to progressively more recent evolutionary events, their development being less firmly anchored in molecular specification. The certainty with which areal boundaries can be delimited, and likely homologies can be assigned, becomes increasingly blurred in parallel with this evolutionary/developmental sequence. For example, while current concepts for the definition of cortical areas have been vindicated in allowing a clarification of the organization of the New World monkey "third tier" visual cortex (the third and dorsomedial areas, V3 and DM), our analyses suggest that more flexible mapping criteria may be needed to unravel the organization of higher-order visual association and polysensory areas.

Anatomy, Comparative↗
PubMed1999

A study of injected dose for brain mapping on the ECAT HR+: activation maps for a parametric verbal working memory task.

The success of the 15O-water PET technique to localize statistically significant changes in regional cerebral blood flow is dependent on factors such as the activity level injected and the magnitude of the flow change. Undetectable changes may occur if insufficient activity is injected leading to high levels of statistical noise or the task performed results in only small changes in blood flow. To explore the relationship between injected activity and statistical significance, we performed a series of studies with the ECAT EXACT HR+, a high resolution PET tomograph. A parametric verbal working memory task (the N-back task) was selected to examine the relationship between regional cerebral blood flow and working memory load across a range of injected doses of 15O-water. At each activity level the volunteers were required to perform four different levels of the N-back task, a task in which a letter displayed on a monitor is matched with the letter displayed N letters previously. With increasing N, this task places increased load on working memory. For this study, 5, 10, and 15 mCi of 15O-water were injected into nine normal volunteers. The complete sequence of four tasks (N = 0, 1, 2, and 3) at three activity levels was repeated twice, for a total of 24 injections of 15O-water. We show that the peak count rate performance for the HR+ is approached at injected activity levels of 15O-water around 15 mCi. For this particular choice of N-back task, robust activation maps can nevertheless be obtained with as little as 5 mCi injected dose.

Adult↗
PubMed1998

Hippocampal morphometry in schizophrenia by high dimensional brain mapping.

Theories of the pathophysiology of schizophrenia have implicated the hippocampus, but controversy remains regarding hippocampal abnormalities in patients with schizophrenia. In vivo studies of hippocampal anatomy using high resolution magnetic resonance scanning and manual methods for volumetric measurement have yielded inconclusive results, perhaps because of the normal variability in hippocampal volume and the error involved in manual measurement techniques. To resolve this controversy, high dimensional transformations of a computerized brain template were used to compare hippocampal volumes and shape characteristics in 15 matched pairs of schizophrenia and control subjects. The transformations were derived from principles of general pattern matching and were constrained according to the physical properties of fluids. The analysis and comparison of hippocampal shapes based on these transformations were far superior to the comparison of hippocampal volumes or other global indices of hippocampal anatomy in showing a statistically significant difference between the two groups. In the schizophrenia subjects, hippocampal shape deformations were found to be localized to subregions of the structure that send projections to prefrontal cortex. The results of this study demonstrate that abnormalities of hippocampal anatomy occur in schizophrenia and support current hypotheses that schizophrenia involves a disturbance of hippocampal-prefrontal connections. These results also show that comparisons of neuroanatomical shapes can be more informative than volume comparisons for identifying individuals with neuropsychiatric diseases, such as schizophrenia.

Brain Mapping↗
PubMedDate not supplied

Mapping brain networks engaged by, and changed by, learning.

Major goals of research into the neurobiology of learning and memory are to identify (1) brain areas/circuitries that subserve different mnemonic functions and (2) chemistries that encode the memory trace. The discovery that activity modulates neuronal gene expression provided techniques attendant to the first goal and candidates for cellular changes pertinent to the second. Studies in our laboratories have exploited activity-regulated changes in c-fos gene expression to map regions engaged in two-odor discrimination learning, with particular interest in neuronal groups in hippocampus and amygdala. The results of these studies demonstrate that the subdivisions of hippocampus and amygdala do not act in concert across behaviors but are differentially activated depending on task demands. In hippocampus, preferential activation of field CA3 was uniquely associated with initial learning of an odor pair, whereas predominant activation of CA1 occurred with exploration of a novel field and with overtrained responding to odors. The reappearance of precisely the same balance of subfield activation within disparate behavioral contexts was taken to suggest that the hippocampus has basic modes of function that recur in different circumstances and make rather generalized contributions to behavior. Within the amygdala, the basolateral division was most prominently active during task acquisition but not during performance of the well-learned discrimination. Indeed, the amygdala appeared to play the dominant role relative to hippocampus in the early stages of associating positive and negative valences with discriminative cues. These results demonstrate that the balance of neuronal activity both within and between limbic structures changes across sequential stages of odor learning in a fashion that is likely to define behavioral output.

Amygdala↗
PubMed2001

Functional brain mapping of monkey tool use.

When using a tool, we can perceive a psychological association between the tool and the body parts-the tool is incorporated into our "body-image." During tool use, visual response properties of bimodal (tactile and visual) neurons in the intraparietal area of the monkey's cerebral cortex were modified to include the hand-held tool. Visual properties of the monkey intraparietal neurons may represent the body-image in the brain. We explored tool use-induced activation within the intraparietal area and elsewhere in alert monkey brain using positron emission tomography (PET). Tool use-related activities compared with the control condition (simple-stick manipulation) revealed a significant increase in cerebral blood flow in the corresponding intraparietal region, basal ganglia, presupplementary motor area, premotor cortex, and cerebellum. These tool use-specific areas may participate in maintaining and updating the body-image for the precise guidance of a hand-held rake onto a distant reward.

Animals↗
PubMed2004

An MRI study of spatial probability brain map differences between first-episode schizophrenia and normal controls.

We created a spatial probability atlas of schizophrenia to provide information about the neuroanatomic variability of brain regions of patients with the disorder. Probability maps of 16 regions of interest (ROIs) were constructed by taking manually parcellated ROIs from subjects' magnetic resonance images (MRIs) and linearly transforming them into Talairach space using the Montreal Neurological Institute (MNI) template. ROIs included temporal, parietal, and prefrontal cortex subregions, with a principal focus on temporal lobe structures. Subject Ns ranged from 11 to 28 for the different ROIs. Our global measure of the spatial distribution of the transformed ROI was the sum of voxels with 50% overlap among subjects. The superior temporal gyrus (STG) and fusiform gyrus (FG) had lower values for schizophrenic subjects than for normal controls, suggestive of greater spatial variability for these ROIs in schizophrenic subjects. For the computation of statistical significance of group differences in portions of the ROI, we used voxel-wise comparisons and Fisher's exact test. First-episode schizophrenic patients compared with controls showed lower probability (P < 0.05) at dorso-posterior areas of planum temporale and Heschl's gyrus, lateral and anterior regions in the left hippocampus (HIPP), and dorsolateral regions of fusiform gyrus. Importantly, most ROIs of schizophrenic subjects showed a significantly lower spatial overlap than controls, even after nonlinear spatial normalization, suggesting a greater heterogeneity in the spatial distribution of ROIs. There is consequently a need for caution in neuroimaging studies where data from schizophrenic subjects are normalized to a particular stereotaxic coordinate system based on healthy controls. Apparent group differences in activation may simply reflect a greater heterogeneity of spatial distribution in schizophrenia.

Adult↗
PubMed1993

[Clinical and EEG/ERP brain mapping studies with vigabatrin in therapy refractory epileptic patients].

In a single blind study the antiepileptic effects and safety of vigabatrin--a new anticonvulsant drug selectively inhibiting GABA-transaminase--was investigated in therapy resistant epilepsy, along with its central effects objectivated by mapping of EEG and event-related potentials (ERP). In addition to their current antiepileptic therapy, 10 patients with complex partial seizures (CP) (4 male, 6 female), aged between 22 and 57 years received placebo for 1 month, subsequently 2 g vigabatrin for 2 months and thereafter a titrated optimal dosage vigabatrin for another 2 months. Clinical investigations were carried out at the afore-mentioned periods, neurophysiological ones pre and post 2 months vigabatrin. After 2 months vigabatrin, 5 out of 10 patients had a 50% or greater decrease in CP frequency, after another 2 months 7 out of 10. The median number of CP per months decreased from 5.5 to 3.75 (p < 0.05) to 2.0 (p < 0.01), respectively. No clinically relevant side effects and laboratory changes were noted. EEG mapping showed decreased fast alpha and slow beta power and increased delta-theta frequency variability, reflecting most likely a decreased CP disposition. ERP mapping showed slightly increased N1 and P2 as well as reduced P300 amplitudes. Unchanged P300 latency indicated no delayed stimulus evaluation time after vigabatrin therapy.

Adult↗
PubMedDate not supplied

Mapping brain activation to odorants in patients with smell loss by functional MRI.

PURPOSE: Our goal was to use functional MRI (fMRI) to develop an objective, noninvasive technique by which patients with smell loss can be identified, their abnormalities quantitated, their results compared with findings in normal subjects, and visual representation of their CNS pathology obtained. METHOD: Functional MR brain scans were obtained in eight patients with hyposmia in response to three olfactory stimuli (pyridine, menthone, amyl acetate) in three coronal brain sections selected from anterior to posterior temporal brain regions using multislice FLASH MRI. Results were compared with similar studies performed in 17 normal subjects. Activation images were derived using correlation analysis, and ratios of area of brain activated to total brain area were obtained. RESULTS: Brain activation to each stimulus was lower in each section in patients compared with normal subjects and reached statistical significance for mean activation for each odor and in six of the nine individual sections studied. Activation in patients was found in regions previously associated with CNS processing of olfactory stimuli in normal subjects, but activation in patients was much less, particularly in inferior frontal and cingulate gyral regions of frontal cortex and in regions of medial and posterior temporal cortex. CONCLUSION: These results demonstrate quantitative CNS changes in smell function in response to olfactory stimuli in patients with hyposmia, demonstrate a novel, objective method by which these patients can be identified, and provide maps of the CNS changes associated with their smell loss.

Adult↗
PubMed1993

Test of repeated operations and logistic regression as to the efficacy of brain mapping.

The object of this paper is to apply two new methods, those of repeated observations and logistic regression in order to verify the validity of qEEG. These methods are applied using children with hyperactivity and attentional disorders, according to DSM III-R. The results of sensitivity and specificity were similar.

Attention Deficit Disorder with Hyperactivity↗
PubMed2002

Intraoperative optical intrinsic signal imaging: a clinical tool for functional brain mapping.

Optical imaging of intrinsic signals (OIS) is a well-established neuroimaging modality by which functional cortical activity is mapped by detecting activity-related changes in cortical light reflectance. Light reflectance changes are detected by a charged-coupled device camera that captures images of the exposed cortex both at rest and during activity. Although to date OIS has only been used for research purposes, intraoperative OIS (iOIS) holds promise as a clinical mapping tool. In general, iOIS demonstrates good spatial correlation with electrocortical stimulation mapping (ECSM) and other electrophysiological modalities. Additionally, iOIS offers high spatial resolution (in microns), does not make contact with the surface of the brain, and introduces no potentially harmful compounds. Moreover, mapping is relatively rapid. The authors review the potential contribution of iOIS to the intraoperative environment. Specifically, they review iOIS methodology, discuss signal origin, compare OIS with other functional mapping modalities, and explain its potential benefits and limitations. They propose that iOIS may, in the future, be used in conjunction with ECSM to improve the resolution and accuracy of intraoperative mapping, decrease total time of intraoperative mapping, and possibly improve neurological outcomes. Additional studies will be required to quantify the sensitivity and specificity of optical maps relative to ECSM before it can be implemented clinically.

Brain Mapping↗
PubMed2005

Comparisons between Alzheimer disease, frontotemporal lobar degeneration, and normal aging with brain mapping.

Alzheimer disease (AD) and frontotemporal lobar degeneration (FTLD) are both common degenerative dementias in the under 65 age group. Although clinical criteria have been defined for both diseases, there is considerable overlap in clinical features, and hence, diagnosis still can be very difficult particularly in the early stages of the disease. As a result, there has been increasing interest in using magnetic resonance imaging to better characterize these diseases and to aid in diagnosis. Voxel-based morphometry (VBM) is an automated technique that assesses patterns of regional gray matter atrophy on magnetic resonance imaging between 2 groups of subjects. It is unbiased in that it looks throughout the whole brain and does not require any a priori assumptions concerning which structures to assess, giving it a significant advantage over traditional region of interest-based methods. Voxel-based morphometry has been widely used to assess patterns of regional atrophy in subjects with AD and FTLD. These studies have demonstrated specific patterns of regional loss in both diseases, compared the 2 diseases to look for differences that could be diagnostically useful, and have correlated regions of gray matter loss to cognitive and behavioral deficits in these subjects. This article will review the findings of these studies and discuss the role of VBM in these neurodegenerative diseases.

Aging↗
PubMed1996

Brain mapping of median nerve somatosensory evoked potentials with combined 99mTc-ECD single-photon emission tomography and magnetic resonance imaging.

Single-photon emission tomography (SPET) was performed during electrical median nerve stimulation and used to detect focal neuronal activation in the somatosensory pathways. Intravenously administered technetium-99m ethyl cysteinate dimer (ECD) was used as a blood flow tracer to obtain baseline and activated images in each of three subjects. After image registration, baseline images were compared voxel by voxel with the activation images. In addition, the mean summation of the activated-state images of the subjects was compared with the mean summation of the baseline-state images of ten normal subjects. Discrete brain regions occupying 0.9%-1.6% of total brain volume showed an increase in signal from 33.6% to 35.0%. For further anatomical localization of regional increases in signal, the MRI scan of each subject was registered and superimposed on the activated-state SPET image. This method may be used to localize lesions in various disorders of the central nervous system.

Adult↗
PubMed1991

The effect of spikes and spike-free epochs on topographic brain maps.

Maps of foci, when no discharges nor obvious slow activity were included in the map, usually (84%) showed changes within the focus itself and also in adjacent areas (58%) and often (47%) in the mirror region. An increase in activity was more often seen in the more active foci, especially in the delta and beta 2 ranges, and decrease in activity was usually seen with inactive foci. When discharges were included in the maps, an increasing number was associated with an increase at the main focus in all ranges, especially in delta and beta 1, but much less often in beta 2. The amount of electrical charge required for a change in the map with spikes was approximately 40 nanocoulombs (nC) for the first and second changes, increasing to around 50 nC with adjacent or separate foci. "Artificial" spikes produce more delta activity than other frequency ranges and the FFT of various pulses show maximal amplitudes at the slowest frequencies.

Brain Mapping↗