Statistical Probability Mapping Research Articles

Statistical probability mapping reveals high-frequency magnetoencephalographic activity in supplementary motor area during self-paced finger movements.

Investigations of both haemodynamic and electroencephalographic measures of brain activity have demonstrated supplementary motor area (SMA) involvement in self-paced finger movements. In contrast, analysis of magnetoencephalographic (MEG) signals in the time domain has usually failed to detect SMA activity in healthy individuals. We investigated oscillatory MEG activity in 12 normal adults during (a) a self-paced, complex sequence of finger movements and (b) a simple finger opposition task paced externally by tactile stimuli presented to the contralateral thumb. Statistical probability mapping revealed enhanced non-phase-locked spectral amplitudes in the 22-28 Hz range over bilateral frontal cortex during self-paced as compared to externally cued finger movements. This activity may reflect recruitment of cell assemblies in SMA during self-paced, complex movements.

Prediction of antidepressant effects of sleep deprivation by metabolic rates in the ventral anterior cingulate and medial prefrontal cortex.

Sleep deprivation has been shown to have an antidepressant benefit in a subgroup of depressed patients. Functional imaging studies by the authors and others have suggested that patients with elevated metabolic rates in the anterior cingulate gyrus at baseline are more likely to respond to either sleep deprivation or antidepressant medications than patients with normal metabolic rates. The authors extend their earlier work in a larger group of patients and explore additional brain areas with statistical probability mapping. Thirty-six patients with unipolar depression and 26 normal volunteers were studied with positron emission tomography before and after sleep deprivation. Response to sleep deprivation was defined as a 40% or larger decrease in total scores on the Hamilton Depression Rating Scale. One-third of the depressed patients had a significant response to sleep deprivation. Responders had higher relative metabolic rates in the medial prefrontal cortex, ventral anterior cingulate, and posterior subcallosal gyrus at baseline than depressed patients who did not respond to sleep deprivation and normal volunteers. Lower Hamilton depression scores correlated significantly with lower metabolic rates in the left medial prefrontal cortex. After sleep deprivation, significant decreases in metabolic rates occurred in the medial prefrontal cortex and frontal pole in the patients who responded positively to sleep deprivation. High pretreatment metabolic rates and decreases in metabolic rates after treatment in the medial prefrontal cortex may characterize a subgroup of depressed patients who improve following sleep deprivation and, perhaps, other antidepressant treatments.

Auditory event-related potentials and statistical probability mapping in obsessive-compulsive disorder.

The current exploratory investigation was undertaken to replicate and extend previous findings of auditory event related potentials (ERPs) observed in obsessive-compulsive disorder (OCD). Similar to previous ERP studies, this study revealed a decreased slow wave (SW) (post P300) latency, a trend towards decreased P300 latency and a greater N200 amplitude in OCD subjects than in controls. In addition, the chronicity of OCD symptoms was correlated with the 140-170 millisecond integrated amplitude and the severity of OCD symptoms correlated with the 386-438 millisecond integrated amplitude. Current findings lend additional support to evidence suggesting OCD represents, in part, hyperarousal of the cortex.

Quantitative EEG and statistical mapping of wakefulness and REM sleep in the evaluation of mild to moderate Alzheimer's disease.

Statistical probability mapping was used to quantify and localize EEG differences between 27 patients with Alzheimer's disease (AD) and 25 age- and gener-matched controls. Differences in mean activity in four EEG frequency bands (delta, theta, alpha, beta) for wakefulness and for REM sleep were examined, t-statistic maps clearly highlighted common pattern anomalies in AD patients in the two states. More specifically, Alzheimer patients were more affected than control subjects in parieto-temporal and frontal regions. These differences were more prominent in REM sleep and consisted primarily in an increase in absolute delta and theta activities, and a decrease in absolute alpha and beta activities. Discriminant analysis, using a ratio of slow over fast frequencies, yielded a classification rate of 90.4% (sensitivity 81.5%, specificity 100%) for REM sleep. For wakefulness, the same measure allowed correct classification of 80.8% of the subjects (sensitivity 66.7%, specificity 96%).

Thinning of the corpus callosum in older alcoholic men: a magnetic resonance imaging study.

A brain image averaging technique was applied to three-dimensional magnetic resonance images to identify visually detectable brain volume abnormalities in chronically alcoholic men, compared with healthy control men. This technique, which was based on pixel-by-pixel statistical probability mapping, revealed a dramatic reduction in the area of the corpus callosum in older alcoholics (age 45 years or older), relative to age-matched controls. Subsequent analysis used anatomical landmarks to outline the borders of midsagittal sections of the corpus callosum in a larger group of alcoholics and controls, who spanned the adult age range from 23 to 71 years. This analysis revealed significant reduction, most prominent in the genu and body, of total callosal area in the alcoholic group relative to the control group; the results were the same whether raw area measures or head size plus age adjusted measure were analyzed. Significant thinning of the callosal body in alcoholics is usually attributed to the relatively rare, nutritional-deficient condition, Marchiafava-Bignami disease. However, callosal thinning was present in vivo in chronic alcoholics without clinical symptoms of severe liver disease, amnesia, or alcoholic dementia. These data suggest that chronic alcoholism can be characterized by a continuum of graded brain dysmorphology, rather than classical alcoholic-related subsyndromes, such as Marchiafava-Bignami disease.

Projection onto centroids difference vectors: a new approach to determine between group topographical differences, applied to P3 amplitude in schizophrenia.

A common problem in electrophysiological research concerns between group analysis of EEG and ERP topography. This paper proposes a new technique for determining whether or not a significant difference exists between multiple scalp site measurements from two groups. The method requires no a priori assumptions about the data and is thus ideal for exploratory data analysis, and it also requires that only one statistical test need be performed (significantly reducing the possibility of type I errors). The Projection onto Centroids Difference Vectors (PCDV) method involves deriving a measure from each individual of whether their measurements across sites are closer overall to the mean measurements of the rest of their experimental group, or to the other group. These measures from each individual are then compared between groups using a Student's t test, which indicates whether one group's data is significantly spatially different from the other. In this study we describe the method in detail and apply it to both stimulated data and to real auditory P3 data in unmedicated, medicated schizophrenics and matched normal controls. The PCDV method was also compared with statistical probability mapping (SPM). The PCDV method revealed the differences between the normal and patient groups more unambiguously than SPM, and the simulated data revealed that it was not liable to type I errors. PCDV provides an appropriate method for testing any between group EEG and ERP topographical differences.

Cerebral Mapping in Subjects Suffering from Migraine With Aura

Cerebral mapping of the spontaneous electroencephalographic activity was performed in 31 subjects suffering from migraine with aura and the results were compared with those of a matched control group. All the patients were examined during the interictal period. While traditional visual interpretation of EEG records was negative in all but five cases (16.1%) spectral analysis showed an asymmetry in alpha total power over the posterior regions in 13 cases (41.9%) and an asymmetry in alpha band peak frequency in 17 (54.8%). By means of cerebral mapping and statistical significance probability mapping we were able to demonstrate a significant increase in alpha total power in 13 cases (41.9%) and a regional increase in delta and theta total power in 20 cases (64.5%). In comparison with the control group, the migraine patients showed a widespread increase in slow activity (theta and delta) mostly over the temporal regions.