Walt Karniski

An exact statistical method for comparing topographic maps, with any number of subjects and electrodes

SummaryStatistical methods for testing differences between neural images (e.g., PET, MRI or EEG maps) are problematic because they require (1) an untenable assumption of data sphericity and (2) a high subject to electrode ratio. We propose and demonstrate an exact and distribution-free method of significance testing which avoids the sphericity assumption and may be computed for any combination of electrode and subject numbers. While this procedure is rigorously rooted in permutation test theory, it is intuitively comprehensible. The sensitivity of the permutation test to graded changes in dipole location for systematically varying levels of signal/noise ratio, intersubject variability and number of subjects was demonstrated through a simulation of 70 different conditions, generating 5,000 different data sets for each condition. Data sets were simulated from a homogenous single-shell dipole model. For noise levels commonly encountered in evoked potential studies and for situations where the number of subjects was less than the number of electrodes, the permutation test was very sensitive to a change in dipole location of less than 0.75 cm. This method is especially sensitive to localized changes that would be “washed-out‘ by more traditional methods of analysis. It is superior to all previous methods of statistical analysis for comparing topographical maps, because the test is exact, there is no assumption of a multivariate normal distribution or of the correlation structure of the data requiring correction, the test can be tailored to the specific experimental hypotheses rather than allowing the statistical tests to limit the experimental design, and there is no limitation on the number of electrodes that can be simultaneously analyzed.

Topographical and temporal stability of the P300.

Sixteen normal adults listened to a standard oddball auditory paradigm 3 times, each time separated by 15 min, and this protocol was then repeated 1-2 months later. Stability of the wave forms was measured between 250 and 500 msec for each subject and for each of 16 electrodes by the cross-correlation technique described by Glaser and Ruchkin (1976) and Gevins (1987) in which points on 2 digitized wave forms are paired to produce a correlation coefficient. For each subject, the correlation coefficient was generated for each electrode and then averaged across the 2 parietal and 2 central electrodes to produce a single stability measure for the central electrodes, while the cross-correlation coefficients for the 12 remaining electrodes were averaged for a peripheral stability measure. Three-way repeated measures ANOVAs were performed to determine the significance of cross-correlation coefficient differences. The stability over 15 min for the central electrodes was 0.80, indicating that the P300 was very stable over a short time. The peripheral electrodes were significantly less stable than the central electrodes (P = 0.001). The stability of the wave forms was virtually unchanged when assessed over 1 month (P = 0.9). The target wave forms were significantly more stable than the difference waves (target minus non-target) for both the central and peripheral electrodes (P = 0.04 and 0.01). When the 3 blocks within each session were averaged, there was a significant increase in stability (P less than 0.0005). The wave form cross-correlation coefficients can be used as a measure of the stability of a topographical map over time. The map of the target P300 wave form is very stable, showing no loss in stability from 15 min to 1 month, is more stable than the difference wave form and significantly increases in stability when separate trial blocks are averaged together.

An Analysis of the Learning Styles of Adolescent Delinquents

The association between school failure and antisocial behavior has been the focus of much discussion but little consensus. In the present study, 53 delinquent adolescents and 51 junior high school students were compared on the basis of their learning profiles. An educational battery was devised to evaluate quality of learning style and error clusters in addition to traditional grade-equivalents. Significant differences were found in the type and prevalence of multiple error clusters within each of the eight educational skill areas and across the eight combined skills. In a second part of the study early school records and parent questionnaires were reviewed. Results indicated a significantly higher prevalence of school problems among the delinquents as early as kindergarten. By second grade, 45% of the delinquents were already delayed in reading and 36% in handwriting, in contrast to only 14% of the comparison group (p < .001). Finally, the prevalence of special education services recommended or provided over the years was surveyed. It is concluded that the learning styles of delinquents may be qualitatively different and that early learning difficulties may provide a sensitive indicator of risk for later delinquency.

The late somatosensory evoked potential in premature and term infants. II. Topography and latency development

The maturation of latency and scalp voltage topography of the simultaneously bilateral somatosensory evoked potential was studied in 53 neurologically intact pre-term and term infants, from 31 to 40 weeks post-menstrual age. Four peaks (N1, P1, N2 and P2) were reliably identified in all infants. The latency of each peak decreased as the infants matured. Each peak had a unique voltage scalp topography that remained stable as infants matured, even though the maps changed in amplitude intensity. N2 was large, easily identifiable with a central peak, and extremely stable in topography, suggesting that it might be used to evaluate the functional status of the somatosensory cortex in pre-term and term infants who are at high risk for developing intracranial hemorrhage leading to abnormalities of tone and delays in motor development.

The late somatosensory evoked potential in premature and term infants. I. Principal component topography

Very little is known about the topographic distribution of the cortical somatosensory evoked potential in premature infants. Principal component analysis (PCA) was applied to the wave forms generated from right median nerve stimuli over a relatively long sweep (483 msec post stimulus) at 16 electrodes in 53 infants with postconceptual ages from 31 to 40 weeks, subdivided into 5 groups by 2 week increments. Factor scores were averaged across subjects, within groups and displayed as topographical maps. Four factors accounted for 71-76% of the variance in each of the 5 groups and the factors extracted from the PCA performed independently in each group were markedly consistent. The first factor (N1/P1) had a left posterior minimum and a left frontal-central maximum and probably represents a tangential dipole located in the post-central gyrus. The second factor (N2) was characterized by a consistent left central minimum with a systematic developmental change in the maximum that seemed to imply that its neural generator was changing in orientation as the infants matured. A third factor (N3) accounted for the most variance and appeared to represent the first evidence of activity in the ipsilateral cortex. Finally, a very late fourth factor appeared only in the more mature groups, with uncertain localization. The topographic maps of the factor scores for these 4 factors appear to account for independent generators in the SEP of the premature and term infant.

A Treatment Program for Failure to Thrive: A Cost-Effectiveness Analysis.

Failure to thrive (FTT) is a frequent cause for the admission of infants to the hospital. Such hospitalizations are often lengthy and expensive, and usually do not contribute to an understanding of the etiology of FTT. Generally, organic causes of FTT can be ruled out by a thorough history and physical examination. In this study two groups were examined: 17 infants who were admitted to foster medical placement homes (MPH), private homes with specially trained parents; and a comparison group of 18 infants who were treated in a more traditional way with diagnostic hospitalization. The groups were similar in all regards prior to admission. All infants were less than a year of age. Family disruption was a prominent feature in both groups, but socio-demographic analysis showed them to be similar in all areas studied. The comparison group gained an average of 276 grams in the hospital over 8.6 days. The MPH group gained 362 grams in the hospital over 8.7 days, with an additional 1270 grams in the medical placement home over 31.1 days. Five children were admitted to the medical placement home without hospitalization. After correcting for an expected weight gain of 15 grams per day (normal growth), the comparison group showed a catch-up growth of 16 gms/day, while the MPH group gained 29 gms/day in excess of expectation, almost twice the comparison group. A 100-gram weight gain cost +308 in the MPH program and +1,635 in the traditional approach. This five-fold difference was felt to be a significant deterrent to the continuing approach of admitting children to the hospital for for the workup of FTT.(ABSTRACT TRUNCATED AT 250 WORDS)