Biomedical subjects

B I Turetsky

Publications and source records attributed to B I Turetsky.

23 records · Page 2Linked to original sources

PubMed1994

Sex differences in aging of the human frontal and temporal lobes.

This study investigated effects of age and sex on regional brain structure in humans, focusing on the frontal and temporal lobes. Hemispheric volumes were obtained from magnetic resonance images (MRIs) of 96 young (53 men, 43 women; aged 18-40 years) and 34 older (17 men, 17 women; aged 41-80) healthy volunteers. Images (5 mm axial spin-echo, repetition time of 3000 msec and echo times of 30 and 80 msec) were resliced along the anterior commissure-posterior commissure (AC-PC) axis to standardize for difference in head tilt, and imported into a computer program where borders of the frontal and temporal lobes were delineated. The program calculated regional brain volumes based on slice data from which CSF was segmented out. An age x sex x hemisphere x region interaction indicated that age-related reductions in brain volume were sexually dimorphic, lateralized, and region specific. Greater decrements in brain volume occurred with age in the frontal lobe than in the temporal lobe. Age-related reductions in both regions were greater in men than in women, demonstrating that sexual dimorphisms in human neuroanatomy are not fixed, but continue to change throughout adulthood. The possibility that gonadal hormones play a role in the promotion and/or prevention of neural atrophy with aging is discussed.

Adolescent↗

PubMed1991

Partitioning of deep versus superficial intracranial sources using current source densities is not valid.

An analytic method has recently been proposed for partitioning scalp-recorded EEG and evoked potential (EP) data into parts arising from deep (i.e., subcortical) vs. superficial (i.e., cortical) sources. The method is based on the observation that the current source density (CSD) is selectively sensitive to electrical activity arising from superficial sources, and the conjecture that the residual potential which remains after subtracting the CSD from the scalp potentials, represents activity from deep sources. We investigated the validity of this procedure by simulating scalp potential data for superficial and deep dipole sources with known locations and orientations. Our single-dipole simulations demonstrated that, when the actual location of the source was superficial, the partitioning procedure erroneously attributed a sizeable proportion of the total topographic variance to the activity of deeper sources. This produced a consistent bias in the simulations with two dipoles, when both superficial and deep sources were present. In such cases, the relative contribution of the deeper source was consistently overestimated, and the scalp topography of the deep source activity was profoundly misrepresented by the residual which results from subtracting the CSD from the scalp potential. We conclude that the proposed method for partitioning EEG and EP data into components arising from deep vs. superficial intracranial sources is not valid.

Electrodes↗

PubMed1989

Estimation of trial-to-trial variation in evoked potential signals by smoothing across trials.

Averaging single trial evoked potential data to produce an estimate of the underlying signal obscures trial-to-trial variation in the response. We describe a method for estimating slow changes in the evoked potential signal by smoothing the data over trials. We discuss the crucial issue of deciding how much to smooth and suggest that an appropriate smoothing parameter is one that minimizes the estimated mean average square error of the smoothed data. Equations to estimate the mean average square error for a one-dimensional local linear regression smoother are presented. Performance of the method is assessed using simulated evoked potential data with several different models of a changing signal and different values of the signal-to-noise ratio. We find that the method rarely imputes trial-to-trial variation to data sets that have an unchanging signal, while it almost always produces less error than averaging when estimating a varying signal. The ability of the method to reveal signal heterogeneity is hampered by very low signal-to-noise ratios. When applied to real auditory evoked potential data from a sample of elderly subjects, the method indicated a changing signal in 35% of all subjects and in 56% of subjects with signal-to-noise ratios above 0.6. Consistent patterns of variation in the auditory evoked potential were present in this sample.

Aged↗

PubMedDate not supplied

Noise and signal power and their effects on evoked potential estimation.

Signal power, noise power and their ratio (SNR) are important variables underlying estimation of evoked potential signals, yet, they are rarely explicitly considered in the design or analysis of EP experiments. A model is developed which relates the reliability of the average evoked potential (AEP) wave form to signal power, noise power, SNR, and the number of single trials included in the average. Measurements taken from auditory and visual EP experiments in elderly subjects show that noise power is highly reliable across experimental conditions and probably reflects global CNS anatomic or physiologic factors. In contrast, signal power and SNR are variable across conditions and sensory modalities, but are stable across replications. Thus signal power reflects CNS processes specific to the experimental paradigm. These results have importance for EP estimation. The expected reliability of the AEP cannot be adequately predicted from estimates of a subject's noise power, or from SNR estimated under different experimental conditions. These findings suggest the need for on-line estimation of SNR during data acquisition to ensure adequate reliability of AEPs.

Aged↗

PubMedDate not supplied

Olfactory identification in elderly schizophrenia and Alzheimer's disease.

In the present study we assessed olfactory identification ability using the University of Pennsylvania Smell Identification Test (UPSIT) in 16 elderly patients with schizophrenia (ES), 20 patients with a diagnosis of probable Alzheimer's disease (AD), and 20 healthy elderly controls (EC). Both patient groups exhibited marked deficits in UPSIT performance relative to controls. ES and AD patients with similar levels of general cognitive impairment did not differ on the UPSIT, suggesting that the two disorders may share a common dysfunction in olfactory brain regions. While there have been recent reports of greater olfactory impairment in males, neither patient group exhibited significant gender differences on the UPSIT.

Aged↗