Use of a small process control computer in a psychophysiological laboratory.
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Computers↗
Biomedical subjects
A Pfefferbaum
Publications and source records attributed to A Pfefferbaum.
Hypoparathyroidism in a patient with longstanding iron storage disease.
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Adult↗
ERPs to stimuli requiring response production and inhibition: effects of age, probability and visual noise.
Sixty-six normal adults ranging in age from 20 to 85 years were presented with stimuli containing explicit instructions to initiate or to inhibit a motor response (the words 'push' or 'wait'). In one task, the effect of stimulus probability was investigated by varying probability between 0.25 and 0.75 for both Go and No-go stimuli. In another task, the effect of visual noise was investigated by degrading the stimuli with ampersands on half of the trials. Regression analysis was used to examine the effects of age on P3 amplitude and latency for each stimulus type. The effects of stimulus variables on P3, independent of age, were examined by standardizing each subject's data to those expected for a 20 year old. P3 latency to all stimuli and RT to Go stimuli increased with age. The latency of P3s to No-go stimuli was less sensitive to age than Go stimuli. P3 amplitude at Cz and Pz (but not Fz) diminished with age. P3s to Go stimuli were maximal at Pz and earlier than P3s to No-go stimuli. P3s to No-go stimuli were maximal at Cz. These differences between Go and No-go stimuli remained true under visual noise and probability manipulations. Visual noise prolonged the latency of Go and No-go P3. Less probable Go and No-go stimuli elicited larger and later P3s than more probable stimuli. Decreasing the probability of the No-go stimulus enhanced its central distribution.
Adult↗
Age-related decline in MRI volumes of temporal lobe gray matter but not hippocampus.
The effect of normal aging on the volume of the hippocampus and temporal cortex was assessed cross-sectionally with quantitative Magnetic Resonance Imaging (MRI) in 72 healthy men, spanning 5 decades of the adult age range (21 to 70 years). Neither the hippocampal nor cortical white matter volumes were significantly correlated with age. By contrast, left and right temporal lobe gray matter volumes, exclusive of the hippocampal measures, each decreased with age (p < 0.01). Volumes of temporal lobe sulcal CSF and the ventricular system (temporal horns and lateral and third ventricles) significantly increased with age. Measures of verbal and nonverbal working memory showed age-related declines and were related to enlargement of the three ventricular regions, which may be indicative of age-related atrophy of the adjacent cortex but not the hippocampus, at least up to age 70 years.
Adult↗
Late event-related potential changes in alcoholics.
The P3 component of the event-related potential (ERP) was recorded during a Go/No-Go task from 42 alcoholic subjects, abstinent for 11-63 days, and 66 normal adult volunteers. In two different tasks, ERPs were elicited by visually presented words which provided explicit response instructions to Go (PUSH) or No-Go (WAIT). In the Noise Task, half of both Go and No-Go stimuli were degraded with ampersands (&P&U&S&H&, &W&A&I&T&). In the Probability Task, the probability of the Go stimulus was 25% and No-Go 75% on one run and the proportion reversed on another run. For both tasks, the amplitude of alcoholics' P3 was smaller than that of controls to the Go but not to the No-Go stimulus. There was a similar, but less pronounced trend for P3 latency to be delayed in alcoholic subjects for the Go, but not No-Go stimuli for the Noise Task. The P3 changes in alcoholics are consistent with those seen in several disease states which produce cognitive impairment.
Adult↗
Model estimates of CSF and skull influences on scalp-recorded ERPs.
Dipole source localization promises to enhance knowledge about the structural and functional processes underlying differences in scalp-recorded ERPs observed between normal and patient populations. In this paper the Cuffin and Cohen (1) four-compartment model of volume conduction is used to examine the effects of variations in size of different compartments on scalp-recorded potentials. Using single discrete current dipoles located various distances from the center of the head, the effect of varying the thickness of the superficial extra-sulcal subarachnoid layer of CSF and the thickness of the skull are examined. Changing the thickness of the CSF layer alters amplitude recorded at the scalp and also alters the topographic distribution of the potential; these effects are more pronounced the closer the dipole source is to the surface. Changes in skull thickness have similar, but even greater effects.
Cerebrospinal Fluid↗
Neuroimaging studies of schizophrenia.
Neuroimaging studies of schizophrenia have identified abnormalities in neuroanatomy, regional brain metabolism and receptor physiology. Computerized tomographic (CT) studies have demonstrated gross ventricular and sulcal enlargement. These findings are probably nonprogressive, and it is not yet clear whether they are present only in a subgroup of patients; whether they represent a reduction in tissue from a previously normal condition or an abnormality in brain development; and what relationship they have to genetic risk for schizophrenia, clinical features, or longterm prognosis. Magnetic resonance imaging (MRI) studies, which offer higher resolution and greater flexibility in imaging plane, are currently focussing on specific neuroanatomic sites, such as the limbic system, basal ganglia and frontal cortex, implicated by neuropathological or clinical studies in the pathophysiology of schizophrenia. Positron emission tomographic (PET) scanning now enables investigators to study brain metabolism and receptor physiology. Evidence to date suggests that there may be significant abnormalities in the pattern of cerebral glucose utilization as well as in the density of dopamine receptors in patients with schizophrenia. Much future work is needed to determine the sensitivity and specificity of these observations as well as the extent to which they are affected by changes in clinical state, attention and medication exposure.
Brain↗
Brain structure in men remains highly heritable in the seventh and eighth decades of life.
The midsagittal cross-sectional dimensions of the corpus callosum, the coronal cross-sectional area of the lateral ventricles at the level of the pons, and a three-dimensional estimate of intracranial volume were derived from magnetic resonance brain images obtained from 45 monozygotic and 40 dizygotic male twin pairs aged 68 to 78. Univariate genetic analyses indicated strong genetic influences contributing significantly to the variability of each brain structure. The estimated proportion of genetic variance (i.e. heritability) was 81% for intracranial volume, 79% for the midline cross-sectional area of the corpus callosum, and 79% for lateral ventricle size. There was no evidence that shared environmental influences contributed significantly to twin-pair similarities. We further used bivariate genetic modeling to estimate the genetic and environmental correlation between correlated brain structures. Intracranial volume and corpus callosum area was highly correlated, and this relationship was entirely due to shared genetic effects between these two brain structures. By contrast, the relationship between the height of the corpus callosum and the size of the lateral ventricles was due to both genetic and environmental influences in common. Corresponding genetic and environmental correlations were 0.68 and 0.58, respectively, indicating that more than half of the genetic and environmental influences on these two brain structures were shared. The manner in which the brain responds to the environment with advancing age is highly genetically determined, both for the lateral ventricles, which dilate with aging and disease, and for the corpus callosum, which is deformed in shape by age-related ventricular enlargement, whereas its midline cross-sectional area remains unchanged.
Aged↗
Sex differences in corpus callosum size: relationship to age and intracranial size.
This quantitative MRI study reports measurement of corpus callosum area taken from midsagittal brain images in 51 healthy men and 41 healthy women, spanning the adult age range (22 to 71 years). Men had larger brains and corpora callosa than women, but callosal size did not correlate with age in either sex. Intracranial (i.c.) volume (ICV) and midsagittal i.c. area (ICA) of brain were used in covariate, regression, and ratio analyses to determine whether sex differences in the corpus callosum endured with statistical adjustment for sex differences in maximally attained brain size. With the exception of one ratio measure, the different statistical adjustments for the contribution of sex differences in brain size to corpus callosum size all indicated that men had larger corpora callosa than women for their brain size. A subsample of men and women selected to be matched on i.c. volume and age confirmed this statistical observation. Sexual dimorphism in the corpus callosum is not a simple artifact of sex differences in brain size and may reflect differences in connectivity necessitated by differences in brain size.
Adult↗
Automatic and effortful processing in aging and dementia: event-related brain potentials.
Automatic and effortful processes were investigated using event-related brain potentials (ERPs) recorded from moderately impaired subjects with probable Alzheimer's Disease (AD), normal elderly, and normal young controls. The effects of effortful attention on ERPs to loud noises and the effects of stimulus intrusiveness on effortfully elicited ERPs were studied. First, ERPs to task relevant and irrelevant startling noises were compared. Second, ERPs to startling noises and moderate tones were compared when both were targets. The effects of age (young vs. elderly controls) and effects of dementing disease (AD subjects vs. elderly controls) were also assessed. Effortful attention augmented noise-elicited P300 amplitude in elderly subjects, but not in young. Intrusiveness augmented task-relevant P300 amplitude in young subjects, but not in elderly. Neither variable affected P300 amplitude in AD subjects. Thus, effects of age and disease depended on how P300 was elicited: when effortfully elicited, P300 amplitude was affected by disease but not age; when automatically elicited, P300 amplitude was affected by age but not disease. N1 effects differed from P300 effects.
Acoustic Stimulation↗
Drugs and criminal assaults by adolescents: a replication study.
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Adolescent↗
Computer-interactive method for quantifying cerebrospinal fluid and tissue in brain CT scans: effects of aging.
Presented here is a modification of a previously developed, computed, semiautomated system for quantifying the amount of CSF and tissue on brain CT scans. The technique automatically strips skull from brain and applies a two-dimensional high-pass filter to reduce spectral-shift artifact. The resultant images are presented along with the raw images, section by section, on a screen for fluid-tissue differentiation by a human scorer. This is accomplished by adjusting a one-bit display of the filtered image until a satisfactory separation threshold is found. Data can be summed within or across sections to provide measures of CSF volume in specific regions of interest such as the ventricles and sulci. A major advantage is the improved accuracy of sulcal measurement. This method has been applied to scans of 57 community volunteers, 20-84 years old. High correlations have been established between rankings performed by an experienced clinician and automated rankings (r = 0.88 with rankings based on ventricular size, and r = 0.83 with rankings based on sulcal size). Furthermore, significant correlations were found between computed measures of ventricular size and age and between sulcal widening and age.
Adult↗
Segmentation of MR brain images into cerebrospinal fluid spaces, white and gray matter.
An interactive computer method for quantifying CSF, white matter, and gray matter in magnetic resonance (MR) axial brain scans is presented. A stripping algorithm is used to remove the skull and scalp from each axial section. The images are then filtered to correct for radiofrequency inhomogeneity image artifacts. Late echo images are subtracted from or added to early echo images to enhance fluid/tissue and gray/white tissue contrast, respectively. Thresholds for fluid/tissue and gray/white separation are set interactively. A boundary pixel locking algorithm is used to handle ambiguities due to partial voluming between the fluid and tissue compartments. The MR brain scans from five healthy, young, normal men were obtained using a standard neuroanatomical reference technique. These data were processed and percentages computed for fluid, gray matter and white matter compartments. The gray/white ratios compare favorably with those determined in a published postmortem brain study.
Algorithms↗