Biomedical subjects

David Glahn

Publications and source records attributed to David Glahn.

8 recordsLinked to original sources

PubMed2005

Spatial working memory function in twins with schizophrenia and bipolar disorder.

BACKGROUND: Family studies are in conflict as to whether schizophrenia and bipolar disorder have independent genetic etiologies. Given the relatively low prevalence (approximately 1%) of these disorders, the use of quantitative endophenotypic markers of genetic liability might provide a more sensitive strategy for evaluating their genetic overlap. We have previously demonstrated that spatial working memory deficits increase in a dose-dependent fashion with increasing genetic proximity to a proband among the unaffected co-twins of schizophrenic patients. Here, we evaluated whether such deficits might also mark genetic susceptibility to bipolar disorder. METHODS: The Wechsler Memory Scale-Revised Visual Memory Span and Digit Span subtests were administered to 46 schizophrenic patients, 32 of their unaffected co-twins, 22 bipolar patients, 16 of their unaffected co-twins, and 100 control twins, representing unselectively nationwide twin samples. RESULTS: Schizophrenic patients and their unaffected co-twins performed significantly worse than control subjects on the spatial working memory task, whereas only the schizophrenic patients performed significantly below the control subjects on the verbal working memory task. Neither bipolar patients nor their unaffected co-twins differed from control subjects on these measures. CONCLUSIONS: Our findings support the hypothesis that impairment in spatial working memory might effectively reflect an expression of genetic liability to schizophrenia but less clearly to bipolar disorder.

Aged↗

PubMed2005

Fronto-limbic brain abnormalities in juvenile onset bipolar disorder.

BACKGROUND: Advances in brain imaging techniques and cognitive neuropsychology have brought new possibilities for the in vivo study of the pathophysiology of neuropsychiatric disorders, including bipolar disorder (BD). Recently, such studies have been extended to the pediatric age range. Here we review the neuroimaging and neuropsychological studies conducted in BD children and adolescents. METHODS: A review of the peer-reviewed published literature was conducted in Medline for the period of 1966 to April 2005. RESULTS: Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) studies suggest abnormalities in fronto-limbic structures in pediatric BD patients, similar to those found in adults. A notable exception in pediatric BD patients is smaller amygdala volumes compared to healthy controls, contrary to what has been reported in most adult studies. CONCLUSIONS: Further research evaluating children and adolescents is needed to study the normal neurodevelopmental process and to answer how and when the illness processes that result in bipolar disorder exert their effects on the developing brain.

Adolescent↗

PubMed2005

Attention deficits in bipolar disorder: a comparison based on the Continuous Performance Test.

Although attentional deficits measured by Continuous Performance Tests (CPTs) have been observed in patients with bipolar disorder, their relationship with clinical state is not well understood. The identical pairs Continuous Performance Test (CPT-IP) shows particular promise as a measure sensitive to trait abnormalities in attentional function. In this study, the CPT-IP was administered to 27 patients with bipolar disorder (22 type I, 5 type II) and 25 demographically matched healthy comparison subjects, in order to assess the presence and nature of attentional deficits as a function of mood symptoms. Results showed significantly impaired CPT performance in bipolar patients compared with healthy subjects. Patients made fewer hits (p < 0.01), were slower to respond (p < 0.007), and had poorer discrimination (p < 0.05) and bias (p < 0.006) than comparison subjects. Severity of mania and depression was not correlated with any of the CPT measures. Our findings suggest that attentional dysfunction may be a trait deficit associated with bipolar illness. However, within-subjects longitudinal studies examining fluctuations in performance over time are needed.

Adult↗

PubMed2005

Disparity of activation onset in sensory cortex from simultaneous auditory and visual stimulation: Differences between perfusion and blood oxygenation level-dependent functional magnetic resonance imaging.

PURPOSE: To compare the temporal behaviors of perfusion and blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) in the detection of timing differences between distinct brain areas, and determine potential latency differences between stimulus onset and measurable fMRI signal in sensory cortices. MATERIALS AND METHODS: Inversion recovery (IR) spin-echo echo-planar imaging (EPI) and T2*-weighted gradient-echo EPI sequences were used for perfusion- and BOLD-weighted experiments, respectively. Simultaneous auditory and visual stimulations were employed in an event-related (ER) paradigm. Signal time courses were averaged across 40 repeated trials to evaluate the onset of activation and to determine potential differences of activation latency between auditory and visual cortices and between these scanning methods. RESULTS: Temporal differences between visual and auditory areas ranged from 90-200 msec (root-mean-square (RMS) = 134 msec) and from -80 to 930 msec (RMS = 604 msec) in perfusion and BOLD measurements, respectively. The temporal variability detected with BOLD sequences was larger between subjects and was significantly greater than that in the perfusion response (P < 0.04). The measured time to half maximum (TTHM) values for perfusion imaging (visual, 3260 +/- 710 msec; auditory, 3130 +/- 700 msec) were earlier than those in BOLD responses (visual, 3770 +/- 430 msec; auditory, 3360 +/- 460 msec). CONCLUSION: The greater temporal variability between brain areas detected with BOLD could result from differences in the venous contributions to the signal. The results suggest that perfusion methods may provide more accurate timing information of neuronal activities than BOLD-based imaging.

Acoustic Stimulation↗

PubMed2005

Memory and verbal learning functions in twins with bipolar-I disorder, and the role of information-processing speed.

BACKGROUND: Euthymic bipolar-I disorder (BP I) patients and their siblings have shown impairments in verbal learning and memory functions compared with controls, suggesting that these impairments may be genetic in origin. Reduced information-processing speed has been associated with impaired memory in the elderly, and recently in schizophrenia. The authors compared verbal learning and memory functioning in twins with BP I and co-twins to control twins, and examined whether the observed deficits are related to information-processing speed. METHOD: Finnish Medical and Population Registers and Twin Cohorts were used to identify the BP I and control twins. Neuropsychological tests assessing verbal learning and memory, working memory, facial recognition, visual memory, and information-processing speed were administered to 26 BP I twins, 19 non-bipolar co-twins, and 114 controls. Group differences were analyzed by generalized estimation equation modeling. RESULTS: BP I patients, but not co-twins, showed impairments in all memory tests compared with controls. Female co-twins showed impairment in verbal learning and memory. Information-processing speed had a significant effect on encoding and learning efficiency. CONCLUSIONS: This study showed for the first time that information-processing speed is related to memory functioning and verbal learning in BP I in a population-based, representative and euthymic sample. Furthermore, the data support the view that defects in verbal memory may be related to the genetic factors predisposing to BP I in females.

Adult↗

PubMed2005

Regional brain activity associated with visual backward masking.

In visual backward masking, the visibility of a briefly presented visual target is disrupted by a mask that is presented shortly thereafter. The goal of the current study was to identify regions in the human cortex that may provide the neural basis of visual masking. We searched for areas whose activity correlated with perception as we systematically varied the strength of masking. A total of 13 subjects performed a backward masking task during functional magnetic resonance imaging. Target and mask were presented at three delay intervals (34, 68, and 102 msec) and behavioral measures confirmed that the targets were more visible at longer masking intervals. Two sets of regions of interest were identified: Distinct regions in the visual cortex (V1/V2, LO, hMT+) were segregated using scans to localize visual processing drawn from the existing literature. Additional cortical regions were selected in a data-driven approach based on their activity during the backward masking task. For each set, we determined the regions whose magnitude of activation increased at longer masking intervals. Nine of the subjects provided valid behavioral performance data on the visual masking task and imaging data from these subjects were used for subsequent analysis. The scans of visual processing areas identified four regions, including: early visual areas (V1 and V2), the motion-sensitive regions in the lateral occipital (LO) lobe (hMT+), and two components (dorsal and ventral) of the object-sensitive region, LO. Of these, the ventral and dorsal LO regions were sensitive to the strength of the mask. For the data-driven approach, six regions were identified on the basis of a difference map in which all masking intervals were contrasted with rest. These included the inferior parietal, anterior cingulate, precentral, insula, thalamic, and occipital areas. The predicted effects of more activity with weaker masking were seen in the thalamus, inferior parietal, and anterior cingulate. This study isolated three types of visual processing areas. The first included regions that subserve key stages of vision (including object and motion processing). The second type responded to the presentation of brief ly presented visual stimuli, regardless of masking interval. The third type (selected from the first two) included regions sensitive to the interval between the target and mask. These latter regions (including ventral LO, inferior parietal, anterior cingulate, and thalamus) may form the neural substrate of backward masking.

Adult↗

PubMed2004

Comparison of TCA and ICA techniques in fMRI data processing.

PURPOSE: To make a quantitative comparison of temporal cluster analysis (TCA) and independent component analysis (ICA) techniques in detecting brain activation by using simulated data and in vivo event-related functional MRI (fMRI) experiments. MATERIALS AND METHODS: A single-slice MRI image was replicated 150 times to simulate an fMRI time series. An event-related brain activation pattern with five different levels of intensity and Gaussian noise was superimposed on these images. Maximum contrast-to-noise ratio (CNR) of the signal change ranged from 1.0 to 2.0 by 0.25 increments. In vivo visual stimulation fMRI experiments were performed on a 1.9 T magnet. Six human volunteers participated in this study. All imaging data were analyzed using both TCA and ICA methods. RESULTS: Both simulated and in vivo data have shown that no statistically significant difference exists in the activation areas detected by both ICA and TCA techniques when CNR of fMRI signal is larger than 1.75. CONCLUSION: TCA and ICA techniques are comparable in generating functional brain maps in event-related fMRI experiments. Although ICA has richer features in exploring the spatial and temporal information of the functional images, the TCA method has advantages in its computational efficiency, repeatability, and readiness to average data from group subjects

Brain Mapping↗

PubMed2003

Voltage-clamp study of the activation currents and fast block to polyspermy in the egg of Xenopus laevis.

Voltage-clamped mature, jelly-intact Xenopus eggs were used to carefully examine the ionic currents crossing the plasma membrane before, during, and after fertilization. The bulk of the fertilization current was transient, of large amplitude, and reversed at the predicted Cl- reversal potential. However, the large amplitude fertilization current was preceded by a small, step-like increase in holding current. This small increase in holding current is referred to in this paper as Ion to acknowledge its qualitative similarity to the Ion current previously described in the sea urchin. It was observed in both fertilized and artificially activated eggs, and was found to be unaffected by 10 mm tetra-ethyl ammonium (TEA), a concentration found to block K+ currents in Rana pipiens. Current-voltage relationships are presented for the large fertilization potential, and show that the fertilization currents have a marked outward rectification and are voltage sensitive. These properties are in contrast to the total lack of rectification and slight voltage sensitivity seen before or after the fertilization currents. The time required for sperm to fertilize the egg was found to be voltage dependent with a relatively more depolarized voltage requiring a longer time for fertilization to occur. The percentage of eggs blocked with varying potential levels was determined and this information was fitted to a modified Boltzmann equation having a midpoint of -9 mV.

Animals↗