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Biomedical subjects

I Law

Publications and source records attributed to I Law.

27 records · Page 2Linked to original sources
PubMed1998

Brain activation during word identification and word recognition.

Previous memory research has suggested that the effects of prior study observed in priming tasks are functionally, and neurobiologically, distinct phenomena from the kind of memory expressed in conventional (explicit) memory tests. Evidence for this position comes from observed dissociations between memory scores obtained with the two kinds of tasks. However, there is continuing controversy about the meaning of these dissociations. In recent studies, Ostergaard (1998a, Memory Cognit, 26:40-60; 1998b, J. Int. Neuropsychol. Soc., in press) showed that simply degrading visual word stimuli can dramatically alter the degree to which word priming shows a dissociation from word recognition; i.e., effects of a number of factors on priming paralleled their effects on recognition memory tests when the words were degraded at test. In the present study, cerebral blood flow changes were measured while subjects performed the word identification (reading) and recognition memory tasks used previously by Ostergaard. The results are the direct comparisons of the two tasks and the effects of stimulus degradation on blood flow patterns during the tasks. Clear differences between word identification and word recognition were observed: the latter task evoked considerably more prefrontal activity and stronger cerebellar activation. Stimulus degradation was associated with focal increases in bilateral fusiform regions within the occipital lobe. No task, degradation, or item repetition effects were demonstrated in mesial temporal regions, no repetition effects were observed in any region, and there was no evidence for different effects of stimulus degradation in the priming and recognition memory conditions. Power limitations may have contributed to the null effects.

Adult↗
PubMed1998

Heritability of ECG measurements in adult male twins.

To assess the genetic contribution to electrocardiographic (ECG) measurements, heritability analysis was performed on ECG data collected on 251 pairs of adult male twins during the second examination of the National Heart, Lung and Blood Institute twin study, a multicenter study of cardiovascular risk factors. Resting 12-lead ECGs were obtained on each twin, pair and, the R-R, QRS, QT, and JT intervals were measured. Both the R-R and QT intervals demonstrated significant heritable components, accounting for 77% and 36%, respectively, of the variability. No significant heritable component of the QRS complex could be identified. Although the MZ intraclass correlation was higher than the DZ intraclass correlation, the JT interval did not demonstrate significant heritability. Therefore, in adult males both heart rate and the duration of ventricular repolarization have significant heritable components. These heritable components may need to be considered when using ECG measurements to screen for patients at risk for cardiovascular disorders or sudden cardiac death.

Adult↗
PubMed1998

Parieto-occipital cortex activation during self-generated eye movements in the dark.

A number of extrastriate visual areas in the parieto-occipital cortex are known from single-cell recordings of the macaque monkey to be involved in the coding of eye-position signals in the brain. These are important for the accurate location of visual objects in extrapersonal space. It can be predicted that these areas will show increased activation during the performance of eye movements at high frequency. In the present study PET and measurements of the regional distribution of cerebral blood flow (rCBF) were used as indirect measures of neural activity. Two independent groups of normal volunteers performed large-amplitude self-generated eye movements in complete darkness, thus removing the confounding effects of visual stimulation on parieto-occipital activation. The first group (group A; n = 5) served as a hypothesis-generating group and the second group (group B; n = 4) served as a hypothesis-testing group. The data were analysed using statistical parametric mapping at a significance level corrected for multiple comparisons (group A, Z > 4.08; group B, Z > 4.04). Significant rCBF increases were found for both groups in the frontal eye fields, supplementary eye fields, cerebellar vermis and putamina/thalami. Additionally, activation was found in the cunei in the posterior bank of the parieto-occipital sulcus. Also, the extraocular muscles were activated and, as a consequence of the partial volume effect, projected to the orbitofrontal cortices. At a less conservative threshold, activation was found close to the intraparietal sulci on the left side (Z = 3.91, P = 0.09) and right side (Z = 3.33, P = 0.42). The locations of these areas were confirmed in group B with reference to high-resolution structural MRI scans. The activation of the parieto-occipital cortex without overt visual stimuli is interpreted as the result of neural activity related to the reception of efferent copies of motor commands and/or the activation of neurons coding for eye position relative to the orbits. These are important constituents for the location and remapping of visual stimuli in space.

Adult↗
PubMed1997

The activation pattern in normal humans during suppression, imagination and performance of saccadic eye movements.

The distribution of activated cerebral regions was examined in nine normal subjects during four different eye movement-related conditions: (1) fixation-fixation on a central light emitting diode; (2) saccadic suppression-fixation on a diode in the presence of flashing lateral targets; (3) reflexive/volitional saccades-performance of overt eye movements to two laterally lit targets and back to the centre; and (4) imagined saccades-imagining, but not performing, the same eye movements. The regional neural activity was measured indirectly using repetitive bolus injections of oxygen-15-labelled water and positron emission tomography (PET) to yield time-integrated images of the normalized count distribution. These were aligned and anatomically normalized to a standard stereotactic space and the averages of each condition were analysed categorically using statistical parametric mapping. Compared to central fixation, reflexive/volitional saccades significantly activated regions in the classically known cortical oculomotor regions. The most notable activation during the saccade suppression task, compared to central fixation alone, was a bilateral activation of the parietal cortex with a right-sided preponderance, activation of the supplementary eye field/caudal cingulate regions, and activation of frontal regions close to the frontal eye fields. Imagined performance of eye movements without overt eye movements activated the supplementary eye field and frontal eye fields identically to regions involved in overt eye movements, thus demonstrating that over eye movements are not a prerequisite of the activation of these regions in normal humans.

Adult↗
PubMed1996

Rate dependence of regional cerebral activation during performance of a repetitive motor task: a PET study.

Using repeated positron emission tomography (PET) measures of regional cerebral counts, we investigated the regional cortical activations induced in eight normal subjects performing eight different frequencies of fingertapping (0.5-4 Hz) with the right index finger. The task was auditorially cued and the performance recorded during the scanning procedure. Performance evaluation showed increased error rates, during fingertapping, of high and low frequencies, and the best tapping performance was measured in the midrange of frequencies. Significantly activated areas (p < 0.05) of normalized cerebral counts were located in the left sensorimotor cortex (MISI), right motor cortex, left thalamus, right insula, supplementary motor area (SMA), and bilaterally in the primary auditory cortex and the cerebellum. Statistical evaluation showed a significant (p < 0.01) and positive dependence of cerebral activation upon movement rate in the contralateral MISI. There was no significant rate dependence of cerebral activation in other activated motor areas. The SMA and the right cerebellar hemisphere showed a more uniform activation throughout the tapping frequency range. Furthermore, we found a stimulus rate dependence of cerebral activation in the primary auditory cortex. We believe that the present data provide useful information for the preparation and interpretation of future motor activation studies of normal human subjects and may serve as reference points for studies of pathological conditions.

Adult↗
PubMed1992

Potential language and attentional networks revealed through factor analysis of rCBF data measured with SPECT.

We used changes in regional cerebral blood flow (rCBF) to disclose regions involved in central auditory and language processing in the normal brain. rCBF was quantified with a fast-rotating, single-photon emission computerized tomograph (SPECT) and inhalation of 133Xe. rCBF data were obtained simultaneously from parallel, transverse slices of the brain. The lower slice was positioned to include both Broca's and Wernicke's areas. The upper slice included regions generally regarded by neurobehaviorists as less related to primary auditory or linguistic functions. We presented three types of auditory stimuli to ten healthy, young volunteers: (a) diotically presented Danish speech, (b) dichotic word stimulation, and (c) white noise. Wilcoxon's signed ranks sum test revealed increased rCBF in language-related areas of cortex, viz., Wernicke's area and its right-sided homologous area as well as in Broca's area (left hemisphere), when subjects listened to narrative speech, compared to white noise (baseline). No significant rCBF differences were detected with this test during dichotic stimulation vs. white noise. A more sophisticated statistical method (factor analysis) disclosed patterns of functionally intercorrelated regions. The factor analysis reduced the highly intercorrelated rCBF measures from 28 regions of interest to a set of three independent factors. These factors accounted for 77% of the total variation in rCBF values. These three factors appeared to represent statistical analogues of independent brain networks involved in (I) auditory/linguistic, (II) attentional, and (III) visual imaging activity.

Acoustic Stimulation↗
PubMed1990

Use of biological glue to control pulmonary air leaks.

Biological glue is a natural adhesive generated by the interaction between fibrinogen (pre-glue) and thrombin to produce fibrin. The pre-glue is prepared from a single donor (to avoid the problems of pooled plasma) and stored as cryoprecipitate. Before being used it is thawed, dissolved in saline, and activated into an adhesive by the addition of topical thrombin. Biological glue was used prophylactically to prevent air leaks from bronchial suture lines and raw lung surfaces after pulmonary resections in six patients. In addition two new methods of using biological glue have been developed for the control of persisting air leaks. In selective intrabronchial tamponade the glue is instilled into the bronchial tree through a flexible bronchoscope, and in therapeutic pleurodesis it is instilled into the pleural cavity through a chest drainage tube. The air leaks were resolved in all cases. Seven procedures using selective intrabronchial tamponade were carried out in six patients. Four were immediately successful but three were not and required further interventions. Therapeutic pleurodesis alone was successfully carried out in one patient and as an adjunct to selective intrabronchial tamponade on two occasions. A thoracotomy was eventually needed in one of the seven patients.

Bronchi↗
PubMed1976

Immunological monitoring and immunotherapy in carcinoma of the lung.

One hundred and seven patients with carcinoma of the lung underwent immunologic testing, and 62 of these patients were randomized to an immunotherapy protocol comparing the effects of Pasteur strain BCG, either alone or combined with allogeneic tumor cells, to the effects of no immunotherapy. Patients with residual disease left at the time of surgery or with metastatic disease at the time of diagnosis showed no increase in survival as a result of this form of immunotherapy. An insufficient number of patients with less advanced disease, in whom we would expect the most beneficial effect, have been entered in this study. In general, we were unable to document substantial effects of immunotherapy on the immunologic parameters tested. Only in recall antigen skin testing was there a statistically significant increase in reactivity in the immunotherapy groups. Tests of general immune status appeared to have a predictive value in monitoring lung cancer patients. Anergic patients had a poorer prognosis than did patients who demonstrated skin test reactivity. Patients with normal percentages of lymphocytes (T cells) forming rosettes with sheep erythrocytes at 29 degrees C were generally normal in other tests of immune competence. In serial studies of rosette formation, all patients who developed recurrent disease had a pattern of depressed or falling rosette values, and these abnormalities occurred an average of 3.1 months prior to clinical detection of recurrence. Patients with large-cell anaplastic carcinoma were found to have a significantly higher incidence of depressed rosette levels than the other histologic types. Both large and small-cell anaplastic patients had significantly depressed lymphocyte proliferation by mitogens and allogeneic cells. Although lung cancer patients have been described as immunologically depressed, they are capable of recognizing tumor-associated antigens. When tested in leukocyte migration inhibition assays with tumor-associated antigens, the majority of the patients in our study were found to be reactive. The use of a 3 M KCl extract of pleural effusion cells from a patient with pulmonary adenocarcinoma has given good reactivity and specificity in lung cancer patients of all histologic types. In addition, these patients have been shown to respond in a mixed lymphocyte/tumor interaction to tumor-associated antigens (Dean, 1976b).

Adenocarcinoma↗