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Biomedical subjects

E L Maclin

Publications and source records attributed to E L Maclin.

6 recordsLinked to original sources
PubMed2001

Visual spatial localization conflict: an fMRI study.

fMRI and ERP studies have shown that tasks comprising conflicting stimulus-response associations activate a variety of cortical regions. It remains unclear whether any of these areas are activated by all conflict tasks, or whether conflict resolution is a common property of a number of distinct anatomical regions. Several regions in frontal and parietal cortex are activated by both exogenous (position) and endogenous (arrow direction) localization cues. The present event-related fMRI study used a version of the Simon task with independent positional and directional cues. The results indicated that spatial localization conflict activated pre-motor and superior parietal regions in the right hemisphere known to be involved in spatial localization, but anterior cingulate activation did not reach threshold. This suggests that conflict within a single functional modality may be processed in the region embodying that modality, and anterior cingulate may be called on only to resolve conflict between modalities.

Adolescent↗
PubMed1994

Somatosensory evoked magnetic fields in patients with stroke.

We used magnetoencephalography to evaluate areas of sensory cortex in patients with ischemic strokes involving the somatomotor system. We measured somatosensory evoked magnetic fields using a 7-channel neuromagnetometer and estimated the location of cortical responses to median nerve stimulation in 5 patients with cortical or subcortical strokes involving the somatomotor system. All patients underwent quantitative neurological examinations and a high resolution volumetric magnetic resonance imaging. The estimated current dipoles were localized onto the patient's own MRI scan in all patients with measurable responses. The location of the estimated dipole was always in non-infarcted tissue in the anatomical region of the somatosensory cortex. In 1 patient the somatosensory dipole localized to a peninsula of cortex flanked by infarcted tissue. Single photon emission computed tomography found the localized area of cortex to have significant blood flow. The estimated current dipole strengths of somatosensory evoked fields from median nerve stimulation correlated significantly (r = 0.95, P < 0.02) with the patient's ability to recognize numbers written on the involved palm (graphesthesia). The combination of evoked magnetic field recording and magnetic resonance imaging is a promising non-invasive technology for studying brain function in patients with cerebrovascular disease.

Aged↗
PubMed1994

Cortical organization in adulthood is modified by neonatal infarct: a case study.

PURPOSE: To assess anomalous cortical organization of somatosensory function in a 23-year-old man who had had a neonatal infarct involving the left middle cerebral artery. MATERIALS AND METHODS: The infarct destroyed the primary and secondary somatosensory areas of the subject's left hemisphere but caused only mild perturbation of somatosensation on the right side of his body. With magnetic source imaging, the authors integrated magnetoencephalographic data with magnetic resonance imaging data to create magnetic source localization images that showed the mapping between brain function and structure. RESULTS: Electrical stimulation of the right median nerve evoked activity in two nontraditional areas: (a) an intact region of the left inferior temporal gyrus and (b) the ipsilateral right medial parietal cortex. CONCLUSION: These data suggest that bilateral neural reorganization can be induced by unilateral neonatal damage.

Adult↗
PubMed1993

Effects of single dose haloperidol administration on plasma homovanillic acid levels in normal subjects.

Homovanillic acid (HVA), an oxidative metabolite of dopamine, has been shown in a number of studies to reflect severity of symptoms and to predict response to neuroleptic treatment in schizophrenic patients. In several clinical studies, HVA levels have been shown to have a positive relationship with symptom severity and to decline over time upon treatment with antipsychotic agents. The magnitude of this decline appears to be related to the degree of symptom reduction in patients so treated. However, administration of dopamine postsynaptic antagonists should be expected to increase synaptic dopamine availability, thereby increasing HVA concentrations, according to traditional models of drug action. While in some studies, this appears to be the case, we saw no evidence of an early phase of HVA elevation after administration of 4- and 10-milligram doses of haloperidol to human volunteers. Rather, HVA levels declined during the period of absorption and attainment of peak haloperidol levels. Baseline HVA levels of 51.6 +/- 3.83 pmoles/ml and 56.8 +/- 5.70 pmoles/ml (after 4 mg and 10 mg., respectively) declined to minima of 35.6 +/- 1.67 pmoles/ml and 26.3 +/- 5.34 pmoles/ml respectively, at 3-4 hours after haloperidol administration. A trend was noted for the 10-mg dose to produce a greater decline than the 4-mg dose, which was most apparent at 4 hours after drug administration. The shape of both curves did not appear to be substantially different than expected on the basis of diurnal variation. These preliminary findings support the concept that dopamine turnover in humans is not increased and may be decreased by short-term administration of conventional neuroleptics.

Adolescent↗
PubMed1986

Flash and pattern electroretinograms in normal and laser-induced glaucomatous primate eyes.

Experimental glaucoma was produced in one eye of five cynomolgus monkeys with the argon laser delivering 100-200 50-mu spots at 1200-1500 mW power and 0.5 sec to 360 degrees of the mid-trabecular meshwork. Monocular electroretinograms (ERGs) were recorded prior to and 2, 3, and 4 mo following the laser treatment. In the laser-treated (glaucoma) eyes, normal flash ERGs were observed using 1-Hz stimulation; however, pattern ERGs (PERGs) elicited using steady-state counterphase modulation of a 0.51 cpd square wave grating showed statistically significant reductions of amplitude. Only small reductions of PERG amplitude were seen with a 1.25 cpd grating. In three animals, abnormalities of the PERG occurred prior to clinically significant cupping of the optic nervehead. Moreover, reductions of PERG amplitude were progressive and associated with the magnitude of cupping of the optic nervehead and elevation of intraocular pressure. PERG amplitude did not change following acute reductions in intraocular pressure in the glaucoma eyes. Several control experiments were conducted to insure that results were not due to alterations in pupil size, refractive state, or accommodation in the glaucoma eyes. The authors believe they now have a monkey model for the electrophysiologic study of glaucoma.

Animals↗