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Biomedical subjects

D W Loring

Publications and source records attributed to D W Loring.

At least 109 records · Page 6Linked to original sources

Cholinergic and serotonergic effects on the P3 potential and recent memory.

The effects of scopolamine (anticholinergic) and methysergide (antiserotonergic) on memory and long-latency auditory cognitive evoked potentials (EPs) were tested in 16 normal adults. Recent memory was impaired by both drugs. In contrast, scopolamine, but not methysergide, significantly delayed P3 latency and decreased P3 amplitude. Immediate memory and the earlier EP components (i.e., N1 and P2) were unaffected. The findings support the hypothesis that cholinergic neurons are important in the neuronal networks generating the P3 potential. Serotonergic neurons do not appear to play a major role in the networks that generate the P3.

Adult↗

Hemisphere asymmetry for eye gaze mechanisms.

To investigate left/right asymmetries in cerebral gaze mechanisms, eye deviation was evaluated in 90 patients following intracarotid sodium amylobarbitone injections. For right-handed subjects with left cerebral language dominance, the occurrence and severity of eye deviation were greater for right versus left hemisphere injections. In contrast, subjects with mixed cerebral dominance for language/handedness exhibited no left/right difference in the incidence of eye deviation. The results are consistent with right cerebral dominance for attentional/intentional mechanisms directed at external space. Further analysis suggests that the cerebral asymmetry for gaze may be due to an evolutionary loss of attentional/intentional mechanisms by the left cerebral hemisphere as language function developed.

Adolescent↗

Surgical management of epilepsy.

About 300,000 people in the United States suffer from medically uncontrolled focal epilepsy. It is estimated that about 40,000 of these patients are candidates for surgery. Underuse of surgical treatment of epilepsy is reflected by the fact that only about 1% of these candidates are operated on. Candidates for ablative surgery (ie, removal of seizure focus) must have a focus demonstrated by either extracranial or intracranial electrode recordings. Nearly half of the patients who have ablative surgery become seizure-free, and nearly two thirds have no seizures or only rare ones. Candidates for corpus callosotomy are those patients with multiple seizure types and nonfocal EEG abnormalities. Almost half of these patients have at least a 50% reduction in seizure frequency. Patients with infantile hemiplegia and seizures may have marked improvement in seizure control after physiologic hemispherectomy.

Corpus Callosum↗

Adult-onset chorea and dementia with propionic acidemia.

Propionic acidemia usually presents in the newborn period with severe metabolic acidosis and lethargy. A 31-year-old man with adult onset chorea and dementia had propionic acidemia due to propionyl CoA carboxylase deficiency. Metabolic investigations may prove useful in patients with movement disorder of unknown etiology.

Adult↗

Attentional mechanisms during the intracarotid amobarbital test.

We investigated the integrity of attentional mechanisms following unilateral intracarotid amobarbital injection in 23 patients undergoing preoperative evaluation for epilepsy surgery. Performance for ipsilateral hand-button response to a quasi-random strobe flash was markedly altered following unilateral amobarbital injection as evidenced by decreased correct responses and increased perseverative errors. The increase in perseverations was inversely correlated with subsequent memory performance. The results indicate that unilateral amobarbital injection commonly produces a marked reduction in attention as well as disturbances in strategic control mechanisms.

Adolescent↗

Central nervous system effects of antihistamines on evoked potentials.

Sedation is the most common side effect of antihistamine therapy. As with many behavioral constructs, attempts at quantification are difficult, and consequently, subjective reports of antihistamine sedation are frequently relied upon. Evoked potential activity is one method to quantitate the brain's response to subtle cognitive change. Evoked potentials are characteristic shifts in the brain's electrical activity that are obtained by time-locking the ongoing EEG to a stimulus over repeated trials. A late positive component of the evoked potential (P3) has been related to various psychologic properties including expectation, selective attention, and information processing speed. Because of this relationship, we employed the latency of the P3 evoked potential to measure the cognitive effects of chlorpheniramine and terfenadine. In healthy young subjects, we observed that terfenadine produces significantly less cognitive slowing of the P3 potential than chlorpheniramine. This finding supports the subjective findings of reduced sedative side effects of terfenadine.

Adult↗

Issues in memory assessment of the elderly.

The pattern of memory test performance by elderly individuals demonstrates significant overlap between populations. Consequently, the memory tests themselves poorly differentiate normal aging, dementia, and depression. The additional problem of relatively little adequate normative information for elderly individuals compounds this problem. Thus, inferences regarding the nature of assessed deficits should be based in part on information that extends beyond the traditional quantitative numerical analyses of test performances. For example, depressed individuals tend to make fewer false-positive responses and frequently will respond stating "I don't know." Similarly, if there is evidence for risk of memory impairment, the threshold for inferring assessed memory deficit may be altered. Finally, when independent information is present to confirm the presence of structural change in the brain, the inference of specific memory impairments can be strengthened. One not only needs to look at the entire pattern of neuropsychological deficits, but also use the neuropsychological findings in the context of other clinical findings. Perhaps the greatest utility of neuropsychological memory assessment of the elderly is providing standardized assessments for repeat evaluations. By repeating the assessment, deterioration as a function of a progressive dementia can be assessed. Alternatively, the effect of treatment for depression can be monitored and an improvement in memory test scores would be expected. Throughout, however, the careful clinician will remember that the inferences regarding an individual's level of function are not stronger than the reliability, representativeness, and validity of the instruments employed.

Aged↗

The P3 evoked potential and transient global amnesia.

The P3 evoked potential has been linked to memory mechanisms, but its neuronal generators are uncertain. Transient global amnesia (TGA) is a disorder of recent memory that has been postulated to result from ischemia or focal seizures in the medial temporal lobes and/or thalamus. To our knowledge, this is the first report of a recording of P3 evoked potential and sphenoidal electroencephalogram during TGA. The tonal P3 was not decremented in comparison to P3 recordings one month and two years after recovery. Sphenoidal electroencephalogram was normal. The results suggest that the neuronal networks which generate the tonal P3 are not involved in the part of the memory system affected by TGA.

Amnesia↗

Spectral power of human limbic evoked potentials: relationship to seizure onset.

Limbic evoked potentials were recorded from intracerebral electrodes bilaterally implanted in the hippocampi of 16 epileptic patients undergoing evaluation for surgical resection of a seizure focus. Spectral analysis of the limbic evoked potentials revealed consistently lower spectral power of both low-band (1-12.6 Hz) and high-band (13-20 Hz) components recorded form the hippocampus that was associated with the electrographically confirmed seizure focus as compared to the contralateral side. Limbic evoked potential recordings appear to be useful in the determination of a focal functional deficit and thus in identifying the site of epileptogenic pathology. Further, the results support the hypothesis of a local generator for limbic evoked potentials and demonstrate that limbic evoked potentials in humans include not only low-frequency, high-amplitude electric field changes, but also a high-frequency component.

Adolescent↗

Hallervorden-Spatz syndrome: clinical and magnetic resonance imaging correlations.

Two women with a presumptive diagnosis of Hallervorden-Spatz syndrome had a combination of dystonia and parkinsonism. One had retinitis pigmentosa. Neuropsychological testing revealed decreased verbal fluency and visuoconstructional and motor deficits. Magnetic resonance imaging performed with a high-field-strength unit (1.5 Tesla) showed striking abnormalities in the globus pallidus bilaterally ("eye-of-the-tiger" sign). Magnetic resonance imaging may prove useful in the diagnosis of Hallervorden-Spatz syndrome.

Adult↗

Electrical stimulation of the human hippocampus produces verbal intrusions during memory testing.

Verbal memory testing was conducted during electrical stimulation of the human hippocampus in 12 epilepsy surgery candidates with unilateral temporal lobe seizure onset. Performance was assessed during baseline, left hippocampal stimulation and right hippocampal stimulation. Verbal intrusion errors were greater during electrical stimulation of the hippocampus contralateral to the seizure focus. These findings suggest that verbal intrusions are related to memory deficits, and that patients with cerebral disease who intrude words from an earlier portion of a learning test are likely to have bilateral cerebral dysfunction.

Adult↗

In vivo probe of central cholinergic systems.

Age-related cognitive impairments and dementia of Alzheimer type have been linked to alterations in the cholinergic system. In the present study, evoked potentials and neuropsychological testing were obtained in healthy subjects during neuropharmacological manipulations including: scopolamine (anticholinergic), scopolamine plus physostigmine (anticholinesterase), scopolamine plus methylphenidate (adrenergic), and placebo. Scopolamine prolonged P3 latency and reduced spectral power of long latency evoked potentials without significantly altering earlier components. Physostigmine partially reversed these effects, but methylphenidate did not. Motor speed was slowed by scopolamine, but not by scopolamine plus methylphenidate. Cholinergic systems appear to be involved in generation or modulation of the P3 potential, possibly secondary to the cholinergic role in selective attention. Similar techniques may be useful as in vivo probes of central cholinergic function and thus as research and diagnostic aids in aging and disease.

Adult↗

Virgil Sydenstricker: special reference to niacin deficiency encephalopathy.

Virgil Sydenstricker was a member of a notable American family which included authoress Pearl S. Buck and the eminent epidemiologist Edgar Sydenstricker. Dr. Sydenstricker's contributions in the fields of hematology and nutritional disease are legion. His landmark work in sickle cell anemia characterized a definite symptom complex with specific hematologic findings and inheritance pattern. He wrote on the complications of malnutrition and attempted to delineate the specific effects of individual nutritional factors. Dr. Sydenstricker and his associate H. M. Cleckley first described the syndrome of niacin deficiency encephalopathy. Today, the syndrome is still occasionally reported. Niacin deficiency should be considered when unexplained acute confusional states or neurologic deficits occur in the setting of malnutrition, antituberculous drug use, or chronic partial nutritional deficiency with acute increase in metabolic demand.

Brain Diseases↗

Relationship of limbic evoked potentials to recent memory performance.

The relationship between limbic evoked potentials (LEPs) and memory performance was investigated in eight patients with intractable epilepsy who were candidates for temporal lobectomy. No relationship between the presence or absence of unilateral LEP and memory deficits was present. However, in both patients with bilaterally poorly developed hippocampal LEPs, verbal and visual-spatial memory tasks were impaired. In one patient with well developed LEPs bilaterally, memory function was normal. These data suggest that LEPs may assist in the evaluation of memory function during the preoperative work-up for temporal lobectomy.

Epilepsy↗

Right cerebral specialization for tactile attention as evidenced by intracarotid sodium amytal.

Although several components of neglect syndrome have been reported to occur more frequently following right cerebral lesions, a right cerebral predominance for directed tactile attention has not been demonstrated. The intracarotid sodium amytal procedure (ISA, or Wada test) offers the opportunity to investigate differential effects for symmetric acute dysfunction of each cerebral hemisphere in each subject. In the present study, 18 patients undergoing preoperative evaluation for epilepsy surgery were trained in a nonverbal task of tactile attention. Left/right mean ISA dosages and left/right tactile test times postinjection were matched. Results revealed more correct responses following left ISA, and greater tactile inattention with more extinction-type responses following right ISA. No effect of seizure focus, sex, order of injection, or dosage was present. The finding that tactile inattention occurs more frequently with right cerebral dysfunction is consistent with right cerebral dominance for scanning attentional mechanisms directed at the external milieu.

Adolescent↗

Severe behavioral complications following intracarotid sodium amobarbital injection: implications for hemispheric asymmetry of emotion.

The intracarotid sodium amobarbital (ISA) procedure is effective in determining cerebral language dominance. However, severe emotional and behavioral reactions during ISA evaluation may invalidate the results or necessitate aborting the procedure. In an effort to identify patients at risk for behavioral complications, we reviewed 92 patients undergoing ISA evaluation and found five with severe changes in affect and behavior following amobarbital injection, ranging from prolonged coma to an extended confusional state. Severe behavioral disturbances were more likely to occur in patients with left frontal structural lesions upon injecting amobarbital into the right hemisphere. Analysis of patients with structural lesions of the anterior regions of the right hemisphere showed no evidence of similar behavioral complications. These findings suggest a special role for the left frontal region in the inhibition of affective expression and provide further evidence of the importance of right hemisphere mechanisms in emotion.

Adult↗

Preserved crossmodal association following bilateral amygdalotomy in man.

The present study investigated the role of the amygdala in crossmodal association in man. Recent experimental evidence indicates amygdalectomized monkeys show deficits when required to identify, through vision, objects that have been previously examined by touch. We employed a delayed nonmatching to sample task pre- and postoperatively in a patient who underwent bilateral stereotaxic amygdalotomy for intractable aggressivity. Bilateral amygdalotomy did not impair our patient's ability to associate an object from one sensory modality to another, following a short delay. The results suggest that sensory association memory does not depend upon the amygdala in humans. Examination of the neuroanatomic structures affected by the differing surgical procedures in the two species revealed entorhinal and perirhinal cortices were damaged in amygdalectomized monkeys but not in the present case. Because entorhinal cortex is an important structure for the formation of new memory traces, it is possible that damage to the entorhinal and surrounding cortical regions, rather than damage to the amygdala itself, is responsible for the crossmodal association deficit in monkeys.

Adult↗

Hemispatial-limb hypometria.

Patients with unilateral cerebral stroke and healthy controls were studied for limb and hemispatial hypometria. Subjects were required to reproduce lateral and medial horizontal displacements of each arm, with their eyes closed. Patients exhibited significant hypometria when moving toward hemispace contralateral to the lesion, and also when moving the limb contralateral to the lesion. Possible mechanisms for the hemispatial-limb hypometria are discussed.

Adult↗