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Biomedical subjects

D W Loring

Publications and source records attributed to D W Loring.

At least 145 records · Page 8Linked to original sources
PubMed1985

Stimulus offset P3 and temporal resolution of uncertainty.

Stimulus offset evoked potentials were recorded to short (1 250 ms) and long (2 500 ms) tones in the context of the odd-ball paradigm. In one condition, the short tone was presented frequently with a probability of 0.85 and the long tone with a probability of 0.15, and in a second condition, the probabilities of tone presentation were reversed. Offset P3s were obtained only to short and not to long rare tones, indicating that resolution of uncertainty rather than stimulus probability or task relevance is responsible for eliciting this late positive component in the context of this experiment.

Adult↗
PubMed1985

Choice reaction time modifiability in dementia and depression.

The effects of cognitive impairment resulting from either dementia of the Alzheimer type (DAT) or major depression (pseudodementia) on choice reaction time were examined in two conditions hypothesized to influence group performance selectively. Elderly controls had shorter reaction times than depressed patients who, in turn, were faster than dementia patients in the standard choice reaction time test. Elderly control and depressed subjects responded more quickly under conditions designed to reduce task demands. However, no effect was detected for DAT patients, presumably due to the neural constraints imposed on cognitive functioning in dementia. These results highlight the different etiologies for the intellectual decline in dementia and pseudodementia.

Aged↗
PubMed1985

Temporal pattern effects on auditory evoked potentials.

The question whether stimuli forming temporal patterns are processed differently from identical stimuli belonging to irregular temporal aggregates was investigated. Tones forming either regular or irregular triads were presented to eight normal subjects. The N1-P2 amplitude of evoked potentials to tones forming temporal patterns were consistently lower than those to tones in the irregular aggregates. These data indicate that the perceptual phenomenon of subordination of constituent parts to a well-formed whole is demonstrable in electrophysiological terms.

Adult↗
PubMed1985

Probe-evoked potential correlates of hemispheric asymmetries during a speech shadowing task.

Evoked potentials (EPs) to a monaurally presented probe stimulus were recorded from the vertex in subjects engaged in shadowing a word list presented simultaneously to the contralateral ear. Greater attenuation of the N1-P2 and baseline-P2 amplitude of the probe EPs was observed when the probe stimulus was presented to the right ear and the verbal material presented to the left ear than when the opposite stimulation arrangement was used. The baseline-N1 amplitude, however, was equally attenuated during the two stimulation arrangements. The implication of these findings for the issue of differential, task-specific attenuation of probe EPs are discussed.

Dichotic Listening Tests↗
PubMed1984

Age-related differences in recovery cycle of auditory evoked potentials.

Age-related differences in cerebral responsiveness to stimuli as reflected by the recovery cycle of cortical auditory evoked potentials (EPs) were investigated in healthy young and elderly adults. Pairs of identical tones separated by a fixed 350 msec interval were presented at rates of 1.0/sec, 0.5/sec, and 0.2/sec (inter-pair-intervals of 650, 1650, or 4650 msec). No age difference in the P1-N1 or N1-P2 amplitudes to either tone of the pair was present with the two faster stimulation rates. However, age-specific amplitude effects emerged for the slowest rate. The P1-N1 and especially the N1-P2 amplitude of the EP to the first as compared to that of the second tone was greatly enhanced among the young, but not as much among the elderly adults. Similarly, group differences in baseline to N1 and P2 amplitude measures of EPs to the first tone of the pair were most pronounced at the fastest stimulation rate. These data indicate clear differences in the recovery cycle of EPs between normal young and elderly subjects and demonstrate the applicability of the two-tone stimulation procedure in the assessment of cerebral responsivity in normal and pathologic populations.

Acoustic Stimulation↗
PubMed1984

Period analysis of the EEG in early putative Alzheimer's disease.

The EEG of patients with presumptive diagnoses of mild-to-moderate dementia of the Alzheimer type (DAT) and still residing in the community was examined using period analytic techniques. DAT patients were found to have significantly slower major and intermediate period EEG activity as compared to controls. Furthermore, one DAT patient, whose clinical EEG was read as normal, had period analytic EEG descriptors that were greater than one standard deviation below the mean of the control group. Results suggest that EEG activity, as quantified by period analysis, can be detected very early in the course of DAT.

Aged↗
PubMed1984

Auditory evoked potentials in senescent forgetfulness.

Two evoked potential (EP) techniques and the selective reminding test were employed to investigate an apparently benign forgetfulness in seven elderly subjects and seven age-matched elderly subjects with normal memory. EPs were also recorded in a group of seven young adults. Latency of the P3 component, which has been demonstrated to increase in primary degenerative dementia, displayed the normal age-related variation in both elderly groups, but did not differ between the forgetful subjects and the elderly controls. Further, no difference in the recovery cycle of the EP, as measured in a two tone stimulation paradigm, was present between forgetful and elderly control groups. Reexamination of memory after nearly a year disclosed no evidence of deterioration in either elderly group. These findings suggest that senescent forgetfulness, as defined herein, may be a nonprogressive memory disorder.

Aged↗
PubMedDate not supplied

Effects of scopolamine on visual evoked potentials in aging and dementia.

The unusual combination of a normal pattern reversal VEP and a delayed flash VEP has been reported in patients with dementia of Alzheimer's type (DAT). Hyoscine hydrobromide has been reported to produce a similar VEP abnormality in young, healthy subjects. In the present study, we assessed the relative sensitivity of DAT patients and healthy young, middle-aged and elderly subjects to temporary cholinergic blockade. We report VEP latency values following 3 doses of scopolamine and after a peripheral anticholinergic agent. Flash P2 latency was not significantly slower in DAT patients than in the healthy elderly. Scopolamine increased P2 latency in the young controls but did not affect any other group. The pattern reversal P100 was normal in DAT, and a significant increase in latency occurred following scopolamine administration in both the control and patient groups.

Adult↗
PubMedDate not supplied

Spectral analysis of sphenoidal evoked potentials predicts epileptic focus.

Sphenoidal evoked potentials (SpEPs) were recorded in 14 patients with intractable temporal lobe epilepsy. Twelve patients had electrographically proven unilateral seizure onset (five left, seven right). Two patients had partial complex seizures and unilateral mesial temporal lobe lesions shown by magnetic resonance imaging (MRI). Thirteen patients subsequently underwent temporal lobectomy. SpEPs were recorded using the P3 tonal oddball paradigm from sphenoidal electrodes referenced to scalp electrodes (i.e., T3, T4, C3, C4, Cz) and were subjected to spectral analysis for whole band (1-12.6 Hz) power. A significant relationship was found for side of seizure focus and reduced spectral power of the sphenoidal-temporal target SpEPs. In 10 of 14 patients, SpEP spectral power was less from the "epileptogenic" than from the "nonepileptogenic" temporal lobe. Of the remaining 4 patients, 2 had bilaterally equal spectral power, and 2 had lower SpEP power from the nonepileptogenic side. Postoperatively, all 13 patients are seizure-free except for the 2 patients with reduced SpEP power opposite to the ictal onset and 1 patient with fluctuations in SpEP asymmetries. Spectral analysis of SpEPs appears to have utility in the assessment of temporal lobe dysfunction and thus in the preoperative evaluation for epilepsy surgery.

Adolescent↗
PubMedDate not supplied

Effects of carbamazepine and phenytoin on EEG and memory in healthy adults.

Using a randomized, double-blind, cross-over design, we investigated the effects of carbamazepine (CBZ) and phenytoin (PHT) on memory and spectral EEG components in 15 healthy adults. Each subject was treated with each drug for 1 month, separated by a 1-month washout. Evaluations were conducted at baseline, at the end of each treatment month, and 1 month after the last treatment phase. EEG was collected during an eyes-closed resting condition and a verbal memory activation task. Spectral analysis of the EEG in the nondrug conditions showed that the memory task significantly reduced theta components and increased delta components. As compared with nondrug conditions, the antiepileptic drugs (AEDs) significantly impaired memory performance and produced mild EEG slowing. Memory performance did not differ statistically between the AEDs, but minor differences in spectral EEG components were noted. The results suggest that differences in the cognitive and EEG effects of CBZ and PHT are not clinically significant.

Adult↗
PubMedDate not supplied

Amnesia after unilateral temporal lobectomy: a case report.

We report a mixed handed (L > R) patient with exclusive right cerebral language representation who developed a permanent anterograde amnestic syndrome after right anterotemporal lobectomy. Preoperative neuropsychological performance consisted of impaired verbal memory and normal nonverbal memory. Wada memory performance was asymmetrical for objects presented soon after amobarbital injection in conjunction with no memory asymmetry for items presented later in the Wada evaluation. Pre- and postoperative magnetic resonance imaging (MRI) scans showed no structural lesions; however, postoperative MRI hippocampal volume measurements suggested decreased hippocampal volume for the nonresected temporal lobe. These results confirm the risk of anterograde amnesia after unilateral temporal lobectomy and demonstrate that baseline neuropsychological testing may falsely literalize material-specific memory functions in patients with atypical cerebral language dominance.

Adult↗
PubMedDate not supplied

Central anticholinergic hypersensitivity in aging.

Although neurochemical reductions in cholinergic systems have been found to occur during aging, such changes do not necessarily translate to functional deficits. The cognitive deficits of normal aging have been attributed in part to hypocholinergic function, but anticholinergic hypersensitivity in the elderly has not been systematically documented. To test the cholinergic hypothesis of aging, we investigated the effects of scopolamine on memory and attention in healthy young and elderly subjects. Treatments included intramuscular glycopyrrolate (0.0044 mg/kg) and scopolamine (0.002, 0.004, and 0.007 mg/kg) in a randomized double-blind design. The test battery included the Selective Reminding Task (SRT), Digit Span, Paired Associates Learning (PAL), Symbol Digit Modalities Test (SDMT), and the Continuous Performance Task. Elderly controls were more impaired at lower scopolamine doses than were the young on SRT, PAL, and SDMT. These results demonstrate anticholinergic hypersensitivity and are consistent with decremental changes in cholinergic status during normal aging.

Adult↗
PubMedDate not supplied

Age-related changes in the neurologic examination of healthy sexagenarians, octogenarians, and centenarians.

Although numerous studies have focused on age-related changes in the nervous system, few have systematically assessed global neurologic examination changes, and even fewer have included the most elderly population, ie, the centenarians. To perform such a study, we developed a quantitative assessment that includes the major components of a standard bedside neurologic evaluation, with special emphasis on cognitive function. First, we demonstrated that the quantitated examination could correctly classify healthy controls and patients with stroke or dementia based on discriminant analysis. This examination was then applied to healthy community-dwelling elderly ranging from 60 to 108 years of age. Significant age-related neurobehavioral changes were apparent across even these most "successfully" aged groups. Analysis of the full pattern of cognitive and neurologic findings provided the most accurate assessment. Pathologic reflexes, reportedly associated with normal aging, occurred infrequently in this healthy geriatric population, suggesting that age-related changes in the neurologic examination may be more accurately interpreted when assessed in conjunction with cognitive status. This quantitative examination may be useful in future population-based studies of neurologic function in the aged.

Aged↗
PubMedDate not supplied

[Intracarotid amytal testing in the evaluation for epilepsy surgery].

INTRODUCTION: The Wada test for language and memory still plays an important role in evaluating the surgery performed on epileptic patients. The measures of the functional deficits carried out with the Wada test, associated with known brain lesions, aid in determining the lateralization of the onset of seizures and provide some estimate of the risk to memory after a temporal lobotomy. DEVELOPMENT: A more refined procedure, based on the correlations with the titration from MRI, fMR and MR spectroscopy, will be needed. Moreover, using the Wada test it is possible to make long term forecasts about the cognitive outcome and about the control of seizures. When used together with other neurological, functional and psychometric evaluations, it becomes easier to select the patients with most chances of benefiting from surgical epilepsy treatment. Finally, the non invasive measures of brain functioning include fMR, which provides far more information than that obtained using the Wada test. However, it remains to be determined whether the procedure based on activation provides data of the same quality as those obtained by the Wada test, which can provide a more adequate reversible model of the effects of surgery on cognition. CONCLUSION: . Ideally, as MRI and other imaging techniques progress, they will be able to offer complementary images, which will improve our capacity to forecast and prevent important post operative cognitive deficiencies.

Adult↗