Biomedical subjects

D W Loring

Publications and source records attributed to D W Loring.

At least 127 records · Page 7Linked to original sources

PubMed1988

Cholinergic modulation of human limbic evoked potentials.

Limbic evoked potentials (LEPs) were recorded from the hippocampi of three epilepsy surgery patients with unilateral medial temporal lobe seizure onset. In each patient, stable large amplitude LEPs which displayed polarity inversion across successive levels of hippocampus were present unilaterally, but were absent or rudimentary in the hippocampus corresponding to the electrographically proven seizure onset. After administration of scopolamine, LEPs in the "normal" hippocampi were markedly altered with slowing of the individual components and increased trial to trial variability. In addition, two patients developed reliable, high amplitude, polarity inverting LEPs on the side of seizure onset which had either absent or rudimentary LEPs in the baseline state. The results suggest that LEPs are under cholinergic modulation.

Acetylcholine↗

PubMed1988

Revising the Rey-Osterrieth: rating right hemisphere recall.

Recall performance of the Rey-Osterrieth Complex Figure was examined in patients with partial complex seizures originating from either the right or left temporal lobe and who underwent subsequent unilateral temporal lobectomy. A scoring system was developed to assess the types of errors frequently observed in the recall of patients with right temporal lobe epilepsy (TLE), but absent in left TLE patients. The scoring system was initially developed on a single group of patients, and then "cross-validated" on an independent sample. Performance analysis of the cross-validation group revealed a significant difference in the frequency of right hemisphere errors. In contrast, no significant difference using standard quantitative scoring was present. By applying the new scoring criteria alone, a rater blind to seizure onset correctly predicted seizure laterality in 15/18 of the cross-validation patients. These results suggest that evaluation of qualitative errors may be a valuable adjunct to standard scoring criteria, thereby extending the range of applications for this test.

Journal Article↗

PubMed1988

Differential forgetting in patients with temporal lobe dysfunction.

Delayed recall performance was investigated in 13 patients with temporal lobe epilepsy (TLE) and 13 healthy age-matched controls who were matched on a pairwise basis for initial learning on the Selective Reminding test. TLE patients performed significantly worse on the 30-minute delayed recall condition despite equivalent initial continuous long-term retrieval scores. These data suggest that TLE patients forget at disproportionately rapid rates as compared to healthy controls despite equivalent initial learning. Consequently, delayed recall may increase group discrimination when initial learning levels are similar.

Journal Article↗

PubMed1987

Convergent evoked potential and cerebral blood flow evidence of task-specific hemispheric differences.

Two independent measures of cerebral activation, probe evoked potentials (EPs) and regional cerebral blood flow (rCBF) were used to assess the relative contribution of the left and right parietal areas during a task requiring mental rotation of geometric figures. The objective of the study was to ascertain the degree of concordance in these two measures in revealing task-specific hemispheric activation. Since rCBF is a direct measure of regional metabolic rate and has been shown to reflect expected task-specific hemispheric asymmetries, its concordance with probe EP data could serve to validate the assumptions underlying interpretation of the latter. EPs to strobe flashes and rCBF were simultaneously measured in 19 dextral normal adults during a mental rotation task and during a control task involving similar stimulation and response requirements. A high degree of concordance in these two measures was obtained, with both revealing significantly greater activation of the right parietal region during the mental rotation task. Besides supporting the notion of predominant right hemisphere involvement in this type of visuo-spatial operation, this study suggests that either measure may be used as a reliable index of task-specific regional cerebral asymmetries.

Adult↗

PubMed1987

Memory assessment in neuropsychology: theoretical considerations and practical utility.

Memory assessment is one of the principal objectives of neuropsychological evaluation. Yet, careful examination reveals very clear shortcomings in the memory tests employed by neuropsychologists. Specifically, most procedures are selected on the basis of their ability to detect structural brain pathology rather than their ability to assess memory performance per se or the constituent operations that underlie it. This paper addresses the shortcomings in the structure of several representative memory tests in neuropsychology, how some of these limitations have been overcome with newer scales, and presents practical and theoretical considerations for the development of new clinical memory measures.

Brain Damage, Chronic↗

PubMed1987

Limbic evoked potentials predict site of epileptic focus.

Limbic evoked potentials (LEPs) were recorded from intracerebral electrodes in the hippocampi of seven preoperative epilepsy surgery patients. LEPs were evaluated using amplitude, form, and asymmetry by raters blinded as to the side of electrographically proven seizure onset. Raters correctly predicted the side of focus in all four patients with proven unilateral temporal lobe seizure onset. Further, LEP amplitudes in two patients with bilateral independent temporal lobe seizure onset were markedly diminished compared with one patient with a nontemporal lobe seizure onset. LEP recordings may assist in determination of the site of epileptogenic pathology.

Epilepsies, Partial↗

PubMed1987

Remote memory and neglect syndrome.

Three patients with right cerebral infarctions and neglect syndrome failed to recall left hemispatial remote memories, even when the imagined orientation was reversed by 180 degrees. One patient was retested 4 months later and, although improved, continued to consistently recall more right-sided items. He was tested at east and west mental orientations with his head/eyes oriented physically to each side. Recall for items imagined in left hemispace improved 26% when his head/eye orientation was physically shifted from right to left hemispace. Findings suggest that the engrams for left-sided visuospatial memories in neglect syndrome are not destroyed, but rather fail to be activated.

Attention↗

PubMed1987

Cognitive evoked potentials and disorders of recent memory.

P3 potentials evoked by spoken words were recorded from seven patients with disorders of recent memory and seven age-matched controls. Inclusion criteria included a clearly identifiable P3 to pure tone stimuli. Absence or marked decrement of P3 to word stimuli was seen in the patients even though they could perform the word task. The results are consistent with an encoding disorder and failure in elaboration of information processing.

Adult↗

PubMed1987

Auditory P3 correlates of phonemic and semantic processing.

Auditory evoked potentials were recorded in twelve healthy subjects using phonemic and semantic word tasks. The late positive component (P3), analogous to tonal P300, varied as a function of cognitive task with increased latency and amplitude associated with semantic processing. These data are consistent with levels of processing theories in which semantic analysis is associated with a greater elaboration of stimulus evaluation.

Adult↗

PubMed1987

Central cholinergic systems and the P3 evoked potential.

A cognitive evoked potential, the P3, is commonly altered in dementia states but little is known of the specific neuronal generators that are the source of this potential. Event-related evoked potentials and neuropsychological testing were obtained in six normal subjects during neuropharmacological manipulation of the central cholinergic system. Scopolamine (an anticholinergic) impaired recent memory, prolonged P3 latency and decreased P3 amplitude. These abnormalities were partially reversed by physostigmine (an anticholinesterase). The results imply that the cholinergic system is involved in the generation of the P3 potential.

Adult↗

PubMed1986

CBF gradient changes elicited by visual stimulation and visual memory tasks.

Normal volunteers underwent three successive scans of regional cerebral blood flow (rCBF) using the 133Xe inhalation technique during visual stimulation, a recognition memory task and a resting state defined by high EEG alpha content. Since the stimulation was virtually identical in both non-rest conditions, we were able to separate the CBF pattern resulting from simple stimulation and that resulting from the cognitive (recognition memory) component alone. These turned out to have very nearly opposite effects on the normal anterior-to-posterior resting state gradient: the sensory component diminished the gradient, while the cognitive component exaggerated it. It is suggested that these normative data can be of clinical value in the study of cerebral recovery/reorganization following post-traumatic amnesia.

Adult↗

PubMed1986

Brain stem evoked response suppression during speech production.

Auditory brain stem evoked responses (BSERs) to repetitive clicks were recorded in subjects engaged in overt speech, whispering, silent articulation, and covert verbal rehearsal tasks and during a control condition of attending to the clicks. Overt speech and whispering resulted in a significant amplitude reduction of the fifth peak of BSERs without affecting the amplitudes or the latencies of the earlier peaks. These data strongly suggest efferent inhibition of irrelevant auditory input at the level of the upper brain stem.

Adolescent↗

PubMed1986

Second prior stimulus interval effects on auditory evoked potentials.

The question whether the stimulation interval prior to the interstimulus interval preceding the target tone, the second prior interval, produces an effect on evoked potential amplitude when the tones are presented periodically was investigated in 12 young adults. Increased N1 amplitude was associated with the longer second prior interval. No effect on P2 amplitude was observed. These data suggest the importance of the second prior interval length on N1 amplitude when tones are presented periodically.

Adult↗

PubMed1986

Auditory brain stem evoked responses in comatose head-injured patients.

Brain stem evoked responses (BSERs) were obtained within the first 72 hours after hospital admission from 38 patients with closed head injuries whose Glasgow coma scale scores were 8 or less. Peak V latency differentiated patients with unfavorable outcomes (vegetative or dead) from patients with more favorable outcomes, but no features of the response could further discriminate good, moderate, and severe outcomes as assessed by the Glasgow outcome scale. These data provide further support that BSERs are generally resistant to central nervous system trauma but, when impaired, are prognostic of unfavorable outcome.

Brain Injuries↗

PubMed1986

Task-related EEG asymmetries: a comparison of alpha blocking and beta enhancement.

Alpha and beta content of spectrally analyzed EEG were used to assess differential hemispheric engagement during two linguistic tasks (semantic and phonetic) and one acoustic task involving detection of target items embedded within the same stimulus series. Beta content of the EEG increased reliably in the left hemisphere during the linguistic tasks, whereas the expected attenuation or blocking of alpha did not occur reliably. These data suggest that left hemisphere beta enhancement rather than alpha blocking is a more efficient index of differential hemispheric engagement during language processing.

Acoustic Stimulation↗

PubMed1986

Neuropsychological performance in dementia of the Alzheimer type and multi-infarct dementia.

Neuropsychological performance was examined in patients with dementia of the Alzheimer type (DAT) and in age- and education-matched patients with multi-infarct dementia (MID). Significant differences were observed for FSIQ, VIQ, and Picture Completion. This contrasts to no difference in verbal memory, visual-spatial skills, and sustained attention/concentration. This report illustrates that neuropsychological testing of elderly patients is unable to aid in the differential diagnosis between clinically similar forms of dementia, and should be employed to establish the level of cognitive function to make inferences regarding the patient's functional independence.

Journal Article↗

PubMed1985

Neuropsychological patterns of presenile and senile dementia of the Alzheimer type.

Thirty-seven patients with a presumptive diagnosis of dementia of the Alzheimer type were divided into presenile and senile groups according to the age at which they first received a clinical diagnosis. Although there were no differences in mental status, dementia rating, or chronicity of disease, multivariate analyses of WAIS subtests revealed the presenile subjects to be relatively impaired on Performance subtests. Univariate tests of Verbal, Performance, and Full Scale IQ measures were significantly lower in the presenile group. There was no group effect detected for Digits forward, adjusted for age differences based upon performance of 40 age-matched controls, while the presenile group performed significantly more poorly on backward span. Further, significant differences were detected for an embedded figure task, as well as graphomotor speed. These data suggest that patients who develop a degenerative dementia during the presenile period are more impaired than their senile counterparts on age-adjusted measures of sustained concentration and mental tracking.

Age Factors↗

PubMed1985

Evoked potential attenuation in the two-tone paradigm.

The recovery cycle and two variants of the habituation hypothesis invoked to explain the N1-P2 amplitude attenuation of evoked potentials (EPs) to the second tone in two-tone series, were investigated. Paired stimuli were presented with a constant 360 ms inter-stimulus interval (ISI), but with different, fixed inter-pair intervals (IPIs) of 800, 1 000 and 1 200 ms in addition to a variable IPI averaging 1 000 ms. Amplitude reduction of the second tone EP was present for only the 1 000 and the 1 200 ms IPI series. These data contradict the specific predictions of all three hypotheses, although one prediction of the recovery cycle hypothesis was supported, stating that for a given relation of IPI to ISI the second tone attenuation effect disappears. To account for all findings in this experiment, an alternative explanation is advanced incorporating the concept of recovery cycle and involving the effects of rhythmic stimulation, whereby tone pairs are processed as units whose perceptual cohesiveness determines the distribution of response resources to each tone.

Adult↗