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D W Loring

Publications and source records attributed to D W Loring.

At least 19 recordsLinked to original sources
PubMed1992

Differential effects of left versus right seizure focus on human hippocampal evoked responses.

Hippocampal evoked potentials were recorded using the P3 tonal oddball paradigm in 30 patients with unilateral temporal lobe seizure focus. Spectral power of the evoked potentials was decreased on the side of seizure focus, but this reduction was much greater when the focus was on the left. The effect of left/right focus does not appear to be due to group differences in age, sex, seizure duration, or operative pathology. Remote or finer left/right structural differences or differential left/right hippocampal processing for the sequential tonal task are possible explanations.

Adolescent↗
PubMed1992

Diazepam effects on the P3 event-related potential.

Cerebral event-related potentials arise from synchronous neural activity associated with cognitive processing. The P3 is a late positive component that is related to task complexity and is directly proportional to stimulus evaluation time. P3 latency and amplitude were examined after oral administration of diazepam, a commonly prescribed medication with known cognitive side effects. Latency of the P3 was significantly increased after a single dose of both 5 and 10 mg of diazepam but not after placebo. P3 amplitude decreased slightly, but not significantly after 10 mg of diazepam. Changes in P3 occurred in the absence of significant changes in the preceding evoked waves (N1, P2). These findings should be considered when the P3 is obtained for clinical or research purposes from medicated patients.

Acoustic Stimulation↗
PubMed1991

Allochiria vs allesthesia. Is there a misperception?

Allochiria is the mislocation of sensory stimuli to the corresponding opposite half of the body or space. Obersteiner (1882) introduced the term allochiria (Greek allos = other + chiria = hand), and more than 20 authors employed it in this context over the next 25 years. Stewart (1894) described a related phenomenon in which stimuli are displaced to a different point on the same extremity. He noted that the displacements were different than allochiria and coined the term allachaesthesia (ie, allesthesia) (Greek allaché = elsewhere + aisthésis = perception). Despite this historical background, Jones (1907) redefined both terms in an attempt to increase diagnostic specificity and attributed allochiria to hysteria. Jones' reinterpretation does not appear to be justified historically, etymologically, or scientifically and has resulted in contradictory definitions of allochiria and allesthesia in present-day medical dictionaries and neurologic textbooks. We advocate a return to usage consistent with the original descriptions and word derivations.

Europe↗
PubMed1991

Hippocampal contribution to verbal recent memory following dominant-hemisphere temporal lobectomy.

The effects of hippocampal encroachment in the language dominant-hemisphere were studied in 41 patients who underwent previous temporal lobectomy (TL). Patients undergoing dominant-hemisphere TL including anterior hippocampus (n = 13) performed significantly worse than nondominant TL patients (n = 16) on a verbal learning test (Selective Reminding; p less than or equal to .00001), thereby confirming the sensitivity of this procedure to lateralized temporal-lobe dysfunction. However, no significant difference was present on this or other primary measures of material-specific memory when contrasting dominant TL patients in whom the anterior hippocampus was spared (n = 12) to those in whom anterior hippocampus was resected. These data suggest that more extensive and posterior mesial temporal-lobe resection is not necessarily associated with a greater verbal material-specific memory deficit following dominant-hemisphere temporal lobectomy.

Adult↗
PubMed1991

Differential effects of unilateral temporal lobectomy on visuospatial memory and attention.

We investigated free recall of visuospatial arrays in a free-field format in epileptic patients following unilateral temporal lobectomy (TL) (left = 15, right = 17). TL patients exhibited leftward deviation in right hemispace, but more variable response in left hemispace, a pattern that has been observed in healthy adults. This finding is postulated to result from combined preferential right cerebral activation and a tendency to err toward peri-personal space. Temporal lobectomy affected overall leftward deviation by initially shifting deviation more toward the side of lesion. The initial directional shift in immediate memory dissipated over time suggesting that these subtle attentional shifts may be compensated by learning. Consistent with differential cerebral hemispheric mechanisms, absolute vertical errors were greater in right than left TL patients, and absolute horizontal errors were worse in right hemispace.

Adult↗
PubMed1991

Comparative cognitive effects of carbamazepine and phenytoin in healthy adults.

We investigated neuropsychological effects of carbamazepine and phenytoin in 21 healthy adults using a randomized, double-blind, double-crossover design and treating each subject with each drug for 1 month, separated by a 1-month washout. There were neuropsychological evaluations at baseline, the end of each treatment month, and 1 month after the last treatment phase. Cognitive measures included Symbol Digit Modalities Test, Selective Reminding Test, Complex Figures, Paced Auditory Serial Addition Test, Stroop, Finger Tapping, Grooved Pegboard, Choice Reaction Time, P3 Event-Related Potential, Hopkins Symptom Checklist, and Profile of Mood States (POMS). Compared with nondrug conditions, the anticonvulsants significantly impaired Stroop, Choice Reaction Time, Grooved Pegboard, Hopkins, and POMS. Employing anticonvulsant blood levels as covariates, there were only two significant differences between drugs, one in favor of carbamazepine (ie, Finger Tapping) and one in favor of phenytoin (ie, Stroop). The results suggest that differences in cognitive effects of carbamazepine and phenytoin are not clinically significant.

Adult↗
PubMed1991

Behavioral state-specific changes in human hippocampal theta activity.

Although there has been extensive examination of the behavioral and physiologic correlates of hippocampal theta activity in animals, the human literature consists of a single case study. We investigated the differential effects of four behavioral states on human hippocampal theta activity in 16 epilepsy surgery patients. Behavioral conditions included resting eyes closed (RC), resting eyes open (RO), eyes open with auditory word activation (AW), and eyes open with visuospatial activation (VS). Hippocampal theta activity decreased during both RO and VS compared to both RC and AW. There were reciprocal changes in delta activity. Comparisons of RO to VS and of RC to AW were nonsignificant. The results demonstrate state-specific changes in human hippocampal theta and are consistent with the animal literature that relates hippocampal theta to sensorimotor integration and forebrain volitional mechanisms.

Adolescent↗
PubMed1990

The effects of lateralized temporal lobe dysfunction on formal and semantic word fluency.

Word fluency performance was studied in 32 patients with unilateral temporal lobe epilepsy (TLE) and 25 healthy dextral controls. Two word fluency tasks were administered conforming to either formal-based criteria or semantic-based criteria. Performance for TLE patients was assessed both pre-operatively and approximately 1 week following anterior temporal lobectomy. Both formal and semantic word fluency decreased regardless of resection laterality. Left TLE patients performed significantly worse at both pre- and post-operative assessments compared to the right TLE patients, while right TLE patients performed significantly poorer than controls on all verbal fluency criteria at pre- and post-operative assessments. In addition, both TLE and control groups produced significantly fewer formal and semantic words during the second 30-sec portion of each task. These findings are discussed in terms of temporal lobe contributions to word fluency production and lexical semantic processing.

Adult↗
PubMed1990

Cerebral language lateralization: evidence from intracarotid amobarbital testing.

Cerebral language lateralization was investigated in 103 patients undergoing intracarotid amobarbital testing as part of their diagnostic work-up for epilepsy surgery. Inclusion criteria included adequate bilateral intracarotid amobarbital studies and no radiologic lesion in areas other than the temporal lobe. Language was evaluated with respect to strict presence or absence of language representation, in which a patient was considered to have bilateral language despite potentially having asymmetric language representation, and with respect to forced relative hemispheric dominance, in which a single side could be considered dominant despite bilateral language representation. Seventy-nine patients displayed exclusive left hemisphere language representation, two patients showed exclusive right hemisphere language representation, and 22 patients had language represented in each hemisphere. In the 22 patients with bilateral language, an asymmetry was present in 17 cases (13 L greater than R, 4 R greater than L). These data indicate that language restricted only to the right hemisphere is rare, and that in the absence of purely left hemisphere language, most patients exhibit bilateral representation. Previously reported incidence of exclusive right hemisphere language may be an artifact of dichotomizing a continuous variable.

Amobarbital↗
PubMed1990

Hemispheric specialization for emotional expression: a reexamination of results from intracarotid administration of sodium amobarbital.

Emotional and behavioral responses to sodium amobarbital injection were examined in 44 epilepsy surgery candidates. Thirty-three emotional reactions occurred in 26 patients, 44% of the reactions following right hemisphere injection and 32% after injection of the left hemisphere. Among all patients examined, laughter/elated mood was statistically more frequent following right hemisphere injection while crying was statistically associated with left hemisphere injections. These observed effects were not related to amobarbital dose, sex, bilateral hemispheric inactivation (angiographic crossflow), general cognitive status, or side of seizure onset. These results support differing specialization of emotional expression in the right and left cerebral hemispheres and their subcortical connections.

Adolescent↗
PubMed1990

Material specific learning during electrical stimulation of the human hippocampus.

Material specific learning was assessed during unilateral electrical stimulation of the hippocampus through intracerebrally implanted electrodes in 30 patients with unilateral temporal lobe epilepsy (TLE). Verbal learning significantly decreased in patients with right TLE after stimulation of the left, but not the right, hippocampus. No verbal learning impairment was observed in left TLE patients following stimulation of either hippocampus. Visuospatial memory performance significantly decreased following stimulation of the right hippocampus regardless of the side of seizure onset. Results suggest that the contralateral "nonepileptic" hippocampus does not assume the material specific mnestic functions of the dysfunctional hippocampus associated with longstanding epilepsy.

Analysis of Variance↗
PubMed1990

The contribution of an imagery code to verbal memory.

Free recall for auditorially presented spatial information was examined in a patient with a large right cerebral infarction. Despite normal verbal memory at immediate and 30-minute conditions, the patient exhibited a significant loss in verbal recall at 24 hours and a more severe deficit in the recall of the spatial components of prose passages across all delayed recall conditions. These results suggest that although the verbal code is important early in the learning process, spatial imagery exerts an increasing influence over time. Thus, reliance upon a left hemispheric mediated verbal encoding process may only allow for partial integration of linguistic and visuospatial properties.

Adult↗
PubMed1990

Crossed aphasia in a patient with complex partial seizures: evidence from intracarotid amobarbital testing, functional cortical mapping, and neuropsychological assessment.

We report a right-handed patient who became transiently aphasic following a right temporal lobectomy for control of intractable complex partial seizures. Preoperative intracarotid amobarbital testing revealed right-hemisphere language dominance, although bilateral language representation was present. Memory testing during unilateral electrical hippocampal simulation with depth electrodes indicated reliance on left-hemisphere mesial temporal lobe structures for verbal memory. Functional mapping for language during surgery established several right perisylvian regions that, when stimulated, produced speech arrest and/or paraphasic substitution. One-year follow-up neuropsychological assessment demonstrated an increase in verbal learning and decrease in visual memory, a pattern associated with patients who have undergone right temporal lobectomy. These data demonstrate that (1) right cerebral language dominance can be observed when ipsilateral seizure onset is present (2) verbal memory and language dominance are not necessarily linked, and (3) some reported cases of crossed aphasia may in fact have bilateral language representation.

Adult↗
PubMed1990

Comparative cognitive effects of anticonvulsants.

We investigated the neuropsychological effects of carbamazepine, phenobarbital, and phenytoin in 15 partial complex epilepsy patients treated with each drug for 3 months, using a randomized double-blind, triple crossover design. Neuropsychological evaluation at the end of each treatment period included Digit Span, Selective Reminding Test, Digit Symbol, Finger Tapping, Grooved Pegboard, Choice Reaction Time, P3 evoked potential, and Profile of Mood States. Employing anticonvulsant blood levels and seizure frequencies as covariates, the only significant difference was for Digit Symbol. Performance with phenobarbital was significantly worse than with the other 2 anticonvulsants despite phenobarbital's having had the lowest overall blood levels. Our data show that patients receiving carbamazepine, phenobarbital, and phenytoin have comparable neuropsychological performance on most measures. The results suggest that the differential cognitive effects of anticonvulsants may be subtle.

Adult↗
PubMed1990

The intracarotid amobarbital procedure as a predictor of memory failure following unilateral temporal lobectomy.

We investigated the efficacy of the intracarotid amobarbital procedure to accurately predict post-temporal lobectomy anterograde amnesia. We presented items at 2 separate times during amobarbital assessment; both early and late item recall were decreased during the injection contralateral to seizure onset indicating sensitivity to bilateral temporal lobe dysfunction. Ten patients for whom follow-up neuropsychological assessment was available failed either the early or late item recognition portions of their amobarbital evaluation ipsilateral to seizure onset, but had hippocampus included in the temporal lobectomy by virtue of satisfactory performance on other tests of hippocampal function. None of these 10 patients displayed postoperative anterograde amnesia, although there was a reduction in material-specific memory in some patients. These results indicate that relying solely on amobarbital memory testing to assess the functional ability of the contralateral temporal lobe to sustain global memory prior to temporal lobectomy may needlessly exclude patients from a viable therapeutic option.

Amnesia↗
PubMed1990

Human hippocampal EEG: effects of behavioral activation.

We studied spectral components of human hippocampal EEG in relation to behavioral status in 19 patients with intractable complex partial seizures who had depth electrodes implanted into the anterior hippocampi as a part of their preoperative evaluations. Behavioral conditions included: eyes closed resting, eyes open resting, eyes open with a verbal task, and eyes open with a visuospatial task. Hippocampal EEG spectral power uniformly decreased during behavioral activation. EEG activation was quantitatively different among the 3 activated conditions, with the most prominent change occurring during the visuospatial task. The degree of EEG activation corresponded inversely with the site of epileptic focus during the verbal task. The results demonstrate the response of human hippocampal EEG to behavioral activation. The magnitude of EEG change may reflect the degree of functional activation of the given hippocampus.

Adult↗
PubMed1990

Unilateral cerebral inactivation produces differential left/right heart rate responses.

We studied heart rate following unilateral hemispheric inactivation by intracarotid amobarbital in 25 patients undergoing preoperative evaluation for epilepsy surgery. Heart rate increased after left hemisphere inactivation, but decreased following right hemisphere inactivation. The results are consistent with differential left/right cerebral hemispheric effects on autonomic function, and appear related to functional and anatomic asymmetries in both the central and peripheral nervous systems.

Adolescent↗