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Biomedical subjects

K J Meador

Publications and source records attributed to K J Meador.

At least 55 records · Page 3Linked to original sources
PubMed1999

Time perception following unilateral amobarbital injection in patients with temporal lobe epilepsy.

Estimates of elapsed time were obtained from 53 patients with unilateral temporal lobe epilepsy (Left TLE = 27; Right TLE = 26) following Wada (intracarotid amobarbital) assessment. After resolution of drug effects, patients were asked to estimate how much time had passed since amobarbital administration. Estimates were also obtained from 24 healthy control subjects using the same cognitive tasks over a similar time frame. Elapsed time was significantly underestimated by both left and right TLE groups following right hemisphere injection. In addition, there was an interaction effect involving patient group, side of injection, and sequence of injection. Left TLE patients, consistent with normal controls, made more accurate time estimates when they could anticipate the estimation task following the second amobarbital administration. More accurate time estimates, however, occurred only when left hemisphere injection was second in sequence. In contrast, right TLE patients did not improve regardless of the order of injection. These results suggest that right hemisphere function plays a critical role in the accuracy of time estimations of intermediate temporal duration and that interhemispheric interaction may be required to make accurate retrospective temporal judgments. These findings are discussed in the context of the growing evidence for a right-hemispheric attentional network.

Adult↗
PubMed1999

A comparison of magnetoencephalography, MRI, and V-EEG in patients evaluated for epilepsy surgery.

PURPOSE: To determine the efficacy and relative contribution of several diagnostic methods [ictal and interictal scalp and intracranial EEG, magnetic resonance imaging (MRI), and magnetoencephalography (MEG)] in identifying the epileptogenic zone for resection. METHODS: This was a prospective study using a masked comparison-to-criterion standard. Fifty-eight consecutive patients with refractory partial epilepsy from two university comprehensive epilepsy programs were studied. Patients who were evaluated for and underwent epilepsy surgery were recruited. The main outcome measure was the efficacy of each diagnostic method to identify the resected epileptogenic zone, when referenced to surgical outcome. RESULTS: MEG (52%) was second only to ictal intracranial V-EEG in predicting the epileptogenic zone for the entire group of patients who had an excellent surgical outcome (seizure free or rare seizure). In a subanalysis, for patients who had temporal lobe surgery, this same relation was seen (MEG, 57%, ictal intracranial V-EEG, 62%). With extratemporal resection, ictal (81%) and interictal (75%) intracranial EEG were superior to MEG (44%) in predicting the surgery site in those patients with an excellent outcome. Finally, for all patients who had a good surgical outcome, MEG (52%) was better than ictal (33%) or interictal (45%) scalp VEEG in predicting the site of surgery. CONCLUSIONS: These results indicate that MEG is a very promising diagnostic method and raise the possibility that it may obviate the need for invasive EEG in some cases or reduce the length of scalp EEG evaluation in others.

Adolescent↗
PubMed1999

Differential cognitive effects of carbamazepine and gabapentin.

PURPOSE: The cognitive effects of the newer antiepileptic drugs (AEDs) compared with the older standard AEDs are uncertain. METHODS: We directly compared the cognitive effects of carbamazepine (CBZ) and gabapentin (GBP) in 35 healthy subjects by using a double-blind, randomized crossover design with two 5-week treatment periods. During each treatment condition, subjects received either GBP, 2,400 mg/day, or CBZ (mean, 731 mg/day) adjusted to a dose to achieve midrange standard therapeutic blood levels (mean, 8.3 microg/ml). Subjects were tested at the end of each AED treatment period and in four drug-free conditions [two pretreatment baselines and two post-treatment washout periods (1 month after each AED)]. The neuropsychological test battery included 17 measures yielding 31 total variables. RESULTS: Direct comparison of the two AEDs revealed significantly better performance on eight variables for GBP, but none for CBZ. Comparison of CBZ and GBP to the nondrug average revealed significant statistical differences for 15 (48%) of 31 the variables. Pairwise follow-up analyses of the 15 variables revealed significantly better performance for nondrug average on 13 variables compared with CBZ, and on four compared with GBP. GBP was better than nondrug average on one variable. CONCLUSIONS: Although both CBZ and GBP produced some effects, GBP produced significantly fewer untoward cognitive effects compared with CBZ at the dosages used in this study.

Acetates↗
PubMed1999

A 13-year experience with epilepsy surgery.

Between 1985 and 1997, 563 therapeutic craniotomies were performed: 311 anterior temporal (ATL) and 158 extramesial temporal (XMT) resections, 67 callosotomies, 20 hemispherectomies and 7 multiple subpial transections. Sixty-seven percent of nonlesional ATL cases were seizure free (SF), and 76% of nonlesional ATL cases < or =18 years old were SF. Seventy-eight percent of lesional ATL cases with complete resection were SF. Seventy-three percent of lesional cases < or =18 were SF. Thirty-seven percent of nonlesional XMT cases were SF. Seventy percent of XMT lesional cases with complete resection were SF, and 82% of lesional XMT cases < or =18 were SF. Of the anterior callosotomy cases, there was a > or =90% decrease in generalized tonic-clonic seizures in 50% of patients, and in tonic seizures, drop attacks, absence and myoclonic seizures in approximately 60-70% of patients. Of 20 hemispherectomies, 65% were SF. Of 7 multiple subpial transections, 29% were SF.

Adult↗
PubMed1998

Verapamil for severe hyperkinetic movement disorders.

The use of verapamil in three cases of severe hyperkinetic movement disorders resulted in dramatic improvement in patients who had been refractory to many other treatments over a prolonged period. A videotape illustration of one of the patients is provided. The mechanism of action and evidence of efficacy of calcium-channel blockers for abnormal movements are discussed.

Adult↗
PubMed1998

Cognitive side effects of medications.

Iatrogenically induced cognitive deficits are common with pharmacological therapy. The deficits may range from gross encephalopathy with delirium to subtle subjective alterations (e.g., mood and perception of well being). The risks are increased for certain drug types, polypharmacy, the elderly, and patients with dementia or metabolic abnormalities. This review examines methodological concerns and the neuropsychological data on cognitive side effects across a variety of commonly used medicines in clinical practice.

Cognition Disorders↗
PubMed1998

Magnetic stimulation of visual cortex: factors influencing the perception of phosphenes.

Using transcranial magnetic stimulation of occipital cortex, the authors studied the stimulus parameters that generate phosphenes in healthy volunteers. Single pulses or trains of stimuli readily elicited phosphenes in all subjects. The threshold current needed to elicit perception of phosphenes was essentially the same for stimulus trains from 250 msec to 2000 msec in length, but increased dramatically for trains of shorter duration. The effect of stimulus frequency was variable, with each subject having a distinctive "frequency tuning curve," but overall, the threshold current necessary to produce phosphenes decreased as frequency of stimulation increased. Using paired pulses, the perceptual threshold was flat for interstimulus intervals between 2 msec and 100 msec, but increased rapidly as the interstimulus interval was increased above 100 msec. Stimulation of sites lateral to the midline elicited phosphenes in the contralateral visual field. Phosphenes were dominant in the lower and peripheral aspects of the visual fields. The findings are discussed in relation to similar studies of electrical stimulation of somatosensory cortex.

Adult↗
PubMed1998

Clinical and physiological effects of stereotaxic bilateral amygdalotomy for intractable aggression.

The amygdala is thought to be an important neural structure underlying the "fight-or-flight" response, but information on its role in humans is scarce. The clinical and psychophysiological effects of amygdalar destruction were studied in 2 patients who underwent bilateral amygdalotomy for intractable aggression. After surgery, both patients showed a reduction in autonomic arousal levels to stressful stimuli and in the number of aggressive outbursts, although both patients continued to have difficulty controlling aggression. The "taming effect" reported after bilateral amygdalar destruction may be due to the amygdala's inadequate processing of perceived threat stimuli that would normally produce a fight-or-flight response.

Adult↗
PubMed1998

Physiology of somatosensory perception: cerebral lateralization and extinction.

OBJECTIVE: To demonstrate the effects of cerebral lateralization and temporal dynamics on somatosensory perception. BACKGROUND: We postulated that perceptual thresholds for simple somatosensory stimuli would be less in the left than the right hand, and that a left/right asymmetry in extinction would exist in healthy right-handed subjects (but not in left-handed subjects). During the course of these experiments we also examined the controversy concerning the temporal dynamics of somatosensory perception. METHODS: A total of 126 healthy subjects (age range, 6 to 73 years) participated in the study. Effects of handedness, age, vigilance, gaze, and temporal interval on somatosensory perception were examined in a series of experiments. Brief electric pulses were applied to the index finger of one or both hands. RESULTS: Perceptual thresholds are lower in the left than the right hand of healthy right-handed subjects in a large cohort across a wide age range. Left-handed subjects have no overall asymmetry. Even after compensation for baseline threshold differences, single stimuli in right-handed subjects are perceived more readily in the left than the right hand, and left-hand targets are more difficult to mask. Leftward eye/head gaze lowers thresholds in both hands of right-handed subjects (compared with right or straight gaze). Extinction was consistently maximal when the mask followed the target by 50 to 100 msec. CONCLUSIONS: The findings demonstrate clearly that left/right perceptual thresholds for simple somatosensory stimuli are asymmetric in healthy right-handed subjects. Both central and peripheral asymmetries exist. The central asymmetry and gaze effects are consistent with right cerebral dominance for externally directed attention. Access of somatosensory stimuli to conscious awareness is delayed and particularly vulnerable to disruption at 50 to 100 msec after onset of the stimulus.

Adolescent↗
PubMed1997

Level of consciousness and memory during the intracarotid sodium amobarbital procedure.

Controversy exists regarding differential effects on consciousness of left/right cerebral inactivation via intracarotid amobarbital. Further, the effects of level of consciousness (LOC) on memory during the intracarotid sodium amobarbital procedure (IAP) are unclear. A modified version of the Glasgow Coma Scale altered to avoid the confounding effects of aphasia was employed to assess LOC in 97 patients during the IAP. A greater impairment in LOC occurred with left cerebral inactivation. Memory was more impaired following left hemisphere injections as well as from injections contralateral to seizure focus. Memory was correlated with LOC, and this effect was more prominent for right hemisphere injections and for injections ipsilateral to seizure focus. These findings support differential cerebral roles in consciousness and demonstrate that IAP memory performance may be affected by the patient's LOC.

Adolescent↗
PubMed1997

Wada memory and timing of stimulus presentation.

We compared Wada memory performance for stimuli presented at two timing intervals following amobarbital injection in 47 non-lesional patients with complex partial seizures (L = 26; R = 21). A significant interaction between seizure focus and timing of presentation was present (P < 0.03). Memory performance for objects whose presentation began approximately 50-55 s following amobarbital administration differed as a function of ipsilateral vs. contralateral injection at a very high level of statistical significance (P < 0.00001). Items presented approximately 4 min, 30 s post injection were also related to seizure onset literality, but at a lower statistical level (P < 0.01). Presentation of Wada memory stimuli earlier during hemispheric anaesthesia yields results that are more sensitive to lateralized temporal lobe seizure onset than does presentation of items later during the procedure.

Adult↗
PubMed1997

A comparison of tension headache sufferers and nonpain controls on the State-Trait Anger Expression Inventory: an exploratory study with implications for applied psychophysiologists.

Studies that have examined the relationship between personality characteristics and tension headache have arrived at conflicting and, for the most part, negative results. In recent years, a number of investigators have begun examining the relationship between anger and psychophysiological disorders, focusing mostly on anger which is suppressed or held in rather than expressed behaviorally. The present study explored the relationship between anger in 59 tension headache subjects and compared their results to 33 nonpain controls. Materials consisted of the revised research edition of the Spielberger State-Trait Anger Expression Inventory. As predicted, tension headache sufferers were found to have significantly more anger held inward than nonpain controls. Implications for applied psychophysiology treatment and future research directions are discussed.

Adult↗
PubMed1997

Effect of Wada memory stimulus type in discriminating lateralized temporal lobe impairment.

PURPOSE: To examine the effects of memory stimulus type on Wada memory performance. METHOD: Ninety-six patients (left, 47; right, 49) from four epilepsy centers who were candidates for anterior temporal lobectomy (ATL) and who have subsequently undergone surgery were studied. Patients with atypical cerebral language lateralization or with evidence on magnetic resonance imaging (MRI) to suggest a lesion other than hippocampal sclerosis were excluded. Wada memory performance was obtained by using both real objects and line drawings as memory stimuli. RESULTS: Wada memory laterality scores with either real objects or line drawings as memory stimuli discriminated left from right-ATL groups. However, objects were superior to line drawings in making this differentiation. Further, objects were superior to line drawings in individual patient classification of candidates for left ATL, with no difference in the classification rates using either objects or line drawings in candidates for right ATL. CONCLUSIONS: Type of memory stimuli is an important factor affecting memory results during the Wada test.

Amobarbital↗
PubMed1997

Results of lesional vs. nonlesional frontal lobe epilepsy surgery.

Fifty-three seizure focus resections limited to the frontal lobe were performed. Forty-nine had adequate follow-up. Five of 17 (29%) nonlesional (NL) cases and 21 of 32 (66%) lesional (L) cases were seizure free (SF) at 1 year postoperatively. Eight of 9 (89%) L cases < or = 18 years old vs. 13 of 23 (57%) > 18 years old were SF. Eight of 10 (80%) tumor vs. 13 of 22 (59%) nontumor L cases were SF. Sixteen NL cases were localized by invasive recording. Five (31%) were SF. Ictal localization was obtained in 4 of 32 L cases. Three of 4 (75%) were SF. Eighteen of 24 (64%) L cases without ictal localization were SF. Nine of 12 (75%) lateral resections, 7 of 12 (58%) lobectomies, and 2 of 13 (15%) mesial resections were SF. Three of 20 cases with at least 90% reduction in seizures became SD > or = 2 years postresection. No case with < 90% seizure reduction at one year showed improvement with longer follow-up.

Adolescent↗
PubMed1997

Behavioral and cognitive effects of lamotrigine.

Lamotrigine is a new antiepileptic drug that may possess unique cognitive and behavioral characteristics. Although lamotrigine can produce neurobehavioral toxicity, it is generally well tolerated. In one study directly comparing lamotrigine to placebo as add-on therapy in patients with intractable epilepsy, no objective cognitive effects were observed in a limited neuropsychological battery. Several studies have demonstrated favorable effects of lamotrigine on psychological well-being that were not explained by simple effects on seizure frequency and severity. In direct comparisons with carbamazepine and phenytoin, lamotrigine has been reported to produce positive effects on quality of life scales of patient perception. In addition, positive behavioral effects have also been observed in two blinded studies and several open trials for patients with severe mental disability and refractory epilepsy. Future studies with more extensive neuropsychological assessments are needed to delineate the differential cognitive and behavioral effects of lamotrigine in epilepsy and psychiatric disorders.

Adult↗