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Biomedical subjects

K J Meador

Publications and source records attributed to K J Meador.

At least 73 records · Page 4Linked to original sources
PubMed1996

Dementia associated with dorsal midbrain lesion.

Although the dorsal midbrain has been implicated in cognitive processes in animals, its role in humans is unclear. We report the neuropsychological and postmortem neuropathological findings of a 52-yr-old university professor who developed a profound dementia in association with a focal dorsal midbrain lesion. The patient's disorder appeared to result from a tuberculous granuloma based on the clinical course and autopsy results. Neuropsychologically, he exhibited a generalized impairment across most of the cognitive domains assessed. His deficits were not explained by impaired arousal, specific sensory or motor defects, depression, or hydrocephalus. Although there are inherent limitations to a single-case investigation, our observations are consistent with animal studies that have demonstrated that focal dorsal midbrain lesions may result in cognitive impairment. We propose that the dorsal midbrain is involved in cognitive processing via modulation of thalamocortical networks.

Arousal↗
PubMed1996

Amobarbital evaluation of neurobehavioral function prior to therapeutic occlusion of brain arteriovenous malformations: a new neuropsychological procedure.

Because untreated arteriovenous malformations (AVMs) frequently result in some form of permanent neurological complication, treatment of AVMs is aggressively pursued A relatively new treatment consists of sending micropellets into blood vessels supplying the AVM core to block blood flow and "shrink" the AVM When vessels supplying the AVM are thought to also irrigate vital portions of brain, evaluations of neurobehavioral function after injection of amobarbital into intracranial vessels (Wada testing) may be performed to prevent significant complications folIowing embolization This study details our preliminary experience with Wada testing and electroencephalography (EEG) prior to AVM embolization in seven patients Neurobehavioral functions were continuously monitored after injection of 50-75 mg of amobarbital into target cerebral vessels No change in sensorimotor, cognitive, or EEG functions were detected in any of the superselective Wada examinations Embolization was performed following all negative Wada evaluations The only irreversible complication after embolization was a superior quadrantanopia No other permanent neurobehavioral sequelae resulted from embolization These preliminary findings suggest that simultaneous Wada/EEG monitoring may be useful in predicting neurobehavioral complications prior to AVM embolization.

Journal Article↗
PubMed1996

Epilepsy, anticonvulsant drugs and cognition.

The use of AEDs in the management of epilepsy requires an ongoing risk-benefit analysis that attempts to maximize seizure control while minimizing adverse cognitive side-effects. Although the effects of other factors on cognition are generally greater than AED effects in patients with epilepsy, the cognitive effects of AEDs are of special concern because they are iatrogenically induced. Baseline evaluation of mental functioning is essential and should be repeated whenever a change in cognitive performance is suspected. The cognitive effects of the major AEDs, including phenytoin, carbamazepine and valproate, appear modest when dosages are kept within standard therapeutic ranges and polypharmacy is avoided. Violation of these guidelines increases the risk of alterations in arousal, attention, memory and psychomotor functioning. In turn, dysfunction in these areas can contribute to deficits in higher cognitive processes. Evidence suggests that these primary and secondary deficits are relatively greater for benzodiazepines, bromide and phenobarbital. Initial studies involving the newer AEDs suggest that the cognitive profile of these drugs is favourable, but further research is required to determine their relative effects to each other and to the older AEDs. For some patients, optimal seizure management may require the use of polypharmacy or AED dosages that exceed the standard therapeutic range. In such cases, the physician should remain sensitive to the increased risk of cognitive side-effects. The impact of such effects will be greatest for those whose daily functioning requires sustained attention or psychomotor speed. Although the cognitive risks of AEDs appear rather modest for most adults, questions remain regarding the impact of AEDs on patients at extremes of age. Initial studies with children and older adults suggest that the effects of the major AEDs are comparable across the developmental lifespan. However, during the formative years of a child's intellectual development, close scrutiny should be paid to the possibility that subtle attentional or arousal deficits could contribute to cumulative deficits in learning or memory. Preliminary studies involving both animals and humans suggest that the impact of AEDs might be greatest during in utero exposure; however, additional research is required to fully delineate the long-term effects of AED exposure in this earliest period of neurodevelopment.

Adolescent↗
PubMed1995

The relationship of neuropsychological functioning to quality of life in epilepsy.

OBJECTIVE: To examine the relationship of objectively assessed cognitive functioning to self-reported quality of life. DESIGN: Correlational, multiple regression, and factor analytic comparisons of a new self-report quality of life inventory with neuropsychological tests of cognition and mood. SUBJECTS: Two hundred fifty-seven patients with epilepsy. SETTING: Twenty-five epilepsy centers and neurology clinics across the United States. MEASURES: A recently developed self-report (ie, Quality of Life in Epilepsy-89 inventory) and objective tests of memory, verbal abilities, spatial functions, psychomotor and cognitive processing speed, cognitive flexibility, and mood. RESULTS: Factors that assessed mood, psychomotor speed, verbal memory, and language correlated significantly with selected scales of the Quality of Life in Epilepsy-89 inventory (P < .0001) and were predictive of overall quality of life (P < .002 to P < .0001). The mood factor showed the highest correlations (r = -.20 to r = -.73) and was the strongest predictor of quality of life in regression analyses (46.7% explained variance, P < .0001). CONCLUSIONS: Mood may be adversely affected by diminished quality of life, or perceived quality of life may be affected by mood disturbance. Quantitative quality of life assessments can be used in conjunction with formal neuropsychological testing of mood and cognition when evaluating patients with epilepsy.

Adult↗
PubMed1995

MRI hippocampal volume and neuropsychology in epilepsy surgery.

A review is provided of recent findings on relationships between neurocognitive test data and magnetic resonance imaging (MRI)-determined hippocampal volumes in nonlesional temporal lobectomy patients. The difference between the right and left hippocampal volumes is correlated with postoperative verbal memory in left temporal lobectomy patients who do not have lesional pathology. MRI hippocampal volume data are not associated with measures of executive functioning or naming. Sex differences have been found for verbal memory outcome as women have better verbal memory following left temporal lobectomy. Sex differences have also been found in the relationships between verbal and visual memory, and hippocampal volume data. The systematic combination of MRI-acquired morphological data and neuropsychological test data may further our understanding of neurocognitive function, and provide clinically useful data for counseling epilepsy surgery patients. The current data are promising with regard to prediction of memory outcome following temporal lobectomy, but they do not yet allow for prediction of specific individual patient outcomes. Rather, the currently available data support counseling patients based on the memory outcome of others with similar characteristics.

Dominance, Cerebral↗
PubMed1995

Synergistic anticholinergic and antiserotonergic effects in humans.

Animal research suggests an important interactive role for ascending cholinergic and serotonergic systems in modulation of cerebral function. Employing a randomized, double-blind, crossover design, 11 healthy young adults were tested in each of four conditions: (1) placebo, (2) fenfluramine (a serotonin depleting agent), (3) scopolamine (a muscarinic antagonist), and (4) fenfluramine and scopolamine. P3 latency was slowed by the dual drug treatment to an extent greater than the sum of individual drug effects. EEG mean frequency was decreased by behavioral activation, and this decrease was reversed by the combined drug treatment but not by single drugs. In contrast, verbal memory, EEG alpha power, and P3 amplitude were significantly affected only by scopolamine. No drug effects were found for the N1 and P2 potentials. The results provide the first demonstration of combined anticholinergic and antiserotonergic effects in humans, and offer partial support to the concept of an interactive role of cholinergic and serotonergic systems in cerebral mechanisms.

Adult↗
PubMed1995

Wada memory asymmetries predict verbal memory decline after anterior temporal lobectomy.

We examined Wada memory and neuropsychological memory function in 34 nonlesional patients who underwent anterior temporal lobectomy (ATL) and who were seizure free at 1-year follow-up. Patients who displayed a decline on verbal memory measures that exceeded 1 SD after left ATL had significantly smaller left/right Wada memory asymmetries than left ATL patients without a significant verbal memory decline. When Wada memory asymmetries were used to predict verbal memory decline after left ATL in individual patients, similar statistically significant effects were present. No significant relationship between Wada memory and postoperative memory was present in right ATL patients, and postoperative memory function was not related to Wada memory performance after either left hemisphere or right hemisphere injection alone. We conclude that Wada memory asymmetries provide one measure of the risk to material-specific decline in verbal memory after left ATL.

Analysis of Variance↗
PubMed1995

Comparative cognitive effects of phenobarbital, phenytoin, and valproate in healthy adults.

The relative effects of antiepileptic drugs (AEDs) on cognition are controversial. We compared the cognitive effects of phenobarbital, phenytoin, and valproate in 59 healthy adults using a randomized, double-blind, incomplete-block, crossover design. Cognitive assessments were conducted at baseline, after 1 month on each drug (two AEDs per subject), and at two repeat baselines 11 weeks after each AED treatment. The neuropsychological battery included 12 tests, yielding 22 variables: Choice Reaction Time, P3 Event-Related Potential, Finger Tapping, Lafayette Grooved Pegboard, Selective Reminding Test, Paragraph Memory, Complex Figures, Symbol Digit Modalities Test, Stroop Test, Visual Serial Addition Test, Hopkins Symptom Checklist, and Profile of Mood States. More than one-half of the variables exhibited AED effects when compared with nondrug baselines, and all three AEDs produced some untoward effects. Differential AED effects on cognition were present for approximately one-third of the variables. Phenobarbital produced the worst performance; there was no clinically significant difference between phenytoin and valproate.

Adult↗
PubMed1994

Stimulus timing effects on Wada memory testing.

OBJECTIVE: To determine the effects of presenting Wada memory stimuli at different times after intracarotid amobarbital injection on Wada memory asymmetries. DESIGN: Wada memory asymmetries from three timing series were related to the laterality of eventual temporal lobectomy. SETTING: Academic institution epilepsy surgery program. PATIENTS: Forty-three patients with complex partial seizures who later underwent anterior temporal lobectomy (left temporal lobectomy, 24 patients; right temporal lobectomy, 19 patients). No patient included had abnormalities on magnetic resonance imaging scans to suggest a lesion other than gliosis. RESULTS: Memory performance for objects whose presentation began approximately 45 seconds after amobarbital administration differentiated laterality of seizure onset. Memory for items presented later and after partial return of language (on average 3 minutes 40 seconds postinjection) also differed as a function of ipsilateral vs contralateral injection, but at a lower level of statistical significance. Memory for items presented last during the procedure (on average 6 minutes postinjection) discriminated seizure groups at a still lower level of statistical significance. When used to predict lateralized temporal lobe impairment in individual patients, early object memory performance was significantly better than memory performance employing either middle (56%) or late (43%) stimulus presentation timings. CONCLUSION: The results of early object memory testing are superior to those obtained from stimulus presentation later in the procedure in documenting temporal lobe dysfunction associated with a lateralized seizure onset.

Adult↗
PubMed1994

Reliability of an ambulatory electromyographic activity device for musculoskeletal pain disorders.

A number of investigators in recent years have called for the development of devices that can monitor surface EMG levels in individuals' normal environments for use with patients who suffer from disorders in which the etiology or maintenance of the pathology is presumed to be due at least in part to musculoskeletal dysfunction, such as low back pain, phantom limb pain and tension headache. This study examined the test-retest reliability of just such a device. Twenty-six healthy controls wore a lightweight (24 ounce) device which measured bilateral upper trapezius EMG, as well as peak and integral motion, for 5 consecutive days for up to 18 h each day. ANOVAs on the four measures revealed no difference between any of the four measures over the 5 days. Intra-class correlation coefficients for the two EMG variables across 5 days were both significant with alpha levels set at 0.01. The two EMG measures were highly correlated (r = 0.77); the two motion measures were also highly correlated (r = 0.60), but at a lower magnitude than EMG values; the relationship between EMG and motion was significant, but the magnitude of the between EMG motion correlations (0.26 and 0.35) were lower than the within EMG or motion ones. It was concluded that the test-retest reliability of the ambulatory monitoring device is within acceptable limits. Implications for the use of the device with musculoskeletal pain disorders--particularly headache--are discussed.

Adult↗
PubMed1994

Do dichotic word listening asymmetries predict side of temporal lobe seizure onset?

Dichotic word listening asymmetries are thought to be useful in predicting side of temporal lobe dysfunction. However, little direct evidence exists to support this assumption in practice, especially in patients with subtle epileptogenic lesions. To determine if word listening ear asymmetries are valid predictors of side of temporal lobe seizure onset, we examined the preoperative dichotic word listening performance of 80 patients with either left (N = 41) or right (N = 39) temporal lobe (TL) seizure foci. On a group level, patients showed a statistically significant 'lesion effect' as evidenced by a relative deficit in the ear contralateral to the side of lesion. Prediction of side of seizure focus in individual cases, however, was poor: depending upon the criteria used, 61% to 80% of epileptics with unilateral temporal lobe foci did not show the expected contralateral ear deficit. Results suggest that caution be exercised when inferring side of temporal lobe seizure focus through dichotic word listening asymmetries in individual temporal lobe epilepsy cases.

Adult↗
PubMed1994

Cognitive side effects of antiepileptic drugs.

All of the established antiepileptic drugs (AEDs) can produce cognitive side effects, which are increased with polypharmacy and with increasing dosage and anticonvulsant blood levels. However, cognitive side effects are usually modest for AED monotherapy with anticonvulsant blood levels within the standard therapeutic ranges. Further, these effects are offset in part by reduced seizure activity. Controversy exists regarding possible differential cognitive effects of AEDs. A large portion of the literature examining the comparative cognitive effects of AEDs is limited by inadequate study designs. When these design flaws are considered, there is no convincing evidence of clinically significant differences in cognitive side effects of AEDs except possibly for bromide, phenobarbital and benzodiazepines. The role of cognitive side effects should be kept in proper perspective when choosing AED therapy. The cognitive side effects of anticonvulsant drugs may be overt but many times are rather subtle. It is important though to be able to recognize these effects and to put them into perspective as to how they affect our patients.

Anticonvulsants↗
PubMed1994

Wada memory performance predicts seizure outcome following anterior temporal lobectomy.

We examined the ability of Wada memory testing to predict seizure outcome 1 year following anterior temporal lobectomy. Asymmetry scores for Wada memory performance, using amobarbital doses of 125 mg or less, were calculated for 55 patients under the age of 45 years who had no radiologic evidence of structural lesions other than gliosis. Wada memory asymmetries were significantly greater (p < 0.02) in patients who were seizure free compared with those who continued to experience seizures. Furthermore, patients with Wada memory score asymmetries of at least three objects (maximum = 8) were more likely to be seizure free compared with patients with Wada memory asymmetries less than three (p < 0.01). Of the 36 patients who had Wada memory score asymmetries of at least three objects, 32 (89%) were seizure free. In contrast, of the 19 patients whose Wada memory score asymmetries were less than three, only 12 (63%) were seizure free. These data suggest that Wada memory performance is related to seizure outcome following anterior temporal lobectomy.

Adult↗
PubMed1994

Effects of temporal lobectomy on generative fluency and other language functions.

We investigated the acute effects of unilateral temporal lobectomy on multiple language measures and standardized generative word fluency tasks, as well as longer term effects measured 1 year following surgery. All patients were left cerebral dominant for language functioning as determined by Wada testing. Results indicate consistent acute language decline for left but not right temporal lobectomy patients. In contrast, verbal generative fluency decreased independent of lesion laterality, suggesting diffuse acute lesion effects on certain tasks mediated primarily by the left hemisphere. When examining language performance in an independent patient group at their 1-year follow-up assessment, no negative surgery effects were present on any language measure. Further, significant improvement over baseline performance for word fluency was present 1 year following surgery. In the acute assessment of cognition following temporal lobectomy, the relative sensitivity of neuropsychological measures to acute cerebral lesions should be considered.

Journal Article↗