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Biomedical subjects

B S Oken

Publications and source records attributed to B S Oken.

29 records · Page 2Linked to original sources
PubMed1991

Test-retest reliability in EEG frequency analysis.

This study was performed to gain a better understanding of EEG frequency analysis test-retest reliability in normal healthy adults, and to evaluate factors which could influence the measured inter-record differences. Nineteen subjects underwent serial EEG recordings at 5 min and 12-16 week intervals. Records were visually edited using a standardized protocol, and FFT frequency analysis performed on segments of 60, 40, or 20 sec total length. Correlation coefficients for broad band features averaged 0.92 over the 5 min retest interval and 0.84 over the 12-16 week interval. There was essentially no difference between correlation coefficients of absolute and relative power features. Coefficients based on 60 sec records were marginally higher than those of 40 or 20 sec records. On the other hand, test-retest percent differences were typically lower for relative as opposed to absolute power features, and 60 sec records showed consistently lower percent differences than did 40 or particularly 20 sec records. Peak alpha frequency and mean frequency were the most stable EEG features at either interval. Montage had significant effects on test-retest differences at the 12-16 week interval. A significant association between intra-record and inter-record variability could not be demonstrated.

Brain↗
PubMed1989

Computerized EEG frequency analysis: sensitivity and specificity in patients with focal lesions.

We performed computerized EEG frequency analysis (C-EEGFA) in 69 controls and 20 patients with focal brain lesions and focally abnormal conventional EEGs. Individual channel EEG frequency analysis variables that were helpful in differentiating the 2 groups were absolute delta and theta band power, relative delta, theta, and alpha band powers, and median-power frequency. High-frequency beta band power (20 to 32 Hz) was not useful. Changes in EEG with age were seen only after age 50 and generally consisted of an increase in anterior alpha power, with no significant increase in slowing. Correlations of C-EEGFA variables with posterior alpha power were more significant than correlations with age. Calculating normative C-EEGFA data for 5 subsets of controls, each with a different amount of posterior alpha power, increased the sensitivity of the EEG frequency analysis test without altering the specificity. Even with this correction 2 of 20 patients with focal lesions and focally abnormal conventional EEGs had normal C-EEGFA studies. If these obvious focal lesions produced normal results, more subtle diseases might not be detected. A significant clinical utility of C-EEGFA remains to be proven.

Adult↗
PubMed1988

Short-term variability in EEG frequency analysis.

Knowledge of short-term EEG variability in computerized analysis is important before interpreting spectral EEGs or assessing changes that may be due to inherent variability and not necessarily related to a task (e.g., listening to a story), therapy or changes in underlying disease. Eighty to 120 sec of 14-channel, edited, bipolar EEG were recorded in normal subjects and analyzed using an FFT. Absolute and relative power in 5 standard frequency bands, and median and peak power frequencies were obtained for each 4 sec epoch, and the mean and standard deviation calculated for each parameter. The average variation of the mean power, absolute and relative, in the frequency bands was less than 10% although some parameters varied by up to 50% in an individual subject. Median and peak power had the least variability, about 3%. Changes in total power correlated positively with relative alpha power, but negatively or not at all with the other relative power measures. This suggests that interpretation of relative measures of delta, theta and beta in individual spectra may be dependent on total power or absolute alpha power. In addition, mathematical transformations were necessary to normalize the epoch data, suggesting that the mean and standard deviation of data from a series of epochs may not have maximal value unless a transformation is used. These results also indicate that caution is needed in interpreting changes in EEG frequency analysis data that are of the same magnitude as spontaneous EEG variability.

Adolescent↗
PubMed1987

Normal temporal variability of the P100.

Determination of clinically significant temporal changes in P100 latency requires knowledge of the degree of normal intraindividual variability. Checkerboard visual evoked potentials using 3 check sizes (17', 35' and 70') were performed serially on 20 healthy volunteers. Each subject was tested at least twice an average of 6 months apart. The P100 latency was measured at Oz with a forehead reference (Pz, O1 and O2 channels were also recorded). The overall average P100 latency change between studies for all check sizes and both eyes was 2.9 msec. However, the maximum absolute latency change was 11 msec. There was no significant difference between the average latency change for the 3 check sizes. The P100 interocular difference changed a mean of 2.5 msec (maximum 9 msec). Amplitude was more variable, with a mean change of about 1.5 microV or 25% (maximum was a 60% decrease in amplitude). A P100 latency change of up to at least 11 msec needs to be acknowledged as normal when assessing the clinical significance of changes in P100 latencies in patients. Also, P100 latency changes greater than 11 or 12 msec are very suggestive of an abnormality in the visual pathway.

Adult↗
PubMed1986

Filtering and aliasing of muscle activity in EEG frequency analysis.

Muscle artifact contains activity at frequencies more than half the usual data acquisition rates for spectral EEG that may contribute power at conventional EEG frequencies by aliasing. In spectral analysis work, excessive EMG activity is usually rejected by visual inspection, but significant amounts may still remain and special steep low-pass filters are usually used to inhibit aliasing. A 24 dB/octave variable filter was used in various combinations with conventional EEG amplifier filters to study aliasing of EMG activity. Aliased EMG activity entered as noise across all frequencies. With the usual amount of EMG activity that is present in EEG undergoing frequency analysis, a 6 dB/octave 35 Hz low-pass filter is equivalent to the 24 dB/octave 35 Hz low-pass filter in preventing aliasing using a sampling rate at least 128 Hz.

Electroencephalography↗
PubMedDate not supplied

Methylphenidate increases the motor effects of L-Dopa in Parkinson's disease: a pilot study.

We determined whether methylphenidate, a dopamine transporter blocker, modifies motor, cognitive, or affective responses to L-Dopa in Parkinson's disease (PD). Five patients who reported benefit from L-Dopa/carbidopa and motor fluctuations were admitted and withdrawn from their usual antiparkinsonian medications. On 3 consecutive days in a randomized double-blinded fashion, they took 0.2 mg/kg oral methylphenidate or placebo followed 30 minutes later by a 1-hour intravenous L-Dopa (2 mg/kg per h) or placebo infusion. Vital signs, tapping, walking, dyskinesias, mood, anxiety, concentration, and arousal were monitored every 30 minutes. Cognitive testing was performed before and following the infusion. Methylphenidate combined with L-Dopa led to greater peak right-hand tapping speed than either alone. Dyskinesia severity increased most when methylphenidate and L-Dopa were co-administered. There were no differences between conditions on the Stroop test, digit ordering, simple reaction time, or covert orienting of attention validity effect. Methylphenidate alone led to improvement in choice reaction time. Change in self-assessed analogue ratings of mood, anxiety, arousal, or concentration did not differ between conditions. Methylphenidate increased the motor effects of L-Dopa with minimal effects on cognitive or affective functions, suggesting a physiologic role for the dopamine transporter in patients with PD with motor fluctuations.

Aged↗
PubMedDate not supplied

Age-related differences in visual search task performance: relative stability of parallel but not serial search.

The hypothesis that visual search tasks requiring effortful, serial processing are more sensitive to aging than those requiring relatively automatic, parallel processing was tested in 96 healthy adults who performed parallel and serial visual search tasks with fixed presentation times. Reaction times and error rates increased with age in both tasks, but there was no difference between young and old in the effect of increasing numbers of distractors on reaction times. However, the older subjects made significantly more errors with increasing numbers of distractors in the serial search task. Older subjects have disproportionately more difficulty performing serial compared to parallel visual search tasks than do younger subjects. Additionally, this difference is not caused solely by cautious response strategies in the elders.

Adult↗
PubMedDate not supplied

Early noncognitive change in Alzheimer's disease and healthy aging.

Recent studies in Alzheimer's disease have focused on behavioral disturbances in the more advanced stages of the illness rather than behavioral and personality changes occurring early in the disease course. We present a new instrument, the Oregon Noncognitive Inventory for Dementia (ONID), that was developed specifically for patients in the early stages of dementia, to identify subtle behavioral alterations that may precede the more severe cognitive changes of Alzheimer's disease. Mildly demented Alzheimer's patients were compared with age-matched healthy subjects on the ONID. Caregivers of these patients reported significantly more of the behaviors addressed by the ONID than did relatives of the healthy elderly. The results indicate that changes in behavior and personality can be reliably reported by family caregivers of patients with mild dementia. Future clinical applications of the ONID might include measuring change in drug trials, longitudinal studies of the progression of change, and differentiating Alzheimer's disease from other dementias based on a characteristics pattern of change.

Activities of Daily Living↗