PubMed Health⌕ Search

Biomedical subjects

H J Michalewski

Publications and source records attributed to H J Michalewski.

15 recordsLinked to original sources
PubMed1995

Readiness to respond in a target detection task: pre- and post-stimulus event-related potentials in normal subjects.

Brain potentials were recorded from 12 normal subjects engaged in an auditory target detection task (target stimulus probability of 0.2, stimulus rate of 1 every 2 sec) when instructions were (1) to press a response button with the thumb of the dominant hand to each target or (2) to keep a mental count of each target. A pre-stimulus slow negative potential was identified before every stimulus except non-targets immediately after targets. The amplitude of the pre-stimulus negativity was significantly affected by task instructions and was up to 4 times larger during the button press than the mental count condition. In contrast, the amplitudes and latencies of the event-related components (N100, P200, N200 and P300), when slow potentials were removed by filtering, were not different as a function of press or count instructions. The immediately preceding stimulus sequence affected both the amplitude and onset latency of the pre-stimulus negativity; both measures increased as the number of preceding non-targets increased. The amplitude of the pre-stimulus negative shift to targets also increased significantly as RT speed decreased. The major portion of the pre-stimulus negative potential is considered a readiness potential (RP) reflecting preparations to make a motor response. The amplitude of the RP during the target detection task did not significantly lateralize in contrast to the RP accompanying self-paced movements.

Adult↗
PubMed1989

Brain potentials in a memory-scanning task. III. Potentials to the items being memorized.

Cerebral potentials evoked by items presented for memorization in a memory-scanning task were recorded from subjects ranging in age from 18 to 86 years old. Subjects were divided into younger (average age = 29 years) and older groups (average age = 66 years). Both verbal (digits) and non-verbal (musical notes) stimuli were used. Digits were presented in the auditory as well as the visual modality, and notes were presented acoustically. Potentials are described in terms of their scalp distribution, latency, and amplitude and are compared between the young and old subjects. Potentials evoked by the memorized items consisted of a positive (P50-90), negative (N100-150), positive (P185-225) sequence in the first 250 msec following stimulus onset. A sustained potential shift then followed whose amplitude differed with the items being memorized. The shift was positive in the parietal region being largest (5 microV) with verbal items presented visually and slightly smaller (3 microV) with non-verbal auditory stimuli (the notes); in contrast, verbal auditory digits were not associated with a detectable sustained parietal potential shift. In the frontal recordings there was a sustained potential shift accompanying all stimulus types, which was more negative in the young subjects. The amplitude of these sustained potential shifts differed as a function of the position of the item in the memorized set. These results provide electrophysiological evidence of brain activity during memorization that varies with the items being processed as well as differing between young and old subjects.

Acoustic Stimulation↗
PubMed1989

Brain potentials in a memory-scanning task. I. Modality and task effects on potentials to the probes.

Event-related potentials were measured in normal young subjects during a memory-scanning paradigm modified from one proposed by Sternberg. The stimuli used were verbal (digits) and non-verbal (musical notes) with the verbal stimuli and notes presented acoustically and the verbal stimuli also presented visually. In this paradigm each set of stimuli was presented for memorization, and then, after a 2 sec interval, a probe item appeared and was identified by the subject as belonging or not belonging to the memorized set. Memorized set sizes of 1, 3 and 5 items were studied. The potentials are described in terms of scalp distribution, latency and amplitude, and are compared with behavioral descriptors of performance (accuracy and reaction time). These potentials are also compared with those evoked by an auditory target-detection task ('odd-ball' paradigm) in the same subject at the same session. The potentials evoked by the probe stimuli consisted of a positive (P50-90), negative (N100-150), positive (P185-225) sequence in the first 250 msec, followed by a later, long-lasting (approximately 700 msec) positive component (labeled P3). This positivity consisted of an earlier component (latency of approximately 350-400 msec) with a frontal distribution, followed by a larger and later parietal component. The amplitude of the frontal component and the latency of the parietal component varied with the number of items in the memorized set differently from behavioral reaction times. Stimulus modality also affected both the amplitude and latency of the sustained parietal positive potential. Memory processes associated with the P3 complex in the 'odd-ball' task and the long-lasting positivity in the memory-scanning task are discussed.

Adult↗
PubMed1989

Brain potentials in a memory-scanning task. II. Effects of aging on potentials to the probes.

Brain potentials accompanying the classification of probe items as being members of a previously presented list were recorded from subjects ranging in age from 18 to 86 years old. A group of older subjects (average age = 66 years) was compared to a younger group (average age = 29 years). The items tested were verbal (digits) and non-verbal (musical notes). Digits were presented in the auditory and visual modalities, and notes were presented acoustically. Reaction times (RTs) and performance accuracy were computed. Potentials are described in terms of scalp distribution, latency and amplitude as a function of the type of stimulus (verbal/non-verbal, auditory/visual) and age group (younger/older). Evoked potentials to target notes in an auditory target-detection ('odd-ball') task were also recorded for comparison with the memory tasks. Potentials evoked by probes consisted of a sequence of sensory components in the first 250 msec followed by a cognitive component that was positive in polarity and sustained in duration (approximately 700 msec labeled P3), consisting of an earlier frontal component, P3a (mean latency: younger = 385 msec, older = 406 msec), and a large (15 microV) and later parietal constituent, P3b (mean latency: younger = 574 msec, older = 630 msec). The frontal derivation of the younger subjects showed a sustained negative bias of the wave forms in the latency range of 200-500 msec (P2 to P3) compared to the older subjects. Reaction times were longer in older subjects than in younger subjects for all stimulus types and set sizes. For the potentials evoked by the probes the younger group had consistently larger late parietal components (P3b) than the older group, whereas the late frontal potentials (P3a) were larger for the older than younger subjects. Except for visual stimuli, the latencies of the parietal sustained potentials were not influenced by subject age in contrast to the uniform changes in RT for all stimulus types. Significant amplitude and latency effects on the parietal sustained potentials accompanied the different stimulus types and memorized-set sizes which were similar for the two age groups. These results suggest that the effects of aging on short-term memory are primarily on response selection, as evidenced by RT slowing with aging, and not on memory-scanning processes as evidenced by the similarity of the latency measures of the accompanying brain potentials between the two age groups.

Adult↗
PubMed1988

Brain potentials during mental distance judgments.

Visual event-related potentials were recorded from a group of 10 normal subjects while they judged the proximity of two letters of the alphabet. Subjects viewed singly the letters A, D, G, L, N, T, W and Z and indicated by button press whether the letter displayed occurred before or after the comparison letter M. Reaction times to close letters (L and N) were longer than ordinally more distant letters (A, D, G, T, W, Z). A late parietally positive potential of approximately 475 ms covaried in latency and amplitude with these judgments. Late potentials were delayed in latency and reduced in amplitude to close letter (L and N) judgments compared to the other letters. The results suggest that mental processes, such as alphabetic distance judgments, may be usefully studied by examining their associated event-related potentials.

Adult↗
PubMed1986

Latency variability and temporal interrelationships of the auditory event-related potentials (N1, P2, N2, and P3) in normal subjects.

Peak latency variation and the temporal interrelationships of the auditory event-related potential were investigated in 12 normal adults (ages 28-42). Measures of variation were based on both conventional averages and single trials. Estimates of N1, P2, N2 and P3 latencies were made on a trial-by-trial basis to target stimuli recorded from Fz, Cz and Pz scalp locations. Results showed that single-trial latency variability of the auditory ERP differed both among the various components and between subjects. Larger standard deviations were measured for the later N2 and P3 components than the earlier N1 and P2 components. Regression analyses between various component latencies indicated a strong covarying relationship between N2 and P3, with N2 accounting for up to 61% of the variance of P3 latency at Pz. Earlier N1 and P2 components added little to the overall prediction of either P3 or N2. For the other components, P2 accounted for 9-16% of the variance of N2, while N1 accounted for approximately 1% of the variance of N2; N1 accounted for 8-10% of the latency variation of P2. The correlations between single-trial peak latencies and RTs were positive but of low magnitude. The highest correlations between peak latency and RT were found for N2 (r = 0.33) and P3 (r = 0.24). The low correlations between the single-trial latencies of N1 and P3 suggest that the processes reflected by these components are independent and support a distinction between the earlier and the later components of the ERP. The close temporal coupling between N2 and P3 suggests that N2 may reflect cognitive properties in common to P3 in stimulus evaluation processes.

Adult↗
PubMed1982

A comparison of the emitted late positive potential in older and young adults.

An emitted potential paradigm was used to investigate P3 scalp potentials in a group of older individuals (M = 66.8 years) and a group of younger persons (M = 22.0 years). Since no physical stimulus is necessary to elicit an emitted potential, an age comparison of P3 can be made which does not depend on normal sensory transmission channels. Both traditional and latency corrected averages to missing auditory clicks were analyzed from electrodes placed over midline frontal, central, and parietal locations. Results indicated that while the scalp distribution of emitted potentials was similar for both age groups, amplitudes at Pz and Cz were significantly smaller in the older group. Latency corrected potentials indicated similar trends but did not reach significant levels. No group differences were seen for N2 or P3 latencies for either traditional or corrected averages. The findings support age differences in the amplitudes of the P3 component and suggest that when P3 is not synchronized with a sensory event, latencies in this component may not be sensitive to age differences.

Adult↗
PubMed1981

Age and sex differences in the human auditory brainstem response.

Age and sex differences in the brainstem auditory evoked response (BAER) were investigated in older (60 to 79 yrs), middle-aged (40 to 59 years), and young (20 to 39 yrs) individuals. Within each age group the number of males (N = 10) and females (N = 10) were divided equally. Scalp potentials were recorded from the vertex to clicks presented at 60, 70, and 80 dB(SL) for stimulus rates of 5, 10, and 15 clicks/sec. Results indicated that older adults had longer latencies at Wave III than either middle-aged or young adults. Age effects were also found for Waves I, II, and IV but were restricted to the lowest intensity and were more evident in older males than females. Significant sex effects showed that the females in each group had shorter Wave IV and V latencies than males. The results suggest that age affects neural propagation at the level of the olivary complex (Wave III) and that BAER latencies are also influenced by the sex of the individual.

Adult↗
PubMed1980

Sex differences in the amplitudes and latencies of the human auditory brain stem potential.

Sex differences in the amplitudes and latencies of the auditory brain stem potential (BAEP) were investigated using 3 levels of intensity and 3 stimulus presentation rates. The females displayed consistently larger BAEPs for waves IV, V, VI, VII than the males. The only latency differences which reached significance over all the intensities and rates occurred for wave V. The females showed significantly shorter wave V latencies than the males. Since hearing losses and individually determined click thresholds were comparable between the two groups tested, the exact sources of the uneven distribution of amplitude and latency effects are in question. Differences in the relative distances of the anatomical generators are considered in accounting for the sex differences. Because the precise origin of the sex differences cannot be stated with certainty at this time, attempts to develop normative data for the BAEP should consider the possible influences of sex differences.

Adult↗
PubMed1980

Auditory averaged evoked potentials and aging: factors of stimulus, task and topography.

The averaged evoked potential to brief tones was compared for 10 young and 10 elderly female subjects. The amplitudes of the sensory components (P1, N1 and P2) were not affected by an infrequent change in pitch of the tones or instructing subjects to count or ignore them; but overall the elderly had a larger P1 and smaller P2 amplitude and a difference in the scalp distribution of P2. Repetition of the tones produced a decrement in these sensory components and a differential one for young and old subjects A slow potential complex consisting of components N2, P3 and SW appeared to changes in tone pitch and became more pronounced when attention was directed to the tones. Overall smaller SPs for oder subjects were interpreted as evidence for a change with age in the cortical representation of the orienting response. Topographical analysis of SPs indicated diminished activity in frontal (Fz) electrodes for elderly persons, suggestive of an enhanced aging process in the frontal cortices.

Adult↗
PubMed1980

Age differences in the contingent negative variation (CNV): reduced frontal activity in the elderly.

The effects of distraction on the contingent negative variation (CNV) were investigated in a group of 11 elderly (mean = 72.2 years) and a group of 12 young (mean = 23.3 years) subjects. Scalp electrical activity was recorded from midline sites at frontal, central, and parietal locations. Three experimental conditions included Recall, No Recall, and Control situations. In the Recall, or distraction condition, spoken consonant-vowel-consonant (CVC) letters were presented concurrently with the CNV signal interval and were recalled by the subjects after each trial. The No Recall condition was similar to the Recall task except that subjects were not required to repeat the CVSs. The Control condition presented a standard S1 - S2 CNV situation without CVCs. Amplitudes of the CNV, reaction times (RTs), and heart rate (HR) served as indices of distraction. The effects of distraction for both age groups indicated reduced CNVs, lengthened RTs, and elevated HRs. However, a significant age by electrode interaction revealed that while CNV amplitudes at central and parietal sites were comparable between age groups, amplitudes at the frontal placement were consistently reduced in the elderly compared to the young in all conditions. The finding of diminished frontal activity, as measured by the CNV, suggests a process of selective cortical aging and possible cellular loss which may be linked to performance deficits.

Adult↗
PubMed1977

The contingent negative variation (CNV) and speech production: slow potentials and the area of Broca.

The lateral distribution of the CNV was investigated during conditions that required normal male and female subjects to vocalize simple English words in a CNV paradigm. In addition to a non-verbal or comparison condition (Tone-Clicks/Button Press), two word conditions presented stimulus words in either S1 or S2 positions (Word-Tone/Speak; Tone-Word/Speak) and a third condition required a one-word association to the stimulus words (Word-Tone/Speak Association). Monopolar scalp activity was collected from sites that included a location approximating Broca's speech area on the left hemisphere, a homologous comparison site on the right hemisphere, frontal sites (F3, F4) and the vertex (Cz). Although several subjects showed some asymmetrical activity in some of the word conditions, amplitude measures based on CNV averages indicated no consistent lateralization effects over the left hemisphere prior to word vocalizaiton. Negative pretrial shifting was suspected in those conditions in which words appeared as S1 signals.

Acoustic Stimulation↗
PubMedDate not supplied

Latency variability of the components of auditory event-related potentials to infrequent stimuli in aging, Alzheimer-type dementia, and depression.

Auditory event-related potentials (ERPs) were investigated in 15 demented (12 presumed Alzheimer's, 3 cerebrovascular), 8 depressed, and 15 normal older, and 12 normal young, subjects. Both latencies from conventional averages and latency variability measures from single trials were derived for the N100, P200, N200, and P300 components of the ERP recorded from Fz, Cz and Pz scalp placements in a task requiring detection of an infrequent target tone among a series of frequent non-target tones. The P300 component most consistently separated the groups. Demented subjects had longer P300 latencies and greater P300 latency variability than both control groups and the depressed group. Age differences were observed for P300 latency, but not for P300 latency variability. Amplitudes were not significantly different among the groups. Reaction times (RTs) to the targets were longest for the demented subjects and shortest for the young controls, with the depressed and normal older control groups falling in between. Correlations between RT and P300 latency from single trials did not differentiate the groups. Using regression analysis to evaluate the deviation of P300 latency and latency variability for the patients from the predicted values for normal controls, no misclassifications of depressed patients occurred, but only 27% of the demented individuals were correctly classified using P300 variability, and 13% using P300 latency. These findings indicate that ERP measures using the 'oddball' target detection paradigm were useful in describing group differences, but were not sufficiently sensitive to be used in differentiating demented persons on an individual basis for clinical diagnosis.

Adult↗