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PubMed1979

Cortical slow negative waves following non-paired stimuli: effects of modality, intensity and rate of stimulation.

Using a simple stimulus counting task, negative after-waves following single (unpaired) stimuli were investigated under a variety of stimulus conditions. Responses were obtained to tones at 3 intensities, to light flashes at 3 intensities, and to tones at 3 rates of presentation. The acoustic stimuli led to a negative after-wave that peaked at frontal sites around 500 or 600 msec, and then trailed off to a more central scalp representation. This negative after-wave was increased in amplitude by slowing the rate of stimulus presentation. In comparison, no appreciable or sustained after-wave was elicited by visual stimuli. No significant effects in the negative after-wave were associated with intensity, either for visual or for acoustic stimuli. When analyzed by Principal Components Analysis, the negative after-waves were shown to comprise in all cases two underlying factors, although the factors contributed less to the total wave form for visual stimuli than for acoustic stimuli. Two interpretations for the negative after-wave were contrasted, one considering it to be an integral feature of the auditory evoked potential. A second interpretation, more compatible with the data obtained here, links the negative after-wave with non-specific activation processes.

Acoustic Stimulation↗
PubMed1979

Event-related potentials recorded from young and old adults during a memory retrieval task.

Six healthy old and 8 healthy young subjects each received a series of trials in a memory retrieval task devised by Sternberg (1966). On each trials, the subject received a memory set of 1-4 digits and was then shown a test digit. The subject's task was to press one of two response buttons indicating whether the test digit was a member of the memory set for that trial. Response time (RT) was found to be an increasing, linear function of the number of items held in memory. The slope of the RT function was a composite measure of the time necessary to process each additional item in memory while the intercept was a measure of stimulus encoding and response processes that do not depend on memory set size (see Sternberg 1966, 1969, 1975). We found that the latency of P3 to the test stimulus also increased with increases in memory set size, although the slope of the P3 was less than that for RT. We have suggested that the intercept of the P3 slope reflects the time it takes to encode the test stimulus before the evaluation of the stimulus starts, while the slope reflects the amount of time per digit needed to evaluate the set. We have suggested that the difference between RT and P3 slopes represents the additional time per digit which the subjects waits before making a response, due to low confidence occurring with more difficult task conditions (i.e., when set size = 4). We further suggest that the intercept of the RT-P3 latency slope is a reflection of pure response processes. Time estimates of these processes are made for young and old subjects.

Adult↗
PubMed1979

Observations on the M-wave and the CNV in the squirrel monkey.

A typical CNV paradigm, with food as reward, evokes in the squirrel monkey's post-arcuate and post-central cortices both M-waves in response to the cues and what appears to be a CNV in the interstimulus interval. Both wave forms appear to be generated locally in cortex and to be more closely related temporally to the cues than to the animal's behavioral response. The CNV, like the M-wave, appears to reflect the animal's level of interest in obtaining the reward. It is smaller when the animal misses the cues than when he responds correctly. It decreases as food pellets are consumed. It varies with the level of interest of the animal in a particular type of food pellet, as judged from the animal's behavior. At some recording sites in some animals it appears to reflect both interest in the reward and interest in manipulating the environment to obtain the reward. It can be maintained for at least 2 sec, but differs from the human CNV in that, with the paradigm used, it is not well resolved by the imperative cue. Averaging evoked activity with the animal's motor response as reference point reveals another negative wave form which just precedes the motor response.

Acoustic Stimulation↗
PubMed1979

Cerebral potentials preceding unilateral and simultaneous bilateral finger movements.

Cerebral potentials preceding voluntary bilateral simultaneous finger movements were investigated in 19 right-handed young adult subjects, and were compared with unilateral right-sided finger m n the same experiment. With bilateral movements, the Bereitschaftspotential (BP) was not symmetrical or larger over the dominant hemisphere, but surprisingly, it was larger over the minor hemisphere. The BP averaged -3.66 microV (S.D. 1.96) over the left precentral region and -4.82 microV (S.D. 3.73) over the right precentral region in this condition. The difference was significant at 2P less than 0.01. This difference was pronounced in precentral leads but very small and almost missing in parietal leads. The pre-motion positivity (PMP) was well developed and even larger with bilateral than with unilateral (right-sides) movements. At the vertex it averaged +1.33 microV (S.D.4.16) with bilateral movements and only +0.15 microV (S.D. 1.42) with right-sided unilateral movements (2P less than 0.05). With bilateral movements the PMP could be observed in any record, but with unilateral movements it was missing at the left precentral lead, in accordance with previous publications (Deecke et al. 1969, 1976). The motor potential (MP), measured in a bipolar record from left and right precentral leads, was larger with unilateral (-1.25 microV, S.D. 1.33) than with bilateral movements (-0.36 microV, S.D. 0.92). Onset time differences of the BP preceding unilateral and bilateral movements were very small. However, there was a tendency towards earlier onset with unilateral than with bilateral movements (1031 msec, S.D. 358, as compared with 951 msec, S.D. 305). The averaged EMG revealed differences in movement onset. Muscular contraction tended to be earlier in the right than in the left m. flexor indicis in our right-handed subjects, on the average by 16 msec (S.D. 15). With unilateral right-sided movements, the left m. flexor indicis was not silent but showed an abortive mirror activity in the EMG, without visible movement. This activity occurred on the average 50 msec (S.D. 39) later on the non-moving side.

Adult↗
PubMed1980

Evolution of negative and positive SP shifts in cats learning RT tasks.

Cortical slow potential (SP) shifts were recorded in freely moving cats while they learned reaction time tasks differing in the duration of the inter-stimulus interval (ISI). ISI durations were either 6 or 4 sec in experiment I; in experiment II, a reaction time paradigm with a 1 sec ISI was compared to a time estimation task. SP shifts of opposite polarity development throughout the experiments. It seems that: (1) positive SP shifts reflect motor processes and mechanisms of proprioceptive feedback related to the cat's preparatory movements for pressing the lever; (2) negative-going shifts peaking at the end of the ISI reflect temporal information processing related to ISI duration. Analogies with potentials found in man and animals in similar paradigms are discussed.

Animals↗
PubMed1980

Biofeedback of slow cortical potentials. I.

An experiment was performed to investigate the self-regulation of slow cortical potentials (SCP) found in a previous study (Elbert et al. 1979). Seventeen subjects received continuous visual feedback of their actual cortical shift perceptible as a rocket moving across a TV-screen during intervals of 6 sec; subjects had to direct the rocket into one of two goals representing more or less cortical negativity, depending on the pitch of two signal tones. Within two identical experimental sessions feedback trials alternated with test trials without feedback. Highly significant differences of SCP between the two required polarities were demonstrated. The most pronounced differences were observed during test trials without feedback of the second session in which a positive shift below baseline level occurred when positivity (or less negativity) was required.

Adult↗
PubMed1980

Biofeedback of slow cortical potentials. II. Analysis of single event-related slow potentials by time series analysis.

A single trial analysis of slow cortical potentials treating the EEG as a time series was developed. The method was applied to data resulting from an experiment on self-regulation of slow cortical potentials (SCP). Parametric models of the EEG were developed on the basis of autoregressive filter models and a two-component model of SCP (during 6 sec intervals), taking into account ocular influences as a further parameter. Results from different models were compared with each other and with results of averaging SCP data. For the present data time series analysis and traditional analysis provided qualitatively equal results, but fewer trials were necessary for analysis in the single trial approach and more detailed structures of the data became evident. If the EEG was filtered above 5 Hz it could be described by an autoregressive filter model of low order. Ocular influences were estimated as too small in a non-filtered EEG compared to the filtered EEG.

Biofeedback, Psychology↗
PubMed1980

Event-related potentials evoked by sensory stimulation in normal mentally retarded and autistic children.

Evoked potentials (EPs) and slow potentials (SPs) were recorded during two sessions of sound (S) and light (L) conditioning (habituation: S alone; conditioning: coupling of SL; extinction: S alone after SL series). 125 children from 0 to 15 were examined: 82 exhibited signs of autistic behaviour and/or mental retardation; 43 were normally adapted. Two studies were performed. The first was an analysis of relationships: 65 clinical characters were noted for each child with behaviour scales and psychometric tests, 88 electrophysiological data were measured on averaged tracings. The second compared with t and chi 2 square methods the electrophysiological data of 3 groups clinically defined for age and typical syndrome. Results of the two studies supplemented each other. From the clinical point of view 3 major groups appeared: (1) autism, (2) mental retardation, (3) normal adaptation. From an electrophysiological point of view 2 major groups could be defined: (1) few conditioned EPs with small amplitude, generalized conditioned SPs, small unconditioned EPs, generalized unconditioned SPs, conditioning 'to time'; (2) many conditioned EPs, many conditioned rhythmic potentials, absence of generalized SPs, many localized vertex negative SPs (CNVs), large unconditioned EPs, no conditioning to time. Some differences were observed in generalized SPs, small and positive in mentally retarded children, negative or positive in autistic children. EP and SP data clearly help to differentiate pathological groups from a normal group but are insufficient to distinguish the autistic from the mentally retarded children.

Adolescent↗
PubMed1980

The M-wave and CNV in the squirrel monkey: generality of cue modality and of reward.

Typical M-waves and CNVs were produced in squirrel monkey frontal and rostral parietal cortex by light cues, as well as by tone cues. With light cues, M-waves were about 50% as large as with tone cues, whereas CNVs were of about the same magnitude with either type of cue. Typical M-waves and CNVs were also produced when avoidance of tail-shock was substituted for food as a reinforcer. The magnitude of both ERPs appeared to follow an inverted-U function with increasing shock intensity. The use of tail-shock as a reinforcer generated more complexities both in ERP changes and in behavior than did food. In some animals, at high shock intensities, ERP increased, rather than decreased, as each session progressed. In some animals, a combination of food and avoidance of tail-shock produced a decrease, rathan than an increase, in ERPs and did not improve behavioral performance. Furthermore, animals would not perform effectively on a CNV paradigm with punishment for aborting the trial. It was also demonstrated that increased stress (immobilization of head or tail) resulted in a reduced magnitude of both the M-wave and the CNV. This may account for some of the complexities encountered with avoidance of tail-shock as a reinforcer.

Animals↗
PubMed1983

Removal of eye movement and ECG artifacts from the non-cephalic reference EEG.

A method is described that automatically eliminates eye movement artifacts from EEG records and creates an extracranial reference electrode in one single process. The usefulness of this method is illustrated for both standard EEG recording as well as for CNV and P300 potentials. The artifact signals are measured with a special set of electrodes and are combined in order to subtract the artifacts from contaminated EEG records. The subtraction ratios are determined as those that minimize the variance in the result corrected EEG signal.

Contingent Negative Variation↗
PubMed1983

Late components of saccade-related brain potentials in guessing tasks.

The late positive components of lambda responses were studied in a guessing task modified in such a way that subjects had to perform a saccadic eye movement in order to perceive task-relevant information. Responses from 6 scalp areas were investigated in 9 subjects and in 2 conditions: control and guessing. In both conditions subjects performed two consecutive saccades in a given trial: the first to the middle light, the second to the target area. In the control condition the subjects knew beforehand what the 'target' would be. In the guessing condition they had to make a guess before each trial as to which of the three target stimuli would appear. The target stimuli occurred with unequal probability and were presented in a randomized sequence. Unlike the control condition, the guessing task led to the appearance of a late positive component in the lambda response. Similar to traditional ERP findings, this late positivity showed an amplitude maximum at the parietal area and a peak latency at 375 msec from saccade onset. Furthermore, Principal Component-Varimax Analysis (PCVA) of the lambda responses revealed a first factor giving the strongest loading in the latency range of the P300, and a second factor which was identified as the slow wave. These factors are quite similar to the factors found in the PCVA of ERPs. Our results suggest that the late components of lambda responses reflect the effects of information processing in cognitive tasks similarly to the way the late positive components of ERPs do.

Adult↗
PubMed1983

Automatic classification of electromyographic signals.

The results of the application of classification methods to electromyograph signals of weak contractions in normal and myopathic subjects are described. Methods of pattern recognition, previously presented, allow the selection of representative motor unit action potentials. The analysis is done with ordinal qualitative variables obtained by identification of shape descriptive parameters (amplitude, duration, number of phases, number of extrema). From this analysis, characteristic classes for normality and myopathy appear, from which a diagnostic aid by assignment can be made.

Action Potentials↗
PubMed1984

Movement-related slow potentials. I. A contrast between finger and foot movements in right-handed subjects.

Movement-related potentials ( MRPs ) preceding a finger flexion and a plantar flexion of the foot on either side were compared over the frontal, central and parietal areas of both hemispheres. MRP amplitudes were larger preceding foot than preceding finger movements. In the first case their onset was earlier and their presence in the frontal area was more marked. Prior to a finger flexion amplitudes over the hemisphere contralateral to the movement side were larger than those recorded over the ipsilateral hemisphere. On the contrary, prior to a plantar flexion of the foot, amplitudes were larger over the hemisphere ipsilateral to the movement. These findings point to differently localized sources of the MRPs in the two cases. In other experiments larger amplitudes preceding foot movements were found near the midline. It is suggested that the ipsilateral preponderance prior to foot movements is caused by a contralateral source in the depth near the longitudinal fissure. The dipoles are presumably directed obliquely to the median plane. The ipsilateral preponderance is present both prior to and following the plantar flexion. This suggests comparable directions of the dipoles in the motor and somatosensory areas.

Adolescent↗
PubMed1984

Event-related potential concomitants of information processing dysfunction in schizophrenic children.

ERPs were recorded from 10 schizophrenic and 13 normal children during the performance of the Span of Apprehension task (Span). This task involves the discrimination of a randomly placed target letter among distractors, and it has been shown to discriminate between normal and schizophrenic individuals. The EEG was recorded at 7 scalp loci, and ERPs were averaged over a 1500 msec interval initiated by a warning tone which preceded the visual Span stimuli by 500 msec. Stimulus arrays were grouped into 4 levels of difficulty. The data from both subject groups were combined in a single principal components analysis (separate PCAs exhibited few differences between groups) generating 8 rotated factors which were readily interpreted in terms of conventional ERP components. Factor scores for the two groups were examined using Analysis of Variance. The schizophrenic children produced a small CNV which was slow to develop and resolve as well as diminished amplitudes for the N1, P3 and slow wave components. This suggests that these children are impaired in their ability to regulate processes involved in the mobilization and direction of attention and the discrimination of target stimuli. Significantly, the schizophrenic children did not show progressive increases in N1 and SW amplitudes in response to increases in information processing demand (array difficulty) as was the case in the normal children. ERP components of the schizophrenic children were most aberrant at frontal leads, but midline and lateralized deficits were also seen at vertex and posterior recording sites.

Adolescent↗