Morton D. Low

Questions regarding the sequential neural generator theory of the somatosensory evoked potential raised by digital filtering

Digital bandpass filtering (300-2500 Hz) designed for zero phase shift was applied to somato-sensory evoked potentials recorded with cephalic bipolar montages. Four consistent negative and corresponding positive peaks with latencies of about 16, 18, 19, and 20 msec were elicited with median nerve stimulation. Peroneal nerve stimulation also elicited 4 reproducible negative-positive peaks having latencies of about 24, 26, 28, and 30 msec. Interpeak latencies measured 1.3 +/- 0.2 msec and 1.8 +/- 0.25 msec for median and peroneal elicited SEPs respectively. Because cephalic bipolar recordings cancel most far-field potentials, multiple generators cannot account for all the additional components seen. It is hypothesized that some of the high frequency components recorded are due to activity in recurrent intrathalamic neuronal networks.

The CNV and semantic content of stimuli in the experimental paradigm: Effects of feedback

Abstract The usual contingent negative variation (CNV) paradigm S1S2R was modified by requiring a discrimination at S2 and by adding a feedback stimulus: S1SdΔR…..FB. It was demonstrated that as the discrimination task became more difficult and therefore the feedback (FB) more important informationally, the CNV became prolonged until the FB signal and the amplitude of the evoked response to this stimulus increased in size. It is suggested that the discharge of a CNV occurs at the time of significant informational feedback. In the normal CNV paradigm this is usually intrinsic in S2 and R, but in a discrimination task it may be delayed to an explicit feedback stimulus. The FB evoked response changes reinforce the concept that the amplitude of at least some components of an evoked response reflect the psychological significance of the stimulus. Psychiatric patients, including five schizophrenics, showed changes similar to those observed in normals, but the patient data were unusable because of significant contimination by EOG and galvanic skin response artifact.

The contingent negative variation and the "resting" D.C. potential of the human brain: effects of situational anxiety.

Abstract The contingent negative variation, or CNV, a slow, surface negative potential which appears maximally in frontal regions of the brain of man during psychophysiological states of preparation set or expectancy, is shown in a non-patient population (a) to be smaller in amplitude in high anxiety S s than in low anxiety S s in a moderately stressful experimental situation and (b) to diminish in amplitude as the anxiety or stress content of the experiment is increased.

Monitoring the Level of Anesthesia by Automatic Analysis of Spontaneous EEG Activity

Recent advances in the fields of automatic EEG analysis and pattern recognition provide a valuable new perspective for reconsidering the question of whether or not the level of anesthesia can be reliably estimated by analyzing spontaneous EEG activity. The feasibility of developing a computer-based EEG pattern recognition system capable of continuously estimating the level of anesthesia of patients during surgical operations is investigated in this paper. Anesthetists were asked to define five clinically significant levels of anesthesia for a commonly used anesthetic in terms of meaningful non-EEG criteria. The subsequent development of various EEG pattern recognition systems in an attempt to reliably estimate the levels of anesthesia as determined by the non-EEG criteria is described. All such systems employ Bayes decision rule under the assumption that pattern features are statistically independent. System performance is evaluated in terms of the estimated probability of misclassification error. Systems based on the recognition of spectral or frequency-domain EEG patterns are compared to those based on the recognition of time-domain EEG patterns.

Electroencephalographic localization of conative aspects of language production in the human brain.

Publisher Summary The language system in the brain of man is presumed to reside primarily in the left hemisphere, and Brocas area is presumed to function as a coding unit for articulation. These presumptions are based on considerable clinical lesion data and much indirect evidence. However, the question of the specific relationship of handedness to speech lateralization remains open, and it is unclear what proportion of functionally pure left-handers also have left hemispheric speech lateralization and whether functional mixed handedness is ever or always an indication of mixed speech dominance. This chapter describes an experiment in which, following EEG testing, epileptic patients were subjected to bilateral carotid amytal tests for language dominance. Determination of dominance with carotid amytal tests was made without the knowledge of the predictions from EEG evaluation.

Cognitive and task-related EEG correlates of arithmetic performance in adolescents

Cognitive and neurophysiological correlates of arithmetic calculation, concepts, and applications were examined in 41 adolescents, ages 12-15 years. Psychological and task-related EEG measures which correctly distinguished children who scored low vs. high (using a median split) in each arithmetic subarea were interpreted as indicative of processes involved. Calculation was related to visual-motor sequencing, spatial visualization, theta activity measured during visual-perceptual and verbal tasks at right- and left-hemisphere locations, and right-hemisphere alpha activity measured during a verbal task. Performance on arithmetic word problems was related to spatial visualization and perception, vocabulary, and right-hemisphere alpha activity measured during a verbal task. Results suggest a complex interplay of spatial and sequential operations in arithmetic performance, consistent with processing model concepts of lateralized brain function.

Identifying academic aptitude in adolescent children by psychological testing and EEG spectral analysis.

Abstract Task-related EEG measures and psychological assessments were evaluated as a means of identifying academic aptitudes in adolescents. The addition of measures derived from power spectral analysis of EEG recording during verbal and perceptual tasks to the psychological testing results greatly improved identification of the childrens level of visuospatial reasoning, but only slightly improved identification of verbal reasoning level. Right hemisphere EEG measures appeared to be more important than left in determining the level of both verbal and visuospatial aptitudes.

Psychiatric status of the marihuana user.

This paper is concerned with the psychiatric evaluation of 81 volunteers in a marihuana project. The psychiatric status has been evaluated in a standard manner and the drug history, both prescribed and non-prescribed, has been determined. A method of classification of the non-adverse and adverse drug effects is suggested. Observations are made with respect to the subjective responses of the volunteers in regard to their drug intake, and these are compared to the hard data obtained in the neurophysiological and neuropsychological parts of the study and from fifteen key papers reviewed. The serious lack of precise methodological design and the need for more accurate information with respect to placebo effects, suggestibility and the social set in the area of marihuana use are noted.