Robert Cohn

DC RECORDINGS OF PAROXYSMAL DISORDERS IN MAN.

Abstract It has been shown that paroxysmal brain activity is ordinarily associated with relatively slow components which attain gross negative shifts when detonated by high voltage generator pulses. The observed electrical behavior in paroxysmal output can be modeled by: (1) a physiological system in which the nervous activity behaves as a dipole with regenerative properties; and (2) by a physical system in which the paroxysmal activity behaves as transients introduced in the nervous tissue; under this latter condition the tissue behaves as a passive electric network.

Pattern reading of the clinical electroencephalogram with a digital computer

Summary A digital computer program has been constructed which defines those visually apparent maxima and minima in a way comparable to that of a human electroencephalographer. The program computes wave parameters from the time and amplitude values of the maxima and minima. These parameters can be used to monitor a pattern over a short or long duration, and can be used to quantitate patterns and to quantitate changes in patterns seen in the EEG.

Synchronization characteristics of paroxysmal EEG activity.

Abstract 1. 1. Direct superimposition of highly resolved potential contours was capable of only first order measurements. 2. 2. Cross-correlations of contemporaneous potentials were made in an attempt to achieve a higher order of precision measurement. 3. 3. Using both types of measurement it was shown that physiological cortical visual system activities, in both man and cat, were closely synchronized following retinal stimulation. 4. 4. Convulsive discharges, even when primarily involving the visual system in man, showed a marked variability in the time of occurrence of measurable elements of the potential discharge derived from homologous regions of the head. 5. 5. These latter measurements suggested that the convulsive discharge was a contingent, adventitious action superimposed on the passive electrical characteristics of the anatomical network.

Bilateral simultaneous summated cortical responses to delayed bilateral and single median nerve stimulation

Abstract Single and bilateral electrical stimulation of the median nerves show evidence of hemispheric interaction by alterations of summated responses contralateral to the delayed stimulus and by the appearance of a new wave on the delayed side, with bilateral stimulation, and on the same side in single nerve stimulation. This new wave has a delay in major peaking of 2–4 msec.

Some characteristics of the cortical potential fields of the optic chiasm-sectioned cat

Abstract Precisely time-locked unit cortical potentials are not generally observed in cats with divided (or sectioned) optic chiasm when light is shined into the contralateral eye. The amplitude of the concomitant slow component of the contralateral cortical responses is much smaller than that observed in the simultaneously responding ipsilateral cortex. Partial and complete section of the corpus callosum does not alter the pattern of the summated (averaged) contralateral and ipsilateral cortical responses to light. It thus appears that various commissures other than the corpus callosum mediate the observed cortical response. These bilateral cortical responses probably subserve some element of binocular vision in the cat.

A METHOD FOR OBTAINING A FREQUENCY DISTRIBUTION OF BRAIN WAVES.

Abstract A new automatic, electronic method is described for obtaining the frequency distribution of random frequency bio-electric activity. It consists of translating the critical rise times of the biopotentials into pulses. These pulses are presented directly to the computer for average transients (CAT 400A) operating in the HISTOGRAM mode. Following the attainment of an adequate number of counts (this adequacy is entirely dependent on the primary data) the data is displayed by analog or digital techniques (CRO, X-Y recorder, tape printer etc.).

Impedance Measurements of Tissue

Impedance properties of tissue have been fairly extensively investigated (1, 2, 3). In general it has been difficult to obtain consistent data at very low frequencies of oscillation; and all measurements have had to be technically sophisticated and time consuming, because of the null methods used. These fundamental problems have limited the routine use of tissue impedance measurement. The introduction of the Hewlett-Packard Vector Impedance Meters have made tissue impedance measurements consistent, reproducible and rapid. A functional schematic of this instrument is shown in figure 1. The frequency range is continuous between 5 and 500 kHz, the impedance magnitude range is 1 to 10 megohms and the impedances and phase angles are read directly from large meters on the face of the instrument. No specific nulling is employed in these measurements, and a significant set of Z and θ values can be obtained and repeated (for checking) in minutes. The rapidity of measurement allowed us to accumulate an adequate number of data points without undue fatigue to the patient under study.

Three-dimensional spectral analysis of spike-dome activity

Abstract A technique is described in which three-dimensional spectral analyses of the EEG are rapidly produced. Several minutes of the transformed EEG are displayed in a single page, with the dimensions of time, frequency and intensity (or energy). This method of contour plotting generates details not observed in the conventional EEG pattern.