The focus of our laboratory investigation is the brain activity of human subjects before, during and after the subjects have performed a cognitive task. The technique that I and my students use is to record the Electroencephalogram (EEG) of the subject each time that he/she performs the task and then, after 30 to 50 recordings under similar experimental and instructional conditions, average the EEG epochs about the point of the initiation of the task. The end result is a wave form that represents the electrical activity which the brain consistently produced before, during and after the subject's task performance. With the elimination of the as of yet uninterpertable segments of the EEG that are not task- or stimulus-related, it is possible to begin building hypotheses concerning the activity of the neurons and their organization that produced the EEG records.

Slow shifts of the scalp-recorded EEG are valid indicators of the amount and the pattern of synaptic activity in the superficial cortical areas. Evidence is accumulating that would point to the source of the EEG waves as being synchronized Excitatory Post Synaptic Potentials in the superficial cortical layers on the apical pyramidal cell dendrites receiving inputs from, among other places, the contralateral cortex.

Four Research Projects:

1. While on my third research sabbatical leave during the academic year 1990- 1991 in Vienna, Austria, I developed a research design to investigate the brain processes, their timing and organization involved with correct, as opposed to incorrect, performance on a difficult task. This study was designed to investigate the predictive value of the ERP preceding the initiation of a difficult perceptual-memory task and to investigate whether these ERPs require a motor movement on the part of the subject for their occurrence. Across 4 conditions the ERP was recorded from 23 right-handed subjects using DC amplifiers. Although the start of each trial began with a ready signal, the conditions differed in that the subjects initiated the task by a button press in 2 conditions and the computer initiated it in 2 others without a press.

The results showed that, especially in the frontal/central electrode sites, the ERP waves which began those trials ending in correct performance were more negative relative to those trials ending in an incorrect response. Those conditions which required the subjects to self-initiate the trial and those which were initiated by the computer showed similar results indicating that the negative ERP waves preceding correct performance are not produced by nor depend on a task initiating motor movement. The onset of the slow negative ERP waves preceded task initiation by up to 4.1 sec indicating that they were more than the Bereitschaftspotential - an ERP wave related to the preparation of a voluntary motor movement beginning approximately 1« to 2 seconds before the actual movement. A proposal to extend this research using EEG, MEG, & MRI while on sabbatical leave in Vienna, Austria, 1997-1998

Need: (1) This will allow the recording of psychophysiological measures of emotions (i.e. heat rate), attention (i.e. galvanic skin response), tension (i.e. skeletal muscle activity) during the pre-task 6.5 second period. (2) The ERP waves may have had more to do with the shortness (70 milliseconds) of the presentation of the task stimuli than with cognitive preparation. To investigate this possibility, a new task (e.g. three levels of difficulty of mental division) will be used in which the stimuli remain visible on the screen for 2 seconds. (3) Differences in the lateralization of the ERP would be expected if letters of the alphabet and/or geometric shapes were used as stimuli rather than numbers. (4) We also need to employ more electrode sites about the frontal/central region in order to more precisely localize the brain generators of the ERP. A grant proposal to fund a practical application of this basic research

2. While on my second research sabbatical leave during the academic year 1982-1983 in Leuven, Belgium, I developed a research design that studied the brain's activity before, during and after the decision process of the human subject directed to the sensation of warm and/or pain. The ERP, produced by subjects who were experiencing a gradually increasing heat stimulus, was recorded 3.5 sec before and 1 sec after a motor response. Subjects responded when the stimulus was 'just warm', 'just at prickling pain' or 'above the temperature of just prickling pain'. Two control procedures mimicked the Bereitschaftspotential (BP). The results showed that the steadily-rising, negative BP was modified to a positive wave before the decision of 'warm'. During the 'pain' and 'above pain' conditions, the pre-decision slow wave was less negative then the BP but more negative than that of the 'warm' condition. A temperature control condition confirmed that rising temperature alone did not produce these results. Principal components analysis confirmed these differences by producing factors which were interpreted as representing the ERPs of the conditions of 'warm', 'pain', 'above pain' and the BP.

It was evident from pilot studies that uncontrolled electrical activity from the skin potential response (SPR) was contaminating the results. SPR forced all ERP curves in the positive direction and several attempts to eliminate the SPR from the ERP failed. While the SPR was produced differentially across conditions and across the experimental sessions, the smaller the variability in the electrooculogram (EOG) recorded from above and below the orbits of the right eye, the smaller was the SPR contamination. Therefore, in 1982 we selected subjects who showed a stable orbital EOG.

Since the original experiment was published in 1984, 2 students have replicated and expanded the results with their theses. They have concentrated on the elimination of artifacts from the SPR and from the emotional reactions to anticipated pain and the force of movement that people in pain may exert when responding.

Need: attention to slower brain waves, the continued sharpening of the design to eliminate SPR and other emotionally driven artifacts, e.g. by a 'scratch' of the scalp at each electrode site, by a comparison of the results of a pretest screening and the use of Analysis of CoVariance, etc. needed before further publication of these studies. Also the following design changes will help to substantiate our findings: (1) the testing of additional subjects using a cold stimulus, which is presently available and functioning, under the same experimental conditions will test the generality of the findings; (2) Recording the electromyogram (muscle activity) of the response finger as a measure of tension and a correlate of force of the response which affects the ERP; (3) Recording the galvanic skin response as a measure of attention and its correlate with the ERP; (4) Recording with a long time constant to investigate more of the slow wave component of the ERP, (5) examining the effects of equating the length of each trial across each condition by manipulating warming and cooling rates.

3. The purpose of this third approach is to investigate the active decision making process in humans utilizing subliminal and supraliminal stimuli, subject response, and the ERP. The psychophysical procedures of the Method of Limits and the Staircase Method are both used to identify the shortest duration of light exposure necessary to produce the verbal response "Yes, I see the light" (visual absolute threshold) of each subject.

The detectibility of the stimulus can either be increased or decreased by changing the duration of time that the light-emitting diode is activated. The experimenter determines a set of stimulus durations which will produce a response from the subject indicating that they have seen the light on 10%, 30%, 50% 70% and 90% of the trials.

In a predetermined, randomized order these 5 stimulus durations are presented so that each subject is stimulated by 15 presentations of each and the subjects are required to indicate whether they have seen the light and how confident they are about that judgement.

The results showed that the positive ERP wave occurring about 350 msec (P3) after the onset of the light was extraordinarily greater in amplitude on those trials in which the subjects indicated that they had seen the stimulus as opposed to those trials in which they did not indicate that they had seen the light. A large P3 wave is indicative of brain processes involved with task-relevant stimuli associated with discrimination, attention and decision making tasks. The absence of a discriminable P3 wave on those trials in which the subject did not say that they had seen the stimulus, although the stimulus was actually presented, is taken as strong evidence that at least higher-order brain processes are not activated by stimuli that do not reach consciousness. We then concluded by rejecting the notion that Subliminal Perception occurs, at least as it relates to higher- order, non-emotionally related tasks and stimuli.

Need: more subjects, concentration on subcortical recordings as well as cortical potentials, concentration on unconscious as well as conscious responding, the use of variable intensity of the light source instead of its duration are among the retest variables important for us.

4. During Biofeedback training subjects receiving a feedback signal indicating the state of a certain physiological function can learn to regulate that function. The regulation is at first slow and conscious but eventually becomes automatic and immediate. This project is designed to investigate the brain processes involved when the subject learns to lower his/her skeletal muscle function. Biofeedback machines that are designed to assist the subject in learning to control muscle activity (Electromyogram - EMG) incorporate a device that, when set just below the present functioning of the muscle group, will allow the feedback to increase in pitch in response to more contracted muscles and to decrease upon relaxation. When the relaxation reaches the setting, this threshold device turns off the feedback auditory signal completely, thus creating a very easily distinguishable feedback (silence) of partially successful relaxation.

Subjects return for at least 8 experimental sessions and experience two complete 5 minute episodes of each of the following 3 conditions on each session. While recording the ERP and the EMG: (1) Experimental condition - the threshold device turns off the feedback completely when relaxation is achieved; (2) Control condition - the feedback signal continues to increase or decrease after relaxation as it did before relaxation is achieved; (3) Baseline condition - no feedback is heard by the subject although the computer is still recording the ERP and EMG before, during and after relaxation as it was in the previous conditions.

These three conditions allow for the separate analysis of the effect of the feedback reward on brain waves during Biofeedback learning. We found that a large P3 wave occurred during the experimental condition to the rewarding silence in the central and parietal areas but that this same ERP response did not occur in the other conditions. Therefore, the subjects seem to be responding differently across conditions both in their behavior (learn faster with the experimental condition) and in their brain waves. Large frontal negative waves occurred prior to success, relating back to the preparatory phase of research project 1 (see above).

Need: More subjects, more electrode sites and attention to slower EEG waves are required. Go back to the beginning

Copyright © 1995, Dr. John M. Morgan, All rights reserved - This page last edited August 26, 1996
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