Experimental enhancement of alpha activity

Abstract

1. 1. A cross-over randomised latin-square design was used to test eight normal subjects for their EEG responses to auditory, tactile and visual discrimination tasks, and to mental arithmetic. 2. 2. Enhanced alpha activity occurred in 24 out of 64 test occasions. There were significant differences between subjects' mean alpha responses; enhanced responses occurred at least once in seven of the eight subjects. There were also significant differences between tests, tactile testing being most often associated with enhanced responses and visual tests least often. 3. 3. No association was found between the type of resting EEG and alpha change scores on testing. 4. 4. Arousal, as defined by EMG criteria, was positively correlated with degree of blocking, but the association was too weak to account for the differences in alpha activity between individuals or between tests. 5. 5. Two patterns of “adaptation” during testing are described. During the period of stimulation (2 min) blocking responses showed a gradual return towards the resting level, while enhancement responses showed a continuous rise. 6. 6. The role of visual activity, including imagery, is thought to be an unlikely explanation of our results. Alpha activity probably has more than a single determinant. Theories of alpha activities which fail to account for enhancement effects must be reformulated, and in this context the study of adaptation patterns to constant stimuli might prove rewarding.