Slow potential waves in the human brain associated with expectancy, attention and decision

Abstract

1. Stimuli in any modality evoke responses over wide regions of frontal non-specific human cortex. 2. When identical stimuli are monotonously repeated these responses diminish irregularly and finally disappear. 3. When stimuli are presented frequently in association, the responses to the first or conditional stimuli are amplified while those to the second or indicative stimuli are attenuated. 4. When a subject is instructed to perform a relevant operant action to the second “imperative” stimulus the primary response to the conditional stimulus is followed by a prolonged negative wave which submerges the negative component of the imperative response. 5. The negative wave linking the conditional and imperative responses is described as an Expectancy Wave (E-wave) because it reflects very accurately the attitude of the subject to the stimulus association and his intention to act on it. 6. Comparison of intra-cranial and scalp records suggests that the E-wave arises from depolarisation of a small proportion of the apical dendrites in the frontal and premotor cortex. 7. Development of the E-wave is accompanied by economical abbreviation of the motor reaction time to the imperative stimuli by synchronisation and restriction of the efferent motor volleys. 8. When the imperative stimuli are withdrawn (extinction) without warning the E-wave subsides slowly over about 50 trials in normal adults. However, when a previous verbal warning is given the E-wave disappears at once. 9. When the significance of the association between conditional and imperative stimuli is diluted by presenting a proportion of unreinforced conditional stimuli (equivocation) the E-wave is diminished accordingly and in normal adults vanishes when the probability of association falls to about 0.5. 10. Stimuli involving no energy transfer to the subject but with a high information content evoke E-waves as long as the subject considers the signals interesting and important, whether they are isolated, imperative or conditional. 11. The E-wave seems to indicate the subjective significance assigned by a particular person to the signal association or “Gestalt” used for the experiment. The significance thus determined includes the need for recognition or decision, and involves social as well as physiological influences.