Very slow brain potentials relating to expectancy: The CNV.

S INCE THE publication by W. 6. Walter and his colleagues (1964), in which the contingent negative variation (ICNV) was initially reported, there has been a steady growth of interest in this phenomenon. Grey Walter's findings were confirmed and extended in several laboratories. The clinical applications of such techniques are now being explored. Dr. Walter's group reported that the effect consists of a slow shift in the average baseline potential that is correlated with conditional expectancy and thus represents a cerebral response in the Pavlovian sense. They hypothesized that the CNV is a shift in the apical cortical dendritic potentials in the direction of depolarization that "primes" the cortex for action and that reducing the excitability threshold facilitates cortical responsivity, with the result that the efficiency of overt activity is increased (Walter, 1964b). In this paper, I shall review studies of "steady" cortical potentials, sometimes referred to as dc shifts or very slow potential changes. This includes phenomena with a latency of 200 to 300 milliseconds and a duration of 0.5 second or more. There is no implication of a dc generator as a source of a steady potential between the surface of the brain and a neutral reference. I am dealing with activity slower than delta waves ( I to 4 Hz). Sensory evoked responses (ER) have rapid primary components with a latency of about 50 milliseconds, later secondary components with a latency of 100 to 200 milliseconds, and often "slow" components from 200 to 500 milliseconds with variable durations. There has been interest in the study of baseline changes since the development of stable, high-input-impedance dc amplifiers. Caspers