CNV (Contingent Negative Variation) in Neurosurgical Patients

Since the first description of CNV (contingent negative variation) by Walter in 1964, many reports on this phenomenon have appeared, mainly in the psychiatric field. In this report, CNV was recorded in neurosurgical patients under three experimental conditions which differed as to the level of difficulty in concentrating on the conditioned tasks. Under the 1st condition, CNV was recorded without distractive stimuli. Under the 2nd condi tion, CNV was recorded during distraction by definite words in a meaningless context. Under the 3rd condition, CNV was recorded during distraction by music. This was based on the fact that the amplitude of CNV is increased in the state of heightened attentiveness and concentration, and is decreased during distraction. As a result, at least three types of CNV patterns were recognized. In Type I, the CNV was well developed under all conditions, with slight to moderate reduction of the amplitude of CNV during distraction. Distraction by words reduced the amplitude more than by music. This type of CNV was seen among normal controls and the patients with no mental deficits and no visible CT lesions in the frontal lobe. In Type II, CNV was already slightly inhibited under the 1st condition with further inhibition or disappearance under the other two conditions. This type was seen among patients with slight intellectual and memory disturbances and with visible CT lesions in the frontal lobe, including mild ventricular dilatation. In Type III, CNV was not elicited at all under any conditions. This type was seen among patients with evident intellectual and memory deficits and more extensive CT lesions. In all cases with ventricular dilatation, CNV was inhibited or disappeared. In a case of hypertensive hydrocephalus treated by a V-P shunt, CNV which had not been evoked before the shunt became normalized together with clinical improvement and normalization of the ventricular size. In another case of hydrocephalus in which ventricular dilatation remained after the V-P shunt, no CNV was elicited before or after the procedure.