Contingent Negative Variation Resolution Research Articles

The Contingent Negative Variation – An Electrophysiological Correlate of Temporal Processing or Reference Memory?

In EEG research, the contingent negative variation (CNV) is considered to be strongly related to interval timing (e.g., Macar & Vidal, 2004; Macar, Vidal, & Casini, 1999). However, it is discussed controversially whether certain properties of the CNV (e.g., amplitude, peak latency and resolution) directly reflect the process of temporal accumulation or rather processes related to reference memory or decision stages in temporal information processing (van Rijn et al., 2011). This present study was designed in order to investigate the relationship between CNV mean amplitude, CNV resolution, and memory processes as well as processes of temporal accumulation. The task design aimed at dissociating between processes of reference memory and temporal accumulation. Three different categories of cognitive tasks were developed: temporal tasks related to reference memory, temporal tasks related to immediate memory and reference memory, and tasks without temporal components. Assuming correlations between post S2 CNV resolution and reference memory capacity (negative) as well as CNV amplitude and reference memory capacity (positive), no correlations were expected to be found between these CNV measures and performance in less reference memory related temporal tasks. The results do not support our hypotheses and methodological problems are discussed primarily.

Decoupling interval timing and climbing neural activity: a dissociation between CNV and N1P2 amplitudes.

It is often argued that climbing neural activity, as for example reflected by the contingent negative variation (CNV) in the electroencephalogram, is the signature of the subjective experience of time. According to this view, the resolution of the CNV coincides with termination of subjective timing processes. Paradoxically, behavioral data indicate that participants keep track of timing even after the standard interval (SI) has passed. This study addresses whether timing continues after CNV resolution. In Experiment 1, human participants were asked to discriminate time intervals while evoked potentials (EPs) elicited by the sound terminating a comparison interval (CI) were measured. As the amplitude of N1P2 components increases as a function of the temporal distance from the SI, and the latency of the P2 component followed the hazard rate of the CIs, timing processes continue after CNV resolution. Based on a novel experimental paradigm, statistical model comparisons and trial-by-trial analyses, Experiment 2 supports this finding as subjective time is more accurately indexed by the amplitude of early EPs than by CNV amplitude. These results provide the first direct evidence that subjective timing of multisecond intervals does not depend on climbing neural activity as indexed by the CNV and that the subjective experience of time is better reflected by distinct features of post-CI evoked potentials.

Differential effects of age and executive functions on the resolution of the contingent negative variation: a reexamination of the frontal aging theory

The "frontal aging theory" assumes the deterioration of executive/inhibitory functions as causal factors for the cognitive decline in human aging. The contingent negative variation resolution (CNV-R) is an electroencephalographic potential elicited after the second (informative) stimulus in warned Go/NoGo tasks requiring a response to one type of stimulus (Go) but not to the other (NoGo). Whereas the CNV-R across conditions is a measure of executive functions, the augmented potential in the NoGo condition is a specific measure of inhibitory processes. The aim was to examine the presumed linkage between executive processes and the CNV-R with special regard to inhibition in the NoGo condition, and to test whether any effects of age on this potential can be explained by a failure of (inhibitory) executive functions. Nineteen young and 15 elderly non-demented healthy volunteers were examined in a Go/NoGo CNV-R paradigm and on a test of executive functions focussed on set shifting (Trail Making test). Results showed: (1) Better executive functions are associated with higher amplitudes of the CNV-R across conditions. (2) The CNV-R is higher for elderly than younger subjects; this increment is much stronger in the NoGo condition. In conclusion, the CNV-R across conditions reflects executive processes such as the shift of motor set. A higher CNV-R for elderly subjects (particularly of the inhibition-related NoGo CNV-R) indicates that this group is not impaired in the available amount of executive control but may exert such control for task demands where young subjects do not require it.

C- and Aδ-fiber components of heat-evoked cerebral potentials in healthy human subjects

Feedback-controlled laser heat was used to stimulate the hairy skin of the hand dorsum and forearm, and heat-evoked cerebral potentials were recorded at midline (Fz, Cz, Pz) and temporal (T3, T4) scalp positions. Based on data from primary afferent electrophysiology a stimulus level (40°C) was chosen, which is above C-fiber heat threshold, but clearly below Aδ-nociceptor heat threshold in order to excite selectively C-fibers without concomitant excitation of Aδ-fibers. Feedback-controlled stepped heat stimuli to 40°C elicited ultralate laser evoked potentials (LEPs) at the vertex in a high proportion of experiments (90%). Estimates of conduction velocity calculated from latency shifts between the hand and forearm sites of ultralate LEPs (2.4 m/s) and of reaction times (2.8 m/s) confirmed mediation of ultralate potentials by unmyelinated nerve fibers (nociceptors and/or warm fibers). The ultralate LEP could be differentiated from resolution of contingent negative variation (CNV), an endogenous potential related to expectation and response preparation, by its scalp topography. Strong heat stimuli of 48°C, which is suprathreshold for most Aδ- and C-fiber nociceptors, elicited the well-known late LEPs mediated by nociceptive Aδ-fibers confirming previous studies. The LEP waveform to strong heat stimuli also contained an ultralate component reminiscent of an ultralate LEP following the late LEP. Ultralate and late LEP had identical scalp topography. In conclusion, the method of temperature-controlled laser heat stimuli allows the selective and reliable examination of Aδ- and C-fiber-mediated afferent pathways and the related cortical processing without the complication of dissociating A-fiber nerve blocks.

Changes in bit-mapped contingent negative variation (CNV) activity due to initial normal involutional processes of the human brain

Bit-color mapped multicomponent CNV complexes and RTs to S2 evoked with a simple warned CNV/RT paradigm were recorded and measured in 20 selected right-handed very healthy volunteers (10 young adults and 10 presenile subjects, mean age 28.3 and 59.6, respectively). EEG and CNV components (post S1, N1, P2, P3; early CNV; N1200; late CNV; CNV resolution) were recorded from Fz, C3, Cz, C4, P3, Pz, and P4 referenced to linked mastoid electrodes. EOG, RT and stimuli were also recorded. The presenile group differed significantly from the younger group in the auditory post-S1 N1 and early (O-wave) and late (P-wave) CNV complex components. A progressive amplitude reduction limited to frontal leads between O-wave and P-wave, the lowest point being reached in the P-wave, was characteristic in the presenile group. Moreover, presenile subjects showed relatively flat CNV waveshapes of low amplitude and, on the whole, performed a little less well than young ones. This finding suggests that the statistically significant changes in auditory post-S1 N1 and CNV activity recorded in our presenile subjects, without any appreciable deficits in behavioral or mental performance, could be alerting signs of early brain involutional processes related to minimal and subclinical decline in orienting, attentiveness and response preparation capabilities. If such is the case, and it could be confirmed in a larger sample of very healthy subjects, these age-related changes in the presenium might prove to be of considerable practical importance for clinical research.

An early resolution of contingent negative variation (CNV) in time discrimination

This study investigates slow potential shifts that occur during a time discrimination task in man. Three experimental series were presented. In series A, each trial included a 5 sec standard interval (SI) followed by a 3 sec SI-TI delay and then by a 4.5, 5.0 or 5.5 sec test interval (TI). The subjects had to estimate whether SI and TI were equal or different and responded by pressing a left or a right button after TI. In series B, the responses was postponed after a 3 sec pre-response interval (PRI) succeeding to TI. Series C established an easier discrimination: only 5 or 8 sec TIs were randomly presented in each trial, and the subject had to judge whether he had been given the ‘short’ or ‘long’ interval. The intervals SI and TI, in which the subject had to collect temporal information, yielded a systematic pattern of slow potential shifts: CNV was followed by an early and prolonged resolution of negativity in the second half of the interval. By contrast, SI-TI delay and PRI only yielded a classical CNV. The ‘CNV-early resolution’ complex appears as a typical feature of temporal tasks. Its possible relation with cognitive processes leading to temporal judgements is discussed, whereas the presence of the only CNV is interpreted as an indice of expectancy.

Electrophysiological measures (CNV — EEG) and Nitrous Oxide at low doses in man

Nitrous oxide (N2O) is a widely used inhalational anesthetic gas, but its exact mode of action and its distribution in the CNS are not yet well known. The aim of this research was to study the effects of N2O at low doses (10 percent) in the CNS of humans. Five healthy volunteers were tested. Contingent Negative Variation (CNV), Reaction time (RT) and quantified EEG recordings were taken while subjects were breathing air and then N2O. A significant reduction of the post-imperative positive CNV components during N2O inhalation was observed; no changes in EEG power spectrum and RT values were seen. These results could be consistent with an early N2O interference with processes underlying CNV resolution, while vigilance and attention were still maintained.

The timing of CNV resolution in a memory retrieval task

Twelve men performed the Sternberg memory retrieval task while the EEG and EOG were recorded. Subjects saw a target set of 1 to 4 digits followed by a warning tone that was followed after 1.5 sec by a probe digit. Subjects indicated by pressing one of two levers whether the probe digit was in or out of the target set. The timing of contingent negative variation (CNV) resolution was measured as the latency of 50% resolution in stimulus-synchronized waveforms (SSWs), response-synchronized waveforms (RSWs), and model waveforms (MWs). The MWs were constructed by adding each RSW to itself using time displacements derived from the reaction times of the single trials of which the RSW was an average. The results indicated that CNV resolution is related to the timing of the motor response. MWs had resolution latencies close to those of the SSWs. In SSWs the N1 and P3 to the warning tone also varied with target set size.

The contingent negative variation during a memory retrieval task

Evoked potentials were recorded from the human scalp during performance of a memory retrieval task modeled after a paradigm originated by Sternberg (1966). Subjects were required to decide whether a probe digit was contained in a series of one to four target digits presented a few seconds before. The amplitude of the contingent negative variation (CNV) preceding the probe digit and the speed of CNV resolution after the probe varied as a function of target set size. CNV amplitude was greatest when the set size was one. The smaller the set size, the more positive the evoked potential 300 msec after the probe, regardless of whether a motor response was required.

Selective attention, contingent negative variation and the evoked potential

Contingent negative variation (CNV), N1-P2 amplitude of the evoked potential (EP), and positivity at 300, 400 and 500 msec latency (P300, P400 and P500) were measured in relation to task relevant (R) or irrelevant (I) tones presented alternately or unpredictably at 1 sec intervals. High concordance of P300, 400 and 500 indicated a slow, relatively unpeaked wave thought to be the CNV resolution. Both N1-P2 and P300 appeared small only when stimuli were both irrelevant and predictably so. With predictable presentation correlations were observed between CNV, N1-P2 and P300 in terms of both absolute level and, particularly, relevant/irrelevant difference. Holding CNV constant statistically, and to a lesser extent P300, reduced these correlations. It is suggested that CNV resolution in the post-stimulus trace reflects selective attention paid to the stimulus, and may be responsible, through summation, for claims that N1-P2, and sometimes P300, does so.

Determinants of the post-stimulus resolution of contingent negative variation (CNV)

Subjects were six women. They heard a warning click (W) followed by one of two tones (S1), followed again by one of two clicks (S2). In half the trials they made a choice key pressing response (R) to the tone; in half no response (NR) was required. Within these trials they made a further choice response to the click (S2) if the tone at S1 was high tone (continued expectancy, CE) but not if S1 was a low tone (non-continued expectancy, NCE). The CNV present at S1 was resolved towards the baseline whether or not an overt response had to be made to S1 and whether or not the information in S1 counselled continued expectancy. With CE this CNV resolution was arrested when a further CNV developed in preparation for S2. This created a sharp divergence of the CE trace from the NCE trace, the latter continuing its positive-going resolution. The latency at this point of CE/NCE divergence correlated positively with motor reaction time to S1 and was delayed when a motor response was required to S1. Conclusions: (1) The cause of return of CNV to baseline is neither the overt response nor the final decision concerning the nature of the stimulus, but probably the first coarse identification of the stimulus as one of a relevant class of stimuli. (2) The point of CE/NCE divergence may mark the completion of a second stage of finer analysis and may be an EEG index of final decision latency. (3) Inter-individual variance in reaction time is confined mainly to transactions before this point in processing. (4) The need to make an overt response may absorb processing capacity and therefore delay decision time.