An investigation of the event-related slow-wave potential (0.01-2 HZ) in normal children

A Developmental Investigation of Stop-Signal Inhibition

Abstract. The present study examined the development of response inhibition in the stop-signal task across child (8-13 years), young-adult (18-22 years), and middle-aged adult (29-47 years) groups through a dissociation of low- and higher-frequency ERP activity. Fifty-one subjects (n = 17 in each group) performed the stop-signal task, which consisted of a visual choice reaction time (RT) task and auditory stop-signals, while EEG was recorded. The original EEG data (0.01-30 Hz) was subsequently filtered to separate slow-wave (0.01-2 Hz) and residual (2-30 Hz) activity. Performance findings revealed that stop-signal reaction time (SSRT) decreased from the child to young-adult group and then showed a small increase in the middle-aged adult group. Original ERPs revealed decreasing N1 and N2 amplitudes and increasing P2 and P3 amplitudes across the scalp with increasing age for successful-stop trials. These developmental effects did not occur in the residual waveforms after removal of slow-wave activity. For failed-stop trials, a response-locked negative component, identified as the error-negativity (Ne), showed an age-related decrease in amplitude across the scalp in the residual, but not the original, waveform. The error-positivity (Pe) increased in amplitude with age in the original data, but this was accounted for by a positive slow-wave (PSW). Together, the findings suggest that underlying slow-wave activity accounts for a large number of developmental effects in the traditionally quantified ERP components, but may also obscure effects occurring in residual activity. These findings highlight the importance of dissociating low- and higher-frequency ERP activity in developmental research.

Removal of CNV Effects from the N2 and P3 ERP Components in a Visual Go/NoGo Task

Abstract. In an S1-S2 Go/NoGo task the impact of slow potentials following S1, particularly the late component of the contingent negative variation (CNV), on the following cognitive-processing waveforms to S2 (e.g., N2 and P3) remains unclear. A common method to correct for these confounding slow waves has used a forced baseline shortly before S2. The impact of this on ERP measures relating to S2 is unclear. An earlier method of CNV correction, devised to remove its effect on P3 measures by using different baselines for each condition, appears questionable. This study explored the removal of the CNV from both Go and NoGo waveforms to clarify the sensory and cognitive components elicited by S2. Principal Component Analysis (PCA) was performed on the ERP means, and a component relating to the CNV was subtracted from each subject's raw data for each site and condition. Results showed that this effectively removed the CNV without distortion of the S2 ERP morphology. This technique may prove useful in the analysis of the N2 and P3 as indicators of processes involved in response inhibition.

Event-related slow-wave activity in two subtypes of attention-deficit/hyperactivity disorder

OBJECTIVE

Previous time-frequency studies have indicated that event-related low-frequency activity has important effects on component topography and developmental effects in auditory event-related potentials (ERPs) of children and adolescents. This study investigated the influence of event-related slow-wave (SW) (0.01-2 Hz) activity in the group differences seen between children with and without attention-deficit/hyperactivity disorder (AD/HD) of different subtypes.

METHODS

Time-frequency analysis techniques were applied to auditory ERP data derived from children with AD/HD predominantly inattentive type (n = 30), AD/HD combined type (n = 30) and age-matched control subjects (n = 30).

RESULTS

Event-related early frontal negative and late posterior positive SW components were reduced in the AD/HD combined type group, but not AD/HD inattentive type group, relative to controls. The RESIDUAL ERPs, which represented event-related 2-12 Hz activity, showed clinical vs. control group differences in components that were similar in both AD/HD subtype groups.

CONCLUSIONS

The time-frequency results showed that event-related SW (0.1-2 Hz) activity contributes importantly to group differences between AD/HD and control children, and the pattern of group differences from controls for each of the AD/HD subtype groups, which are evident in raw ERPs. These results emphasise both the clinical and developmental importance of this form of analysis.

SIGNIFICANCE

This novel approach revealed additional specific information about stimulus processing and regional inhibition/activation in two AD/HD subtypes, relative to control subjects.