Yuping Wang

Event-related potential N270 is elicited by mental conflict processing in human brain

We recorded event-related potentials (ERPs) in 15 subjects in order to elicit a N270 of arithmetic conflict. Subjects calculated an arithmetic problem and matched their calculation result to an answer digit. They pressed a button when the presented digit is a true answer (condition 1) and pressed another button when the answer is false (condition 2). ERP components of P90, N130, P180, N200 and late positive component (LPC) were recorded in condition 1. In condition 2, N270 was elicited between N200 and LPC and it peaked at approximately 270 ms (268.6 +/- 29.0 ms at Cz). The peak latency of LPC in condition 2 (405.7 +/- 51.3 ms) is significantly delayed than condition 1 (307.5 +/- 22.7 ms). N270 reflects the endogenous conflict processing in human brain.

Event-related potentials evoked by multi-feature conflict under different attentive conditions

Abstract. Event-related potentials (ERPs) were recorded in subjects while they were performing a matching task. The focus of the present study was on the contributions made by ERP recording to revealing the time-course of multi-conflict information processing in the brain during visual attention. Participants were instructed to discriminate whether the attributes of the first stimulus (S1) were the same as those of the second one (S2) of a pair. Stimuli were defined by three features: color, global shape, and local shape. In condition 1, all attributes of the two stimuli of the pair were constant (no conflict); in condition2, S2 was different from S1 in all attributes (conflict). The experiment comprised three tasks. In task 1, subjects attended to the color of the stimuli and ignored the other attributes. In task 2, they were asked to attend to both color and global shape of stimuli and disregard the local shape. In task 3, all attributes were attended to. An ERP component N270 was elicited by attending to the color conflict in session one. In task 2, attending to color and global shape induced two ERP effects in the conflict condition: N270 and N400. The results suggest that the attended different conflicts of the two visual attributes of the stimuli were processed in series. However, in task 3, only one apparent negative component, N270, was observed in the conflict condition. The difference between data from task 2 and 3 showed that more than one processing model exists in the human brain for processing multiple visual attribute conflicts.

Enhancement of conflict processing activity in human brain under task relevant condition

To investigate the working mechanism of the conflict processing system, pairs of colored numbers were sequentially presented on a screen to subjects. They were asked to determine if the magnitude or the color of the two numbers was identical. Event-related potentials (ERPs) were recorded at the same time. A negative potential peaking at 270 ms (N270) after the onset of the second number (S2) was elicited when S2 conflicted with the first number (S1) in task-relevant and (or) irrelevant attribute conflicts. The mean amplitude of the N270 was more negative in task relevant conflict than in irrelevant conflict. Therefore, the conflict processing activity can be initiated independently of the task, but is enhanced in task relevant conflict.

The N270 component of the event-related potential reflects supramodal conflict processing in humans

It is unclear whether crossmodal information conflict can initiate the conflict processing system indexed by a component of the event-related potential (ERP) called the N270, which previously has been observed only for visual conflict. ERPs were recorded in ten subjects, while they were engaged in a visual-auditory discrimination task. A visual stimulus of a facial photograph was followed by an auditory stimulus of Chinese syllable [a] or [i], which might be sounded by the same gender of its preceding photograph (gender match) or by different gender (gender conflict). Subjects pressed a button for gender match and another for gender conflict. A prominent N270, similar to that evoked by visual conflicts, was elicited by the auditory stimuli in gender conflict condition. It is likely that N270 reflects the brain activity of a supra-modal conflict processing system.

Event-related potential N270, a negative component to identification of conflicting information following memory retrieval.

OBJECTIVEnN270, an endogenous ERP component of conflict effect, was evoked in previous studies with S1-S2 paradigm. The present experiment is designed to confirm the speculation that this conflict-related negativity could also be elicited by stimulus probes having conflict with a memorized item in a visual post-retrieval comparison task.nnnMETHODSnA Sternberg probe-matching paradigm was modified in the present study. The stimuli consisted of a memory set of 3 different items (simple figures) and a retrieval set of 3 probe figures. Subjects matched each probe to its corresponding item in the memory set. The tasks were designed with different conflict loads of no-conflict, low-conflict and high-conflict in the probe retrieval test.nnnRESULTSnProbes of no-conflict elicited a major positive going component, P300, with bilateral parietal distribution. Probes of low- and high-conflict evoked N270, while N430 was elicited only in high-conflict condition. N270 was more negative in high-conflict condition than in low-conflict condition. The N270 was right hemispheric prominent in the low-conflict task and remarkably distributed over the right prefrontal areas. On the other hand, both N270 and N430 were distributed bilaterally on the scalp in the high-conflict task.nnnCONCLUSIONSnThe present results demonstrate that the N270 is an index to the conflict identification, while the N430 of the high-conflict task reflects the processing for complex conflicts following probe retrieval. These negativities are related to the processing of conflicts.

Event-related potentials elicited by stimulus spatial discrepancy in humans

Sixteen subjects were instructed to discriminate whether the spatial locations of two visual stimuli presented in sequence were identical and event-related potentials (ERPs) were recorded from their scalps. The first and the second stimuli were presented in the same location in condition 1, but were in different locations in condition 2. ERP components of P100, N150, late positive component (LPC) and slow negative wave (SNW) were recorded in condition 1; in condition 2, N150 was enhanced and N270 was elicited before LPC. N150, N270 and SNW were all mainly distributed bilaterally over P3, P4, Pz, O1, O2, and Oz. N270 represents the brain activity for processing spatial discrepancy. There are several specialized brain areas involved in the generation of the N270.

Different processes are involved in human brain for shape and face comparisons.

Fifteen subjects participated in a matching task of visual stimuli. Two sequentially presented stimuli in a pair were the same shape (shape match), different shapes (shape mismatch), same human face (face match) or different faces (face mismatch). All four kinds of stimulus pairs were of equal probability. The shape mismatch pairs elicited a negative event-related potential component N270 (Peak latency: 262.1+/-16.5 ms, P4) after the second stimulus onset, while the face mismatch evoked N270 with longer peak latency (301.2+/-19.8 ms, P4) and N450. There exists a specific system for mismatch processing of a complex stimulus (face) in the human brain.

A functional MRI evaluation of frontal dysfunction in patients with severe obstructive sleep apnea

BACKGROUNDnThis study focused on frontal dysfunction during a brief visual delayed matching-to-sample (DMS) task in patients with severe obstructive sleep apnea syndrome (OSAS). We also aimed to assess whether mismatch- or match-task would be more sensitive in the evaluation of OSAS frontal impairment and to determine the factors responsible for the association of the task performance and frontal activation.nnnMETHODSnNine severe OSAS patients and 9 age-matched healthy subjects were studied with an event-related functional magnetic resonance imaging (fMRI). The performance and activation of frontal region of interests (ROIs) were compared between the two groups. The ROIs included anterior cingulate cortices (ACC), anterior prefrontal gyri (aPFG), middle frontal gyri (MFG) and inferior frontal gyri (IFG). The association of reaction time (RTs) and ROIs activation with severe nocturnal hypoxia (as measured by duration of time with oxygen desaturation SaO(2) below 80%) and arousals was estimated.nnnRESULTSnPatients with OSAS showed reduced frontal activation in ACCs, MFGs and IFGs and significantly increased activity in the right aPFG when being involved in mismatch tasks, when compared with healthy subjects. In addition, both the oxygen desaturation duration and arousal index were associated with the slower reaction times (RT) and greater reduction in the frontal activation in ROIs for OSAS patients during mismatch information processing. Other OSAS variables, including apneic index (AI), hypopneic index (HI), desaturation index, and the Epworth Sleepiness Scale (ESS), were not associated with changes in ROI response to either mismatch or match tasks.nnnCONCLUSIONSnPatients with severe OSAS showed decreased mismatch-related activation in frontal ROIs when compared to healthy subjects during a brief visual DMS task. The association of arousal index and severe hypoxia with slow RTs and frontal mismatch-related activation suggests that both hypoxia and sleep fragmentation contributed to frontal dysfunction in OSAS patients. Moreover, the mismatch-related activity is more sensitive than match-related activity in the evaluation of OSAS frontal dysfunction during a brief visual DMS task.

Early detection of cognitive impairment in patients with obstructive sleep apnea syndrome: an event-related potential study.

Event-related potentials (ERPs) were recorded to visual stimuli in a task that required matching the shape and serial position of the probes against previously memorized items. The effects of hypoxia on ERP were investigated in 24 patients with obstructive sleep apnea syndrome (OSAS) and a matched control group. N2b-late positive-going (LPC) components were elicited by probes that identically matched the memorized items (no-conflict condition). In contrast, N270-LPC and N270-N430-LPC components were elicited by probes having low-conflict and high-conflict with the memory set. Conflict ERP effect decreased in mild, while both no-conflict and conflict ERP effects decreased in amplitude in severe OSAS patients. Conflict ERPs associated with processing of conflicting information are more vulnerable than no-conflict ERPs to hypoxic cerebral damage.

A mismatch process in brief delayed matching-to-sample task: an fMRI study

Our previous ERP studies have consistently demonstrated that a negativity N270 elicited by incongruent information in visual S1–S2 matching task represents a type of conflict process, which is distinct from that represented by the classic conflict task or other negative components in delayed matching-to-sample stimulus presentation patterns, since the inter-stimulus interval between S1 and S2 was presented as shorter as 500xa0ms. The N270 component of ERP was shown to reflect conflict processing during the simple working memory operations. In the present study, a functional MRI (fMRI) was used to investigate the visuospatial characteristics of brain activation associated with the task eliciting N270. The fMRI data showed an increased activation in the right anterior cingulate cortex (ACC, BA 24) and right dorsolateral prefrontal cortex (DLPFC, BA 46), and activation biased to the left occipitotemporal cortex (BA 37) in the incongruent condition. It is suggested that the greater activations of the right ACC coupling with right DLPFC to incongruent task reflect functional efficiency of the right cingulo-prefrontal network during the brief visual delayed period discrimination performance and mismatched information processing.