S1-S2 Paradigm Research Articles

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

N270, 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. A 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. Probes 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. The 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 during visual S1–S2 paradigm in multiple system atrophy: relation to morphologic changes on brain MRI measurement

Although mild cognitive deficits in multiple system atrophy (MSA) have been proved on neuropsychological testing, the cognitive function in MSA has not been investigated sufficiently from an electrophysiological view point. We performed a visual Event-related potential (ERP) examination and quantitative magnetic resonance imaging (MRI) measurements on 24 MSA patients and 18 normal subjects, and investigated the relationship between the ERP abnormalities and the morphological changes of the brain in MSA patients. To elicit ERPs, we used S1–S2 task which needs frontal lobe function for execution. We found significant prolongation of P3 latency and reaction time and significant attenuation of P3 amplitude in MSA, compared with normal control values. We performed the square and linear MRI measurements on MSA and normal subjects. The cerebellum, the pons, the perisylvian cerebral area and the deep cerebral gray matter in MSA were significantly smaller than those in normal subjects. The mean value in MSA was significantly increased for the bicaudate index and Huckman number compared with those in normal subjects. In MSA, we found significant correlation between P3 latency and atrophy of the cerebellum and the pons, while we found no correlation between ERP abnormalities and quantitative MRI measurements of any other regions. Our results showed that the prolongation of visual P3 latency during S1–S2 task was significantly associated with atrophy of the cerebellum and the pons.

Early sensory information processes are enhanced on visual oddball and S1–S2 tasks in Parkinson's disease: a visual event-related potentials study

To observe sensory and cognitive information processing in Parkinson's disease (PD), 34 PD patients and 26 controls were investigated. A visual oddball paradigm and an S1–S2 paradigm were employed to record the early (P1, N1, P2) and late (N2, P3) event-related potentials (ERPs) at Cz, Pz and Oz. Results showed: (1) enlarged P1 amplitude at all electrode locations on both tasks, (2) shortened N1 latency and enlarged P2 amplitude at Oz on both tasks, (3) enlarged N1 amplitude at Cz during an oddball paradigm, (4) delayed N2 latency and decreased N2, P3 amplitude on both tasks, and (5) delayed P3 latency and reaction time during the S1–S2 paradigm. Abnormal ERP changes were correlated with worsened scores on Wechsler Adult Intelligence Scale-Revised and motor dysfunction scales in PD. We surmise overactive aspects or failed inhibitory modulation of sensory information processing in the early ERP stage and deficient cognitive information processing during the late ERP stage in PD.

Anticipation of a non-aversive reaction time task facilitates the blink startle reflex

The conditions under which blink startle facilitation can be found in anticipation of a reaction time task were investigated to resolve inconsistent findings across previous studies. Four groups of participants ( n=64) were presented with two visual stimuli, one predicting a reaction time task (S+) and the second presented alone (S−). Participants were asked to make a speeded response to the offset of the S+ (S1 paradigm) or were asked to respond to a tactile stimulus presented at the offset of the S+ (S1-S2 paradigm). Half of the participants in each paradigm condition received performance feedback. Overall, blink latency shortening and magnitude facilitation were larger during S+ than during S−. More detailed analyses, however, found these differences to be reliable only in the Feedback conditions. Ratings of S+ pleasantness did not change across the experiment. Electrodermal responses to S+ were larger than to S− in all groups with differential electrodermal responding emerging earlier in the S1 paradigm. Taken together, the data support the notion that startle facilitation can occur during non-aversive Pavlovian conditioning.

Modulation of event-related potentials in normal human subjects by visual divided attention to spatial and color factors

We investigated how visual event-related potentials (ERPs) are modulated by visual divided attention using an S1-S2 paradigm. Stimulus S2 consisted of non-target stimuli (Stimulus 1, 2, 3) and a target stimulus (Stimulus 4). The spatial/color factor was compared between S1 and S2: same/same (Stimulus 1); same/different (Stimulus 2); different/same (Stimulus 3); and different/different (Stimulus 4). The P1/N1 (90~150 ms) showed significantly greater amplitude in Stimulus 3 than in Stimuli 1 and 2. The N2 (230~290ms) showed significantly greater amplitude in Stimulus 2 than in Stimuli 1 and 3. We assumed that the P1/N1 was related to spatial attention, enhanced by alterations to the spatial factor, and that the N2 was related to color attention, enhanced by alterations to the color factor.

The influence of time pressure and cue validity on response force in an S1-S2 paradigm

Hypotheses about variations of response force have emphasised the influences of arousal and of motor preparation. To study both types of influences in one experiment, the effects of time pressure and of validity of S1 were investigated in tasks wherein a first stimulus (S1) indicated the most probable response (80% valid) required after a second stimulus (S2). Under time pressure, responses were executed more forcefully while, as could be expected, response times were shorter and errors were more frequent. This pattern of results was not only obtained when time pressure was varied between blocks, but also when varied from trial to trial, by information given by S2. Also invalidly cued responses were executed more forcefully but, as could be expected, in contrast to time pressure, response times were longer and errors were more frequent. The results demonstrate that latency and force of responses may vary in different directions. Ways are outlined on how current hypotheses must be extended in order to account for these results.

Cortical potentials related to the nogo decision.

The go/nogo reaction time task has been frequently used to assess volitional inhibition. Psychophysiological studies of the correlates of the go/nogo decision have almost exclusively been concerned with N2 and P3 potentials of the event-related potentials (ERPs). However, in studies where the EMG onset latency was available, it was obvious that this latency was shorter than or at least equal to the latencies of the studied cerebral potentials. In this study, by concurrent recording of the EEG and EMG activity we aimed to better define the temporal relationship between cortical activity and motor response. Particularly, we wanted to identify the early (i.e. pre EMG-onset) electrophysiological correlates of the nogo decision. We used a modified S1-S2 paradigm that involved a two-stage go/nogo decision. In this task both S1 and S2 were informative and required the subject to make a decision, but the nature of the decision differed. The decision at S1 involved whether to prepare a movement, whereas the decision at S2 involved whether to initiate or inhibit an already prepared response. To better visualise the nogo decision related components of the ERPs, the go ERPs were subtracted from the corresponding nogo ERPs and difference ERPs were formed. Before EMG onset, a small negative component common to both go/nogo difference traces and corresponding roughly with the N1 wave was detected. It is suggested that this early negativity may be a more specific electrophysiological reflection of the nogo decision proper.

Event-related potential index of semantic mnemonic dysfunction in abstinent alcoholics

Background: The objective of the study was to expand the investigation of the match/mismatch mnemonic impairment in the semantic domain in sober alcoholics. Methods: Event-related potentials (ERPs) were recorded from 28 healthy adults and 36 sober alcoholics in a category (either animals or fruits/vegetables) match/nonmatch S1–S2 paradigm. Results: There was a significant interaction of ERP amplitude (c3) between groups (controls vs. alcoholics) and stimulus conditions (category match vs. nonmatch) at the posterior brain regions; the c3 component was smaller for the category match than for nonmatch trials in controls, with the absence of such c3 differences in alcoholics. There were no significant ERP differences between the two groups in processing the sample stimuli. The ERPs (c2) elicited by the animal category were larger than those for the vegetable category in both groups. The alcoholics showed prominent suppressed activation of left temporo-occipital brain regions under both matching and nonmatching conditions, as demonstrated by the current source density maps. The alcoholics were also slower and less accurate than the controls in judging both category matching and nonmatching stimuli, while neither of the two groups demonstrated shorter response times to the matching stimuli. Conclusions: These data suggest that alcoholics are less efficient in the semantic mnemonic match/nonmatch process, and are less likely to be deteriorated in the stage of forming the template for such match/nonmatch comparisons.

Topographic differences in CNV amplitude reflect different preparatory processes

Topographic differences in Contingent Negative Variation (CNV) were recorded while people were preparing for cognitive versus motor tasks in an S1–S2 paradigm. CNV had a frontal distribution when people prepared to encode words into long-term memory, whereas CNV was more centrally distributed when the tasks were predominantly motoric. These topographic differences appeared to be related to the type of task rather than the amount of information extracted from the S2, because a direct manipulation of the level of S2 processing had little effect on CNV amplitude. The topographic differences in CNV suggest that preparation for motor activity is a different psychological process from preparation for stimulus processing and that these two processes are subserved by different neural structures. This experiment also demonstrated that a recognition memory paradigm can be useful in the investigation of the psychological correlates of CNV.

ERP components in category matching tasks

The current experiment attempts to investigate (1) the effect of semantic information on the ERP correlate of visual short-term memory (VMP) and (2) the utilizing of the ERP as an objective investigative tool for the clinical observation of the existence of category-specific brain systems. Event-related potentials (ERPs) were recorded from 61 locations on the scalp of 39 healthy adults in a category (either animals or fruits/vegetables) match/non-match S1-S2 paradigm. The ERPs revealed a substantially smaller amplitude for the category matching than for non-matching pictures at the posterior brain regions, with greater activation of temporo-occipital brain regions changing from the right hemisphere at first to the left hemisphere later, as demonstrated by the current source density (CSD) maps. The ERPs elicited by the category of animal were larger than the vegetable category, similarly, the animal-animal matching condition elicited larger ERPs than did the vegetable-vegetable matching condition. In addition, the topographic distribution of the vegetable-elicited ERPs revealed additional involvement of the right frontal cortex which was absent in the topographic distribution of the animal-elicited ERPs. The spatial pattern of the VMP possesses features specific to semantic processing, and the ERPs differentiate the animal category from the vegetable category, suggesting an objective on-line method to investigate the category-specific information processing among brain-damaged patients.

Evoked heart rate and blood pressure in an S1–S2 paradigm

Phasic changes in heart rate (HR) and blood pressure (BP) in an S1–S2 paradigm were studied in three experiments. In each experiment, a memory search task was performed at S1. The outcome of this task indicated whether a fast or a delayed response had to be given after S2. Besides this response instruction, there were two other task manipulations: in one experiment the memory load at S1 was varied, whereas in each experiment a different kind of performance feedback was given. Both HR and BP showed a triphasic pattern, consisting of an initial decrease, followed by an increase and another decrease. The BP patterns were quite consistent, and delayed a few seconds relative to the HR pattern. The memory load manipulation at S1 showed that the changes early in the S1–S2 interval (initial decrease and subsequent increase) reflect the processing of S1. The effects of response instruction showed that the second HR deceleration, and the subsequent BP decrease, reflect the preparation of the motor response. In Experiment 2 the level of the evoked HR and BP patterns was shifted as a function of the type of reward (a bonus or noise).

P50 Suppression among schizophrenia and normal comparison subjects: A methodological analysis

The present report investigated the relationship between P50 suppression and habituation among 20 schizophrenia and 20 normal comparison subjects. Subjects were presented with clicks delivered over headphones in a S1-S2 paradigm (clicks were separated by 500 msec; average intertrial interval was 8 sec). There were 60 total trials; the data were analyzed separately for the first and second 30 trials. The groups did not differ either on the number of usable trials or on the morphology of their P50 responses. Consistent with previous reports, schizophrenia patients demonstrated deficient P50 suppression. The overall suppression effect was not due to a group difference on S1 P50 amplitudes, but was associated with schizophrenia patients having smaller S1-S2 P50 amplitude difference scores than normal comparison subjects. Furthermore, the suppression effect appears to be more pronounced during the first than during the second block of trials. Thus, it may be important to evaluate changes in P50 responses over time among schizophrenia and normal comparison subjects.

Subdural potentials at orbitofrontal and mesial prefrontal areas accompanying anticipation and decision making in humans: a comparison with Bereitschaftspotential

Field potentials associated with the execution of a warned choice Go/No-Go reaction task were recorded from prefrontal, supplementary (SMA) and primary motor cortex (MI) by using subdural electrodes in 5 epileptic patients during presurgical evaluation. The choice was between a Go and a No-Go imperative stimulus (S2) in the S1–S2 paradigm. Orbitofrontal and mesial prefrontal areas generated a slow preceding potential before S2 (most likely late CNV), and bilateral mesial prefrontal areas generated a transient potential, most likely related to decision making, upon S2 in both Go and No-Go conditions. In self-paced, repetitive movement, the Bereitschaftspotential was seen only at SMA and MI, but not in the prefrontal area. The present result, therefore, suggests that in humans orbitofrontal and mesial prefrontal areas play an important role in preparation for cognition and in decision making, whereas SMA and MI do so in motor preparation.

Associative learning in degenerative neostriatal disorders: Contrasts in explicit and implicit remembering between Parkinson's and huntington's diseases

The performances of 12 patients with Parkinson's disease (PD), 16 with Huntington's disease (HD), and young and old healthy controls were assessed on a number of tests of verbal and nonverbal declarative memory, on a test of nonmotor conditional associative learning (words and colors), and on a number of reaction time (RT) tasks. The RT tasks consisted of cued simple and choice reactions. The relationship between the precue and the imperative stimulus in the S1-S2 paradigm was nonarbitrary in the first series and arbitrary in the second series. The series with arbitrary S1-S2 associations was repeated across two successive blocks of trials. The rationale of the study was to investigate the function of the basal ganglia "complex loop," and it was postulated that HD patients would show greater deficits because of greater involvement of the caudate nucleus. The patients with HD had the slowest RTs. Across the two blocks with arbitrary S1-S2 associations, the patients with HD but not PD nevertheless showed evidence of learning in their precued RTs. In contrast, the patients with PD were better able to remember the associations in free recall than were the HD patients. It is concluded that patients with PD have relatively greater deficits in procedural learning, whereas those with HD have relatively more impairments in declarative memory, and the greater level of cognitive impairment in HD overall is interpreted as being due to more serious damage to the caudate loop.

Role of prefrontal cortex in generation of the contingent negative variation.

The contingent negative variation (CNV) is a brain potential generated during delay periods that has been proposed to measure prefrontal cortex (PFCx) activity. The CNV was recorded in neurological patients with PFCx damage centered in Brodmann areas 9, 44, 45, and 46 in a classical auditory S1-S2 paradigm employing a 3 sec interstimulus interval. Subjects pressed a button upon detection of an acoustically cued imperative tone (S2, 1000 Hz, GO). Responses were withheld if the warning tone (S1, 1500 Hz in GO trials) was lower in frequency (500 Hz, NOGO). The early phase of the CNV (500-700 msec after S1) was not reduced in patients with PFCx damage. PFCx lesions reduced the later phase of the CNV beginning about 1000 msec prior to S2. Reductions were maximal over PFCx sites but extended to posterior scalp electrodes over the lesioned hemisphere. The results are consistent with a late CNV generator in dorsolateral PFCx that also modulates generation of the potential in posterior regions of the ipsilateral hemisphere. The CNV findings coupled with behavioral evidence of impaired preparatory processes in these patients support the role of PFCx in sustaining distributed neural activity during delay periods.

Personality effects on brain potentials in an S1-S2 paradigm

Event-related brain potentials (ERPs) were recorded in an S1-S2 paradigm. S1 was a warning signal that indicated whether subjects had to respond as quickly as possible, or had to delay their responses until 1 sec after S2. The amplitudes of the frontal N1, the negative slow wave (NSW) and the terminal contingent negative variation (CNV) were larger following the speed-instruction than after the delay-instruction. To investigate the influence of personality, comparisons were made between groups differing in negative affectivity, positive affectivity, sensation seeking, and impulsivity. Persons scoring high on sensation seeking (SS) showed larger NSW amplitudes than low-scorers on SS. This finding is interpreted as suggesting that larger NSW amplitudes reflects emotions that were approach-related rather than avoidance-related. It is suggested that mechanisms generating the NSW are influenced by the affective characteristics of S1.

Simple and choice reaction time and the use of advance information for motor preparation in Parkinson's disease.

The effects of different types of advance information (warning signal, temporal cue, movement parameter cue), presented at different intervals before an imperative stimulus on reaction time (RT) were examined. Sixteen patients with Parkinson's disease and 16 age-matched normal controls performed a simple reaction time (SRT) task, an uncued, two partially cued (cueing of direction of movement or hand) and a fully cued visual four choice reaction time (CRT) tasks. An S1-S2 paradigm was used, where a warning signal/precue (S1) preceded the imperative signal (S2) by 0 (uncued and unwarned conditions), 200 ms, 800 ms, 1600 ms or 3200 ms. When the unwarned SRT and uncued CRT conditions were compared, the patients were slower than the controls in both conditions, with the group differences being larger for the CRT than the SRT task. Both patients and controls benefited from a warning signal presented before the imperative stimulus (S2), especially when it occurred 200 ms prior to S2. Advance information about the parameters of the required response was used by both patients and controls to preprogramme responses before the onset of S2. In both groups, RTs were generally faster for longer S1-S2 intervals. With an S1-S2 interval of 3200 ms, advance information about two movement parameters was 'fully' used by the patients to preprogramme responses such that their fully cued CRT was reduced to the level of SRT. In the controls, this process was complete by 800 ms. The most parsimonious explanation of the pattern of results across the SRT, fully cued CRT and uncued CRT conditions would be in terms of a slowness in response initiation in Parkinson's disease, which is a stage of processing common to all RT conditions. Deficits at one or more of the stages of processing unique to CRT are, however, necessary to explain the differentially greater slowness of uncued CRT in Parkinson's disease.