P350 Component Research Articles

Dynamics of the Duration of Gaze Fixation and Event-Related Potentials on Presentation of Fading-In Images and Distractors

A method of studying the dynamics of visual attention in humans at different stages of examining and recognizing complex images is described. The characteristics of the method include presenting dynamically formed whole images and distractors in the foveal area of the visual field. Experimental data on the effects of acclimation to distractors, the bimodal distribution of fixation duration when distractors are used, and the relationship between the effect of the distractor and the complexity of the target image are presented. Most EEG leads, except the occipital leads, showed significant decreases in the latent period of the P350 component of fixation-linked potentials on simultaneous presentation of whole images and distractors. The potential for using these results to create work-oriented tests for assessment of the state of visual attention in human operators without interfering with their work is discussed.

Neurophysiological markers of retrieval-induced forgetting in multiplication fact retrieval

Event-related potential (ERP) counterparts of practice effects in multiplication fact retrieval were examined. Participants performed a multiplication verification task after having practiced a specific problem set. Practice was either active (retrieval of solutions to multiplication problems) or passive (reexposure to the same operands plus the correct result). Behavioral data showed retrieval-induced facilitation for practiced items and retrieval-induced forgetting for related, unpracticed items, irrespective of practice type. ERPs revealed that, for the active practice group, forgetting was reflected in a reduced N100 component time-locked to result onset. Irrespective of practice type, forgetting was also reflected in a reduced result-locked P350 component, whereas facilitation was associated with an increased amplitude of the same component. These results suggest that beneficial and detrimental effects of practice may be mediated by partially distinct processes.

Auditory processing in an inter-modal oddball task: Effects of a combined auditory/visual standard on auditory target ERPs

Previous research examining auditory target ERPs in an inter-modal oddball task has shown that early components are affected by intra-modal processes, whilst components in the later part of the ERP, around 200–400 ms, are affected by both inter-modal and intra-modal processes. These findings led to the conclusion that there are separate stages of auditory target processing — an early modality-specific stage and a later context-dependent stage. The present study investigated this further by simultaneously presenting a visual standard stimulus with an auditory standard stimulus in an oddball task. The aim was to determine whether the inclusion of the visual standard stimulus in this task affected the ERP to targets. The auditory–visual oddball task consisted of a regularly presented combined auditory and visual standard stimulus (80%) and an infrequent auditory target (20%). The ERPs to targets in the auditory–visual oddball task were compared to those in an auditory oddball task, which had identical auditory stimuli and no visual standards. The results showed that the early components N100, P200 and N200 did not differ between tasks. This was in line with earlier results, and confirmed that activity up to 200 ms is unaffected by visual standard stimuli. The later components P250, P300 and P350 were larger and showed topographic differences in the auditory–visual oddball task. This was interpreted as reflecting separate inter-modal and intra-modal processes at later stages. In particular, the P300 and P350 components were argued to represent separate inter-modal and intra-modal components. Overall, this study provides further evidence of auditory processing occurring in two stages, an early modality-dependent stage and a later context-dependent stage.

263 EFFECTS OF EXPECTATION ON SOMATOSENSORY EVENT-RELATED POTENTIALS (SEPS) ELICITED BY PAINFUL ELECTRIC STIMULI

Background and Aims: Pain perception is typically measured by questionnaires and behavioural responses. Somatosensory Evoked Potentials (SEPs) however provide a direct measure of stimulus processing in the brain. To investigate whether expectancy influences SEPs we applied a cross‐modal oddball paradigm. The P3 EP component is modulated by expectancy, anticipation and novelty. We hypothesize that the number of background stimuli preceding the painful target determines the expectancy of the target and consequently the amplitude of the P3. Methods: A multi‐channel EEG was recorded (band pass 0.1–100 Hz, sample frequency 1000Hz) from 11 volunteers. Trials commenced with 3, to 11 auditory stimuli, followed by a painful electric target stimulus (ring finger, 1ms duration, individually set to a subjective pain intensity level of 9; 0 = no pain; 10 = maximum pain). Inter‐stimulus intervals were 800 ms. After target presentation the participants rated the stimulus painfulness (0–9). Results and Discussion: An increase in the number of auditory background stimuli preceding the painful stimulus was accompanied with a larger lateralised N130, possibly due to an increase in attention. The centrally localized P350 decreased, as hypothesized, as did the late N450. SEP changes were observed up to 7 preceding background stimuli, after which the effect levelled off. No effects of number of backgrounds was found with respect to the perceived intensity. We propose that SEP P350 components elicited by oddball paradigm behave similarly to P3 EP components observed in other modalities. It will be interesting to study whether cognitive SEP modulation differs between chronic pain patients and healthy volunteers.

Radiation-Induced DNA Damage and Repair in Cells of a Radiosensitive Human Malignant Glioma Cell Line

The induction and repair of DNA double-strand breaks were studied in cells of two isogenic human malignant glioma cell lines which vary in their SF2 values by a factor of approximately 30. M059J cells are radiosensitive (SF2 = 0.02) and lack the p350 component of DNA-dependent protein kinase (DNA-PK); M059K cells are radioresistant (SF2 = 0.64) and express normal levels of DNA-PK. Zero integrated field gel electrophoresis and alkaline sucrose gradient experiments indicated that equivalent numbers of DNA lesions were produced by ionizing radiation in M059J and M059K cells. To compare the capacity of both lines to repair sublethal damage, the split-dose recovery experiment after exposure to equitoxic doses of radiation was carried out. Significant sublethal damage repair was shown for M059K cells, with a 5.8-fold increase in relative survival peaking at 4 h, whereas M059J cells showed little repair activity. Electrophoresis studies indicated that more double-strand breaks were repaired by 30 min in M059K cells than in M059J cells. These results suggest that deficient DNA repair processes may be a major determinant of radiosensitivity in M059J cells.

Slow potential shifts and decision P350 interactions in tasks with random sequences of near-threshold clicks and finger stimuli delivered at regular intervals

In 12 successful experiments on normal human adults, random sequences of equiprobable acoustic clicks or electrical stimuli to the index finger were delivered at regular intervals of 2.5 sec. In alternate runs either the clicks or the finger stimuli were designated as targets to be identified and mentally counted by the subject. The stimulus intensities were carefully adjusted near threshold to provide a feasible, but exacting, task. Scalp-recorded brain potentials were recorded with long time constant (8 sec) on FM tape, edited for removal of sections with artifacts, and averaged. Potentials associated with motor activities were excluded. Large P350 components were elicited by the stimuli designated as targets, but not by identical stimuli when they were non-targets. In many experiments the stimuli were preceded by a transient negative shift of up to 3 μV. The size of P350 to targets correlated with the size of this negative shift. After non-targets a slow transient positive shift could be observed, but no P350 component. The P350 and negative shift were maximal at the vertex and symmetrically distributed on the two sides. The primary components of ERPs to finger stimuli were not modified by the cognitive task. It is hypothesized that both the transient shifts and the P350 are produced by variations in the level of neuromodulation of the cortical circuits by the mesencephalic reticular formation (MRF). These different cortical events reflect corresponding variations in the MRF control by efferent pathways from the prefrontal granular cortex.

Wave form and neural mechanism of the decision P350 elicited without pre-stimulus CNV or readiness potential in random sequences of near-threshold auditory clicks and finger stimuli

In 17 successful experiments on normal human adults random sequences of equiprobable acoustic clicks or electrical stimuli to the index finger were delivered at intervals varying at random from 1 to 15 sec. The stimuli were of low intensity and provided a feasible, but exacting task. No motor activity was involved. In alternate runs either the clicks or the finger stimuli were designated as targets to be identified and mentally counted by the subject. The accuracy of the counts was checked after each run. Scalp recorded brain potentials were stored on FM tape, edited for removal of sections with artifacts and averaged. Large P350 components were elicited by the targets, but not by identical stimuli when they were non-targets. The reciprocal experimental design provided consistent controls. No pre-stimulus negative shift of the CNV type was observed in spite of the use of long time constants (8 sec). The background EEG did not affect the results. The P350 to targets was maximal in the centro-parietal region and of equal amplitude on the left and right hemispheres. Because there was little overlap from other ERP components, the wave form of P350 could be analyzed, namely the latency to onset, the time from onset to peak and the total duration. The primary components of ERPs to finger stimuli were not modified by the cognitive task, which excludes centrifugal gating of corticipetal input as a mechanism. The ERPs to targets presented an increased N120. The latter was symmetrically distributed over the central region for target clicks, but was larger in the contralateral parietal region for target finger stimuli. The neural basis of CNV, P350 and N120 is discussed in detail. It is suggested that the mesencephalic reticular formation (MRF) exerts a diffuse bilateral facilitatory neuromodulation of cortical circuits which can be transiently adjusted (to produce CNV) by MRF control from prefrontal granular cortex. P350 is a post-decision event with bilateral distribution and results from a phasic inhibition of MRF at the closure of a cognitive processing epoch. P350 and CNV are dissociable: they are distinct events that involve roughly coextensive brain generators, but result from the operation of different prefrontal cortex controls on the MRF output to the telencephalon, in cognitive behavior. N120 indexes modality-specific focal processors engaged for stimulus identification before a decision is reached. N120 may involve the more specific thalamic reticular system that is also controlled by prefrontal cortex.

Late components of the visual evoked potential to search in short-term memory

The present paper investigated the changes in the morphology of the VEP as a function of the amount of search in short-term memory. The task required that the subject responds with a ‘yes’ or ‘no’, depending on whether a test digit has been part of a set of digits he had just seen. Six sizes of sets were used, 1, 3, 5, 7, 9 and 11. EEG was recorded from C 3, C 4, T 3, T 4, C z, P z and O z, and sampled every 4 msec to obtain VEP to the test digit. Two late components were found to increase in latency with increasing set size: (a) P270, which was masked by the P350 component for small set sizes; it preceded P350 for longer memory sets and its latency increased up to set size 7 with an average slope of 20.5 msec per item and (b) P350, which increased in latency up to set size 7 with an average slope of 22 msec per item. It was suggested that P270 reflects the serial search process. When search is terminated another general processor is called into action. This process is reflected in the P300 and is believed to be independent of the memory set size. Amplitude did not correlate with the amount of search. The morphology of the VEP changed for sets above short-term span, and latency changes in P270 and P350 no longer predicted RT changes. Since subject's strategy was not controlled for supra-span sets, no definite conclusions were offered.

On the influence of task relevance and stimulus probability on event-related-potential components

Fifteen subjects were presented with series of tones. Any one tone was either loud or soft, and in any one series the probability of one tone intensity was either 0.9 or 0.1. Subjects were instructed to count the frequent tones or to count the rare tones. The stimuli were also presented while the subjects were solving a word-puzzle. Event-related potentials (ERPs) were recorded from 9 scalp locations (F 3, C 3, P 3, F z, C z, P z, F 4, C 4, P 4) referred to linked mastoids. ERP components were measured with a Principal Components analysis and the relations between these measures and the independent variables were evaluated with the ANOVA procedure. This paradigm allowed an evaluation of the effect of stimulus probability, stimulus relevance, and task relevance on the waveform of the ERPs. We conclude that the P350 component is enhanced whenever the eliciting stimulus is both rare and in some sense relevant to the subject's task and the degree of enhancement is greatest when the rare—relevant tone is loud. A “slow wave” component which follows P350 is related to the same variables but has a scalp distribution quite different from that of P350. The slow waves shows a progressive shift in polarity from negative to positive from the frontal to the parietal sites, while the P350 is of nearly equal amplitude (and positive) at the central and parietal sites and has a smaller (positive) amplitude at F z. A third prominent component, negative in polarity, peaking at about 210 msec, is most pronounced following rare stimuli, whether or not they were task relevant. The amplitude of N210 tended to be largest at the frontal electrode. This study then demonstrates that when suitable measurement techniques are used, multiple endogenous ERP components can be observed, each related to distinct aspects of cognitive behavior.