P300 generation by novel somatosensory stimuli.

Event-related potentials (ERPs) to task-relevant target and task-irrelevant novel stimuli were recorded in a somatosensory discrimination task. Subjects pressed a button to mechanical taps of the fifth finger (targets, P = 0.12), randomly interposed in sequences of taps to the second finger (standards, P = 0.76). Two types of infrequent novel stimuli were delivered; one was a mechanical tap to the third or fourth finger (tactile novels, P = 0.06), another was an electric shock at the wrist (shock novels, P = 0.06). Correctly detected targets generated a parietal maximal P300 (P3b, latency 335 msec). Shock novels generated a central maximal P300 with a shorter peak latency (298 msec) than the P3b. Tactile novels generated a P300 with a scalp distribution comparable to the shock novels. Unlike the P3b, P300 amplitude to both the shock and tactile novel stimuli habituated by 20-30% across the first several stimulus presentations. These results indicate that, similar to the auditory and visual modality, task-irrelevant novel somatosensory stimuli generate a novelty P300 ERP. Differences in scalp distribution, latency and habituation characteristics suggest that the novelty P300 may have contributions from intracranial generators independent from target P300 sources.     

网络成瘾对青少年注意功能的影响

目的 探讨网络成瘾对青少年注意功能的影响. 方法 对符合网络成瘾诊断标准的青少年和无网络成瘾倾向的青少年各18例分别进行有关注意功能的神经心理学测评,对比了解网络成瘾组注意功能损害程度;利用听觉和视觉Oddball范式,刺激包括标准刺激、靶刺激和新异刺激,采集脑电后分析网络成瘾组和对照组对新异刺激和靶刺激所产生的P3a、P3b的差异. 结果 网络成瘾组与对照组相比,神经心理学测评中出现明显的注意功能下降,事件相关电位检测中对新异刺激(计算机开机声音和画面)所形成的P3a的潜伏期缩短、波幅升高,而对靶刺激所形成的P3b的潜伏期延长、波幅下降. 结论 网络成瘾造成青少年注意功能下降,与P300变化具有一定的相关性.     

Spatial and temporal distribution of visual information coding in lateral prefrontal cortex

Prefrontal neurons code many kinds of behaviourally relevant visual information. In behaving monkeys, we used a cued target detection task to address coding of objects, behavioural categories and spatial locations, examining the temporal evolution of neural activity across dorsal and ventral regions of the lateral prefrontal cortex (encompassing parts of areas 9, 46, 45A and 8A), and across the two cerebral hemispheres. Within each hemisphere there was little evidence for regional specialisation, with neurons in dorsal and ventral regions showing closely similar patterns of selectivity for objects, categories and locations. For a stimulus in either visual field, however, there was a strong and temporally specific difference in response in the two cerebral hemispheres. In the first part of the visual response (50–250 ms from stimulus onset), processing in each hemisphere was largely restricted to contralateral stimuli, with strong responses to such stimuli, and selectivity for both object and category. Later (300–500 ms), responses to ipsilateral stimuli also appeared, many cells now responding more strongly to ipsilateral than to contralateral stimuli, and many showing selectivity for category. Activity on error trials showed that late activity in both hemispheres reflected the animal's final decision. As information is processed towards a behavioural decision, its encoding spreads to encompass large, bilateral regions of prefrontal cortex.     

Effects of crossmodal divided attention on late ERP components. I. Simple and choice reaction tasks.

We studied several effects of dividing attention between visual and acoustic inputs on different processing stages. Simple and choice responses were required to single letter stimuli. RTs and P300 latencies were delayed for divided attention (variable stimulus modality) as compared to focused attention (constant stimulus modality). In all but one condition, RT and P300 delays were similar. The exception was choice tasks to auditory stimuli, in which the RT delay was far larger than the P300 delay. Since the amplitude of the late ERP was larger in choice tasks than in simple tasks, the differences between the ERPs of choice and simple tasks were computed. They revealed that an additional late positive wave ("P-CR") occurred in all choice ERPs. In the divided attention condition the auditory (but not the visual) P-CR showed a longer delay compared to focused attention. We interpret the P-CR to be time-related to the response selection process. Our results suggest that the division of attention causes a slight impairment of stimulus evaluation (shown in P300 latency) and, after auditory stimuli only, a strong impairment of response selection (shown in P-CR latency). We therefore conclude that the observed RT effects are due to a bias of processing resources towards the visual modality, which mainly affects response selection. The results are in accordance with the theory of visual dominance.     

Frontal and parietal components of a cerebral network mediating voluntary attention to novel events

Despite the important role that attending to novel events plays in human behavior, there is limited information about the neuroanatomical underpinnings of this vital activity. This study investigated the relative contributions of the frontal and posterior parietal lobes to the differential processing of novel and target stimuli under an experimental condition in which subjects actively directed attention to novel events. Event-related potentials were recorded from well-matched frontal patients, parietal patients, and non-brain-injured subjects who controlled their viewing duration (by button press) of line drawings that included a frequent, repetitive background stimulus, an infrequent target stimulus, and infrequent, novel visual stimuli. Subjects also responded to target stimuli by pressing a foot pedal. Damage to the frontal cortex resulted in a much greater disruption of response to novel stimuli than to designated targets. Frontal patients exhibited a widely distributed, profound reduction of the novelty P3 response and a marked diminution of the viewing duration of novel events. In contrast, damage to posterior parietal lobes was associated with a substantial reduction of both target P3 and novelty P3 amplitude; however, there was less disruption of the processing of novel than of target stimuli. We conclude that two nodes of the neuroanatomical network for responding to and processing novelty are the prefrontal and posterior parietal regions, which participate in the voluntary allocation of attention to novel events. Injury to this network is indexed by reduced novelty P3 amplitude, which is tightly associated with diminished attention to novel stimuli. The prefrontal cortex may serve as the central node in determining the allocation of attentional resources to novel events, whereas the posterior parietal lobe may provide the neural substrate for the dynamic process of updating one's internal model of the environment to take into account a novel event.     

Visual perception of Kanji characters and complicated figures. II. Visual P300 event-related potentials in patients with mental retardation

In order to objectively evaluate visual perception of patients with mental retardation (MR), the P300 event-related potentials (ERPs) for visual oddball tasks were recorded in 26 patients and 13 age-matched healthy volunteers. The latency and amplitude of visual P300 in response to the Japanese ideogram stimuli (a pair of familiar Kanji characters or unfamiliar Kanji characters) and a pair of meaningless complicated figures were measured. In almost all MR patients visual P300 was observed, however, the peak latency was significantly prolonged compared to control subjects. There was no significant difference of P300 latency among the three tasks. The distribution pattern of P300 in MR patients was different from that in the controls and the amplitudes in the frontal region was larger in MR patients. The latency decreased with age even in both groups. The developmental change of P300 latency corresponded to developmental age rather than the chronological age. These findings suggest that MR patients have impairment in processing of visual perception. Assessment of P300 latencies to the visual stimuli may be useful as an objective indicator of mental deficit.     

Age-related changes in the electrophysiological response to visual stimulus novelty: A topographical approach

The relationship of task relevance and stimulus probability to P300 morphology, latency and distribution was assessed. Eight year olds and adults completed visual oddball tasks of recognition memory with frequent non-target (60%), infrequent target (20%), and infrequent novel (20%) stimuli. Stimuli consisted of 2 female faces posing neutral expressions, and 40 trial unique novel photographs depicting scenes, animals, objects or abstract patterns. Event-related potentials were recorded from 17 electrodes over frontal, central and parietal scalp, including lateral temporal sites. All stimuli elicited P300 responses at parietal electrodes, with the largest responses to the target stimuli (relevant and infrequent). The P300 responses of adults and children were morphologically dissimilar, with children showing broader peaks and latency shifts across electrodes. In addition, the eight year olds displayed a frontal negativity to novel stimuli which was absent in the responses of adult participants. Results suggest that different anatomical or functional circuitry may be involved in the processing of novelty for adults as compared to eight year olds.     

The development of Alzheimer's disease in Down's syndrome assessed by auditory event-related potentials

ABSTRACT. Several studies have reported changes in auditory event-related potentials in patients with Alzheimer's type dementia, These include an increase in latency and a reduction in amplitude of the P300 (P3) response, a late positive component generated about 300 ms after an unexpected stimulus. Alzheimer's type dementia is an almost invariable acompaniment of ageing in Down's syndrome. This study was designed to assess the usefulness of the auditory P300 response as a measure of the onset of dementia in Down's subjects, who because of poor language development may be difficult to assess by psychological tests. Auditory event-related potentials were recorded from 89 Down's subjects, aged 16–66 years. A control group of 29 mentally retarded subjects with fragile-X syndrome and 83 normal volunteer controls were also tesled. Clinical psychological testing found evidence of dementia in 16 Down's subjects and none with fragile-X. Furthermore, in the Down's population but not the fragile-X or control groups, there was a marked increase in P300 latency with age starting around 37 years. In controls, the effect of age on P300 latency became significant some 17 years later around the age of 54 years. The premature effect of age on P300 in Down's syndrome was due to the prolonged P300 latency in the 16 subjects showing signs of dementia. It was confirmed that P300 latency increase reflects the development of Alzheimer's dementia in Down's subjects.     

Prefrontal unit activity in the monkey: relation to visual stimuli and movements

Prefrontal single-unit activity in response to the behavioral significance of a visual stimulus was examined in the monkey. Tasks in which the position of the eyes was controlled behaviorally were devised to change the behavioral significance of the visual stimulus. The effect of the change in the spatial position and color of the visual stimulus was also examined. The monkey was required to perform either hand or eye movements. The effect of the difference in the required movement on unit activity was examined. Sixty percent of the cells tested (15 of 25 units) showed differential activity between significant and nonsignificant stimuli. Most cells tested showed similar response to the red and green stimuli. Fifty-two percent (15 of 27 neurons) fired vigorously when the visual stimulus was presented in the visual field contralateral to the recording hemisphere. Moreover, most cells related to these movements showed a similar discharge when either hand or eye movements were performed. I discuss the effect of the behavioral significance of a stimulus on unit activity in the prefrontal cortex and other association cortex.     

Electrical responses reveal the temporal dynamics of brain events during involuntary attention switching

Surviving in the natural environment requires the rapid switching of attention among potentially relevant stimuli. We studied electrophysiologically the involuntary switching time in humans performing a task designed to study brain mechanisms of involuntary attention and distraction (C. Escera et al., 1998, J. Cogn. Neurosci., 10, 590-604). Ten subjects were instructed to discriminate visual stimuli preceded by a task-irrelevant sound, this being either a repetitive tone (P = 0.8) or a distracting sound, i.e. a slightly higher deviant tone (P = 0.1) or an environmental novel sound (P = 0.1). In different conditions, the sounds preceded the visual stimuli by 245 or 355 ms. Deviant tones and novel sounds prolonged reaction times significantly to subsequent visual stimuli by 7.4 (P < 0.02) and 15.2 ms (P < 0.003), respectively. In addition to a mismatch negativity (MMN) and a positive-polarity, 320-ms latency, P3a event-related potential associated, respectively, with detection of the distracting sound and the subsequent orienting of attention to it, a late frontal negative deflection was observed in distracting trials. The peak latency of this brain response from sound onset was 580 ms in the 245-ms condition and 115 ms longer in the 355-ms condition (P < 0.001), peaking consequently at 340 ms from visual stimulus onset, irrespective of the onset of the distracting sound. We suggest that this late frontal negative response may signal over the scalp the process of reallocating attention back to the original task after momentary distraction, and therefore that recovering from distraction may take a similar shifting time as orienting attention involuntarily towards unexpected novelty.     

Auditory and visual P300 topography from a 3 stimulus paradigm.

OBJECTIVE: The P300 event-related brain potential (ERP) was elicited with auditory and visual stimuli in a separate session of a 3 stimulus oddball paradigm, and the scalp topography was assessed with 15 electrode locations. METHODS: Target (0.10), standard (0.80), and infrequent non-target (0.10) stimuli in the auditory task were 2000, 1000 and 500 Hz tone, and in the visual task, 'X', 'O', and 'H', respectively. The stimuli were presented in a random series, once every 2 s, and participants responded only to the target (N = 12). RESULTS: Target stimuli elicited larger P300 components than non-target did in both stimulus modalities. For both target and non-target stimuli, P300 amplitude was larger and latency longer for the visual compared with the auditory stimulus. Analysis of normalized P300 amplitude data indicated that the target and non-target P300s from both modalities had identical topography. CONCLUSION: The findings suggest that both target and non-target stimuli in 3 stimulus oddball paradigm elicited the same type of P300 (P3b) for both stimulus modalities.     

Prefrontal dysfunction and treatment response in geriatric depression.

BACKGROUND: This study investigated the relationship of clinical, neuropsychological, and electrophysiological measures of prefrontal dysfunction with treatment response in elderly patients with major depression. METHODS: Forty-nine depressed elderly subjects were studied before and after 6 weeks of adequate antidepressant treatment and compared with 22 psychiatrically normal controls. The psychomotor retardation item of the Hamilton Depression Rating Scale, the initiation/perseveration subscore of the Mattis Dementia Rating Scale, and the latency of the P300 auditory evoked potential were used as indices of prefrontal dysfunction. The intensity of antidepressant drug treatment was classified and monitored for a 6-week period. RESULTS: Abnormal initiation/perseveration score, psychomotor retardation, and long P300 latency predicted 58% of the variance in change of depression scores from baseline to 6 weeks (F3= 20.1, P<.001). Depressed patients who remained symptomatic (n = 25) had more abnormal initiation/perseveration scores and longer P300 latency compared with depressed patients who achieved remission (n = 24) and control subjects. There were no differences between the last 2 groups. The association between psychomotor retardation, initiation/perseveration scores, P300 latency, and response to antidepressant treatment could not be explained by differences in demographic and clinical characteristics or treatment intensity between remitted and nonremitted depressed patients. CONCLUSIONS: Prefrontal dysfunction was associated with poor or delayed antidepressant response in depressed elderly patients. This observation, if confirmed, may aid clinicians in identifying candidates for aggressive somatic therapies and for interventions offering structure of daily activities.     

ERPs to stimuli requiring response production and inhibition: effects of age, probability and visual noise

Sixty-six normal adults ranging in age from 20 to 85 years were presented with stimuli containing explicit instructions to initiate or to inhibit a motor response (the words 'push' or 'wait'). In one task, the effect of stimulus probability was investigated by varying probability between 0.25 and 0.75 for both Go and No-go stimuli. In another task, the effect of visual noise was investigated by degrading the stimuli with ampersands on half of the trials. Regression analysis was used to examine the effects of age on P3 amplitude and latency for each stimulus type. The effects of stimulus variables on P3, independent of age, were examined by standardizing each subject's data to those expected for a 20 year old. P3 latency to all stimuli and RT to Go stimuli increased with age. The latency of P3s to No-go stimuli was less sensitive to age than Go stimuli. P3 amplitude at Cz and Pz (but not Fz) diminished with age. P3s to Go stimuli were maximal at Pz and earlier than P3s to No-go stimuli. P3s to No-go stimuli were maximal at Cz. These differences between Go and No-go stimuli remained true under visual noise and probability manipulations. Visual noise prolonged the latency of Go and No-go P3. Less probable Go and No-go stimuli elicited larger and later P3s than more probable stimuli. Decreasing the probability of the No-go stimulus enhanced its central distribution.     

Visual event-related potentials index focused attention within bilateral stimulus arrays. II. Functional dissociation of P1 and N1 components.

Event-related potentials (ERPs) were recorded from 12 subjects as they attended to the left or right hemifield of a visual display while fixating a central point. Stimuli were presented to the left or right visual fields on separate trials (unilateral stimuli) or to both fields simultaneously (bilateral stimuli). In different conditions, the stimulus sequences contained only bilateral stimuli, only unilateral stimuli, or a mixture of unilateral and bilateral stimuli. Bilateral stimuli elicited an enhanced positivity lasting from about 75 to 250 msec that was largest at posterior electrode sites contralateral to the attended hemifield. The early phase of this attention-related positivity appeared to be an enhancement of the exogenous P1 component. In contrast, both the posterior P1 and N1 components were enhanced in response to attended unilateral stimuli. Moreover, the N1 attention effect was reduced when the preceding stimulus contained elements in the attended field. It was concluded that modulations of the N1 and P1 components in these experiments represent different aspects of visual spatial attention: N1 may represent the orienting of attention to a task-relevant stimulus, whereas P1 may represent a facilitation of early sensory processing for items presented to a location where attention is already focused.     

Differential auditory processing continues during sleep.

Auditory evoked potentials (AEPs) were used to examine selective stimulus processing in sleep. In waking, repetitive stimuli generate exogenous P1, N1 and P2 components of the auditory evoked potential (AEP). Deviant stimuli generate endogenous cognitive components including the mismatch negativity (MMN), N2 and P3 components. We examined long-latency auditory evoked potentials elicited by repetitive and deviant stimuli during waking and stage II-IV sleep to assess whether stimulus deviance is detected during sleep. The waking P1, N1b and P2 had maximal amplitudes at fronto-central scalp sites, with additional peaks (N1a, N1c) at temporal sites. Deviant tones generated a frontal maximal MMN, and complex novel tones generated an additional P3 component maximal at centro-parietal sites. During stages II-IV sleep N1a, b, c amplitudes were reduced. During stage II sleep all stimuli generated increased P2 amplitudes and a late negative component (N340). Deviant stimuli generated greater P2 and N340 amplitudes than frequent stimuli in stage II sleep, as well as an additional P420 component. In stage III-IV sleep the P420 was absent and the AEP was dominated by a negativity of long duration whose amplitude increased in response to deviant stimuli. These data indicate that auditory evoked activity changes from wakefulness to sleep. The differential response to deviant sounds observed during waking and all sleep stages supports the theory that selective processing of auditory stimuli persists during sleep.     

P300 and blink instructions.

OBJECTIVES: The effects of instructions to refrain from blinking on the P300 event-related brain potential (ERP) from auditory and visual stimuli were assessed. METHODS: An oddball paradigm was employed in which young adult subjects (n = 20) silently counted the infrequent target stimuli and were given either no instructions or told "do not blink" in different conditions, with auditory and visual stimulus tasks employed for all subjects. ERPs were recorded from the midline electrodes, with amplitude and latency of the P300 and other components obtained. RESULTS: P300 amplitude for both modalities and target/standard stimulus conditions was smaller and visual peak latency longer in the "do not blink" condition. Blink instructions did not directly affect the other components. CONCLUSIONS: Instructions to refrain from blinking can decrease P300 amplitude and can increase peak latency.     

A subcortical correlate of P300 in man

Event-related potentials in visual and auditory target detection tasks were recorded simultaneously from the scalp, somatosensory thalamus and periaqueductal gray in a chronic pain patient with electrodes implanted subcortically for therapeutic purposes. Short latency tactile responses confirmed the location of the thalamic electrodes. Rare auditory stimuli which were detected by the subject were accompanied by a prominent P300 component at the scalp, and by negative activity at the subcortical sites with the same latency as the scalp positivity. This activity was not seen in responses to frequent non-target stimuli and was not dependent on an overt motor response. Similarly, rare visual stimuli generated a scalp P300 and negative activity subcortically; both scalp and subcortical waves had a longer latency than in the auditory experiment. The reaction time was similarly longer to visual targets. These data are inconsistent with a hippocampal generator for P300, but are consistent with a generator in the thalamus or more dorsally located structures.     

Sex differences in perceptual processing: performance on the color-Kanji stroop task of visual stimuli

During color, colored Kanji characters and Stroop task of the visual stimuli, the P300 component of the event-related brain potential (ERPs) was used in conjunction with response time to identify sex differences in perceptual processing. Participants were instructed to respond to the display colors and name colored Kanji characters as quickly as possible in the respective stimulus conditions. Response time varied in all stimulus conditions, the males took longer than females. The P300 latency of males was longer and amplitude was smaller than females. The results suggest that cognitive strategy of males is different from females.     

SEX DIFFERENCES IN PERCEPTUAL PROCESSING: PERFORMANCE ON THE COLOR-KANJI STROOP TASK OF VISUAL STIMULI

During color, colored Kanji characters and Stroop task of the visual stimuli, the P300 component of the event-related brain potential (ERPs) was used in conjunction with response time to identify sex differences in perceptual processing. Participants were instructed to respond to the display colors and name colored Kanji characters as quickly as possible in the respective stimulus conditions. Response time varied in all stimulus conditions, the males took longer than females. The P300 latency of males was longer and amplitude was smaller than females. The results suggest that cognitive strategy of males is different from females.