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.     

Decreased response to novel stimuli after prefrontal lesions in man

Experiments were conducted to study the contribution of prefrontal cortex to the generation and modulation of two varieties of P300 activity. Control subjects generated typical parietal maximal P300 responses to detected target stimuli. Unexpected, novel auditory stimuli presented to controls generated an earlier latency, fronto-centrally distributed P300 response. A similar earlier latency, fronto-central P300 is generated to unexpected, novel visual stimuli. The occurrence of this phenomenon in both the auditory and visual modalities suggests that it may reflect neural activity of a common CNS system involved in the orienting response. Subjects with unilateral prefrontal damage generated P300 complexes to target stimuli that did not differ from the control responses. Prefrontal damage, however, resulted in a specific defect in the P300 response to the unexpected novel stimulus. Prefrontal patients showed neither N200 enhancement nor the fronto-central P300 response to the novel stimulus that was found in control subjects. These findings indicate that prefrontal regions are critical for the organism's response to unexpected novel stimuli. Abnormalities in prefrontal control of sensory-limbic integration may be a critical element in the decreased P300 to novel stimuli found in these unilateral prefrontal lesioned patients. It is suggested that major features of the human frontal lobe syndrome may be explained by a physiological inability to control attention and orientation systems after prefrontal damage.     

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.     

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.     

Dipolar source modeling of the P300 event-related potential after somatosensory stimulation.

The cerebral generators of the P300 potential evoked by somatosensory stimuli were investigated. Event-related potentials elicited by an oddball paradigm were recorded in 15 healthy subjects by 19 scalp electrodes. Nontarget and target electric stimuli were delivered on the anterior surface of the left elbow and of the wrist, respectively. Target traces showed an N140 potential followed by a widely distributed P300 response. Dipolar source modeling of target traces resulted in a six-dipole model. In the earlier latency range (up to 200 ms), one dipole in the contralateral perirolandic region and two dipoles in the parasylvian cortex of both hemispheres were activated. Two dipolar sources located bilaterally in the medial temporal region (MTR) showed their maximal activity at the P300 latency. Finally, a dipole in the contralateral frontal lobe was activated both at the latency of the N140 response and after 200 ms. It was found that two symmetrical MTR sources and a frontal dipole contributed to P300 generation.     

Age effects on the P300 to novel somatosensory stimuli.

Event-related brain potentials (ERPs) to somatosensory task-relevant targets and task-irrelevant novel (tactile and shock) stimuli were studied in 30 subjects between the ages of 18 and 79. Target and novel P300 latencies increased linearly with age at comparable rates. P300 amplitudes and scalp topographies also changed with age. P300 amplitudes remained constant at frontal sites and decreased at central and parietal sites for both target and novel stimuli with increasing age. The current results extend the age-related novel P300 changes reported in the auditory and visual modalities to the somatosensory system. The age-related amplitude reduction at posterior scalp sites supports independent contributions of frontal and posterior association cortex to P300 generation.     

Event-related brain potentials in response to novel sounds in dementia.

OBJECTIVE: Non-target, deviant stimuli generate an earlier latency, front-central novelty P3, whereas correctly detected task-relevant stimuli generate a parietal maximal target P3. We examined whether the P3 component to novel stimuli is affected by dementing processes, and is therefore useful for distinguishing Alzheimer's type dementia (AD) from vascular dementia (VD). METHODS: We recorded ERPs to task-relevant stimuli (target P3) and novel task-irrelevant stimuli (novelty P3) in an auditory oddball task in AD (n = 16), VD (n = 16), and age-matched controls (n = 18). The amplitude, latency, and scalp topography of target and novelty P3 were compared among 3 groups using ANOVA. The relationship between P3 measures and intelligence scores were evaluated by correlation analysis. RESULTS: The amplitude, latency and scalp topography of the target P3 were comparably affected by both AD and VD. However, the amplitude of the novelty P3 was markedly reduced in VD, but not in AD, and the scalp topographics were different in the 3 groups. The amplitude was maximal at frontal sites in controls, at central sites in AD, and at parietal sites in VD. The target P3 latency was prolonged in both AD and VD, whereas the novelty P3 latency was only prolonged in VD. AD was discriminated satisfactorily from VD by using the novelty amplitude at Cz and the ratio of the amplitudes at Fz and Pz as independent variables. CONCLUSIONS: These results suggest that the response to novel stimuli is differentially affected by dementia with degenerative and vascular etiology.     

The impact of motor activity on intracerebral ERPs: P3 latency variability in modified auditory odd-ball paradigms involving a motor task.

The P3 wave of event-related potentials was recorded with intracranial electrodes in 24 epileptic patients during the pre-surgical evaluation of epilepsy surgery. Three different cognitive auditory paradigms were used: (1) odd-ball paradigm with no output required (PGI) where patients had simply to recognize target tones, (2) odd-ball with motor response (PGII), where patients had to press a button in response to target tones, and (3) odd-ball with both counting task and motor response (PGIII), where patients had to recognize target tones, press a button in response to them, and count their number. The occurrence of P3 potential, its latency and amplitude, and the dependence of P3 latency on the task complexity were calculated. Identifiable P3 potentials in all the three paradigms were recorded from locations in mesial cortex (18 locations mesial temporal, eight locations mesial frontal, two locations mesial parietal) and lateral sites (eight sites lateral temporal, five lateral frontal, and two lateral parietal). P3 latency values ranged from 257 to 320 ms in all explored cortical areas when PGI was used; they significantly increased or decreased during PGII and PGIII, depending on the task and structure explored. In the mesial temporal cortex, the changes of P3 latency between paradigms were minimal. In the mesial parietal cortex, there was significant P3 delay in both PGII and PGIII relative to PGI. In the mesial frontal cortex, there was a significant latency decrease in PGII, and practically identical mean latency in PGI and PGIII. In all lateral cortices (temporal, frontal and parietal), there was always a P3 latency increase in PGII and PGIII relative to PGI, the most significant results being observed in the parietal and frontal lateral areas. The results support the multi-generator theory of P3. Prolongation of the mean P3 latency in lateral frontal and parietal cortices when the paradigm involved the execution of a motor task might reflect specific gating in this area during active movements, while the absence of modification in the temporal lobe may reflect minimal involvement of this region in motor planning or processing. The prolongation of mean P3 latency in practically all lateral structures in PGIII suggests that most cortical areas were involved in the cognitive functions needed for this test. The finding of reduction and subsequent prolongation of P3 latency in the mesial frontal cortex might reflect the unique specialization of this area and its specific involvement in motor processing.     

Somatosensory mismatch negativity in healthy children

Aim  Event-related potentials (ERPs) obtained when focused attention is kept away from the stimulus (unnoticed stimulation) are possibly linked to automatic mismatch-detection mechanisms, and could be a useful tool to investigate sensory discrimination ability. By considering the high impact of impaired somatosensory integration on many neurological disturbances in children, we aimed to verify whether mismatch-related responses to somatosensory stimulation could be obtained in healthy children.
Method  Eleven healthy participants (age range 6–11y, mean 8y 2mo, SD 1y 7mo; seven males, four females) underwent 'oddball' electrical stimulation of the right hand (80% frequent stimuli delivered to the thumb, 20% deviant stimuli delivered to the fifth finger). Data were compared with those obtained when the frequent stimuli to the thumb were omitted ('standard-omitted' protocol). ERPs were recorded at frontal, central, and parietal scalp locations. Children's overt attention was engaged by a demanding video game.
Results  In the oddball protocol, deviant stimulation elicited a left central negativity at about 160ms latency, followed by a left frontal negative response at about 220ms latency. Standard-omitted traces showed only a left parietal negative response spreading to right parietal regions.
Interpretation  Mismatch-related somatosensory responses can be reliably obtained in children, providing that appropriate technical contrivances are used. In clinical use, the frontal components, which are present only during the oddball protocol, could be a reliable and unequivocal neurophysiological marker of the automatic mismatch-detection mechanism.     

P22 and N30 of median nerve SSEPs--independence of the frontal waves from parietal waves

Median nerve short-latency somatosensory evoked potentials (MN-SSEPs) were recorded from the scalp to assess frontal lobe functions in children. Forty-nine patients, aged between three and fifty years old underwent 87 examinations. They were divided into four groups: A (3 to 4 years old); B (5 to 6 years old); C (7 to 15 years old) and D (20 to 50 years old). Stimulus electrodes were placed near the wrist on the median nerve. The study was done mostly in the waking state. To evaluate the independence of the frontal lobe from the parietal lobe we correlated the frontal P22 and parietal N20, and compared the frontal N30 with parietal negative waves. The intervals of the peak latency differed between P22 and N20 by -1.5 to 1.5 msec. Significant differences were noted between groups A and D, and between C and D. N30 and negative parietal waves resembled each other in children 3 to 4 years of age, but became different from 5 years old. They were dissimilar after 6 years old. Therefore, N30 waves were useful for evaluating the frontal elements in children over 5 years of age.     

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.     

Contributions of temporal-parietal junction to the human auditory P3

The P3 component of the event-related potential (ERP) is generated in humans and other mammalian species when attention is drawn to infrequent stimuli. We assessed the role of subregions of human posterior association cortex in auditory P3 generation in groups of patients with focal cortical lesions. Auditory P3s were recorded to target (P3b) and unexpected novel stimuli (P3a) in monaural and dichotic signal detection experiments. Two groups of patients were studied with lesions of: (1) temporal-parietal junction including posterior superior temporal plane and adjacent caudal inferior parietal cortex; and (2) the lateral parietal lobe including the rostral inferior parietal lobe and portions of superior parietal lobe. Extensive lateral parietal cortex lesions had no effect on the P3. In contrast, discrete unilateral lesions centered in the posterior superior temporal plane eliminated both the auditory P3b and P3a at electrodes over the posterior scalp. The results indicate that auditory association cortex in the human temporal-parietal junction is critical for auditory P3 generation.     

Mapping early somatosensory evoked potentials in selective attention: critical evaluation of control conditions used for titrating by difference the cognitive P30, P40, P100 and N140

Detailed procedures are described for the study of somatosensory event-related potentials (ERPs) to electric stimulation of fingers. Control responses to homogeneous (100%) series of identical stimuli (thus eliminating input mismatch) while the subject reads a novel (thus providing a distinct attention-capturing activity and maintaining vigilance level) are validated as reflecting the exogenous obligatory profiles required for assessing cognitive component in ERPs to target relevant stimuli. With these 'neutral' conditions, the control responses have a similar profile even at larger ISIs such as those separating the infrequent targets in Attention runs. Conversely, series of stimuli identical to those in control runs can elicit cognitive components in a 'Lie' experiment when the subject is induced to treat the stimuli like targets even though there is no discrimination involved. On this basis, the somatosensory P30, P40, P100 and N140 components appearing in the target profiles are considered genuine cognitive components. They have been analyzed with scatter displays, electronic subtraction, bit-mapped displays and with calculation of Z and dilation factors. The cognitive P30 and P40 reflect selective attention-related enhancements of the neural generators in receiving somatosensory cortex. The early parietal positivity P27 can thus be modulated separately from the frontal N30 component and is thought to be generated by a radial dipole in area 1. The later cognitive P100 and N140 reflect the invocation of distinct processors in conjunction with the behavioral use of the sensory input. The evolving topographical patterns of the P100 and N140 electrogeneses, revealed by bit-mapped data, suggest complex interactions between posterior parietal and prefrontal cortex whereby the sensory information is placed into spatial coordinate systems and matched with representations of relevant objects or relationships in space for target processing in the sequential tasks.     

Clinical neurophysiological study of verbal and non-verbal sound perception: normal development of P300 event-related potential to different sound stimuli

Developmental changes of P300 event related potential were evaluated in healthy children and adults aged from 7 to 29 years old, adopting 2 pairs of oddball stimuli: a non-verbal sound (tone burst: TB) pair and a verbal sound (VS) pair. P300 was evident for the target stimuli. In adult subjects, P300 was dominant at Pz for both stimuli. Peak latency of P300 was significantly longer for VS than for TB in both groups. P300 amplitude of the child group was higher than that of the adult group, however, there was no difference in P300 amplitude between stimuli conditions. Developmental changes of P300 from each stimuli condition were simulated by a quadratic equation. The age showing the shortest P300 peak latency was younger for TB (20.3 years) than for VS (23.6 years). The P300 peak latency reduced around 10 years old more rapidly for VS than for TB. In conclusion, there was no difference of the dominancy of P300 between the stimuli. The developmental changes of P300 were regulated by several components of the sound stimuli, such as their frequency.     

Mapping somatosensory evoked potentials to finger stimulation at intervals of 450 to 4000 msec and the issue of habituation when assessing early cognitive components

Somatosensory evoked potentials (SEPs) to mild electric stimulation of two fingers of the left hand were studied at regular interstimulus intervals (ISIs) of 450, 800, 1400, 2500 and 4000 msec. Habituation was evaluated while the subject was reading a novel so as to virtually ignore the finger stimuli while maintaining steady vigilance levels. Brain SEPs recorded from 25 scalp electrodes were assessed by scatter displays, electronic subtraction, bit-mapped potential fields, and by calculating the Z estimator and dilation factor. Similar results were obtained with randomly varying ISIs. The P14 farfield and cortical N20 did not change with ISIs. The parietal P27-P45 decreased at ISIs of 800 and 450 msec, but showed no significant habituation at ISIs of 1400, 2500 or 4000 msec. This validated the control conditions used for assessing the early cognitive P30 and P40 to attended target stimuli. The frontal N30 also decremented the shorter ISIs but still habituated up to ISIs of 2500 msec. The clear dissociation between frontal N30 and parietal P27 at the larger ISIs suggests that they involve at least in part distinct neural generators.     

Luminance and spatial attention effects on early visual processing

Event-related potentials (ERPs) were recorded from healthy subjects in response to unilaterally flashed high and low luminance bar stimuli presented randomly to left and right field locations. Their task was to covertly and selectively attend to either the left or right stimulus locations (separate blocks) in order to detect infrequent shorter target bars of either luminance. Independent of attention, higher stimulus luminance resulted in higher ERP amplitudes for the posterior N95 (80–110 ms), occipital P1 (110–140 ms), and parietal N1 (130–180 ms). Brighter stimuli also resulted in shorter peak latency for the occipital N1 component (135–220 ms); this effect was not observed for the N1 components over parietal, central or frontal regions. Significant attention-related amplitude modulations were obtained for the occipital P1, occipital, parietal and central N1, the occipital and parietal P2, and the parietal N2 components; these components were larger to stimuli at the attended location. In contrast to the relatively short latencies of both spatial attention and luminance effects, the first interaction between luminance and spatial attention effects was observed for the P3 component to the target stimuli (350–750 ms). This suggests that interactions of spatial attention and stimulus luminance previously reported for reaction time measures may not reflect the earliest stages of sensory/perceptual processing. Differences in the way in which luminance and attention affected the occipital P1, occipital N1 and parietal N1 components suggest dissociations among these ERPs in the mechanisms of visual and attentional processing they reflect. Nonetheless, scalp current density mappings of the attention effects throughout the latency ranges of the P1 and N1 components show the most prominent attention-related activity to be in lateral occipital scalp areas. Such a pattern is consistent with the spatially selective filtering of information into the ventral stream of visual processing which is reponsible for complex feature analysis and object identification.     

Visual P3a in male subjects at high risk for alcoholism.

BACKGROUND: Voltage of the P300 component of event-related potentials (ERPs) has been proposed as a phenotypic marker of risk for alcoholism. P3a elicited by intrusive events is important in the context of deficits in inhibition found during psychophysiological and behavioral evaluations in children of alcoholics. METHODS: ERPs were recorded from a group of adult children of alcoholics (n = 26) and controls (n = 23) with a three-stimulus visual oddball paradigm. The task required a difficult perceptual discrimination between a frequent (.80) vertical line and an infrequent (.10) 2 degrees tilted line (target). An easily discriminable nontarget infrequent horizontal line also occurred (.10). Subjects were required to press a button to the target. P3a was compared using mixed-model ANCOVAs at 31 sites organized in 5 scalp regions. Current source density (CSD) maps were also analyzed. RESULTS: High-risk (HR) subjects manifested reduced P3a amplitudes compared to controls at frontal, central, parietal, and temporal electrodes. CSD analyses supported these findings with group differences found for all the scalp regions. CONCLUSIONS: The results are discussed in relation to previous HR studies. P3a reductions may be related to deficits in neuronal inhibition during stimulus processing. These results suggest that P3a amplitude may be important as a marker for vulnerability to alcoholism.     

Impaired novelty detection and frontal lobe dysfunction in Parkinson's disease

Recent evidence suggests that the frontal lobe plays an important role in an orienting response to novel events, and that frontal lobe dysfunction is linked to attentional and cognitive deficits in Parkinson's disease (PD). We tested the hypothesis that the neural network involved in novelty detection may be impaired in PD patients by studying event-related brain potentials to target and novel stimuli and their correlation to performance in neuropsychological tests in non-demented PD patients. The PD patients showed prolonged P3 latency to novel stimuli compared with age-matched controls, whereas their P3 latency to target stimuli was not different from that in controls. The PD patients also manifested amplitude reduction and less habituation of the P3 to novel stimuli over frontal scalp sites compared with controls. The prolonged latency and frontal reduction of novelty P3 correlated with a poor performance in the Wisconsin Card Sorting Test. These results suggest that the orienting response of PD patients to novel events is impaired and that recording novelty P3 might provide a neurophysiological and quantitative measure of attentional and cognitive deficits linked to the frontal lobe in non-demented PD patients.     

Auditory event-related potentials in the squirrel monkey: Parallels to human late wave responses

Event-related potentials (ERPs) were recorded from the brain surface in squirrel monkeys during the presentation of two auditory stimulus paradigms which have previously been utilized to elicit scalp-recorded ERPs in humans. In the first paradigm, inter-stimulus interval (ISI) was systematically varied during the presentation of a series of tone pips. The tones produced a negative (70 ms)-positive (130 ms) sequence of components similar in morphology to the human scalp-recorded N1-P2 'vertex' potential. The amplitude of the N70 and P130 components recorded from midline electrodes decreased with decreasing ISI, as previously shown for the human vertex potential. However, this amplitude change with ISI was not observed in ERPs recorded from lateral frontal and temporal electrodes. These results agree with previous studies of monkeys and humans which suggest at least two different sources contribute to N1-P2 components recorded in response to tones. The effects of stimulus probability and novelty on ERP morphology and amplitude were studied in the second paradigm. ERPs elicited by frequent (P = 0.92) and infrequent (P = 0.08) tone pips presented in an unpredictable order were compared. N70 - P130 components were produced by both stimuli, and the infrequent stimuli also elicited a broad, long latency (300 ms) positive complex that decreased in amplitude with repeated presentations. In humans the same infrequent auditory stimuli produce a frontally distributed late positive component that has been interpreted as indicating the activation of orientation mechanisms or of a 'mismatch detector'. These data suggest that in these paradigms squirrel monkeys exhibit ERPs which are similar in several respects to ERPs recorded to identical stimuli in humans.     

Age-related loss in attention-based modulation of tactile stimuli at early stages of somatosensory processing

Normal aging has been linked to impairments in gating of irrelevant sensory information and neural markers of diminished cognitive processing. Whilst much of the research in this area has focussed on visual and auditory modalities it is unclear to what degree these findings apply to somatosensation. Therefore we investigated how age impacts early event-related potentials (ERPs) arising from relevant or irrelevant vibrotactile stimuli to the fingertips. Specifically, we hypothesised that older adults would demonstrate reduced attention-based modulation of tactile ERPs generated at early stages of cortical somatosensory processing. In accord with previous research we also expected to observe diminished P300 responses to attended targets and behavioural deficits. Participants received vibrotactile stimulation to the second and fifth digit on the left hand and reported target stimuli on one digit only (as instructed) with comparisons between two age groups: (1) Young adults (age range 20-39) and (2) Older adults (age range 62-89). ERP amplitudes for the P50, N70, P100, N140 and long latency positivity (LLP) were quantified for attended and non-attended trials at several electrodes (C4, CP4, CP3 and FC4). The P300 in response to attended target stimuli was measured at CPZ. There was no effect of attention on the P50 and N70 however the P100, N140 and LLP were modulated with attention. In both age groups the P100 and LLP were more positive during trials where the stimuli were attended to, whilst the N140 was enhanced for non-attended stimuli. Comparisons between groups revealed a reduction in P100 attention-based modulation for the older adults versus the young adults. This effect was due to a loss of suppression of the non-attended stimuli in older subjects. Moreover, the P300 was both slower and reduced in peak amplitude for older subjects in response to attended targets. Finally, older adults demonstrated impaired performance in terms of both reduced target detection accuracy and in reporting more false positives. Overall, present results reveal a deficit in suppressing irrelevant tactile information during an attention-demanding task which possibly relates to reduced markers of performance. Such a loss of inhibitory function is consistent with age-related change associated with a decline in executive control via prefrontal regions.