Response Inhibition Processes Research Articles

Dissociable influences of NR2B-receptor related neural transmission on functions of distinct associative basal ganglia circuits

Glutamate is an important excitatory neurotransmitter within functional prefrontal-basal ganglia loops. These distinct loops mediate different cognitive functions. One function of the anterior-cingulate loop is error processing. One function of the orbito-frontal loop is response inhibition. These functions are altered in several neuro-psychiatric disorders like Huntington's disease (HD). Because of the known role of the GRIN2B C2664T polymorphism in HD neuropathology, which is partly due to increased glutamatergic neural transmission, we analyze how this polymorphism influences error processing and response inhibition in a sample of healthy probands (N=65).Combining a genetic approach with event-related potential (ERP) measurements of response inhibition (OFC-loop function) and error processing (ACC-loop function), we provide robust results showing a selective modulation of response inhibition processes by the GRIN2B C2664T polymorphism at the behavioural and neurophysiological level. Response inhibition processes were stronger in the CT/TT genotype group, compared to the CC genotype group. Since error processing functions were not affected, the results suggest for differential influences of the GRIN2B C2664T polymorphism on response inhibition and error processing functions. The results provide first insight into cognitive-neurophysiological effects of the GRIN2B C2664T polymorphism. The dissociation obtained may be due to a differential importance of N-methyl-d-aspartate receptors for glutamatergic neural transmission in different striatal compartments (matrix and striosomes). We provide a model on this that may be a target for future research.

Single-trial EEG Power and Phase Dynamics Associated with Voluntary Response Inhibition

Human voluntary response inhibition has frequently been investigated using go/no-go RT tasks. Recent studies have indicated that not only the traditional averaging waveforms of EEG activities (ERPs) but also the power and phase dynamics of single-trial EEG are important in studying the neural correlates of various human cognitive functions. Therefore, here, we aimed to undertake a detailed study of the time/frequency power and phase dynamics of single-trial EEG during go/no-go RT tasks, with focus particularly on the no-go-specific power and phase dynamics, which are presumed to involve the voluntary response inhibition processes. Thus, we demonstrated no-go-specific theta band EEG power increases and intertrial phase-locking in the midline-frontal areas, which are related to no-go-specific midline-frontal negative-positive ERP waveforms (no-go N2/no-go P3). In addition, we observed no-go-specific alpha band EEG intertrial phase-locking with an adjacent dephasing phenomenon, which is mainly associated with the early part of no-go N2. The estimated time point when the no-go-specific midline-frontal dephasing phenomenon occurred corresponded to the initial part of the voluntary response inhibition process (decision to withhold). Moreover, the no-go-specific phase dynamics in the midline-frontal areas just before and around the no-go N2 peak latency, unlike the power modulations, were affected by changes in the no-go stimulus probability, suggesting the dependence of only phase dynamics on no-go stimulus probability. From these results, we conclude that the complex power and phase dynamics of the theta and alpha band EEG in the midline-frontal areas are specific to no-go trials, being the underlying bases of the no-go-specific ERP waveforms, and suggest that the phase dynamics just before and around the no-go N2 peak latency may involve, at least, the initial part of the voluntary response inhibition process (decision to withhold).

Distinct frontal systems for response inhibition, attentional capture, and error processing

Stopping an action in response to an unexpected event requires both that the event is attended to, and that the action is inhibited. Previous neuroimaging investigations of stopping have failed to adequately separate these cognitive elements. Here we used a version of the widely used Stop Signal Task that controls for the attentional capture of stop signals. This allowed us to fractionate the contributions of frontal regions, including the right inferior frontal gyrus and medial frontal cortex, to attentional capture, response inhibition, and error processing. A ventral attentional system, including the right inferior frontal gyrus, has been shown to respond to unexpected stimuli. In line with this evidence, we reasoned that lateral frontal regions support attentional capture, whereas medial frontal regions, including the presupplementary motor area (pre-SMA), actually inhibit the ongoing action. We tested this hypothesis by contrasting the brain networks associated with the presentation of unexpected stimuli against those associated with outright stopping. Functional MRI images were obtained in 26 healthy volunteers. Successful stopping was associated with activation of the right inferior frontal gyrus, as well as the pre-SMA. However, only activation of the pre-SMA differentiated stopping from a high-level baseline that controlled for attentional capture. As expected, unsuccessful attempts at stopping activated the anterior cingulate cortex. In keeping with work in nonhuman primates these findings demonstrate that successful motor inhibition is specifically associated with pre-SMA activation.

Acute citalopram administration may disrupt contextual information processing in healthy males

Selective serotonin reuptake inhibitors (SSRI) are the most commonly prescribed antidepressants. It has been suggested however that SSRI administration may affect response inhibition and contextual processing but the available evidence is minimal. Therefore, the purpose of this study was to identify the effect size of acute (within 24 hours) and chronic (28 days) administration of the highly selective SSRI, Citalopram, compared to placebo on response inhibition (measured by the Degraded Symbol Continuous Performance Task [DS-CPT]) and contextual processing (assessed using a Delayed Non-Matching to Sample Task [DNMS]) in healthy males (n=20) using a randomised double-blind design. We found no effect of Citalopram on participants' performance on the DS-CPT which suggests either that SSRIs do not affect response inhibition or that this measure is insensitive to any potential disinhibition effects of SSRI. Acute, but not chronic, Citalopram administration was associated with a measurable decrement in the DNMS suggestive of a negative impact of SSRI administration on contextual processing at least during treatment initiation. These findings provide a useful guide for designing future studies in clinical populations.

The Influence of Alcohol Ingestion on Cognitive Response Inhibition and Error Processing

Alcohol consumption has been known to affect behavior and cognition. In this paper, we review evidence for the idea that alcohol disrupts two important cognitive processes critical to flexible interaction with a changing environment: the individual’s ability to successfully and intentionally inhibit or suppress a prepotent response, and to detect the occurrence of an error. In compromising an individual’s ability to withhold a prepotent response and in attenuating the brain’s capacity to detect action slips, the consumption of alcohol may also prevent the mobilization of further flexible executive control in response to environmental prompts (e.g., to stop drinking when intending to drive a car). Individual differences in these cognitive processes prior to or following the ingestion of alcohol are also discussed.

Electrophysiological evidence for abnormal preparatory states and inhibitory processing in adult ADHD

BackgroundAttention deficit hyperactivity disorder (ADHD) is a common neurodevelopmental disorder that starts in childhood and frequently persists in adults. Several theories postulate deficits in ADHD that have effects across many executive functions or in more narrowly defined aspects, such as response inhibition. Electrophysiological studies on children, however, indicate that ADHD is not associated with a core deficit of response inhibition, as abnormal inhibitory processing is typically preceded or accompanied by other processing deficits. It is not yet known if this pattern of abnormal processing is evident in adult ADHD.MethodsThe objective of this paper was to investigate event-related potential indices of preparatory states and subsequent response inhibition processing in adults with ADHD. Two cued continuous performance tasks were presented to 21 adults meeting current criteria for adult ADHD and combined type ADHD in childhood, and 20 controls.ResultsThe ADHD group exhibited significantly weaker orienting attention to cues, cognitive preparation processes and inhibitory processing. In addition, we observed a strong correlation between the resources allocated to orienting to cues and the strength of the subsequent response strength control processes, suggesting that orienting deficits partly predict and determine response control deficits in ADHD.ConclusionsThese findings closely resemble those previously found in children with ADHD, which indicate that there is not a core response inhibition deficit in ADHD. These findings therefore suggest the possibility of developmental stability into adulthood of the underlying abnormal processes in ADHD.

Paradoxical association of the brain-derived-neurotrophic-factor val66met genotype with response inhibition

Response inhibition is a basic executive function which is dysfunctional in various basal ganglia diseases. The brain-derived-neurotrophic-factor (BDNF) plays an important pathophysiological role in these diseases. In the current study we examined the functional relevance of the BDNF val66met polymorphism for response inhibition processes in 57 healthy human subjects using event-related potentials (ERPs), i.e. the Nogo-N2 and Nogo-P3, which likely reflect different aspects of inhibition. Our results support the pre-motor inhibition theory of the Nogo-N2. We show that the BDNF val66met polymorphism selectively modulates the Nogo-N2. Response inhibition was better in the val/met–met/met group, since this group committed fewer false alarms, and their Nogo-N2 was larger, compared to the val/val group. This is the first study showing that met alleles of the BDNF val66met polymorphism confer an advantage for a specific cognitive function. We propose a neuronal model how this advantage gets manifest on a neuronal level.

Sport is not always healthy: Executive brain dysfunction in professional boxers

We measured ERPs of professional boxers in a Go/No-Go task, comparing them to fencers and non-athletes. Results showed that fencing improved attention and motor response control, but boxing did not. More strikingly, in boxers, as in brain trauma patients, the P3 component was delayed and reduced. The P3 delay of boxers was correlated with the amount of performed sport exercise. Furthermore, in terms of behavior, boxers showed increased intra-individual variability and switch cost. Results were consistent with the hypothesis of specific impairment at the level of response inhibition processing. We suggest that this impairment is derived from the cumulative effect of blows to the head. The changes found in boxers suggest that ERPs and reaction times may be a tool for early detection of specific brain dysfunction.

The Effects of Fetal Alcohol Syndrome on Response Execution and Inhibition: An Event‐Related Potential Study

Both executive function deficits and slower processing speed are characteristic of children with fetal alcohol exposure, but the temporal dynamics of neural activity underlying cognitive processing deficits in fetal alcohol spectrum disorder have rarely been studied. To this end, event-related potentials (ERPs) were used to examine the nature of alcohol-related effects on response inhibition by identifying differences in neural activation during task performance. We recorded ERPs during a Go/No-go response inhibition task in 2 groups of children in Cape Town, South Africa (M age = 11.7 years; range = 10 to 13)-one diagnosed with fetal alcohol syndrome (FAS) or partial FAS (FAS/PFAS; n = 7); the other, a control group whose mothers abstained or drank only minimally during pregnancy (n = 6). Children were instructed to press a "Go" response button to all letter stimuli presented except for the letter "X," the "No-go" stimulus, which occurred relatively infrequently. Task performance accuracy and reaction time did not differ between groups, but differences emerged for 3 ERP components-P2, N2, and P3. The FAS/PFAS group showed a slower latency to peak P2, suggesting less efficient processing of visual information at a relatively early stage ( approximately 200 ms after stimulus onset). Moreover, controls showed a larger P2 amplitude to Go versus No-go, indicating an early discrimination between conditions that was not seen in the FAS/PFAS group. Consistent with previous literature on tasks related to cognitive control, the control group showed a well-defined, larger N2 to No-go versus Go, which was not evident in the FAS/PFAS group. Both groups showed the expected larger P3 amplitude to No-go versus Go, but this condition difference persisted in a late slow wave for the FAS/PFAS group, suggesting increased cognitive effort. The timing and amplitude differences in the ERP measures suggest that slower, less efficient processing characterizes the FAS/PFAS group during initial stimulus identification. Moreover, the exposed children showed less sharply defined components throughout the stimulus and response evaluation processes involved in successful response inhibition. Although both groups were able to inhibit their responses equally well, the level of neural activation in the children with FAS/PFAS was greater, suggesting more cognitive effort. The specific deficits in response inhibition processing at discrete stages of neural activation may have implications for understanding the nature of alcohol-related deficits in other cognitive domains as well.

Response inhibition subprocesses and dopaminergic pathways: Basal ganglia disease effects

Response inhibition is a component of executive functions, which can be divided into distinct subprocesses by means of event-related potentials (ERPs). These subprocesses are (pre)-motor inhibition and inhibition monitoring, which are probably reflected by the Nogo-N2 and Nogo-P3, respectively. Here we ask, if these subprocesses may depend on distinct basal ganglia subsystems. We examined response inhibition processes in an extended sample of young and elderly subjects, patients with Parkinson's disease (PD) and Huntington’ disease (HD). This combination of groups also allow us to study whether, and to what degree, pathological basal ganglia changes and healthy aging have similar and/or different effects on these processes. We show that subprocesses of response inhibition are differentially modulated by distinct basal ganglia circuits. Processes related to (pre)-motor inhibition appear to be modulated by the nigrostriatal system, and are sensitive to aging and age-related basal ganglia diseases (i.e. PD). Parkinson's disease induces additive effects of aging and pathology. In contrast, inhibition monitoring is most likely modulated by the mesocortico-limbic dopamine system. These processes are equally affected in healthy aging and both basal ganglia diseases (i.e. PD, HD).

Structural and functional brain correlates of subclinical psychotic symptoms in 11–13 year old schoolchildren

Studying children experiencing psychotic symptoms provides a unique opportunity to examine the vulnerability to psychosis within the context of development. Using neuroimaging techniques this study investigated cognitive control functions, brain volumetrics and white matter integrity in an at-risk cohort of children. Between-subjects assessment of brain function and structure among 11 school-going, non-treatment seeking children aged 11–13 who were at symptomatic risk for psychosis (AR) and 14 healthy control children aged 11–12 without subclinical psychotic symptoms (CON). MRI assessments included functional measures of response inhibition and error-related processes, whole brain voxel-based morphometry (VBM) of gray matter (GM) and diffusion tensor imaging (DTI) utilizing fractional anisotropy to probe white matter (WM) integrity. fMRI results showed reduced activity in the AR group within right frontal and bilateral temporal cortex for response inhibition and reduced activity within the anterior cingulate, insula and middle frontal gyrus for error-related processing (p<.05, corrected). VBM analysis revealed GM increases in the AR group within middle and superior temporal gyri, angular gyrus, orbitofrontal gyrus and GM decrease within the inferior temporal gyrus (p<.05, corrected). DTI analysis identified WM decreases in the AR group along the inferior fronto–occipital fasciculus, cingulum and inferior longitudinal fasciculus (p<.05, corrected). This multimodal investigation revealed aberrant prefrontal–temporal dysfunction in addition to cingulate and insular dysfunctions which provide potential early neurocognitive risk markers related to the susceptibility for developing psychosis and subsequently the neurodevelopmental trajectory leading to schizophrenia.

Functional developmental changes underlying response inhibition and error-detection processes

This study examined the developmental trajectories associated with response inhibition and error processing as exemplar executive processes. We present fMRI data showing developmental changes to the functional networks underlying response inhibition and error-monitoring, comparing activation between adults and young adolescents performing the sustained attention to response task (SART). During successful inhibitions, we observed greater activation for the young adolescents than for the adults, in a widely distributed network including frontal, parietal and medial regions. When inhibition failed, however, adults showed increased activation compared to young adolescents in a number of regions, including bilateral parahippocampal gyrus, left and right lingual gyri, the right insula, and cerebellar regions. These differences largely remained even when the two groups were matched for performance, suggesting that performance differences are unlikely to be the driving factor behind these developmental differences. Instead, the neurodevelopmental trajectory of these important executive functions may reveal the basis for the immature executive functioning of the young adolescent.

Activation of the pre-supplementary motor area but not inferior prefrontal cortex in association with short stop signal reaction time – an intra-subject analysis

BackgroundOur previous work described the neural processes of motor response inhibition during a stop signal task (SST). Employing the race model, we computed the stop signal reaction time (SSRT) to index individuals' ability in inhibitory control. The pre-supplementary motor area (preSMA), which shows greater activity in individuals with short as compared to those with long SSRT, plays a role in mediating response inhibition. In contrast, the right inferior prefrontal cortex (rIFC) showed greater activity during stop success as compared to stop error. Here we further pursued this functional differentiation of preSMA and rIFC on the basis of an intra-subject approach.ResultsOf 65 subjects who participated in four sessions of the SST, we identified 30 individuals who showed a difference in SSRT but were identical in other aspects of stop signal performance between the first ("early") and last two ("late") sessions. By comparing regional brain activation between the two sessions, we confirmed greater preSMA but not rIFC activity during short as compared to long SSRT session within individuals. Furthermore, putamen, anterior cerebellum and middle/posterior cingulate cortex also showed greater activity in association with short SSRT.ConclusionThese results are consistent with a role of medial prefrontal cortex in controlled action and inferior frontal cortex in orienting attention. We discussed these findings with respect to the process of attentional monitoring and inhibitory motor control during stop signal inhibition.

Inhibition, Reinforcement Sensitivity and Temporal Information Processing in ADHD and ADHD+ODD: Evidence of a Separate Entity?

This study compared children with ADHD-only, ADHD+ODD and normal controls (age 8–12) on three key neurocognitive functions: response inhibition, reinforcement sensitivity, and temporal information processing. The goal was twofold: (a) to investigate neurocognitive impairments in children with ADHD-only and children with ADHD+ODD, and (b) to test whether ADHD+ODD is a more severe from of ADHD in terms of neurocognitive performance. In Experiment 1, inhibition abilities were measured using the Stop Task. In Experiment 2, reinforcement sensitivity and temporal information processing abilities were measured using a Timing Task with both a reward and penalty condition. Compared to controls, children with ADHD-only demonstrated impaired inhibitory control, showed more time underestimations, and showed performance deterioration in the face of reward and penalty. Children with ADHD+ODD performed in-between children with ADHD-only and controls in terms of inhibitory controls and the tendency to underestimate time, but were more impaired than controls and children with ADHD-only in terms of timing variability. In the face of reward and penalty children with ADHD+ODD improved their performance compared to a neutral condition, in contrast to children with ADHD-only. In the face of reward, the performance improvement in the ADHD+ODD group was disproportionally larger than that of controls. Taken together the findings suggest that, in terms of neurocognitive functioning, comorbid ADHD+ODD is a substantial different entity than ADHD-only.

Sub-centimeter scale functional organization in human inferior frontal gyrus

Functional areas in sensory/motor cortices are usually organized, on a finer scale, in a seamless manner along related functional units that represent, for example, certain visual fields to analyze and certain body parts to control. However, fine-scale functional organization in the prefrontal cortex has rarely been reported. In the present functional magnetic resonance imaging study, we show an example of sub-centimeter scale functional organization in the posterior part of the inferior frontal gyrus (IFG) in the right hemisphere. The spatial relationship was examined in the same subjects with regard to the activations associated with response inhibition and negative feedback processing, which are known to activate similar right IFG regions. We found that these activations were segregated, the activation during response inhibition being more caudal than that during feedback processing, and that the distance between the two activations was only 8.7 mm. Examination of the two-dimensional surface mapping of individual subjects confirmed that the two activations were located in adjacent but different regions. These results provide a specific example of a pair of functionally characterized regions that are located in the close vicinity within the right IFG.

Electrophysiological manifestations of stimulus evaluation, response inhibition and motor processing in Tourette syndrome patients

Gilles de la Tourette syndrome (GTS) is a neuropsychiatric disorder with childhood onset presenting with multiple fluctuating motor tics and one or more phonic tics. A significant proportion of people suffering from GTS are still symptomatic in adulthood and present other emotional and cognitive difficulties, along with motor problems that often accompany these comorbid conditions. The nature of these difficulties is still poorly understood and multiple comorbidities are often inadequately controlled. The current study investigates both stimulus evaluation and motor processing in GTS while controlling for comorbidity. Fifteen adults with GTS and 20 control participants were matched on gender, laterality and intelligence. The P300 component, the no-go anteriorization (NGA) as well as the stimulus and response-locked lateralized-readiness potentials (S-LRP, R-LRP) were elicited during a stimulus–response compatibility (SRC) paradigm. The standard version of the Stroop Color–Word Test (SCWT) was also administered. Reaction times showed that participants with GTS processed both the SRC and the SCWT more rapidly than the control group, while producing a delayed P300 peak latency. The GTS group also showed faster S-LRP onset in response to the incompatible and faster processing of interference in the SCWT. There was also a tendency toward a greater frontal shift of the NGA in the GTS group. The P300 latency showed that with GTS patients, stimulus evaluation occurs later whereas the overlapping pre-motor response selection processes occur faster. Our findings are congruent with a probable cortical motor over-activation hypothesis of GTS involving faster motor program selection in processing conflicting SR configuration.

Auditory-induced emotion modulates processes of response inhibition: an event-related potential study

This study investigated the impact of auditory-induced emotion on response inhibition. Fifty kinds of positive, neutral, and negative sounds were used as emotional materials whose presentation was followed by a Go/Nogo task. Event-related potentials were recorded for Go and Nogo tones. The response times for Go stimuli were longer under negative than under positive and neutral emotions. In addition, Go and Nogo stimuli elicited larger N1 amplitudes during neutral than during emotional conditions. Moreover, Nogo-related N2 was larger for neutral sounds than for positive and negative sounds. The Nogo-N2, however, was not different between positive and negative sounds. Therefore, auditory-induced emotions significantly modulated the behavioral performance and the process of response conflict monitoring, a central component to the activity of response inhibition.

A no-go related prefrontal negativity larger to irrelevant stimuli that are difficult to suppress

BackgroundThere is a wide debate in the literature about whether N2/P3 effects in no-go trials reflect the inhibition of an intended action, or the absence of a negative movement-related potential typical of go trials. The aim of this study was to provide an objective measure of the suppression of irrelevant information (in a conjoined selective visual attention task) under conditions that were perfectly comparable from the viewpoint of the motoric processes involved.MethodsTwenty-nine right-handed students took part in the study. Their EEGs were recorded from 128 scalp sites while they viewed gratings of four different spatial frequencies (from 0.75 to 6 c/deg) randomly flashed in the four upper and lower quadrants of the visual field. The tasks consisted of attending and responding to a conjunction of spatial frequency and space location. Intermediate frequencies (1.5 and 3 c/deg) acted as distracters or lures. Analysis of the ERPs elicited by the same physical stimulus, close in spatial frequency to the actual target and falling within the attended quadrant (pseudo-target) vs. a non-target location, allowed us to identify the time course and neural bases of brain activation during the suppression of irrelevant information.ResultsFAs were on average 9% for pseudo-targets and 0.2% for other types of lures, indicating that the former were more difficult to suppress. Target-related ERP components (occipito/temporal selection negativity, posterior P3b and precentral motor N2) were greater to pseudo-targets than other distracters. A large prefrontal negativity (370–430 ms) was also identified, much larger to pseudo-targets than non-targets (and absent in response to real targets), thus reflecting response inhibition and top-down cognitive control processes.ConclusionA LORETA inverse solution identified the neural generators of this effect in the left dorsolateral prefrontal cortex (DLPF), left and right fusiform gyri and bilateral superior temporal cortices. The tentative hypothesis is advanced that these activations might reflect the modulatory effects exerted by the fronto/temporal circuit for the suppression of irrelevant information.

Dissociating interference-control processes between memory and response.

The ability to mitigate interference is of central importance to cognition. Previous research has provided conflicting accounts about whether operations that resolve interference are singular in character or form a family of functions. Here, the authors examined the relationship between interference-resolution processes acting on working memory representations versus responses. The authors combined multiple forms of interference into a single paradigm by merging a directed-forgetting task, which induces proactive interference, with a stop-signal task, which taps response inhibition processes. The results demonstrated that proactive interference and response inhibition produced distinct behavioral signatures that did not interact. By contrast, combining two different measures of response inhibition by merging a go/no-go task variant and a stop signal produced overadditive behavioral interference, demonstrating that different forms of response inhibition tap the same processes. However, not all forms of response conflict interacted, suggesting that inhibition-related functions acting on response selection are dissociable from those acting on response inhibition. These results suggest that inhibition-related functions for memory and responses are dissociable.

Alpha Brain Oscillations and Inhibitory Control

A major challenge for developmental cognitive neuroscience is to understand how changes in cognitive functions related to aging are associated with changes in the neuronal information processing architecture. Previous studies on EEG event-related brain oscillations suggest functional changes in alpha-bands with age during sensory and memory tasks. Specifically, the topographical distribution of both single-trial lower and upper alpha magnitude and the corresponding phase coherence is altered in elderly persons. Thus, alpha oscillations, associated not only with sensory, but also with sensorimotor functions, may be altered with age. Compensatory mechanisms, possibly reflected in increased frontal alpha synchronization, may thereby be of profound relevance. The present study investigates age-related differences in the modulation of alpha oscillatory activity related to sensory and sensorimotor functions, including response preparation, execution, and inhibition. EEG was recorded while 10 young and 10 elderly persons performed a visual evoked potential (VEP), a cued stimulus response (S-R), and a cued visual Go&amp;#47;NoGo task. Early event-related synchronization (ERS, 0&amp;#8211;250 ms) and late event-related desynchronization (ERD, 200&amp;#8211;600 ms) of single-trial lower and upper alpha was analyzed using poststimulus amplitude enhancement and intertrial phase coherence measures. The results show comparable modulations of lower (8&amp;#8211;10 Hz) and upper (10&amp;#8211;15 Hz) alpha activity in young and elderly related to the sensory and different forms of motor response processing. Specifically, reduced early lower alpha ERS as well as late upper alpha ERD at central locations characterized response inhibition processing in both age groups. We discuss the counterintuitive hypothesis that reduced efficacy of some basal neural inhibitory mechanisms enables older observers to perform better than or comparable to younger observers on some visual tasks, and conclude that alterations in alpha oscillatory networks with age may depend on the stimuli applied.