The transverse occipital sulcus and intraparietal sulcus show neural selectivity to object-scene size relationships

To optimize visual search, humans attend to objects with the expected size of the sought target relative to its surrounding scene (object-scene scale consistency). We investigate how the human brain responds to variations in object-scene scale consistency. We use functional magnetic resonance imaging and a voxel-wise feature encoding model to estimate tuning to different object/scene properties. We find that regions involved in scene processing (transverse occipital sulcus) and spatial attention (intraparietal sulcus) have the strongest responsiveness and selectivity to object-scene scale consistency: reduced activity to mis-scaled objects (either unusually smaller or larger). The findings show how and where the brain incorporates object-scene size relationships in the processing of scenes. The response properties of these brain areas might explain why during visual search humans often miss objects that are salient but at atypical sizes relative to the surrounding scene.

Blind Visualization of Task-Related Networks From Visual Oddball Simultaneous EEG-fMRI Data: Spectral or Spatiospectral Model?

Various disease conditions can alter EEG event-related responses and fMRI-BOLD signals. We hypothesized that event-related responses and their clinical alterations are imprinted in the EEG spectral domain as event-related (spatio)spectral patterns (ERSPat). We tested four EEG-fMRI fusion models utilizing EEG power spectra fluctuations (i.e., absolute spectral model - ASM; relative spectral model - RSM; absolute spatiospectral model - ASSM; and relative spatiospectral model - RSSM) for fully automated and blind visualization of task-related neural networks. Two (spatio)spectral patterns (high δ 4 band and low β 1 band) demonstrated significant negative linear relationship (p FWE < 0.05) to the frequent stimulus and three patterns (two low δ 2 and δ 3 bands, and narrow θ 1 band) demonstrated significant positive relationship (p < 0.05) to the target stimulus. These patterns were identified as ERSPats. EEG-fMRI F-map of each δ 4 model showed strong engagement of insula, cuneus, precuneus, basal ganglia, sensory-motor, motor and dorsal part of fronto-parietal control (FPCN) networks with fast HRF peak and noticeable trough. ASM and RSSM emphasized spatial statistics, and the relative power amplified the relationship to the frequent stimulus. For the δ 4 model, we detected a reduced HRF peak amplitude and a magnified HRF trough amplitude in the frontal part of the FPCN, default mode network (DMN) and in the frontal white matter. The frequent-related β 1 patterns visualized less significant and distinct suprathreshold spatial associations. Each θ 1 model showed strong involvement of lateralized left-sided sensory-motor and motor networks with simultaneous basal ganglia co-activations and reduced HRF peak and amplified HRF trough in the frontal part of the FPCN and DMN. The ASM θ 1 model preserved target-related EEG-fMRI associations in the dorsal part of the FPCN. For δ 4, β 1, and θ 1 bands, all models provided high local F-statistics in expected regions. The most robust EEG-fMRI associations were observed for ASM and RSSM.

Awake fMRI Reveals Brain Regions for Novel Word Detection in Dogs

How do dogs understand human words? At a basic level, understanding would require the discrimination of words from non-words. To determine the mechanisms of such a discrimination, we trained 12 dogs to retrieve two objects based on object names, then probed the neural basis for these auditory discriminations using awake-fMRI. We compared the neural response to these trained words relative to "oddball" pseudowords the dogs had not heard before. Consistent with novelty detection, we found greater activation for pseudowords relative to trained words bilaterally in the parietotemporal cortex. To probe the neural basis for representations of trained words, searchlight multivoxel pattern analysis (MVPA) revealed that a subset of dogs had clusters of informative voxels that discriminated between the two trained words. These clusters included the left temporal cortex and amygdala, left caudate nucleus, and thalamus. These results demonstrate that dogs' processing of human words utilizes basic processes like novelty detection, and for some dogs, may also include auditory and hedonic representations.

Assessing cross-modal target transition effects with a visual-auditory oddball

Prior research has shown contextual manipulations involving temporal and sequence related factors significantly moderate attention-related responses, as indexed by the P3b event-related-potential, towards infrequent (i.e., deviant) target oddball stimuli. However, significantly less research has looked at the influence of cross-modal switching on P3b responding, with the impact of target-to-target cross-modal transitions being virtually unstudied. To address this gap, this study recorded high-density (256 electrodes) EEG data from twenty-five participants as they completed a cross-modal visual-auditory oddball task. This task was comprised of unimodal visual (70% Nontargets: 30% Deviant-targets) and auditory (70% Nontargets: 30% Deviant-targets) oddballs presented in fixed alternating order (i.e., visual-auditory-visual-auditory, etc.) with participants being tasked with detecting deviant-targets in both modalities. Differences in the P3b response towards deviant-targets as a function of preceding deviant-target's presentation modality was analyzed using temporal-spatial PCA decomposition. In line with predictions, the results indicate that the ERP response to auditory deviant-targets preceded by visual deviant-targets exhibits an elevated P3b, relative to the processing of auditory deviant-targets preceded by auditory deviant-targets. However, the processing of visual deviant-targets preceded by auditory deviant-targets exhibited a reduced P3b response, relative to the P3b response towards visual deviant-targets preceded by visual deviant-targets. These findings provide the first demonstration of temporally and perceptually decoupled target-to-target cross-modal transitions moderating P3b responses on the oddball paradigm, generally providing support for the context-updating interpretation of the P3b response.

Reduced processing of alcohol cues predicts abstinence in recently detoxified alcoholic patients in a three-month follow up period: an ERP study

One of the major challenges in alcohol dependence is relapse prevention, as rates of relapse following detoxification are high. Drug-related motivational processes may represent key mechanisms in alcoholic relapse. In the present study, event-related potentials (ERPs) were recorded during a visual oddball task administered to 29 controls (11 females) and 39 patients (9 females). Deviant stimuli were related or unrelated to alcohol. For patients, the task was administered following a 3-week detoxification course. Of these, 19 relapsed during the three months follow-up period. The P3, an ERP component associated with activation of arousal systems in the brain and motivational engagement, was examined with the aim to link the fluctuation of its amplitude in response to alcohol versus non-alcohol cues to the observed relapse rate. Results showed that compared to relapsers, abstainers presented with a decreased P3 amplitude for alcohol related compared to non-alcohol related pictures (p=.009). Microstate analysis and sLORETA topography showed that activation for both types of deviant cues in abstainers originated from the inferior and medial temporal gyrus and the uncus, regions implicated in detection of target stimuli in oddball tasks and of biologically relevant stimuli. Through hierarchical regression, it was found that the P3 amplitude difference between alcohol and non-alcohol related cues was the best predictor of relapse vulnerability (p=.013). Therefore, it seems that a devaluation of the motivational significance of stimuli related to alcohol, measurable through electrophysiology, could protect from a relapse within three months following detoxification in alcohol-dependent patients.

Frontoparietal activity during deceptive responses in the P300-based guilty knowledge test: an sLORETA study

The cortical source activity during the P300-based guilty knowledge test (GKT) conducted using Korean sentences was investigated. Thirty male students performed a guilty or an innocent scenario, and then underwent an electroencephalogram test. The stimuli consisted of target, probe, and irrelevant stimuli that were presented visually. A target stimulus is a task-relevant stimulus that is presented rarely, attracts subjects' attention, and induces a P300 wave. A probe stimulus, also presented rarely, contains crime-relevant information that induces P300 in a guilty subject. A guilty subject would be also attentive to the probe stimulus as to the target stimulus. An irrelevant stimulus is not related to the task or to the crime, and is frequently presented. Event-related potential (ERP) data showed a marked difference between the guilty and innocent groups. Compared to irrelevant stimuli, the probe stimulus elicited larger P300 amplitude in the bilateral frontoparietal region in the guilty group. However, this pattern was not observed in the innocent group. Standardized low-resolution electromagnetic tomography (sLORETA) analysis showed significant activation increases for the probe stimulus in the guilty group. It appears that the guilty and innocent groups use different cognitive mechanisms when processing the crime-relevant sentence. With regards to the cortical activity in response to the probe stimulus, the frontal activation for verb elements seems to reflect a working memory process, episodic memory retrieval, and response inhibition, while parietal activation for complement (adverb) and object (noun) elements seems to reflect selective attention and target discrimination. To our knowledge, this is the first research to examine the cortical source of the ERP evoked by the P300-based GKT using separate Korean sentence elements.

Brain activity underlying auditory perceptual learning during short period training: simultaneous fMRI and EEG recording

BACKGROUND

There is an accumulating body of evidence indicating that neuronal functional specificity to basic sensory stimulation is mutable and subject to experience. Although fMRI experiments have investigated changes in brain activity after relative to before perceptual learning, brain activity during perceptual learning has not been explored. This work investigated brain activity related to auditory frequency discrimination learning using a variational Bayesian approach for source localization, during simultaneous EEG and fMRI recording. We investigated whether the practice effects are determined solely by activity in stimulus-driven mechanisms or whether high-level attentional mechanisms, which are linked to the perceptual task, control the learning process.

RESULTS

The results of fMRI analyses revealed significant attention and learning related activity in left and right superior temporal gyrus STG as well as the left inferior frontal gyrus IFG. Current source localization of simultaneously recorded EEG data was estimated using a variational Bayesian method. Analysis of current localized to the left inferior frontal gyrus and the right superior temporal gyrus revealed gamma band activity correlated with behavioral performance.

CONCLUSIONS

Rapid improvement in task performance is accompanied by plastic changes in the sensory cortex as well as superior areas gated by selective attention. Together the fMRI and EEG results suggest that gamma band activity in the right STG and left IFG plays an important role during perceptual learning.

The association between p3 amplitude at age 11 and criminal offending at age 23

Reduced P3 amplitude to targets is an information-processing deficit associated with adult antisocial behavior and may reflect dysfunction of the temporal-parietal junction. This study aims to examine whether this deficit precedes criminal offending. From a birth cohort of 1,795 children, 73 individuals who become criminal offenders at age 23 and 123 noncriminal individuals were assessed on P3 amplitude. The two groups did not differ on gender, ethnicity, and social adversity. P3 amplitude was measured over the temporal-parietal junction during a visual continuous performance task at age 11, together with antisocial behavior. Criminal convictions were assessed at age 23. Reduced P3 amplitude at age 11 was associated with increased antisocial behavior at age 11. Criminal offenders showed significantly reduced P3 amplitudes to target stimuli compared to controls. Findings remained significant after controlling for antisocial behavior and hyperactivity at age 11 and alcoholism at age 23. P3 deficits at age 11 are associated with adult crime at age 23, suggesting that reduced P3 may be an early neurobiological marker for cognitive and affective processes subserved by the temporal-parietal junction that place a child at risk for adult crime.

Response inhibition in adults and teenagers: spatiotemporal differences in the prefrontal cortex

Inhibition is a core executive function reliant on the frontal lobes that shows protracted maturation through to adulthood. We investigated the spatiotemporal characteristics of response inhibition during a visual go/no-go task in 14 teenagers and 14 adults using magnetoencephalography (MEG) and a contrast between two no-go experimental conditions designed to eliminate a common confound in earlier studies comparing go with no-go trials. Source analyses were performed using an event-related beamformer algorithm with co-registered individual structural MRIs. Performance was controlled to be similar across subjects. Analyses of MEG data revealed bilateral prefrontal activity in the inhibitory condition for both age groups, but with different spatiotemporal patterns: around 300ms after stimulus onset in middle frontal gyri in teenagers vs. around 260ms in inferior frontal gyri in adults. Moreover, the inhibition of a prepotent motor response showed a stronger recruitment of the left hemisphere in teenagers than in adults and of the right hemisphere in adults than in teenagers. These findings provide high-resolution temporal and spatial information regarding response inhibition in adolescents compared to adults, independent of motor components and performance differences.

Brain activation disturbance for target detection in patients with mild cognitive impairment: an fMRI study

Functional brain imaging in mild cognitive impairment (MCI) reveals differences in activation of task-relevant brain areas between patients and age-matched healthy controls. However, some studies reported hyperactivation and others hypoactivation in MCI compared with controls. The inconsistencies may be explained by compensatory mechanisms due to high complexity of the applied tasks. The oddball task is a simple paradigm that is known to activate a widespread network in the brain, involving attentional and monitoring mechanisms. In the present study, we examined amnestic or amnestic multidomain MCI patients (n = 12) and healthy controls (n = 13) in an auditory oddball task. Participants had to respond to infrequent targets and inhibit response to infrequent novel-nontarget stimuli. Lower stimulus related activation was found in MCI patients compared with healthy controls in parts of the middle temporal gyrus, the temporal pole, regions along the superior temporal sulcus, in the left cuneus, the left supramarginal gyrus, the anterior cingulated cortex and in the left inferior and middle frontal gyrus. Activation for oddball stimuli is assumed to reflect an automatic reflexive engagement of many brain regions in response to potentially important changes in the environment as well as cognitive control to monitor responses. The mechanisms of attention and cognitive control may be severely impaired in MCI and thus, underlie the cognitive deficits of this clinical group.

Ketamine effects on brain function--simultaneous fMRI/EEG during a visual oddball task

BACKGROUND

Behavioral and electrophysiological human ketamine models of schizophrenia are used for testing compounds that target the glutamatergic system. However, corresponding functional neuroimaging models are difficult to reconcile with functional imaging and electrophysiological findings in schizophrenia. Resolving the discrepancies between different observational levels is critical to understand the complex pharmacological ketamine action and its usefulness for modeling schizophrenia pathophysiology.

METHODS

We conducted a within-subject, randomized, placebo-controlled pharmacoimaging study in twenty-four male volunteers. Subjects were given low-dose S-ketamine (bolus prior to functional imaging: 0.1mg/kg during 5min, thereafter continuous infusion: 0.015625mg/kg/min reduced by 10% every ten minutes) or placebo while performing a visual oddball task during simultaneous functional magnetic resonance imaging (fMRI) with continuous recording of event-related potentials (P300) and electrodermal activity (EDA). Before and after intervention, psychopathological status was assessed using the Positive and Negative Syndrome Scale (PANSS) and the Altered State of Consciousness (5D-ASC) Rating Scale.

RESULTS

P300 amplitude and corresponding BOLD responses were diminished in the ketamine condition in cortical regions being involved in sensory processing/selective attention. In both measurement modalities separation of drug conditions was achieved with area under the curve (AUC) values of up to 0.8-0.9. Ketamine effects were also observed in the clinical, behavioral and peripheral physiological domains (Positive and Negative Syndrome Scale, reaction hit and false alarm rate, electrodermal activity and heart rate) which were in part related to the P300/fMRI measures.

CONCLUSION

The findings from our ketamine experiment are consistent across modalities and directly related to observations in schizophrenia supporting the validity of the model. Our investigation provides the first prototypic example of a pharmacoimaging study using simultaneously acquired fMRI/EEG.

Developmental effects of reward on sustained attention networks

Adolescence is typified by significant maturation in higher-level attention functions coupled with less developed control over motivation, and enhanced sensitivity to novelty and reward. This study used event-related functional magnetic resonance imaging (fMRI) in seventy male and female participants aged between 10 and 43 years to identify age-related linear changes in cognitive sustained attention systems and the impact of reward on these systems, using a sustained attention task with and without a rewarded condition. For the non-rewarded sustained attention contrast, increasing age was associated with activation increases in typical regions of sustained attention including right inferior frontal, superior temporo-parietal and cerebellar cortices. Age-related activation decreases were observed within more posterior regions including posterior cingulate, insula and posterior cerebellar cortices, presumably mediating visual-spatial saliency detection. The effect of reward on sustained attention networks was associated with increased activation with age in regions associated with both executive attention control and reward processing, including dorsolateral, inferior and ventromedial prefrontal cortices (PFC), striatum, and temporo-parietal regions, suggestive of greater integration and executive control of motivation and cognition with maturity. Activation in paralimbic posterior cingulate and inferior temporal brain regions of visual-spatial saliency processing was progressively reduced in activation with increasing development. Thus, with increasing development between adolescence and adulthood, reward appears to enhance maturing cognitive sustained attention and executive reward-processing networks, whilst reducing paralimbic regions of saliency detection. These findings may be the neural underpinnings for the progressive maturation of motivational control over risk taking behaviours between adolescence and adulthood.

Early Negativity Bias Occurring Prior to Experiencing of Emotion

The present study analyzed event-related potentials (ERPs) in different valence conditions to investigate whether negativity bias can occur prior to the experiencing of negative emotion. There were two tasks: One was challenging and participants were asked to react as quickly as possible; the other was easy and participants were asked to react after the stimuli disappeared. ERPs were compared to determine if negativity bias had occurred. Anterior hemispheric asymmetries tests (AHAT) were conducted to test emotion-evoking effects. The ERP results showed that negativity bias occurred in both tasks. However, AHAT showed that emotion was not effectively evoked in the challenging task. These results suggested that negativity bias could occur even without effective experiencing of emotion. This prompted a new viewpoint regarding the properties of negativity bias: Early negativity bias was caused by the features of negative stimuli but not by negative emotions.

A supramodal network for response inhibition

Response inhibition is the capacity to suppress inappropriate actions and is considered to be a fundamental executive function. This study investigated whether the neural correlates of response inhibition are organized along supramodal or modality-specific principles. For this purpose, we used event-related functional magnetic resonance imaging in a go-nogo task with auditory and visual stimuli. Common activation relating to response inhibition across modalities was observed in a frontoparietal network including the ventrolateral prefrontal cortex. In contrast, there was no modality-specific activation related to response inhibition in the prefrontal cortex. These findings suggest that the neural correlates of response inhibition have a supramodal organization, which is consistent with its role as a core executive function.

Violation of expectation: neural correlates reflect bases of prediction

Setting perceptual expectations can be based on different sources of information that determine which functional networks will be involved in implementing preparatory top-down influences and dealing with situations in which expectations are violated. The goal of the present study was to investigate and directly compare brain activations triggered by violating expectations within two different task contexts. In the serial prediction task, participants monitored ordered perceptual sequences for predefined sequential deviants. In contrast, the target detection task entailed a presentation of stimuli which had to be monitored for predefined nonsequential deviants. Detection of sequential deviants triggered an increase of activity in premotor and cerebellar components of the "standard" sequencing network and activations in additional frontal areas initially not involved in sequencing. This pattern of activity reflects the detection of a mismatch between the expected and presented stimuli, updating of the underlying sequence representation (i.e., forward model), and elaboration of the violation. In contrast, target detection elicited activations in posterior temporal and parietal areas, reflecting an increase in perceptual processing evoked by the nonsequential deviant. The obtained results suggest that distinct functional networks involved in detecting deviants in different contexts reflect the origin and the nature of expectations being violated.

Cognitive conflict in audiovisual integration: an event-related potential study

This study used event-related potentials (ERPs) to investigate the electrophysiological correlates of cognitive conflict in audiovisual integration during an audiovisual task. ERP analyses revealed: (i) the anterior N1 and P1 were elicited in both matched and mismatched conditions and (ii) audiovisual mismatched answers elicited a more negative ERP deflection at 490 ms (N490) than matched answers. Dipole analysis of the difference wave (mismatched minus matched) localized the generator of the N490 to the posterior cingulate cortex, which may be involved in the control and modulation of conflict processing of Chinese characters when visual and auditory information is mismatched.

The event-related potential effects of cognitive conflict in a Chinese character-generation task

High-density event-related potentials were recorded to examine the electrophysiologic correlates of the evaluation of possible answers provided during a Chinese character-generation task. We examined three conditions: the character given was what participants initially generated (Consistent answer), the character given was correct (Unexpected Correct answer), or it was incorrect (Unexpected Incorrect answer). Results showed that Unexpected Correct and Incorrect answers elicited a more negative event-related potential deflection (N320) than did Consistent answers between 300 and 400 ms. Dipole source analysis of difference waves (Unexpected Correct or Incorrect minus Consistent answers) localized the generator of the N320 in the anterior cingulate cortex. The N320 therefore likely reflects the cognitive change or conflict between old and new ways of thinking while identifying and judging characters.

Brain potentials implicate temporal lobe abnormalities in criminal psychopaths

Psychopathy is associated with abnormalities in attention and orienting. However, few studies have examined the neural systems underlying these processes. To address this issue, the authors recorded event-related potentials (ERPs) while 80 incarcerated men, classified as psychopathic or nonpsychopathic via the Hare Psychopathy Checklist--Revised (R. D. Hare, 1991, 2003), completed an auditory oddball task. Consistent with hypotheses, processing of targets elicited larger frontocentral negativities (N550) in psychopaths than in nonpsychopaths. Psychopaths also showed an enlarged N2 and reduced P3 during target detection. Similar ERP modulations have been reported in patients with amygdala and temporal lobe damage. The data are interpreted as supporting the hypothesis that psychopathy may be related to dysfunction of the paralimbic system--a system that includes parts of the temporal and frontal lobes.

Tracking the subprocesses of decision-based action in the human frontal lobes

Situationally adaptive behavior relies on the identification of relevant target stimuli, the evaluation of these with respect to the current context and the selection of an appropriate action. We used functional magnetic resonance imaging (fMRI) to disentangle the neural networks underlying these processes within a single task. Our results show that activation of mid-ventrolateral prefrontal cortex (PFC) reflects the perceived presence of a target stimulus regardless of context, whereas context-appropriate evaluation is subserved by mid-dorsolateral PFC. Enhancing demands on response selection by means of response conflict activated a network of regions, all of which are directly connected to motor areas. On the midline, rostral anterior paracingulate cortex was found to link target detection and response selection by monitoring for the presence of behaviorally significant conditions. In summary, we provide new evidence for process-specific functional dissociations in the frontal lobes. In target-centered processing, target detection in the VLPFC is separable from contextual evaluation in the DLPFC. Response-centered processing in motor-associated regions occurs partly in parallel to these processes, which may enhance behavioral efficiency, but it may also lead to reaction time increases when an irrelevant response tendency is elicited.

The hemodynamics of oddball processing during single-tone and two-tone target detection tasks

Event-related potential (ERP) studies have shown that the neural systems engaged during performance of oddball tasks are sensitive to contextual manipulations, such as the number of stimulus classes. Some ERP components (i.e., N1) are modulated by the number of stimulus types, while others (i.e., P3) are not greatly affected. However, little is known about how these contextual manipulations affect the hemodynamics underlying oddball processing. The purpose of this study was to examine the hemodynamic correlates of target stimulus processing in single-tone (targets alone) and two-tone (targets and standard tones) auditory oddball tasks. The primary hypothesis was that processing of salient stimuli in both contextual conditions would engage the same spatially distributed cortical and subcortical networks observed in previous oddball fMRI studies. Results were consistent with this hypothesis and suggest that the brain engages many potentially useful brain regions during salient stimulus processing despite the low probability that said regions are necessary for task performance, which likely reflects a form of "adaptive reflexive processing". Results were also consistent with ERP data that shows that the N1 is larger for single-tone tasks by showing greater amplitude of hemodynamic response for single-tone targets, relative to two-tone targets, in bilateral temporal cortex and bilateral inferior lateral frontal cortex. The results are discussed as they relate to the understanding of neurocognitive function pertaining to contextual manipulations in general, and orienting processes in particular.

An adaptive reflexive processing model of neurocognitive function: supporting evidence from a large scale (n = 100) fMRI study of an auditory oddball task

Recent hemodynamic imaging studies have shown that processing of low probability task-relevant target stimuli (i.e., oddballs) and low probability task-irrelevant novel stimuli elicit widespread activity in diverse, spatially distributed cortical and subcortical systems. The nature of this distributed response supports the model that processing of salient and novel stimuli engages many brain regions regardless of whether said regions were necessary for task performance. However, these latter neuroimaging studies largely employed small sample sizes and fixed-effect analyses, limiting the characterization and inference of the results. The present study addressed these issues by collecting a large sample size (n = 100) and employed random effects statistical models. Analyses were also conducted to determine the inter-subject reliability of the hemodynamic response and the effects of gender and age on target detection and novelty processing. Group data demonstrated highly significant activation in all 34 specified regions of interest for target detection and all 24 specified regions of interest for processing of novel stimuli. Neither age nor gender systematically influenced the results. These data are discussed within the context of a model that proposes that the mammalian brain has evolved to adopt a strategy of engaging distributed neuronal systems when processing salient stimuli despite the low probability that many of these brain regions are required for successful task performance. This process may be termed 'adaptive reflexive processing.' The implications of these results for interpreting functional MRI studies are discussed.

Hemispheric differences in hemodynamics elicited by auditory oddball stimuli

Evidence from neuroimaging studies suggests that the right hemisphere of the human brain might be more specialized for attention than the left hemisphere. However, differences between right and left hemisphere in the magnitude of hemodynamic activity (i.e., 'functional asymmetry') rarely have been explicitly examined in previous neuroimaging studies of attention. This study used a new voxel-based comparison method to examine hemispheric differences in the amplitude of the hemodynamic response in response to infrequent target, infrequent novel, and frequent standard stimuli during an event-related fMRI auditory oddball task in 100 healthy adult participants. Processing of low probability task-relevant target stimuli, or 'oddballs', and low probability task-irrelevant novel stimuli is believed to engage in orienting and attentional processes. It was hypothesized that greater right-hemisphere activation compared to left would be observed to infrequent target and novel stimuli. Consistent with predictions, greater right hemisphere than left frontal, temporal, and parietal lobe activity was observed for target detection and novelty processing. Moreover, asymmetry effects did not differ with respect to age or gender of the participants. The results (1) support the proposal that the right hemisphere is differentially engaged in processing salient stimuli and (2) demonstrate the successful use of a new voxel-based laterality analysis technique for fMRI data.

A supramodal limbic-paralimbic-neocortical network supports goal-directed stimulus processing

Limited processing resources are allocated preferentially to events that are relevant for behavior. Research using the novelty "oddball" paradigm suggests that a widespread network of limbic, paralimbic, and association areas supports the goal-directed processing of task-relevant target events. In that paradigm, greater activity in diverse brain areas is elicited by rare task-relevant events that require a subsequent motor response than by rare task-irrelevant novel events that require no response. Both stimulus infrequency (unexpectedness) and novelty, however, may contribute to the pattern of activity observed using that paradigm. The goal of the present study was to examine the supramodal neural activity elicited by regularly occurring, equiprobable, and non-novel stimuli that differed in the subsequent behavior they prescribed. We employed event-related functional magnetic resonance imaging (fMRI) during auditory and visual versions of a Go/NoGo task. Participants made a motor response to the designated "Go" (target) stimulus, and no motor response to the equiprobable "NoGo" (nontarget) stimulus. We hypothesized that task-relevant Go events would elicit relatively greater hemodynamic activity than would NoGo events throughout a network of limbic, paralimbic, and association areas. Indeed, Go events elicited greater activity than did NoGo events in the amygdala-hippocampus, paralimbic cortex at the anterior superior temporal sulcus, insula, posterior orbitofrontal cortex, and anterior and posterior cingulate cortex, as well as in heteromodal association areas located at the temporoparietal junction, anterior intraparietal sulcus and precuneus, and premotor cortex. Paralimbic cortex offers an important site for the convergence of motivational/goal-directed influences from limbic cortex with stimulus processing and response selection mediated within the frontoparietal areas.

Errors without conflict: Implications for performance monitoring theories of anterior cingulate cortex

Recent theories of the neural basis of performance monitoring have emphasized a central role for the anterior cingulate cortex (ACC). Replicating an earlier event-related potential (ERP) study, which showed an error feedback negativity that was modeled as having an ACC generator, we used event-related fMRI to investigate whether the ACC would differentiate between correct and incorrect feedback stimuli in a time estimation task. The design controlled for response conflict and frequency and expectancy effects. Although participants in the current study adjusted their performance following error feedback, we did not observe error feedback-evoked ACC activity. In contrast, we did observe ACC activity while the same subjects performed the Stroop task, in which an area of the ACC activated during both conflict and error trials. These findings are inconsistent with previous dipole models of the error feedback negativity, and suggest the ACC may not be involved in the generation of this ERP component. These results question involvement of the ACC in the detection of errors per se when controlling for conflict.

Probability effects on the neural correlates of retrieval success: an fMRI study

Event-related fMRI was employed to investigate the influence of the relative probability of old and new test items on the neural correlates of recognition memory. Twelve subjects undertook three study-test cycles, each consisting of an identical study phase in which a series of words was encoded in an incidental task, followed by a test phase in which yes/no recognition judgments were made to a mixture of studied (old) and unstudied (new) words. The ratio of old to new words differed in each test phase, and was either 25:75, 50:50, or 75:25. In lateral inferior and medial parietal cortex, and the posterior cingulate, greater activity was elicited by correctly classified old than new items independently of old:new ratio. By contrast, in other regions, including anterior, dorsolateral, and ventrolateral prefrontal cortex, differences in the activity elicited by old and new items varied according to old:new ratio, demonstrating in some cases a complete crossover interaction. The results suggest that differential activity elicited by old and new test items is likely to support successful recognition in only a subset of the regions identified in previous studies as exhibiting such differences. In other regions, most notably prefrontal cortex, differences in the activity elicited by old and new items appear to reflect processes that are contingent upon, rather than in support of, successful recognition.

Sparse imaging of the auditory oddball task with functional MRI

Cortical reactions to rare task-related stimuli have been studied with electrophysiological methods in the assessment of the P300 component as well as in functional imaging studies with regard to oddball tasks. While functional magnetic resonance imaging studies using auditory stimuli have to deal with interference between auditory stimuli and scanner noise, the aim of our study was to assess auditory target processing with the sparse imaging method. Single volumes of echo-planar imaging were acquired 4 s following the onset of the stimuli of interest. In keeping with previous studies, target stimuli activated the insula, superior temporal gyrus, cingulate gyrus, middle frontal gyrus, parietal cortex and the cerebellum. Our results encourage the application of the sparse imaging method in experiments on cognitive processing elicited by auditory stimulation in a silent environment.