Theta rhythm supports hippocampus-dependent integrative encoding in schematic/semantic memory networks.

Integrating new information into existing schematic/semantic structures of knowledge is the basis of learning in our everyday life as it enables structured representation of information and goal-directed behaviour in an ever-changing environment. However, how schematic/semantic mnemonic structures aid the integration of novel elements remains poorly understood. Here, we showed that the ability to integrate novel picture information into learned structures of picture associations that overlapped by the same picture scene (i.e., simple network) or by a conceptually related picture scene (i.e., schematic/semantic network) is hippocampus-dependent, as patients with lesions at the medial temporal lobe (including the hippocampus) were impaired in inferring novel relations between pictures within these memory networks. We also found more persistent and widespread scalp EEG theta oscillations (3-5 Hz) while participants integrated novel pictures into schematic/semantic memory networks than into simple networks. On the other hand, greater neural similarity was observed between EEG patterns elicited by novel and related events within simple networks than between novel and related events within schematic/semantic memory networks. These findings have important implications for our understanding of the neural mechanisms that support the development and organization of structures of knowledge.

The interplay between domain-general and domain-specific mechanisms during the time-course of verbal associative learning: An event-related potential study.

Humans continuously learn new information. Here, we examined the temporal brain dynamics of explicit verbal associative learning between unfamiliar items. In the first experiment, 25 adults learned object-pseudoword associations during a 5-day training program allowing us to track the N400 dynamics across learning blocks within and across days. Successful learning was accompanied by an initial frontal N400 that decreased in amplitude across blocks during the first day and shifted to parietal sites during the last training day. In Experiment 2, we replicated our findings with 38 new participants randomly assigned to a consistent learning or an inconsistent learning group. The N400 amplitude modulations that we found, both within and between learning sessions, are taken to reflect the emergence of novel lexical traces even when learning concerns items for which no semantic information is provided. The shift in N400 topography suggests that different N400 neural generators may contribute to specific word learning steps through a balance between domain-general and language-specific mechanisms.

Arcuate fasciculus architecture is associated with individual differences in pre-attentive detection of unpredicted music changes.

The mismatch negativity (MMN) is an event related brain potential (ERP) elicited by unpredicted sounds presented in a sequence of repeated auditory stimuli. The neural sources of the MMN have been previously attributed to a fronto-temporo-parietal network which crucially overlaps with the so-called auditory dorsal stream, involving inferior and middle frontal, inferior parietal, and superior and middle temporal regions. These cortical areas are structurally connected by the arcuate fasciculus (AF), a three-branch pathway supporting the feedback-feedforward loop involved in auditory-motor integration, auditory working memory, storage of acoustic templates, as well as comparison and update of those templates. Here, we characterized the individual differences in the white-matter macrostructural properties of the AF and explored their link to the electrophysiological marker of passive change detection gathered in a melodic multifeature MMN-EEG paradigm in 26 healthy young adults without musical training. Our results show that left fronto-temporal white-matter connectivity plays an important role in the pre-attentive detection of rhythm modulations within a melody. Previous studies have shown that this AF segment is also critical for language processing and learning. This strong coupling between structure and function in auditory change detection might be related to life-time linguistic (and possibly musical) exposure and experiences, as well as to timing processing specialization of the left auditory cortex. To the best of our knowledge, this is the first time in which the relationship between neurophysiological (EEG) and brain white-matter connectivity indexes using DTI-tractography are studied together. Thus, the present results, although still exploratory, add to the existing evidence on the importance of studying the constraints imposed on cognitive functions by the underlying structural connectivity.

Gossip information increases reward-related oscillatory activity.

Previous research has described the process by which the interaction between the firing in midbrain dopamine neurons and the hippocampus results in promoting memory for high-value motivational and rewarding events, both extrinsically and intrinsically driven (i.e. curiosity). Studies on social cognition and gossip have also revealed the activation of similar areas from the reward network. In this study we wanted to assess the electrophysiological correlates of the anticipation and processing of novel information (as an intrinsic cognitive reward) depending on the degree of elicited curiosity and the content of the information. 24 healthy volunteers participated in this EEG experiment. The task consisted of 150 questions and answers divided into three different conditions: trivia-like questions, personal-gossip information about celebrities and personal-neutral information about the same celebrities. Our main results from the ERPs and time-frequency analysis pinpointed main differences for gossip in comparison with personal-neutral and trivia-like conditions. Specifically, we found an increase in beta oscillatory activity in the outcome phase and a decrease of the same frequency band in the expectation phase. Larger amplitudes in P300 component were also found for gossip condition. Finally, gossip answers were the most remembered in a one-week memory test. The arousing value and saliency of gossip information, its rewarding effect evidenced by the increase of beta oscillatory power and the recruitment of areas from the brain reward network in previous fMRI studies, as well as its potential social value have been argued in order to explain its differential processing, encoding and recall.

Brain oscillatory activity of skill and chance gamblers during a slot machine game.

Gambling behavior presents a broad variety of individual differences, with a continuum ranging from nongamblers to pathological gamblers. The reward network has been proposed to be critical in gambling behavior, but little is known about the behavioral and neural mechanisms underlying individual differences that depend on gambling preference. The main goals of the present study were to explore brain oscillatory responses to gambling outcomes in regular gamblers and to assess differences between strategic gamblers, nonstrategic gamblers, and nongamblers. In all, 54 healthy volunteers participated in the study. Electroencephalography was recorded while participants were playing a slot machine task that delivered win, near-miss, and full-miss outcomes. Behaviorally, regular gamblers selected a larger percentage of risky bets, especially when they could select the image to play. The time-frequency results showed larger oscillatory theta power increases to near-misses and increased beta power to win outcomes for regular gamblers, as compared to nongamblers. Moreover, theta oscillatory activity after wins was only increased in nonstrategic gamblers, revealing differences between the two groups of gamblers. The present results reveal differences between regular gamblers and nongamblers in both their behavioral and neural responses to gambling outcomes. Moreover, the results suggest that different brain oscillatory mechanisms might underlie the studied gambling profiles, which might have implications for both basic and clinical studies.

Unraveling the Role of the Hippocampus in Reversal Learning.

Research in reversal learning has mainly focused on the functional role of dopamine and striatal structures in driving behavior on the basis of classic reinforcement learning mechanisms. However, recent evidence indicates that, beyond classic reinforcement learning adaptations, individuals may also learn the inherent task structure and anticipate the occurrence of reversals. A candidate structure to support such task representation is the hippocampus, which might create a flexible representation of the environment that can be adaptively applied to goal-directed behavior. To investigate the functional role of the hippocampus in the implementation of anticipatory strategies in reversal learning, we first studied, in 20 healthy individuals (11 women), whether the gray matter anatomy and volume of the hippocampus were related to anticipatory strategies in a reversal learning task. Second, we tested 20 refractory temporal lobe epileptic patients (11 women) with unilateral hippocampal sclerosis, who served as a hippocampal lesion model. Our results indicate that healthy participants were able to learn the task structure and use it to guide their behavior and optimize their performance. Participants' ability to adopt anticipatory strategies correlated with the gray matter volume of the hippocampus. In contrast, hippocampal patients were unable to grasp the higher-order structure of the task with the same success than controls. Present results indicate that the hippocampus is necessary to respond in an appropriately flexible manner to high-order environments, and disruptions in this structure can render behavior habitual and inflexible.SIGNIFICANCE STATEMENT Understanding the neural substrates involved in reversal learning has provoked a great deal of interest in the last years. Studies with nonhuman primates have shown that, through repetition, individuals are able to anticipate the occurrence of reversals and, thus, adjust their behavior accordingly. The present investigation is devoted to know the role of the hippocampus in such strategies. Importantly, our findings evidence that the hippocampus is necessary to anticipate the occurrence of reversals, and disruptions in this structure can render behavior habitual and inflexible.

The right inferior frontal cortex in response inhibition: A tDCS-ERP co-registration study.

In any given common situation, when an individual controls him/herself or obeys and stops a current action when asked to do, it is because the brain executes an inhibitory process. This ability is essential for adaptive behaviour, and it is also a requirement for accurate performance in daily life. It has been suggested that there are two main inhibitory functions related to behaviour, as inhibition is observed to affect behaviour at different time intervals. Proactive inhibition permits the subject to control his behavioural response over time by creating a response tendency, while reactive inhibition is considered to be a process that usually inhibits an already initiated response. In this context, it has been established that inhibitory function is implemented by specific fronto-basal-ganglia circuits. In the present study, we investigated the role of the right inferior frontal cortex (rIFC) in response inhibition by combining into a single task the Go-NoGo task and the Stop-Signal task. Concurrently, we applied transcranial direct current stimulation (tDCS) over the IFC and recorded electroencephalography (EEG). Thus, we obtained online EEG measurements of the tDCS-induced modifications in the IFC together with the participant's performance in a response inhibition task. We found that applying bilateral tDCS on the IFC (right anodal/left cathodal) significantly increased proactive inhibition, although the behavioural parameters indicative of reactive inhibition were unaffected by the stimulation. Finally, the inhibitory-P3 component reflected a similar modulation under both inhibitory conditions induced by the stimulation. Our data indicates that an online tDCS-ERP approach is achievable, but that a tDCS bilateral montage may not be the most efficient one for modulating the rIFC.

Individual differences in error tolerance in humans: Neurophysiological evidences.

When interacting in error-prone environments, humans display different tolerances to changing their decisions when faced with erroneous feedback information. Here, we investigated whether these individual differences in error tolerance (ET) were reflected in neurophysiological mechanisms indexing specific motivational states related to feedback monitoring. To explore differences in ET, we examined the performance of 80 participants in a probabilistic reversal-learning task. We then compared event-related brain responses (ERPs) of two extreme groups of participants (High ET and Low ET), which showed radical differences in their propensity to maintain newly learned rules after receiving spurious negative feedback. We observed that High ET participants showed reduced anticipatory activity prior to the presentation of incoming feedback, informing them of the correctness of their performance. This was evidenced by measuring the amplitude of the stimulus-preceding negativity (SPN), an ERP component indexing attention and motivational engagement of incoming informative feedback. Postfeedback processing ERP components (the so-called Feedback-Related Negativity and the P300) also showed reduced amplitude in this group (High ET). The general decreased responsiveness of the High ET group to external feedback suggests a higher proneness to favor internal(rule)-based strategies, reducing attention to external cues and the consequent impact of negative evaluations on decision making. We believe that the present findings support the existence of specific cognitive and motivational processes underlying individual differences on error-tolerance among humans, contributing to the ongoing research focused on understanding the mental processes behind human fallibility in error-prone scenarios.

Can the knight capture the queen? The role of supramarginal gyrus in chess rule-retrieval as evidenced by a novel combined awake brain mapping and fMRI protocol.

Brain tumours represent a burden for society, not only due to the risks they entail but also because of the possibility of losing relevant cognitive functions for the patient's life after their resection. In the present study, we report how we monitored chess performance through a multimodal Electrical Stimulation Mapping (ESM) - functional Magnetic Resonance Imaging (fMRI) combined protocol. The ESM was performed under a left parietal lobe tumour resection surgery on a patient that expressed the desire to preserve his chess playing ability post-operative. We designed an ad-hoc protocol to evaluate processes involved in chess performance that could be potentially affected by the tumour location: (i) visual search, (ii) rule-retrieval, and (iii) anticipation of checkmate. The fMRI study reported functional regions for chess performance, some of them proximal to the lesion in the left parietal lobe. The most relevant result was a positive eloquent point encountered in the vicinity of the left supramarginal gyrus while performing the rule-retrieval task in the ESM. This functional region was convergent with the activations observed in the pre-operative fMRI study for this condition. The behavioural assessment comparison revealed post-operative an increase in reaction time in some tasks but correctness in performance was maintained. Finally, the patient maintained the ability to play chess after the surgery. Our results provide a plausible protocol for future interventions and suggest a role of the left supramarginal gyrus in chess cognitive operations for the case presented.

De novo depression following temporal lobe epilepsy surgery.

Surgical removal of the mesial temporal lobe can effectively treat drug-resistant epilepsy but may lead to mood disorders. This fact is of particular interest in patients without a prior psychiatric history. The study investigates the relationship between Temporal Lobe Epilepsy (TLE), mood disorders, and the functional connectivity of the Hippocampus (Hipp) and Nucleus Accumbens (NAcc). In this case control study, twenty-seven TLE patients and 18 control subjects participated, undergoing structural and functional magnetic resonance imaging (MRI) scans before and after surgery. Post-surgery, patients were categorized into those developing de novo depression (DnD) within the first year and those without depression (nD). Functional connectivity maps between NAcc and the whole brain were generated, and connectivity strength between the to-be-resected Hipp area and NAcc was compared. Within the first year post-surgery, 7 out of 27 patients developed DnD. Most patients (88.8 %) exhibited a significant reduction in NAcc-Hipp connectivity compared to controls. The DnD group showed notably lower connectivity values than the nD group, with statistically significant disparities. Receiver Operating Characteristic (ROC) curve analysis identified a potential biomarker threshold (Crawford-T value of -2.08) with a sensitivity of 0.83 and specificity of 0.76. The results suggest that functional connectivity patterns within the reward network could serve as a potential biomarker for predicting de novo mood disorders in TLE patients undergoing surgery. This insight may assist in identifying individuals at a higher risk of developing DnD after surgery, enhancing therapeutic guidance and clinical decision-making.

Electrophysiological correlates of anticipating improbable but desired events.

Psychological studies have emphasized that motivation is regulated by the anticipation of the emotional impact from the possible occurrence of unexpected rewarding events. Here, we scrutinized the existence of a corresponding neural signal by means of event-related potentials (ERPs) and computational modeling. In the first experiment, we designed a task that manipulated the probability of gaining a monetary reward and measured ERPs during anticipation and at reward delivery. A sustained frontocentral neural activity (i.e., the stimulus preceding negativity, SPN) was evidenced during the anticipation period. Critically, the SPN was found to increase in amplitude as the reward became more unexpected. Changes in the SPN were found to be predictive of individual differences in risk seeking, suggesting that a greater risk attitude involved a greater motivational state for receiving an improbable reward. In the second experiment, SPN results associated with unexpected monetary gains were replicated in a condition in which participants avoided monetary losses and the occurrence of unexpected rewards was also associated with an increase in the amount of self-reported pleasure. These findings support the existence of a neural ERP signature that encodes the process of tuning our motivation to the possibility of receiving a desirable but improbable rewarding outcome.

Neurophysiological differences in reward processing in anhedonics.

Anhedonia is characterized by a reduced capacity to experience pleasure in response to rewarding stimuli and has been considered a possible candidate endophenotype in depression and schizophrenia. However, it is still not well understood whether these reward deficits are confined to anticipatory and/or to consummatory experiences of pleasure. In the present study, we recorded electrophysiological responses (event-related brain potentials [ERPs] and oscillatory activity) to monetary gains and losses in extreme groups of anhedonic and nonanhedonic participants. The anhedonic participants showed reduced motivation to incur risky decisions, especially after monetary rewards. These sequential behavioral effects were correlated with an increased sensitivity to punishment, which psychometrically characterized the anhedonic group. In contrast, both electrophysiological measures associated with the impacts of monetary losses and gains--the feedback-related negativity (FRN) and the beta-gamma oscillatory component--clearly revealed preserved consummatory responses in anhedonic participants. However, anhedonics showed a drastic increase in frontal medial theta power after receiving the maximum monetary gain. This increase in theta oscillatory activity could be associated with an increase in conflict and cognitive control for unexpected large positive rewards, thus indexing the violation of default negative expectations built up across the task in anhedonic participants. Thus, the present results showed that participants with elevated scores on Chapman's Physical Anhedonia Scale were more sensitive to possible punishments, showed deficits in the correct integration of response outcomes in their actions, and evidenced deficits in sustaining positive expectations of future rewards. This overall pattern suggests an effect of anhedonia in the motivational aspects of approach behavior rather than in consummatory processes.

Reward-based decision-making in mesial temporal lobe epilepsy patients with unilateral hippocampal sclerosis pre- and post-surgery.

BACKGROUND: Correct functioning of the reward processing system is critical for optimizing decision-making as well as preventing the development of addictions and/or neuropsychiatric symptoms such as depression, apathy, and anhedonia. Consequently, patients with mesial temporal lobe epilepsy due to unilateral hippocampal sclerosis (mTLE-UHS) represent an excellent opportunity to study the brain networks involved in this system. OBJECTIVE: The aim of the current study was to evaluate decision-making and the electrophysiological correlates of feedback processing in a sample of mTLE-UHS patients, compared to healthy controls. In addition, we assessed the impact of mesial temporal lobe surgical resection on these processes, as well as general, neuropsychological functioning. METHOD: 17 mTLE-UHS patients and 17 matched healthy controls completed: [1] a computerized version of the Game of Dice Task, [2] a Standard Iowa Gambling Task, and [3] a modified ERP version of a probabilistic gambling task coupled with multichannel electroencephalography. Neuropsychological scores were also obtained both pre- and post-surgery. RESULTS: Behavioral analyses showed a pattern of increased risk for the mTLE-UHS group in decision-making under ambiguity compared to the control group. A decrease in the amplitude of the Feedback Related Negativity (FRN), a weaker effect of valence on delta power, and a general reduction of delta and theta power in the mTLE-UHS group, as compared to the control group, were also found. The beta-gamma activity associated with the delivery of positive reward was similar in both groups. Behavioral performance and electrophysiological measures did not worsen post-surgery. CONCLUSIONS: Patients with mTLE-UHS showed impairments in decision-making under ambiguity, particularly when they had to make decisions based on the outcomes of their choices, but not in decision-making under risk. No group differences were observed in decision-making when feedbacks were random. These results might be explained by the abnormal feedback processing seen in the EEG activity of patients with mTLE-UHS, and by concomitant impairments in working memory, and memory. These impairments may be linked to the disruption of mesial temporal lobe networks. Finally, feedback processing and decision-making under ambiguity were already affected in mTLE-UHS patients pre-surgery and did not show evidence of clear worsening post-surgery.

The effects of COMT (Val108/158Met) and DRD4 (SNP -521) dopamine genotypes on brain activations related to valence and magnitude of rewards.

People's sensitivity to reinforcing stimuli such as monetary gains and losses shows a wide interindividual variation that might in part be determined by genetic differences. Because of the established role of the dopaminergic system in the neural encoding of rewards and negative events, we investigated young healthy volunteers being homozygous for either the Valine or Methionine variant of the catechol-O-methyltransferase (COMT) codon 158 polymorphism as well as homozygous for the C or T variant of the SNP -521 polymorphism of the dopamine D4 receptor. Participants took part in a gambling paradigm featuring unexpectedly high monetary gains and losses in addition to standard gains/losses of expected magnitude while undergoing functional magnetic resonance imaging at 3 T. Valence-related brain activations were seen in the ventral striatum, the anterior cingulate cortex, and the inferior parietal cortex. These activations were modulated by the COMT polymorphism with greater effects for valine/valine participants but not by the D4 receptor polymorphism. By contrast, magnitude-related effects in the anterior insula and the cingulate cortex were modulated by the D4 receptor polymorphism with larger responses for the CC variant. These findings emphasize the differential contribution of genetic variants in the dopaminergic system to various aspects of reward processing.

Neurophysiological markers of novelty processing are modulated by COMT and DRD4 genotypes.

Humans are faced with the dilemma to maintain a stable cognitive set on the one hand and to be able to redirect and switch attention to novel stimuli of potential importance. The dopaminergic system has been implicated in the balance between these two antagonistic constraints and in particular in novelty processing. Here we studied the impact of two polymorphisms affecting dopaminergic functioning (COMT Val108/158Met and DRD4 SNP -521) on neurophysiological correlates of novelty processing. Recording event-related potentials (ERPs) and oscillatory activity in a modified oddball task that featured infrequent but task-irrelevant novel sounds in addition to frequent standard and rare target tones, we examined participants homozygous for the Met or Val variant of COMT as well as homozygous for the C or T variant of DRD4. We found effects mainly on the P3a component to novel stimuli. A greater P3a amplitude was found for the COMT-ValVal group relative to MetMet. There was a tendency for DRD4-TT participants to show greater P3a amplitude and shorter P3a latency. Finally, DRD4-TT and COMT-ValVal participants showed the greatest increase of theta-power to novel stimuli. By contrast, the P3b component to target stimuli showed little influence of the studied polymorphism. Individual differences in dopaminergic genes explain part of the interindividual variance in the neural correlates of novelty but not target processing.

ADHD candidate gene (DRD4 exon III) affects inhibitory control in a healthy sample.

BACKGROUND: Dopamine is believed to be a key neurotransmitter in the development of attention-deficit/hyperactivity disorder (ADHD). Several recent studies point to an association of the dopamine D4 receptor (DRD4) gene and this condition. More specifically, the 7 repeat variant of a variable number of tandem repeats (VNTR) polymorphism in exon III of this gene is suggested to bear a higher risk for ADHD. In the present study, we investigated the role of this polymorphism in the modulation of neurophysiological correlates of response inhibition (Go/Nogo task) in a healthy, high-functioning sample. RESULTS: Homozygous 7 repeat carriers showed a tendency for more accurate behavior in the Go/Nogo task compared to homozygous 4 repeat carriers. Moreover, 7 repeat carriers presented an increased nogo-related theta band response together with a reduced go-related beta decrease. CONCLUSIONS: These data point to improved cognitive functions and prefrontal control in the 7 repeat carriers, probably due to the D4 receptor's modulatory role in prefrontal areas. The results are discussed with respect to previous behavioral data on this polymorphism and animal studies on the impact of the D4 receptor on cognitive functions.

Electrophysiological correlates of feedback processing in subarachnoid hemorrhage patients.

Patients with subarachnoid hemorrhage (SAH) secondary to anterior communicating artery (AComA) aneurysm rupture often experience deficits in executive functioning and decision-making. Effective decision-making is based on the subjects' ability to adjust their performance based on feedback processing, ascribing either positive or negative value to the actions performed reinforcing the most adaptive behavior in an appropriate temporal framework. A crucial brain structure associated to feedback processing is the medial prefrontal cortex (mPFC), a brain region frequently damaged after AComA aneurysm rupture. In the present study, we recorded electrophysiological responses (event-related potentials (ERPs') and oscillatory activity (time frequency analysis) during a gambling task in a series of 15 SAH patients. Previous studies have identified a feedback related negativity (FRN) component associated with an increase on frontal medial theta power in response to negative feedback or monetary losses, which is thought to reflect the degree of negative prediction error. Our findings show a decreased FRN component in response to negative feedback and a delayed increase of theta oscillatory activity in the SAH patient group when compared to the healthy controls, indicating a reduced sensitivity to negative feedback processing and an effortful signaling of cognitive control and monitoring processes lengthened in time, respectively. These results provide us with novel neurophysiological markers regarding feedback processing and performance monitoring patterns in SAH patients, illustrating a dysfunctional reinforcement learning system probably contributing to the maladaptive day-to-day functioning in these patients.

The impact of catechol-O-methyltransferase and dopamine D4 receptor genotypes on neurophysiological markers of performance monitoring.

Dynamic adaptations of one's behavior by means of performance monitoring are a central function of the human executive system, that underlies considerable interindividual variation. Converging evidence from electrophysiological and neuroimaging studies in both animals and humans hints at the importance of the dopaminergic system for the regulation of performance monitoring. Here, we studied the impact of two polymorphisms affecting dopaminergic functioning in the prefrontal cortex [catechol-O-methyltransferase (COMT) Val108/158Met and dopamine D4 receptor (DRD4) single-nucleotide polymorphism (SNP)-521] on neurophysiological correlates of performance monitoring. We applied a modified version of a standard flanker task with an embedded stop-signal task to tap into the different functions involved, particularly error monitoring, conflict detection and inhibitory processes. Participants homozygous for the DRD4 T allele produced an increased error-related negativity after both choice errors and failed inhibitions compared with C-homozygotes. This was associated with pronounced compensatory behavior reflected in higher post-error slowing. No group differences were seen in the incompatibility N2, suggesting distinct effects of the DRD4 polymorphism on error monitoring processes. Additionally, participants homozygous for the COMT Val allele, with a thereby diminished prefrontal dopaminergic level, revealed increased prefrontal processing related to inhibitory functions, reflected in the enhanced stop-signal-related components N2 and P3a. The results extend previous findings from mainly behavioral and neuroimaging data on the relationship between dopaminergic genes and executive functions and present possible underlying mechanisms for the previously suggested association between these dopaminergic polymorphisms and psychiatric disorders as schizophrenia or attention deficit hyperactivity disorder.

Human oscillatory activity associated to reward processing in a gambling task.

Previous event-related brain potential (ERP) studies have identified a medial frontal negativity (MFN) in response to negative feedback or monetary losses. In contrast, no EEG correlates have been identified related to the processing of monetary gains or positive feedback. This result is puzzling considering the large number of brain regions involved in the processing of rewards. In the present study we used a gambling task to investigate this issue with trial-by-trial wavelet-based time-frequency analysis of the electroencephalographic signal recorded non-invasively in healthy humans. Using this analysis a mediofrontal oscillatory component in the beta range was identified which was associated to monetary gains. In addition, standard time-domain ERP analysis showed an MFN for losses that was associated with an increase in theta power in the time-frequency analysis. We propose that the reward-related beta oscillatory activity signifies the functional coupling of distributed brain regions involved in reward processing.

Auditory Target and Novelty Processing in Patients with Unilateral Hippocampal Sclerosis: A Current-Source Density Study.

The capacity to respond to novel events is crucial for adapting to the constantly changing environment. Here, we recorded 29-channel Event Related Brain Potentials (ERPs) during an active auditory novelty oddball paradigm and used for the first time Current Source Density-transformed Event Related Brain Potentials and associated time-frequency spectra to study target and novelty processing in a group of epileptic patients with unilateral damage of the hippocampus (N = 18) and in healthy matched control participants (N = 18). Importantly, we used Voxel-Based Morphometry to ensure that our group of patients had a focal unilateral damage restricted to the hippocampus and especially its medial part. We found a clear deficit for target processing at the behavioral level. In addition, compared to controls, our group of patients presented (i) a reduction of theta event-related synchronization (ERS) for targets and (ii) a reduction and delayed P3a source accompanied by reduced theta and low-beta ERS and alpha event-related synchronization (ERD) for novel stimuli. These results suggest that the integrity of the hippocampus might be crucial for the functioning of the complex cortico-subcortical network involved in the detection of novel and target stimuli.