Francisco Zamorano

Oscillatory Brain Activity Correlates with Risk Perception and Predicts Social Decisions

In social interactions, the perception of how risky our decisions are depends on how we anticipate other peoples behaviors. We used electroencephalography to study the neurobiology of perception of social risk, in subjects playing the role of proposers in an iterated ultimatum game in pairs. Based on statistical modeling, we used the previous behaviors of both players to separate high-risk [HR] offers from low-risk [LR] offers. The HR offers present higher rejection probability and higher entropy (variability of possible outcome) than the LR offers. Rejections of LR offers elicited both a stronger mediofrontal negativity and a higher prefrontal theta activity than rejections of HR offers. Moreover, prior to feedback, HR offers generated a drop in alpha activity in an extended network. Interestingly, trial-by-trial variation in alpha activity in the medial prefrontal, posterior temporal, and inferior pariental cortex was specifically modulated by risk and, together with theta activity in the prefrontal and posterior cingulate cortex, predicted the proposers subsequent behavior. Our results provide evidence that alpha and theta oscillations are sensitive to social risk and underlie a fine-tuning regulation of social decisions.

Intra-individual response variability assessed by ex-Gaussian analysis may be a new endophenotype for attention-deficit/hyperactivity disorder

Intra-individual variability of response times (RTisv) is considered as potential endophenotype for attentional deficit/hyperactivity disorder (ADHD). Traditional methods for estimating RTisv lose information regarding response times (RTs) distribution along the task, with eventual effects on statistical power. Ex-Gaussian analysis captures the dynamic nature of RTisv, estimating normal and exponential components for RT distribution, with specific phenomenological correlates. Here, we applied ex-Gaussian analysis to explore whether intra-individual variability of RTs agrees with criteria proposed by Gottesman and Gould for endophenotypes. Specifically, we evaluated if normal and/or exponential components of RTs may (a) present the stair-like distribution expected for endophenotypes (ADHD > siblings > typically developing children (TD) without familiar history of ADHD) and (b) represent a phenotypic correlate for previously described genetic risk variants. This is a pilot study including 55 subjects (20 ADHD-discordant sibling-pairs and 15 TD children), all aged between 8 and 13 years. Participants resolved a visual Go/Nogo with 10% Nogo probability. Ex-Gaussian distributions were fitted to individual RT data and compared among the three samples. In order to test whether intra-individual variability may represent a correlate for previously described genetic risk variants, VNTRs at DRD4 and SLC6A3 were identified in all sibling-pairs following standard protocols. Groups were compared adjusting independent general linear models for the exponential and normal components from the ex-Gaussian analysis. Identified trends were confirmed by the non-parametric Jonckheere–Terpstra test. Stair-like distributions were observed for μ (p = 0.036) and σ (p = 0.009). An additional “DRD4-genotype” × “clinical status” interaction was present for τ (p = 0.014) reflecting a possible severity factor. Thus, normal and exponential RTisv components are suitable as ADHD endophenotypes.

P300 amplitude is insensitive to working memory load in schizophrenia

BackgroundWorking memory (WM) tasks usually elicit a P300 ERP component, whose amplitude decreases with increasing WM load. So far, this effect has not been studied in schizophrenics (SZs), a group that is considered to have an aberrant brain connectivity and impairments in WM capacity. The aim of this study was to determine the dependency of the P300 component on WM load in a sample of SZ subjects.MethodsWe recorded 26 subjects (13 SZ patients and their matched controls) with an 80-channel electroencephalogram. Subjects performed an N-back task, a WM paradigm that manipulates the number of items to be stored in memory.ResultsIn healthy subjects, P300 amplitude was highest in the low WM load condition, and lowest in both the attentional control condition and the high WM load condition. In contrast, SZs evidenced low P300 amplitude in all conditions. A significant between group difference in P300 amplitude was evidenced only at the low WM load condition (1 -back), being smaller in SZs.ConclusionsSZ subjects display a lower than normal P300 amplitude, which does not vary as a function of memory load. These results are consistent with a general impairment in WM capacity in these patients.

Functional Cortical Network in Alpha Band Correlates with Social Bargaining

Solving demanding tasks requires fast and flexible coordination among different brain areas. Everyday examples of this are the social dilemmas in which goals tend to clash, requiring one to weigh alternative courses of action in limited time. In spite of this fact, there are few studies that directly address the dynamics of flexible brain network integration during social interaction. To study the preceding, we carried out EEG recordings while subjects played a repeated version of the Ultimatum Game in both human (social) and computer (non-social) conditions. We found phase synchrony (inter-site-phase-clustering) modulation in alpha band that was specific to the human condition and independent of power modulation. The strength and patterns of the inter-site-phase-clustering of the cortical networks were also modulated, and these modulations were mainly in frontal and parietal regions. Moreover, changes in the individuals’ alpha network structure correlated with the risk of the offers made only in social conditions. This correlation was independent of changes in power and inter-site-phase-clustering strength. Our results indicate that, when subjects believe they are participating in a social interaction, a specific modulation of functional cortical networks in alpha band takes place, suggesting that phase synchrony of alpha oscillations could serve as a mechanism by which different brain areas flexibly interact in order to adapt ongoing behavior in socially demanding contexts.

Functional differences of low- and high-frequency oscillatory dynamics during illusory border perception.

Neuronal oscillations are an essential part of several brain processes like perception, memory and attention, but little is known about the simultaneous dynamics of different frequency bands in such processes. Here, we studied the low- and high-frequency dynamics of neuronal oscillations in a task that involves covert searching and visual perception of an illusory contour figure (Kanisza square). Subjects were cued to a particular region of the space, and then a matrix of illusory contour inductors appeared. Illusory contour could appear at the cued position, in a different position or not appear at all. We analyze the condition in which an illusory contour appears and those in which the illusory borders do not appear. During the visual perception of the illusory contour, we found a significant increase in a narrow and sustained gamma frequency band (55-65 Hz). We also found a transient increase in the theta band (4-10 Hz), 0.3 s after stimuli onset. This low-frequency power increase correlates strongly with the detection of the illusory contour and it is inversely correlated with the gamma-band response. When illusory contours were absent, a sustained low-frequency response in the same frequency range was present until appearance of the motor response. The intensity of this low-frequency power response was also related to the speed of the motor response. We hypothesize that theta and gamma interact to process different aspects of the task. Gamma would be related to perception of the stimuli, while theta would be involved in search mechanisms or the initiation of a motor response.

Intratask Variability As a Correlate for DRD4 and SLC6A3 Variants A Pilot Study in ADHD

Behavioral variability may be an ADHD key feature. Currently used ex-Gaussian/Fast Fourier Transform analyses characterize general distribution and oscillatory/rhythmic components of performance but are unable to demonstrate slow cumulative changes over entire tasks. Objective: To explore how performance of ADHD children and unaffected sibs gradually evolves in relation to genetic variants linked to ADHD. Method: A total of 40 kids (20 ADHD-discordant sib pairs) between 8 and 13 years resolved a visual Go/NoGo with 10% NoGo probability. Variable number tandem repeats (VNTRs) at DRD4 and SLC6A3 were identified following standard protocols. Performance changes were assessed by linear/logistic mixed-effect models. Results: Models exploring SLC6A3 effects demonstrated less accentuated increments of response time (RT) (p = .046) and cumulative increments in the correct responses to “NoGo” (p = .00027) in 10R/10R participants. Models for DRD4 showed faster decline of correct responses to “Go” (p = .0078) in 2R/7R carriers. Conclusion: Dynamical analysis of attention/inhibition measures may unravel new correlates to DRD4 and SLC6A3 variants.

Temporal constraints of behavioral inhibition: relevance of inter-stimulus interval in a Go-Nogo task.

The capacity to inhibit prepotent and automatic responses is crucial for proper cognitive and social development, and inhibitory impairments have been considered to be key for some neuropsychiatric conditions. One of the most used paradigms to analyze inhibitory processes is the Go-Nogo task (GNG). This task has been widely used in psychophysical and cognitive EEG studies, and more recently in paradigms using fMRI. However, a technical limitation is that the time resolution of fMRI is poorer than that of the EEG technique. In order to compensate for these temporal constraints, it has become common practice in the fMRI field to use longer inter-stimulus intervals (ISI) than those used in EEG protocols. Despite the noticeable temporal differences between these two techniques, it is currently assumed that both approaches assess similar inhibitory processes. We performed an EEG study using a GNG task with both short ISI (fast-condition, FC, as in EEG protocols) and long ISI (slow-condition, SC, as in fMRI protocols). We found that in the FC there was a stronger Nogo-N2 effect than in the SC. Moreover, in the FC, but not in the SC, the number of preceding Go trials correlated positively with the Nogo-P3 amplitude and with the Go trial reaction time; and negatively with commission errors. In addition, we found significant topographical differences for the Go-P3 elicited in FC and SC, which is interpreted in terms of different neurotransmitter dynamics. Taken together, our results provide evidence that frequency of stimulus presentation in the GNG task strongly modulates the behavioral response and the evoked EEG activity. Therefore, it is likely that short-ISI EEG protocols and long-ISI fMRI protocols do not assess equivalent inhibitory processes.

Balance en la cuerda floja: la neurobiología del trastorno por déficit atencional e hiperactividad

Resumen En este articulo discutimos investigaciones recientes relacionadas a los mecanismos neurobiologicos subyacentes al Trastorno por Deficit Atencional e Hiperactividad, (TDAH) en particular la dinamica de senalizacion dopaminergica y la llamada red por defecto, que consiste en patrones de actividad que se generan durante el reposo. Ambos tipos de fenomenos han sido asociados al TDAH y aqui proponemos una relacion entre ambas dinamicas, y como esta puede estar afectada en el TDAH.