Sara López-Martín

Emotional context modulates response inhibition: Neural and behavioral data

Although recent hemodynamic studies indicate that neural activity related to emotion and that associated with response inhibition constitute closely interrelated and mutually dependent processes, the nature of this relationship is still unclear. In order to explore the temporo-spatial characteristics of the interaction between emotion and inhibition, event-related potentials (ERPs) were measured as participants (N=30) performed a modified version of the Go/Nogo task that required the inhibition of prepotent responses to neutral cues during three different emotional contexts: negative, neutral, and positive. Temporal and spatial principal component analyses were employed to detect and quantify, in a reliable manner, those ERP components related to response inhibition (i.e., Nogo-N2 and Nogo-P3), and a source-localization technique (sLORETA) provided information on their neural origin. Behavioral analyses revealed that reaction times (RTs) to Go cues were shorter during the positive context than during neutral and negative contexts. ERP analyses showed that suppressing responses to Nogo cues within the positive context elicited larger frontocentral Nogo-P3 amplitudes and enhanced anterior cingulate cortex (ACC) activation than within the negative context. Regression analyses revealed that Nogo-P3 (i) was inversely related to RTs, supporting its association with the inhibition of a prepotent response, and (ii) was associated with contextual valence (amplitude increased as context valence was more positive), but not with contextual arousal. These results suggest that withholding a prepotent response within positively valenced contexts is more difficult and requires more inhibitory control than within negatively valenced contexts.

An electrophysiological study on the interaction between emotional content and spatial frequency of visual stimuli

Previous studies suggest that the magnocellular pathway, a visual processing system that rapidly provides low spatial frequency information to fast-responding structures such as the amygdala, is more involved in the processing of emotional facial expressions than the parvocellular pathway (which conveys all spatial frequencies). The present experiment explored the spatio-temporal characteristics of the spatial frequency modulation of affect-related neural processing, as well as its generalizability to non-facial stimuli. To that aim, the event-related potentials (ERPs) elicited by low-pass filtered (i.e., high spatial frequencies are eliminated) and intact non-facial emotional images were recorded from 31 participants using a 60-electrode array. The earliest significant effect of spatial frequency was observed at 135 ms from stimulus onset: N135 component of the ERPs. In line with previous studies, the origin of N135 was localized at secondary visual areas for low-pass filtered stimuli and at primary areas for intact stimuli. Importantly, this component showed an interaction between spatial frequency and emotional content: within low-pass filtered pictures, negative stimuli elicited the highest N135 amplitudes. By contrast, within intact stimuli, neutral pictures were those eliciting the highest amplitudes. These results suggest that high spatial frequencies are not essential for the initial affect-related processing of visual stimuli, which would mainly rely on low spatial frequency visual information. According to present data, high spatial frequencies would come into play later on.

The role of the anterior cingulate cortex in emotional response inhibition

Although the involvement of the anterior cingulate cortex (ACC) in emotional response inhibition is well established, there are several outstanding issues about the nature of this involvement that are not well understood. The present study aimed to examine the precise contribution of the ACC to emotion‐modulated response inhibition by capitalizing on fine temporal resolution of the event‐related potentials (ERPs) and the recent advances in source localization. To this end, participants (N = 30) performed an indirect affective Go/Nogo task (i.e., unrelated to the emotional content of stimulation) that required the inhibition of a motor response to three types of visual stimuli: arousing negative (A−), neutral (N), and arousing positive (A+). Behavioral data revealed that participants made more commission errors to A+ than to N and A−. Electrophysiological data showed that a specific region of the ACC at the intersection of its dorsal and rostral subdivisions was significantly involved in the interaction between emotional processing and motor inhibition. Specifically, activity reflecting this interaction was observed in the P3 (but not in the N2) time range, and was greater during the inhibition of responses to A+ than to N and A−. Additionally, regression analyses showed that inhibition‐related activity within this ACC region was associated with the emotional content of the stimuli (its activity increased as stimulus valence was more positive), and also with behavioral performance (both with reaction times and commission errors). The present results provide additional data for understanding how, when, and where emotion interacts with response inhibition within the ACC. Hum Brain Mapp 33:2147–2160, 2012.

Spatiotemporal characterization of response inhibition

Despite an extensive literature on the neural substrates of response inhibition, when and where this process occurs in the brain remain unclear. The present study aimed to shed light on this issue by exploiting the high temporal resolution of the event-related potentials (ERPs) and recent advances in source localization. Temporo-spatial principal component analysis was employed to define more precisely the two ERP components most often associated with response inhibition (i.e., frontocentral N2 and frontocentral P3), as well as to improve the accuracy of source localization. In addition, participants (N=40) performed a modified Go/Nogo task composed of three types of stimuli (frequent-Go, infrequent-Go, and infrequent-Nogo), which allowed us to dissociate neural activity associated with response inhibition from that related to novelty processing by directly contrasting nogo and go trials matched with respect to frequency of occurrence. Scalp ERP data indicated that the frontocentral P3, but not the frontocentral N2, showed larger amplitudes for infrequent-Nogo than for infrequent-Go trials. Source localization data parallel the results obtained at the scalp level: only P3-related activity showed differences between infrequent-Nogo and infrequent-Go trials. This increased activation was observed predominantly in the presupplementary motor area (preSMA). Present results suggest that the frontocentral P3 and the preSMA play a core role in response inhibition. The findings of this study substantiate and complement previous results obtained by hemodynamic procedures.

Voltage-based versus factor score-based source localization analyses of electrophysiological brain activity: a comparison.

SummaryThough, traditionally, electrophysiological recordings have been limited to provide temporal information on neural activity, the development of mathematical algorithms capable of solving the inverse problem is facilitating, in recent years, the access to spatial information (i.e., on the origin of neural activation). This study explored a new strategy in order to increase the reliability of inverse problem solutions: applying these algorithms on factor scores (and not on voltages), a parameter that can be defined as “clean amplitude”. Factor scores derive from Principal Component Analysis (PCA) applied to event-related potentials (ERPs). The main advantage of PCA is its capability to extract and quantify ERP components free of the influence of adjacent or subjacent components. The LORETA algorithm for source localization was applied on peak voltage, average voltage and factor scores for the motor potential recorded from 25 subjects, who had to repeatedly press a button with their right hand. The solutions given by LORETA in these three modalities were compared. The motor potential, a negative wave that begins just before any voluntary movement and is centrally distributed in the scalp, is particularly useful to the scope of this study, since its origin is known: contralateral motor cortex. Results show that the three modalities (peak voltage, mean voltage and factor scores) provided the same main focus (left motor cortex), though the “cleanest” solution (i.e., the main focus was more salient with respect to other secondary, noisy foci) was achieved by the factor score‐based LORETA.

THE STRIATUM BEYOND REWARD: CAUDATE RESPONDS INTENSELY TO UNPLEASANT PICTURES

The involvement of striatum in affective processes has been consistently reported in recent years. However, studies within this field have mainly focused on positive affect, revealing the involvement of striatum in reward situations. The present research aimed to explore the involvement of striatum in negative affect through fMRI. To that aim, participants (n=18) were presented with negative, positive and neutral pictures while they performed an indirect task, a strategy repeatedly recommended to avoid cognitive interferences. Positive and negative stimuli did not differ in their arousal levels, as assessed by participants themselves. Analyses of variance showed that caudate nucleus was sensitive to the emotional content of stimulation, negative pictures eliciting greater caudate responses than positive and neutral. Regression analyses indicated that both valence and arousal content of visual stimuli synergically contributed to explain the activation of caudate, whose strong response to negative pictures supports models proposing striatum as a key element in withdrawal situations.

Danger is worse when it moves: neural and behavioral indices of enhanced attentional capture by dynamic threatening stimuli.

Both dynamic non-emotional stimuli (moving dots or digits) and danger-related static stimuli have previously shown to capture attention. This study explored whether the combination of the two factors (i.e., threatening moving stimuli), frequent in natural situations, enhances attentional capture. To this end, static and moving distractors containing emotionally negative and non-negative information were presented to 30 volunteers while they were engaged in a digit categorization task. Behavioral responses and event-related potentials (ERPs) were analyzed. Behavioral and electrophysiological data were convergent: moving negative distractors produced the longest reaction times in the digit categorization task, and elicited the highest amplitudes in the P1 component of the ERPs (peaking at 112ms), an electrophysiological signal of attentional capture. These results suggest that motion provides additional salience to threatening stimuli that facilitates attentional capture.

Decomposing unpleasantness: Differential exogenous attention to disgusting and fearful stimuli

Negative stimuli have consistently been shown to efficiently attract exogenous attention. Two different types of unpleasant stimuli, disgusting and fearful, sharing similar arousal and valence, are usually employed as a single category. However, since they diverge in several important aspects (biological functionality, associated feelings, and central and peripheral physiological correlates), it may be expected that their potential to capture attention differs. Event-related potentials and behavioral indices were recorded while participants were engaged in a digit categorization task in response to three types of irrelevant, distracting pictures: disgusting, fearful and neutral. Disgusting trials were associated with worse performance than fearful trials in the digit categorization task as revealed by reaction times and number of errors. Moreover, P2-associated cuneus activation and scalp anterior P2 amplitude were greater for disgusting than for fearful distracters. All these indices reveal that, under the experimental conditions employed in the present study, disgusting distracters are more efficient at attracting exogenous attention than are fearful distracters.

Cortical thinning of temporal pole and orbitofrontal cortex in medication-naïve children and adolescents with ADHD

Structural and functional brain studies on attention deficit/hyperactivity disorder (ADHD) have primarily examined anatomical abnormalities in the prefronto-striatal circuitry (especially, dorsal and lateral areas of the prefrontal cortex and dorsal striatum). There is, however, increased evidence that several temporal lobe regions could play an important role in ADHD. The present study used MRI-based measurements of cortical thickness to examine possible differences in both prefrontal and temporal lobe regions between medication-näive patients with ADHD (N = 50) and age- and sex-matched typically developing controls (N = 50). Subjects with ADHD exhibited significantly decreased cortical thickness in the right temporal pole and orbitofrontal cortex (OFC) relative to healthy comparison subjects. These differences remained significant after controlling for confounding effects of age, overall mean cortical thickness and comorbid externalizing conditions, such as oppositional defiant and conduct disorders. These results point to the involvement of the temporal pole and OFC in the neuropathology of ADHD. Moreover, present findings add evidence to the assumption that multiple brain regions and psychological processes are associated with ADHD.

Cortical thickness differences in the prefrontal cortex in children and adolescents with ADHD in relation to dopamine transporter (DAT1) genotype

Several lines of evidence suggest that the dopamine transporter gene (DAT1) plays a crucial role in attention deficit hyperactivity disorder (ADHD). Concretely, recent data indicate that the 10-repeat (10R) DAT1 allele may mediate neuropsychological functioning, response to methylphenidate, and even brain function and structure in children with ADHD. This study aimed to investigate the influence of 10R DAT1 on thickness of the prefrontal cortex in children and adolescents with ADHD. To this end, brain magnetic resonance images were acquired from 33 patients with homozygosity for the 10R allele and 30 patients with a single copy or no copy of the allele. The prefrontal cortex of each MRI scan was automatically parceled into regions of interest (ROIs) based on Brodmann areas (BA). The two groups were matched for age, gender, IQ, ADHD subtype, symptom severity, comorbidity and medication status. However, patients with two copies of the 10R allele exhibited significantly decreased cortical thickness in right BA 46 relative to patients with one or fewer copies of the allele. No other prefrontal ROI differed significantly between the two groups. Present findings suggest that cortical thickness of right lateral prefrontal cortex (BA 46) is influenced by the presence of the DAT1 10 repeat allele in children and adolescents with ADHD.