Transient interference of right hemispheric function due to automatic emotional processing

We examined the effects of emotional stimuli on right and left hemisphere detection performance in a hemifield visual discrimination task. A group of 18 healthy subjects were asked to discriminate between upright and inverted triangles (target). Targets were randomly presented in the left or right visual hemifield (150 ms target duration). A brief emotional picture (pleasant or unpleasant; 150 ms stimulus duration) or neutral picture selected from the International Affective Picture System was randomly presented either in the same (47%) or the opposite (47%) spatial location to the subsequent target. Emotional or neutral stimuli offset 150 ms prior to the subsequent target. Subjects were instructed to ignore the pictures and respond to the targets as quickly and accurately as possible. Independent of field of presentation, emotional stimuli prolonged reaction times (P < 0.01) to LVF targets, with unpleasant stimuli showing a greater effect than pleasant stimuli. The current study shows that brief emotional stimuli selectively impair right hemispheric visual discrimination capacity. The findings suggest automatic processing of emotional stimuli captures right hemispheric processing resources and transiently interferes with other right hemispheric functions.     

The parietal cortex and attentional modulations of activities of the visual cortex

We recorded high density event-related brain potentials (ERPs) from a patient with focal left parietal damage in a covert visual orienting task requiring detection of targets in the attended or unattended hemifield. A positivity peaking at 120 ms (P1) to the left visual field stimuli was enlarged when attended than unattended and was localized to the right extrastirate cortex. However, spatial attention did not influence the ERPs to the right visual field stimuli. The leftward cue elicited an enlarged P1 relative to the rightward cue. The results suggest that human parietal cortex is critical for the attentional modulation of the neural activities in the extrastriate cortex associated with stimuli in the contralateral hemifield.     

Visual event-related potentials index focused attention within bilateral stimulus arrays. II. Functional dissociation of P1 and N1 components.

Event-related potentials (ERPs) were recorded from 12 subjects as they attended to the left or right hemifield of a visual display while fixating a central point. Stimuli were presented to the left or right visual fields on separate trials (unilateral stimuli) or to both fields simultaneously (bilateral stimuli). In different conditions, the stimulus sequences contained only bilateral stimuli, only unilateral stimuli, or a mixture of unilateral and bilateral stimuli. Bilateral stimuli elicited an enhanced positivity lasting from about 75 to 250 msec that was largest at posterior electrode sites contralateral to the attended hemifield. The early phase of this attention-related positivity appeared to be an enhancement of the exogenous P1 component. In contrast, both the posterior P1 and N1 components were enhanced in response to attended unilateral stimuli. Moreover, the N1 attention effect was reduced when the preceding stimulus contained elements in the attended field. It was concluded that modulations of the N1 and P1 components in these experiments represent different aspects of visual spatial attention: N1 may represent the orienting of attention to a task-relevant stimulus, whereas P1 may represent a facilitation of early sensory processing for items presented to a location where attention is already focused.     

Electrocortical reactivity to emotional images and faces in middle childhood to early adolescence

The late positive potential (LPP) is an event-related potential (ERP) component that indexes sustained attention toward motivationally salient information. The LPP has been observed in children and adults, however little is known about its development from childhood into adolescence. In addition, whereas LPP studies examine responses to images from the International Affective Picture System (IAPS; Lang et al., 2008) or emotional faces, no previous studies have compared responses in youth across stimuli. To examine how emotion interacts with attention across development, the current study used an emotional-interrupt task to measure LPP and behavioral responses in 8- to 13-year-olds using unpleasant, pleasant, and neutral IAPS images, as well as sad, happy, and neutral faces. Compared to older youth, younger children exhibited enhanced LPPs over occipital sites. In addition, sad but not happy faces elicited a larger LPP than neutral faces; behavioral measures did not vary across facial expressions. Both unpleasant and pleasant IAPS images were associated with increased LPPs and behavioral interference compared to neutral images. Results suggest that there may be developmental differences in the scalp distribution of the LPP, and compared to faces, IAPS elicit more robust behavioral and electrocortical measures of attention to emotional stimuli.     

Concurrent recording of steady-state and transient event-related potentials as indices of visual-spatial selective attention.

OBJECTIVES: The present study investigated the effects of spatial attention on concurrently recorded visual event-related potentials (ERPs) and steady-state visual evoked potentials (SSVEPs) to isoluminant color changes embedded in rapidly flickering stimuli. METHODS: EEG was recorded while subjects attended to flickering LEDs in either the right or left visual hemifield and responded by a button press to isoluminant color changes (targets). RESULTS: Target isoluminant color changes elicited the typical ERP components P1, N1, N2 and P3, which were enhanced for attended targets compared to unattended targets. Consistent with previous findings, SSVEP amplitude was enlarged for attended flicker stimuli at posterior electrode sites contralateral to the attended visual hemifield. In addition, significant correlations were found between the N1, N2 and the SSVEP attention effects, whereas no such correlations were found between the P1, P3 and SSVEP attention effects. CONCLUSIONS: Results suggest that the SSVEP and ERP reflect partially overlapping attentional mechanisms that facilitate the discriminative processing of stimuli at attended locations.     

Valence and arousal influence the late positive potential during central and lateralized presentation of images

The motivated attention network is believed to be the system that allocates attention toward motivationally relevant, emotional stimuli in order to better prepare an organism for action [Lang, P. J., Bradley, M. M., & Cuthbert, B. N. (1997). Motivated attention: Affect, activation, and action. In P. J. Lang, R. F. Simons, M. Balaban, & R. Simons (Eds.), Attention and orienting: Sensory and motivational processes (pp. 97–135). Psychology Press]. The late positive potential (LPP), an event-related potential (ERP) that is a manifestation of the motivated attention network, has not been found to reliably differentiate the valence of emotionally relevant stimuli. In two studies, we systematically varied epoch, stimulus arousal, stimulus valence, and hemisphere of presentation (Study 2) to investigate valence effects in the LPP. Both central and divided visual field presentations of emotional stimuli found the LPP to be sustained in later windows for high-arousing unpleasant images compared to pleasant images. Further, this effect was driven by sustained LPP responses following left hemisphere presentations of unpleasant stimuli compared to right. Findings are discussed regarding hemispheric processing of emotion and how lateralized emotion processes might contribute to psychopathology.     

Right brain,left brain in depressive disorders: Clinical and theoretical implications of behavioral,electrophysiological and neuroimaging findings

The right and left side of the brain are asymmetric in anatomy and function. We review electrophysiological (EEG and event-related potential), behavioral (dichotic and visual perceptual asymmetry), and neuroimaging (PET, MRI, NIRS) evidence of right-left asymmetry in depressive disorders. Recent electrophysiological and fMRI studies of emotional processing have provided new evidence of altered laterality in depressive disorders. EEG alpha asymmetry and neuroimaging findings at rest and during cognitive or emotional tasks are consistent with reduced left prefrontal activity in depressed patients, which may impair downregulation of amygdala response to negative emotional information. Dichotic listening and visual hemifield findings for non-verbal or emotional processing have revealed abnormal perceptual asymmetry in depressive disorders, and electrophysiological findings have shown reduced right-lateralized responsivity to emotional stimuli in occipitotemporal or parietotemporal cortex. We discuss models of neural networks underlying these alterations. Of clinical relevance, individual differences among depressed patients on measures of right-left brain function are related to diagnostic subtype of depression, comorbidity with anxiety disorders, and clinical response to antidepressants or cognitive behavioral therapy.     

“Emotions Guide Us”: Behavioral and MEG correlates

Affectively salient stimuli are capable of capturing attentional resources which allow the brain to change the current course of action in order to respond to potentially advantageous or threatening stimuli. Here, we investigated the behavioral and cerebral impact of peripherally presented affective stimuli on the subsequent processing of foveal information. To this end, we recorded whole-head magnetoencephalograms from 12 participants while they made speeded responses to the direction of left- or right-oriented arrows that were presented foveally at fixation. Each arrow was preceded by a peripherally presented pair of pictures, one emotional (unpleasant or pleasant), and one neutral. Paired pictures were presented at 12° of eccentricity to the left and right of a central fixation cross. We observed that the participants responded more quickly when the orientation of the arrow was congruent with the location of the previously presented emotional scene. Results show that non-predictive emotional information in peripheral vision interferes with subsequent responses to foveally presented targets. Importantly, this behavioral effect was correlated with an early (∼135 msec) increase of left fronto-central activity for the emotionally congruent combination, whose cerebral sources were notably located in the left orbitofrontal cortex. We therefore suggest that the prior spatial distribution of emotional salience, like physical salience, grabs attentional resources and modifies the performance in the center of the visual field. Thus, these data shed light on the neurobehavioral correlates of the emotional coding of visual space.     

Orbitofrontal cortex biases attention to emotional events

We examined the role of orbitofrontal (OF) cortex in regulating emotion-attention interaction and the balance between involuntary and voluntary attention allocation. We studied patients with OF lesion applying reaction time (RT) and event-related potential (ERP) measures in a lateralized visual discrimination task with novel task-irrelevant affective pictures (unpleasant, pleasant, or neutral) preceding a neutral target. This allowed for comparing the effects of automatic attention allocation to emotional versus neutral stimuli on subsequent voluntary attention allocation to target stimuli. N2-P3a and N2-P3b ERP components served as measures of involuntary and voluntary attention allocation correspondingly. Enhanced N2-P3a amplitudes to emotional distractors and reduced N2-P3b amplitudes to targets preceded by emotional distractors were observed in healthy subjects, suggesting automatic emotional orienting interfered with subsequent voluntary orienting. OF patients showed an opposite pattern with tendency towards reduced N2-P3a responses to emotional distractors, suggesting impaired automatic orienting to emotional stimuli due to orbitofrontal damage. Enhanced N2-P3b responses to targets preceded by any affective distractor were observed in OF patients, suggesting bias towards voluntary target-related attention allocation due to orbitofrontal lesion. Behavioral evidence indicated that left visual field (LVF) attention performance was modulated by emotional stimuli. Specifically, OF patients responded faster to LVF targets subsequent to pleasant emotional distractors. We suggest that damage to the orbitofrontal circuitry leads to dysbalance between voluntary and involuntary attention allocation in the context of affective distractors with predisposition to posterior target-related processing over frontal novelty and affect-related processing. Furthermore, we suggest that orbitofrontal influence on emotion-attention interaction is valence and hemisphere dependent.     

Emotionally negative stimuli can overcome attentional deficits in patients with visuo-spatial hemineglect

Left unilateral spatial neglect resulting from right brain damage is characterized by loss of awareness for stimuli in the contralesional side of space, despite intact visual pathways. We examined using fMRI whether patients with neglect are more likely to consciously detect in the neglected hemifield, emotionally negative complex scenes rather than visually similar neutral pictures and if so, what neural mechanisms mediate this effect. Photographs of emotional and neutral scenes taken from the IAPS were presented in a divided visual field paradigm. As expected, the detection rate for emotional stimuli presented in the neglected field was higher than for neutral ones. Successful detection of emotional scenes as opposed to neutral stimuli in the left visual field (LVF) produced activations in the parahippocampal and anterior cingulate areas in the right hemisphere. Detection of emotional stimuli presented in the intact right visual field (RVF) activated a distributed network of structures in the left hemisphere, including anterior and posterior cingulate cortex, insula, as well as visual striate and extrastriate areas. LVF-RVF contrasts for emotional stimuli revealed activations in right and left attention related prefrontal areas whereas RVF-LVF comparison showed activations in the posterior cingulate and extrastriate visual cortex in the left hemisphere. An additional analysis contrasting detected vs. undetected emotional LVF stimuli showed involvement of left anterior cingulate, right frontal and extrastriate areas. We hypothesize that beneficial role of emotion in overcoming neglect is achieved by activation of frontal and limbic lobe networks, which provide a privileged access of emotional stimuli to attention by top-down modulation of processing in the higher-order extrastriate visual areas. Our results point to the importance of top-down regulatory role of the frontal attentional systems, which might enhance visual activations and lead to greater salience of emotional stimuli for perceptual awareness.     

Behavioral and electrophysiological evidence of a right hemisphere bias for the influence of negative emotion on higher cognition

We examined how responses to aversive pictures affected performance and stimulus-locked event-related potentials (ERPs) recorded during a demanding cognitive task. Numeric Stroop stimuli were brief ly presented to either left or right visual hemifield (LVF and RVF, respectively) after a centrally presented aversive or neutral picture from the International Affective Picture System. Subjects indicated whether a quantity value from each Stroop stimulus matched the preceding Stroop stimulus while passively viewing the pictures. After aversive pictures, responses were more accurate for LVF Stroops and less accurate for RVF Stroops. Early-latency extrastriate attention-dependent visual ERPs were enhanced for LVF Stroops. The N2 ERP was enhanced for LVF Stroops over the right frontal and parietal scalp sites. Slow potentials (300-800 msec) recorded over the frontal and parietal regions showed enhanced picture related modulation and amplitude for LVF Stroops. These results suggest that emotional responses to aversive pictures selectively facilitated right hemisphere processing during higher cognitive task performance.     

A shift of visual spatial attention is selectively associated with human EEG alpha activity

Event-related potentials and ongoing oscillatory electroencephalogram (EEG) activity were measured while subjects performed a cued visual spatial attention task. They were instructed to shift their attention to either the left or right visual hemifield according to a cue, which could be valid or invalid. Thereafter, a peripheral target had to be evaluated. At posterior parietal brain areas early components of the event-related potential (P1 and N1) were higher when the cue had been valid compared with invalid. An anticipatory attention effect was found in EEG alpha magnitude at parieto-occipital electrode sites. Starting 200 ms before target onset alpha amplitudes were significantly stronger suppressed at sites contralateral to the attended visual hemifield than ipsilateral to it. In addition, phase coupling between prefrontal and posterior parietal electrode sites was calculated. It was found that prefrontal cortex shows stronger phase coupling with posterior sites that are contralateral to the attended hemifield than ipsilateral sites. The results suggest that a shift of attention selectively modulates excitability of the contralateral posterior parietal cortex and that this posterior modulation of alpha activity is controlled by prefrontal regions.     

Electrophysiologic evidence of increased distractibility after dorsolateral prefrontal lesions

Patients with left prefrontal lesions and control subjects showed enhanced event-related potentials (ERPs) to attended tone sequences presented in a dichotic attention task. ERP enhancements were comparable at short and long interstimulus intervals (ISIs), and did not depend upon whether attended stimuli were preceded by other attended stimuli or by distracting stimuli in the opposite ear. In contrast, patients with right prefrontal lesions showed absent ERP attention effects to contralateral (left ear) tones at all ISIs, and reduced attention effects to ipsilateral tones at long ISIs and when these were preceded by distracting sounds. The results are consistent with an asymmetric organization of dorsolateral prefrontal cortex, and indicate that increased distractibility may contribute to the attention disorders that follow prefrontal lesions.     

Spatial frequency of visual image modulates neural responses in the temporo-occipital lobe. An investigation with event-related fMRI

Our visual environment consists of information ranging from coarse to fine patterns with respect to spatial frequency (SF). Neurophysiological studies using experimental animals have shown that there exist specific SF channels in striate and extrastriate visual cortices. In the present study, we used event-related functional magnetic resonance imaging (fMRI) and healthy subjects to investigate whether manipulation of the SF of visual images modulates neural responses in the temporo-occipital lobes. Subjects were scanned while performing "one-back task" with high-pass or low-pass filtered images of a face and house. We demonstrated that visual attention to the stimuli with high SF more specifically involves cortical activation in the left fusiform gyrus and inferior occipital gyrus as compared to that with low SF. High-SF specificity in the left fusiform gyrus was confirmed by voxel-by-voxel comparison of original images with left-right flipped images. There was no low-SF region in the right hemisphere; however, processing of low-SF images may be category-specific in face- and house-related regions. These results may shed light on the neural correlates of behavioral evidence that high-SF stimuli are handled faster and more accurately when presented to the right visual hemifield than to the left counterpart. The present results were also discussed in a viewpoint of local/global processing and functional asymmetry of cerebral hemispheres.     

Isolating endogenous visuo-spatial attentional effects using the novel visual-evoked spread spectrum analysis (VESPA) technique

In natural visual environments, we use attention to select between relevant and irrelevant stimuli that are presented simultaneously. Our attention to objects in our visual field is largely controlled endogenously, but is also affected exogenously through the influence of novel stimuli and events. The study of endogenous and exogenous attention as separate mechanisms has been possible in behavioral and functional imaging studies, where multiple stimuli can be presented continuously and simultaneously. It has also been possible in electroencephalogram studies using the steady-state visual-evoked potential (SSVEP); however, it has not been possible in conventional event-related potential (ERP) studies, which are hampered by the need to present suddenly onsetting stimuli in isolation. This is unfortunate as the ERP technique allows for the analysis of human physiology with much greater temporal resolution than functional magnetic resonance imaging or the SSVEP. While ERP studies of endogenous attention have been widely reported, these experiments have a serious limitation in that the suddenly onsetting stimuli, used to elicit the ERP, inevitably have an exogenous, attention-grabbing effect. Recently we have shown that it is possible to derive separate event-related responses to concurrent, continuously presented stimuli using the VESPA (visual-evoked spread spectrum analysis) technique. In this study we employed an experimental paradigm based on this method, in which two pairs of diagonally opposite, non-contiguous disc-segment stimuli were presented, one pair to be ignored and the other to be attended. VESPA responses derived for each pair showed a strong modulation at 90–100 ms (during the visual P1 component), demonstrating the utility of the method for isolating endogenous visuo-spatial attention effects.     

Electrophysiological analysis of cortical mechanisms of selective attention to high and low spatial frequencies.

OBJECTIVES: This study investigated whether short-latency (<100ms) event-related potential (ERP) components were modulated during attention to spatial frequency (SF) cues. METHODS: Sinusoidally modulated checkerboard stimuli having high (5 cycles per degree (cpd)) or low (0.8cpd) SF content were presented in random order at intervals of 400-650ms. Subjects attended to either the high or low SF stimuli, with the task of detecting targets of slightly higher or lower SF, respectively, than the above standards. ERPs were recorded from 42 scalp sites during task performance and spatio-temporal analyses were carried out on sensory-evoked and attention-related components. RESULTS: Attended high SF stimuli elicited an early negative difference potential (ND120) starting at about 100ms, whereas attended low SF stimuli elicited a positivity (PD130) in the same latency range. The neural sources of both effects were estimated with dipole modeling to lie in dorsal, extrastriate occipital areas. Earlier evoked components evoked at 60-100ms that were modeled with striate and extrastriate cortical sources were not affected by attention to SF. Starting at 150ms, attended stimuli of both SFs elicited a broad selection negativity (SN) that was localized to ventral extrastriate visual cortex. The SN was larger over the left/right cerebral hemisphere for attended stimuli of high/low SF. CONCLUSIONS: These results support the view that attention to SF does not involve a mechanism of amplitude modulation of early-evoked components prior to 100ms. Attention to high and low SF information involves qualitatively different and hemispherically specialized neural processing operations.     

Attending to multiple visual streams: interactions between location-based and category-based attentional selection

Behavioral studies indicate that subjects are able to divide attention between multiple streams of information at different locations. However, it is still unclear to what extent the observed costs reflect processes specifically associated with spatial attention, versus more general interference due the concurrent monitoring of multiple streams of stimuli. Here we used a factorial design to disentangle the correlates of location- versus category-based selection processes during fMRI. In all conditions, participants were presented with two overlapping visual stimuli (red shapes and green shapes) in each hemifield. In different blocks, subjects either: (1) attended to one single stimulus category, red shapes or green shapes, in one hemifield; (2) attended to both stimulus categories in the same hemifield; (3) attended to one single stimulus category, but monitoring both hemifields at the same time; or (4) attended to one stimulus category in one hemifield, and the other category in the opposite hemifield. The behavioral data showed the expected costs of dividing spatial attention across the two hemifields, and the cost of monitoring two stimulus categories versus one category. The imaging data revealed activation of a dorsal fronto-parietal network, both for dividing spatial attention and for monitoring multiple stimulus categories. However, unlike behavioral data, the imaging results also showed a significant interaction between location- and category-based attention within the same network. This demonstrates that the fronto-parietal cortex engages in both of these selective attention functions, and that a mere increase in task difficulty cannot explain colocalization of these processes. We conclude that, under conditions of multiple streams monitoring, fronto-parietal regions control location- and category-based attentional selection.     

Causal interactions in attention networks predict behavioral performance

Lesion and functional brain imaging studies have suggested that there are two anatomically nonoverlapping attention networks. The dorsal frontoparietal network controls goal-oriented top-down deployment of attention; the ventral frontoparietal network mediates stimulus-driven bottom-up attentional reorienting. The interaction between the two networks and its functional significance has been considered in the past but no direct test has been carried out. We addressed this problem by recording fMRI data from human subjects performing a trial-by-trial cued visual spatial attention task in which the subject had to respond to target stimuli in the attended hemifield and ignore all stimuli in the unattended hemifield. Correlating Granger causal influences between regions of interest with behavioral performance, we report two main results. First, stronger Granger causal influences from the dorsal attention network (DAN) to the ventral attention network (VAN), i.e., DAN→VAN, are generally associated with enhanced performance, with right intraparietal sulcus (IPS), left IPS, and right frontal eye field being the main sources of behavior-enhancing influences. Second, stronger Granger causal influences from VAN to DAN, i.e., VAN→DAN, are generally associated with degraded performance, with right temporal-parietal junction being the main sources of behavior-degrading influences. These results support the hypothesis that signals from DAN to VAN suppress and filter out unimportant distracter information, whereas signals from VAN to DAN break the attentional set maintained by the dorsal attention network to enable attentional reorienting.     

Hemispheric asymmetry for selective attention

A letter-identification task, previously demonstrated to show activation of the pulvinar nucleus of the thalamus with fluodeoxyglucose position emission tomography, was administered to 20 normal volunteers. The letter to be detected could appear alone as a big stimulus or as a small one stimulus surrounded by flanking letters. To test for a hemispheric specialization for filtering processes, the stimuli were displayed horizontally, either in the left or in the right hemifield, or vertically, either above or below the fixation point. In addition, to study the effect of cognitive processes on selective attention resources, we varied the feedback conditions, by delivering or not delivering a blue flash in cases of misses or mistakes. The results show a significant interaction between the type of stimulus (alone or surrounded by flankers) and the hemifield of presentation (left or right) only in the condition where the subjects were presented stimuli horizontally without any feedback. In this condition, reaction times (RTs) were shorter in the left hemifield than in the right hemifield for single stimuli, whereas for stimuli surrounded by flankers, the opposite pattern was observed, that is, shorter RT in the right hemifield than in the left one. The present findings suggest a hemispheric specialization for selective attention, in particular at the subcortical level.     

Intra-modal and cross-modal spatial attention to auditory and visual stimuli. An event-related brain potential study.

This study investigated cross-modal interactions in spatial attention by means of recording event-related brain potentials (ERPs). Noise bursts and light flashes were presented in random order to both left and right field locations separated by 60 degrees in free-field. One group of subjects was instructed to attend selectively to the noise bursts (attend-auditory group), and a second group attended only to the flashes (attend-visual group). On different runs attention was directed to either the right or left field stimuli of the designated modality. In the attend-auditory group, noise bursts at the attended location elicited a broad, biphasic negativity (Nd) beginning at 70 ms. The cross-modal spatial attention effect on the auditory ERPs in the attend-visual group was very similar in morphology, but the Nd was reduced in amplitude relative to the intra-modal effect. In the attend-visual group, flashes at the attended location elicited enhanced early (100-200 ms) and late (200-350 ms) ERP components relative to unattended-location flashes. The cross-modal effect in the attend-auditory group included small but significant enhancements of early components of the visual ERPs. It was concluded that spatial attention has a multi-modal organization such that the processing of stimuli at attended locations is facilitated at an early, sensory level, even for stimuli of an unattended modality.