Altered salience processing in attention deficit hyperactivity disorder

Attentional problems in patients with attention deficit hyperactivity disorder (ADHD) have often been linked with deficits in cognitive control. Whether these deficits are associated with increased sensitivity to external salient stimuli remains unclear. To address this issue, we acquired functional brain images (fMRI) in 38 boys with and without ADHD (age: 11–16 years). To differentiate the effects of item novelty, contextual rareness and task relevance, participants performed a visual oddball task including four stimulus categories: a frequent standard picture (62.5%), unique novel pictures (12.5%), one repeated rare picture (12.5%), and a target picture (12.5%) that required a specific motor response. As a main finding, we can show considerable overlap in novelty‐related BOLD responses between both groups, but only healthy participants showed neural deactivation in temporal as well as frontal regions in response to novel pictures. Furthermore, only ADHD patients, but not healthy controls, engaged wide parts of the novelty network when processing the rare but familiar picture. Our results provide first evidence that ADHD patients show enhanced neural activity in response to novel but behaviorally irrelevant stimuli as well as reduced habituation to familiar items. These findings suggest an inefficient use of neuronal resources in children with ADHD that could be closely linked to increased distractibility. Hum Brain Mapp 36:2049–2060, 2015. © 2015 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.     

The processing of edge information in visual areas of the cortex as evidenced by evoked potentials

Using averaged visually evoked potentials (VEPs), recorded from bipolar cortical electrodes, as indicators of sensory information processing, the sensitivity to stimulus differences of parafoveal and foveal striate, foveal prestriate, and inferotemporal cortex was measured in 3 rhesus monkeys. The stimuli used were a blank field and a series of 5 checkerboard patterns in which check size was varied from 2°24′ to 9′ of retinal arc subtended per check. All stimuli had equal luminance (5.0 ft.-Lamberts) and duration (9 μsec).The results of this study indicate that: (1) VEPs obtained in all of the cortical regions were sensitive to stimulus differences simultaneously at several points along the temporal continuum following the stimulus; (2) the earliest signs of sensitivity to stimulus differences in the VEPs generally appeared initially in the parafoveal striate cortex at about 70 msec post stimulus and tended to be followed in succession by foveal striate, foveal prestriate, and inferotemporal cortex; (3) sensitivity was found for at least 190 msec and as long as 400 msec after stimulus presentation for all of the cortical regions examined and was generally maintained in foveal and parafoveal striate cortex for longer periods than in foveal prestriate and inferotemporal cortex; (4) the most significant signs of sensitivity were found in the parafoveal striate cortex and a simple transformation of edge information into VEP amplitude was shown to occur there; and (5) none of the cortical regions demonstrated long-term habituation of sensitivity to stimulus differences.These data give evidence for both serial and parallel processing of edge information between and within the different regions of the primary visual and visual association cortex with an apparent focus of edge information processing in parafoveal striate cortex.     

Abnormal visual processing in migraine with aura: a study of steady-state visual evoked potentials

BACKGROUND: Although a number of studies reported different interictal findings between migraine with aura (MA) and migraine without aura (MO), the pathophysiology of the visual aura in migraine remains unclear. OBJECTIVE: To investigate the visual processing in patients who experience MA between attacks using steady-state visual evoked potentials (SSVEPs). METHODS: SSVEPs to high (98%) and low (29%) contrast black and white checkerboard gratings with two spatial frequencies (0.5 and 2.0 cpd) at 5 and 10 Hz (10 and 20 reversal/s) were recorded binocularly from 10 patients with MA, 10 patients with MO between attacks and 20 healthy controls (HC). The SSVEPs were Fourier analyzed to obtain the amplitude and phase of the second (2F) and fourth (4F) harmonic response. RESULTS: In the amplitude of 2F, at 0.5 cpd, there was significant increased amplitude in both MA and MO in comparison to HC at 5 Hz in high and low contrast. However, no significant differences were detected at 2.0 cpd in both 5 and 10 Hz in high and low contrast. In the amplitude of 4F, at 2.0 cpd, there was significant increased amplitude in MA in comparison to MO and HC at 10 Hz in high contrast. However, there were no significant differences at 0.5 cpd at both 5 and 10 Hz in high and low contrast. There were no significant phase differences between MA, MO, and HC. CONCLUSION: The high amplitude of the SSVEPs suggests that interictally migraine patients have abnormal excitability in the primary visual cortex, and this change in excitability may exist, at least partially, in the visual association cortex in MA.     

Hemispheric differences in the neural processing of stimulus location and type: Effects of selective attention on visual evoked potentials

Hemispheric differences in a negative brain potential associated with selectively attending the location and type of stimulation were investigated. The earlier portion of this negativity (between 125 and 222 msec after stimulation) was associated with attending the location of the stimulus. It was symmetrical in the central scalp regions but was greater in the hemisphere contralateral to the attended visual field in the posterior scalp region. The later portion of this negativity (from 222 to 272 msec after stimulation) primarily was associated with attending one of the different types of stimuli presented at a given location and was greater over the left posterior regions of the scalp. These results were interpreted in relationship to the time-course of different types of information processing in the left and right hemispheres.     

Role of visual attention on auditory evoked potentials in unanesthetized cats

Click-evoked potentials were recorded from unanesthetized cats with electrodes chronically implanted in the auditory cortex, cochlear nucleus, and round window. The clicks (irrelevant stimuli) were presented continuously as background before, during, and after the presentation of a visual discrimination task (relevant stimuli) which attempted to alter the attentive state of the animals. The mean peak-to-peak amplitudes of averaged click-evoked responses from six adult female cats were significantly smaller during attention to the visual discrimination stimuli when compared with the prediscrimination and control periods. This relationship was present at all electrode placements for five experimental animals with middle ear muscles cut as well as one control animal with middle ear muscles intact. The results suggest that during attention, a central inhibitory mechanism, independent of middle ear muscles, modified click-evoked responses possibly via the olivocochlear bundle which terminates on the hair cells in the cochlea.     

Altered early visual processing components in hallucination-prone individuals

Of the nonpathological general population, 0.5% experience one or more visual hallucinations on a regular basis without meeting the criteria for clinical psychosis. We investigated the relationship between a proneness to visual hallucinations in 'normal' individuals and early visual event-related potentials during the perception of faces, Mooney faces and scrambled Mooney faces. Findings indicated that individuals prone to visual hallucinations displayed significantly reduced early event-related potential components (P1, P2, but not N170) over parieto-temporal regions. These findings support previous suggestions that individuals who experience visual hallucinations exhibit abnormal early visual processing resulting from degraded visual input, in this case owing to disruption of low level visual processes.     

Temporal attention enhances early visual processing: a review and new evidence from event-related potentials

Two fundamental cognitive functions, selective attention and processing of time, have been simultaneously explored in recent studies of temporal orienting of attention. A temporal-orienting procedure may consist of a temporal analogue to the Posner's paradigm, such that symbolic cues indicate the most probable moment for target arrival. Behavioral measures suggest that performance is improved for events appearing at expected vs. unexpected moments. However, there is no agreement on the locus of stimulus processing at which temporal attention operates. Thus, it remains unclear whether early perceptual or just late motor processes can be modulated. This article reviews current ERP research on temporal orienting, with an emphasis on factors that might determine the modulation of temporal orienting at early stages of processing. We conclude that: First, late components (N2 and P300) are consistently modulated by temporal orienting, which suggests attentional preparation of decision and/or motor processes. Second, early components (e.g., N1) seem to be modulated only when the task is highly demanding in perceptual processing. Hence, we conducted an ERP experiment which aimed to observe a modulation of early visual processing by using a perceptually demanding task, such as letter discrimination. The results show, for the first time, that targets appearing at attended moments elicited a larger P1 component than unattended targets. Moreover, temporal attention modulated the amplitude and latency of N2 and P300 components. This suggests that temporal orienting of attention not only modulates late motor processing, but also early visual processing when perceptually demanding tasks are used.     

Auditory-evoked potentials and selective attention: different ways of information processing in cannabis users and controls

The present study tested the hypothesis that chronic cannabis use leads to persistent attentional dysfunctions and that age of onset of cannabis use is a potential predictor of impaired test performance and information processing. Brain event-related potentials (ERPs) during a complex auditory selective attention task were recorded from 21 cannabis users divided into two groups according to age of onset and from 13 controls comparable with respect to age, IQ and educational background. Participants were instructed to detect target tones of a particular location, pitch and duration from a total sample of random frequencies. The study reveals that the latency of the greatest negative peak of ERPs (200 and 300 ms) to target tones was shorter in controls, while there was no clear difference between target and non-target within cannabis users. In addition, users displayed a reduced P3 to target tones. This was more pronounced in early-onset cannabis users. These data suggest that chronic cannabis use relates to different types of information processing under conditions of selective attention. There is some evidence that users employed different strategies of attention allocation. The results are discussed with respect to possible underlying mechanisms and clinical implications.     

Altered automatic face processing in individuals with high-functioning autism spectrum disorders: Evidence from visual evoked potentials

Individuals with autism spectrum disorders (ASDs) have different automatic responses to faces than typically developing (TD) individuals. We recorded visual evoked potentials (VEPs) in 10 individuals with high-functioning ASD (HFASD) and 10 TD individuals. Visual stimuli consisted of upright and inverted faces (fearful and neutral) and objects presented subliminally in a backward-masking paradigm. In all participants, the occipital N1 (about 100 ms) and P1 (about 120 ms) peaks were major components of the evoked response. We calculated “subliminal face effect (SFE)” scores by subtracting the N1/P1 amplitudes and latencies of the object stimuli from those of the face stimuli. In the TD group, the SFE score for the N1 amplitude was significantly higher for upright fearful faces but not neutral faces, and this score was insignificant when the stimuli were inverted. In contrast, the N1 amplitude of the HFASD subjects did not show this SFE in the upright orientation. There were no significant group differences in SFE scores for P1 amplitude, latency, or N1 latency. Our findings suggest that individuals with HFASD have altered automatic visual processing for emotional faces within the lower level of the visual cortex. This impairment could be a neural component of the disrupted social cognition observed in individuals with HFASD.     

Altered processing of novel information in N-CAM-deficient mice

N-CAM-deficient mice display anatomical and electrophysiological abnormalities in the CNS and behavioral deficits. Here, we address the question whether information processing is altered in these mice by analysis of the expression of c-fos and arg 3.1/arc in N-CAM-deficient mice after presentation of saccharin as novel or familiar and water as neutral gustatory stimulus. When compared to their wild-type control littermates, increased expression of c-fos mRNA in the amygdala after the novel taste and of arg 3.1/arc mRNA in the dentate gyrus 4.5 h after the neutral taste was detected in the absence of N-CAM. Furthermore, the novelty-induced increase in arg 3.1/arc expression in the cingulate cortex 4.5 h after the novel taste was not observed in N-CAM-deficient mice. These data suggest that information processing mediated by immediate-early gene expression is altered in N-CAM-deficient mice.     

Altered emotional information processing in borderline personality disorder: An electrophysiological study

Emotional dysregulation is one of the key symptoms of patients with borderline personality disorder (BPD). In the present study it is hypothesized that borderline patients display a cortical hyper-responsivity to emotional stimuli compared with a healthy control group. Further, we aimed to examine whether BPD patients were able to suppress stimuli with negative emotional valence as well as healthy control participants could. This is the first study addressing the electrophysiological processing of emotional stimuli in BPD. The electrophysiological response to emotional information was studied among 30 BPD patients and compared with the response in 30 normal controls using event-related potentials (ERPs). Participants were shown pictures selected from the International Affective Picture System with neutral, positive, and negative valence. After performing an attentional task, the participants were asked to perform a reappraisal task. The assignment was to consciously suppress emotions that might occur after viewing pictures with an unpleasant content. Borderline patients displayed larger late positive potentials (LPP) to pictures with an unpleasant valence as compared with the control group, indicating an enhanced elaborative processing of unpleasant stimuli. However, they did not differ on the reappraisal task. Borderline patients show an enhanced emotional cortical reactivity to unpleasant stimuli as compared with a control group. This suggests an emotional dysfunctioning in BPD patients. This feature might be an important focus in the treatment of BPD.     

Effects of visual attention on the intensity of auditory evoked potentials.

Click-evoked potentials were recorded from the round window (cochlear microphonic and auditory nerve), cochlear nucleus, and auditory cortex of unanesthetized cats during periods of visual attention and increased auditory intensity. The clicks (irrelevant stimuli) were presented continuously as background before, during, and after the presentation of a visual discrimination task (relevant stimuli) which attempted to alter the attentive state of the animals. At all electrode sites, the mean peak-to-peak amplitudes of click-evoked potentials were significantly smaller during attention to the visual discrimination stimuli when compared with the pretest and posttest control periods. Although the amplitudes of the click-evoked potentials were suppressed at all intensities during visual attention, much greater suppression occurred at low auditory intensities than at high auditory intensities. The results suggest that during attention, a central inhibitory mechanism suppresses irrelevant auditory stimuli presumably via the olivo-cochlear bundle at the peripheral stages in the afferent auditory pathways.     

Effects of expectation on negative potentials during visual processing

ERPs were recorded during several RT tasks: simple RT; oddball choice RT; a LIE condition in which subjects were told stimuli would infrequently change, but did not; differential responding to two equiprobable stimuli that were randomized in one condition and alternated in another condition. Subtracting ERPs elicited during simple RT from those elicited during the other conditions, it was found that a negative component, NA, was enhanced, relative to simple RT, in all the other RT tasks. The data of the LIE condition indicated that NA was enhanced by the expectation that unpredictable stimulus changes would occur, even when they did not. The data of the 50/50 alternating RT condition indicated that stimulus changes by themselves enhance NA, even when they are predictable. There appear to be several deflections that comprise NA. NA was obtained with a variety of subtractions that balanced stimulus probability, the structure of the stimulus sequence and task instructions. Similar results were obtained whether subjects made a finger lift response or counted stimuli.     

Luminance and spatial attention effects on early visual processing

Event-related potentials (ERPs) were recorded from healthy subjects in response to unilaterally flashed high and low luminance bar stimuli presented randomly to left and right field locations. Their task was to covertly and selectively attend to either the left or right stimulus locations (separate blocks) in order to detect infrequent shorter target bars of either luminance. Independent of attention, higher stimulus luminance resulted in higher ERP amplitudes for the posterior N95 (80–110 ms), occipital P1 (110–140 ms), and parietal N1 (130–180 ms). Brighter stimuli also resulted in shorter peak latency for the occipital N1 component (135–220 ms); this effect was not observed for the N1 components over parietal, central or frontal regions. Significant attention-related amplitude modulations were obtained for the occipital P1, occipital, parietal and central N1, the occipital and parietal P2, and the parietal N2 components; these components were larger to stimuli at the attended location. In contrast to the relatively short latencies of both spatial attention and luminance effects, the first interaction between luminance and spatial attention effects was observed for the P3 component to the target stimuli (350–750 ms). This suggests that interactions of spatial attention and stimulus luminance previously reported for reaction time measures may not reflect the earliest stages of sensory/perceptual processing. Differences in the way in which luminance and attention affected the occipital P1, occipital N1 and parietal N1 components suggest dissociations among these ERPs in the mechanisms of visual and attentional processing they reflect. Nonetheless, scalp current density mappings of the attention effects throughout the latency ranges of the P1 and N1 components show the most prominent attention-related activity to be in lateral occipital scalp areas. Such a pattern is consistent with the spatially selective filtering of information into the ventral stream of visual processing which is reponsible for complex feature analysis and object identification.     

Residual information processing in the neglected visual half-field

Summary A patient with neglect of visual half-field without hemianopia performed same/different interfield comparisons and named stimuli presented either unilaterally or bilaterally in the visual half-fields. With unilateral presentation he could name all stimuli in both fields, whereas with simultaneous bilateral stimulation his performance decreased to about 50% correct naming of left visual field (LVF) stimuli. This performance was not improved by cueing for the presence of LVF stimuli. Interfield comparisons were 100% correct in all conditions. It is concluded that inattention for the left hemispace in patients with visual neglect occurs whenever information in the right hemi-space attracts attention or must be consciously processed. Simple same/different judgements are presumably performed on a pre-attentional level and are not affected by neglect.     

Time information in Poggendorff visual illusion: visual evoked potentials.

Using the component sets of the Poggendorff visual illusion as optical stimuli (comprising two horizontal and parallel segments intersected by two oblique segments), we recorded the respective visual evoked potentials (VEPs). Depending on the different delta t passing between the constitutive elements of the Poggendorff illusion, it was found that there was a greater latency of VEP components for the visual stimulus presentation sequence in which oblique segments are projected before horizontal segments.     

Early visual information processing in schizophrenia compared to recurrent depression

Patients with schizophrenia have repeatedly shown deficits in early visual processing using backward masking (VBM) tasks. Whether this represents a specific dysfunction in schizophrenia is an unsolved question. Patients with recurrent unipolar depression represent an interesting comparison group to examine the question of specificity, but have never previously been assessed on VBM. In addition to comparing VBM performance in patients with schizophrenia and patients with depression, we wanted to examine the relations between VBM and clinical symptoms. Fifty-one patients with schizophrenia were compared to 49 patients with recurrent unipolar depression and 47 healthy controls. All subjects were administered a two-digit identification task in a no-masking and four masking conditions. Patients with schizophrenia performed significantly worse than normal controls on four of the five conditions. No significant difference was found between depression patients and normal controls. The effect of masking stimuli had no differential effects on the three groups. VBM correlated strongly with positive symptoms in the schizophrenia group.