Neural systems for orienting attention to the location of threat signals: an event-related fMRI study

Attention may reflexively shift towards the location of perceived threats, but it is still unclear how these spatial biases recruit the distributed fronto-parietal cortical networks involved in other aspects of selective attention. We used event-related fMRI to determine how brain responses to a neutral visual target are influenced by the emotional expression of faces appearing at the same location during a covert orienting task. On each trial, two faces were briefly presented, one in each upper visual field (one neutral and one emotional, fearful or happy), followed by a unilateral target (a small horizontal or vertical bar) replacing one of the faces. Participants had to discriminate the target orientation, shown on the same (valid) or opposite (invalid) side as the emotional face. Trials with faces but no subsequent target (cue-only trials) were included to disentangle activation due to emotional cues from their effects on target detection. We found increased responses in bilateral temporo-parietal areas and right occipito-parietal cortex for fearful faces relative to happy faces, unrelated to the subsequent target and cueing validity. More critically, we found a selective modulation of intraparietal and orbitofrontal cortex for targets following an invalid fearful face, as well as an increased visual response in right lateral occipital cortex for targets following a valid fearful face. No such effects were observed with happy faces. These results demonstrate that fearful faces can act as exogenous cues by increasing sensory processing in extrastriate cortex for a subsequent target presented at the same location, but also produce a cost in disengaging towards another location by altering the response of IPS to invalidly cued targets. Neural mechanisms responsible for orienting attention towards emotional vs. non-emotional stimuli are thus partly shared in parietal and visual areas, but also partly distinct.     

Cerebral correlates of the "Kohnstamm phenomenon": an fMRI study

This paper addresses the issue of the central correlates of the "Kohnstamm phenomenon", i.e. the long-lasting involuntary muscle contraction which develops after a prolonged isometric voluntary contraction. Although this phenomenon was described as early as 1915, the mechanisms underlying these post-effects are not yet understood. It was therefore proposed to investigate whether specific brain areas may be involved in the motor post-effects induced by either wrist muscle contraction or vibration using the fMRI method. For this purpose, experiments were carried out on the right wrist of 11 healthy subjects. Muscle activity (EMG) and regional cerebral blood flow were recorded during isometric voluntary muscle contraction and muscle vibration, as well as during the subsequent involuntary contractions (the post-effects) which occurred under both conditions. Brain activations were found to occur during the post-contraction and post-vibration periods, which were very similar under both conditions. Brain activation involved motor-related areas usually responsible for voluntary motor command (primary sensory and motor cortices, premotor cortex, anterior and posterior cingulate gyrus) and sensorimotor integration structures such as the posterior parietal cortex. Comparisons between the patterns of brain activation associated with the involuntary post-effects and those accompanying voluntary contraction showed that cerebellar vermis was activated during the post-effect periods whereas the supplementary motor area was activated only during the induction periods. Although post-effects originate from asymmetric proprioceptive inputs, they might also involve a central network where the motor and somatosensory areas and the cerebellum play a key role. In functional terms, they might result from the adaptive recalibration of the postural reference frame altered by the sustained proprioceptive inputs elicited by muscle contraction and vibration.     

Automatic attention orienting by social and symbolic cues activates different neural networks: an fMRI study

Visual attention can be automatically re-oriented by another person's non-predictive gaze as well as by symbolic arrow cues. We investigated whether the shifts of attention triggered by biologically relevant gaze cues and biologically non-relevant arrow cues rely on the same neural systems by comparing the effects of gaze-cued and arrow-cued orienting on blood oxygenation level-dependent (BOLD) signal in humans. Participants detected laterally presented reaction signals preceded by centrally presented non-predictive gaze and arrow cues. Directional gaze cues and arrow cues were presented in separate blocks. Furthermore, two separate control blocks were run in which non-directional cues (straight gaze or segment of a line) were used. The BOLD signals during the control blocks were subtracted from those during the respective blocks with directional cues. Behavioral data showed that, for both cue types, reaction times were shorter on congruent than incongruent trials. Imaging data revealed three foci of activation for gaze-cued orienting: in the left inferior occipital gyrus and right medial and inferior occipital gyri. For arrow-cued orienting, a much more extensive network was activated. There were large postcentral activations bilaterally including areas in the medial/inferior occipital gyri and medial temporal gyri and in the left intraparietal area. Interestingly, arrow cuing also activated the right frontal eye field and supplementary eye field. The results suggest that attention orienting by gaze cues and attention orienting by arrow cues are not supported by the same cortical network and that attention orienting by symbolic arrow cues relies on mechanisms associated with voluntary shifts of attention.     

A parametric fMRI study of overt and covert shifts of visuospatial attention

It has recently been demonstrated that a cortical network of visuospatial and oculomotor control areas is active for covert shifts of spatial attention (shifts of attention without eye movements) as well as for overt shifts of spatial attention (shifts of attention with saccadic eye movements). Studies examining activity in this visuospatial network during attentional shifts at a single rate have given conflicting reports about how the activity differs for overt and covert shifts. To better understand how the network subserves attentional shifts, we performed a parametric study in which subjects made either overt attentional shifts or covert attentional shifts at three different rates (0.2, 1.0, and 2.0 Hz). At every shift rate, both overt and covert shifts of visuospatial attention induced activations in the precentral sulcus, intraparietal sulcus, and lateral occipital cortex that were of greater amplitude for overt than during covert shifting. As the rate of attentional shifts increased, responses in the visuospatial network increased in both overt and covert conditions but this parametric increase was greater during overt shifts. These results confirm that overt and covert attentional shifts are subserved by the same network of areas. Overt shifts of attention elicit more neural activity than do covert shifts, reflecting additional activity associated with saccade execution. An additional finding concerns the anatomical organization of the visuospatial network. Two distinct activation foci were observed within the precentral sulcus for both overt and covert attentional shifts, corresponding to specific anatomical landmarks. We therefore reappraise the correspondence of these two precentral areas with the frontal eye fields.     

When and where perceptual load interacts with voluntary visuospatial attention: an event-related potential and dipole modeling study

Perceptual load is recognized to affect visual selective attention, but at an unknown spatiotemporal locus in the brain. To examine this issue, event-related potentials (ERPs) were recorded while participants performed an orientation discrimination task, under conditions of low or high perceptual load. Participants were required to respond to targets (10% of trials) presented in the attended visual field while ignoring all stimuli in the unattended visual field. The interaction between voluntary attention and perceptual load was significant for the posterior N1 component (190 ms) but not for the earlier C1 (84 ms) or P1 (100 ms) components. This load by attention interaction for N1 was localized to the temporoparietal-occipital (TPO) gyrus by dipole modeling analysis. Dipole modeling also showed that a reversed attentional effect in the C1 time range was due to ERP overlap from the subsequent attention-sensitive P1 component. Results suggest that perceptual load affects voluntary visuospatial attention at an early (but not the earliest) processing stage and that the TPO gyrus mediates target selection at the discrimination stage.     

Sex differences in the neural correlates of child facial resemblance: an event-related fMRI study

Detection of genetic relatedness (i.e. kinship) impacts the social, parental, and sexual behavior of many species. In humans, self-referent phenotype matching based on facial resemblance may indicate kinship. For example, faces that resemble ours are perceived as more trustworthy and attractive. Sex differences in behavioral reactions to facial resemblance among children have also been demonstrated and are consistent with evolutionary theory suggesting that resemblance might serve as a paternity cue. Using event-related fMRI, we show that specific regions of the brain are implicated in processing facial resemblance and a sex difference in cortical response to facial resemblance expressed in children. We found a consistent activation in the fusiform gyrus across all face conditions, which is consistent with previous research on face processing. There were no sex differences in overall response to faces in the fusiform gyrus, and also to faces that did not resemble subjects. When resemblance was not modeled, females showed greater activation to child faces than males. Consistent with parental investment theory and theories of sexual selection, males showed greater cortical activity than females in response to children's faces that resembled them. These data suggest natural selection may have crafted a sexually differentiated neuro-sensory module implicated in detection of facial resemblance that may serve as a kin detection and paternity cue. This process may capitalize on neural substrates involved in self-referent processing and familiarity detection.     

Neural correlates of a reversal learning task with an affectively neutral baseline: an event-related fMRI study

Reversal learning may conceptually be dissected into acquiring stimulus-reinforcement associations and subsequently altering behavior by switching to new associations as stimulus-reinforcement contingencies reverse (i.e., affective switching). Previous imaging studies have found regions of the ventrolateral and orbitofrontal cortex (OFC) to be involved in both subprocesses. However, these studies did not contain an affectively neutral baseline, which precluded adequate assessment of main effects of reward, punishment, and affective switching. We aimed to determine the neural substrate of these main effects, and of common and dissociable regions for reward and punishment. Furthermore, we aimed to discriminate between stimulus-punishment association and affective switching, i.e., to assess affective switching proper. To this end, we implemented a reversal learning task with an affectively neutral baseline condition that matched the experimental task in visual complexity and motor demands. Interestingly, we found dorsolateral prefrontal cortex (DLPFC) and anterior PFC to be engaged in affective switching, a finding that has not been reported before to our knowledge. Enhanced responses in these areas may represent their involvement in cognitive set shifting per se unrelated to the affective context in a reversal learning design. In addition, OFC, insular and medial prefrontal cortex regions were involved in affective switching. Left medial and lateral OFC were shown to be common areas for feedback processing, whereas left ventral striatum and left lateral OFC were specifically activated by reward and punishment, respectively. These results extend our understanding of the neural substrate of reversal learning in humans.     

Neural correlates of distance and congruity effects in a numerical Stroop task: an event-related fMRI study

This study aimed at investigating the neural correlates of a number-size congruity task. Using an event-related fMRI design, we presented one-digit number pairs to 17 participants in a number-size interference task that required subjects to focus on one stimulus property (e.g., numerical size) and to ignore the other (physical size). In different blocks, participants were asked to decide which digit of a digit pair was numerically larger (numerical comparison task) or physically larger (physical comparison task). Stimuli were classified into three categories: (a) congruent: physical and numerical comparison leads to the same response; (b) incongruent: physical and numerical comparison leads to different responses; (c) neutral: the stimuli differ only with regard to the task-relevant stimulus property. Behavioral results reflect robust distance effects (quicker reaction times for long distances relative to short ones) and size congruity effects (longer reaction times for incongruent relative to congruent stimuli) in both tasks. Imaging results reveal that-compared to congruent trials-incongruent trials led to a stronger activation in the dorsolateral prefrontal cortex and the anterior cingulate cortex, areas associated with attentional control. The distance effect (neutral condition only) led to a stronger activation in bilateral parietal areas including the intraparietal sulcus (IPS).     

Feeling-of-knowing in episodic memory: an event-related fMRI study

An individual may fail to recall an item from memory but still feel that it would be recognized on a later test, a retrieval state termed the "feeling-of-knowing" (FOK). In this study we used event-related fMRI and the FOK to examine both encoding- and retrieval-related factors that are associated with different levels of recall performance: successful retrieval of a previously studied item, retrieval failure accompanied by the FOK, and retrieval failure without any FOK. The results revealed one predominant pattern of retrieval-related activation: an intermediate level of activation for FOK-less than that associated with successful recall and greater than that associated with unsuccessful recall (frontal and left parietal cortices). Two further patterns were also observed: greater activation for both successful recall and FOK than for unsuccessful recall (left midlateral prefrontal cortex) and greater activation for successful recall than for both FOK and unsuccessful recall (left MTL). Analysis of encoding trials conditional upon subsequent retrieval success revealed a pattern of activation that appeared to predict subsequent recall, but which further analysis indicated to be a better predictor of subsequent recognition. These results provide evidence that the phenomenology of graded recall is represented neurally in frontal and parietal cortices, but that activation at encoding may not precipitate the different levels of recall experience.     

Neural correlates of incongruous visual information. An event-related fMRI study

Incongruous information is better remembered than ordinary information. This result has been attributed both to semantic incongruity and surprise. To determine the contribution of each factor, we performed a functional magnetic resonance imaging study in which participants viewed pictures depicting ordinary and incongruous objects (e.g., head of a wrench fused onto a sheep body). To maximize surprise we administered novel incongruent pictures infrequently in an initial scan. (This scan also included infrequent color-inverted pictures as a control for frequency.) To obtain a pure measure of the effect of incongruity we conducted a second scan in which participants viewed equal numbers of ordinary and incongruous pictures. Signal increases were greater for incongruous versus ordinary and oddball stimuli throughout the ventral and dorsal visual pathways, and in prefrontal cortex bilaterally. Signal decreases were larger for incongruous than for ordinary stimuli bilaterally in lateral parietal regions. A subset of regions near the right frontal operculum and extending laterally responded only to, or more strongly to, infrequent incongruous pictures. A second, purely behavioral, experiment involving a separate group of participants demonstrated that incongruous pictures were better recognized than ordinary pictures. We interpret our results as suggesting that, although correlates of a surprise response can be observed, better memory for incongruous visual information is attributable mainly to more processing and, consequently, better encoding.     

The functional anatomy of inspection time: an event-related fMRI study

Twenty healthy young adults underwent functional magnetic resonance imaging (fMRI) of the brain while performing a visual inspection time task. Inspection time is a forced-choice, two-alternative visual backward-masking task in which the subject is briefly shown two parallel vertical lines of markedly different lengths and must decide which is longer. As stimulus duration decreases, performance declines to chance levels. Individual differences in inspection time correlate with higher cognitive functions. An event-related design was used. The hemodynamic (blood oxygenation level-dependent; BOLD) response was computed as both a function of the eight levels of stimulus duration, from 6 ms (where performance is almost at chance) to 150 ms (where performance is nearly perfect), and a function of the behavioral responses. Random effects analysis showed that the difficulty of the visual discrimination was related to bilateral activation in the inferior fronto-opercular cortex, superior/medial frontal gyrus, and anterior cingulate gyrus, and bilateral deactivation in the posterior cingulate gyrus and precuneus. Examination of the time courses of BOLD responses showed that activation was related specifically to the more difficult, briefer stimuli and that deactivation was found across most stimulus levels. Functional connectivity suggested the existence of two networks. One comprised the fronto-opercular area, intrasylvian area, medial frontal gyrus, and the anterior cingulate cortex (ACC), possibly associated with processing of visually degraded percepts. A posterior network of sensory-related and associative regions might subserve processing of a visual discrimination task that has high processing demands and combines several fundamental cognitive domains. fMRI can thus reveal information about the neural correlates of mental events which occur over very short durations.     

Reading anomalous sentences: an event-related fMRI study of semantic processing

We report a random-effects analysis of an event-related fMRI study (n = 28) of cerebral activity during the reading of sentences that ended with a word that was either congruent or incongruent with the previous sentence context. Event-related potential studies have shown that this task elicits a late negativity peaking around 400 ms poststimulus (N400) that is larger for incongruent than for congruent sentence endings. A direct comparison of the activation for incongruent words versus that for congruent words revealed significantly greater activation for incongruent words than congruent words in bilateral inferior frontal and inferio-medial temporal cortex, left lateral frontal cortex, left posterior fusiform gyrus, bilateral motor cortex, and supplementary motor area. These results are consistent with data from intracranial electrical recording studies of the N400 electrical potential. The results are discussed as they relate to the localization of the cerebral sites underlying semantic processing in general and the localization of the scalp recorded N400 event-related potential in particular.     

Auditory processing of different types of pseudo-words: an event-related fMRI study

Imaging results on real word and pseudo-word processing have been heterogeneous, allowing only cautious claims about the neuroanatomical loci of lexico-semantic processing. In order to shed more light on this issue, we examined the impact of different structures of non-lexical stimuli on the outcome of comparisons between such items and matched real words. We anticipated that the degree to which a pseudo-word still resembles a particular real word template determines how word-like it is processed. To verify this idea, we tested different types of pseudo-words (either phonotactically legal and transparently or opaquely derived from real words or phonotactically illegal) in an event-related fMRI paradigm utilizing a lexical decision task. All types of pseudo-words elicited a stronger hemodynamic brain response than real words in the bilateral superior temporal gyri. Real words produced stronger brain activations than pseudo-words in the left posterior middle temporal and angular gyri, the rostral and caudal cingulate gyrus, the precuneus and the right inferior temporal gyrus. When contrasted to opaque pseudo-words transparent pseudo-words elicited a stronger brain response in a temporo-parietal region adjacent to the one observed for real words. Our results provide further support for the involvement of the left posterior middle temporal and angular gyri in lexical-semantic processing. The data also indicate that transparently derived pseudo-words are processed similarly to real words. In contrast, semantic operations are blocked when opaquely derived pseudo-words are processed.     

Neural correlates of fear of movement in high and low fear-avoidant chronic low back pain patients: an event-related fMRI study

The fear-avoidance model postulates that in chronic low back pain (CLBP) a fear of movement is acquired in the acute phase, which leads to subsequent avoidance of physical activity and contributes to the pain syndrome's becoming chronic. In the present event-related functional magnetic resonance imaging (fMRI) study of the neural correlates of the fear of movement, 60 women (30 CLBP patients, 15 healthy controls, and 15 women with spider phobia; mean age 46.8±9.8 years) participated. The CLBP patients were divided into a high and low fear-avoidant group on the basis of the Tampa Scale of Kinesiophobia. The participants viewed photographs depicting neutral and aversive (back-stressing) movements, generally fear-inducing and neutral pictures from the International Affective Picture System, and pictures of spiders while fMRI data were acquired. It was hypothesized that the high fear-avoidant CLBP patients would show fear-related activations when viewing the aversive movements and that they would differ from CLBP patients with low fear-avoidance and controls in this regard. No such activations were found for high or low fear-avoidant CLBP patients. The random-effects analysis showed no differences between high and low fear-avoidant CLBP patients or high fear-avoidant CLBP patients and controls. Normal fear-related activations were present in the high fear-avoidant CLBP patients for the generally fear-inducing pictures, demonstrating the validity of the stimulation paradigm and a generally unimpaired fear processing of the high fear-avoidant CLBP patients. Our findings do not support the fear component of the fear avoidance model.     

The effect of preceding context on inhibition: an event-related fMRI study

In this study we combined event-related fMRI with a parametric manipulation of the go nogo paradigm to examine the effect of preceding context on inhibitory processes. Nogo trials were preceded by either 1, 3, or 5 go trials and then compared to one another. Two distinct patterns of activation were associated with behavioral inhibition: First, the ventral prefrontal cortex, cingulate gyrus, and superior parietal regions showed a context effect with an increase in MR signal to nogo trials with increasing number of preceding go trials. Second, anterior regions in the supplementary and premotor cortex showed an increase in MR signal on the nogo condition after 5 preceding go trials, but not after only 1 or 3. A model using the BOLD response in our data was used to verify that the effect of context was not an artifact of the randomization scheme used in the design.     

A fronto-parietal circuit for tactile object discrimination: an event-related fMRI study

Previous studies of somatosensory object discrimination have been focused on the primary and secondary sensorimotor cortices. However, we expected the prefrontal cortex to also become involved in sequential tactile discrimination on the basis of its role in working memory and stimulus discrimination as established in other domains. To investigate the contributions of the different cerebral structures to tactile discrimination of sequentially presented objects, we obtained event-related functional magnetic resonance images from seven healthy volunteers. Our results show that right hand object exploration involved left sensorimotor cortices, bilateral premotor, parietal and temporal cortex, putamen, thalamus, and cerebellum. Tactile exploration of parallelepipeds for subsequent object discrimination activated further areas in the dorsal and ventral portions of the premotor cortex, as well as parietal, midtemporal, and occipital areas of both cerebral hemispheres. Discriminating a parallelepiped from the preceding one involved a bilateral prefrontal-anterior cingulate-superior temporal-posterior parietal circuit. While the prefrontal cortex was active with right hemisphere dominance during discrimination, there was left hemispheric prefrontal activation during the delay period between object presentations. Delay related activity was further seen in the anterior intraparietal area and the fusiform gyrus. The results reveal a prominent role of the human prefrontal cortex for somatosensory object discrimination in correspondence with recent models on stimulus discrimination and working memory.     

功能磁共振观察儿童文盲与非文盲语言加工相关脑区

目的 利用事件相关功能磁共振成像技术(fMRI)对儿童文盲和非文盲汉语加工相关脑区进行探讨.方法 分别对38名儿童(19名文盲和19名非文盲)进行汉字和简单图形判断的测试,同时采集其脑部的fMRI数据.使用基于Matlab7.0的SPM2软件进行数据分析,并生成脑功能区激活图像,对组内和组间数据分别进行单样本和双样本t检验分析.结果 儿童汉字加工激活了由多个脑区构成的神经网络,与成人基本一致,其中非文盲组和文盲组的差异性脑区位于左侧额中回(BA46/9),左侧角回(BA39),左侧梭状回(BA37).结论 左侧额中回(BA46/9)、左侧角回(BA39)及左侧梭状回(BA37)与汉语语义加工密切相关,读写能力在一定程度上改变了语言加工的神经网络联结模式.     

Perirhinal cortex activity during visual object discrimination: an event-related fMRI study

Previous fMRI studies have demonstrated preferential involvement of the perirhinal cortex and hippocampus in tasks of object and spatial memory, respectively. Here we investigated whether similar activity would also be present when object and spatial discrimination was assessed in the absence of explicit declarative memory demands. On each trial in the scanner, participants were presented simultaneously with two arrays of objects and were asked to indicate whether both arrays were identical, differed with respect to the identity of one object or differed with respect to the spatial arrangement of the objects. It was found that the detection of an object identity change was associated with significant right perirhinal cortex activity. We suggest that this perirhinal activity indicates a role of this structure in processes beyond declarative memory, for example, short-term visual working memory or higher order perception. Significantly greater hippocampal activity was not, however, observed during the spatial arrangement condition, perhaps due to the relatively low spatial processing demands of this task.     

Change detection in children with autism: an auditory event-related fMRI study

Autism involves impairments in communication and social interaction, as well as high levels of repetitive, stereotypic, and ritualistic behaviours, and extreme resistance to change. This latter dimension, whilst required for a diagnosis, has received less research attention. We hypothesise that this extreme resistance to change in autism is rooted in atypical processing of unexpected stimuli. We tested this using auditory event-related fMRI to determine regional brain activity associated with passive detection of infrequently occurring frequency-deviant and complex novel sounds in a no-task condition. Participants were twelve 10- to 15-year-old children with autism and a group of 12 age- and sex-matched healthy controls. During deviance detection, significant activation common to both groups was located in the superior temporal and inferior frontal gyri. During 'novelty detection', both groups showed activity in the superior temporal gyrus, the temporo-parietal junction, the superior and inferior frontal gyri, and the cingulate gyrus. Children with autism showed reduced activation of the left anterior cingulate cortex during both deviance and novelty detection. During novelty detection, children with autism also showed reduced activation in the bilateral temporo-parietal region and in the right inferior and middle frontal areas. This study confirms previous evidence from ERP studies of atypical brain function related to automatic change detection in autism. Abnormalities involved a cortical network known to have a role in attention switching and attentional resource distribution. These results throw light on the neurophysiological processes underlying autistic 'resistance to change'.