Neurocognitive Mechanisms Underlying Attention Bias Towards Pain: Evidence From a Drift-Diffusion Model and Event-Related Potentials

Although combining computational modeling with event-related potentials (ERPs) can precisely characterize neurocognitive processes involved in attention bias, it has yet to be applied in the context of pain. Here, a hierarchical drift-diffusion model (DDM) along with ERPs was used to characterize the neurocognitive mechanisms underlying attention bias towards pain. A spatial cueing paradigm was adopted, in which the locations of targets were either validly or invalidly predicted by spatial cues related to pain or nonpain signals. DDM-derived nondecision time was shorter for targets validly cued by pain signals than by nonpain signals, thus indicating speeded attention engagement towards pain; drift rate was slower for targets invalidly cued by pain signals than by nonpain signals, reflecting slower attention disengagement from pain. The facilitated engagement towards pain was partially mediated by the enhanced lateralization of cue-evoked N1 amplitudes, which relate to the bottom-up, stimulus-driven processes of detecting threatening signals. On the other hand, the retarded disengagement from pain was partially mediated by the enhanced target-evoked anterior N2 amplitudes, which relate to the top-down, goal-driven processes of conflict monitoring and behavior regulating. These results demonstrated that engagement and disengagement components of pain-related attention bias are governed by distinct neurocognitive mechanisms. However, it remains possible that the findings are not pain-specific, but rather, are related to threat or aversiveness in general. This deserves to be further examined by adding a control stimulus modality.PerspectiveThis study characterized the neurocognitive processes involved in attention bias towards pain through combining a hierarchical DDM and ERPs. Our results revealed distinctive neurocognitive mechanisms underlying engagement and disengagement components of attention bias. Future studies are warranted to examine whether our findings are pain-specific or not.     

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.     

Cerebral correlates of alerting, orienting and reorienting of visuospatial attention: an event-related fMRI study

The identification of brain systems contributing to different aspects of visuospatial attention is of both clinical and theoretical interest. Cued target detection tasks provide a simple means to dissociate attentional subcomponents, such as alerting, orienting or reorienting of attention. Event-related functional magnetic resonance imaging (fMRI) was used to study neural correlates of these distinct attentional processes. Volunteers were scanned while performing a centrally cued target detection task. Four different types of trials (no cue, neutral cue, valid cue and invalid cue trials) with targets appearing either in the right or left hemifield were randomly intermixed. Behaviourally, the data provided evidence for alerting, spatial orienting and reorienting of attention. Neurally, the alerting effect was seen in bilaterally increased extrastriatal blood oxygenation level-dependent (BOLD) activity in neutral as compared to no cue trials. Neural correlates of spatial orienting were seen in anterior cingulate cortex, which was more active during valid as compared to neutral cue trials. Neural correlates of reorienting of attention, that is, higher BOLD activity to invalid as compared to validly cued trials were evident in several brain regions including left and right intraparietal sulcus, right temporo-parietal junction and middle frontal gyrus bilaterally. The data suggest that frontal and parietal regions are specifically involved in reorienting rather than orienting attention to a spatial position. Alerting effects were seen in extrastriate regions which suggest that increased phasic alertness results in a top-down modulation of neural activity in visual processing areas.     

The large-scale neural network for spatial attention displays multifunctional overlap but differential asymmetry

Functional magnetic resonance imaging (fMRI) was used to determine the brain regions activated by two types of covert visuospatial attentional shifts: one based on exogenous spatial priming and the other on foveally presented cues which endogenously regulated the direction of spatial expectancy. Activations were seen in the cortical and subcortical components of a previously characterized attentional network, namely, the frontal eye fields, posterior parietal cortex, the cingulate gyrus, the putamen, and the thalamus. Additional activations occurred in the anterior insula, dorsolateral prefrontal cortex, temporo-occipital cortex in the middle and inferior temporal gyri, the supplementary motor area, and the cerebellum. Direct comparisons showed a nearly complete overlap in the location of activations resulting from the two tasks. However, the spatial priming task displayed a more pronounced rightward asymmetry of parietal activation, and a conjunction analysis showed that the area of posterior parietal cortex jointly activated by both tasks was more extensive in the right hemisphere. Furthermore, the posterior parietal and temporo-occipital activations were more pronounced in the task of endogenous attentional shifts. The results show that both exogenous (based on spatial priming) and endogenous (based on expectancy cueing) shifts of attention are subserved by a common network of cortical and subcortical regions. However, the differences between the two tasks, especially in the degree of rightward asymmetry, suggests that the pattern of activation within this network may show variations that reflect the specific attributes of the attentional task.     

Neural processing of overt word generation in healthy individuals: the effect of age and word knowledge

Verbal fluency is a classical and widely used neuropsychological instrument to assess cognitive abilities. Results of previous studies indicate an influence on verbal fluency performance of both, age and word knowledge. So far, no imaging study has investigated the neural mechanisms underlying an age and word knowledge related decline on the quantitative verbal output in a highly demanding overt and continuous semantic fluency task. Fifty healthy volunteers (age 22-56 years, verbal IQ 95-143) overtly and continuously articulated words in response to ten visually presented semantic categories while BOLD signal was measured with fMRI. Verbal responses were recorded with an MRI compatible microphone and transcribed after the scanning session. The number of produced words as well as age, word knowledge and level of education was implemented in the design matrix enabling a separate analysis of these factors on both, neural responses and behavioral differences. There was a significant correlation of level of education and number of generated words, but no significant correlations of generated words and age or word knowledge were observed. On the neural level, a widespread network was found for the word production task as contrasted with the resting condition, encompassing the bilateral superior temporal gyri, the cerebellum and the SMA. An age related positive correlation was found in the bilateral inferior and middle frontal gyri, the anterior cingulate gyrus, the left precentral gyrus and the right insula. A lower word knowledge resulted in enhanced BOLD responses in the right superior temporal gyrus and the left superior frontal gyrus. Results are interpreted in terms of compensation mechanisms countervailing potential age and word knowledge related effects.     

Dynamic interactions in the fronto-parietal network during a manual stimulus-response compatibility task

Attentional orienting can be modulated by stimulus-driven bottom-up as well as task-dependent top-down processes. In a recent study we investigated the interaction of both processes in a manual stimulus-response compatibility task. Whereas the intraparietal sulcus (IPS) and the dorsal premotor cortex (dPMC) were involved in orienting towards the stimulus side facilitating congruent motor responses, the right temporoparietal junction (TPJ), right dorsolateral prefrontal cortex (DLPFC) as well as the preSMA sustained top-down control processes involved in voluntary reorienting. Here we used dynamic causal modelling to investigate the contributions and task-dependent interactions between these regions. Thirty-six models were tested, all of which included bilateral IPS, dPMC and primary motor cortex (M1) as a network transforming visual input into motor output as well as the right TPJ, right DLPFC and the preSMA as task-dependent top-down regions influencing the coupling within the dorsal network. Our data showed the right temporoparietal junction to play a mediating role during attentional reorienting processes by modulating the inter-hemispheric balance between both IPS. Analysis of connection strength supported the proposed role of the preSMA in controlling motor responses promoting or suppressing activity in primary motor cortex. As the results did not show a clear tendency towards a role of the right DLPFC, we propose this region, against the usual interpretation of an inhibitory influence in stimulus-response compatibility tasks, to subserve generic monitoring processes. Our DCM study hence provides evidence for context-dependent top-down control of right TPJ and DLPFC as well as the preSMA in stimulus-response compatibility.     

The effect of appraisal level on processing of emotional prosody in meaningless speech

In visual perception of emotional stimuli, low- and high-level appraisal processes have been found to engage different neural structures. Beyond emotional facial expression, emotional prosody is an important auditory cue for social interaction. Neuroimaging studies have proposed a network for emotional prosody processing that involves a right temporal input region and explicit evaluation in bilateral prefrontal areas. However, the comparison of different appraisal levels has so far relied upon using linguistic instructions during low-level processing, which might confound effects of processing level and linguistic task. In order to circumvent this problem, we examined processing of emotional prosody in meaningless speech during gender labelling (implicit, low-level appraisal) and emotion labelling (explicit, high-level appraisal). While bilateral amygdala, left superior temporal sulcus and right parietal areas showed stronger blood oxygen level-dependent (BOLD) responses during implicit processing, areas with stronger BOLD responses during explicit processing included the left inferior frontal gyrus, bilateral parietal, anterior cingulate and supplemental motor cortex. Emotional versus neutral prosody evoked BOLD responses in right superior temporal gyrus, bilateral anterior cingulate, left inferior frontal gyrus, insula and bilateral putamen. Basal ganglia and right anterior cingulate responses to emotional versus neutral prosody were particularly pronounced during explicit processing. These results are in line with an amygdala-prefrontal-cingulate network controlling different appraisal levels, and suggest a specific role of the left inferior frontal gyrus in explicit evaluation of emotional prosody. In addition to brain areas commonly related to prosody processing, our results suggest specific functions of anterior cingulate and basal ganglia in detecting emotional prosody, particularly when explicit identification is necessary.     

Towards a fronto-temporal neural network for the decoding of angry vocal expressions

Vocal expressions commonly elicit activity in superior temporal and inferior frontal cortices, indicating a distributed network to decode vocally expressed emotions. We examined the involvement of this fronto-temporal network for the decoding of angry voices during attention towards (explicit attention) or away from emotional cues in voices (implicit attention) based on a reanalysis of previous data (Frühholz, S., Ceravolo, L., Grandjean, D., 2012. Cerebral Cortex 22, 1107-1117). The general network revealed high interconnectivity of bilateral inferior frontal gyrus (IFG) to different bilateral voice-sensitive regions in mid and posterior superior temporal gyri. Right superior temporal gyrus (STG) regions showed connectivity to the left primary auditory cortex and secondary auditory cortex (AC) as well as to high-level auditory regions. This general network revealed differences in connectivity depending on the attentional focus. Explicit attention to angry voices revealed a specific right-left STG network connecting higher-level AC. During attention to a nonemotional vocal feature we also found a left-right STG network implicitly elicited by angry voices that also included low-level left AC. Furthermore, only during this implicit processing there was widespread interconnectivity between bilateral IFG and bilateral STG. This indicates that while implicit attention to angry voices recruits extended bilateral STG and IFG networks for the sensory and evaluative decoding of voices, explicit attention to angry voices solely involves a network of bilateral STG regions probably for the integrative recognition of emotional cues from voices.     

Continuous ASL perfusion fMRI investigation of higher cognition: quantification of tonic CBF changes during sustained attention and working memory tasks

Arterial spin labeling (ASL) perfusion fMRI is an emerging method in clinical neuroimaging. Its non-invasiveness, absence of low frequency noise, and ability to quantify the absolute level of cerebral blood flow (CBF) make the method ideal for longitudinal designs or low frequency paradigms. Despite the usefulness in the study of cognitive dysfunctions in clinical populations, perfusion activation studies to date have been conducted for simple sensorimotor paradigms or with single-slice acquisition, mainly due to technical challenges. Using our recently developed amplitude-modulated continuous ASL (CASL) perfusion fMRI protocol, we assessed the feasibility of a higher level cognitive activation study in twelve healthy subjects. Taking advantage of the ASL noise properties, we were able to study tonic CBF changes during uninterrupted 6-min continuous performance of working memory and sustained attention tasks. For the visual sustained attention task, regional CBF increases (6-12 ml/100 g/min) were detected in the right middle frontal gyrus, the bilateral occipital gyri, and the anterior cingulate/medial frontal gyri. During the 2-back working memory task, significantly increased activations (7-11 ml/100 g/min) were found in the left inferior frontal/precentral gyri, the left inferior parietal lobule, the anterior cingulate/medial frontal gyri, and the left occipital gyrus. Locations of activated and deactivated areas largely concur with previous PET and BOLD fMRI studies utilizing similar paradigms. These results demonstrate that CASL perfusion fMRI can be successfully utilized for the investigation of the tonic CBF changes associated with high level cognitive operations. Increased applications of the method to the investigation of cognitively impaired populations are expected to follow.     

Attentional systems in target and distractor processing: a combined ERP and fMRI study

The interplay of "top-down" and "bottom-up" regulated mechanisms is of particular relevance for the rapid (re-)focusing of attention to environmental changes. The purpose of the study was to explore the differential contributions of frontoparietal attentional networks involved in top-down and stimulus-driven processing to the detection of "target" and "distractor" events in a visual three-stimulus oddball paradigm. Thirteen healthy subjects underwent separate event-related potential (ERP) and whole-brain functional magnetic resonance imaging (fMRI) measurements during the oddball task. The targets, which were difficult to detect, elicited a classical posterior P3b whereas the distractor stimuli were followed by a centro-frontal P3a ERP. The fMRI data showed activation of the temporoparietal junction (TPJ) bilaterally and right prefrontal cortex associated with both the target and distractor conditions. This network has previously been described as an attentional system that is predominantly stimulus driven and that responds to rare events. Furthermore, target processing produced bilateral perisylvian activity, which has been related to the "retrieval mode". Processing of the distractors activated the frontal eye fields (FEFs) and bilateral superior parietal cortex, areas engaged in attention switching and voluntary allocation of attention. Additional left prefrontal activation suggested an involvement of the cortical system for working memory encoding. Our results thus demonstrate that distractor and target processing engage a common neuronal system for the detection of rare events, but also task-specific subsystems related to attention and memory processes.     

Hypervigilance to learned pain signals: a componential analysis.

We report 2 experiments investigating hypervigilance to pain signals in healthy individuals. In order to allow a detailed analysis, we decomposed attention in 3 different processes: 1) initial shifting, 2) engagement, and 3) disengagement. We used a spatial cueing paradigm in which the location of targets is validly or invalidly predicted by spatial cues. In the first experiment, cues were differentially conditioned to create pain signals, allowing the investigation of engagement and disengagement of attention. Because this procedure does not allow an adequate isolation of the shift component, we introduced a new adaptation of the spatial cueing paradigm in the second experiment, in which targets instead of cues were differentially conditioned. We replicated previous findings, showing enhanced engagement to and retarded disengagement from pain signals compared to control signals. In addition, we demonstrated that participants were still hypervigilant to pain signals after extinction. We were not able to demonstrate speeded shifting to pain signals. Instead we found a generally faster detection of pain signals compared to control signals. We conclude that hypervilance to pain signals does not emerge as rapid initial shifting to the pain signal but rather as enhanced processing once it is detected. Theoretical and clinical implications of these findings are discussed. PERSPECTIVE: We investigated the fundamental processes associated with hypervigilance to pain. Our findings suggest that treatment approaches using attention techniques should not focus on preventing patients to shift their attention to the pain but rather on diminishing the threat value and learning to disengage from their pain.     

Cue validity modulates the neural correlates of covert endogenous orienting of attention in parietal and frontal cortex

Parietal brain regions have been implicated in reorienting of visuospatial attention in location-cueing paradigms when misleading advance information is provided in form of a spatially invalid cue. The difference in reaction times to invalidly and validly cued targets is termed the "validity effect" and used as a behavioral measure for attentional reorienting. Behavioral studies suggest that the magnitude of the validity effect depends on the ratio of validly to invalidly cued targets (termed cue validity), i.e., on the amount of top-down information provided. Using fMRI, we investigated the effects of a cue validity manipulation upon the neural mechanisms underlying attentional reorienting using valid and invalid spatial cues in the context of 90% and 60% cue validity, respectively. We hypothesized that increased parietal activation would be elicited when subjects need to reorient their attention in a context of high cue validity. Behaviorally, subjects showed significantly higher validity effects in the high as compared to the low cue validity condition, indicating slower reorienting. The neuroimaging data revealed higher activation of right inferior parietal and right frontal cortex in the 90% than in the 60% cue validity condition. We conclude that the amount of top-down information provided by predictive cues influences the neural correlates of reorienting of visuospatial attention by modulating activation of a right fronto-parietal attentional network.     

Effective connectivity during haptic perception: a study using Granger causality analysis of functional magnetic resonance imaging data

Although it is accepted that visual cortical areas are recruited during touch, it remains uncertain whether this depends on top-down inputs mediating visual imagery or engagement of modality-independent representations by bottom-up somatosensory inputs. Here we addressed this by examining effective connectivity in humans during haptic perception of shape and texture with the right hand. Multivariate Granger causality analysis of functional magnetic resonance imaging (fMRI) data was conducted on a network of regions that were shape- or texture-selective. A novel network reduction procedure was employed to eliminate connections that did not contribute significantly to overall connectivity. Effective connectivity during haptic perception was found to involve a variety of interactions between areas generally regarded as somatosensory, multisensory, visual and motor, emphasizing flexible cooperation between different brain regions rather than rigid functional separation. The left postcentral sulcus (PCS), left precentral gyrus and right posterior insula were important sources of connections in the network. Bottom-up somatosensory inputs from the left PCS and right posterior insula fed into visual cortical areas, both the shape-selective right lateral occipital complex (LOC) and the texture-selective right medial occipital cortex (probable V2). In addition, top-down inputs from left postero-supero-medial parietal cortex influenced the right LOC. Thus, there is strong evidence for the bottom-up somatosensory inputs predicted by models of visual cortical areas as multisensory processors and suggestive evidence for top-down parietal (but not prefrontal) inputs that could mediate visual imagery. This is consistent with modality-independent representations accessible through both bottom-up sensory inputs and top-down processes such as visual imagery.     

fMRI-acoustic noise alters brain activation during working memory tasks

Scanner noise during functional magnetic resonance imaging (fMRI) may interfere with brain function and change blood oxygenation level dependent (BOLD) signals, a problem that generally worsens at the higher field strengths. Therefore, we studied the effect of increased acoustic noise on fMRI during verbal working memory (WM) processing. The sound pressure level of scanner noise was increased by 12 dBA from "Quiet" to "Loud" echo planar imaging (EPI) scans by utilizing resonant vibration modes of the gradient coil. A WM paradigm with graded levels of task difficulty was used to further access WM load. Increased scanner noise produced increased BOLD responses (percent signal change) bilaterally in the cerebellum, inferior (IFG), medial (medFG), and superior (SFG) frontal, fusiform (FusG), and the lingual (LG) gyri, and decreased BOLD responses bilaterally in the anterior cingulate gyrus (ACG) and the putamen. This finding suggests greater recruitment of attention resources in these brain regions, probably to compensate for interference due to louder scanner noise. Increased working memory load increased the BOLD signals in IFG and the cerebellum, but decreased the BOLD signals in the putamen and the LG. These findings also support the idea that brain function requires additional attention resources under noisier conditions. Load- and acoustic-noise-related changes in BOLD responses correlated negatively in the WM network. This study demonstrates that MR noise affects brain activation pattern. Future comparisons between studies performed under different acoustic conditions (due to differing magnetic field strengths, pulse sequences, or scanner manufacturers) might require knowledge of the sound pressure level of acoustic noise during fMRI.     

Top-down and bottom-up processes in speech comprehension

Speech comprehension includes both bottom-up and top-down processes, and imaging studies have isolated a frontal-temporal network of brain areas active during speech perception. However, the precise role of the various areas in this network during normal speech comprehension is not yet fully understood. In the present fMRI study, the signal-to-noise ratio (SNR) of spoken sentences was varied in 144 steps, and speech intelligibility was measured independently in order to study in detail its effect on the activation of brain areas involved in speech perception. Relative to noise alone, intelligible speech in noise evoked spatially extended activation in left frontal, bilateral temporal, and medial occipital brain regions. Increasing SNR led to a sigmoid-shaped increase of activation in all areas of the frontal-temporal network. The onset of the activation with respect to SNR was similar in temporal and frontal regions, but frontal activation was found to be smaller than temporal activation at the highest SNRs. Finally, only Broca's area (BA44) showed activation to unintelligible speech presented at low SNRs. These findings demonstrate distinct roles of frontal and temporal areas in speech comprehension in that temporal regions subserve bottom-up processing of speech, whereas frontal areas are more involved in top-down supplementary mechanisms.     

Self, mother and abstract other: an fMRI study of reflective social processing

Using fMRI, we studied the neural correlates of self-referential processing by comparing BOLD signal changes during self and mother conditions of a self-reference effect (SRE) task. Conjunction analysis of these two conditions showed several common areas of significant activation, including the medial aspects of the superior frontal gyri, left inferior frontal gyrus, bilateral temporal poles, left superior temporal sulcus and left precuneus. The locations of the 7 strongest peak activations for the self condition and for the mother condition were compared on a subject-by-subject basis in native space. Of the 119 pairs of peaks explored, 87% were located within 2 voxels of each other, demonstrating the commonality of the brain regions subserving both self- and mother-referential processing within an individual subject. In group analyses of the self-referential vs. mother-referential contrast, small differences in activation strength were observed in the left superior frontal sulcus, right cingulate gyrus and the left fusiform gyrus. Greater activation for mother than for self was observed in bilateral temporal lobes. Subjects also performed a social attribution task (SAT) in which they inferred mental states about interacting geometric shapes. Activations from this visual theory of mind task were compared with the activations demonstrated during self-referential processing. Striking similarities were found, including overlapping activations in bilateral medial prefrontal cortices, left inferior frontal gyrus and precuneus. These data suggest that reflective analysis of self, mother and abstract others relies predominantly on the same neural architecture.     

Dissociated brain organization for single-digit addition and multiplication

This study compared the patterns of brain activation elicited by single-digit addition and multiplication problems. 20 Chinese undergraduates were asked to verify whether arithmetic equations were true or false during functional magnetic resonance imaging. Results showed that both addition and multiplication were supported by a broad neural system that involved regions within SMA, precentral gyrus, intraparietal sulcus, occipital gyri, superior temporal gyrus, and middle frontal gyrus, as well as some subcortical structures. Nevertheless, addition problems elicited more activation in the intraparietal sulcus and middle occipital gyri at the right hemisphere, and superior occipital gyri at both hemispheres, whereas multiplication had more activation in precentral gyrus, supplementary motor areas, and posterior and anterior superior temporal gyrus at the left hemisphere. This pattern of dissociated activation supports our hypothesis that addition has greater reliance on visuospatial processing and multiplication on verbal processing.     

EEG signatures of auditory activity correlate with simultaneously recorded fMRI responses in humans

We recorded auditory-evoked potentials (AEPs) during simultaneous, continuous fMRI and identified trial-to-trial correlations between the amplitude of electrophysiological responses, characterised in the time domain and the time–frequency domain, and the hemodynamic BOLD response. Cortical AEPs were recorded from 30 EEG channels within the 3 T MRI scanner with and without the collection of simultaneous BOLD fMRI. Focussing on the Cz (vertex) EEG response, single-trial AEP responses were measured from time-domain waveforms. Furthermore, a novel method was used to characterise the single-trial AEP response within three regions of interest in the time–frequency domain (TF-ROIs). The latency and amplitude values of the N1 and P2 AEP peaks during fMRI scanning were not significantly different from the Control session (p > 0.16). BOLD fMRI responses to the auditory stimulation were observed in bilateral secondary auditory cortices as well as in the right precentral and postcentral gyri, anterior cingulate cortex (ACC) and supplementary motor cortex (SMC). Significant single-trial correlations were observed with a voxel-wise analysis, between (1) the magnitude of the EEG TF-ROI1 (70–800 ms post-stimulus, 1–5 Hz) and the BOLD response in right primary (Heschl's gyrus) and secondary (STG, planum temporale) auditory cortex; and (2) the amplitude of the P2 peak and the BOLD response in left pre- and postcentral gyri, the ACC and SMC. No correlation was observed with single-trial N1 amplitude on a voxel-wise basis. An fMRI-ROI analysis of functionally-identified auditory responsive regions identified further single-trial correlations of BOLD and EEG responses. The TF amplitudes in TF-ROI1 and TF-ROI2 (20–400 ms post-stimulus, 5–15 Hz) were significantly correlated with the BOLD response in all bilateral auditory areas investigated (planum temporale, superior temporal gyrus and Heschl's gyrus). However the N1 and P2 peak amplitudes, occurring at similar latencies did not show a correlation in these regions. N1 and P2 peak amplitude did correlate with the BOLD response in bilateral precentral and postcentral gyri and the SMC. Additionally P2 and TF-ROI1 both correlated with the ACC. TF-ROI3 (400–900 ms post-stimulus, 4–10 Hz) correlations were only observed in the ACC and SMC. Across the group, the subject-mean N1 peak amplitude correlated with the BOLD response amplitude in the primary and secondary auditory cortices bilaterally, as well as the right precentral gyrus and SMC. We confirm that auditory-evoked EEG responses can be recorded during continuous and simultaneous fMRI. We have presented further evidence of an empirical single-trial coupling between the EEG and BOLD fMRI responses, and show that a time–frequency decomposition of EEG signals can yield additional BOLD fMRI correlates, predominantly in auditory cortices, beyond those found using the evoked response amplitude alone.     

Thinner prefrontal cortex in veterans with posttraumatic stress disorder

Structural neuroimaging studies in posttraumatic stress disorder (PTSD) have focused primarily on structural alterations in the medial temporal lobe, and only a few have examined grey matter reductions in the cortex. Recent advances in computational analysis provide new opportunities to use semi-automatic techniques to determine cortical thickness, but these techniques have not yet been applied in PTSD. Twenty-five male veterans with PTSD and twenty-five male veterans without PTSD matched for age, year and region of deployment were recruited. All the subjects were scanned using MRI. Subjects' brains were aligned using cortex-based alignment in a region of interest based approach. Individual cortical thickness maps were calculated from the MR images. Regions of interest examined included the bilateral superior frontal gyri, bilateral middle frontal gyri, bilateral inferior frontal gyri, bilateral superior temporal gyri, and bilateral middle temporal gyri. In a large number of patients and controls, IQ scores and memory scores were also obtained. Individual cortical thickness maps were calculated from the MR images. Veterans with PTSD revealed reduced cortical thickness in the bilateral superior and middle frontal gyri, the left inferior frontal gyrus, and the left superior temporal gyrus. Veterans with PTSD performed significantly worse on memory measures compared to control veterans. Cortical thickness correlated with memory measures in the veterans without PTSD, but not in the veterans with PTSD. Cortical thinning in these regions may thus correspond to functional abnormalities observed in patients with PTSD.     

Endogenous and exogenous attention shifts are mediated by the same large-scale neural network

Event-related fMRI was used to examine the neural basis of endogenous (top-down) and exogenous (bottom-up) spatial orienting. Shifts of attention were induced by central (endogenous) or peripheral (exogenous) cues. Reaction times on subsequently presented targets showed the expected pattern of facilitation and inhibition in both conditions. No difference in brain activity was observed when the two orienting conditions were contrasted with a liberal threshold, showing that both forms of orienting were mediated by the same neural network. Compared to within-block control trials, both endogenous and exogenous orienting activated a fronto-parietal network consisting of premotor cortex, posterior parietal cortex, medial frontal cortex and right inferior frontal cortex. Within these regions, equally strong activation was observed for both orienting conditions. It is concluded that endogenous and exogenous orienting are mediated by the same large-scale network of frontal and parietal brain areas.