True and phantom recollection: an fMRI investigation of similar and distinct neural correlates and connectivity

Although research suggests that most false memories are mediated by a sense of familiarity, behavioral evidence indicates that some are characterized by retrieval of item-specific details associated with recollection. However, neuroimaging studies have yet to isolate and analyze the neural correlates of false (or phantom) recollection, focusing instead on general recognition processes. In doing so, results are mixed with respect to the role of the medial temporal lobes (MTL) in distinguishing between true and false retrieval. The present study sought to investigate the neural basis of true and phantom recollection and clarify the role of the MTL in dissociating between the two processes. Results showed that true and phantom recollection were associated with a largely overlapping retrieval network including activity in bilateral anterior parahippocampal gyrus, fusiform gyrus, anterior cingulate cortex, and right superior parietal cortex. However, connectivity analyses using two common MTL seeds revealed a more inferior network (fusiform gyrus, hippocampus, middle temporal gyrus) associated with true recollection and a more superior network (superior parietal, superior frontal gyrus, posterior cingulate cortex) associated with false recollection. Finally, direct comparisons between true and phantom recollection showed greater activity in right hippocampus and early visual cortex for true recollection, whereas no region exhibited greater activity for false recollection. Results indicate that while both true and phantom recollection show similar patterns of activation, there are also distinctions in the neural networks contributing to the two recollection processes. Moreover, results conclude that within the MTL, the hippocampus proper can distinguish between true and phantom recollection.     

Rearranging the world: neural network supporting the processing of temporal connectives

Temporal connectives (before/after) give us the freedom to describe a sequence of events in different orders. Studies have suggested that ‘before-initiating’ sentences, in which events are expressed in an order inconsistent with their actual order of occurrence, might need additional computation(s) during comprehension. The results of independent component analysis suggest that these computations are supported by a neural network connecting the bilateral caudate nucleus with the right middle frontal gyrus, left precentral gyrus, bilateral parietal lobule and inferior temporal gyrus. Among those regions, the caudate nucleus and the left middle frontal gyrus showed greater activations for ‘before’ than ‘after’ sentences. The functional network observed in this study may support sequence learning and processing in a general sense.     

Working memory dysfunction in schizophrenia compared to healthy controls and patients with depression: evidence from event-related fMRI

Studies on working memory (WM) dysfunction in schizophrenia have reported several functionally aberrant brain areas including the lateral prefrontal cortex, superior temporal areas and the striatum. However, less is known about the relationship of WM-dysfunction, cerebral activation, task-accuracy and diagnostic specificity. Using a novel WM-task and event-related functional magnetic resonance imaging (fMRI), we studied healthy control subjects (n=17) and partially remitted, medicated inpatients meeting DSM-IV criteria for schizophrenia (n=19) and major depressive disorder (n=12). Due to the event-related technique, we excluded incorrectly performed trials, thus controlling for accuracy-related activation confounds. Compared with controls, patients with schizophrenia showed less activation in frontoparietal and subcortical regions at high cognitive load levels. Compared with patients with depression, schizophrenic patients showed less prefrontal activation in left inferior frontal cortex and right cerebellum. In patients with schizophrenia, a lack of deactivation of the superior temporal cortex was found compared to both healthy controls and patients with depression. Thus, we could not confirm previous findings of impaired lateral prefrontal activation during WM performance in schizophrenic patients after the exclusion of incorrectly performed or omitted trials in our functional analysis. However, superior temporal cortex dysfunction in patients with schizophrenia may be regarded as schizophrenia-specific finding in terms of psychiatric diagnosis specificity.     

Self awareness and speech processing: an fMRI study

Language production and perception imply motor system recruitment. Therefore, language should obey the theory of shared motor representation between self and other, by means of mirror-like systems. These mirror-like systems (referring to single-unit recordings in animals) show the property to be recruited both when accomplishing and when perceiving a goal-directed action, whatever the sensory modality may be. This hypothesis supposes that a neural network for self-awareness is involved to distinguish speech production from speech listening. We used fMRI to test this assumption in 12 healthy subjects, who performed two different block-design experiments. The first experiment showed involvement of a lateral mirror-like network in speech listening, including ventral premotor cortex, superior temporal sulcus and the inferior parietal lobule (IPL). The activity of this mirror-like network is associated with the perception of an intelligible speech. The second experiment looked at a self-awareness network. It showed involvement of a medial resting-state network, including the medial parietal and medial prefrontal cortices, during the 'self-generated voice' condition, as opposed to passive speech listening. Our results support the fact that deactivation of this medial network, in association with modulation of the activity of the IPL (part of the mirror-like network previously described), is linked to self-awareness in speech processing. Overall, these results support the idea that self-awareness is present when distinguishing between speech production and speech listening situations, and may depend on these two different parieto-frontal networks.     

Differential effects of distraction during working memory on delay-period activity in the prefrontal cortex and the visual association cortex

Maintaining relevant information for later use is a critical aspect of working memory (WM). The lateral prefrontal cortex (PFC) and posterior sensory cortical areas appear to be important in supporting maintenance. However, the relative and unique contributions of these areas remain unclear. We have designed a WM paradigm with distraction to probe the contents of maintenance representations in these regions. During delayed recognition trials of faces, selective interference was evident behaviorally with face distraction leading to significantly worse performance than with scene distraction. Event-related fMRI of the human brain showed that maintenance activity in the lateral PFC, but not in visual association cortex (VAC), was selectively disrupted by face distraction. Additionally, the functional connectivity between the lateral PFC and the VAC was perturbed during these trials. We propose a hierarchical and distributed model of active maintenance in which the lateral PFC codes for abstracted mnemonic information, while sensory areas represent specific features of the memoranda. Furthermore, persistent coactivation between the PFC and sensory areas may be a mechanism by which information is actively maintained.     

The role of precuneus and left inferior frontal cortex during source memory episodic retrieval

The posterior medial parietal cortex and left prefrontal cortex (PFC) have both been implicated in the recollection of past episodes. In a previous study, we found the posterior precuneus and left lateral inferior frontal cortex to be activated during episodic source memory retrieval. This study further examines the role of posterior precuneal and left prefrontal activation during episodic source memory retrieval using a similar source memory paradigm but with longer latency between encoding and retrieval. Our results suggest that both the precuneus and the left inferior PFC are important for regeneration of rich episodic contextual associations and that the precuneus activates in tandem with the left inferior PFC during correct source retrieval. Further, results suggest that the left ventro-lateral frontal region/frontal operculum is involved in searching for task-relevant information (BA 47) and subsequent monitoring or scrutiny (BA 44/45) while regions in the dorsal inferior frontal cortex are important for information selection (BA 45/46).     

Scanning silence: mental imagery of complex sounds

In this functional magnetic resonance imaging (fMRI) study, we investigated the neural basis of mental auditory imagery of familiar complex sounds that did not contain language or music. In the first condition (perception), the subjects watched familiar scenes and listened to the corresponding sounds that were presented simultaneously. In the second condition (imagery), the same scenes were presented silently and the subjects had to mentally imagine the appropriate sounds. During the third condition (control), the participants watched a scrambled version of the scenes without sound. To overcome the disadvantages of the stray acoustic scanner noise in auditory fMRI experiments, we applied sparse temporal sampling technique with five functional clusters that were acquired at the end of each movie presentation. Compared to the control condition, we found bilateral activations in the primary and secondary auditory cortices (including Heschl's gyrus and planum temporale) during perception of complex sounds. In contrast, the imagery condition elicited bilateral hemodynamic responses only in the secondary auditory cortex (including the planum temporale). No significant activity was observed in the primary auditory cortex. The results show that imagery and perception of complex sounds that do not contain language or music rely on overlapping neural correlates of the secondary but not primary auditory cortex.     

Attitudes to the right- and left: frontal ERP asymmetries associated with stimulus valence and processing goals

We used dense-array event-related potentials (ERP) to examine the time course and neural bases of evaluative processing. Participants made good vs. bad (evaluative) and abstract vs. concrete (nonevaluative) judgments of socially relevant concepts (e.g., "murder," "welfare"), and then rated all concepts for goodness and badness. Results revealed a late positive potential (LPP) beginning at about 475 ms post-stimulus and maximal over anterior sites. The LPP was lateralized (higher amplitude and shorter latency) on the right for concepts later rated bad, and on the left for concepts later rated good. Moreover, the degree of lateralization for the amplitude but not the latency was larger when participants were making evaluative judgments than when they were making nonevaluative judgments. These data are consistent with a model in which discrete regions of prefrontal cortex (PFC) are specialized for the evaluative processing of positive and negative stimuli.     

Age differences in neural correlates of route encoding and route recognition

Spatial memory deficits are core features of aging-related changes in cognitive abilities. The neural correlates of these deficits are largely unknown. In the present study, we investigated the neural underpinnings of age-related differences in spatial memory by functional MRI using a navigational memory task with route encoding and route recognition conditions. We investigated 20 healthy young (18-29 years old) and 20 healthy old adults (53-78 years old) in a random effects analysis. Old subjects showed slightly poorer performance than young subjects. Compared to the control condition, route encoding and route recognition showed activation of the dorsal and ventral visual processing streams and the frontal eye fields in both groups of subjects. Compared to old adults, young subjects showed during route encoding stronger activations in the dorsal and the ventral visual processing stream (supramarginal gyrus and posterior fusiform/parahippocampal areas). In addition, young subjects showed weaker anterior parahippocampal activity during route recognition compared to the old group. In contrast, old compared to young subjects showed less suppressed activity in the left perisylvian region and the anterior cingulate cortex during route encoding. Our findings suggest that age-related navigational memory deficits might be caused by less effective route encoding based on reduced posterior fusiform/parahippocampal and parietal functionality combined with diminished inhibition of perisylvian and anterior cingulate cortices correlated with less effective suppression of task-irrelevant information. In contrast, age differences in neural correlates of route recognition seem to be rather subtle. Old subjects might show a diminished familiarity signal during route recognition in the anterior parahippocampal region.     

Impact of brain networks involved in vigilance on processing irrelevant visual motion

The ability to sustain attention over prolonged periods of time is called vigilance. Vigilance is a fundamental component of attention which impacts on performance in many situations. We here investigate whether similar neural mechanisms are responsible for vigilant attention over long and short durations of time and whether neural activity in brain regions sensitive to vigilant attention is related to processing irrelevant information. Brain activity was measured by means of functional magnetic resonance imaging (fMRI) in a 32 min visual vigilance task with varying inter-target intervals and irrelevant peripheral motion stimuli. Changes in neural activity were analysed as a function of time on task to capture long-term aspects of vigilance and as a function of time between target stimuli to capture short-term aspects of vigilance. Several brain regions including the inferior frontal, posterior parietal, superior and middle temporal cortices and the anterior insular showed decreases in neural activity as a function of time on task. In contrast, increasing inter-target intervals resulted in increased neural activity in a widespread network of regions involving lateral and medial frontal areas, temporal areas, cuneus and precuneus, inferior occipital cortex (right), posterior insular cortices, the thalamus, nucleus accumbens and basal forebrain. A partial least square analysis revealed that neural activity in this latter network covaried with neural activity related to processing irrelevant motion stimuli. Our results provide neural evidence that two separate mechanisms are responsible for sustaining attention over long and short durations. We show that only brain areas involved in sustaining attention over short durations of time are related to processing irrelevant stimuli and suggest that these areas can be segregated into two functionally different networks, one possibly involved in motivation, the other in arousal.     

Removing the effect of response time on brain activity reveals developmental differences in conflict processing in the posterior medial prefrontal cortex

In functional magnetic resonance imaging (fMRI) studies, researchers often attempt to ensure that group differences in brain activity are not confounded with group differences in mean reaction time (RT). However, even when groups are matched for performance, they may differ in terms of the RT-BOLD relationship: the degree to which brain activity varies with RT on a trial-by-trial basis. Group activation differences might therefore be influenced by group differences in the relationship between brain activity and time on task. Here, we investigated whether correcting for this potential confound alters group differences in brain activity. Specifically, we reanalyzed data from a functional MRI study of response conflict in children and adults, in which conventional analyses indicated that conflict-related activity did not differ between groups. We found that the RT-BOLD relationship was weaker in children than in adults. Consequently, after removing the effect of RT on brain activity, children exhibited greater conflict-related activity than adults in both the posterior medial prefrontal cortex and the right dorsolateral prefrontal cortex. These results identify the RT-BOLD relationship as an important potential confound in fMRI studies of group differences. They also suggest that the magnitude of the RT-BOLD relationship may be a useful biomarker of brain maturity.     

Large-scale brain networks emerge from dynamic processing of musical timbre, key and rhythm

We investigated the neural underpinnings of timbral, tonal, and rhythmic features of a naturalistic musical stimulus. Participants were scanned with functional Magnetic Resonance Imaging (fMRI) while listening to a stimulus with a rich musical structure, a modern tango. We correlated temporal evolutions of timbral, tonal, and rhythmic features of the stimulus, extracted using acoustic feature extraction procedures, with the fMRI time series. Results corroborate those obtained with controlled stimuli in previous studies and highlight additional areas recruited during musical feature processing. While timbral feature processing was associated with activations in cognitive areas of the cerebellum, and sensory and default mode network cerebrocortical areas, musical pulse and tonality processing recruited cortical and subcortical cognitive, motor and emotion-related circuits. In sum, by combining neuroimaging, acoustic feature extraction and behavioral methods, we revealed the large-scale cognitive, motor and limbic brain circuitry dedicated to acoustic feature processing during listening to a naturalistic stimulus. In addition to these novel findings, our study has practical relevance as it provides a powerful means to localize neural processing of individual acoustical features, be it those of music, speech, or soundscapes, in ecological settings.     

General and specific contributions of the medial prefrontal cortex to knowledge about mental states

Recent neuroimaging research (Mitchell, J.P., Heatherton, T.F., Macrae, C.N., 2002. Distinct neural systems subserve person and object knowledge. Proc. Natl. Acad. Sci. U. S. A. 99, 15238-15243.) has suggested that semantic knowledge about the psychological aspects of other people draws on a pattern of neural activity that differentiates social from nonsocial semantics. Although the medial prefrontal cortex (mPFC) clearly plays a central role in a range of such social-cognitive tasks, little is known about the precise contributions made by this region to social semantics. The current study addressed two outstanding questions regarding mPFC function. First, do mPFC contributions to processing words that refer to psychological states extend to other, nonhuman targets or are they specific to understanding the psychological experience of conspecifics? Second, does the mPFC respond generally to tasks that require processing another person, or is its activity specific to understanding psychological characteristics? To address these questions, participants were scanned using fMRI while judging the applicability of words to one of two types of targets: people or dogs. For each target, participants made one of two types of semantic judgment: does this word describe a potential psychological state of the target or does this word refer to a physical part of the target? Results demonstrated that greater mPFC activation accompanied judgments of psychological states than of body parts regardless of whether the target was a person or a dog, indicating that mPFC contributions to social semantics are specific for understanding psychological states--directly countering recent suggestions that mPFC responds generally to any judgment about another person--and that mPFC activity extends to targets other than conspecifics.     

The Role of the Fusiform Gyrus in Successful Encoding of Face Stimuli

PET was used to measure regional cerebral blood flow (rCBF) while memorizing pictures of unfamiliar human faces presented one at a time (FaceMemory). Other conditions included: (1) FaceRepeat—memorization of four individual faces presented repeatedly; (2) FaceWatching—viewing passively single faces without overt memory demands; and (3) Scrambled—counting dots superimposed on pictures of scrambled faces. After each FaceMemory condition and after the final FaceWatching condition scan, recall was tested by measuring face recognition. Contrasting FaceMemory and Scrambled conditions revealed several temporal activations: right midfusiform and bilateral anterior fusiform gyri. Contrasting FaceWatching and Scrambled conditions showed bilateral activation in the temporal poles and in the anterior fusiform gyri. No hippocampal activation arose from any contrast. Region of interest analyses on the above areas showed correlations with performance: (1) only rCBF in the right midfusiform correlated positively with encoding during the FaceMemory and FaceWatching conditions; (2) in the right temporal polar cortex rCBF decreased during FaceMemory and correlated positively with performance, whereas rCBF increased during FaceWatching and correlated negatively with incidental performance; and (3) activity in the anterior fusiform gyri remained constant across the conditions of FaceMemory, FaceRepeat, FaceWatching, and Scrambled and was uncorrelated with performance. These data suggest an expanded mnemonic role for the right midfusiform in depth of processing/encoding of face information, temporal polar cortex in face perception and recognition, and anterior fusiform activity in featural visual feature processing.     

Hemispheric Activation of Anterior and Inferior Prefrontal Cortex during Verbal Encoding and Recognition: A PET Study of Healthy Volunteers

Evidence of bilateral prefrontal activation during memory encoding and retrieval has increased attention given to anatomical subdivisions within the prefrontal cortex. The current study examined anterior and inferior aspects of the prefrontal cortex to determine their degree of functional and hemispheric overlap during encoding and recognition. Cerebral blood flow of 25 healthy volunteers was measured using PET ¹⁵O-water methods during four conditions: resting baseline, sequential finger movement, word encoding, and word recognition. Resting and motor images were averaged to provide a single reference that was subtracted from encoding and recognition using statistical parametric mapping (SPM96). Memory conditions were also subtracted from each other to identify differences in regional activity. Subjects performed well (86% correct) and had a slightly conservative response bias. Baseline subtraction from encoding revealed focal activation of left inferior prefrontal cortex (area 45) without significant contralateral activation. Recognition minus baseline subtraction produced a focal right anterior prefrontal activation (areas 9 and 10) that was not present in the left hemisphere. Bilateral effects were seen in area 45 during recognition. Subtraction of memory tasks from each other did not reveal any areas of greater activity during encoding. However, the recognition task produced greater activation in right area 9 extending into the anterior cingulate. Greater activity during recognition was also observed in left insula and bilateral visual integration areas. These results are discussed in relation to the prevailing model of prefrontal hemispheric asymmetry during episodic memory.     

Automated computation of the Gyrification Index in prefrontal lobes: methods and comparison with manual implementation

In this paper, we introduce an automated method of calculating Gyrification Index (GI), a measure of cortical folding. Automated GI (A-GI) is an in vivo GI implementation applied to MRI T1 weighted scans and is designed as an extension to the SPM analysis package. The A-GI tool is unbiased in its application, and is unlimited in the size of test cohort to which it can be applied. In comparison to manual methods, A-GI substantially reduces the time costs and improves repeatability. The current A-GI implementation is limited to analysis of prefrontal lobes, but an extension to provide whole brain A-GI is under consideration. In determination of the GI inner contour, A-GI traces high spatial frequencies typically missed in manual tracing, and thus, A-GI reports a high GI value. We examine the operation of this tool in two scan cohorts. We establish that the tool has good repeatability through its application to a cohort where 5 well individuals were scanned 5 times over a period of 6 months. This indicates that A-GI has low susceptibility to scanner noise and is not affected by the variability in brain representation given by repeat scans. We demonstrate replication of hand tracing results by comparisons with a manual GI study that has shown differences between high risk subjects who go on to develop schizophrenia and those who are at high risk but remain well. Direct scan by scan comparisons are carried out between manual and A-GI methods. In respect of scan orientation and coronal sampling, the methods differ, and these considerations contribute to a between methods right prefrontal ICC of 0.67 and left prefrontal ICC of 0.63. The replication results demonstrate that A-GI has discriminatory power equivalent to manual methods. A-GI is therefore a reliable measure of cortical folding that could be usefully applied to a number of MRI data sets of the brain in health and disease.     

Stroop任务的执行加工成分及其神经机制的功能磁共振研究

目的 采用事件相关功能磁共振（ER-fMRI）方法研究Stroop任务的执行加工成分及其相应的神经机制。方法对16例右利手的健康志愿者进行了冲突试次分别占不同比例的两种任务条件的Stroop色词一颜色命名任务。其中一种任务条件冲突试次占30％，一致试次占70％；另一种任务条件冲突试次占70％，一致试次占30％；，同时采用Phillips 3．0 T成像系统，采集其脑部的fMRI数据，图像后处理和分析采用SPM5分析软件得到脑功能活动的图像。结果 16例被试者中12例的资料符合研究条件而被采用。①两种Stroop任务条件的脑激活区域没有差别，与有关实验结果类似。②被试对两种任条件中的冲突试次分别形成了不同等级的冲突和策略加工，高冲突、低策略条件表现为左侧前扣带回（ACC），双侧VLPFC，双侧额极，双侧视区，左侧中颞叶，右侧顶下小叶（IPL），双侧小脑激活增强；高策略、低冲突条件右侧DLPFC，左侧SMA，右侧岛叶，双侧梭状回，右侧丘脑激活增强。③高抑制加工相应于VLPFC激活增强。结论揭示认知控制加工需要扣带-前额通路在内的PFC内不同亚区的功能协同，支持DLPFC和ACC的功能分离，提示抑制功能可能与控制加工分离。     

Relating neuronal dynamics for auditory object processing to neuroimaging activity: a computational modeling and an fMRI study

We investigated the neural basis of auditory object processing in the cerebral cortex by combining neural modeling and functional neuroimaging. We developed a large-scale, neurobiologically realistic network model of auditory pattern recognition that relates the neuronal dynamics of cortical auditory processing of frequency modulated (FM) sweeps to functional neuroimaging data of the type obtained using PET and fMRI. Areas included in the model extend from primary auditory to prefrontal cortex. The electrical activities of the neuronal units of the model were constrained to agree with data from the neurophysiological literature regarding the perception of FM sweeps. We also conducted an fMRI experiment using stimuli and tasks similar to those used in our simulations. The integrated synaptic activity of the neuronal units in each region of the model, convolved with a hemodynamic response function, was used as a correlate of the simulated fMRI activity, and generally agreed with the experimentally observed fMRI data in the brain areas corresponding to the regions of the model. Our results demonstrate that the model is capable of exhibiting the salient features of both electrophysiological neuronal activities and fMRI values that are in agreement with empirically observed data. These findings provide support for our hypotheses concerning how auditory objects are processed by primate neocortex.     

Activations related to "mirror" and "canonical" neurones in the human brain: an fMRI study

In the macaque monkey ventral premotor cortex (F5), "canonical neurones" are active when the monkey observes an object and when the monkey grasps that object. In the same area, "mirror neurones" fire both when the monkey observes another monkey grasping an object and when the monkey grasps that object. We used event-related fMRI to investigate where in the human brain activation can be found that reflects both canonical and mirror neuronal activity. There was activation in the intraparietal and ventral limbs of the precentral sulcus when subjects observed objects and when they executed movements in response to the objects (canonical neurones). There was activation in the dorsal premotor cortex, the intraparietal cortex, the parietal operculum (SII), and the superior temporal sulcus when subjects observed gestures (mirror neurones). Finally, activations in the ventral premotor cortex and inferior frontal gyrus (area 44) were found when subjects imitated gestures and executed movements in response to objects. We suggest that in the human brain, the ventral limb of the precentral sulcus may form part of the area designated F5 in the macaque monkey. It is possible that area 44 forms an anterior part of F5, though anatomical studies suggest that it may be a transitional area between the premotor and prefrontal cortices.     

Small-world directed networks in the human brain: multivariate Granger causality analysis of resting-state fMRI

Small-world organization is known to be a robust and consistent network architecture, and is a hallmark of the structurally and functionally connected human brain. However, it remains unknown if the same organization is present in directed influence brain networks whose connectivity is inferred by the transfer of information from one node to another. Here, we aimed to reveal the network architecture of the directed influence brain network using multivariate Granger causality analysis and graph theory on resting-state fMRI recordings. We found that some regions acted as pivotal hubs, either being influenced by or influencing other regions, and thus could be considered as information convergence regions. In addition, we observed that an exponentially truncated power law fits the topological distribution for the degree of total incoming and outgoing connectivity. Furthermore, we also found that this directed network has a modular structure. More importantly, according to our data, we suggest that the human brain directed influence network could have a prominent small-world topological property.