Reactivation of visual cortex during memory retrieval: content specificity and emotional modulation

Studies on memory retrieval suggest a reactivation of cortical regions engaged during encoding, such that visual or auditory areas reactivate for visual or auditory memories. The content specificity and any emotion dependency of such reactivations are still unclear. Because distinct visual areas are specialized in processing distinct stimulus categories, we tested for face and word specific reactivations during a memory task using functional magnetic resonance imaging (fMRI). Furthermore, because visual processing and memory are both modulated by emotion, we compared reactivation for stimuli encoded in a neutral or emotionally significant context. In the learning phase, participants studied pairs of stimuli that consisted of either a scene and a face, or a scene and a word. Scenes were either neutral or negative, but did not contain faces or words. In the test phase scenes were presented alone (one in turn), and participants indicated whether it was previously paired with a face, a word, or was new. Results from the test phase showed activation in a functionally defined face-responsive region in the right fusiform gyrus, as well as in a word-responsive region in the left inferior temporal gyrus, for scenes previously paired with faces and words, respectively. Reactivation tended to be larger in both the face- and word-responsive regions when the associated scene was negative as compared to neutral. However, relative to neutral context, the recall of faces and words paired with a negative context produced smaller activations in brain regions associated with social and semantic processing, respectively, as well as poorer memory performance overall. Taken together, these results support the idea of cortical memory reactivations, even at a content-specific level, and further suggest that emotional context may produce opposite effects on reactivations in early sensory areas and more elaborate processing in higher-level cortical areas.     

Reactivation of memory by hypnosis and suggestion

The effects of hypnotic susceptibility (high vs. low), hypnotic condition (hypnotized vs. waking), and the order of testing (hypnosis first vs. waking first) on S's ability to recall meaningful material (specific facts about a rare chemical) 2 weeks after it was originally learned were studied using a 3-way, repeated-measures, factorial design. 52 college students (both male and female) acted as Ss for the study. No significant main effects were found, and the only significant interaction effect indicated that the memory was enhanced when tested the second time, regardless of whether it was in the waking or the hypnotized condition. The results were compared with the findings of other studies in this area using a less complex design.     

Dynamics of brain activity in motor and frontal cortical areas during music listening: a magnetoencephalographic study

There are formidable problems in studying how 'real' music engages the brain over wide ranges of temporal scales extending from milliseconds to a lifetime. In this work, we recorded the magnetoencephalographic signal while subjects listened to music as it unfolded over long periods of time (seconds), and we developed and applied methods to correlate the time course of the regional brain activations with the dynamic aspects of the musical sound. We showed that frontal areas generally respond with slow time constants to the music, reflecting their more integrative mode; motor-related areas showed transient-mode responses to fine temporal scale structures of the sound. The study combined novel analysis techniques designed to capture and quantify fine temporal sequencing from the authentic musical piece (characterized by a clearly defined rhythm and melodic structure) with the extraction of relevant features from the dynamics of the regional brain activations. The results demonstrated that activity in motor-related structures, specifically in lateral premotor areas, supplementary motor areas, and somatomotor areas, correlated with measures of rhythmicity derived from the music. These correlations showed distinct laterality depending on how the musical performance deviated from the strict tempo of the music score, that is, depending on the musical expression.     

磁共振观察运动准备与执行的脑功能分布

目的 探索运动指令与运动执行的脑功能区空间分布.方法 被试者为15名健康大学生,根据屏幕上出现的指令,分别进行运动准备和手指对指运动,磁共振采集数据,以最大峰值作为聚类依据,自编聚类程序,对作业活动脑区进行聚类统计处理.结果 在M1区出现大面积的运动激活,且有少量运动准备活动出现;发现SMA、PPC等辅助运动区有较大面积运动准备激活,也有少量运动执行活动的脑激活.在运动脑区,两种功能活动的空间分布清晰.结论 M1、SMA、PPC等脑区并非单一脑功能区,而是多功能混合脑区.     

Posthypnotic amnesia for material learned before or during hypnosis: explicit and implicit memory effects

This article focuses on dissociations between explicit and implicit expressions of memory during posthypnotic amnesia (PHA). Despite evidence of such dissociations, experimental design in this area has not always been consistent with contemporary memory research. Within a paradigm that aimed for conceptual and methodological clarity, we presented 40 high and 38 low hypnotizable individuals with a word list either before or during hypnosis, gave them a PHA suggestion for the word list, and tested them on explicit and implicit memory tasks. In the absence of conscious recollection, highs showed equivalent levels of priming (perceptual and semantic) to lows. However, when analysis focused only on those highs who remained amnesic after the implicit memory tasks, we confirmed perceptual, but not semantic, priming. These findings highlight the impact of methodological choices on theoretical interpretations of memory performance following a suggestion for PHA.     

Task relevance modulates successful retrieval effects during explicit and implicit memory tests

The successful retrieval effect refers to greater activation for items identified as old compared to those identified as new. This effect is particularly apparent in the ventral posterior parietal cortex (vPPC), though its functional properties remain unclear. In two experiments, we assessed the activation for old and new items during explicit and implicit tests of memory. In Experiment 1, significant effects were observed during explicit recognition performance and during an implicit lexical decision task. In both tasks, determining mnemonic status provides relevant information to task goals. Experiment 2 included a second implicit task in which determining mnemonic status was not relevant (color discrimination task). In this case, vPPC activation did not distinguish between old and new items. These findings suggest that automatic or implicit processes can drive retrieval-related activation in the vPPC, though such processes are gated by stimulus relevancy and task goals.     

Evaluation of the effective connectivity of supplementary motor areas during motor imagery using Granger causality mapping

Brain activation during motor imagery has been studied extensively for years, but only a few of these studies focused on investigating the effective connectivity in the brain. The existence of interactions or closed loop circuits between the SMA and other brain regions during motor imagery still remains unclear. In the present study, selecting the SMA as the region of interest, we used the Granger causality mapping (GCM) method to explore the effective connectivity in the brain during motor imagery. Our results demonstrated that more brain regions showed effective connections to the SMA during the right-hand motor imagery than during the left-hand motor imagery, but the strength of the casual influence during the left-hand motor imagery was stronger than that of the right-hand motor imagery. We further found forward and backward effective connectivity between the SMA and three regions, including the bilateral dorsal premotor area (PMd), the contralateral primary and secondary somatosensory cortex (S1), and the primary motor cortex (M1). these results might indicate how the brain regions were inter-activated during motor 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.     

Multivariate time-frequency analysis of electromagnetic brain activity during bimanual motor learning

Although the relationship between brain activity and motor performance is reasonably well established, the manner in which this relationship changes with motor learning remains incompletely understood. This paper presents a study of cortical modulations of event-related beta activity when participants learned to perform a complex bimanual motor task: 151 channel MEG data were acquired from nine healthy adults whilst learning a bimanual 3:5 polyrhythm. Sources of MEG activity were determined by means of synthetic aperture magnetometry that yielded locations and time courses of beta activities. The relationship between changes in performance and corresponding changes in event-related power were assessed using partial least squares. Behavioral data revealed that participants successfully learned to perform the 3:5 polyrhythm and that performance improvement was mainly achieved through the proper timing of the finger producing the slow rhythm. We found event-related modulation of beta power in the contralateral motor cortex that was inversely related to force output. The degree of beta modulation increased during the experiment - although the force level remained constant - and was positively correlated with motor performance, in particular for the motor cortex contralateral to the slow hand. These electrophysiological findings support the view that activity in motor cortex co-varies closely with behavioral changes over the course of learning.     

Cortical motor areas are activated early in a characteristic sequence during post-movement processing

During motor learning in goal-directed reactions, a specific movement has to be associated with feedback about the movement's success. Such feedback often follows when the movement is already over. We investigated the time-course of post-movement cortical motor processing by high-resolution analysis of lateralized post-movement potentials in forewarned and simple reaction time tasks. In both paradigms we could separate a post-movement component (motor postimperative negative variation-mPINV) peaking about 500 ms after the button press (confirmed by electromyogram and accelerometer). mPINV could not be sufficiently explained by motor cortex activity related to EMG output and/or by sensory feedback. mPINV was enhanced by long intertrial intervals and its lateralization changed with response movement side. Its scalp potential distribution resembled (pre-)motor cortex activity during preceding movement stages and differed from the frontal motor potential peak (proprioceptive and somatosensory reafferent feedback); suggesting post-movement activation of pre-/primary motor cortex. Dipole source analysis yielded a single radial source near premotor cortex which explained lateralized mPINV almost completely. mPINV was present in simple reaction time tasks, indicating that mPINV is an independent component and does not represent delayed resolution of pre-movement negativity. An equivalent of "classical" PINV (cPINV) occurred later over prefrontal and anterior temporal sites in simple and forewarned reaction time tasks. Our results suggest that high-resolution analysis of lateralized movement-related potentials allows to image post-movement motor cortex activity and might provide insights into basic mechanisms of motor learning: A characteristic sequence might involve motor cortex activation (mPINV) before "higher order associative areas" come into play (cPINV).     

Piecemeal recruitment of left-lateralized brain areas during reading: a spatio-functional account

Neuroimaging studies of reading converge to suggest that linguistically elementary stimuli are confined to the activation of bilateral posterior regions, whereas linguistically complex stimuli additionally recruit left hemispheric anterior regions, raising the hypotheses of a gradual bilateral-to-left and a posterior-to-anterior recruitment of reading related areas. Here, we tested these two hypotheses by contrasting a repertoire of eight categories of stimuli ranging from simple orthographic-like characters to words and pseudowords in a single experiment, and by measuring BOLD signal changes and connectivity while 16 fluent readers passively viewed the stimuli. Our results confirm the existence of a bilateral-to-left and posterior-to-anterior recruitment of reading related areas, straightforwardly resulting from the increase in stimuli's linguistic processing load, which reflects reading processes: visual analysis, orthographic encoding and phonological decoding. Connectivity analyses strengthened the validity of these observations and additionally revealed an enhancement of the left parieto-frontal information trafficking for higher linguistic processing. Our findings clearly establish the notion of a gradual spatio-functional recruitment of reading areas and demonstrate, to the best of our knowledge, the first evidence of a robust and staged link between the level of linguistic processing, the spatial distribution of brain activity and its information trafficking.     

Implicit and explicit memory for catastrophic associations to bodily sensation words in panic disorder

This study investigated explicit (cued recall) and implicit memory (word completion) memory bias for catastrophic associations among individuals with panic disorder (n=24), clinician controls (n=24), and normal controls (n=24). Compared to both control groups, the panic disorder group showed biased explicit and implicit memory for catastrophic associations to bodily sensation words (e.g., palpitation-coronary) compared to positive (e.g., smiles-elation) and neutral (e.g., groceries-coupons) word pairs of equal relatedness. These results support cognitive formulations of panic disorder which suggest that individuals with panic disorder have biased memory for This research was supported by a Faculty Development Award to the first author, by NIMH grants MH42430 and MH5964-02 to the second author, and by a University of Toronto New Staff Grant to the fourth author. The authors thank Jane Levitan, Diane Sholomskas, and Tim Brown for their help in recruiting subjects. We would like to thank all the clinicians from the various sites of the MultiCenter Comparative Treatment Study of Panic Disorder and the individuals with panic disorder who participated in the study.     

Different brain correlates for watching real and virtual hand actions

We investigated whether observation of actions reproduced in three-dimensional virtual reality would engage perceptual and visuomotor brain processes different from those induced by the observation of real hand actions. Participants were asked to passively observe grasping actions of geometrical objects made by a real hand or by hand reconstructions of different quality in 3D virtual reality as well as on a 2D TV screen. We found that only real actions in natural environment activated a visuospatial network including the right posterior parietal cortex. Observation of virtual-reality hand actions engaged prevalent visual perceptual processes within lateral and mesial occipital regions. Thus, only perception of actions in reality maps onto existing action representations, whereas virtual-reality conditions do not access the full motor knowledge available to the central nervous system.     

Reactivation of hepatitis B virus during targeted therapies for cancer and immune-mediated disorders

ABSTRACT

Introduction: Targeted therapies have gained popularity in the treatment of several oncologic and immune-mediated diseases. Immunosuppression caused by these drugs has been associated to reactivation of hepatitis B virus (HBV) in both hepatitis B surface antigen (HBsAg) positive patients (overt infection) and HBsAg negative/anti-hepatitis B core antigen (anti-HBc) positive carriers (resolved infection), leading to premature discontinuation of therapy and potentially fatal hepatitis.

Areas covered: This review summarizes the evidence of HBV reactivation in patients with overt or resolved HBV infection undergoing targeted therapies for cancer or immune-mediated disorders, providing recommendations for the management of these patients.

Expert opinion: The risk of HBV reactivation relies on the immunosuppressive potency and duration of these therapies, the underlying disease and the virological patient’s profile. However, HBV reactivation is preventable by screening for HBV markers in all patients scheduled to receive targeted therapies, assessing the virological profile and patient’s clinical state, followed by appropriate antiviral treatment or prophylaxis in those patients at high risk of HBV reactivation. Close monitoring of HBV carriers at low risk of reactivation is warranted with the aim to start antiviral therapy as soon as HBV reactivates.     

Dissociable brain activations during the retrieval of different kinds of spatial context memory

Although memory for spatial information has often been regarded as unitary, it may be divided into two distinct types: memory for the place where an individual experienced an event and memory for the location of an experienced event within a specific reference object. We used functional magnetic resonance imaging (fMRI) to elucidate the distinctions between the retrieval of these two types of spatial context memory. During scanning, subjects judged the room (Place task) in which a photograph had been presented or the location of the photograph on the computer display (R-L task) during the encoding phase. In a control task, subjects were asked to judge whether the photograph had been presented or not. The left middle frontal gyrus, lateral parietal and occipital regions, and bilateral precunei were found to be active during both the Place task and the R-L task compared with the control task. Critically, the place task, compared with the R-L task, was associated with activations in the right lateral prefrontal gyri, the posterior part of the left parahippocampal gyrus, bilateral retrosplenial and lateral parieto-occipital areas, whereas the R-L task, relative to the place task, with activation only in the right lateral parietal cortex. These findings indicate that the retrieval processes of spatial context memory are not associated with a single network, but may vary and recruit different neural networks depending on the type of spatial information to be retrieved.     

Estradiol treatment altered anticholinergic-related brain activation during working memory in postmenopausal women

Diffusion MRI is used extensively to investigate changes in white matter microstructure related to brain development and pathology. Ageing, however, is also associated with significant white and grey matter loss which in turn can lead to cerebrospinal fluid (CSF) based partial volume artefacts in diffusion MRI metrics. This is especially problematic in regions prone to CSF contamination, such as the fornix and the genu of corpus callosum, structures that pass through or close to the ventricles respectively. The aim of this study was to model the effects of CSF contamination on diffusion MRI metrics, and to evaluate different post-acquisition strategies to correct for CSF-contamination: Controlling for whole brain volume and correcting on a voxel-wise basis using the Free Water Elimination (FWE) approach. Using the fornix as an exemplar of a structure prone to CSF-contamination, corrections were applied to tract-specific and voxel-based [tract based spatial statistics (TBSS)] analyses of empirical DT-MRI data from 39 older adults (53-93 years of age). In addition to significant age-related decreases in whole brain volume and fornix tissue volume fraction, age was also associated with a reduction in mean fractional anisotropy and increase in diffusivity metrics in the fornix. The experimental data agreed with the simulations in that diffusivity metrics (mean diffusivity, axial and radial diffusivity) were more prone to partial volume CSF-contamination errors than fractional anisotropy. After FWE-based voxel-by-voxel partial volume corrections, the significant positive correlations between age and diffusivity metrics, in particular with axial diffusivity, disappeared whereas the correlation with anisotropy remained. In contrast, correcting for whole brain volume had little effect in removing these spurious correlations. Our study highlights the importance of correcting for CSF-contamination partial volume effects in the structures of interest on a voxel-by-voxel basis prior to drawing inferences about underlying changes in white matter structures and have implications for the interpretation of many recent diffusion MRI results in ageing and disease.     

直接皮质电刺激在脑功能区手术中对脑功能的保护作用

目的:探讨脑重要功能区手术中应用直接皮质电刺激联合皮质体感诱发电位定位脑功能区的方法及意义。方法:16例脑重要功能区病变的患者在唤醒麻醉下进行显微外科手术,利用皮质诱发电位及皮质直接电刺激定位感觉区、运动区及语言区,在保护脑功能区功能不受损的前提下,最大限度的手术切除病变。结果:12例位于运动感觉区的患者利用体感诱发电位及皮质电刺激确定出运动感觉区,其中6例利用体感诱发电位总位相倒置确定出中央沟,记录到明显的P20-N25倒置波形,波幅最大及波形分化最佳,经直接皮质电刺激确认为运动区。4例病变位于左侧额颞叶的患者通过皮质直接电刺激确定出语言区。术后无一例出现长期的功能障碍加重,并且术后功能均较术前明显好转。皮质电刺激未出现特殊并发症。结论:术中体感诱发电位及直接皮质电刺激可准确实时确定脑功能区,可最大限度的保护患者功能,最大限度的切除病变。     

fMRI evidence of brain reorganization during attention and memory tasks in multiple sclerosis

Functional magnetic resonance imaging (fMRI) data on motor function have shown adaptive functional changes related to brain injury in multiple sclerosis (MS). We investigated whether patients with MS have altered fMRI activation patterns during attention and memory tasks, and whether functional changes in the brain correlate with the extent of overall tissue damage on conventional MRI. Twenty-two right-handed patients with relapsing-remitting MS (RRMS) and no or only mild deficits at neuropsychological testing and 22 matched healthy subjects were scanned during the Paced Auditory Serial Addition Test (PASAT) and a recall task. fMRI data were analyzed using Statistical Parametric Mapping (SPM99). The relation between fMRI changes during both tasks and T2 lesion load was investigated. During both tasks, patients exhibited significantly greater brain activation than controls and recruited additional brain areas. Task-related functional changes were more significant in patients whose performance matched that of controls than in patients with a lower performance. During the PASAT, brain functional changes involved the right supplementary motor area and cingulate, the bilateral prefrontal, temporal and parietal areas, whereas during the recall task they involved the prefrontal and temporal cortex and basal ganglia bilaterally, and the left thalamus. In patients, activation in specific brain areas during performance of both tasks positively correlated with T2 brain lesions. Patients with RRMS exhibit altered patterns of activation during tasks exploring sustained attention, information processing and memory. During these tasks, fMRI activity is greater in patients with better cognitive function than in those with lower cognitive function. Functional changes in specific brain areas increase with increasing tissue damage suggesting that they may also represent adaptive mechanisms that reflect underlying neural disorganization or disinhibition, possibly associated with MS.