Effects of incidental and intentional feature binding on recognition: a behavioural and PET activation study

Frequency-specific alterations of the frontal-cerebellar circuit in first-episode, drug-naive somatization disorder

BACKGROUND

With the development of imaging techniques, evidence of abnormal neural activity has been implicated in patients with somatization disorder (SD). It remains unclear whether abnormal spontaneous neural activities are related to specific frequency bands. In this study, resting-state functional magnetic resonance imaging (fMRI) using the frequency-specific amplitude of low frequency fluctuation (ALFF) approach was applied to investigate changes in spontaneous neural activity in different frequency bands in patients with SD.

METHODS

Twenty-five first-episode, medication-naive patients with SD and 28 age-, sex-, education-matched healthy controls (HCs) underwent resting-state fMRI. The ALFF method with the classical low-frequency (0.01 - 0.08 Hz), slow-5 (0.01 - 0.027 Hz) and slow-4 (0.027 - 0.08 Hz) bands was employed to analyze the data.

RESULTS

With the classical low-frequency and slow-5 bands, patients with SD showed significantly increased ALFF in the left orbitofrontal cortex (OFC) and reduced ALFF in the right cerebellum compared with HCs. With the slow-4 band, patients with SD exhibited significantly reduced ALFF in the right cerebellum compared with HCs. However, no significant correlation was observed between the ALFF value in the left OFC or right cerebellum and clinical/cognitive variables.

CONCLUSIONS

Our findings indicate that there are abnormal regional activities of the left OFC and right cerebellum in first-episode, treatment-naive patients with SD, suggesting that these alterations occur early in the course of the disease and are independent of medication status. Our study provides novel evidence that different regional activities of the frontal-cerebellar circuit may be involved in the pathophysiology of SD.

Widespread higher fractional anisotropy associates to better cognitive functions in individuals at ultra-high risk for psychosis

In schizophrenia patients, cognitive functions appear linked to widespread alterations in cerebral white matter microstructure. Here we examine patterns of associations between regional white matter and cognitive functions in individuals at ultra-high risk for psychosis. One hundred and sixteen individuals at ultra-high risk for psychosis and 49 matched healthy controls underwent 3 T magnetic resonance diffusion-weighted imaging and cognitive assessments. Group differences on fractional anisotropy were tested using tract-based spatial statistics. Group differences in cognitive functions, voxel-wise as well as regional fractional anisotropy were tested using univariate general linear modeling. Multivariate partial least squares correlation analyses tested for associations between patterns of regional fractional anisotropy and cognitive functions. Univariate analyses revealed significant impairments on cognitive functions and lower fractional anisotropy in superior longitudinal fasciculus and cingulate gyrus in individuals at ultra-high risk for psychosis. Partial least squares correlation analysis revealed different associations between patterns of regional fractional anisotropy and cognitive functions in individuals at ultra-high risk for psychosis compared to healthy controls. Widespread higher fractional anisotropy was associated with better cognitive functioning for individuals at ultra-high risk for psychosis, but not for the healthy controls. Furthermore, patterns of cognitive functions were associated with an interaction-effect on regional fractional anisotropy in fornix, medial lemniscus, uncinate fasciculus, and superior cerebellar peduncle. Aberrant associations between patterns of cognitive functions to white matter may be explained by dysmyelination.

State-Related Alterations of Spontaneous Neural Activity in Current and Remitted Depression Revealed by Resting-State fMRI

Purpose: Although efforts have been made to identify neurobiological characteristic of major depressive disorder (MDD) in recent years, trait- and state-related biological characteristics of MDD still remains unclear. Using functional magnetic resonance imaging (fMRI), the aim of this study was to explore whether altered spontaneous neural activities in MDD are trait- or state- related.

Materials and Methods: Resting-state fMRI data were analyzed for 72 current MDD (cMDD) patients (first-episode, medication-naïve), 49 remitted MDD (rMDD) patients, and 78 age- and sex- matched healthy control (HC) subjects. The values of amplitude of low-frequency fluctuation (ALFF) were compared between groups.

Results: Compared with the cMDD group, the rMDD group had increased ALFF values in the left middle occipital gyrus, left middle temporal gyrus and right cerebellum anterior lobe. Besides, compared with the HC group, the cMDD group had decreased ALFF values in the left middle occipital gyrus. Further analysis explored that the mean ALFF values in the left middle occipital gyrus, left middle temporal gyrus and right cerebellum anterior lobe were correlated positively with BDI scores in rMDD patients.

Conclusion: Abnormal activity in the left middle occipital gyrus, left middle temporal gyrus and right cerebellum anterior lobe may be state-specific in current (first-episode, medication-naïve) and remitted (medication-naïve) depression patients. Furthermore, the state-related compensatory effect was found in these brain areas.

Out and about: Subsequent memory effect captured in a natural outdoor environment with smartphone EEG

Spatiotemporal context plays an important role in episodic memory. While temporal context effects have been frequently studied in the laboratory, ecologically valid spatial context manipulations are difficult to implement in stationary conditions. We investigated whether the neural correlates of successful encoding (subsequent memory effect) can be captured in a real-world environment. An off-the-shelf Android smartphone was used for wireless mobile EEG acquisition and stimulus presentation. Participants encoded single words, each of which was presented at a different location on a university campus. Locations were approximately 10-12 m away from each other, half of them with striking features (landmarks) nearby. We predicted landmarks would improve recall performance. After a first free recall task of verbal stimuli indoors, participants performed a subsequent recall outdoors, in which words and locations were recalled. As predicted, significantly more words presented at landmark locations as well as significantly more landmark than nonlandmark locations were recalled. ERP analysis yielded a larger posterior positive deflection during encoding for hits compared to misses in the 400-800 ms interval. Likewise, time-frequency analysis revealed a significant difference during encoding for hits compared to misses in the form of stronger alpha (200-300 ms) and theta (300-400 ms) power increases. Our results confirm that a vibrant spatial context is beneficial in episodic memory processing and that the underlying neural correlates can be captured with unobtrusive smartphone EEG technology. The advent of mobile EEG technology promises to unveil the relevance of natural physical activity and natural environments on memory.

Microstructural Changes in Patients With Parkinson's Disease Comorbid With REM Sleep Behaviour Disorder and Depressive Symptoms

The diagnosis of Parkinson's disease (PD) is currently anchored on clinical motor symptoms, which appear more than 20 years after initiation of the neurotoxicity. Extra-nigral involvement in the onset of PD with probable nonmotor manifestations before the development of motor signs, lead us to the preclinical (asymptomatic) or prodromal stages of the disease (various nonmotor or subtle motor signs). REM sleep behavior disorder (RBD) and depression are established prodromal clinical markers of PD and predict worse motor and cognitive outcomes. Nevertheless, taken by themselves, these markers are not yet claimed to be practical in identifying high-risk individuals. Combining promising markers may be helpful in a reliable diagnosis of early PD. Therefore, we aimed to detect neural correlates of RBD and depression in 93 treatment-naïve and non-demented early PD by means of diffusion MRI connectometry. Comparing four groups of PD patients with or without comorbid RBD and/or depressive symptoms with each other and with 31 healthy controls, we found that these two non-motor symptoms are associated with lower connectivity in several white matter tracts including the cerebellar peduncles, corpus callosum and long association fibers such as cingulum, fornix, and inferior longitudinal fasciculus. For the first time, we were able to detect the involvement of short association fibers (U-fibers) in PD neurodegenerative process. Longitudinal studies on larger sample groups are needed to further investigate the reported associations.

Altered Effective Connectivity of Hippocampus-Dependent Episodic Memory Network in mTBI Survivors

Traumatic brain injuries (TBIs) are generally recognized to affect episodic memory. However, less is known regarding how external force altered the way functionally connected brain structures of the episodic memory system interact. To address this issue, we adopted an effective connectivity based analysis, namely, multivariate Granger causality approach, to explore causal interactions within the brain network of interest. Results presented that TBI induced increased bilateral and decreased ipsilateral effective connectivity in the episodic memory network in comparison with that of normal controls. Moreover, the left anterior superior temporal gyrus (aSTG, the concept forming hub), left hippocampus (the personal experience binding hub), and left parahippocampal gyrus (the contextual association hub) were no longer network hubs in TBI survivors, who compensated for hippocampal deficits by relying more on the right hippocampus (underlying perceptual memory) and the right medial frontal gyrus (MeFG) in the anterior prefrontal cortex (PFC). We postulated that the overrecruitment of the right anterior PFC caused dysfunction of the strategic component of episodic memory, which caused deteriorating episodic memory in mTBI survivors. Our findings also suggested that the pattern of brain network changes in TBI survivors presented similar functional consequences to normal aging.

Episodic memory in normal aging and Alzheimer disease: Insights from imaging and behavioral studies

Age-related cognitive changes often include difficulties in retrieving memories, particularly those that rely on personal experiences within their temporal and spatial contexts (i.e., episodic memories). This decline may vary depending on the studied phase (i.e., encoding, storage or retrieval), according to inter-individual differences, and whether we are talking about normal or pathological (e.g., Alzheimer disease; AD) aging. Such cognitive changes are associated with different structural and functional alterations in the human neural network that underpins episodic memory. The prefrontal cortex is the first structure to be affected by age, followed by the medial temporal lobe (MTL), the parietal cortex and the cerebellum. In AD, however, the modifications occur mainly in the MTL (hippocampus and adjacent structures) before spreading to the neocortex. In this review, we will present results that attempt to characterize normal and pathological cognitive aging at multiple levels by integrating structural, behavioral, inter-individual and neuroimaging measures of episodic memory.

Frequency-dependent amplitude alterations of resting-state spontaneous fluctuations in late-onset depression

There is limited amplitude of low-frequency fluctuation (ALFF) of resting-state functional magnetic resonance imaging (fMRI) studies in late-onset depression (LOD) but reported different results. This may be due to the impact of different frequency bands. In this study, we examined the ALFF in five different frequency bands (slow-6: 0-0.01 Hz; slow-5: 0.01-0.027 Hz; slow-4: 0.027-0.073 Hz; slow-3: 0.073-0.167 Hz, and slow-2: 0.167-0.25 Hz) within the whole brain during resting-state fMRI in 16 LOD patients and 16 normal control (NC) subjects. The ALFF of primary effect of disease was widely distributed over left cerebellum anterior lobe, left cerebellum posterior lobe, left middle orbitofrontal gyrus, left superior occipital, and right superior parietal, while the interaction effect of disease and frequency was distributed over right superior frontal gyrus. Further relationship analysis findings suggest these abnormal ALFF may relate to cognitive dysfunction of LOD. Therefore, our data show that LOD patients have widespread abnormalities in intrinsic brain activity, which is dependent on the frequency band, and suggest that future studies should take the frequency bands into account when measuring intrinsic brain activity.

Abnormal regional spontaneous neural activity in first-episode, treatment-naive patients with late-life depression: a resting-state fMRI study

BACKGROUND

The previous resting perfusion or task-based studies have provided evidence of functional changes in the brains of patients with late-life depression (LLD). Little is known, so far, about the changes in the spontaneous brain activity in LLD during the resting state. The aim of this study was to investigate the spontaneous neural activity in first-episode, treatment-naive patients with LLD by using resting-state functional magnetic resonance imaging (fMRI).

METHODS

A novel analytical method, coherence-based regional homogeneity (Cohe-ReHo), was used to assess regional spontaneous neural activity during the resting state in 15 first-episode, treatment-naive patients with LLD and 15 age- and gender-matched healthy controls.

RESULTS

Compared to the healthy controls, the LLD group showed significantly decreased Cohe-ReHo in left caudate nucleus, right anterior cingulate gyrus, left dorsolateral prefrontal cortex, right angular gyrus, bilateral medial prefrontal cortex, and right precuneus, while significantly increased Cohe-ReHo in left cerebellum posterior lobe, left superior temporal gyrus, bilateral supplementary motor area, and right postcentral gyrus (p<0.005, corrected for multiple comparisons).

CONCLUSIONS

These findings indicated abnormal spontaneous neural activity was distributed extensively in first-episode, treatment-naive patients with LLD during the resting state. Our results might supply a novel way to look into the underlying pathophysiology mechanisms of patients with LLD.

Abnormal neural activity of brain regions in treatment-resistant and treatment-sensitive major depressive disorder: a resting-state fMRI study

BACKGROUND

Patients with treatment-resistant depression (TRD) and those with treatment-sensitive depression (TSD) responded to antidepressants differently. Previous studies have commonly shown that patients with TRD or TSD had abnormal neural activity in different brain regions. In the present study, we used a coherence-based ReHo (Cohe-ReHo) approach to test the hypothesis that patients with TRD or TSD had abnormal neural activity in different brain regions.

METHODS

Twenty-three patients with TRD, 22 with TSD, and 19 healthy subjects (HS) matched with gender, age, and education level participated in the study.

RESULTS

ANOVA analysis revealed widespread differences in Cohe-ReHo values among the three groups in different brain regions which included bilateral superior frontal gyrus, bilateral cerebellum, left inferior temporal gyrus, left occipital cortex, and both sides of fusiform gyrus. Compared to HS, lower Cohe-ReHo values were observed in TRD group in bilateral superior frontal gyrus and left cerebellum; in contrast, in TSD group, lower Cohe-ReHo values were mainly found in bilateral superior frontal gyrus. Compared to TSD group, TRD group had lower Cohe-ReHo in bilateral cerebellum and higher Cohe-ReHo in left fusiform gyrus. There was a negative correlation between Cohe-ReHo values of the left fusiform gyrus and illness duration in the pooled patients (r = 0.480, p = 0.001). The sensitivity and specificity of cerebellar Cohe-ReHo values differentiating TRD from TSD were 83% and 86%, respectively.

CONCLUSIONS

Compared to healthy controls, both TRD and TSD patients shared the majority of brain regions with abnormal neural activity. However, the lower Cohe-ReHo values in the cerebellum might be as a marker to differentiate TRD from TSD with high sensitivity and specificity.

Alterations of the amplitude of low-frequency fluctuations in treatment-resistant and treatment-response depression: a resting-state fMRI study

BACKGROUND

Patients with treatment-resistant depression (TRD) and those with treatment-response depression (TSD) respond to antidepressants differently and previous studies have commonly reported different brain networks in resistant and nonresistant patients. Using the amplitude of low-frequency fluctuations (ALFF) approach, we explored ALFF values of the brain regions in TRD and TSD patients at resting state to test the hypothesis of the different brain networks in TRD and TSD patients.

METHODS

Eighteen TRD patients, 17 TSD patients and 17 gender-, age-, and education-matched healthy subjects participated in the resting-state fMRI scans.

RESULTS

There are widespread differences in ALFF values among TRD patients, TSD patients and healthy subjects throughout the cerebellum, the visual recognition circuit (middle temporal gyrus, middle/inferior occipital gyrus and fusiform), the hate circuit (putamen), the default circuit (ACC and medial frontal gyrus) and the risk/action circuit (inferior frontal gyrus). The differences in brain circuits between the TRD and TSD patients are mainly in the cerebellum, the visual recognition circuit and the default circuit.

CONCLUSIONS

The affected brain circuits of TRD patients might be partly different from those of TSD patients.

Abnormal neural activities in first-episode, treatment-naïve, short-illness-duration, and treatment-response patients with major depressive disorder: a resting-state fMRI study

BACKGROUND

Abnormality of limbic-cortical networks was postulated in depression. Using a regional homogeneity (ReHo) approach, we explored the regional homogeneity (ReHo) of the brain regions in patients with first-episode, treatment-naïve, short-illness-duration, and treatment-response depression in resting state to test the abnormality hypothesis of limbic-cortical networks in major depressive disorder (MDD).

METHODS

Seventeen patients with treatment-response MDD and 17 gender-, age-, and education-matched healthy subjects participated in the resting-state fMRI scans.

CONCLUSIONS

Our findings suggested the abnormality of limbic-cortical networks in first-episode, treatment-naïve, short-illness-duration, and treatment-response MDD patients, and added an expanding literature to the abnormality hypothesis of limbic-cortical networks in MDD.

Implicit memory for object locations depends on reactivation of encoding-related brain regions

This study explored the correspondence between implicit memory and the reactivation of encoding-related brain regions. By using a classification method, we examined whether reactivation reflects only the similarities between study and test or voxels at the reactivated regions are diagnostic of facilitation in the implicit memory task. A simple detection task served as incidental encoding of object-location pairings. A subsequent visual search task served as the indirect (implicit) test of memory. Subjects did not know that their memory would be tested. Half of the subjects were unaware that some stimuli in the search task are the same as those that had appeared during the detection task. Another group of subjects was made aware of this relationship at the onset of the visual search task. Memory performance was superior for the study-test aware, compared to study-test unaware, subjects. Brain reactivation was calculated using a conjunction analysis implemented through overlaying the neural activity at encoding and testing. The conjunction analysis revealed that implicit memory in both groups of subjects was associated with reactivation of parietal and occipital brain regions. We were able to classify study-test aware and study-test unaware subjects based on the per-voxel reactivation values representing the neural dynamics between encoding and test. The classification results indicate that neural dynamics between encoding and test accounts for the differences in implicit memory. Overall, our study demonstrates that implicit memory performance requires and depends upon reactivation of encoding-related brain regions.

Explicit processing of verbal and spatial features during letter-location binding modulates oscillatory activity of a fronto-parietal network

The present study investigated the binding of verbal and spatial features in immediate memory. In a recent study, we demonstrated incidental and asymmetrical letter-location binding effects when participants attended to letter features (but not when they attended to location features) that were associated with greater oscillatory activity over prefrontal and posterior regions during the retention period. We were interested to investigate whether the patterns of brain activity associated with the incidental binding of letters and locations observed when only the verbal feature is attended differ from those reflecting the binding resulting from the controlled/explicit processing of both verbal and spatial features. To achieve this, neural activity was recorded using magnetoencephalography (MEG) while participants performed two working memory tasks. Both tasks were identical in terms of their perceptual characteristics and only differed with respect to the task instructions. One of the tasks required participants to process both letters and locations. In the other, participants were instructed to memorize only the letters, regardless of their location. Time-frequency representation of MEG data based on the wavelet transform of the signals was calculated on a single trial basis during the maintenance period of both tasks. Critically, despite equivalent behavioural binding effects in both tasks, single and dual feature encoding relied on different neuroanatomical and neural oscillatory correlates. We propose that enhanced activation of an anterior-posterior dorsal network observed in the task requiring the processing of both features reflects the necessity for allocating greater resources to intentionally process verbal and spatial features in this task.

AGING, CONTEXT MEMORY AND BINDING: A COMPARISON OF “WHAT, WHERE AND WHEN” IN YOUNG AND OLDER ADULTS

There is evidence that age-related memory decline does not effect all types of episodic information to an equal extent, but that especially contextual memory and the integration of multiple features in memory deteriorate. The current study investigates contextual memory in a group of healthy young (N = 40) and older (N = 40) adults without dementia. All participants performed a computerized memory task assessing target memory (objects only), contextual memory (positions only) and memory for the combinations of two features (object, space, temporal order), that is, binding of target-context or context-context features. The results showed age-related decline on all task conditions. Furthermore, the performance on conditions requiring the binding of target and context features was affected to a greater extent in older adults compared to younger adults. These findings support the notion that a decline in contextual memory and binding might underlie poorer episodic memory in older participants.

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.

Anatomical signatures of dyslexia in children: unique information from manual and voxel based morphometry brain measures

Thirteen male control and thirteen male dyslexic children (age, 121-152 months) were studied to determine if voxel based morphometry (VBM) could identify anatomical differences in the right cerebellar anterior lobe, and right and left pars triangularis that were identified with manual measures of the same children. VBM demonstrated significant gray and white matter differences in these three brain regions. In contrast to the manual results, these differences were not significant after controlling for brain volume, suggesting the manual measures captured additional important variance that distinguished the groups. Post-hoc VBM comparisons demonstrated white matter volume differences in a left temporal-parietal region that are consistent in location with results from diffusion tensor imaging studies of dyslexia. The VBM analyses also identified, gray matter volume differences in the left and right lingual gyrus, left inferior parietal lobule and cerebellum, areas that had not been examined with manual methods. We conclude that manual and automated methods provide valuable and complementary approaches to the search for functionally significant neurobiological characteristics of dyslexia.

A diffusion tensor imaging study of middle and superior cerebellar peduncle in male patients with schizophrenia

Many studies have confirmed that the cerebellum takes part in higher-order cognitive coordination; profound fibers projecting to and from the cerebellum underlie its cognitive function. Since the superior and middle cerebellar peduncles are the main pathways of neural fibers in the cerebellum, these structures became the focus of our interest in evaluating the cognitive dysfunction reported in schizophrenia. Diffusion tensor imaging (DTI) was used to examine the anatomical integrity of the neural fibers in the superior and middle cerebellar peduncles. DTI was performed on 29 patients and 20 normal controls; we subsequently calculated the fractional anisotropy and mean diffusivity in these regions. Statistical analysis revealed that there was no significant difference between patients with schizophrenia and our matched control group. No structural abnormalities were detected in the white matter of the superior and middle cerebellar peduncles.