Search

Epilepsy surgery is the best therapeutic option for patients with drug-resistant focal epilepsy. During presurgical investigation, interictal spikes can provide important information on eligibility, lateralisation and localisation of the surgical target. However, their relationship to epileptogenic tissue is variable. Interictal spikes with concurrent high-frequency oscillations (HFOs) have been postulated to reflect epileptogenic tissue more reliably. Here, we studied the voltage distribution of scalp-recorded spikes with and without concurrent HFO and identified their respective haemodynamic correlates using simultaneous electroencephalography and functional Magnetic Resonance Imaging (EEG-fMRI).The scalp topography of spikes with and without concurrent HFOs were assessed in 31 consecutive patients with focal drug-resistant epilepsy who showed interictal spikes during presurgical evaluation. Simultaneous EEG-fMRI was then used in 17 patients with spikes and concurrent HFOs. Haemodynamic changes were obtained from the spatial correlation between the patient-specific voltage map of each spike population and the intra-scanner EEG. The haemodynamic response of spikes with and without HFOs were compared in terms of their spatial similarity, strength, the distance between activation peaks and concordance with interictal localisation.Twenty-five patients showed spikes with and without concurrent HFOs. Among patients with both types of spikes, most spikes were not associated with HFOs (p 0.0001, Mann-Whitney test). Twenty of the 25 patients showed an average of 8 ± 6 (standard deviation) electrodes with significant voltage differences (p = 0.025, permutation test corrected for multiple comparisons) on scalp electrodes within and distant to the spike field. Comparing the haemodynamic response between both spike populations, we found no significant differences in the peak strength (p = 0.71, Mann-Whitney test), spatial distribution (p = 0.113, One-sample Wilcoxon test) and distance between activation peaks (p = 0.5, One-sample Wilcoxon test), with all peaks being co-localised in the same lobe.Our data showed that spikes with and without HFOs have different scalp voltage distributions. However, when assessing the haemodynamic changes of each spike type, we found that both elicit similar haemodynamic changes and share high spatial similarity suggesting that the epileptic networks of spikes with and without HFOs have the same underlying neural substrate.

Purpose Quantitative susceptibility mapping is a technique to estimate the magnetic property of tissue with particularly high sensitivity at ultra-high field. However, a key challenge at ultra-high field is the combination of phase data acquired using phased array receive coils. Several methods for combining phase data have been proposed, but the influence of coil combination choices on susceptibility quantitation has not been studied systematically. Methods We combined phase data using COMPOSER (COMbining Phase data using a Short Echo-time Reference scan) and a reference-free channel-by-channel method. We investigated the effect of the chosen combination method on susceptibility results in a group of 28 participants at 7 Tesla. Results Our results show that reference scans can bias susceptibility values. Although the proposed reference-free channel-by-channel method cannot remove transmit field phase, it shows comparable results to the COMPOSER method in which a high-resolution ultrashort echo-time reference scan was used. Conclusions We conclude that ultrashort echo-time reference scans reduce quantitation bias and remove the transmit field phase when using COMPOSER to combine phase data, and not combining the phase data before susceptibility processing avoids this bias, resulting in comparable results. Magn Reson Med 79:97–107, 2018. © 2017 InternationalSociety for Magnetic Resonance in Medicine.

Logopenic progressive aphasia (LPA) is a neurodegenerative disorder characterised by profound naming and sentence repetition disturbances, attributable to disproportionately left-sided temporo-parietal atrophy. Accumulating evidence suggests, in addition to language impairments, the presence of stark verbal and nonverbal episodic memory dysfunction in LPA. The neurocognitive bases of such impairments, however, remain to be clarified. Here, we characterised episodic memory disruption and its corresponding grey and white matter correlates in the LPA syndrome. Nineteen LPA patients were contrasted with 23 matched typical Alzheimer's disease (AD) patients and 31 healthy Controls on standardized verbal and nonverbal episodic delayed recall measures. Participants further underwent structural magnetic resonance and diffusion-weighted imaging. Significant verbal memory deficits were evident in both patient groups, with LPA patients performing at an intermediate level to AD and Controls. For nonverbal memory, however, LPA performance was indistinguishable from that of AD, with both groups displaying marked impairments relative to Controls. Whole-brain voxel-based morphometry analyses revealed significant left temporo-parietal and left hippocampal atrophy in the LPA group. Covariate analyses showed that verbal and nonverbal amnesia in LPA correlated with grey matter integrity of bilateral frontoparietal and left medial temporal lobe regions. Notably, the common regions underpinning verbal and nonverbal memory dysfunction in LPA were the left orbitofrontal cortex and bilateral angular gyri in the inferior parietal cortex. The bilateral angular gyri, along with prefrontal and hippocampal regions further emerged as disease-general correlates of verbal and nonverbal memory performance. Alterations in mean diffusivity in structural connections between the left angular gyrus and medial temporal lobes were further associated with verbal memory performance in all participants. Our findings reveal, for the first time, the presence of pervasive memory impairments in LPA mediated by degeneration of a distributed prefrontal-hippocampal-parietal network, and disrupted parieto-hippocampal structural connectivity.

The processes that characterize the neural development of long-term memory (LTM) are largely unknown. In young adults, the degree of activation of a single large-scale memory network corresponds to the level of contextual detail involved; thus, differentiating between autobiographical, episodic, and semantic retrieval. In contrast to young adults, children and adolescents retrieve fewer contextual details, suggesting that they might not yet engage the entire memory circuitry and that this brain recruitment might lack the characteristic contextual differentiation found in adults. Twenty-one children (10-12 years of age), 20 adolescents (14-16 years of age), and 22 young adults (20-35 years of age) were assessed on a previously validated LTM retrieval task, while their brain activity was measured with functional magnetic resonance imaging. The results demonstrate that children, adolescents, and adults recruit a left-lateralized subset of the large-scale memory network, comprising semantic and language processing regions, with neither developmental group showing evidence of contextual differentiation within this network. Additionally, children and adolescents recruited occipital and parietal regions during all memory recall conditions, in contrast to adults who engaged the entire large-scale memory network, as described previously. Finally, a significant covariance between age and brain activation indicates that the reliance on occipital and parietal regions during memory retrieval decreases with age. These results suggest that both children and adolescents rely on semantic processing to retrieve long-term memories, which, we argue, may restrict the integration of contextual detail required for complex episodic and autobiographical memory retrieval.

Healthy aging is accompanied by neurobiological changes that affect the brain's functional organization and the individual's cognitive abilities. The aim of this study was to investigate the effect of global age-related differences in the cortical white and gray matter on neural activity in three key large-scale networks. We used functional-structural covariance network analysis to assess resting state activity in the default mode network (DMN), the fronto-parietal network (FPN), and the salience network (SN) of young and older adults. We further related this functional activity to measures of cortical thickness and volume derived from structural MRI, as well as to measures of white matter integrity (fractional anisotropy [FA], mean diffusivity [MD], and radial diffusivity [RD]) derived from diffusion-weighted imaging. First, our results show that, in the direct comparison of resting state activity, young but not older adults reliably engage the SN and FPN in addition to the DMN, suggesting that older adults recruit these networks less consistently. Second, our results demonstrate that age-related decline in white matter integrity and gray matter volume is associated with activity in prefrontal nodes of the SN and FPN, possibly reflecting compensatory mechanisms. We suggest that age-related differences in gray and white matter properties differentially affect the ability of the brain to engage and coordinate large-scale functional networks that are central to efficient cognitive functioning.

Highlights • The irritative zone differs on Electrical Source Imaging (ESI) and EEG-fMRI. • Findings differ in functional connectivity and show low temporal correlation. • ESI and EEG-fMRI reveal distinct aspects of the irritative zone. • The differences may reflect differences in temporal resolution of the techniques., Summary Objective The irritative zone - the area generating epileptic spikes - can be studied non-invasively during the interictal period using Electrical Source Imaging (ESI) and simultaneous electroencephalography-functional magnetic resonance imaging (EEG-fMRI). Although the techniques yield results which may overlap spatially, differences in spatial localization of the irritative zone within the same patient are consistently observed. To investigate this discrepancy, we used Blood Oxygenation Level Dependent (BOLD) functional connectivity measures to examine the underlying relationship between ESI and EEG-fMRI findings. Methods Fifteen patients (age 20–54), who underwent presurgical epilepsy investigation, were scanned using a single-session resting-state EEG-fMRI protocol. Structural MRI was used to obtain the electrode localisation of a high-density 64-channel EEG cap. Electrical generators of interictal epileptiform discharges were obtained using a distributed local autoregressive average (LAURA) algorithm as implemented in Cartool EEG software. BOLD activations were obtained using both spike-related and voltage-map EEG-fMRI analysis. The global maxima of each method were used to investigate the temporal relationship of BOLD time courses and to assess the spatial similarity using the Dice similarity index between functional connectivity maps. Results ESI, voltage-map and spike-related EEG-fMRI methods identified peaks in 15 (100%), 13 (67%) and 8 (53%) of the 15 patients, respectively. For all methods, maxima were localised within the same lobe, but differed in sub-lobar localisation, with a median distance of 22.8 mm between the highest peak for each method. The functional connectivity analysis showed that the temporal correlation between maxima only explained 38% of the variance between the time course of the BOLD response at the maxima. The mean Dice similarity index between seed-voxel functional connectivity maps showed poor spatial agreement. Significance Non-invasive methods for the localisation of the irritative zone have distinct spatial and temporal sensitivity to different aspects of the local cortical network involved in the generation of interictal epileptiform discharges.

Co-speech gestures constitute a unique form of multimodal communication because here the hand movements are temporally synchronized and semantically integrated with speech. Recent neuroimaging studies indicate that the perception of co-speech gestures might engage a core set of frontal, temporal, and parietal areas. However, no study has compared the neural processes during perception of different types of co-speech gestures, such as beat, deictic, iconic, and metaphoric co-speech gestures. The purpose of this study was to review the existing literature on the neural correlates of co-speech gesture perception and to test whether different types of co-speech gestures elicit a common pattern of brain activity in the listener. To this purpose, we conducted a meta-analysis of neuroimaging studies, which used different types of co-speech gestures to investigate the perception of multimodal (co-speech gestures) in contrast to unimodal (speech or gestures) stimuli. The results show that co-speech gesture perception consistently engages temporal regions related to auditory and movement perception as well as frontal-parietal regions associated with action understanding. The results of this study suggest that brain regions involved in multisensory processing and action understanding constitute the general core of co-speech gesture perception.

Neuroimaging studies have shown that the neural mechanisms of motor imagery (MI) overlap substantially with the mechanisms of motor execution (ME). Surprisingly, however, the role of several regions of the motor circuitry in MI remains controversial, a variability that may be due to differences in neuroimaging techniques, MI training, instruction types, or tasks used to evoke MI. The objectives of this study were twofold: (i) to design a novel task that reliably invokes MI, provides a reliable behavioral measure of MI performance, and is transferable across imaging modalities; and (ii) to measure the common and differential activations for MI and ME with functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG). We present a task in which it is difficult to give accurate responses without the use of either motor execution or motor imagery. The behavioral results demonstrate that participants performed similarly on the task when they imagined vs. executed movements and this performance did not change over time. The fMRI results show a spatial overlap of MI and ME in a number of motor and premotor areas, sensory cortices, cerebellum, inferior frontal gyrus, and ventrolateral thalamus. MI uniquely engaged bilateral occipital areas, left parahippocampus, and other temporal and frontal areas, whereas ME yielded unique activity in motor and sensory areas, cerebellum, precuneus, and putamen. The MEG results show a robust event-related beta band desynchronization in the proximity of primary motor and premotor cortices during both ME and MI. Together, these results further elucidate the neural circuitry of MI and show that our task robustly and reliably invokes motor imagery, and thus may prove useful for interrogating the functional status of the motor circuitry in patients with motor disorders.

Co-speech gestures have been shown to interact with working memory (WM). However, no study has investigated whether there are individual differences in the effect of gestures on WM. Combining a novel gesture/no-gesture task and an operation span task, we examined the differences in WM accuracy between individuals who gestured and individuals who did not gesture in relation to their WM capacity. Our results showed individual differences in the gesture effect on WM. Specifically, only individuals with low WM capacity showed a reduced WM accuracy when they did not gesture. Individuals with low WM capacity who did gesture, as well as high-capacity individuals (irrespective of whether they gestured or not), did not show the effect. Our findings show that the interaction between co-speech gestures and WM is affected by an individual's WM load.

The perception of co-speech gestures, i.e., hand movements that co-occur with speech, has been investigated by several studies. The results show that the perception of co-speech gestures engages a core set of frontal, temporal, and parietal areas. However, no study has yet investigated the neural processes underlying the production of co-speech gestures. Specifically, it remains an open question whether Broca’s area is central to the coordination of speech and gestures as has been suggested previously. The objective of this study was to use functional magnetic resonance imaging to (i) investigate the regional activations underlying overt production of speech, gestures, and co-speech gestures, and (ii) examine functional connectivity with Broca’s area. We hypothesized that co-speech gesture production would activate frontal, temporal, and parietal regions that are similar to areas previously found during co-speech gesture perception and that both speech and gesture as well as co-speech gesture production would engage a neural network connected to Broca’s area. Whole-brain analysis confirmed our hypothesis and showed that co-speech gesturing did engage brain areas that form part of networks known to subserve language and gesture. Functional connectivity analysis further revealed a functional network connected to Broca’s area that is common to speech, gesture, and co-speech gesture production. This network consists of brain areas that play essential roles in motor control, suggesting that the coordination of speech and gesture is mediated by a shared motor control network. Our findings thus lend support to the idea that speech can influence co-speech gesture production on a motoric level.

The temporal scale of neuroplasticity following acute alterations in brain structure due to neurosurgical intervention is still under debate. We conducted a longitudinal study with the objective of investigating the postoperative changes in a patient who underwent cerebrovascular surgery and who subsequently lost proprioception in the fingers of her right hand. The results show increased activation in contralesional somatosensory areas, additional recruitment of premotor and posterior parietal areas, and changes in functional connectivity with left postcentral gyrus. These findings demonstrate long-term modifications of cortical organization and as such have important implications for treatment strategies for patients with brain injury.

Representations are internal models of the environment that can provide guidance to a behaving agent, even in the absence of sensory information. It is not clear how representations are developed and whether or not they are necessary or even essential for intelligent behavior. We argue here that the ability to represent relevant features of the environment is the expected consequence of an adaptive process, give a formal definition of representation based on information theory, and quantify it with a measure R. To measure how R changes over time, we evolve two types of networks---an artificial neural network and a network of hidden Markov gates---to solve a categorization task using a genetic algorithm. We find that the capacity to represent increases during evolutionary adaptation, and that agents form representations of their environment during their lifetime. This ability allows the agents to act on sensorial inputs in the context of their acquired representations and enables complex and context-dependent behavior. We examine which concepts (features of the environment) our networks are representing, how the representations are logically encoded in the networks, and how they form as an agent behaves to solve a task. We conclude that R should be able to quantify the representations within any cognitive system, and should be predictive of an agent's long-term adaptive success., Comment: 36 pages, 10 figures, one Table