Corticostriatal connectivity fingerprints: Probability maps based on resting‐state functional connectivity

Over the last decade, structure–function relationships have begun to encompass networks of brain areas rather than individual structures. For example, corticostriatal circuits have been associated with sensorimotor, limbic, and cognitive information processing, and damage to these circuits has been shown to produce unique behavioral outcomes in Autism, Parkinson's Disease, Schizophrenia and healthy ageing. However, it remains an open question how abnormal or absent connectivity can be detected at the individual level. Here, we provide a method for clustering gross morphological structures into subregions with unique functional connectivity fingerprints, and generate network probability maps usable as a baseline to compare individual cases against. We used connectivity metrics derived from resting‐state fMRI (N = 100), in conjunction with hierarchical clustering methods, to parcellate the striatum into functionally distinct clusters. We identified three highly reproducible striatal subregions, across both hemispheres and in an independent replication dataset (N = 100) (dice‐similarity values 0.40–1.00). Each striatal seed region resulted in a highly reproducible distinct connectivity fingerprint: the putamen showed predominant connectivity with cortical and cerebellar sensorimotor and language processing areas; the ventromedial striatum cluster had a distinct limbic connectivity pattern; the caudate showed predominant connectivity with the thalamus, frontal and occipital areas, and the cerebellum. Our corticostriatal probability maps agree with existing connectivity data in humans and non‐human primates, and showed a high degree of replication. We believe that these maps offer an efficient tool to further advance hypothesis driven research and provide important guidance when investigating deviant connectivity in neurological patient populations suffering from e.g., stroke or cerebral palsy. Hum Brain Mapp 38:1478–1491, 2017. © 2016 Wiley Periodicals, Inc.     

Somatotopy in the basal ganglia: experimental and clinical evidence for segregated sensorimotor channels

Growing experimental and clinical evidence supports the notion that the cortico-basal ganglia–thalamo-cortical loops proceed along parallel circuits linking cortical and subcortical regions subserving the processing of sensorimotor, associative and affective tasks. In particular, there is evidence that a strict topographic segregation is maintained during the processing of sensorimotor information flowing from cortical motor areas to the sensorimotor areas of the basal ganglia. The output from the basal ganglia to the motor thalamus, which projects back to neocortical motor areas, is also organized into topographically segregated channels. This high degree of topographic segregation is demonstrated by the presence of a well-defined somatotopic organization in the sensorimotor areas of the basal ganglia. The presence of body maps in the basal ganglia has become clinically relevant with the increasing use of surgical procedures, such as lesioning or deep brain stimulation, which are selectively aimed at restricted subcortical targets in the sensorimotor loop such as the subthalamic nucleus (STN) or the globus pallidus pars interna (GPi). The ability to ameliorate the motor control dysfunction without producing side effects related to interference with non-motor circuits subserving associative or affective processing requires the ability to target subcortical areas particularly involved in sensorimotor processing (currently achieved only by careful intraoperative microelectrode mapping). The goal of this article is to review current knowledge about the somatotopic segregation of basal ganglia sensorimotor areas and outline in detail what is known about their body maps.     

Forming tool use representations: a neurophysiological investigation into tool exposure

Prior work has identified a common left parietofrontal network for storage of tool-related information for various tasks. How these representations become established within this network on the basis of different modes of exposure is unclear. Here, healthy subjects engaged in physical practice (direct exposure) with familiar and unfamiliar tools. A separate group of subjects engaged in video-based observation (indirect exposure) of the same tools to understand how these learning strategies create representations. To assess neural mechanisms engaged for pantomime after different modes of exposure, a pantomime task was performed for both tools while recording neural activation with high-density EEG. Motor planning-related neural activation was evaluated using beta band (13-22 Hz) event-related desynchronization. Hemispheric dominance was assessed, and activation maps were generated to understand topography of activations. Comparison of conditions (effects of tool familiarity and tool exposure) was performed with standardized low-resolution brain electromagnetic tomography. Novel tool pantomime following direct exposure resulted in greater activations of bilateral parietofrontal regions. Activations following indirect training varied by tool familiarity; pantomime of the familiar tool showed greater activations in left parietofrontal areas, whereas the novel tool showed greater activations at right temporoparieto-occipital areas. These findings have relevance to the mechanisms for understanding motor-related behaviors involved in new tools that we have little or no experience with and can extend into advancing theories of tool use motor learning.     

Identification of Imaging Biomarkers in Schizophrenia: A Coefficient-constrained Independent Component Analysis of the Mind Multi-site Schizophrenia Study

A number of recent studies have combined multiple experimental paradigms and modalities to find relevant biological markers for schizophrenia. In this study, we extracted fMRI features maps from the analysis of three experimental paradigms (auditory oddball, Sternberg item recognition, sensorimotor) for a large number (n = 154) of patients with schizophrenia and matched healthy controls. We used the general linear model (GLM) and independent component analysis (ICA) to extract feature maps (i.e. ICA component maps and GLM contrast maps), which were then subjected to a coefficient-constrained independent component analysis (CCICA) to identify potential neurobiological markers. A total of 29 different feature maps were extracted for each subject. Our results show a number of optimal feature combinations that reflect a set of brain regions that significantly discriminate between patients and controls in the spatial heterogeneity and amplitude of their feature signals. Spatial heterogeneity was seen in regions such as the superior/middle temporal and frontal gyri, bilateral parietal lobules, and regions of the thalamus. Most strikingly, an ICA feature representing a bilateral frontal pole network was consistently seen in the ten highest feature results when ranked on differences found in the amplitude of their feature signals. The implication of this frontal pole network and the spatial variability which spans regions comprising of bilateral frontal/temporal lobes and parietal lobules suggests that they might play a significant role in the pathophysiology of schizophrenia.     

Learning under social versus nonsocial uncertainty: A meta‐analytic approach

Much of the uncertainty that clouds our understanding of the world springs from the covert values and intentions held by other people. Thus, it is plausible that specialized mechanisms that compute learning signals under uncertainty of exclusively social origin operate in the brain. To test this hypothesis, we scoured academic databases for neuroimaging studies involving learning under uncertainty, and performed a meta‐analysis of brain activation maps that compared learning in the face of social versus nonsocial uncertainty. Although most of the brain activations associated with learning error signals were shared between social and nonsocial conditions, we found some evidence for functional segregation of error signals of exclusively social origin during learning in limited regions of ventrolateral prefrontal cortex and insula. This suggests that most behavioral adaptations to navigate social environments are reused from frontal and subcortical areas processing generic value representation and learning, but that a specialized circuitry might have evolved in prefrontal regions to deal with social context representation and strategic action.     

Context and hand posture modulate the neural dynamics of tool–object perception

Prior research has linked visual perception of tools with plausible motor strategies. Thus, observing a tool activates the putative action-stream, including the left posterior parietal cortex. Observing a hand functionally grasping a tool involves the inferior frontal cortex. However, tool-use movements are performed in a contextual and grasp specific manner, rather than relative isolation. Our prior behavioral data has demonstrated that the context of tool-use (by pairing the tool with different objects) and varying hand grasp postures of the tool can interact to modulate subjects' reaction times while evaluating tool-object content. Specifically, perceptual judgment was delayed in the evaluation of functional tool-object pairings (Correct context) when the tool was non-functionally (Manipulative) grasped. Here, we hypothesized that this behavioral interference seen with the Manipulative posture would be due to increased and extended left parietofrontal activity possibly underlying motor simulations when resolving action conflict due to this particular grasp at time scales relevant to the behavioral data. Further, we hypothesized that this neural effect will be restricted to the Correct tool-object context wherein action affordances are at a maximum.64-channel electroencephalography (EEG) was recorded from 16 right-handed subjects while viewing images depicting three classes of tool–object contexts: functionally Correct (e.g. coffee pot–coffee mug), functionally Incorrect (e.g. coffee pot–marker) and Spatial (coffee pot–milk). The Spatial context pairs a tool and object that would not functionally match, but may commonly appear in the same scene. These three contexts were modified by hand interaction: No Hand, Static Hand near the tool, Functional Hand posture and Manipulative Hand posture. The Manipulative posture is convenient for relocating a tool but does not afford a functional engagement of the tool on the target object. Subjects were instructed to visually assess whether the pictures displayed correct tool-object associations. EEG data was analyzed in time–voltage and time–frequency domains. Overall, Static Hand, Functional and Manipulative postures cause early activation (100–400 ms post image onset) of parietofrontal areas, to varying intensity in each context, when compared to the No Hand control condition. However, when context is Correct, only the Manipulative Posture significantly induces extended neural responses, predominantly over right parietal and right frontal areas [400–600 ms post image onset]. Significant power increase was observed in the theta band [4–8 Hz] over the right frontal area, [0–500 ms]. In addition, when context is Spatial, Manipulative posture alone significantly induces extended neural responses, over bilateral parietofrontal and left motor areas [400–600 ms]. Significant power decrease occurred primarily in beta bands [12–16, 20–25 Hz] over the aforementioned brain areas [400–600 ms].Here, we demonstrate that the neural processing of tool-object perception is sensitive to several factors. While both Functional and Manipulative postures in Correct context engage predominantly an early left parietofrontal circuit, the Manipulative posture alone extends the neural response and transitions to a late right parietofrontal network. This suggests engagement of a right neural system to evaluate action affordances when hand posture does not support action (Manipulative). Additionally, when tool-use context is ambiguous (Spatial context), there is increased bilateral parietofrontal activation and, extended neural response for the Manipulative posture. These results point to the existence of other networks evaluating tool-object associations when motoric affordances are not readily apparent and underlie corresponding delayed perceptual judgment in our prior behavioral data wherein Manipulative postures had exclusively interfered in judging tool-object content.     

Altered resting state connectivity of the default mode network in alexithymia

Alexithymia is a trait characterized by a diminished capacity to describe and distinguish emotions and to fantasize; it is associated with reduced introspection and problems in emotion processing. The default mode network (DMN) is a network of brain areas that is normally active during rest and involved in emotion processing and self-referential mental activity, including introspection. We hypothesized that connectivity of the DMN might be altered in alexithymia. Twenty alexithymic and 18 non-alexithymic healthy volunteers underwent a resting state fMRI scan. Independent component analysis was used to identify the DMN. Differences in connectivity strength were compared between groups. Within the DMN, alexithymic participants showed lower connectivity within areas of the DMN (medial frontal and temporal areas) as compared to non-alexithymic participants. In contrast, connectivity in the high-alexithymic participants was higher for the sensorimotor cortex, occipital areas and right lateral frontal cortex than in the low-alexithymic participants. These results suggest a diminished connectivity within the DMN of alexithymic participants, in brain areas that may also be involved in emotional awareness and self-referential processing. On the other hand, alexithymia was associated with stronger functional connections of the DMN with brain areas involved in sensory input and control of emotion.     

Functional connectivity‐based parcellation of the human sensorimotor cortex

Task‐based functional magnetic resonance imaging (fMRI) has been successfully employed to obtain somatotopic maps of the human sensorimotor cortex. Here, we showed through direct comparison that a similar functional map can be obtained, independently of a task, by performing a connectivity‐based parcellation of the sensorimotor cortex based on resting‐state fMRI. Cortex corresponding to two adjacent Brodmann areas (BA 3 and BA 4) was selected as the sensorimotor area. Parcellation was obtained along a medial–lateral axis, which was confirmed to be somatotopic (corresponding roughly to an upper, middle and lower limb, respectively) by comparing it with maps obtained using motoric task‐based fMRI in the same participants. Interestingly, the resting‐state parcellation map demonstrated higher correspondence to the task‐based divisions after individuals performed the motor task. Using the resting‐state fMRI data, we also observed higher functional correlations between the centrally located hand region and the other two regions, than between the foot and tongue. The functional relevance of these somatosensory parcellation results indicates the feasibility of a wide range of potential applications to brain mapping.     

Mapping the changed hubs and corresponding functional connectivity in idiopathic restless legs syndrome

ObjectiveThe hubs of the brain network play a key role in integrating and transferring information between different functional modules. However, whether the changed pattern in functional network hubs contributes to the onset of leg discomfort symptoms in restless legs syndrome (RLS) patients remains unclear. Using resting-state functional magnetic resonance imaging (rs-fMRI) and graph theory methods, we investigated whether alterations of hubs can be detected in RLS.MethodsFirst, we constructed the whole-brain voxelwise functional connectivity and calculated a functional connectivity strength (FCS) map in each of 16 drug-naive idiopathic RLS patients and 26 gender- and age-matched healthy control (HC) subjects. Next, a two-sample t test was applied to compare the FCS maps between HC and RLS patients, and to identify significant changes in FCS in RLS patients. To further elucidate the corresponding changes in the functional connectivity patterns of the aberrant hubs in RLS patients, whole-brain resting-state functional connectivity analyses for the hub areas were performed.ResultsThe hub analysis revealed decreased FCS in the cuneus, fusiform gyrus, paracentral lobe, and precuneus, and increased FCS in the superior frontal gyrus and thalamus in idiopathic drug-naive RLS patients. Subsequent functional connectivity analyses revealed decreased functional connectivity in sensorimotor and visual processing networks and increased functional connectivity in the affective cognitive network and cerebellar–thalamic circuit. Furthermore, the mean FCS value in the superior frontal gyrus was significantly correlated with Hamilton Anxiety Rating Scale scores in RLS patients, and the mean FCS value in the fusiform gyrus was significantly correlated with Hamilton Depression Rating Scale scores.ConclusionsThese findings may provide novel insight into the pathophysiology of RLS.     

A common right fronto-parietal network for numerosity and duration processing: an fMRI study

Numerosity and duration processing have been modeled by a functional mechanism taking the form of an accumulator working under two different operative modes. Separate investigations of their cerebral substrates have revealed partly similar patterns of activation, mainly in parietal and frontal areas. However, the precise cerebral implementation of the accumulator model within these areas has not yet been directly assessed. In this study, we asked participants to categorize the numerosity of flashed dot sequences or the duration of single dot displays, and we used functional magnetic resonance imaging (fMRI) to examine the common neural correlates of these processes. The results reveal a large right-lateralized fronto-parietal network, including the intraparietal sulcus (IPS) and areas in the precentral, middle and superior frontal gyri, which is activated by both numerosity and duration processing. Complementary psychophysiological interaction (PPI) analyses show a functional connectivity between the right IPS and the frontal areas in both tasks, whereas the right IPS was functionally connected to the left IPS and the right precentral area in the numerosity categorization task only. We propose that the right IPS underlies a common magnitude processing system for both numerosity and duration, possibly corresponding to the encoding and accumulation stages of the accumulator model, whereas the frontal areas are involved in subsequent working-memory storage and decision-making processes.     

Neuronal correlates of appetite regulation in patients with schizophrenia: Is there a basis for future appetite dysfunction?

BackgroundGiven the undesired metabolic side effects of atypical antipsychotic medication it is important to understand the neuronal basis related to processing of appetite regulation in patients affected by schizophrenia.MethodsHere we used functional magnetic resonance imaging (fMRI) to assess brain activity in response to food cues and neutral stimuli in twenty patients with schizophrenia and eleven healthy individuals. In addition to clinical and dietary habits assessments, we collected, in patients, measurements of fasting glucose, ghrelin, leptin, insulin, prolactin and lipids blood concentration and we correlated the cerebral activity with clinical and metabolic measures.ResultsBoth groups engaged a common neuronal network while processing food cues, which included the left insula, primary sensorimotor areas, and inferior temporal and parietal cortices. Cerebral responses to appetitive stimuli in thalamus, parahippocampus and middle frontal gyri were specific only to schizophrenic patients, with parahippocampal activity related to hunger state and increasing linearly over time. Antipsychotic medication dosage correlated positively with a cognitive measure reflecting food cravings, whereas the severity of the disease correlated negatively with a cognitive measure indicating dietary restraint in eating habits. These cognitive variables correlated, in turn, with parahippocampal and thalamic neuronal activities, respectively.ConclusionsWe identified a specific neural substrate underlying cognitive processing of appetitive stimuli in schizophrenia, which may contribute to appetite dysfunction via perturbations in processing of homeostatic signals in relation to external stimuli. Our results also suggest that both antipsychotic medication and the disease severity per se could amplify these effects, via different mechanisms and neuronal networks.     

Sensorimotor‐independent prefrontal activity during response inhibition

A network of brain regions involving the ventral inferior frontal gyrus/anterior insula (vIFG/AI), presupplementary motor area (pre‐SMA) and basal ganglia has been implicated in stopping impulsive, unwanted responses. However, whether this network plays an equal role in response inhibition under different sensorimotor contexts has not been tested systematically. Here, we conducted an fMRI experiment using the stop signal task, a sensorimotor task requiring occasional withholding of the planned response upon the presentation of a stop signal. We manipulated both the sensory modality of the stop signal (visual versus auditory) and the motor response modality (hand versus eye). Results showed that the vIFG/AI and the preSMA along with the right middle frontal gyrus were commonly activated in response inhibition across the various sensorimotor conditions. Our findings provide direct evidence for a common role of these frontal areas, but not striatal areas in response inhibition independent of the sensorimotor contexts. Nevertheless, these three frontal regions exhibited different activation patterns during successful and unsuccessful stopping. Together with the existing evidence, we suggest that the vIFG/AI is involved in the early stages of stopping such as triggering the stop process while the preSMA may play a role in regulating other cortical and subcortical regions involved in stopping. Hum Brain Mapp 35:2119–2136, 2014. © 2013 Wiley Periodicals, Inc.     

Increase in focal concentration of deoxyhaemoglobin during neuronal activity in cerebral ischaemic patients

BACKGROUND AND PURPOSE: Blood oxygenation level dependent contrast functional magnetic resonance imaging (BOLD-fMRI) has been applied to functional mapping in brain disorders, based on the assumption that normal adults and patients with brain disorders exhibit similar evoked cerebral blood oxygenation (CBO) changes. This study compared evoked CBO changes measured by near infrared spectroscopy (NIRS) with the activation mapping obtained by BOLD-fMRI in patients with cerebral ischaemia. METHODS: The study involved six normal adults and six patients with cerebral ischaemia. Hand grasping was performed as a motor task. All patients could perform the task similarly to the controls at the time of examination, but single photon emission computed tomography demonstrated low baseline cerebral blood flow and a decreased haemodynamic reserve in the primary sensorimotor cortex on the lesion side. Using NIRS, concentration changes of deoxyhaemoglobin (Deoxy-Hb), oxyhaemoglobin (Oxy-Hb), and total haemoglobin (Total-Hb) were measured in the primary sensorimotor cortex contralateral to the task. BOLD-fMRI signals were measured by 1.5 T magnetic resonance imaging using an echo-planar technique. Activation maps were calculated by statistical parametric mapping. RESULTS: In the controls, Deoxy-Hb decreased in association with increases of Oxy-Hb and Total-Hb in the primary sensorimotor cortex during the task. However, in the patients, Deoxy-Hb increased significantly from baseline, while Oxy-Hb and Total-Hb also increased, indicating the presence of rCBF increases in response to neuronal activation. BOLD-fMRI demonstrated only limited activation areas in the primary sensorimotor cortex on the lesion side. CONCLUSION: The CBO changes in patients with cerebral ischaemia differed from those of normal adults; Deoxy-Hb was increased in activation areas of the patients. This implies that BOLD-fMRI may overlook activation areas in the patients unless both increases and decreases of signal are taken into consideration.     

Direct evidence from intraoperative electrocortical stimulation indicates shared and distinct speech production center between Chinese and English languages

Chinese processing has been suggested involving distinct brain areas from English. However, current functional localization studies on Chinese speech processing use mostly “indirect” techniques such as functional magnetic resonance imaging and electroencephalography, lacking direct evidence by means of electrocortical recording. In this study, awake craniotomies in 66 Chinese‐speaking glioma patients provide a unique opportunity to directly map eloquent language areas. Intraoperative electrocortical stimulation was conducted and the positive sites for speech arrest, anomia, and alexia were identified separately. With help of stereotaxic neuronavigation system and computational modeling, all positive sites elicited by stimulation were integrated and a series of two‐ and three‐dimension Chinese language probability maps were built. We performed statistical comparisons between the Chinese maps and previously derived English maps. While most Chinese speech arrest areas located at typical language production sites (i.e., 50% positive sites in ventral precentral gyrus, 28% in pars opercularis and pars triangularis), which also serve English production, an additional brain area, the left middle frontal gyrus (Brodmann's areas 6/9), was found to be unique in Chinese production (P < 0.05). Moreover, Chinese speakers’ inferior ventral precentral gyrus (Brodmann's area 6) was used more than that in English speakers. Our finding suggests that Chinese involves more perisylvian region (extending to left middle frontal gyrus) than English. This is the first time that direct evidence supports cross‐cultural neurolinguistics differences in human beings. The Chinese language atlas will also helpful in brain surgery planning for Chinese‐speakers. Hum Brain Mapp 36:4972–4985, 2015. © 2015 Wiley Periodicals, Inc.     

Prefrontal involvement in temporal bridging and timing movement

Brain activity exclusively related to a temporal delay has rarely been investigated using modern brain imaging. In this study we exploited the temporal resolution of functional magnetic resonance imaging (fMRI) to characterise, by sinusoidal regression analysis, differential neuroactivation patterns induced in healthy subjects by two sensorimotor synchronization tasks different in their premovement delay of either 0.6 s or 5 s. The short event rate condition required rhythmic tapping, while the long event rate condition required timing of intermittent movements. Left rostral prefrontal cortex, medial frontal cortex, SMA and supramarginal gyrus demonstrated increased MR signal intensity during low frequency synchronization, suggesting that these brain regions form a distributed neural network for cognitive time management processes, such as time estimation and motor output timing. Medial frontal cortex showed a biphasic pattern of response during both synchronization conditions, presumably reflecting frequency-independent motor output related attention. As predicted, sensorimotor and visual association areas demonstrated increased MR signal intensity during high frequency synchronization.     

A multicentre study of motor functional connectivity changes in patients with multiple sclerosis

In this multicentre study involving eight European centres, we characterized the spatial pattern of functional connectivity (FC) in the sensorimotor network from 61 right-handed patients with multiple sclerosis (MS) and 74 age-matched healthy subjects assessed with the use of functional magnetic resonance imaging (fMRI) and a simple motor task of their right dominant hand. FC was investigated by using: (i) voxel-wise correlations between the left sensorimotor cortex (SMC) and any other area in the brain; and (ii) bivariate correlations between time series extracted from several regions of interest (ROIs) belonging to the sensorimotor network. Both healthy controls and MS patients had significant FC between the left SMC and several areas of the sensorimotor network, including the bilateral postcentral and precentral gyri, supplementary motor area, middle frontal gyri, insulae, secondary somatosensory cortices, thalami, and right cerebellum. Voxel-wise assessment of FC revealed increased connectivity between the left SMC and the right precentral gyrus, right middle frontal gyrus (MFG) and bilateral postcentral gyri in MS patients as compared with controls. ROI analysis also showed a widespread pattern of altered connectivity, characterized by increased FC between the right MFG, the left insula and the right inferior frontal gyrus in comparison with many regions of the sensorimotor network. These results provide further evidence for increased bihemispheric contributions to motor control in patients with MS relative to healthy controls. They further suggest that multicentre fMRI studies of FC changes are possible, and provide a potential imaging biomarker for use in experimental therapeutic studies directed at enhancing adaptive plasticity in the disease.     

Basic mechanisms of central rhythms reactivity to preparation and execution of a voluntary movement: a stereoelectroencephalographic study.

OBJECTIVE: To localize the sources of mu, beta and gamma rhythms and to explore the functional significance of their reactivity. METHODS: We used the method of quantification of event-related desynchronization (ERD) and synchronization (ERS) to analyze the reactivity of intracerebral rhythms recorded in stereoelectroencephalography within the sensorimotor areas during the preparation and the execution of a simple self-paced hand movement. We recorded 3 epileptic subjects who were explored before a surgical treatment. RESULTS: An ERD of mu and beta rhythms has been recorded before the movement onset in the precentral gyrus, spreading then to the postcentral gyrus and to the frontal medial cortex. The frontal lateral cortex was inconstantly involved during the movement. The movement offset was followed by an important and focused beta ERS which was found within the pre- and post-central gyrus and the frontal medial cortex. Within the beta band, we observed several narrower bands with different reactivities and locations. Focused gamma reactivity was also found in the precentral and postcentral gyri. CONCLUSIONS: The reactivities of mu and beta rhythms are different but their locations overlap. Mu ERD is a diffuse phenomenon that reflects the activation of all the sensorimotor areas during a simple movement. Beta band is likely to be composed of different rhythms with different functional significance. The primary motor area seems to contain two distinct areas with different reactivity to the movement preparation and execution.     

Decision and action planning signals in human posterior parietal cortex during delayed perceptual choices

During simple perceptual decisions, sensorimotor neurons in monkey fronto‐parietal cortex represent a decision variable that guides the transformation of sensory evidence into a motor response, supporting the view that mechanisms for decision‐making are closely embedded within sensorimotor structures. Within these structures, however, decision signals can be dissociated from motor signals, thus indicating that sensorimotor neurons can play multiple and independent roles in decision‐making and action selection/planning. Here we used functional magnetic resonance imaging to examine whether response‐selective human brain areas encode signals for decision‐making or action planning during a task requiring an arbitrary association between face pictures (male vs. female) and specific actions (saccadic eye vs. hand pointing movements). The stimuli were gradually unmasked to stretch the time necessary for decision, thus maximising the temporal separation between decision and action planning. Decision‐related signals were measured in parietal and motor/premotor regions showing a preference for the planning/execution of saccadic or pointing movements. In a parietal reach region, decision‐related signals were specific for the stimulus category associated with its preferred pointing response. By contrast, a saccade‐selective posterior intraparietal sulcus region carried decision‐related signals even when the task required a pointing response. Consistent signals were observed in the motor/premotor cortex. Whole‐brain analyses indicated that, in our task, the most reliable decision signals were found in the same neural regions involved in response selection. However, decision‐ and action‐related signals within these regions can be dissociated. Differences between the parietal reach region and posterior intraparietal sulcus plausibly depend on their functional specificity rather than on the task structure.     

Stimulus transformation into motor action: Dynamic graph analysis reveals a posterior‐to‐anterior shift in brain network communication of older subjects

Cognitive performance slows down with increasing age. This includes cognitive processes that are essential for the performance of a motor act, such as the slowing down in response to an external stimulus. The objective of this study was to identify aging‐associated functional changes in the brain networks that are involved in the transformation of external stimuli into motor action. To investigate this topic, we employed dynamic graphs based on phase‐locking of Electroencephalography signals recorded from healthy younger and older subjects while performing a simple visually‐cued finger‐tapping task. The network analysis yielded specific age‐related network structures varying in time in the low frequencies (2–7 Hz), which are closely connected to stimulus processing, movement initiation and execution in both age groups. The networks in older subjects, however, contained several additional, particularly interhemispheric, connections and showed an overall increased coupling density. Cluster analyses revealed reduced variability of the subnetworks in older subjects, particularly during movement preparation. In younger subjects, occipital, parietal, sensorimotor and central regions were—temporally arranged in this order—heavily involved in hub nodes. Whereas in older subjects, a hub in frontal regions preceded the noticeably delayed occurrence of sensorimotor hubs, indicating different neural information processing in older subjects. All observed changes in brain network organization, which are based on neural synchronization in the low frequencies, provide a possible neural mechanism underlying previous fMRI data, which report an overactivation, especially in the prefrontal and pre‐motor areas, associated with a loss of hemispheric lateralization in older subjects.     

Functional and anatomical connectivity abnormalities in left inferior frontal gyrus in schizophrenia

Functional studies in schizophrenia demonstrate prominent abnormalities within the left inferior frontal gyrus (IFG) and also suggest the functional connectivity abnormalities in language network including left IFG and superior temporal gyrus during semantic processing. White matter connections between regions involved in the semantic network have also been indicated in schizophrenia. However, an association between functional and anatomical connectivity disruptions within the semantic network in schizophrenia has not been established. Functional (using levels of processing paradigm) as well as diffusion tensor imaging data from 10 controls and 10 chronic schizophrenics were acquired and analyzed. First, semantic encoding specific activation was estimated, showing decreased activation within the left IFG in schizophrenia. Second, functional time series were extracted from this area, and left IFG specific functional connectivity maps were produced for each subject. In an independent analysis, tract‐based spatial statistics (TBSS) was used to compare fractional anisotropy (FA) values between groups, and to correlate these values with functional connectivity maps. Schizophrenia patients showed weaker functional connectivity within the language network that includes left IFG and left superior temporal sulcus/middle temporal gyrus. FA was reduced in several white matter regions including left inferior frontal and left internal capsule. Finally, left inferior frontal white matter FA was positively correlated with connectivity measures of the semantic network in schizophrenics, but not in controls. Our results indicate an association between anatomical and functional connectivity abnormalities within the semantic network in schizophrenia, suggesting further that the functional abnormalities observed in this disorder might be directly related to white matter disruptions. Hum Brain Mapp, 2009. © 2009 Wiley‐Liss, Inc.