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PubMed1994

Network analysis of cortical visual pathways mapped with PET.

Brain metabolic mapping techniques, such as positron emission tomography (PET), can provide information about the functional interactions within entire neural systems. With the large quantity of data that can accumulate from a mapping study, a network analysis, which makes sense of the complex interactions among neural elements, is necessary. A network analysis was performed on data obtained from a PET study that examined both the changes in regional cerebral blood flow (rCBF) and interregional correlations among human cortical areas during performance of an object vision (face matching) and spatial vision (dot-location matching) task. Brain areas for the network were selected based on regions showing significant rCBF or interregional correlations between tasks. Anterior temporal and frontal lobe regions were added to the network using a principal components analysis. Interactions among selected regions were quantified with structural equation modeling. In the structural equation models, connections between brain areas were based on known neuroanatomy and the interregional correlations were used to calculate path coefficients representing the magnitude of the influence of each directional path. The combination of the anatomical network and interregional correlations created a functional network for each task. The functional network for the right hemisphere showed that in the object vision task, dominant path influences were among occipitotemporal areas, while in the spatial vision task, occipitoparietal interactions were stronger. The network for the spatial vision task also had a strong feedback path from area 46 to occipital cortex, an effect that was absent in the object vision task. There were strong interactions between dorsal and ventral pathways in both networks. Functional networks for the left hemisphere did not differ between tasks. Networks for the interhemispheric interactions showed that the dominant pathway in the right hemisphere also had stronger effects on homologous left hemisphere areas and are consistent with a hypothesis that intrahemispheric interactions were greater in the right hemisphere in both tasks, and that these influences were transmitted callosally to the left hemisphere.

Adult↗
PubMed2005

Advancing the boundaries of high-connectivity network simulation with distributed computing.

The availability of efficient and reliable simulation tools is one of the mission-critical technologies in the fast-moving field of computational neuroscience. Research indicates that higher brain functions emerge from large and complex cortical networks and their interactions. The large number of elements (neurons) combined with the high connectivity (synapses) of the biological network and the specific type of interactions impose severe constraints on the explorable system size that previously have been hard to overcome. Here we present a collection of new techniques combined to a coherent simulation tool removing the fundamental obstacle in the computational study of biological neural networks: the enormous number of synaptic contacts per neuron. Distributing an individual simulation over multiple computers enables the investigation of networks orders of magnitude larger than previously possible. The software scales excellently on a wide range of tested hardware, so it can be used in an interactive and iterative fashion for the development of ideas, and results can be produced quickly even for very large networks. In contrast to earlier approaches, a wide class of neuron models and synaptic dynamics can be represented.

Action Potentials↗
PubMed2006

Functional connectivity of the fusiform gyrus during a face-matching task in subjects with mild cognitive impairment.

Cognitive function requires a high level of functional interaction between regions of a network supporting cognition. Assuming that brain activation changes denote an advanced state of disease progression, changes in functional connectivity may precede changes in brain activation. The objective of this study was to investigate changes in functional connectivity of the right middle fusiform gyrus (FG) in subjects with mild cognitive impairment (MCI) during performance of a face-matching task. The right middle FG is a key area for processing face stimuli. Brain activity was measured using functional MRI. There were 16 MCI subjects and 19 age-matched healthy controls. The linear correlation coefficient was utilized as a measure of functional connectivity between the right middle FG and all other voxels in the brain. There were no statistical differences found in task performance or activation between groups. The right middle FG of the healthy control and MCI groups showed strong bilateral positive linear correlation with the visual cortex, inferior and superior parietal lobules, dorsolateral prefrontal cortex (DLPFC) and anterior cingulate. The healthy controls showed higher positive linear correlation of the right middle FG to the visual cortex, parietal lobes and right DLPFC than the MCI group, whereas the latter had higher positive linear correlation in the left cuneus. In the healthy controls, the right middle FG had negative linear correlation with right medial frontal gyrus and superior temporal gyrus and with left inferior parietal lobule (IPL), angular gyrus, superior frontal gyrus and anterior cingulate gyrus, but the MCI group had negative linear correlation with the left IPL, angular gyrus, precuneus, anterior cingulate, and to right middle temporal gyrus and posterior cingulate gyrus. In the negatively linearly correlated regions, the MCI group had reduced functional connectivity to the frontal areas, right superior temporal gyrus and left IPL. Different regions of the cuneus and IPL had increased functional connectivity in either group. The putative presence of Alzheimer's disease neuropathology in MCI affects functional connectivity from the right middle FG to the visual areas and medial frontal areas. In addition, higher linear correlation in the MCI group in the parietal lobe may indicate the initial appearance of compensatory processes. The results demonstrate that functional connectivity can be an effective marker for the detection of changes in brain function in MCI subjects.

Aged↗
PubMed2000

Brain regulation of feeding behavior and food intake in fish.

In mammals, the orexigenic and anorexigenic neuronal systems are morphologically and functionally connected, forming an interconnected network in the hypothalamus to govern food intake and body weight. However, there are relatively few studies on the brain control of feeding behavior in fish. Recent studies using mammalian neuropeptides or fish homologs of mammalian neuropeptides indicate that brain orexigenic signal molecules include neuropeptide Y, orexins, galanin and beta-endorphin, whereas brain anorexigenic signal molecules include cholecystokinin, bombesin, corticotropin-releasing factor, cocaine- and amphetamine-regulated transcript, and serotonin. Tachykinins may also have an anorectic action in fish. The brain hypothalamic area is associated with regulation of food intake, while sites outside the hypothalamus are also involved in this function. There is correlation between short-term changes in serum growth hormone levels and feeding behavior, although possible mechanisms integrating these functions remain to be defined.

Animals↗
PubMed2006

Superior longitudinal fasciculus subserves vestibular network in humans.

Vestibular function is known to be represented in a large-scale network within the brain. Although much is known about the topography of this cortical network, the subcortical anatomo-functional connectivity has received less attention. We present three patients operated on while conscious for cerebral low-grade gliomas, in which we elicited vestibular symptoms during subcortical stimulation. Anatomo-functional correlations between postoperative imaging and intraoperative findings suggest the involvement of the superior longitudinal fasciculus in the spreading of the vestibular symptoms. We argue that this fasciculus plays a major role in the functional connectivity of the areas involved in the complex multimodal network that controls vestibular function.

Auditory Pathways↗
PubMed1999

['Frontal lobe syndrome' caused by severe head trauma or cerebrovascular diseases].

The term "frontal lobe syndrome" comprises a variety of different clinical syndromes produced by focal lesions involving the prefrontal cortex. However, similar syndromes can be observed after lesions involving subcortical structures connected with the prefrontal cortex in neuronal networks. With respect to the different clinical pictures and underlying brain lesions, prefrontal lobe dysfunction may be divided into a disorganized type, caused by lesion of the dorsolateral prefrontal lobe and its connections, a disinhibited type that can be observed following lesions of the orbitofrontal cortex, and an apathetic type following lesions affecting the functional balance between the cingulum and the supplementary motor area. As intracerebral lesions are rarely limited to the brain regions described, in the majority of patients various degrees of behavioural dysfunction can be observed. The case reports of four patients illustrating the three major prefrontal syndromes following severe head injury (n = 2) or cerebrovascular disease (n = 2) are presented and diagnostic implications as well as possible treatment strategies are discussed.

Aged↗
PubMed2006

Magnetoencephalographic evaluation of resting-state functional connectivity in Alzheimer's disease.

Statistical interdependencies between magnetoencephalographic signals recorded over different brain regions may reflect the functional connectivity of the resting-state networks. We investigated topographic characteristics of disturbed resting-state networks in Alzheimer's disease patients in different frequency bands. Whole-head 151-channel MEG was recorded in 18 Alzheimer patients (mean age 72.1 years, SD 5.6; 11 males) and 18 healthy controls (mean age 69.1 years, SD 6.8; 7 males) during a no-task eyes-closed resting state. Pair-wise interdependencies of MEG signals were computed in six frequency bands (delta, theta, alpha1, alpha2, beta and gamma) with the synchronization likelihood (a nonlinear measure) and coherence and grouped into long distance (intra- and interhemispheric) and short distance interactions. In the alpha1 and beta band, Alzheimer patients showed a loss of long distance intrahemispheric interactions, with a focus on left fronto-temporal/parietal connections. Functional connectivity was increased in Alzheimer patients locally in the theta band (centro-parietal regions) and the beta and gamma band (occipito-parietal regions). In the Alzheimer group, positive correlations were found between alpha1, alpha2 and beta band synchronization likelihood and MMSE score. Resting-state functional connectivity in Alzheimer's disease is characterized by specific changes of long and short distance interactions in the theta, alpha1, beta and gamma bands. These changes may reflect loss of anatomical connections and/or reduced central cholinergic activity and could underlie part of the cognitive impairment.

Aged↗
PubMed2000

Simulation of cognitive disturbances by a dynamic threshold semantic neural network.

A neural network model with dynamic thresholds, asymmetric connections, and clustered memories simulates spread activation that is hypothesized for semantic networks in the brain. By altering the parameters of the dynamic threshold a large range of disturbances can be generated in the model. These disturbances show metaphorical resemblance to certain general clinical descriptions of mental disturbances found in psychiatric patients engaged in various cognitive tasks. Even though the model is highly theoretical and metaphoric, it may help to gain certain insights into the relation between alterations of certain neural parameters, for example, thresholds and connectivity, and clinical symptoms in patients.

Algorithms↗
PubMed2026

Brain network alterations underlying cue reactivity and craving in abstinent methamphetamine users: a systematic review of functional MRI findings.

BACKGROUND: Methamphetamine use disorder (MUD) is marked by intense craving and high relapse risk, often triggered by drug-related cues. Functional magnetic resonance imaging (fMRI) provides key insight into the neural basis of this cue reactivity, implicating large-scale brain networks for reward, motivation, and control. Yet, findings remain inconsistent across studies due to differences in task design, abstinence duration, and participant characteristics. OBJECTIVE: This systematic review synthesises evidence on how abstinence influences brain network alterations underlying cue reactivity and craving in methamphetamine users, integrating task-based and resting-state fMRI findings within leading neurobiological models of addiction. METHODS: A systematic search of PubMed, Scopus, Web of Science, and Ovid was conducted up to August 10, 2025, following PRISMA 2020 guidelines. Eligible fMRI studies examined cue reactivity or craving in abstinent methamphetamine users. Data were extracted on activation, connectivity, and brain-behaviour associations, and synthesised narratively. RESULTS: Task-based studies revealed heightened activation across reward, salience, and control networks during cue exposure, which diminished as parietal and executive control systems re-engaged with longer abstinence. Resting-state findings showed disrupted intrinsic connectivity among default mode, salience, and frontoparietal networks, reflecting persistent imbalances linked to craving and use severity. CONCLUSION: fMRI evidence shows that MUD is marked by network-level disruption linking reward, salience, and control systems. Task-based findings reveal strong cue reactivity in reward circuits, while resting-state data show persistent imbalance among default mode and control networks. With abstinence, partial restoration of network integrity emerges, highlighting both vulnerability and opportunities for targeted, recovery-based interventions.

Humans↗
PubMed2006

Advances in autism neuroimaging research for the clinician and geneticist.

This review focuses on recent advances in the in vivo study of the whole brain in idiopathic autism. The brain is abnormally large in some but not all children with autism during post-natal development. Age-related changes in brain volume in autism are complex and appear to be abnormal from infancy into adulthood. Diffuse differences in total and regional gray and white matter volumes are found. The volumetric abnormalities appear to follow anomalous, complex, and non-uniform developmental curves. Diffuse abnormalities of brain chemical concentrations, neural network anatomy, brain lateralization, intra- and inter-hemispheric morphologic and functional connectivity, and serotonin synthesis capacity are also found. Abnormalities of head growth are first apparent during infancy. Abnormalities of total brain volume, gray and white matter volumes, brain chemistry, serotonin synthesis, and brain electrophysiology are evident by early childhood. Currently, no method of brain imaging helps with diagnosis or treatment of idiopathic autism, but ongoing research aims to unravel the heterogeneity of autism and may provide future diagnostic tools that inform treatment.

Autistic Disorder↗
PubMed1997

Patterns of oculomotor scanning in patients with unilateral posterior parietal or frontal lobe damage.

Eye movements were recorded during the inspection of dot patterns in control subjects and in patients with acquired unilateral brain damage involving posterior parietal or frontal cortical regions. Normal subjects adapted their oculomotor scanning pattern effectively to the stimulus configuration. Patients' oculomotor scanning patterns were characterized by a rather rigid sequence of fixations and saccades, with no evidence for a systematic and flexible spatio-temporal organization. In a stimulus condition where dots were grouped, patients with frontal damage accurately shifted their gaze between the dot groups, but had difficulties with dot sampling. These observations suggest that the posterior parietal damage mainly affected the visuo-spatial guidance of the scanpath, whereas the frontal damage impaired its planning. It is concluded that both, posterior parietal and frontal brain structures, and their reciprocal connections, are part of a distributed neural network subserving visually-guided oculomotor scanning, and that the spatio-temporal organization of the scanpath depends critically on both structures and their close co-operation.

Adult↗
PubMed1999

Expression of a novel protocadherin, OL-protocadherin, in a subset of functional systems of the developing mouse brain.

We cloned a novel protocadherin cDNA, which we named OL-protocadherin (OL-pc), from mouse brain cDNA libraries. Its cytoplasmic region showed no similarities to other protocadherins, indicating that it belongs to a novel subfamily of protocadherins. Experiments using transfectants showed that OL-pc is a homophilic cell-cell adhesion molecule. The molecular mass of OL-pc was 140 kDa in the brain. Expression of OL-pc mRNA was specific to the nervous system, changing over time from the embryonic stage to the adult stage. The OL-pc expression seemed to be restricted to a subset of functionally related brain nuclei and regions such as the nuclei in the main olfactory system, the limbic system, and the olivocortical projection. There were at least two distinct patterns of distribution for the OL-pc protein. First, it was localized in particular brain nuclei or compartments, such as the stripes of the developing cerebellum. Second, it was found at the synapse in regions such as the glomeruli of the olfactory bulb. In addition, the OL-pc protein seemed not to be detected or was detected only weakly in some regions, such as hippocampus in which the mRNA was expressed at high levels. These results indicate that the expression of OL-pc is developmentally regulated in a subset of the functional systems and that it may be involved in the formation of the neural network by segregation of the brain nuclei and mediation of the axonal connections.

Aging↗
PubMed2006

Consistent resting-state networks across healthy subjects.

Functional MRI (fMRI) can be applied to study the functional connectivity of the human brain. It has been suggested that fluctuations in the blood oxygenation level-dependent (BOLD) signal during rest reflect the neuronal baseline activity of the brain, representing the state of the human brain in the absence of goal-directed neuronal action and external input, and that these slow fluctuations correspond to functionally relevant resting-state networks. Several studies on resting fMRI have been conducted, reporting an apparent similarity between the identified patterns. The spatial consistency of these resting patterns, however, has not yet been evaluated and quantified. In this study, we apply a data analysis approach called tensor probabilistic independent component analysis to resting-state fMRI data to find coherencies that are consistent across subjects and sessions. We characterize and quantify the consistency of these effects by using a bootstrapping approach, and we estimate the BOLD amplitude modulation as well as the voxel-wise cross-subject variation. The analysis found 10 patterns with potential functional relevance, consisting of regions known to be involved in motor function, visual processing, executive functioning, auditory processing, memory, and the so-called default-mode network, each with BOLD signal changes up to 3%. In general, areas with a high mean percentage BOLD signal are consistent and show the least variation around the mean. These findings show that the baseline activity of the brain is consistent across subjects exhibiting significant temporal dynamics, with percentage BOLD signal change comparable with the signal changes found in task-related experiments.

Brain↗
PubMed2004

A 4.0-T fMRI study of brain connectivity during word fluency in first-episode schizophrenia.

OBJECTIVE: To use functional magnetic resonance imaging (fMRI) to investigate functional connectivity, and hence, underlying neural networks, in never-treated, first-episode patients with schizophrenia using a word fluency paradigm known to activate prefrontal, anterior cingulate, and thalamic regions. Abnormal connectivity between the prefrontal cortex (PFC) and other brain regions has been demonstrated in chronic, medicated patients in previous positron emission tomography (PET) studies, but has not to our knowledge, previously been demonstrated using both first-episode, drug-naïve patients and fMRI technology. METHODS: A 4.0-Tesla (T) fMRI was used to examine activation and functional connectivity [psychophysiological interactions (PPIs)] during a word fluency task compared to silent reading in 10 never-treated, first-episode patients with schizophrenia and 10 healthy volunteers of comparable age, sex, handedness, and parental education. RESULTS: Compared to healthy volunteers, the schizophrenia patient group exhibited less activation during the word fluency task, mostly in the right anterior cingulate and prefrontal regions. Psychophysiological interactions between right anterior cingulate and other parts of the brain revealed a localized interaction with the left temporal lobe in healthy volunteers during the task and a widespread unfocussed interaction in patients. CONCLUSION: These findings suggest anterior cingulate involvement in the neuronal circuitry underlying schizophrenia.

Adult↗
PubMed2005

Olfactory inputs to hypothalamic neurons controlling reproduction and fertility.

In order to gain insight into sensory processing modulating reproductive behavioral and endocrine changes, we have aimed at identifying afferent pathways to neurons synthesizing luteinizing hormone-releasing hormone (LHRH, also known as gonadotropin-releasing hormone [GnRH]), a key neurohormone of reproduction. Injection of conditional pseudorabies virus into the brain of an LHRH::CRE mouse line led to the identification of neuronal networks connected to LHRH neurons. Remarkably, and in contrast to established notions on the nature of LHRH neuronal inputs, our data identify major olfactory projection pathways originating from a discrete population of olfactory sensory neurons but fail to document any synaptic connectivity with the vomeronasal system. Accordingly, chemosensory modulation of LHRH neuronal activity and mating behavior are dramatically impaired in absence of olfactory function, while they appear unaffected in mouse mutants lacking vomeronasal signaling. Further visualization of afferents to LHRH neurons across the brain offers a unique opportunity to uncover complex polysynaptic circuits modulating reproduction and fertility.

Animals↗
PubMed2003

Membrane Na+-K+ ATPase inhibition mediated quantal model for brain evolution.

The hypothalamus secretes an endogenous membrane Na+-K+ ATPase inhibitor, digoxin. A digoxin-mediated model of quantal perception is proposed. In the quantal state, self replication of self-organized macromolecules is possible. This leads to the origin of molecular organisms like prions. Macromolecules group together to form organelle, which in evolutionary terms are independent bacteria. The organelle/bacteria symbiotically cluster together to form the cell. The human organism, including the brain, can be visualized as an organized cluster or colony of unicellular, symbiotically grouped flagellated bacteria. Synaptic connections form in the bacterial cluster leading to the evolution of the primitive neuronal networks, and later the human brain. The role of quantal perception and the observer function of consciousness in the origin of matter is important. Symbiotically clustered intergalactic magnetotactic bacterial networks are important in the evolution of the universe.

Biological Evolution↗
PubMed2004

Global optimization of cerebral cortex layout.

Functional areas of mammalian cerebral cortex seem positioned to minimize costs of their interconnections, down to a best-in-a-billion optimality level. The optimization problem here, originating in microcircuit design, is: Given connections among components, what is the physical placement of the components on a surface that minimizes total length of connections? Because of unfeasibility of measuring long-range "wire length" in the cortex, a simpler adjacency cost was validated. To deal with incomplete information on brain networks, a size law was developed that predicts optimization patterns in subnetworks. Macaque and cat cortex rank better in this connection optimization than the wiring of comparably structured computer chips, but somewhat worse than the macroeconomic commodity-flow network among U.S. states. However, cortex wiring conforms to the size law better than the macroeconomic patterns, which may indicate cortex optimizing mechanisms involve more global processes.

Animals↗
PubMed2004

The nature of traumatic memories: a 4-T FMRI functional connectivity analysis.

OBJECTIVE: This study used functional connectivity analyses to assess interregional brain activity correlations during the recall of traumatic memories in traumatized subjects with and without posttraumatic stress disorder (PTSD). METHOD: Both 4-T functional magnetic resonance imaging (fMRI) and functional connectivity analyses were used to assess interregional brain activity correlations during script-driven symptom provocation in traumatized subjects with (N=11) and without (N=13) PTSD. Functional connectivity analyses were carried out by using data for brain regions activated in both the PTSD group and the comparison group. The use of functional connectivity analyses in addition to subtraction analyses allowed assessment of specific brain regions involved in the recall of traumatic events and of the neuronal networks underlying the recall of such events. RESULTS: Significant between-group differences in functional connectivity were found. Comparison of connectivity maps at coordinates x=2, y=20, z=36 (right anterior cingulate gyrus) for the two groups showed that the subjects without PTSD had greater correlation than the PTSD subjects in the left superior frontal gyrus (Brodmann's area 9), left anterior cingulate gyrus (Brodmann's area 32), left striatum (caudate), left parietal lobe (Brodmann's areas 40 and 43), and left insula (Brodmann's area 13). In contrast, the PTSD subjects showed greater correlation than the subjects without PTSD in the right posterior cingulate gyrus (Brodmann's area 29), right caudate, right parietal lobe (Brodmann's areas 7 and 40), and right occipital lobe (Brodmann's area 19). CONCLUSIONS: The differences in brain connectivity between PTSD and comparison subjects may account for the nonverbal nature of traumatic memory recall in PTSD subjects, compared to a more verbal pattern of traumatic memory recall in comparison subjects.

Brain↗