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PubMed2004

Recruitment of periventricular parietal regions in processing cluttered point-light biological motion.

Recent findings point to the existence of a cortical-subcortical parietal network that drives attention-related integration of features and elements. Here we ask whether the functioning of this network might be modulated by early periventricular lesions. To this end, a cohort of adolescents who were born premature with different severity of bilateral periventricular leukomalacia (PVL) and two groups of matched peers (term-born adolescents and former preterms with normal MRI scan) were shown a set of impoverished point-light stimuli. Observers had to detect a point-light walker embedded in an array of distracters mimicking the motion of the target's dots. Patients exhibited higher susceptibility to distortions caused by distracters. In patients only, sensitivity to the point-light figure highly correlates not just with performance on additionally administered feature integration tasks but also on visual attention-demanding IQ tasks. Moreover, the sensitivity index, as well as the values of both IQ factors, decreases with an increase in the volumetric PVL extent in the parieto-occipital region. No relationship was found between these variables and the lesion extent in the frontal or temporal periventricular regions. The data suggest that visual integration and attention in processing cluttered point-light displays are intimately connected. Most importantly, periventricular parieto-occipital regions might be part of a distributed network recruited in deployment of the posterior attentional system. The functioning of this system seems to be vulnerable to bilateral periventricular damage even if it occurs very early in brain development.

Adolescent↗
PubMed1985

Moyamoya disease with a developmental anomaly of the mesenchyme.

We treated a Japanese boy with moyamoya disease accompanied by synbrachydactylia, funnel chest, pes equinus and short stature. Angiograms showed the anomalous origin of the occipital artery in addition to the moyamoya vascular network at the base of the brain. A generalised mesenchymal anomaly was suggested in this case.

Abnormalities, Multiple↗
PubMedDate not supplied

Cellular dynamics of network memory.

One example of "emergence" is the development, as a result of neural ontogeny and living experience, of cortical networks capable of representing and retaining cognitive information. A large body of evidence from neuropsychology, electrophysiology and neuroimaging indicates that so-called working memory and long-term memory share the same neural substrate in the cerebral cortex. That substrate consists in a system of widespread, overlapping and hierarchically organized networks of cortical neurons. In this system, any neuron or group of neurons can be part of many networks, and thus many memories. Working memory is the temporary activation of one such network of long-term memory for the purpose of executing an action in the near future. The activation of the network may be brought about by stimuli that by virtue of prior experience are in some manner associated with the cognitive content of the network, including the response of the organism to those stimuli. The mechanisms by which the network stays activated are presumed to include the recurrent re-entry of impulses through associated neuronal assemblies of the network. Consistent with this notion is the following evidence: (1) working memory depends on the functional integrity of cortico-cortical connective loops; and (2) during working memory, remarkable similarities--including "attractor behavior"--have been observed between firing patterns in real cortex and in an artificial recurrent network.

Animals↗
PubMed1996

Neural Network Model of the Visual System: Binding Form and Motion.

We propose a neural network model of the visual system of the brain which processes different kinds of attributes such as form and motion in parallel. The model has two separate channels: a channel processing form and a channel processing motion. Each channel has both forward and backward connections, and exhibits selective attention. The selective attention mechanism, however, does not work independently because of the interaction of the two channels, which occurs at their lower layers. Both channels always focus attention on the same object even when many objects are presented simultaneously to the input layer of the model. The model was simulated on a computer: several objects made of moving random dots were applied to the input layer. At first the model focused attention on one of the objects, and detected its form and motion. It then processed the rest of the objects in turn by switching attention. Copyright 1996 Elsevier Science Ltd.

Journal Article↗
PubMed1992

Motor learning in a recurrent network model based on the vestibulo-ocular reflex.

Most models of neural networks have assumed that neurons process information on a timescale of milliseconds and that the long-term modification of synaptic strengths underlies learning and memory. But neurons also have cellular mechanisms that operate on a timescale of tens or hundreds of milliseconds, such as a gradual rise in firing rate in response to injection of constant current or a rapid rise followed by a slower adaptation. These dynamic properties of neuronal responses are mediated by ion channels that are subject to modulation. We demonstrate here how a neural network with recurrent feedback connections can convert long-term modulation of neural responses that occur over these intermediate timescales into changes in the amplitude of the steady output from the system. This general principle may be relevant to many feedback systems in the brain. Here it is applied to the vestibulo-ocular reflex, whose amplitude is subject to long-term adaptive modification by visual inputs. The model reconciles apparently contradictory data on the neural locus of the cellular mechanisms that mediate this simple form of learning and memory.

Animals↗
PubMed2005

Clustering and the synchronization of oscillator networks.

By manipulating the clustering coefficient of a network without changing its degree distribution, we examine the effect of clustering on the synchronization of phase oscillators on networks with Poisson and scale-free degree distributions. For both types of networks, increased clustering hinders global synchronization as the network splits into dynamical clusters that oscillate at different frequencies. Surprisingly, in scale-free networks, clustering promotes the synchronization of the most connected nodes (hubs) even though it inhibits global synchronization. As a result, they show an additional, advanced transition instead of a single synchronization threshold. This cluster-enhanced synchronization of hubs may be relevant to the brain that is scale-free and highly clustered.

Journal Article↗
PubMed1978

The interactions of central neurons in conditioning and the influence of some limbic structures upon them.

The interactions between the neurons in the cortex and the subcortical visual structures were studied with multimicroelectrode technique. Neurons revealing conditioned reactions were found at various levels of the brain. It is assumed that they are involved, by the conditioning, in a special cellular network: the microsystem, which is considered to be the definite functional level of brain processing mechanisms. The influence of some limbic structures on the formation of the microsystems of conditioning neurons was found. It was concluded that the elaboration or extinction of the temporary connection is performed through formation or destruction of a microsystem which takes part in the conditioning.

Animals↗
PubMedDate not supplied

Theta/gamma networks with slow NMDA channels learn sequences and encode episodic memory: role of NMDA channels in recall.

This paper examines the role of slow N-methyl-D-aspartate (NMDA) channels (deactivation approximately 150 msec) in networks that multiplex different memories in different gamma subcycles of a low frequency theta oscillation. The NMDA channels are in the synapses of recurrent collaterals and govern synaptic modification in accord with known physiological properties. Because slow NMDA channels have a time constant that spans several gamma cycles, synaptic connections will form between cells that represent different memories. This enables brain structures that have slow NMDA channels to store heteroassociative sequence information in long-term memory. Recall of this stored sequence information can be initiated by presentation of initial elements of the sequence. The remaining sequence is then recalled at a rate of one memory every gamma cycle. A new role for the NMDA channel suggested by our finding is that recall at gamma frequency works well if slow NMDA channels provide the dominant component of the EPSP at the synapse of recurrent collaterals: The slow onset of these channels and their long duration allows the firing of one memory during one gamma cycle to trigger the next memory during the subsequent gamma cycle. An interesting feature of the readout mechanism is that the activation of a given memory is due to cumulative input from multiple previous memories in the stored sequence, not just the previous one. The network thus stores sequence information in a doubly redundant way: Activation of a memory depends on the strength of synaptic inputs from multiple cells of multiple previous memories. The cumulative property of sequence storage has support from the psychophysical literature. Cumulative learning also provides a solution to the disambiguation problem that occurs when different sequences have a region of overlap. In a final set of simulations, we show how coupling an autoassociative network to a heteroassociative network allows the storage of episodic memories (a unique sequence of briefly occurring known items). The autoassociative network (cortex) captures the sequence in short-term memory and provides the accurate, time-compressed repetition required to drive synaptic modification in the heteroassociative network (hippocampus). This is the first mechanistically detailed model showing how known brain properties, including network oscillations, recurrent collaterals, AMPA channels, NMDA channel subtypes, the ADP, and the AHP can act together to accomplish memory storage and recall.

Association Learning↗
PubMed2004

Functional MRI mapping of brain activation during visually guided saccades and antisaccades: cortical and subcortical networks.

Antisaccade tasks require a subject to inhibit a saccade toward a briefly appearing peripheral target and instead to immediately generate a saccade to an equivalent point in the opposite hemifield. Using functional magnetic resonance imaging (fMRI), we investigated the neural networks required to inhibit reflexive saccades and to voluntarily generate saccades. The results demonstrated that saccade and antisaccade tasks often bilaterally activate frontal, parietal and supplementary eye fields, lenticular nuclei and occipital cortex. Additional activation of bilateral dorsolateral prefrontal cortices, supramarginal gyri, anterior cingulate cortices and thalamus was observed during antisaccade tasks. These results indicate that fronto-parietal and fronto-striato-thalamo-cortical circuits are involved in antisaccade tasks. The fronto-parietal circuit is thought to be related to the planning of saccadic eye movements that involve attentional control, while the fronto-striato-thalamo-cortical circuits connect to cortical region as a feedback network. We speculate that the abnormalities in spatial attention and eye movement control observed in schizophrenia stem from dysfunctions in the fronto-parietal and fronto-striato-thalamo-cortical circuits.

Adult↗
PubMed2005

Estimating brain functional connectivity with sparse multivariate autoregression.

There is much current interest in identifying the anatomical and functional circuits that are the basis of the brain's computations, with hope that functional neuroimaging techniques will allow the in vivo study of these neural processes through the statistical analysis of the time-series they produce. Ideally, the use of techniques such as multivariate autoregressive (MAR) modelling should allow the identification of effective connectivity by combining graphical modelling methods with the concept of Granger causality. Unfortunately, current time-series methods perform well only for the case that the length of the time-series Nt is much larger than p, the number of brain sites studied, which is exactly the reverse of the situation in neuroimaging for which relatively short time-series are measured over thousands of voxels. Methods are introduced for dealing with this situation by using sparse MAR models. These can be estimated in a two-stage process involving (i) penalized regression and (ii) pruning of unlikely connections by means of the local false discovery rate developed by Efron. Extensive simulations were performed with idealized cortical networks having small world topologies and stable dynamics. These show that the detection efficiency of connections of the proposed procedure is quite high. Application of the method to real data was illustrated by the identification of neural circuitry related to emotional processing as measured by BOLD.

Brain↗
PubMed2002

Protein phosphorylation networks in motor neuron death.

The disorder amyotrophic lateral sclerosis (ALS) is characterized by the death of specific groups of neurons, especially motor neurons, which innervate skeletal muscle, and neurons connecting the cerebral cortex with motor neurons, such as corticospinal tract neurons. There have been numerous attempts to elucidate why there is selective involvement of motor neurons in ALS. Recent observations have demonstrated altered activities and protein levels of diverse kinases in the brain and spinal cord of transgenic mice that overexpress a mutant superoxide dismutase (mSOD) gene that is found in patients with the familial form of ALS, as well as in patients who have died with ALS. These results suggest that the alteration of protein phosphorylation may be involved in the pathogenesis of ALS. The changes in protein kinase and phosphatase expression and activity can affect the activation of important neuronal neurotransmitter receptors such as NMDA receptors or other signaling proteins and can trigger, or modify, the process producing neuronal loss in ALS. These various kinases, phosphatases and signaling proteins are involved in many signaling pathways; however, they have close interactions with each other. Therefore, an understanding of the role of protein kinases and protein phosphatases and the molecular organization of protein phosphorylation networks are useful to determine the mechanisms of selective motor neuron death.

Amyotrophic Lateral Sclerosis↗
PubMed1996

[The participation of mast cells and serotonin-immunoreactive fibers in the innervation of the cerebral vessels].

Interrelations between adrenergic and serotoninergic nerve fibres and mast cells located near the vascular wall were studied on total preparations of rat brain pia mater. Histochemical method with glyoxylic acid revealed the dense network of adrenergic fibres and their terminal regions with variceal endings with mast cells located next to them. Immunohistochemical methods (fluorescent and method with use of peroxidase antiperoxidase complex) with the aid of antiserum serotonin showed the content of serotonin in these cells. Distribution of serotoninergic nerve fibres resemble that of adrenergic fibres with density being significantly lower. The fibres have frequent contacts with mast cells processes. These data indicate the presence of functional connection between serotonin positive nerve fibres and the possibility of their drawings in control of blood circulation of brain.

Animals↗
PubMed2003

The articulatory loop: study of the subcortical connectivity by electrostimulation.

Although a cortical network involving Broca's area and the supramarginal gyrus (SMG) was widely studied using neurofunctional imaging, the functional connectivity underlying this so-called articulatory loop remains poorly documented. We describe a patient operated on for a glioma invading the left parietal operculum, using intraoperative electrical functional mapping under local anesthesia. Following the identification of cortical language sites within Broca's area and SMG, the subcortical pathways connecting these regions were detected and preserved during the resection. Postoperatively, the patient presented a slight dysarthria, then recovered. This is the first report of direct tracking of the subcortical connectivity underlying the fronto-parietal articulatory loop, allowing to better understand the pathophysiology of this network and the consequences of its damage.

Adult↗
PubMedDate not supplied

[Long-term changes in the efficiency of the excitatory and inhibitory connections in the neuronal micronetworks of the motor cortex induced by tetanization of the thalamic nuclei and the sensory cortex].

Assumption was verified that tetanization which produces long-term potentiation (LTP) and long-term depression (LTD) in the efficacy of thalamo-cortical inputs and the inputs from the sensory cortex to motor cortex results also in long-term modifications of the efficacy of interneuronal interactions in the motor-cortical networks. It was shown that monosynaptic excitation of one of the neighbouring neurons in the motor cortex by rhythmical stimulation of some thalamic nuclei or the sensory cortex resulted in LTP or LTD in the efficacy of excitatory and inhibitory transmission between the neurons of the network. The efficacy of the synapses formed by the terminals of one axon on the neighbouring cells could be variously modified. If the network contained the neurons with multiple convergent inputs the tetanization resulted in the LTP of most of them. In the neuronal networks which contained local feed-forward inhibitory circuits, LTP (LTD) of the inhibitory input to the target cell was accompanied by LTD (LTP) of the excitatory input to the same target cell. Different patterns of modified interneuronal connections were caused by tetanization of different brain structures (thalamic nuclei or sensory cortex).

Animals↗
PubMed1990

Substance P-like immunoreactive neurons in the nervous system of Drosophila.

With an antiserum against substance P a small number of neurons could be resolved in great detail in the nervous system of the fruitfly Drosophila melanogaster. In the brain, 10 substance P-like immunoreactive (SPLI) neurons were individually identified. Two of these form extensive bilateral connections with dorsal and ventral protocerebral neuropil. Another two neurons have cell bodies located ventrally in the subesophageal ganglion and processes throughout subesophageal neuropil. In the thoracico-abdominal ganglia 10 SPLI neurons could be identified. Eight of these have large cell bodies located ventrally in thoracic ganglia and two have small cell bodies located posteriorly in the abdominal ganglia. Six of the 8 thoracic SPLI neurons could be resolved in detail and were found to form: (1) processes in dorsal thoracic and abdominal neuropil as well as processes running through the cervical connective into the subesophageal ganglia; and (2) processes running into the dorsal neural sheath of the thoracic ganglia. The latter processes form an extensive network of varicose terminals over the thoracic ganglia. Our results indicate that a substance P-like neuropeptide can act as a neurohormone released into the circulation from terminals in the neural sheath as well as a neurotransmitter/neuromodulator released by interneurons in the brain.

Animals↗
PubMed2003

The cerebral oscillatory network of parkinsonian resting tremor.

Data from experiments in MPTP monkeys as well as from invasive and non-invasive recordings in patients with Parkinson's disease suggest an abnormal synchronization of neuronal activity in the generation of resting tremor in Parkinson's disease. In six patients with tremor-dominant idiopathic Parkinson's disease, we recorded simultaneously surface electromyograms (EMGs) of hand muscles, and brain activity with a whole-head magnetoencephalography (MEG) system. Using a recently developed analysis tool (Dynamic Imaging of Coherent Sources; DICS), we determined cerebro-muscular and cerebro-cerebral coherence as well as the partial coherence between cerebral areas and muscle, and localized coherent sources within the individual MRI scans. The phase lag between the EMG and cerebral activity was determined by means of a Hilbert transform of both signals. After overnight withdrawal from medication, patients showed typical Parkinson's disease resting tremor (4-6 Hz). This tremor was associated with strong coherence between the EMG of forearm muscles and activity in the contralateral primary motor cortex (M1) at tremor frequency but also at double tremor frequency. Phase lags between M1 activity and EMG were between 15 and 25 ms (M1 activity leading) at single, but also at double tremor frequency, corresponding well to the corticomuscular conduction time. Furthermore, significant coherence was observed between M1 and medial wall areas (cingulate/supplementary motor area; CMA/SMA), lateral premotor cortex (PM), diencephalon, secondary somatosensory cortex (SII), posterior parietal cortex (PPC) and the contralateral cerebellum at single tremor and, even stronger at double tremor frequency. Spectra of coherence between thalamic activity and cerebellum as well as several brain areas revealed additional broad peaks around 20 Hz. Power spectral analysis of activity in all central areas indicated the strongest frequency components at double tremor frequency. Partial coherence analysis and the calculation of phase shifts revealed a strong bidirectional coupling between the EMG and diencephalic activity and a direct afferent coupling between the EMG and SII and the PPC. In contrast, the cerebellum, SMA/CMA and PM show little evidence for direct coupling with the peripheral EMG but seem to be connected with the periphery via other cerebral areas (e.g. M1). In summary, our results demonstrate tremor-related oscillatory activity within a cerebral network, with abnormal coupling in a cerebello-diencephalic-cortical loop and cortical motor (M1, SMA/CMA, PM) and sensory (SII, PPC) areas contralateral to the tremor hand. The main frequency of cerebro-cerebral coupling corresponds to double the tremor frequency.

Adult↗
PubMed1992

Projections from cortical visual areas of the superior temporal sulcus to the superior colliculus, in macaque monkeys.

1. The distribution of tectal projections of two visual areas of the superior temporal sulcus (MT and MST areas) has been studied, in five Macaca fascicularis, by means of the autoradiographic method tracing the anterograde transport of tritiated aminoacids intracortically injected. 2. In all cases the ipsilateral superior colliculi (SC) were found labelled, whereas the contralateral ones were devoid of label. 3. The three brains injected in the MT area resulted in SC labels that involved the superficial gray layer (SGS), the stratum opticum (SO) and the intermediate gray layer (SGI), sparing the layers below SGI. 4. The collicular labels found after injections within the MST area exhibited their distribution over the deep SC subdivision, whereas they spared all the superficial layers but the deep part of the SO. 5. In two animals with large uptake zones, one in MT and the other in MST, the labelling within the SGI showed a cluster-like pattern. 6. The distinct found bulk of projections of MT and MST respectively to the superficial and deep subdivisions of the SC, along with a number of peculiar connections of the MST area as mentioned in the text, contribute to depict an overall neural network in which MST appears to be more strongly involved than MT in linking sensory visual with oculomotor attentive functions.

Afferent Pathways↗
PubMed1986

The brain as a self-organizing system.

Clinical evidence and numerous results from animal experimentation indicate that cognitive functions have to be learned. Brain structures subserving these functions require sensory experience for their maturation. Genetic instructions are in principle not sufficient to specify neuronal connections with sufficient precision. Self-organization processes are implemented in addition which allow to optimize genetically determined blue prints of connectivity by making use of functional criteria. Thus, neuronal activity becomes an important shaping factor in the development of the structural and functional architecture of the forebrain. To the extent that this neuronal activity is modulated by sensory signals, environmental factors can influence the development of neuronal networks. Recent experiments indicate that these shaping processes are additionally controlled by modulatory systems. Both, the noradrenergic projection from the locus coeruleus and the cholinergic projection from the basal forebrain facilitate activity-dependent long-term changes of neuronal connections during development. The activity of these modulatory systems in turn depends on central states such as arousal, attention, and perhaps also motivation. It is inferred from this evidence that experience-dependent self-organization should not be considered as a passive imprinting process but rather as an active dialogue between the brain and its environment. The hypothesis is discussed that many developmental disturbances which are commonly attributed to deprivation are in fact due to defaults of the CNS which either lead to the formulation of wrong questions or to the reduction of exploratory drive.

Animals↗