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PubMed1994

Corticocortical connectivity, autonomous networks, and schizophrenia.

Dr. David hypothesizes that increased, not decreased, corticocortical connectivity causes schizophrenia. He cites studies suggesting excessive semantic priming and cross-hemispheric interference in this disorder to support his hypothesis. These findings, David suggests, reflect excessive transmission of information between neurons or within neural systems. However, considerable caution should be exercised in making neuroanatomic inferences on the basis of cognitive studies alone. There is an increasing consensus that information is represented by the brain as patterns of neural activation, where the same neuron or group of neurons participates in many different representations. Our simulations, which reflect this consensus, suggest that persistent or intrusive activation patterns do not emerge from too many neural connections, but from too few. This condition causes subgroups of neurons to disregard information processing by other neurons and to produce autonomously their own output, which interferes with the functioning of the system as a whole. Direct neuroanatomic or neurochemical studies of the cerebral cortex are needed to fully assess hypotheses regarding abnormal corticocortical connectivity in schizophrenia.

Brain Mapping↗
PubMed1992

Respiratory-related neural assemblies in the brain stem midline.

1. The initial objective of this study was to determine whether respiratory-related neural assemblies exist in the brain stem midline. A second goal was to seek evidence for concurrent relationships among the neurons that could generate the detected synchrony. 2. Experiments were conducted on anesthetized, paralyzed, bilaterally vagotomized, artificially ventilated cats. Spike trains of four to nine simultaneously monitored neurons were recorded in the regions of n. raphe obscurus-n. raphe pallidus and n. raphe magnus. 3. Data were analyzed with cycle-triggered histograms, cross-correlograms, snowflakes, and the gravitational representation. A significance test for the gravity method was developed and tested with spike trains generated by simulated networks with defined connections. 4. Ninety-three groups of neurons from 24 cats were studied. Thirty-nine groups from 19 cats included neurons that discharged synchronously on a millisecond time scale; less than or equal to 19 pairs of synchronously discharging neurons were found in one group. Twenty-seven of these 39 groups included neurons that had respiratory-modulated firing rates and discharged synchronously with other group members. Synchronous assemblies included cells monitored at rostral or caudal locations, or both. 5. Six classes of relationships were inferred from groups of neurons with multiple correlations: divergence (n = 11); convergence (n = 7); connections with opposite actions between neurons (n = 5); projections of synchronous neurons to separate targets (n = 5); projections to one neuron in a synchronous group (n = 4); and projections between two synchronous groups with common elements (n = 6). 6. The results document the existence of assemblies of synchronously discharging respiratory-related neurons in midline regions of the brain stem and suggest that divergent excitatory and inhibitory connections within the midline participate in the generation of that synchrony. Links between assemblies may operate to stabilize their collective activity in a particular state.

Afferent Pathways↗
PubMedDate not supplied

[The functional organization of the spatial structures of the neuronal receptive fields in field 21 of the cat cerebral cortex].

In result study of structural organization of neural receptive fields (RFs) and their different zones on the prestriate cortex level was shown that neural RFs in this area have hypercomplex structure and consist of some spatial different excitatory zones. Orientation and velocity selectivity and spatial-frequency characteristics of the excitatory zones of the same RF may differ between zones. The number of zones in RFs correlate with RF sizes: the more RF size the more zones number in them (r = 0.05, P < 0.02). About 66% of zones in RFs have approximately identical sizes (12-16 deg) and sizes those zones an dependence as from their number in RFs (r = 0.03, P > 0.05) as from the eccentricity (r = 0.3, P > 0.05). Zones in RF were distributed so that distance their centres was between 56-65 degrees (an average across all 60 degrees). If two or three zones were tested simultaneously the neuron changed own frequency and orientation tuning. Consequently the functional organization of neural RFs of prestriate cortex depend upon number simultaneously tested zones in spatial information processing. Was shown that important properties of prestriate cortex neurons is their ability to integrate and complex processing of spatial information across wide area of the visual field; in the prestriate cortex thus violate of straight retinotopical representation principle of visual field, characteristics of all investigated areas of visual system. The results represented in this review allow suppose that the structural and functional unit of cortex which make integration of spatial information from different compose this information is prestriate cortex neurons and not is no striate cortex modules. Consequently combined of neurons which make images description from different parts of visual field out of dependence of cortical area in turn integrate in neuron networks. Is known that neurons of any level have characteristics different of (from) characteristics of other levels visual system. The interaction of different elements of visual system form ultrastructure of RFs and their different zones in prestriate cortex, and ensure function of networks. So just on prestriate cortex neurons level appear whole system of surrounding world universe system of connections from different cortical areas which is morphological and functional base in process of spatial information integration RFs which have the central and peripheral representation.

Animals↗
PubMedDate not supplied

[The ensemble organization of the sensorimotor cortex in ontogeny].

Examination of sensomotor zone of the human brain cortex in human subjects (from newborns up to 20 year-olds) with yearly intervals revealed the presence of all neuroglia-vascular ensembles components without any relationship in composition by the moment of birth. Significant increase of the cortical layers and sublayers thickness, connected with growth of the volume of all type neurons and development of dendritic-axonic networks, vessels and glia were noted. Stair-like groups of neurons are present by the moment of birth, and so called racemose groups, the composition of which is diverse in different fields form by the age of three when vertical and horizontal contacts system grows more complicate and the astrocyte glia differentiates. The size of pyramidal neurons (Betz cells included), fusiform and stellate neurons increases by the age of six. By 10-12 years intraensemble, interensemble and transcortical contacts attain the high level of development. By 16-18 years ensemble organization of the cortex reaches the level, characteristic to adults in main parameters of its architectonics.

Adolescent↗
PubMed2003

Sleep function.

A theory of sleep function and brain organization positing that sleep serves a neuronal connectivity function and is a fundamental property of highly interconnected groups of neurons (neuronal groups) is presented. Cellular electrical activity within neuronal groups leads to the production of sleep-promoting substances which are also cytokine growth factors. The somnogenic cytokine growth factors (SCGF) in turn, induce molecules necessary for synaptic connectivity. The SCGFs change the synaptic activation patterns within neuronal groups. SCGFs thus induce changes in the input-output relationships of neuronal groups and thereby, cause a neuronal group state shift. Altered input-output relations result in increased efficacy of some synapses. Sleep is thus, targeted to active neuronal groups and serves to incorporate novel stimulus patterns into a synaptic contextual network and also to preserve that network. Coordination of neuronal group state is brought about by sleep regulatory networks. Organism sleep is an emergent property of a population of neuronal groups in the sleep state. After the neuronal group state shift, environmental input is divorced from output. Sleep is thus, useful to keep the animal stationary at a time when its brain is most dysfunctional. Thus, not only is unconsciousness needed because output activity would be out of phase with environmental events, but it is the consequence of the process itself.

Animals↗
PubMed2002

Vocal-acoustic circuitry and descending vocal pathways in teleost fish: convergence with terrestrial vertebrates reveals conserved traits.

Vocal behavior is multifaceted and requires that vocal-motor patterning be integrated at multiple brain levels with auditory, neuroendocrine, and other social behavior processes (e.g., courtship and aggression). We now provide anatomical evidence for an extensive vocal network in teleost fishes (Batrachoididae: Porichthys notatus; Opsanus beta) that is strongly integrated with neuroendocrine and auditory pathways and that exhibits striking similarities to the vocal-acoustic circuitry known for mammals. Biotin compound injections into neurophysiologically identified vocal regions of the forebrain (preoptic area and anterior hypothalamus) and of the midbrain (periaqueductal gray and paralemniscal tegmentum) reveal extensive connectivity within and between these regions, as well as reciprocal relationships with the auditory thalamus and/or auditory midbrain (torus semicircularis). Thus, specific components of the basal forebrain and midbrain are here designated as the forebrain vocal-acoustic complex (fVAC) and midbrain vocal-acoustic complex (mVAC), respectively. Biotin injections into the mVAC and a previously identified hindbrain vocal pattern generator likewise provide anatomical evidence for a distributed network of descending projections to the vocal pacemaker-motoneuron circuitry. Together, the present experiments establish a vocal-auditory-neuroendocrine network in teleost fish that links the forebrain and midbrain to the hindbrain vocal pattern generator (i.e., fVAC --> mVAC --> pattern generator) and provides an anatomical framework for the previously identified neuropeptide modulation of vocal activity elicited from the forebrain and midbrain, which contributes to the expression of sex- and male morph-specific behavior. We conclude with a broad comparison of these findings with those for other vertebrate taxa and suggest that the present findings provide novel insights into the structure of conserved behavioral regulatory circuits that have led to evolutionary convergence in vocal-acoustic systems.

Animals↗
PubMed2004

Motor cognition: a new paradigm to study self-other interactions.

Accumulative empirical evidence has been reviewed in support of the notion that the production and perception of action as well as the interpretation of others' actions are functionally connected, and indeed, rely on common distributed neural systems in the premotor and parietal cortices. We suggest that these neural systems sustain shared representations between self and other that are crucial in social interactions. The inferior parietal cortex plays a special role in the sense of agency, which is a fundamental aspect to navigate within this neural network. The role of other brain areas that implement and regulate these shared representations remains to be specified.

Brain↗
PubMed1989

Intermittent chaos, self-organization, and learning from synchronous synaptic activity in model neuron networks.

Self-organization of frequencies is studied by using model neurons called VCONs (voltage-controlled oscillator neuron models). These models give direct access to frequency information, in contrast to all-or-none neuron models, and they generate voltage spikes that phase-lock to oscillatory stimulation, similar to phase-locking of action potentials to oscillatory voltage stimulation observed in Hodgkin-Huxley preparations of squid axons. The rotation vector method is described and used to study how networks synchronize, even in the presence of noise or when damaged; the entropy of ratios of phases is used to construct an energy function that characterizes organized behavior. Computer simulations show that rotation numbers (output frequency/input frequency) describe both chaotic and nonchaotic behavior. Learning occurs when synaptic connections strengthen in response to stimulation that is synchronous with cell activity. It is shown that intermittent chaotic firing is suppressed and simple stable responses are enhanced by such learning in VCON networks. This analysis provides a rigorous basis for further investigation of the ideas of Wiener [Wiener, N. (1961) Cybernetics (MIT Press, Cambridge, MA), p. 191] on the origin of slow brain waves due to "the pulling together of frequencies."

Action Potentials↗
PubMed2000

Iron as a vulnerability factor in nigrostriatal degeneration in aging and Parkinson's disease.

Recent findings strengthen the connection between iron accumulation in the basal ganglia, oxidative stress and nigrostriatal degeneration. Oxidative stress appears to be elevated in the normal human substantia nigra in comparison with other brain regions, and further increases occur in Parkinson's disease. Accumulation of iron may contribute to degeneration of nigral dopamine neurons by catalyzing oxidative damage to cell components and also by perturbing the network of interactions that modulate cellular redox status.

Aging↗
PubMed1989

Connectionism and an inescapable defect.

Linear connectionist models of neurocomputing show how input patterns may be recognized, stored, compared, and recalled for output in serial-parallel, quasi-Hebbian networks. This aids the design of hardware and software for better robotics, while offering useful insights to neuroscientists studying sensorimotor systems, but connectivity via quasi-Hebbian nodes and back-propagation layers alone cannot show us how vertebrate cerebellum, allocortex, and neocortex work.

Animals↗
PubMed2006

The precuneus: a review of its functional anatomy and behavioural correlates.

Functional neuroimaging studies have started unravelling unexpected functional attributes for the posteromedial portion of the parietal lobe, the precuneus. This cortical area has traditionally received little attention, mainly because of its hidden location and the virtual absence of focal lesion studies. However, recent functional imaging findings in healthy subjects suggest a central role for the precuneus in a wide spectrum of highly integrated tasks, including visuo-spatial imagery, episodic memory retrieval and self-processing operations, namely first-person perspective taking and an experience of agency. Furthermore, precuneus and surrounding posteromedial areas are amongst the brain structures displaying the highest resting metabolic rates (hot spots) and are characterized by transient decreases in the tonic activity during engagement in non-self-referential goal-directed actions (default mode of brain function). Therefore, it has recently been proposed that precuneus is involved in the interwoven network of the neural correlates of self-consciousness, engaged in self-related mental representations during rest. This hypothesis is consistent with the selective hypometabolism in the posteromedial cortex reported in a wide range of altered conscious states, such as sleep, drug-induced anaesthesia and vegetative states. This review summarizes the current knowledge about the macroscopic and microscopic anatomy of precuneus, together with its wide-spread connectivity with both cortical and subcortical structures, as shown by connectional and neurophysiological findings in non-human primates, and links these notions with the multifaceted spectrum of its behavioural correlates. By means of a critical analysis of precuneus activation patterns in response to different mental tasks, this paper provides a useful conceptual framework for matching the functional imaging findings with the specific role(s) played by this structure in the higher-order cognitive functions in which it has been implicated. Specifically, activation patterns appear to converge with anatomical and connectivity data in providing preliminary evidence for a functional subdivision within the precuneus into an anterior region, involved in self-centred mental imagery strategies, and a posterior region, subserving successful episodic memory retrieval.

Animals↗
PubMed2003

Organization of neural networks in the neocortex.

Implanted semimicroelectrodes were used in conscious cats to record spike discharges from groups of close-lying neurons, i.e., multineuron activity, in the deep layers of the frontal and motor areas of the cortex at different levels of food motivation. Spike activity was extracted from 4-7 neurons and interneuronal interactions were studied by cross-correlation analysis between neighboring neurons in each zone (local networks) and between neurons in two zones (distributed networks) with analysis epochs of 0-100 msec. The results showed that neurons in local networks can be divided into two subgroups: neurons with high-amplitude spikes and a predominance of output (divergent) connections and neurons with low-amplitude spikes and a predominance of input (convergent) connections. Local networks are based on powerful monosynaptic connections (with delays of up to 2 msec) between large and small neurons. Most connections in distributed networks were between small neurons in local networks of the frontal cortex and large neurons in local networks in the motor cortex. Food deprivation for 24 h mainly affected late (with delays of 2-100 msec) cross-correlation interneuronal relationships in both local and distributed networks.

Animals↗
PubMed1997

Attentional systems and the allocation of cerebral resources in reading and grammatical tasks.

To evaluate the possible role of attentional centers as modulators of neural networks that mediate visual tasks involving reading and grammatical manipulations of verbs, we measured cerebral blood flow (CBF) using positron emission tomography (PET), and reaction times as subjects read verbs, "nonce verbs" such as jelt or brep, and formed past tenses of regular, irregular and nonce verbs after viewing their stems. Statistical parametric maps (SPMs) showed significant activation of the pulvinar in the read verb irregular, and generate nonce past tense tasks, compared to rest. This was confirmed by a post hoc ANOVA of CBF values from a discrete locus in the pulvinar (p = .0000417). Functional links between the pulvinar and other brain regions were shown by high correlations of CBF in the pulvinar with CBF in brain regions known to have anatomical connections to the pulvinar, particularly those mediating vision. There was also a significant relationship between task-specific reaction times and rest minus task CBF differences in a multiple regression analysis that included CBF values from the pulvinar, superior colliculus plus reticular formation, and the anterior cingulate, known attentional centers (p = .021, r2 = 0.99). Regression analyses relating reaction time to the amount of brain activated (pixels in the SPMs) and the degree of activation of the pixels (mean Z score) yielded p values of .078 and .074, respectively. Our data provide direct experimental evidence to support the hypothesis that attentional centers are activated in proportion to the complexity of visually mediated language tasks and that the centers that mediate attention modulate the activity of task-specific neural networks.

Adult↗
PubMed1975

The dorsomedial hypothalamic nucleus in autonomic and neuroendocrine homeostasis.

Median eminence and ventromedial hypothalamus have in the past been the principal foci of research in neuroendocrine and neurovisceral control mechanisms. The present report provides an overview of work involving the dorsomedial hypothalamic nucleus (DMV). This structure is located dorsal to the ventromedial hypothalamic nucleus (VMN) to the plane of the dorsal premammillary nucleus. Fibers from the DMN pass with the periventricular system and the dorsal longitudinal fasciculus of Schütz and have been traced to the midbrain tegmentum and reticular formation. Intrahypothalamic connections involve intensive networks between DMN, lateral hypothalamic nucleus (LHN) and VMN. Regarding neurotransmitters, recent studies indicate that the DMN receives noradrenergic innervation along two pathways, a dorsal and a ventral one. Monoamine-containing systems approach the DMN From the lateral hypothalamus and the bulk of these fibers are carried in the medium forebrain bundle from their cells of origin in the brain stem. Studies of the vascular supply indicate that both VMN and DMN receive their blood supply from the internal carotid artery...

Animals↗
PubMed1980

LHRH-systems in the brain of the golden hamster.

Vibratome sections of male hamster brains were treated immunohistochemically with LHRH antiserum, and the anatomical distribution of LHRH immunoreactive cells and nerve fibers was assessed. LHRH-cell bodies are found in the ventral hypothalamus that includes its preoptic, anterior and central parts, in the septum, the olfactory tubercle, the main and accessory olfactory bulb, and the prepiriform cortex. In addition, extracerebral LHRH-neurons and ganglia exist in LHRH-positive nerves at the ventromedial surface of the olfactory tubercle and bulb as well as in olfactory nerves. Dense networks of LHRH-immunoreactive fibers are found in all regions where LHRH-cell bodies exist. Intraseptal connections reach the organum vasculosum of the lamina terminalis, the subfornical organ, and the lateral ventricle. Dorsolateral projections from the septum can be traced via the fimbria hippocampi and alveus to the ventral hippocampus, via the stria terminalis to the amygdala and piriform cortex. Ventrolateral projections extend from the level of the olfactory tubercle and preoptic-anterior hypothalamic area via the ventral amygdalofugal pathway to the prepiriform and piriform cortex as well as the amygdala. Dorsal supracallosal projections via the stria longitudinalis are seen in the induseum griseum and the cingulate cortex. Caudal efferents reach the havenula, interpeduncular nucleus, midbrain raphe, and central gray of the rostral fourth ventricle via the stria medullaris and fasciculus retroflexus and by a ventral projection via the periventricular and subventricular hypothalamus. A major portion of this ventrocaudal projection gives rise to a dense network in the median eminence. Anatomical relationships of LHRH-fibers to certain regions of the inner ventricular and outer brain surface are noted.

Animals↗
PubMed2003

Electroencephalographic signatures of attentional and cognitive default modes in spontaneous brain activity fluctuations at rest.

We assessed the relation between hemodynamic and electrical indices of brain function by performing simultaneous functional MRI (fMRI) and electroencephalography (EEG) in awake subjects at rest with eyes closed. Spontaneous power fluctuations of electrical rhythms were determined for multiple discrete frequency bands, and associated fMRI signal modulations were mapped on a voxel-by-voxel basis. There was little positive correlation of localized brain activity with alpha power (8-12 Hz), but strong and widespread negative correlation in lateral frontal and parietal cortices that are known to support attentional processes. Power in a 17-23 Hz range of beta activity was positively correlated with activity in retrosplenial, temporo-parietal, and dorsomedial prefrontal cortices. This set of areas has previously been characterized by high but coupled metabolism and blood flow at rest that decrease whenever subjects engage in explicit perception or action. The distributed patterns of fMRI activity that were correlated with power in different EEG bands overlapped strongly with those of functional connectivity, i.e., intrinsic covariations of regional activity at rest. This result indicates that, during resting wakefulness, and hence the absence of a task, these areas constitute separable and dynamic functional networks, and that activity in these networks is associated with distinct EEG signatures. Taken together with studies that have explicitly characterized the response properties of these distributed cortical systems, our findings may suggest that alpha oscillations signal a neural baseline with "inattention" whereas beta rhythms index spontaneous cognitive operations during conscious rest.

Attention↗
PubMed2000

Perinatal development of lumbar motoneurons and their inputs in the rat.

The rat is quite immature at birth and a rapid maturation of motor behavior takes place during the first 2 postnatal weeks. Lumbar motoneurons undergo a rapid development during this period. The last week before birth represents the initial stages of motoneuron differentiation, including regulation of the number of cells and the arrival of segmental and first supraspinal afferents. At birth, motoneurons are electrically coupled and receive both appropriate and inappropriate connections from the periphery; the control from supraspinal structures is weak and exerted mainly through polysynaptic connections. During the 1st postnatal week, inappropriate sensori-motor contacts and electrical coupling disappear, the supraspinal control increases gradually and myelin formation is responsible for an increased conduction velocity in both descending and motor axons. Both N-methyl-D-aspartate (NMDA) and non-NMDA receptors are transiently overexpressed in the neonatal spinal cord. The contribution of non-NMDA receptors to excitatory amino acid transmission increases with age. Activation of gamma-aminobutyric acid(A) and glycine receptors leads to membrane depolarization in embryonic motoneurons but to hyperpolarization in older motoneurons. The firing properties of motoneurons change with development: they are capable of more repetitive firing at the end of the 1st postnatal week than before birth. However, maturation does not proceed simultaneously in the motor pools innervating antagonistic muscles; for instance, the development of repetitive firing of ankle extensor motoneurons lags behind that of flexor motoneurons. The spontaneous embryonic and neonatal network-driven activity, detected at the levels of motoneurons and primary afferent terminals, may play a role in neuronal maturation and in the formation and refinement of sensorimotor connections.

Animals↗
PubMed1999

Neurophysiological imaging techniques in dementia.

Neurophysiological methods, such as electroencephalography (EEG) and event-related potentials, are useful tools in the investigation of brain cognitive function in normal and pathological conditions, with an excellent time resolution when compared to that of other functional imaging techniques. Advanced techniques using a high number of EEG channels also enable a good spatial resolution to be achieved. This, together with the possibility of integration with other anatomical and functional images, may increase the ability to localize brain functions. Spectral analysis of the resting EEG, which gives information on the integrity of the cortical and subcortical networks involved in the generation of cortical rhythms, has the limitation of low sensitivity and specificity for the type of cognitive impairment. In almost all types of dementia, decreased power of the high frequencies is indeed observed in mild stages, accompanied by increased power of the slow rhythms in the more advanced phases. The sensitivity for the detection of spectral abnormalities is improved by studying centroid modifications. More specific information on the type of dementia can be provided by coherence analysis of the resting EEG, a measure of functional cortico-cortical connections, which has different abnormal patterns in Alzheimer's disease, cerebrovascular dementia and dementia associated with multiple sclerosis. Another tool for improving the assessment of demented patients is the study of EEG activity related to particular tasks, such as event-related potentials and event-related desynchronization/synchronization of the EEG, which allow the study of brain activation during cognitive and motor tasks.

Brain↗