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At least 739 records · Page 41Linked to original sources
PubMed2002

Firing modes of midbrain dopamine cells in the freely moving rat.

There is a large body of data on the firing properties of dopamine cells in anaesthetised rats or rat brain slices. However, the extent to which these data relate to more natural conditions is uncertain, as there is little quantitative information available on the firing properties of these cells in freely moving rats. We examined this by recording from the midbrain dopamine cell fields using chronically implanted microwire electrodes. (1) In most cases, slowly firing cells with broad action potentials were profoundly inhibited by the dopamine agonist apomorphine, consistent with previously accepted criteria. However, a small group of cells was found that were difficult to classify because of ambiguous combinations of properties. (2) Presumed dopamine cells could be divided into low and high bursting (>40% of their spikes in bursts) groups, with the majority having low bursting rates. The distribution of burst incidence was similar to that previously reported with chloral hydrate anaesthesia, but the average intraburst frequency was higher in the conscious animal at rest and was higher again in bursts triggered by salient stimuli. (3) There was no evidence for spike frequency adaptation within bursts on average, consistent with the hypothesis that afterhyperpolarisation currents may be disabled during behaviourally induced bursting. (4) Presumed dopamine cells responded to reward-related stimuli with increased bursting rates and significantly higher intraburst frequencies compared to bursts emitted outside task context, indicating that modulation of afferent activity might not only trigger bursting, but may also regulate burst intensity. (5) In addition to the irregular single spike and bursting modes we found that extremely regular (clock-like) firing, previously only described for dopamine cells in reduced preparations, can also be expressed in the freely moving animal. (6) Cross-correlation analysis of activity recorded from simultaneously recorded neurones revealed coordinated activity in a quarter of dopamine cell pairs consistent with at least "functional" connectivity. On the other hand, most dopamine cell pairs showed no correlation, leaving open the possibility of functional sub-groupings within the dopamine cell fields. Taken together, the data suggest that the basic firing modes described for dopamine cells in reduced or anaesthetised preparations do reflect natural patterns of activity for these neurones, but also that the details of this activity are dependent upon modulation of afferent inputs by behavioural stimuli.

Action Potentials↗
PubMed2000

Coordinate-independent mapping of structural and functional data by objective relational transformation (ORT).

Neuroscience has produced an enormous amount of structural and functional data. Powerful database systems are required to make these data accessible for computational approaches such as higher-order analyses and simulations. Available databases for key data such as anatomical and functional connectivity between cortical areas, however, are still hampered by methodological problems. These problems arise predominantly from the parcellation problem, the use of incongruent parcellation schemes by different authors. We here present a coordinate-independent mathematical method to overcome this problem: objective relational transformation (ORT). Based on new classifications for brain data and on methods from theoretical computer science, ORT represents a formally defined, transparent transformation method for reproducible, coordinate-independent mapping of brain data to freely chosen parcellation schemes. We describe the methodology of ORT and discuss its strengths and limitations. Using two practical examples, we show that ORT in conjunction with connectivity databases like CoCoMac (http://www.cocomac.org) is an important tool for analyses of cortical organization and structure-function relationships.

Animals↗
PubMed2003

Spontaneous functional viscerosensory regeneration into the adult brainstem.

The dorsal root entry zone of the vagus nerve (vDREZ) is uniquely characterized by peripheral tissue insertions (PTIs) deep to the brainstem surface, consisting of Schwann cells and a reticulum of astrocytic processes. Because Schwann cells permit peripheral axonal regeneration, the capacity of vagal medullary PTIs to allow centripetal regeneration of visceral afferents after vagal dorsal rhizotomy in adult rats was investigated. The present work shows that vagal axons spontaneously regenerate into appropriate and ectopic brainstem nuclei. They accomplish this by first growing along PTIs but then extend along basal laminas of medullary blood vessels. Electrically stimulated regenerated vagal afferents induced Fos expression (indicating functional connectivity) within appropriate but not ectopic nuclei. The unique structure of the vDREZ can thus support spontaneous functional regeneration of visceral primary afferent axons into the adult CNS.

Afferent Pathways↗
PubMed2002

Connected gene neighborhoods in prokaryotic genomes.

A computational method was developed for delineating connected gene neighborhoods in bacterial and archaeal genomes. These gene neighborhoods are not typically present, in their entirety, in any single genome, but are held together by overlapping, partially conserved gene arrays. The procedure was applied to comparing the orders of orthologous genes, which were extracted from the database of Clusters of Orthologous Groups of proteins (COGs), in 31 prokaryotic genomes and resulted in the identification of 188 clusters of gene arrays, which included 1001 of 2890 COGs. These clusters were projected onto actual genomes to produce extended neighborhoods including additional genes, which are adjacent to the genes from the clusters and are transcribed in the same direction, which resulted in a total of 2387 COGs being included in the neighborhoods. Most of the neighborhoods consist predominantly of genes united by a coherent functional theme, but also include a minority of genes without an obvious functional connection to the main theme. We hypothesize that although some of the latter genes might have unsuspected roles, others are maintained within gene arrays because of the advantage of expression at a level that is typical of the given neighborhood. We designate this phenomenon 'genomic hitchhiking'. The largest neighborhood includes 79 genes (COGs) and consists of overlapping, rearranged ribosomal protein superoperons; apparent genome hitchhiking is particularly typical of this neighborhood and other neighborhoods that consist of genes coding for translation machinery components. Several neighborhoods involve previously undetected connections between genes, allowing new functional predictions. Gene neighborhoods appear to evolve via complex rearrangement, with different combinations of genes from a neighborhood fixed in different lineages.

Algorithms↗
PubMed2006

Frequency-following and connectivity of different visual areas in response to contrast-reversal stimulation.

The sensitivity of visual areas to different temporal frequencies, as well as the functional connections between these areas, was examined using magnetoencephalography (MEG). Alternating circular sinusoids (0, 3.1, 8.7 and 14 Hz) were presented to foveal and peripheral locations in the visual field to target ventral and dorsal stream structures, respectively. It was hypothesized that higher temporal frequencies would preferentially activate dorsal stream structures. To determine the effect of frequency on the cortical response we analyzed the late time interval (220-770 ms) using a multi-dipole spatio-temporal analysis approach to provide source locations and timecourses for each condition. As an exploratory aspect, we performed cross-correlation analysis on the source timecourses to determine which sources responded similarly within conditions. Contrary to predictions, dorsal stream areas were not activated more frequently during high temporal frequency stimulation. However, across cortical sources the frequency-following response showed a difference, with significantly higher power at the second harmonic for the 3.1 and 8.7 Hz stimulation and at the first and second harmonics for the 14 Hz stimulation with this pattern seen robustly in area V1. Cross-correlations of the source timecourses showed that both low- and high-order visual areas, including dorsal and ventral stream areas, were significantly correlated in the late time interval. The results imply that frequency information is transferred to higher-order visual areas without translation. Despite the less complex waveforms seen in the late interval of time, the cross-correlation results show that visual, temporal and parietal cortical areas are intricately involved in late-interval visual processing.

Adult↗
PubMedDate not supplied

[The phenomenon of diaschisis in cerebral vascular disease].

INTRODUCTION AND OBJECTIVE: Diaschisis is a physiological phenomenon based on reversible depression of functions anatomically or functionally connected to the damaged area. Its study has become more interesting over the past twenty years, due to the advances made in functional neuroimaging techniques and their possible participation in the recovery of function. Our objective is to review the main types of diaschisis and their clinical contribution. DEVELOPMENT: At present it has mainly been described in cerebrovascular pathology, and been classified according to the connecting fibres involved. When the connecting fibres are intra-hemispheric, the phenomenon of ipsilateral thalamic or subcortical-cortical diaschisis may be seen; when they are interhemispheric, there is transcallosal diaschisis, and if they are cerebellar, the diaschisis is of the contralateral cerebellum or crossed cerebellar diaschisis. Ipsilateral thalamic and crossed cerebellar diaschisis are phenomena which are frequently observed, but have no clinical significance. Regression of the subcortical-cortical and transcallosal diaschisis might explain the neuropsychological and functional neuroimaging changes observed over the first few months after the vascular incident. CONCLUSION: Study of the different types of diaschisis should be considered in patients with cerebrovascular disease since it is potentially reversible, and to differentiate it from focalization due to the lesion.

Aphasia↗
PubMed2004

Encoding pheromonal signals in the mammalian vomeronasal system.

The past few years have delivered substantial progress in understanding the molecular logic of the mammalian vomeronasal system. Selective expression of vomeronasal receptors and high response selectivity of vomeronasal receptor neurons suggest that pheromones are encoded by labeled lines at the level of the vomeronasal organ: each pheromonal compound is represented by the activation of a small and exclusive subset of receptor neurons. Labeled lines might be transferred to the accessory olfactory bulb through convergent connections. The key challenges ahead will be to identify the pheromonal ligands of the receptors and unravel the functional connectivity from the vomeronasal organ to the hypothalamus.

Animals↗
PubMed2002

Artifactual synchrony via capacitance coupling in multi-electrode recording from cat striate cortex.

Elucidation of neural connectivity patterns in the brain are thought to give us a mechanistic understanding of how the brain works. Functional connectivity is best studied by simultaneous recording of single-unit activity from many neurons. Accordingly, various types of multiple-microelectrode systems have been developed. We have studied long-range lateral interactions in cat striate cortex. To physiologically characterize interacting cells recorded simultaneously, we used two microelectrodes whose movements were controlled by two independently-movable microdrives. The tips of the two microelectrodes were separated by approximately 2 mm or more. During preliminary plotting of two receptive fields of cell pairs, we often noted the emergence of perfectly synchronous firing between two spike trains (amplitude ratio, about 20:1) registered with two microelectrodes. Synchronously firing, smaller spikes disappeared when larger spikes of the pair were lost to either substantial advancement of or placing an electrolytic lesion at the electrode registering the latter. The synchrony also disappeared when two microdrive systems were shielded individually. We concluded that the synchrony was attained through capacitance coupling between two microdrive systems. We proposed a few practical recommendations to avoid the contamination of cross correlograms with the false-positive, narrow peak at time zero due to the presence of reflected spike trains.

Action Potentials↗
PubMed2003

Transcranial magnetic stimulation as an investigative tool in the study of visual function.

Transcranial magnetic stimulation (TMS) is a novel and powerful probe to study the relationship between human brain function and behavior. TMS is being widely used to investigate memory, language, attention, learning, and motor function and is even being utilized therapeutically in the treatment of depression. Some of the earliest applications of TMS have been directed toward the investigation of human visual perception. For example, a strong TMS pulse delivered to the occipital cortex in a sighted or even blind individual can evoke the sensation of perceiving light (visual phosphenes). TMS can also be used to suppress visual perception and investigate the timing of visual information processing. Furthermore, the functional connectivity between different brain areas can be mapped using TMS, thus establishing a causal link between visual cortical function and visual perception. The present article is meant as an overview of the technique of TMS and a review of the literature as it pertains to the study of visual function. The application of TMS in the diagnosis as well as possible therapeutic use in various visual disorders is also discussed.

Electromagnetic Fields↗
PubMed2004

[Cerebral mechanisms of hypnosis].

The neural mechanisms underlying hypnosis and especially the modulation of pain perception by hypnosis remain obscure. Using PET we first described the distribution of regional cerebral blood flow during the hypnotic state. Hypnosis relied on revivification of pleasant autobiographical memories and was compared to imaging autobiographical material in < >. The hypnotic state was related to the activation of a widespread set of cortical areas involving occipital, parietal, precentral, premotor, and ventrolateral prefrontal and anterior cingulate cortices. This pattern of activation shares some similarities with mental imagery, from which it mainly differs by the relative deactivation of precuneus. Second, we looked at the anti-nociceptive effects of hypnosis. Compared to the resting state, hypnosis reduced pain perception by approximately 50 %. The hypnosis-induced reduction of affective and sensory responses to noxious thermal stimulation were modulated by the activity in the midcingulate cortex (area 24a'). Finally, we assessed changes in cerebral functional connectivity related to hypnosis. Compared normal alertness (i.e., rest and mental imagery), the hypnotic state, significantly enhanced the functional to modulation between midcingulate cortex and a large neural network involved in sensory, affective, cognitive and behavioral aspects of nociception. These findings show that not only pharmacological but also psychological strategies for pain control can modulate the cerebral network involved in noxious perception.

Brain↗
PubMedDate not supplied

[Participation of the pallidum in formation of different forms of adaptive behavior].

Participation of associative (O2, OP), motor (Prc1) and somatosensory (Pc3) neocortical fields, as well as of the pallidum, in intercentral integrative processes of various kinds of adaptive activity, differing in manifestation of the motor component,-- was studied on dogs with chronically implanted electrodes by parameters of evoked potentials (EP). Establishment of indifference of the non-reinforced stimulus is not connected with elaboration of motor programs. O2 and OP cortical fields are more significant elements, while the pallidum is a less significant element, of the corresponding integration. At the beginning of the elaboration of avoidance reaction, the indifferent meaning of the same stimulus changes to the signal one. The participation of the pallidum in the activated structures is probably connected with an involvement of afferentation from the stimulated limb. During the elaboration of the motor reaction a functional connection is manifested between the pallidum and the motor and somatosensory cortices in the aspect of their involvement in the formation of an adaptive motor program.

Adaptation, Psychological↗
PubMed2004

Elements of dynamics IV: neuronal metaphors--probing neurobiology for psychodynamic meaning.

The essentiality of neuronal connections can be seen by the frenetic activity which dissociated neurons in culture exhibit in an attempt to re-establish functional connections. Through these interactions, neurons gain access to trophic factors, such as nerve growth factor, which determine whether they live or die. Connection and successful interaction with others is thus a biological imperative for neurons. The properties of a given neuron are determined both by the inherent genetic program and by changes in its genetic expression induced by cell-to-cell interaction. In other words, plasticity of neuronal function reflects not only cellular properties but is a consequence of its relationships. Since it is reasonable to assume that the emotional experience of organisms derives from the biological properties of their brain cells, it seems fruitful to probe the basic biology of these cells for metaphors that might yield insight into psychological properties. Clinical examples illustrate how using these concepts can enlighten the processes by which psychotherapeutic change can occur. In addition, perhaps understanding the underlying neurobiology can add scientific legitimacy to clinical psychodynamic work, and can reduce the tension between "biological" and "psychological" psychiatry. These ideas might be used to develop a new framework to strengthen the teaching of psychotherapy.

Brain↗
PubMed2001

Large-scale cortical reorganization following forelimb deafferentation in rat does not involve plasticity of intracortical connections.

Physiological mapping of the body representation 1 month or longer after forelimb removal in adult rats revealed new pockets of shoulder representation in the forepaw barrel subfield (FBS) in the first somatosensory cortex (SI). These "new" shoulder representations have longer evoked response latencies than sites in the shoulder representation within the trunk subfield, hereafter referred to as the "original" shoulder representation. We postulated that the "new" shoulder representations in the FBS were relayed from the "original" shoulder representation. We investigated this hypothesis by studying anatomical connectivity between the "original" shoulder representation and the FBS in intact control and forelimb deafferented adult rats using Phaseolus vulgaris leucoagglutinin (PHA-L), biocytin, and biotin dextran-amine (BDA) as anterograde tracers. The retrograde tracer cholera toxin beta subunit (CT-B) injected into the FBS was also used to study connectivity between the "original" shoulder representation and the FBS. Using these anatomical tracing techniques, we were unable to show the existence of a direct corticocortical connection between the "original" shoulder representation in the trunk subfield and the FBS in either intact or deafferented rats. Functional connectivity between the two cortical regions was studied by ablating the "original" shoulder representation alone or in combination with the shoulder representation in the second somatosensory cortex (SII) while recording evoked responses in the FBS following electrical stimulation of the shoulder. Both ablations failed to eliminate the evoked responses at the "new" shoulder sites in the FBS, suggesting that SI and SII are not necessary for "new" shoulder input in the FBS. It is suggested that subcortical sites may play a major role in large-scale cortical reorganization. Results of projections from the "original" shoulder representation to parietal medial (PM), parietal lateral (PL), SII, parietal ventral (PV), and parietal rhinal (PR) sensory fields and agranular lateral (AgL) and agranular medial (AgM) motor fields are also described.

Afferent Pathways↗
PubMed2006

Functional neuroanatomy of the hypnotic state.

The neural mechanisms underlying hypnosis and especially the modulation of pain perception by hypnosis remain obscure. Using PET we first described the distribution of regional cerebral blood flow during the hypnotic state. Hypnosis relied on revivification of pleasant autobiographical memories and was compared to imaging autobiographical material in "normal alertness". The hypnotic state was related to the activation of a widespread set of cortical areas involving occipital, parietal, precentral, premotor, and ventrolateral prefrontal and anterior cingulate cortices. This pattern of activation shares some similarities with mental imagery, from which it mainly differs by the relative deactivation of precuneus. Second, we looked at the anti-nociceptive effects of hypnosis. Compared to the resting state, hypnosis reduced pain perception by approximately 50%. The hypnosis-induced reduction of affective and sensory responses to noxious thermal stimulation were modulated by the activity in the midcingulate cortex (area 24a'). Finally, we assessed changes in cerebral functional connectivity related to hypnosis. Compared to normal alertness (i.e., rest and mental imagery), the hypnotic state, significantly enhanced the functional modulation between midcingulate cortex and a large neural network involved in sensory, affective, cognitive and behavioral aspects of nociception. These findings show that not only pharmacological but also psychological strategies for pain control can modulate the cerebral network involved in noxious perception.

Brain↗
PubMed1998

Functional imaging of the brain in the evaluation of drug response and its application to the study of aging.

Functional neuroimaging techniques including single photon emission computerised tomography (SPECT), positron emission tomography (PET) and functional magnetic resonance imaging (FMRI) can provide insight into the functional connectivity of the human brain in both health and disease, including the effects of aging and drugs on brain function. Neuroimaging measurement techniques can either be direct, using radio-specific ligands, or indirect, using the neurophysiological consequences of pharmacological interventions. Both approaches can be combined with sensorimotor or cognitive activation to examine the interaction between the targeted receptor function and the sensorimotor or cognitive process implicit in the study design. Using radionuclides, PET can provide absolute measurement of cerebral blood flow to regions of interest and can measure changes in cerebral metabolism using labelled fluorodeoxyglucose. PET offered the first opportunity to image brain activation caused by a variety of stimuli and hence to measure the effect of drugs on brain activation. PET also enables the study of drug disposition within the brain. SPECT has been used to study relative changes in cerebral blood flow associated with disease processes and also receptor occupancy. FMRI, by contrast, does not involve ionising radiation and has better spatial and temporal resolution. It is still a relatively new technique and limited by its ability to only measure haemodynamic changes through the blood oxygen level-dependent (BOLD) signal. The effects of aging on drug responsiveness and the effects of drug treatment of diseases associated with old age are relatively unexplored areas of functional neuroimaging research.

Aging↗
PubMed1979

The specificity of innervation of regenerating motor neurons in the cockroach.

The pattern of neuromuscular connections of cockroach motor neurons regenerating to an intact mesothoracic leg after crushing nerve 5 has been investigated. While a number of anatomically identified motor neurons reestablished functional connections with their correct target muscles, some of the same and other motor neurons were found to functionally innervate inappropriate muscles. Muscles, and in some cases individual fibres, were often simultaneously innervated by both correct and foreign motor neurons. The frequency of innervation errors decreased with increasing post-operative times, although some errors persisted to the latest stages examined (227 days).

Animals↗
PubMedDate not supplied

Afferent connectivity to different functional zones of the optic tectum in goldfish.

This work studies the afferent connectivity to different functionally identified tectal zones in goldfish. The sources of afferents contributed to different degrees to the functionally defined zones. The dorsocentral area of the telencephalon was connected mainly with the ipsilateral anteromedial tectal zone. At diencephalic levels, neurons were found in three different regions: preoptic, thalamic, and pretectal. Preoptic structures (suprachiasmatic and preoptic nuclei) projected mainly to the anteromedial tectal zone, whereas thalamic (ventral and dorsal) and pretectal (central, superficial, and posterior commissure) nuclei projected to all divisions of the tectum. In the mesencephalon, the mesencephalic reticular formation, torus longitudinalis, torus semicircularis, and nucleus isthmi were, in the anteroposterior axis, topographically connected with the tectum. In addition, neurons in the contralateral tectum projected to the injected zones in a symmetrical point-to-point correspondence. At rhombencephalic levels, the superior reticular formation was connected to all studied tectal zones, whereas medial and inferior reticular formations were connected with medial and posterior tectal zones. The present results support a different quantitative afferent connectivity to each tectal zone, possibly based on the sensorimotor transformations that the optic tectum carries out to generate orienting responses.

Afferent Pathways↗
PubMed2002

Development of convergent synaptic inputs to subpopulations of autonomic neurons.

Visceromotor neurons in mammalian prevertebral sympathetic ganglia receive convergent synaptic inputs from spinal preganglionic neurons and peripheral intestinofugal neurons projecting from the enteric plexuses. Vasomotor neurons in the same ganglia receive only preganglionic inputs. How this pathway-specific pattern of connectivity is established is unknown. We have used a combination of immunohistochemical, ultrastructural, and electrophysiological techniques to investigate the development of synaptic inputs onto visceromotor and vasomotor neurons in the celiac ganglion of guinea pigs. Functional synaptogenesis occurred primarily from early fetal (F30-F35) to midfetal (F36-F45) stages, after the neurochemical differentiation of vasomotor and visceromotor neurons but before establishment of their electrophysiological phenotypes. Intestinofugal inputs were detected only on presumptive visceromotor neurons located primarily in medial regions of the ganglion. The number of ultrastructurally identified synaptic profiles increased in parallel with functional synaptogenesis, especially in medial regions, where dendritic growth rates also were higher. However, the expression of immunoreactivity to choline acetyltransferase in the terminals of inputs was very low until late fetal stages, after functional transmission already had been established. These results show that peripheral intestinofugal neurons directly establish appropriate functional connections with their target visceromotor neurons simultaneously with the development of functional preganglionic inputs to both visceromotor and vasomotor neurons. It seems likely that synaptogenesis occurs independently of the neurochemical differentiation of the target neurons but is closely related to the pathway-specific dendritic development of those neurons.

Acetylcholine↗