Biomedical subjects

Giorgio M Innocenti

Publications and source records attributed to Giorgio M Innocenti.

11 recordsLinked to original sources

PubMed2005

Assessment of EEG synchronization based on state-space analysis.

Cortical computation involves the formation of cooperative neuronal assemblies characterized by synchronous oscillatory activity. A traditional method for the identification of synchronous neuronal assemblies has been the coherence analysis of EEG signals. Here, we suggest a new method called S estimator, whereby cortical synchrony is defined from the embedding dimension in a state-space. We first validated the method on clusters of chaotic coupled oscillators and compared its performance to that of other methods for assessing synchronization. Then nine adult subjects were studied with high-density EEG recordings, while they viewed in the two hemifields (hence with separate hemispheres) identical sinusoidal gratings either arranged collinearly and moving together, or orthogonally oriented and moving at 90 degrees . The estimated synchronization increased with the collinear gratings over a cluster of occipital electrodes spanning both hemispheres, whereas over temporo-parietal regions of both hemispheres, it decreased with the same stimulus and it increased with the orthogonal gratings. Separate calculations for different EEG frequencies showed that the occipital clusters involved synchronization in the beta band and the temporal clusters in the alpha band. The gamma band appeared to be insensitive to stimulus diversity. Different stimulus configurations, therefore, appear to cause a complex rearrangement of synchronous neuronal assemblies distributed over the cortex, in particular over the visual cortex.

Adult↗

PubMed2005

Exuberance in the development of cortical networks.

The cerebral cortex is the largest and most intricately connected part of the mammalian brain. Its size and complexity has increased during the course of evolution, allowing improvements in old functions and causing the emergence of new ones, such as language. This has expanded the behavioural and cognitive repertoire of different species and has determined their competitive success. To allow the relatively rapid emergence of large evolutionary changes in a structure of such importance and complexity, the mechanisms by which cortical circuitry develops must be flexible and yet robust against changes that could disrupt the normal functions of the networks.

Animals↗

PubMed2004

Visual areas in the lateral temporal cortex of the ferret (Mustela putorius).

Using systematic electrophysiological mapping, architectonics and the global pattern of interhemispheric connectivity, we have identified three visual areas in the lateral most part of the posterior suprasylvian gyrus. The most posterior and largest area we call area 20a and anterior to this we defined a smaller area, area 20b. These areas lie lateral to the visual areas 18, 19 and 21 and posterior to a third, but incompletely defined, visual area, area PS. Areas 20a and 20b, emphasize the representation of the upper hemifield. Their interhemispheric connections conform to the so called 'midline rule' in that they are abundant in regions representing central portions of the visual field, scarce or absent elsewhere. These areas are probably homologous to the homonymous areas of the cat and might be indicative of a Bauplan from which the temporal areas of primates may have evolved.

Animals↗

PubMed2004

Neurons in the corpus callosum of the cat during postnatal development.

The corpus callosum (CC) is a major telencephalic commissure containing mainly cortico-cortical axons and glial cells. We have identified neurons in the CC of the cat and quantified their number at different postnatal ages. An antibody against microtubule-associated protein 2 was used as a marker of neurons. Immunocytochemical double-labelling with neuron-specific enolase or gamma-aminobutyric acid antibodies in the absence of glial fibrillary acidic protein positivity confirmed the neuronal phenotype of these cells. CC neurons were also stained with anti-calbindin and anti-calretinin antibodies, typical for interneurons, and with an anti-neurofilament antibody, which in neocortex detects pyramidal neurons. Together, these findings suggest that the CC contains a mixed population of neuronal types. The quantification was corrected for double counting of adjacent sections and volume changes during CC development. Our data show that CC neurons are numerous early postnatally, and their number decreases with age. At birth, about 570 neurons are found within the CC boundaries and their number drops to about 200 in the adult. The distribution of the neurons within the CC also changes in development. Initially, many neurons are found throughout the CC, while at later ages they become restricted to the boundaries of the CC, and in the adult to the rostrum of the CC close to the septum pellucidum or to the indusium griseum. Although origin and function of transient CC neurons in development and in adulthood remain unknown, they are likely to be interstitial neurons. Some of them have well-developed and differentiated processes and resemble pyramidal cells or interneurons. An axon-guiding function during the early postnatal period can not be excluded.

Animals↗

PubMed2004

Somatodendritic minicolumns of output neurons in the rat visual cortex.

The apical dendrites of the pyramidal neurons of the cerebral cortex form radial bundles in all species and areas. Using microtubule-associated protein (MAP)2 immunostaining and Voronoi tessellation analysis in the rat visual cortex, we obtained objective criteria to define dendritic bundles in tangential sections: in supragranular layers of the rat visual cortex we found bundles of 6-6.4 dendrites, at a density of 1929 bundles/mm(2) and a centre-to-centre distance of 27 micro m. Using lipophilic tracers to label different pyramidal cell populations, based on the same criteria as in MAP2-immunostained material, we found that in the rat visual cortex the bundles consist of neurons with specific targets. Neurons projecting to the ipsi- or contralateral cortex form bundles together and with neurons projecting to the striatum, but not with those projecting to the superior colliculus, dorsal division of the lateral geniculate nucleus or through the cerebral peduncle. The latter neurons form bundles with neurons projecting to the striatum. Thus, the cerebral cortex is organized in minicolumns of output neurons visible at the earliest ages studied (P3), which might have a higher probability of being interconnected than those outside.

Age Factors↗

PubMed2003

Immature cortex lesions alter retinotopic maps and interhemispheric connections.

Unilateral lesions of the occipital visual areas performed on postnatal day 5 (P5) in the ferret are not compensated by the appearance, in the lesioned hemisphere, of visual responses at ectopic locations. Instead, when parts of the visual areas are spared, they show abnormal retinotopic organizations; furthermore, callosal connections are abnormally distributed in relation to the retinotopic maps. Lesions that completely eliminate the visual areas including the posterior parietal cortex cause the appearance of abnormal callosal connections from the primary somatosensory cortex on the lesion side to the contralateral, intact, posterior parietal cortex. The occipital visual areas (17, 18, 19, and 21) of the intact hemisphere show a normal retinotopy but lose callosal connections in territories homotopic to the lesions. These findings clarify the nature and limits of structural developmental plasticity in the visual cortex. Early in life, certain regions of cortex have been irreversibly allocated to the visual areas, but two properties defining the areas, that is, retinotopy and connections, remain modifiable. The findings might be relevant for understanding the consequences of early-onset visual cortical lesions in humans.

Agenesis of Corpus Callosum↗

PubMed2002

Preserved visual function in a case of occipitoparietal microgyria.

A 20-year-old man with bilateral parasagittal occipitoparietal polymicrogyria and epilepsy, from whom normal functional magnetic resonance imaging and electroencephalogram responses to visual stimuli were obtained, was found to have no visual perceptual deficits. This suggests that microgyric cortex can perform normal visual functions, despite its gross structural abnormalities.

Adolescent↗

PubMed2002

Retinofugal projections following early lesions of the visual cortex in the ferret.

Extensive lesions of the occipital cortex comprising the developing occipital visual areas and beyond in young ferrets (postnatal day 5) are followed by massive, but incomplete, degeneration of the lateral geniculate (LGN) and lateralis posterior (LP) nuclei of the thalamus, and minor volumetric reduction of the superior colliculus. Retinal projections (revealed by intraocular tracer injections), while reduced, remain confined to their territories of normal termination, both in the adult and throughout development. Comparisons with other mammalian species point to several common features in the developmental plasticity of retinofugal pathway.

Animals↗

PubMed2002

Areal organization of the posterior parietal cortex of the ferret (Mustela putorius).

On grounds of electrophysiological mapping, cytoarchitecture, myeloarchitecture and callosal and thalamic connectivity, we have identified two cortical areas in the posterior parietal cortex of the ferret: posterior parietal caudal and rostral (PPc and PPr). These areas occupy the lateral and suprasylvian gyri, from the cingulate sulcus (medially) to the suprasylvian sulcus (laterally) and lie between visual areas 18 and 21 (posteriorly) and the somatosensory areas (anteriorly). Within both areas a coarse representation of the visual field was found and within PPr there was also a representation of the body. Each representation mirrors those within neighboring areas. Cytoarchitectonic and myeloarchitectonic fields within this cortical region did not correspond in any simple way to the physiological representations. The architectonic differences correlate to differential callosal connectivity, with predominant connectivity corresponding to the upper hemifield/head representations. PPr and PPc receive thalamic projections from a different, but overlapping, complement of thalamic nuclei. The superimposition of somatic and visual maps in PPr might relate to the probable role of this area in transforming retinal-centered to body-centered spatial coordinates. The organization of the parietal areas in the ferret resembles that of the flying fox and might unveil a common organizational plan from which the primate posterior parietal cortex evolved.

Animals↗

PubMed2002

Architecture and callosal connections of visual areas 17, 18, 19 and 21 in the ferret (Mustela putorius).

Visual areas 17, 18, 19 and 21 of the ferret can be distinguished on the grounds of cytoarchitecture, myeloarchitecture and cytochrome oxidase reactivity, and with transneuronal tract-tracing from the eye. Each visual area contains callosally connected, as well as acallosal, regions. The callosal connections originate mainly from layers 2 and 3 and, more widely, from layer 6. Callosally projecting neurons and callosal terminals are organized in three roughly medio-laterally oriented bands. The posterior and intermediate bands straddle the 17/18 and 19/21 border, respectively; the third band extends along the medial bank of the lateral suprasylvian sulcus. These bands are linked by a variable number of bridges of connections that demarcate acallosal islands. The distribution of callosal connections predicts the existence of vertical meridian representations corresponding to each of the bands and of non-isotropic representations of the visual field within the bridges and islands.

Animals↗

PubMed2002

The representation of the visual field in three extrastriate areas of the ferret (Mustela putorius) and the relationship of retinotopy and field boundaries to callosal connectivity.

We describe representations of the visual field in areas 18, 19 and 21 of the ferret using standard microelectrode mapping techniques. In all areas the azimuths are represented as islands of peripheral visual field surrounded by central visual field representation. The zero meridian was found at the 17/18 and 19/21 borders; at the 18/19 and anterior border of 21 the relative periphery of the visual field was found. In areas 18 and 19, elevations are represented in a smooth medio-lateral progression from lower to upper visual field. In several cases the elevations in area 21 evidenced a similar medio-lateral progression; however, in others the elevations exhibited a split representation of the horizontal meridian. Anatomically determined callosal connections coincided with the representation of azimuths near the zero meridian. Medio-lateral bands of callosal connectivity that straddle the 17/18 and 19/21 borders are connected by bridges of callosally projecting cells. Acallosal cortical islands corresponded to the peripheral visual field and were found straddling the 18/19 border and the anterior border of area 21. The results are discussed in relation to callosal connectivity and retinotopy in extrastriate visual cortex and to proposed homologies of carnivore and primate visual cortex.

Animals↗