Intercortical Connections Research Articles

Short-term cortical reorganization by deafferentation of the contralateral sensory cortex

The topographic arrangement of the human primary somatosensory cortex following deafferentation of the contralateral cortex has been investigated by means of dipole source analysis. Somatosensory-evoked potentials were obtained by electrical stimulation of digit 1 and digit 5 of the left hand before and after anesthesia of digits 2-4 of the right hand during different terms of attention. Anesthesia induced an expansion of the three-dimensional distance between digits 1 and 5. This suggests intercortical plasticity modulated between bilateral primary somatosensory cortical areas, which is unaffected by spatial attention. These changes occur rapidly and are probably mediated by disinhibition of intercortical connections, leading to hyperexcitability of the primary sensory cortex that is contralateral to the region undergoing deafferentation.

Cyclic AMP-dependent attenuation of oscillatory-activity-induced intercortical strengthening of horizontal pathways between insular and parietal cortices

Cyclic AMP (cAMP) is a key intracellular second messenger, and the intracellular cAMP signaling pathway acts to modulate various brain functions. We have previously reported that low-frequency insular cortex stimulation in rat brain slices switches on a voltage oscillator in the parietal cortex that delivers signals horizontally back and forth under caffeine application. The oscillatory activities are N-methyl- d-aspartate (NMDA) receptor-dependent, and the role of oscillation is to strengthen functional intercortical connections. The present study investigated actions of the cAMP signaling pathway on caffeine-induced strengthening of intercortical connections and tried to confirm the role of oscillation on intercortical strengthening by focusing on the cAMP pathway. After induction of parietal oscillation by insular cortex stimulation in caffeine-containing medium, application of membrane-permeable cAMP analog, bromo-cAMP, diminished oscillatory signal delivery from the parietal cortex, but initial insulo-parietal signal propagation remained strong. When oscillatory activities were reduced with co-application of caffeine and bromo-cAMP from the beginning, initial insulo-parietal propagation was established, but amplitudes of propagating wavelets and propagating velocity were reduced. Thus, cAMP-dependent diminution of caffeine-induced NMDA-receptor-dependent oscillatory signal delivery causes attenuation of intercortical strengthening of horizontal pathways between insular and parietal cortices. This finding suggests that the intracellular cAMP signaling pathway has the ability to regulate extracellular communications at the network level, and also that full expression of strengthened intercortical signal communication requires sufficient NMDA-receptor-dependent oscillatory neural activities.

Cortical Development: New Concepts

Cortical Development: New Concepts

Systems biology versus molecular biology

Molecular biology and systems biology provide answers to the same questions, but the answers are quite different for the two approaches and are, on the surface, unrelated. The molecular biological answers are arguably more fundamental and are unique, but alternative systems biology answers are possible – consider the two systems-level answers to the first question. Nevertheless, the systems-level answers can be in some sense more satisfying, because you feel you have an explanation you can understand and use to make testable predictions; a list of genes together with their interactions is perhaps preferred, but much harder to grasp, explain and remember.That the two types of answer seem to be unrelated reveals an essential flaw in the example I have used. In a really good example, the two levels of explanation would be unified so that the molecular biology explanation would also include the systems biology answers, and vice versa. In our example, the molecular biologist would not only have to identify the genetic networks responsible for cortical patterning, but would also have to discover the molecular basis for the rules that lead to the optimal arrangement of cortical areas and to understand the mechanisms used by the developing cortex to ensure conducting components occupy 3/5 of the volume so that cortical function is optimal. Even if you know all the genetic and epigenetic mechanisms that result in 3/5 of the cortical neuropil volume being conducting components, you still can ask why evolution selected that particular mix of mechanisms. The systems-level approach explains the molecular biologist's answer to this question by appeal to a general principle: evolution selects an optimal partitioning of components.The challenge for systems biology is to discover answers to biology's questions, and the challenge for the molecular biologists is not only to provide answers to these questions, but also to explain the answers given by systems biology. And after molecular biology has given its final answers, the systems biologist must identify the general principles that lead to the actual combination of molecular mechanisms. At its best, then, systems biology and molecular biology work hand-in-hand to provide a complete picture of how and why Biology is the way it is.

Dopamine terminals synapse on callosal projection neurons in the rat prefrontal cortex.

Dopamine (DA) afferents to the prefrontal cortex (PFC) play an important role in the cognitive functions subserved by this cortical area. Within the PFC, DA terminals synapse onto the distal dendrites of both local circuit neurons and pyramidal projection cells. We have previously demonstrated in the rat PFC that some of the dendrites and spines postsynaptic to DA terminals arise from pyramidal neurons that project to the nucleus accumbens. However, it is not known whether the pyramidal cells that give rise to callosal intercortical connections of the PFC also receive DA synaptic input. To address this question, retrograde tract tracing using an attenuated strain of pseudorabies virus (PRV-Bartha) was combined with immunocytochemistry for tyrosine hydroxylase (TH) to identify DA terminals in the PFC. Thirty-six to 40 hours following injection of PRV into the contralateral PFC, numerous callosal projection neurons were extensively labeled throughout their dendritic trees, with no evidence of PRV trans-synaptic passage. In tissue prepared for electron microscopy, labeling for PRV was distributed throughout pyramidal cell somata and extended into distal dendrites and dendritic spines. Some PRV-labeled dendrites and spines received symmetric synaptic input from terminals containing peroxidase labeling for TH. These results demonstrate that DA terminals synapse onto the distal dendrites of callosally projecting PFC neurons and suggest substrates through which DA may modulate interhemispheric cortical communication.

Time organization of frontal-motor cortex interneuron interactions in the cat neocortex in conditions of different levels of food motivation.

Studies were carried out in conscious cats with recording of multicellular activity in moderate hunger and after 24-h food deprivation. Cross-correlation analysis was used to assess statistical interneuron interactions between closely-located neurons in the frontal and sensorimotor regions of the neocortex (local networks), and between the cells of these regions (distributed networks). One-day food deprivation increased the number of interactions formed within both local and distributed neuron networks. Increases in intercortical connections between the frontal and motor regions was seen at all time intervals studied (0-100 msec), though the most significant changes occurred at time intervals of up to 30 msec.

Chapter 27 A proposed reorganization of the cortical input-output system

This paper proposes a new concept for interpretation of the cerebral cortex. In this schema, the cortex is an 'imaging system' which plays an integral part in the 'functional circuit' of the living body. This functional circuit is made up of five components: the 'imaging system' of the cortex, the 'image forming system' of the basal ganglia, thalamus and cerebellum, the 'image-acting system' of the brainstem and spinal cord, the 'sensory system' of the sense organs and the 'external words.' An image constructed in the cortex yields a purposeful movement by way of its outputs through the image-acting system. The image to drive the purposeful movement is formed and accumulated in the cortex by trial and error under the control of the image-forming system. In the proposed organization outlined here, the cortex can be divided into two components, both of which have their own input and output for forming and realizing the image. One is comprised of specific areas for analyzing proper sensations from the sense organs through a specific area of the thalamus (e.g., retinal to lateral geniculate to primary visual cortex). The other system is composed of non-specific areas analyzing more diffuse input from various sensory organs through non-specific areas of the thalamus. These two systems work in concert to form fundamental and detailed images for purposeful movements through tight intercortical connections. Whereas the outputs from non-specific areas yield common behaviors regardless of sensory modality, outputs from the specific areas controls movements related to a specific sensation. Thus, it is proposed that these two systems work cooperatively: the former constructs the image and causes the initial movements, and the latter controls the movements to realize the image from the changing information of transient conditions. This model differs from other models of cortical organization which segregate cortex on the basis of sensory-related input regions and motor-related output regions. Existing data is consistent with the proposed organizational scheme. Although it may be difficult to prove specific aspects of this new model. I believe that the hypotheses contained within it will serve as an important foundation for driving future research.

State of intercortical connections after cranial-cerebral trauma with injury to the lower parietal lobe

State of intercortical connections after cranial-cerebral trauma with injury to the lower parietal lobe

Association connections of the cat's parietal cortex

Intercortical connections of primary sensory (visual, auditory, somatosensory) areas with the parietal association cortex were studied in cats by the retrograde axonal transport of horseradish peroxidase and the Fink-Heimer silver impregnation of degenerated fibers techniques. This combined study revealed the shape, size, and intracortical location of cells connecting the primary sensory areas monosynaptically with the parietal cortex and also the distribution of preterminals and terminals of the fibers of these cells in the parietal association cortex. The greatest number of cells forming connections with area 7 of the parietal association cortex was shown to occur in visual area V1, and with area 5 in somatosensory area S1. Besides pyramidal neurons tagged with horseradish peroxidase, which were located mainly in layers II–IV, a few tagged stellate and fusiform cells also were found. The results supplement and confirm data on afferent connections of the parietal association cortex in cats.

Intercortical connections of the auditory areas with the motor area.

1. One afferent input of the motor area is formed by cortical connections arising in auditory areas AI, AII, and Ep. 2. Interzonal connections of auditory areas AI, AII, and Ep terminate in the motor projection zone of the forelimb. Connections running from area EP are distributed more widely and terminate in the motor projection zone for the head also. 3. The largest number of cortical auditory inputs into the motor area is formed by connections arising in area EP and the smallest by those arising in area aII. 4. Intercortical connections from area AI pass through and terminate on neurons of layers VI-III of the motor cortex, those from area AII on neurons of layers IV and V, and those from area Ep on neurons of layers VI-III.

Columnar cortico-cortical interconnections within the visual system of the squirrel and macaque monkeys

Cortico-cortical interconnections within the visual cortex of squirrel monkeys ( Saimiri sciureus) were studied by means of single or multiple injections of [ 3H]leucine or combined [ 3H]leucine and horseradish peroxidase into the dorsolateral striate and prestriate cortices. Injections of [ 3H]leucine were also made into the dorsolateral striate cortex of a Macaca speciosa for comparison. The results indicated that in Saimiri the dorsolateral prestriate cortex is precisely and reciprocally connected with the striate and peristriate cortex, and with the posterior bank of superior temporal sulcus, including the middle temporal area (MT). The dorsolateral striate area is precisely and reciprocally connected with the prestriate and MT area, but does not project to the perstriate cortex as in the case of the macaque. At each target site, the radioactively labelled terminal fields are distributed in a distinctly columnar fashion, with labelled columns (120–480 μm in diameter, commonly 240 μm) interdigitating with sparsely labelled or unlabelled columns of lesser widths. The HRP-labelled neurons invariably exist within the radioactively labelled columns. For all of the cortical areas examined except area 17, lamina IV is the principal ‘receptive’ layer for associational fibers, while layers III and II, as well as V and VI within the same column, receive progressively less input. As for area 17, associational fibers from the prestriate cortex terminate mainly within lamina I, with laminae II, III, V and VI receiving decreasing amounts of input. The present results indicate that the major visual cortical areas are interconnected in precise, topographical and reciprocal fashion. The columnar arrangement is found to be the basis of both extra- and intercortical connections.

Multiple somatic projections to frontal lobe of the squirrel monkey

Precentral evoked electrical responses in the frontal lobe to subcutaneous electrical stimulation were studied in the chloralose-anesthetized squirrel monkey and were found to consist of essentially three components: a very short-latency, somatotopically organized response in pericentral cortex, interpreted as “primary somatic” on the basis of cytoarchitectonic studies on this area; a longer-latency, somewhat less somatotopically organized wave extending rostrally into Brodmann areas 4, 6, and, perhaps, 8, considered to be due to intracortical conduction from pericentral areas 1–3 since it was abolished by destruction of the latter region; and a widespread heterotopic component independent of pericentral cortex and medial thalamus having some relation to lateral thalamus. Analyses of these components and comparisons with similar data from the macaque were made in an attempt to distill from some sharply disparate data a composite picture of multiple inputs converging on frontal association cortex, perhaps reflecting in some ways the possible sequence of evolution of the neocortex involving differentiation of primary areas out of primitive association cortex, with retention of strong intercortical connections between the two as this occurs and as the association areas grow.

A theory of pattern perception based on human physiology.

The gross connectivity, patterns of information pathways in the primate and human visual systems, when examined by an information processing engineer, bear a curious resemblance to the two-dimensional-pattern optical computers which he builds himself in an attempt to achieve pattern recognition. The portions of the visual system inferior to the primary visual cortex are essentially a topologically accurate homeo-morphic mapping of the retinal image, at least in the vicinity of the fovea. Analysis of the topological aspects of the visual scene and hence ‘ Pattern Recognition ’ must therefore take place in the primary visual cortex and successive cortical areas We have previously reported how intra- and inter-cortical connectivity could support a combined memory and computation scheme capable of performing pattern recognition by a variation of two-dimensional cross correlation. This paper is a report of an extension of the previous model enabling it to perform pattern recognition by computing the two-dimens...

The Efferent Intercortical Connections of the Superficial Cortex of the Temporal Lobe (Macaca Mulatta)

The Efferent Intercortical Connections of the Superficial Cortex of the Temporal Lobe (Macaca Mulatta)