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PubMed1983

[Morphologic criteria of the structural asymmetry of the cortical and subcortical structures of the human brain].

Using a cytoarchitectonic and quantitative methods, the authors investigated the structural organization of Fields 4, 6, 8, 39, 40, 43, 46, 47, caudate and dorsomedial nuclei of the tuber cinereum in the right and the left cerebral hemispheres in a grown-up right-handed man. With the help of electron computers definite parameters of neurons in the cortex (layers III and V) and in the subcortical nuclei were determined. The material obtained was statistically processed. Morphological criteria of the structural organization of the above-listed formations were identified. These included indicators of the total volumetric fraction of neurons and glia, profile fields of neurons, and the neuronal composition. Structural asymmetry was revealed, with the left hemisphere being dominant in the logomotor and motor fields. There were no signs of structural asymmetry in either the frontal and parietal fields or in the subcortical formations. The interpretation of the results obtained is attempted.

Adult↗
PubMed1984

Fine structure of cortical tubers in tuberous sclerosis: a Golgi study.

The fine structure of cerebral cortex, including cortical tubers, was studied in 3 patients with tuberous sclerosis. Tubers were found to consist of two predominant cell populations, astroglia and small multipolar (stellate) neurons. Both cell types tended to form aggregates within tubers, with glia more prominent in the subpial region. The stellate neurons of tubers had beaded or varicose dendrites with few dendritic spines. The findings suggest that neurons within tubers are an aberrant primitive cell type that fails to express the pyramidal cell shape and dendritic morphology that is characteristic of normal human neocortex. Cortex intervening between tubers had basically normal dendritic morphology. However, quantitative study showed a decrease in the length of dendritic branches of pyramidal neurons, as also observed in several other conditions manifested by mental retardation.

Astrocytes↗
PubMed2007

Age-dependent change in the 3D structure of cortical porosity at the human femoral midshaft.

Microstructural change associated with cortical bone remodeling has been extensively explored with 2D techniques. However, relatively little is known regarding the 3D dynamic microstructure of cortical bone. Therefore, we employed micro-CT imaging to investigate 3D remodeling-related change in the structure of cortical bone porosity across the human lifespan. Anterior femoral midshaft specimens (n=51 male, 28 female) spanning 18 to 92 years of age were scanned with 7 mum nominal isotropic resolution. Canal volume fraction (Ca.V/TV), mean diameter (Ca.Dm), mean separation (Ca.Sp), degree of anisotropy (DA), connectivity density (Ca.ConnD), and number (Ca.N) were calculated for subperiosteal cylindrical regions of interest. Ca.N was calculated in 2D (Ca.N(2D)) and 3D (Ca.N(3D)). Regression was used to examine the relation between the structural parameters and age. Additionally, the impact of sex, height, and weight were investigated collectively (MANCOVA) and individually (ANCOVA). For all analyses, Ca.V/TV and Ca.Dm were inverted (Ca.V/TV(-1), Ca.Dm(-1)) to establish normality and linear relations with age. Ca.N values (2D and 3D) were non-linearly (quadratic) related to age, increasing until the 6th decade then decreasing. This relation was only significant for the pooled sexes Ca.N(3D) values (p=0.012). Ca.ConnD was positively related to age (p<0.05), while all remaining 3D parameters, except DA for males (p=0.070), were negatively related (p<0.05). In all cases, the relation with age was strongest for females. MANCOVA revealed that age was the only significant (p<0.001) covariate overall. Univariate ANCOVA indicated significant differences between the sexes for Ca.V/TV(-1) and Ca.Dm(-1) (p=0.018 and 0.010, respectively). Relative to males, females had lower values for these parameters, translating into larger mean canal diameter and overall porosity. Body weight had a significant (p=0.043) positive relation with Ca.Dm(-1), indicating lower weight was also associated with increased mean canal diameter. Therefore, while age was the most important factor, sex and body size were found to play a role in parameters related to canal size and the overall level of porosity. This study is unique in that changes in cortical bone microstructure were examined across the adult human lifespan in three rather than two dimensions.

Adolescent↗
PubMed1998

Spatiotemporal structure of cortical activity: properties and behavioral relevance.

The study was designed to reveal occurrences of precise firing sequences (PFSs) in cortical activity and to test their behavioral relevance. Two monkeys were trained to perform a delayed-response paradigm and to open puzzle boxes. Extracellular activity was recorded from neurons in premotor and prefrontal areas with an array of six microelectrodes. An algorithm was developed to detect PFSs, defined as a set of three spikes and two intervals with a precision of +/-1 ms repeating significantly more than expected by chance. The expected level of repetition was computed based on the firing rate and the pairwise correlation of the participating units, assuming a Poisson distribution of event counts. Accordingly, the search for PFSs was corrected for rate modulations. PFSs were found in 24/25 recording sessions. Most PFSs (76%) were composed of spikes of more than one unit but usually not more than two units (67%). The PFSs spanned hundreds of milliseconds, and the average interval between two events within the PFSs was 200 ms. No traces of periodic oscillations were found in the PFS intervals. The bins of the matrix that were defined as PFSs were isolated temporally: the spikes that generated PFSs were not associated with high-frequency bursts or rapid coherent rate fluctuations. A given PFS tended to be correlated with the animal's behavior. Furthermore, for 19% of the PFS pairs that shared the same unit composition, each member of the pair was associated with a different type of behavior. The PFSs often appeared in clusters that were associated with particular phases of the behavior. The firing rate of single units did not provide a full explanation for the timing and structure of these clusters. A reduced spike train (RST) was defined for each unit by taking all spikes of that unit that were part of any PFS. In 88% of the cases the degree of modulation of the RST was higher than that of the complete spike train. The results suggest that relevant information is carried by the fine temporal structure of cortical activity. A coding scheme that involves such temporal structures is rich and sufficiently flexible to facilitate a rapid organization of cortical neurons into functional groups. The results can be accounted for by the synfire chain model, which suggests that cortical activity is mediated by synchronous activation of neural groups in a reverberatory mode.

Algorithms↗
PubMed2005

Construction of perineuronal net-like structure by cortical neurons in culture.

Perineuronal nets consisting of chondroitin sulfate proteoglycans and hyaluronic acid are associated with distinct neuronal populations in mammalian brain. Whether neurons or glia cells produce these surface-associated chondroitin sulfate proteoglycan perineuronal nets has remained in question. In the present study, we observed perineuronal net-like structure by rat cortical neurons in dissociated culture using Wisteria floribunda aggulutinin, hyaluronic acid binding protein, and the antibodies recognizing chondroitin sulfate proteoglycans. The double labeling experiments showed that perineuronal net-like structure labeled with Wisteria floribunda aggulutinin was observed often at parvalbumin-positive neurons in dissociated cortical culture without glia. Perineuronal net-like structure was not seen at the early stage of culture, but they became visible concomitantly with neuronal maturation after longer culture. High magnification observation further demonstrated that Wisteria floribunda aggulutinin labeling on cortical neurons was seen as numerous puncta along surface of somata and proximal dendrites, but not axons and synapses. Perineuronal net-like structure on cultured neurons was also visualized using chondroitin sulfate proteoglycan-specific antibodies and hyaluronic acid binding protein. Double labeling study demonstrated that perineuronal net-like structure in cultured cortical neurons was composed of chondroitin sulfate proteoglycans such as neurocan and phosphacan. The hyaluronidase treatment of live neurons abolished cellular labeling of hyaluronic acid binding protein and concomitantly diminished that of Wisteria floribunda aggulutinin. These results indicate that cultured cortical neurons are able to construct perineuronal net-like structure without glial cells.

Animals↗
PubMed2004

Cortical midline structures and the self.

For a long time philosophers and psychologists have been intrigued by the question of the self. More recently, this has become a topic of discussion in neuroscience. In this article, we suggest that the processing of self-referential stimuli in cortical midline structures (CMS) is a fundamental component in generating a model of the self. Drawing from neuroimaging studies, we distinguish between representation, monitoring, evaluation and integration of self-referential stimuli. All of these subfunctions are related to distinct regions within the CMS. This relationship between self-referential processing and CMS might provide novel insight into the neural correlates underlying the constitution of the self.

Awareness↗
PubMedDate not supplied

[Dynamics of evoked potentials in cortical projection structures during a retarded instrumental defense reflex in dogs].

Evoked potentials (EP) in the somatosensory and auditory cortical areas were studied in four dogs against the background of a retarded defensive instrumental conditioned reflex to clicks. Four phases of the reflex were singled out by the changes in the structure of EP late components (LC) in the two projection zones. The most complex LC changes in the form of intensified negative components and the appearance of additional negative LC are recorded in response to the first click of the series and to the one followed by the conditioned motor reaction (CMR). Against the background of CMR delay, the EPs increased, while during the CMR, they decreased, owing to the diminished negative components, while the positive components were preserved and sometimes intensified. An assumption has been made that cortical projection structures of paired stimuli function in one and the same regime.

Animals↗
PubMed2001

Differences in time course of ACh and GABA modulation of excitatory synaptic potentials in slices of rat hippocampus.

Activation of muscarinic receptors and GABA(B) receptors causes presynaptic inhibition of glutamatergic synaptic potentials at excitatory feedback connections in cortical structures. These effects may regulate dynamics in cortical structures, with presynaptic inhibition allowing extrinsic afferent input to dominate during encoding, while the absence of presynaptic inhibition allows stronger excitatory feedback during retrieval or consolidation. However, proposals for a functional role of such modulatory effects strongly depend on the time course of these modulatory effects; how rapidly can they turn off and on? In brain slice preparations of hippocampal region CA1, we have explored the time course of suppression of extracellularly recorded synaptic potentials after pressure pulse application of acetylcholine and GABA. Acetylcholine causes suppression of extracellular potentials with onset time constants between 1 and 2 s, and decay constants ranging between 10 and 20 s, even with very brief injection pulses. GABA causes suppression of extracellular potentials with onset time constants between 0.2 and 0.7 s, and decay time constants that decrease to values shorter than 2 s for very brief injection pulses. These techniques do not give an exact measure of the physiological time course in vivo, but they give a notion of the relative time course of the two modulators. The slow changes due to activation of muscarinic acetylcholine receptors may alter the dynamics of cortical circuits over longer intervals (e.g., between different stages of waking and sleep), setting dynamics appropriate for encoding versus consolidation processes. The faster changes in synaptic potentials caused by GABA could cause changes within each cycle of the theta rhythm, rapidly switching between encoding and retrieval dynamics during exploration.

Acetylcholine↗
PubMed1981

Effect of bone strain on cortical bone structure in macaques (Macaca mulatta).

It has recently been shown that the consistency of food significantly affects levels of bone strain in the mandible during mastication (Hylander, '79a). Mandibular bone histology was examined to test the effects of a diet of hard food compared to a diet of soft food in two groups of monkeys. One group of rhesus macaques (Macaca mulatta) was fed a diet of commercially prepared hard biscuits. The second group was fed a soft diet the consistency of fudge. Both diets were nutritionally adequate for normal growth and development. As a control for other factors influencing cortical bone structure, fibular morphology was also examined. At the end of the test period, mandibular and fibular tissue samples from the two groups were prepared to determine the amount of secondary Haversian bone present. Mandibular depth at M2 and fibular anteroposterior diameter were also measured and compared between the two dietary groups. The soft-diet monkeys showed low levels of remodeling in their mandibles. There were large patches of unremodeled bone and resorption spaces were common. The hard-diet monkeys exhibited more extensive evidence of secondary Haversian remodeling in their mandibles. The hard-diet monkeys also had deeper mandibles. In contrast, the fibulae from the two groups had similar mean diameters and showed comparable levels of secondary remodeling. We infer that the higher mandibular bone remodeling levels in the hard-diet monkeys represent an adaptive response to remove and replace fatigued mandibular bone due to higher stress levels associated with the ingestion and mastication of hard foods. We also infer that greater depth of the mandible at M2 found in the hard-diet group represents an adaptive response to higher stress levels associated with the ingestion and mastication of hard foods.

Animals↗
PubMedDate not supplied

Evidence for changes in the Alzheimer's disease brain cortical membrane structure mediated by cholesterol.

Small angle X-ray diffraction analysis of Alzheimer's disease (AD) lipid membranes extracted from cortical gray matter showed significant, reproducible structure changes relative to age-matched control samples. Specifically, there was an average 4 A reduction in the lipid bilayer width and significant changes in the membrane electron density profiles of AD cortical samples. There were no significant structure differences in the membrane bilayers isolated from an unaffected region (cerebellum) of the AD brain. Lipid and protein analysis of 6 AD and 6 age-matched controls showed that the phospholipid:protein mass ratio was unchanged but that the unesterified cholesterol:phospholipid (C:PL) mole ratio decreased by 30% in the AD temporal gyrus relative to age-matched controls. By contrast, the C:PL mole ratio in the cerebellum did not change significantly. X-ray diffraction analysis of a cholesterol enriched AD sample demonstrated a virtual restoration of the normal membrane bilayer width and electron density profile, suggesting that the cholesterol deficit played a major role in the AD lipid membrane structure perturbation. Alterations in the composition and structure of the membrane bilayer may play an important role in the pathophysiology of AD by altering the activity and catabolism of membrane-bound proteins, including the beta-amyloid precursor protein.

Aged↗
PubMed2004

Structure of cortical microcircuit theory.

Recent experimental and theoretical investigations have made considerable advances in three major areas relating to the structural basis of quantitative cortical microcircuit theory. The first concerns the nature of the cellular units, encompassing the increasingly precise identification and progressively more complete listing of the individual cellular species that constitute the various cortical networks. The second element addresses the problem of heterogeneity, including the demonstration of the importance of cell to cell variability within defined interneuronal populations and the application of the Shannon-Wiener diversity index for the quantitative assessment of the number and relative abundance of interneuronal species. The third component relates to the discovery of basic topological principles underlying the circuit wiring, revealing a surprising order in the architectural design of networks. These new advances deepen our understanding of the computational principles embedded in cortical microcircuits, and they also provide novel opportunities for building realistic models of mammalian cortical microcircuits.

Algorithms↗
PubMed1999

A role of cytoskeletal structure of cortical cells in the gravity-regulated formation of a peg in cucumber seedlings.

Seedlings of cucurbitaceous plants develop a protuberant tissue, or peg, on the lower side of the transition region between root and hypocotyl when germinated in a horizontal position. Peg develops due to a change in growth polarity of the cortical cells. We have examined the role of the cytoskeletal structure in peg formation of cucumber seedlings. We observed that in both peg and normal cortical cells of 36 h-old seedlings the microtubules (MTs) were arranged perpendicular to the longitudinal axis of the elongating cells. Application of colchicine perturbed the MTs structure and inhibited the formation of pegs. In 20 h-old seedlings, MTs in cortical cells destined to be a peg tissue had no preferential organization, whereas MTs in normal cortical cells were transversely oriented. After 24 h, the MTs in future peg cells were arranged similar to those of 36 h-old seedlings, although the initiation of peg tissue was not yet visible. These results suggest that reorganization of MTs is required for peg formation and causes the change in growth polarity of the cortical cells.

Cell Polarity↗
PubMed2000

Shifting visual attention in space: an electrophysiological analysis using high spatial resolution mapping.

OBJECTIVES: Evidence from cortical electrophysiology and functional imaging converges on the view that visual spatial selective attention results in a facilitation of early sensory processing in visual cortical structures. Little is known, however, about the neural control processes that lead to this facilitation. The present study was aimed at further investigating these control processes and their neural correlates by analyzing high spatial resolution maps of brain activity that were evoked by attention-directing cues, but occurred prior to presentation of the target stimulus. METHODS: Subjects (n=14) were presented with central arrow cues that instructed them to attend covertly to either a left or right field location in order to compare two subsequent target stimuli simultaneously presented to the location. On half of the trials, targets were presented to the cued location, while in the other half, targets were presented to the opposite visual field location. Subjects had to respond via button press on 16% of the trials when target stimuli were identical. Event-related potentials (ERPs) were recorded from 92 scalp electrodes which allowed a sufficiently finegrained analysis of the regional specificity of the ERP components. RESULTS: In response to the cues, an initial component over occipital-parietal electrode sites was consistent with an early involvement of the posterior-parietal cortex, perhaps in the initial step of attentional orienting. A second component over the lateral-prefrontal cortex is consistent with the voluntary control and maintenance of attention, a function known to be subserved by frontal cortical structures. A late component narrowly focussed over occipital-temporal electrode sites is most plausibly related to activation of parts of the ventral extrastriate cortex. CONCLUSIONS: The data support the current view that voluntarily orienting visual attention in space leads to top-down modulations in cortical excitability of ventral extrastriate regions initiated by posterior-parietal and mediated by lateral-prefrontal cortical structures.

Adult↗
PubMed2005

Method for cortical bone structural analysis from magnetic resonance images.

RATIONALE AND OBJECTIVES: Quantitative evaluation of cortical bone architecture as a means to assess bone strength typically is accomplished on the basis of images obtained by means of dual-energy X-ray absorptiometry (DXA) or computed tomography. Magnetic resonance (MR) imaging has potential advantages for this task in that it allows imaging in arbitrary scan planes at high spatial resolution. However, several hurdles have to be overcome to make this approach practical, including resolution of issues related to nonlinear receive coil sensitivity, variations in marrow composition, and the presence of periosteal isointense tissues, which all complicate segmentation. The aim of this study is to develop MR acquisition and analysis methods optimized for the detection of cortical boundaries in such complex geometries as the femoral neck. MATERIALS AND METHODS: Cortical boundary detection is achieved by radially tracing intensity profiles that intersect the periosteal and endosteal boundaries of bone. Profiles subsequently are normalized to the intensity of the marrow signal, processed with morphologic image operators, and binarized. The resulting boundaries are mapped back onto the spatial image, and erroneous boundary points are removed. From the detected cortical boundaries, cortical cross-sectional area and thickness are computed. The method was evaluated on cortical bone specimens and human volunteers on the basis of high-resolution images acquired at a 1.5-Tesla field strength. To assess whether the method is sensitive to detect the expected dependencies of cortical parameters in weight-bearing bone on overall habitus, 10 women aged 46-73 years (mean age, 56 years) underwent the cortical imaging protocol in the proximal femur, and results were compared with DXA bone mineral density parameters of the hip and spine. RESULTS: Reproducibility was approximately 2%. Double oblique images of the femoral neck in the 10 women studied showed that cortical cross-sectional area correlated strongly with height (r = 0.88; p = .0008), whereas cortical diameter versus age approached significance (r = 0.61; p = .06). Measurements in specimens of some cortical parameters indicated resolution dependence. However, note that specimen ranking within each parameter remained constant across all resolutions studied. CONCLUSION: Data suggest the new method to be robust and applicable on standard clinical MR scanners at arbitrary anatomic locations to yield clinically meaningful quantitative results.

Absorptiometry, Photon↗
PubMed2001

Development of astrocytes in the mouse hippocampus as tracked by tenascin-C gene expression.

Tenascin-C (TN-C) is an astroglia-derived extracellular matrix protein that has been shown to be an early marker for astroglial precursors in the embryonic mouse brain. This study examined astroglial generation, migration, and differentiation in the developing mouse hippocampus by in situ hybridization histochemistry for TN-C mRNA. Special reference was given to the difference in the mode of astroglial development between the two cortical structures of the hippocampus: the dentate gyrus and Ammon's horn. TN-C-positive cells were found in the ventricular germinative zone of the hippocampus as early as the 15th gestational day, and the labeled cells in the zone apposed to the fimbria migrated tangentially through the subpial area towards the forming dentate gyrus. The TN-C-positive cells aligned in the dentate gyrus exhibited the characteristic morphology of unipolar astrocytes as revealed by double labeling with glial fibrillary acidic protein (GFAP)-immunohistochemistry. On the other hand, the TN-C-positive cells ranging over a wide area of the ventricular germinative zone facing the forming Ammon's horn migrated radially towards the cortex, with most of them aligned in the Ammon's horn exhibiting a GFAP-positive stellate morphology. The onset of migration towards the dentate gyrus was two days earlier than that towards the Ammon's horn. TN-C-positive cells in both cortical structures exhibited a DNA-replicating activity after settlement in the early postnatal stage and were considered to further generate astrocytes. On the other hand, TN-C-positive cells with DNA-replicating activity were also found in the subpial migratory stream moving towards the dentate gyrus and were considered to form the subpial matrix for the generation of the dentate astrocytes. Migratory TN-C-positive cells directed towards both the dentate gyrus and Ammon's horn were apposed to radial glial processes and were believed to be guided by contact with these processes in a manner similar to migratory immature neurons. These findings indicate that TN-C-positive cells for the dentate gyrus and those for the Ammon's horn have different migratory patterns and undergo different morphological differentiations depending on their site of origin at the early stage of astrogliogenesis and corresponding to the different modes of neurogenesis in the two cortical structures.

Animals↗
PubMedDate not supplied

[Structurization of cortical layer of loach yolk cell after wounding as a "minimal" model of morphogenesis].

Structural rearrangements of the yolk cell surface were studied in loach embryos using SEM and TEM, which take place within 30 min after a point-like puncture at the late blastula stage. The effects of sucking off or addition of a part of yolk, lowered temperature, and absence of Ca2+ on structurization were studied. Around the area of puncture, the yolk granules were submerged, the number of vesicles increased, and numerous membrane folds were formed. The folds were aggregated to form two sharply distinct types of structures: a group of rounded evaginations around the site of puncture and a system of radial folds in the periphery. Small radial folds are aggregated in radial strands, several dozens folds in each. Sucking off a part of yolk accelerated the above processes, while addition of yolk, cooling, and absence of Ca2+ in the incubation medium slowed down or suppressed these processes. The observed structurization can be considered as self-organization at the level of the yolk cell cortical level, largely similar to that during normal morphogenesis at the level of multicellular sheets. Hence, the membrane dynamics in the yolk cell wall after its damage can be considered as one of simplified ("minimal") models of morphogenesis. A study of this model makes it possible to narrow down the circle of factors essential for self-organization of morphogenetic processes.

Animals↗
PubMed1955

The fine structure of cortical components of Paramecium multimicronucleatum.

The electron microscope was used to study the structure and three dimensional relationships of the components of the body cortex in thin sections of Paramecium multimicronucleatum. Micrographs of sections show that the cortex is covered externally by two closely apposed membranes (together approximately 250 A thick) constituting the pellicle. Beneath the pellicle the surface of the animal is molded into ridges that form a polygonal ridgework with depressed centers. It is these ridges that give the surface of the organism its characteristic configuration and correspond to the outer fibrillar system of the light microscope image. The outer ends of the trichocysts with their hood-shaped caps are located in the centers of the anterior and posterior ridges of each polygon. The cilia extend singly from the depressed centers of the surface polygons. Each cilium shows two axial filaments with 9 peripheral and parallel filaments embedded in a matrix and the whole surrouned by a thin ciliary membrane. The 9 peripheral filaments are double and these are evenly spaced in a circle around the central pair. The ciliary membrane is continuous with the outer member of the pellicular membrane, whereas the plasma membrane is continuous with the inner member of the pellicular membrane. At the level of the plasma membrane the proximal end of the cilium is continuous with its tube-shaped basal body or kinetosome. The peripheral filaments of the cilium, together with the material of cortical matrix which tends to condense around them, form the sheath of the basal body. The kinetodesma connecting the ciliary kinetosomes (inner fibrillar system of the light microscopist) is composed of a number of discrete fibrils which overlap in a shingle-like fashion. Each striated kinetosomal fibril originates from a ciliary kinetosome and runs parallel to other kinetosomal fibrils arising from posterior kinetosomes of a particular meridional array. Sections at the level of the ciliary kinetosomes reveal an additional fiber system, the infraciliary lattice system, which is separate and distinct from the kinetodesmal system. This system consists of a fibrous network of irregular polygons and runs roughly parallel to the surface of the animal. Mitochondria have a fine structure similar in general features to that described for a number of mammalian cell types, but different in certain details. The structures corresponding to cristae mitochondriales appear as finger-like projections or microvilli extending into the matrix of the organelle from the inner membrane of the paired mitochondrial membrane. The cortical cytoplasm contains also a particulate component and a system of vesicles respectively comparable to the nucleoprotein particles and to the endoplasmic reticulum described in various metazoan cell types. An accessory kinetosome has been observed in oblique sections of a number of non-dividing specimens slightly removed from the ciliary kinetosome and on the same meridional line as the cilia and trichocysts. Its position corresponds to the location of the kinetosome of the newly formed cilium in animals selected as being in the approaching fission stage of the life cycle.

Animals↗
PubMed2004

Influence of lateral connections on the structure of cortical maps.

Maps of ocular dominance and orientation in primary visual cortex have a highly characteristic structure. The factors that determine this structure are still largely unknown. In particular, it is unclear how short-range excitatory and inhibitory connections between nearby neurons influence structure both within and between maps. Using a generalized version of a well-known computational model of visual cortical map development, we show that the number of excitatory and inhibitory oscillations in this interaction function critically influences map structure. Specifically, we demonstrate that functions that oscillate more than once do not produce maps closely resembling those seen biologically. This strongly suggests that local lateral connections in visual cortex oscillate only once and have the form of a Mexican hat.

Animals↗