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PubMed2005

The coordinated mapping of visual space and response features in visual cortex.

Whether general principles can explain the layouts of cortical maps remains unresolved. In primary visual cortex of ferret, the relationships between the maps of visual space and response features are predicted by a "dimension-reduction" model. The representation of visual space is anisotropic, with the elevation and azimuth axes having different magnification. This anisotropy is reflected in the orientation, ocular dominance, and spatial frequency domains, which are elongated such that their directions of rapid change, or high-gradient axes, are orthogonal to the high-gradient axis of the visual map. The feature maps are also strongly interdependent-their high-gradient regions avoid one another and intersect orthogonally where essential, so that overlap is minimized. Our results demonstrate a clear influence of the visual map on each feature map. In turn, the local representation of visual space is smooth, as predicted when many features are mapped within a cortical area.

Animals↗
PubMed1998

Contribution of GABAergic inhibition to sensitivity to cross-like figures in striate cortex.

Many neurons in the cat primary visual cortex are sensitive to cruciform and corner figures consisting of two oriented lines. To determine the contribution of inhibition to this property we investigated 85 V1 neurons before and after local blockade of GABAergic inhibition by microiontophoretic application of bicuculline. Cross sensitivity was generated or enhanced by inhibition in roughly 1/3 and suppressed or diminished in another 1/3 of the cells. In the remaining 1/3 cross sensitivity was either absent or not influenced by inhibition. The results demonstrate a substantial contribution of intracortical inhibition to either establish sharp single bar orientation tuning or to generate or modulate the sensitivity of visual cortical neurons to line crossings.

Animals↗
PubMed2001

Dissociating the neural mechanisms of visual attention in change detection using functional MRI.

We investigated using functional magnetic resonance imaging (fMRI) the neural processes associated with performance of a change-detection task. In this task, two versions of the same picture are presented in alternation, separated by a brief mask interval. Even when the two pictures greatly differ (e.g., as when a building is in different locations), subjects report that identification of the change is difficult and often take 30 or more seconds to identify the change. This phenomenon of "change blindness" provides a powerful and novel paradigm for segregating components of visual attention using fMRI that can otherwise be confounded in short-duration tasks. By using a response-contingent event-related analysis technique, we successfully dissociated brain regions associated with different processing components of a visual change-detection task. Activation in the calcarine cortex was associated with task onset, but did not vary with the duration of visual search. In contrast, the pattern of activation in dorsal and ventral visual areas was temporally associated with the duration of visual search. As such, our results support a distinction between brain regions whose activation is modulated by attentional demands of the visual task (extrastriate cortex) and those that are not affected by it (primary visual cortex). A second network of areas including central sulcus, insular, and inferior frontal cortical areas, along with the thalamus and basal ganglia, showed phasic activation tied to the execution of responses. Finally, parietal and frontal regions showed systematic deactivations during task performance, consistent with previous reports that these regions may be associated with nontask semantic processing. We conclude that detection of change, when transient visual cues are not present, requires activation of extrastriate visual regions and frontal regions responsible for eye movements. These results suggest that studies of change blindness can inform understanding of more general attentional processing.

Adult↗
PubMed1999

Cortical evoked potentials due to motion contrast in the blind hemifield.

Subcortical visual inputs to motion-selective cortex in primates survive after damage to the primary visual cortex (area 17/V1). Activation of human motion cortex was examined using scalp electrodes in a V1-damaged hemianope. Blind field motion-onset visual evoked potentials (VEPs) shared many of the characteristics associated with sighted vision but were smaller in amplitude and had longer latencies. The representative negative wave (C(II) peak) showed typical dependency on stimulus contrast, its peak latency increased and amplitude decreased as contrast decreased, reflecting the difficulty with which directional information could be detected. VEPs were present at contrasts below 25% when blind field motion was imperceptible even though direction guessing was paradoxically accurate. Subcortical inputs to motion cortex contribute to visual experience but not to conscious perception.

Adult↗
PubMed1992

Differential distribution of parvalbumin-immunoreactive pericellular clusters of terminal boutons in developing and adult monkey neocortex.

Basket cells are GABAergic inhibitory interneurons and known regulators of pyramidal cells, the major class of excitatory neurons in neocortex. Parvalbumin (PV), a calcium binding protein, has been colocalized with GABA in cortical neurons (Celio, 1986. Science 231: 995-998) and has been reported to be present in the terminal boutons of basket neurons forming pericellular clusters in monkey neocortex (Hendry et al. 1989. Exp. Brain Res. 76: 467-472). In this study, we used immunohistochemical methods to evaluate the regional and laminar distributions of PV-immunoreactive (PV-IR) pericellular clusters of terminal boutons in the neocortex of neonatal, infant, adolescent, and adult rhesus monkeys. PV-IR pericellular clusters were composed of labeled terminal boutons that outlined the somata and proximal dendrites of large pyramidal neurons in layers III and V of primary motor cortex, layers V and VI of primary visual cortex, and layer V of visual association cortex (area 18). This laminar pattern was present in neonatal animals and did not change with age in motor cortex. However, in the visual regions of adolescent and adult animals, such PV-IR structures were not detected. PV-positive pericellular clusters were not observed in the prefrontal cortex at any age. The pattern of distribution of PV-containing pericellular clusters paralleled that of a subpopulation of pyramidal neurons containing nonphosphorylated neurofilament proteins (NFP); double labeling studies confirmed that a subgroup of NFP-positive pyramidal neurons were the targets of PV-IR pericellular clusters. The distribution of PV-IR pericellular clusters was compared to that of PV-IR terminal boutons of another class of interneurons, the chandelier cells. Terminal boutons of chandelier neuron axons align in vertical rod-like structures known as cartridges. Subpopulations of chandelier axon cartridges have been previously shown to be PV-IR and their distribution in visual and prefrontal cortices has been described (DeFelipe et al. 1989. Brain Res. 503: 49-54; Lewis and Lund. 1990. J. Comp. Neurol. 293: 599-615). These two types of structures composed of PV-IR terminal boutons tended to be present in different laminae in all regions and ages examined, except in layer III of primary motor cortex where both PV-IR pericellular clusters and chandelier cartridges were found. These findings indicate that in monkey neocortex PV immunoreactivity is present in pericellular clusters of terminal boutons that are likely to arise from basket cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed2004

Neural correlates of internally-generated disgust via autobiographical recall: a functional magnetic resonance imaging investigation.

Converging lines of evidence suggest the involvement of the insula and basal ganglia in the processing of disgust, an important primary emotion that guides the avoidance of potential physical contamination and disease. Prior human lesion and functional brain imaging studies have employed exteroceptive sensory stimuli such as facial expressions of disgust, and disgust-eliciting pictures. Thus, the neural substrates underlying the internal experience of disgust remain unknown. The present fMRI study examined the neural correlates of self-induced disgust aided by the recall and re-experience of personally salient life events. Subjects were scanned while they recalled and re-experienced either a recent situation that evoked intense disgust or a time-matched, equally vivid neutral/non-emotional event. Relative to the emotionally neutral condition, self-induced disgust was associated with activation of the insula, hippocampus, anterior and posterior cingulate cortex, basal ganglia, thalamus, and primary visual cortex. These findings suggest that areas previously associated with the perception of disgust (e.g., insula, basal ganglia) are also involved interoceptive experience of disgust.

Adult↗
PubMed1998

Infracortical interstitial cells concurrently expressing m2-muscarinic receptors, acetylcholinesterase and nicotinamide adenine dinucleotide phosphate-diaphorase in the human and monkey cerebral cortex.

Intense immunoreactivity for the m2-muscarinic receptor was found in a population of interstitial polymorphic neurons embedded within the infracortical white matter and the adjacent deep layers of the cerebral cortex. These infracortical neurons were evenly distributed throughout architectonic subdivisions of the monkey cortex except for parts of primary visual cortex where they were less numerous. A similar set of m2-immunoreactive interstitial cells was also detected in the human lateral temporal neocortex obtained at surgery. Upon electron microscopic examination, they were found to receive unlabelled synaptic inputs and displayed abundant rough endoplasmic reticulum, a prominent nucleolus, and invaginations of the nuclear membrane. Double labelling of m2 immunoreactivity and acetylcholinesterase histochemistry demonstrated that approximately 90% of the m2-positive infracortical cells were acetylcholinesterase-rich in the monkey and human brains. Conversely, the proportion of acetylcholinesterase-rich infracortical neurons that were m2-immunoreactive was over 90% in the monkey and at least 50% in the human. The concurrent visualization of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) enzyme activity with m2 immunoreactivity in the monkey and human brain showed that 85-95% of m2-immunoreactive infracortical cells were NADPH-d positive. Conversely, about 70% of NADPH-d cells contained m2 immunoreactivity. These observations provide the most convincing information to date that many of the acetylcholinesterase-rich neurons located in the infracortical white matter of the cerebral cortex are likely to be cholinoceptive. The expression of NADPH-d by these neurons suggests that they may also provide a relay through which cholinergic innervation, originating predominantly from the nucleus basalis of Meynert, could regulate the release of nitric oxide in the cerebral cortex and subjacent white matter. The degeneration of these neurons may account for at least some of the depletion of m2 receptors that has been reported in Alzheimer's disease.

Acetylcholinesterase↗
PubMed1999

Cross-modal reorganization of callosal connectivity without altering thalamocortical projections.

Mammalian cerebral cortex is composed of a multitude of different areas that are each specialized for a unique purpose. It is unclear whether the activity pattern and modality of sensory inputs to cortex play an important role in the development of cortical regionalization. The modality of sensory inputs to cerebral cortex can be altered experimentally. Neonatal diversion of retinal axons to the auditory thalamus (cross-modal rewiring) results in a primary auditory cortex (AI) that resembles the primary visual cortex in its visual response properties and topography. Functional reorganization could occur because the visual inputs use existing circuitry in AI, or because the early visual inputs promote changes in AI's circuitry that make it capable of constructing visual receptive field properties. The present study begins to distinguish between these possibilities by exploring whether the callosal connectivity of AI is altered by early visual experience. Here we show that early visual inputs to auditory thalamus can reorganize callosal connections in auditory cortex, causing both a reduction in their extent and a reorganization of the pattern. This result is distinctly different from that in deafened animals, which have widespread callosal connections, as in early postnatal development. Thus, profound changes in cortical circuitry can result simply from a change in the modality of afferent input. Similar changes may underlie cortical compensatory processes in deaf and blind humans.

Afferent Pathways↗
PubMed1990

Organization of local axon collaterals of efferent projection neurons in rat visual cortex.

We have studied the laminar origins of local long-range connections within rat primary visual cortex (area 17), by using retrograde tracing of nerve cell bodies with fluorescent markers. Injections throughout the thickness of cortex produce distinct laminar labeling patterns which indicate that a substantial number of cells in layers 2/3, 5, and 6 have wide local axon collateral arbors, while the local arbors of layer 4 cells are much narrower. Double labeling experiments which combined area 17 injections with injections into different projection targets of area 17 (opposite area 17, area 18a, and area 18b) show that many cortico-cortically projecting cells make widespread projections within area 17. In contrast, the overwhelming majority of subcortically projecting cells have narrow collateral arbors within area 17. Anterograde tracing of local projections within areas 17 with the lectin Phaseolus vulgaris leucoagglutinin shows an extensive system of horizontally running fibers which terminate in distinct 0.15-0.25 mm wide clusters up to 1.8 mm from the injection site. On horizontal sections the termination pattern resembles a closely spaced lattice. The results indicate that cortico-cortically projecting cells provide for long-range interactions between distant points of the visuotopic map, while subcortically projecting cells mediate information within a cortical column. Interestingly, subcortically projecting cells differ functionally from cortico-cortically projecting cells in that they are not orientation selective (Klein et al., Neurosci. 17:57-78, '86; Mangini and Pearlman, J. Comp. Neurol. 193:203-222, '80; Simmons and Pearlman, J. Neurophysiol. 50:838-848, '83). We therefore suggest that cortico-cortically projecting cells with wide collateral arbors are orientation selective and that clustered long-range projections within area 17 connect columns with similar functional specificity.

Animals↗
PubMed2005

Activity-dependent expression of occ1 in excitatory neurons is a characteristic feature of the primate visual cortex.

occ1 is a gene whose expression is particularly abundant in neurons in the macaque primary visual cortex (V1). In the present study, we report that the expression of occ1 mRNA in the macaque neocortex can be classified into two modes. The first mode is associated with excitatory neurons distributed in the major thalamocortical recipient layers that exhibit strong cytochrome oxidase activity. This is highly prominent in V1. The second mode is associated with parvalbumin-positive GABAergic interneurons and is distributed across the macaque neocortex. In V1, monocular deprivation showed that occ1 mRNA expression in excitatory neurons was markedly dependent on afferent activity, whereas that in GABAergic interneurons was not. Cross-species comparison showed specific differences in expression. In marmosets, a strong expression was observed in V1 similarly to macaques. The occ1 mRNA expression, however, was generally weak in the mouse neocortex. In rabbit and ferret cortices, the strong expression was observed only in GABAergic interneurons. We conclude that activity-dependent occ1 mRNA expression in the excitatory neurons of V1 was caused by a novel mechanism acquired by primates after their separation from other lineages.

Action Potentials↗
PubMed2005

Functional organization of visual cortex in the prosimian bush baby revealed by optical imaging of intrinsic signals.

Cells in primary visual cortex (V1) of primates and carnivores respond most strongly to a visual stimulus presented to one eye, in a particular visual field location, and at a particular orientation. Each of these stimulus attributes is mapped across the cortical surface, and, in macaque monkeys and cats, strong geometrical relationships exist between these feature maps. In macaque V1 and V2, correlations between feature maps and cytochrome oxidase (CO)-rich modules have also been observed. To see if such relationships reflect a conserved principle of V1 functional architecture among primate species, we examined these maps in the prosimian bush baby, a species that has been proposed to represent the ancestral primate organization. We found that the layout of individual feature maps in bush baby V1 is similar to that of other primates, but we found an entirely different organization of orientation preference in bush baby V2 compared with that reported in simian primates. Another striking distinction between bush baby and simian species is that we observed no strong relationships among maps of orientation, ocular dominance, and CO blobs in V1. Thus our findings suggest that precise relationships between feature maps are not a common element of the functional organization in all primates and that such relationships are not necessary for achieving basic coverage of stimulus feature combinations. In addition, our results suggest that specific relationships between feature maps in V1, and the subdivision of V2 into functional compartments, may have arisen comparatively late in the evolution of primates.

Animals↗
PubMed1995

Intrauterine cocaine exposure of rabbits: persistent elevation of GABA-immunoreactive neurons in anterior cingulate cortex but not visual cortex.

The effects of prenatal cocaine exposure on the development of the rabbit cerebral cortex were studied. Two cortical areas were compared: primary visual cortex (VC) and anterior cingulate cortex (ACC). ACC was selected because behavioral deficits observed in cocaine-exposed infants suggest the involvement of ACC. In addition, ACC receives dense dopaminergic innervation and cocaine's action in inhibiting the re-uptake of dopamine is believed to underly the rewarding properties of cocaine. VC was selected as a control area because there is no evidence of behavioral deficits associated with visual perception in cocaine-exposed infants, and because VC receives minimal dopaminergic innervation. Two aspects of cortical development were studied: (i) cortical morphology, growth and cytoarchitectonic organization; and (ii) the development of the GABAergic neurotransmitter system. Measures of postnatal cortical growth, including cortical lamination, cell number and soma size, were compared in cocaine-exposed or control (saline) rabbits aged P5-P60. There was no difference between cocaine and saline animals in any of these parameters, and cortical cytoarchitecture appeared normal. However, despite the absence of major abnormalities in cortical development, we found that the number of GABA-immunoreactive neurons in cocaine-exposed animals was significantly higher than normal in ACC. This effect was highly consistent, was present in all laminae and at all ages studied, and persisted into maturity (P60). In contrast, in VC, the number of GABA-immunoreactive neurons in cocaine-exposed animals did not differ from normal. We suggest that increased GABA immunoreactivity may reflect a compensatory response to excessive excitatory input to ACC. A change in the balance of excitation and inhibition in ACC, reflecting 'noisy' or dysfunctional intracortical circuitry, may underly the emotional lability and attentional deficits characteristically described in infants exposed in utero to cocaine.

Animals↗
PubMedDate not supplied

Laminar, tangential and regional organization of the noradrenergic innervation of monkey cortex: dopamine-beta-hydroxylase immunohistochemistry.

An antiserum directed against human dopamine-beta-hydroxylase purified from pheochromocytoma tissue was employed in an immunohistochemical study of the organization of the noradrenergic innervation of monkey neocortex. A detailed description is given of the laminar pattern of noradrenergic innervation in the dorsolateral prefrontal cortex (Brodmann areas 9 and 10) and the primary somatosensory cortex of the postcentral gyrus (Brodmann areas 3,1,2). The noradrenergic innervation of these two regions is similar in the following respects: (1) fibers are present in all six layers, (2) the innervation is dense and terminal-like in layers IV and V, and (3) layer VI is characterized by fibers oriented parallel to the pial surface which follow the contours of the subcortical white matter. However, these regions differ with respect to specific laminar patterns of fiber distribution and orientation and by virtue of the fact that the primary somatosensory cortex has a very dense noradrenergic innervation, while the density of innervation in dorsolateral prefrontal cortex is low relative to the postcentral gyrus and most other neocortical areas. The laminar pattern of noradrenergic innervation in primary visual cortex differs fundamentally from both prefrontal and primary somatosensory cortices. In a separate series of experiments, dorsolateral frontal cortex lesions were used to investigate the intracortical trajectory of noradrenergic fibers. A discrete aspiration lesion confined to the grey matter of the prefrontal cortex led to a substantial loss of noradrenergic fibers in cortical regions caudal to the lesion. The decrease in density of noradrenergic innervation was particularly pronounced in the pre- and postcentral gyri. These results demonstrate that while the noradrenergic innervation of primate cortex exhibits a far greater degree of regional variation than is present in the rat cortex, the tangential intracortical trajectory that is characteristic of the lissencephalic rat brain is also a dominant feature of the noradrenergic innervation of the gyrencephalic primate brain.

Adrenergic Fibers↗
PubMed1988

The development of orientation and direction selectivity in the rabbit visual cortex.

The postnatal development of orientation and direction selectivity of single cells was examined in the primary visual cortex of rabbits. The percentage of cells which were orientation-selective reached adult levels by day 30, whereas the proportion of cells which were direction-selective did not reach adult levels until day 60. Differences in the time course of development of orientation and direction selectivity, together with data previously reported on differences in the effects of deprivation on orientation and direction selectivity, suggest that (1) different mechanisms underly the organization of orientation and direction selectivity and (2) the critical periods for the effects of deprivation on orientation and direction selectivity reflect the different time course of the normal development of these two response properties.

Aging↗
PubMed1999

Dendritic asymmetry cannot account for directional responses of neurons in visual cortex.

A simple model was proposed to account for the direction selectivity of neurons in the primary visual cortex, area V1. In this model, the temporal asymmetries in the summation of inhibition and excitation that produce directionality were generated by structural asymmetries in the tangential organization of the basal dendritic tree of cortical neurons. We reconstructed dendritic trees of neurons with known direction preferences and found no correlation between the small biases of a neuron's dendritic morphology and its direction preference. Detailed simulations indicated that even when the electrotonic asymmetries in the dendrites were extreme, as in cortical Meynert cells, the biophysical properties of single neurons could contribute only partially to the directionality of cortical neurons.

Animals↗
PubMed1999

Anatomical correlates of functional plasticity in mouse visual cortex.

Much of what is known about activity-dependent plasticity comes from studies of the primary visual cortex and its inputs in higher mammals, but the molecular bases remain largely unknown. Similar functional plasticity takes place during a critical period in the visual cortex of the mouse, an animal in which genetic experiments can readily be performed to investigate the underlying molecular and cellular events. The experiments of this paper were directed toward understanding whether anatomical changes accompany functional plasticity in the developing visual cortex of the mouse, as they do in higher mammals. In normal mice, transneuronal label after an eye injection clearly delineated the monocular and binocular zones of area 17. Intrinsic signal optical imaging also showed monocular and binocular zones of area 17 but revealed no finer organization of ocular dominance or orientation selectivity. In normal animals, single geniculocortical afferents serving the contralateral eye showed great heterogeneity and no clustering consistent with the presence of ocular dominance patches. Growth and elaboration of terminal arbor continues beyond postnatal day 40 (P40), after the peak of the critical period. After prolonged monocular deprivation (MD) from P20 to P60, transneuronal labeling showed that the projection serving the ipsilateral eye was severely affected, whereas the effect on the contralateral eye's pathway was inconsistent. Optical imaging also showed profound effects of deprivation, particularly in the ipsilateral pathway, and microelectrode studies confirmed continued functional plasticity past P40. Reconstruction of single afferents showed that MD from P20 to P40 promoted the growth of the open eye's geniculocortical connections without causing the closed eye's contralateral projection to shrink, whereas MD from P20 to P60 caused an arrest of growth of deprived arbors. Our findings reveal numerous similarities between mouse and higher mammals in development and plasticity, along with some differences. We discuss the factors that may be responsible for these differences.

Afferent Pathways↗
PubMed1990

[The dynamics of the orientation adjustment of the neurons in the cat visual cortex under the action of sombrevin].

The dynamics of orientation tuning of 59 neurons in the primary visual cortex of cat was studied by the method of temporal slices before and after narcotization by sombrevine. It was found that in 2/3 of neurons a dynamic shift of the preferred orientation (from 22 up to 157 degrees) was observed during their response. After injection of sombrevine this shift reliably diminished in 45% of neurons, in some cases up to its complete disappearance, while in 30% of cases this shift increased. Differences in dynamics of orientation tuning under narcosis in two groups of units, as well as the mechanisms of the effect are discussed.

Animals↗
PubMed1988

[Temporal correlations and coding of information in the visual cortex of the cat].

We have observed repeated patterns in evoked spike trains recorded from the primary visual cortex of the cat. These patterns are called "triplets" and "ghost doublets". Triplets are groups of three pulses, that may or may not be adjacent to one other, the mutual intervals of which are replicated in one other group of three spikes with a precision higher than 0.15 ms. Ghost doublets are doublets of pulses whose interval replicates, with the above precision, one of the intervals of the repeated triplets and are also present in the record. In one of the 9 recorded cells, in which pulses were clearly emitted in bursts in phase with the drifting of the sinusoidal grating used as a stimulus, we could show that local temporal correlations in the form of replicating triplets and ghost doublets correspond very precisely to the temporal phase of the grating: the study of the distance between triplets, or between triplets and ghost doublets, gives a remarkably precise value of the time frequency of the grating.

Animals↗