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At least 19 recordsLinked to original sources
PubMed1993

Cortical hierarchy reflected in the organization of intrinsic connections in macaque monkey visual cortex.

Neuronal response properties vary markedly at increasing levels of the cortical hierarchy. At present it is unclear how these variations are reflected in the organization of the intrinsic cortical circuitry. Here we analyze patterns of intrinsic horizontal connections at different hierarchical levels in the visual cortex of the macaque monkey. The connections were studied in tangential sections of flattened cortices, which were injected with the anterograde tracer biocytin. We directly compared the organization of connections in four cortical areas representing four different levels in the cortical hierarchy. The areas were visual areas 1, 2, 4 and Brodman's area 7a (V1, V2, V4 and 7a, respectively). In all areas studied, injections labeled numerous horizontally coursing axons that formed dense halos around the injection sites. Further away, the fibers tended to form separate clusters. Many fibers could be traced along the way from the injection sites to the target clusters. At progressively higher order areas, there was a striking increase in the spread of intrinsic connections: from a measured distance of 2.1 mm in area V1 to 9.0 mm in area 7a. Average interpatch distance also increased from 0.61 mm in area V1 to 1.56 mm in area 7a. In contrast, patch size changed far less at higher order areas, from an average width of 230 micron(s) in area V1 to 310 micron(s) in area 7a. Analysis of synaptic bouton distribution along axons revealed that average interbouton distance remained constant at 6.4 micron(s) (median) in and out of the clusters and in the different cortical areas. Larger injections resulted in a marked increase in the number of labeled patches but only a minor increase in the spread of connections or in patch size. Thus, in line with the more global computational roles proposed for the higher order visual areas, the spread of intrinsic connections is increased with the hierarchy level. On the other hand, the clustered organization of the connections is preserved at higher order areas. These clusters may reflect the existence of cortical modules having blob-like dimensions throughout macaque monkey visual cortex.

Animals↗
PubMed1983

The connections of the middle temporal visual area (MT) and their relationship to a cortical hierarchy in the macaque monkey.

The cortical and subcortical connections of the middle temporal visual area (MT) of the macaque monkey were investigated using combined injections of [3H]proline and horseradish peroxidase within MT. Cortical connections were assigned to specific visual areas on the basis of their relationship to the pattern of interhemispheric connections, revealed by staining for degeneration following callosal transection. MT was shown to be reciprocally connected with many topographically organized cortical visual areas, including V1, V2, V3, and V4. These pathways link regions representing corresponding portions of the visual field in the different areas. In addition, MT has reciprocal connections with two previously unidentified cortical areas, which we have designated the medial superior temporal area (MST) and the ventral intraparietal area (VIP). The laminar distribution of terminals and cell bodies in cortical areas connected with MT follows a consistent pattern. In areas V1, V2, and V3, the projections to MT arise largely or exclusively from cells in supragranular layers, and the reciprocal connections from MT terminate mainly in supragranular and infragranular layers. In contrast, the projections to MST and VIP terminate mainly in layer IV, and the reciprocal pathways originate from cells in both superficial and deep layers. On the basis of this pattern, each connection can be designated as forward or feedback in nature, and a hierarchical arrangement of visual areas can be determined. In this hierarchy, MT is at a higher level than V1, V2, and V3, and at a lower level than MST and VIP. Subcortical projections were seen from MT to the claustrum, the putamen, the caudate nucleus, the inferior and lateral subdivisions of the pulvinar complex, the ventral lateral geniculate nucleus, the reticular nucleus of the thalamus, the superior colliculus, and the pontine nuclei.

Animals↗
PubMed2026

Alternative splicing in layer 3 pyramidal neurons differs across regions of the human cortical hierarchy.

The primate neocortex is organized as hierarchical networks of functionally distinct regions. In the dorsal visual stream network, information is conveyed from primary visual (V1) to posterior parietal (PPC) and dorsolateral prefrontal (DLPFC) cortices. This information transfer is mediated primarily by layer 3 pyramidal neurons (L3PNs), which differ across these regions in morphology, excitability, and intracellular Ca2+ regulation. These region-specific L3PN properties may be influenced by alternative splicing (AS) of pre-mRNA, which occurs extensively in the human brain. To explore the potential impact of AS of region-specific L3PN properties, we analyzed RNA-seq data from pools of L3PNs dissected from human V1, PPC, and DLPFC. We found that&#x2009;<6% of genes with regional differences in expression also differed in AS. This finding indicates that the absence of transcriptional differences is insufficient to conclude that a gene does not contribute functional differences between regions. Additionally, there were numerous regional differences in AS, particularly between V1 and DLPFC or PPC L3PNs, which involved genes associated with neuron morphology and Ca2+ regulation; >&#x2009;90% of these AS differences involved functionally relevant sequences (eg phosphorylation sites, etc.). These findings suggest AS contributes to region-specific L3PN properties relevant to the function of the dorsal visual stream.

Humans↗
PubMed2006

Combined activation and deactivation of visual cortex during tactile sensory processing.

The involvement of occipital cortex in sensory processing is not restricted solely to the visual modality. Tactile processing has been shown to modulate higher-order visual and multisensory integration areas in sighted as well as visually deprived subjects; however, the extent of involvement of early visual cortical areas remains unclear. To investigate this issue, we employed functional magnetic resonance imaging in normally sighted, briefly blindfolded subjects with well-defined visuotopic borders as they tactually explored and rated raised-dot patterns. Tactile task performance resulted in significant activation in primary visual cortex (V1) and deactivation of extrastriate cortical regions V2, V3, V3A, and hV4 with greater deactivation in dorsal subregions and higher visual areas. These results suggest that tactile processing affects occipital cortex via two distinct pathways: a suppressive top-down pathway descending through the visual cortical hierarchy and an excitatory pathway arising from outside the visual cortical hierarchy that drives area V1 directly.

Adult↗
PubMed2005

Modelling event-related responses in the brain.

The aim of this work was to investigate the mechanisms that shape evoked electroencephalographic (EEG) and magneto-encephalographic (MEG) responses. We used a neuronally plausible model to characterise the dependency of response components on the models parameters. This generative model was a neural mass model of hierarchically arranged areas using three kinds of inter-area connections (forward, backward and lateral). We investigated how responses, at each level of a cortical hierarchy, depended on the strength of connections or coupling. Our strategy was to systematically add connections and examine the responses of each successive architecture. We did this in the context of deterministic responses and then with stochastic spontaneous activity. Our aim was to show, in a simple way, how event-related dynamics depend on extrinsic connectivity. To emphasise the importance of nonlinear interactions, we tried to disambiguate the components of event-related potentials (ERPs) or event-related fields (ERFs) that can be explained by a linear superposition of trial-specific responses and those engendered nonlinearly (e.g., by phase-resetting). Our key conclusions were; (i) when forward connections, mediating bottom-up or extrinsic inputs, are sufficiently strong, nonlinear mechanisms cause a saturation of excitatory interneuron responses. This endows the system with an inherent stability that precludes nondissipative population dynamics. (ii) The duration of evoked transients increases with the hierarchical depth or level of processing. (iii) When backward connections are added, evoked transients become more protracted, exhibiting damped oscillations. These are formally identical to late or endogenous components seen empirically. This suggests that late components are mediated by reentrant dynamics within cortical hierarchies. (iv) Bilateral connections produce similar effects to backward connections but can also mediate zero-lag phase-locking among areas. (v) Finally, with spontaneous activity, ERPs/ERFs can arise from two distinct mechanisms: For low levels of (stimulus related and ongoing) activity, the systems response conforms to a quasi-linear superposition of separable responses to the fixed and stochastic inputs. This is consistent with classical assumptions that motivate trial averaging to suppress spontaneous activity and disclose the ERP/ERF. However, when activity is sufficiently high, there are nonlinear interactions between the fixed and stochastic inputs. This interaction is expressed as a phase-resetting and represents a qualitatively different explanation for the ERP/ERF.

Animals↗
PubMed2001

Cortical substrates of perceptual stability during eye movements.

We are usually unaware of retinal image motion resulting from our own movement. For instance, during slow-tracking eye movements, the world around us remains perceptually stable despite the retinal image slip induced by the eye movement. This example of perceptual invariance is achieved by subtracting an internal reference signal, reflecting the eye movement, from the retinal motion signal. If the two cancel each other, visual structures, which do not move, will also be perceived as nonmoving. If, however, the reference signal is too small or too large, a false eye-movement-induced motion of the external world will be perceived. We have exploited our ability to manipulate the size of the reference signal in an attempt to reveal the structures in visual cortex, encoding the perception of self-induced visual motion rather than the retinal motion signal. Using EEG and lately also MEG recordings in human subjects and single-unit recordings in monkeys, we have been able to show that our ability to perceive the world as stationary despite eye-movement-induced retinal image slip is based on "late" parts of the cortical hierarchy of motion processing, sparing the early stages up to cortical area MT and, among others, involving cortex at the junction between the parietal and temporal lobes close to the parieto-insular-vestibular cortex. Lesions of this network in humans render the visual system unable to compensate for the visual consequences of eye movements, giving rise to severe dizziness, whenever the eyes move smoothly.

Animals↗
PubMed2004

Neuromagnetic activity in medial parietooccipital cortex reflects the perception of visual motion during eye movements.

We usually perceive a stationary, stable world despite coherent visual motion induced by eye movements. This astonishing example of perceptual invariance results from a comparison of visual information with internal reference signals (nonretinal signals) predicting the visual consequences of an eye movement. The important consequence of this concept is that our subjective percept of visual motion reflects the outcome of this comparison rather than retinal image slip. To localize the cortical networks underlying this comparison, we compared magnetoencephalography (MEG) responses under two conditions of pursuit-induced retinal image motion, which were identical physically but--due to different calibrational states of the nonretinal signal prompted under our experimental conditions--gave rise to different percepts of visual motion. This approach allows us to demonstrate that our perception of self-induced visual motion resides in comparably "late" parts of the cortical hierarchy of motion processing sparing the early stages up to cortical area MT/V5 but including cortex in and around the medial aspect of the parietooccipital cortex as one of its core elements.

Attention↗
PubMed1999

Decision-related activity in the macaque dorsal visual pathway.

Brain areas at higher levels of cortical organization are thought to be more involved in decision processes than are earlier, i.e. lower, sensory areas. Hence, neuronal activity correlated with decisions should vary with an area's position in the cortical hierarchy. To test this proposal, we investigated whether a change in neuronal activity during error trials depends in a systematic way on cortical hierarchical position. While macaque monkeys discriminated the direction of moving visual stimuli, the activity of direction-selective neurons was recorded in four extrastriate visual areas: V3A, the middle temporal area, the middle superior temporal area and the posterior part of the superior temporal polysensory area. Neuronal activity was significantly reduced in all areas when the monkeys made errors in judging the direction of stimuli moving in the preferred direction with low and intermediate luminance contrast. The amount of activity reduction was approximately 50% in all of the visual areas. Thus, the activity on error trials is reduced in early visual processing, independent of the hierarchy in the dorsal visual pathway. The activity reduction depended on stimulus contrast and the direction of the decision relative to the stimulus motion. It was profound and significant in all areas at low stimulus contrast. However, it was nonsignificant at high stimulus contrast. Our data suggest that activity reduction on error trials is due to lack of attention in association with stimulus expectation.

Animals↗
PubMed2006

Macaque V2 neurons, but not V1 neurons, show choice-related activity.

In the macaque extrastriate cortex, robust correlations between perceptual choice and neuronal response have been demonstrated, frequently quantified as choice probabilities (CPs). Such correlations are modest in early visual cortex, suggesting that CPs may depend on the position of a neuron in the hierarchy of visual processing. However, previous studies have not compared neurons with similar precision in equivalent tasks. We investigated the role of cortical hierarchy on CP using a task for which significant CPs have been described previously for middle temporal area (MT). We measured CPs in disparity-selective neurons from both V1 and V2. The stimulus was a dynamic random dot stereogram, presented with a near or a far disparity, masked by varying numbers of binocularly uncorrelated dots. Two macaque monkeys reported whether they perceived a circular patch in front or behind a surrounding annulus in a forced choice task. For V2 (n = 69), CP was on average 0.56, the first demonstration of systematic CPs in a visual area as early as V2. In V1 (n = 74), average CP was at chance level (0.51). The pattern was similar in a subgroup of neurons selected such that the statistical precision in the task was on average identical to that reported for MT (mean CP, 0.51 for V1, n = 33; 0.58 for V2, n = 54). This difference between V1 and V2 could not be explained by eye movements, stimulus size relative to the receptive field, or differences in disparity tuning. Rather, it seems to reflect a functional difference (at least in disparity processing) between striate and extrastriate cortex.

Action Potentials↗
PubMed2003

Auditory cortical neurons respond to somatosensory stimulation.

The prevailing hierarchical model of cortical sensory processing holds that early processing is specific to individual modalities and that combination of information from different modalities is deferred until higher-order stages of processing. In this paper, we present physiological evidence of multisensory convergence at an early stage of cortical auditory processing. We used multi-neuron cluster recordings, along with a limited sample of single-unit recordings, to determine whether neurons in the macaque auditory cortex respond to cutaneous stimulation. We found coextensive cutaneous and auditory responses in caudomedial auditory cortex, an area lying adjacent to A1, and at the second stage of the auditory cortical hierarchy. Somatosensory-auditory convergence in auditory cortex may underlie effects observed in human studies. Convergence of inputs from different sensory modalities at very early stages of cortical sensory processing has important implications for both our developing understanding of multisensory processing and established views of unisensory processing.

Acoustic Stimulation↗
PubMed2006

Normal and abnormal fMRI activation patterns in the visual cortex after recovery from optic neuritis.

Recovery to normal or near normal visual acuity after an optic neuritis episode is common, despite frequent persistence of conduction abnormalities, evident in prolonged visual evoked potential (VEP) latencies. Improvement of visual function is commonly attributed to peripheral nerve recovery. However, central reorganization processes may also be involved. To assess this, we compared the patterns of fMRI activation, elicited by stimulation of the affected and the normal eye, along the visual cortical hierarchy. Activation was assessed in 8 subjects, which recovered clinically from an episode of optic neuritis but still had prolonged VEP latencies. In all patients, reduced fMRI activation was seen in V1 during stimulation of the affected eye, compared to the normal eye. The fMRI signal difference decreased in magnitude with progression along the visual hierarchy, and in some regions within the lateral occipital complex even showed the opposite preference (for the affected eye). These results may indicate a built-in robustness of the object-related areas to disruption of the visual input. Alternatively, it could reflect an adaptive functional reorganization of the cortical response to an abnormal input.

Adult↗
PubMed2006

Seeing invisible motion: a human FMRI study.

A common view about visual consciousness is that it could arise when and where activity reaches some higher level of processing along the cortical hierarchy. Reports showing that activity in striate cortex can be dissociated from awareness , whereas the latter modulates activity in higher areas , point in this direction. In the specific case of visual motion, a central, "perceptual" role has been assigned to area V5: several human and monkey studies have shown V5 activity to correlate with the motion percept. Here we show that activity in this and other higher cortical areas can be also dissociated from perception and follow the physical stimulus instead. The motion information in a peripheral grating modulated fMRI responses, despite being invisible to human volunteers: under crowding conditions , areas V3A, V5, and parietal cortex still showed increased activity when the grating was moving compared to when it was flickering. We conclude that stimulus-specific activation of higher cortical areas does not necessarily result in awareness of the underlying stimulus.

Adult↗
PubMed1990

Pathways for motion analysis: cortical connections of the medial superior temporal and fundus of the superior temporal visual areas in the macaque.

To identify the cortical connections of the medial superior temporal (MST) and fundus of the superior temporal (FST) visual areas in the extrastriate cortex of the macaque, we injected multiple tracers, both anterograde and retrograde, in each of seven macaques under physiological control. We found that, in addition to connections with each other, both MST and FST have widespread connections with visual and polysensory areas in posterior prestriate, parietal, temporal, and frontal cortex. In prestriate cortex, both areas have connections with area V3A. MST alone has connections with the far peripheral field representations of V1 and V2, the parieto-occipital (PO) visual area, and the dorsal prelunate area (DP), whereas FST alone has connections with area V4 and the dorsal portion of area V3. Within the caudal superior temporal sulcus, both areas have extensive connections with the middle temporal area (MT), MST alone has connections with area PP, and FST alone has connections with area V4t. In the rostral superior temporal sulcus, both areas have extensive connections with the superior temporal polysensory area (STP) in the upper bank of the sulcus and with area IPa in the sulcal floor. FST also has connections with the cortex in the lower bank of the sulcus, involving area TEa. In the parietal cortex, both the central field representation of MST and FST have connections with the ventral intraparietal (VIP) and lateral intraparietal (LIP) areas, whereas MST alone has connections with the inferior parietal gyrus. In the temporal cortex, the central field representation of MST as well as FST has connections with visual area TEO and cytoarchitectonic area TF. In the frontal cortex, both MST and FST have connections with the frontal eye field. On the basis of the laminar pattern of anterograde and retrograde label, it was possible to classify connections as forward, backward, or intermediate and thereby place visual areas into a cortical hierarchy. In general, MST and FST receive forward inputs from prestriate visual areas, have intermediate connections with parietal areas, and project forward to the frontal eye field and areas in the rostral superior temporal sulcus. Because of the strong inputs to MST and FST from area MT, an area known to play a role in the analysis of visual motion, and because MST and FST themselves have high proportions of directionally selective cells, they appear to be important stations in a cortical motion processing system.

Animals↗
PubMed2002

Beyond phrenology: what can neuroimaging tell us about distributed circuitry?

Unsupervised models of how the brain identifies and categorizes the causes of its sensory input can be divided into two classes: those that minimize the mutual information (i.e., redundancy) among evoked responses and those that minimize the prediction error. Although these models have the same goal, the way that goal is attained, and the functional architectures required, are fundamentally different. This review describes the differences, in the functional anatomy of sensory cortical hierarchies, implied by the two models. We then consider how neuroimaging can be used to disambiguate between them. The key distinction reduces to whether backward connections are employed by the brain to generate a prediction of sensory inputs. To ascertain whether backward influences are evident empirically requires a characterization of functional integration among brain systems. This review summarizes the approaches to measuring functional integration in terms of effective connectivity and proceeds to address the question posed by the theoretical considerations. In short, it will be shown that the conjoint manipulation of bottom-up and top-down inputs to an area can be used to test for interactions between them, in elaborating cortical responses. The conclusion, from these sorts of neuroimaging studies, points to the prevalence of top-down influences and the plausibility of generative models of sensory brain function.

Animals↗
PubMed2002

Functional integration and inference in the brain.

Self-supervised models of how the brain represents and categorises the causes of its sensory input can be divided into two classes: those that minimise the mutual information (i.e. redundancy) among evoked responses and those that minimise the prediction error. Although these models have similar goals, the way they are attained, and the functional architectures employed, can be fundamentally different. This review describes the two classes of models and their implications for the functional anatomy of sensory cortical hierarchies in the brain. We then consider how empirical evidence can be used to disambiguate between architectures that are sufficient for perceptual learning and synthesis. Most models of representational learning require prior assumptions about the distribution of sensory causes. Using the notion of empirical Bayes, we show that these assumptions are not necessary and that priors can be learned in a hierarchical context. Furthermore, we try to show that learning can be implemented in a biologically plausible way. The main point made in this review is that backward connections, mediating internal or generative models of how sensory inputs are caused, are essential if the process generating inputs cannot be inverted. Because these processes are dynamical in nature, sensory inputs correspond to a non-invertible nonlinear convolution of causes. This enforces an explicit parameterisation of generative models (i.e. backward connections) to enable approximate recognition and suggests that feedforward architectures, on their own, are not sufficient. Moreover, nonlinearities in generative models, that induce a dependence on backward connections, require these connections to be modulatory; so that estimated causes in higher cortical levels can interact to predict responses in lower levels. This is important in relation to functional asymmetries in forward and backward connections that have been demonstrated empirically. To ascertain whether backward influences are expressed functionally requires measurements of functional integration among brain systems. This review summarises approaches to integration in terms of effective connectivity and proceeds to address the question posed by the theoretical considerations above. In short, it will be shown that functional neuroimaging can be used to test for interactions between bottom-up and top-down inputs to an area. The conclusion of these studies points toward the prevalence of top-down influences and the plausibility of generative models of sensory brain function.

Animals↗
PubMed1988

Connections of area 8 with area 6 in the brain of the macaque monkey.

The corticocortical connections between the arcuate area (Walker's areas 8A and 45 or Brodmann's area 8) and the premotor and supplementary motor areas (Vogts' area 6) in the brain of the macaque monkey were studied microscopically with wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP), which was injected into Brodmann's area 8 primarily to elucidate the projections of area 8 into area 6. In addition, in the same material, the pattern of connections between the arcuate area and area 46 of the prefrontal cortex was studied. On the basis of the findings of the present study, an anatomical cortical hierarchy for areas 8, 6, and 46 is discussed. Anterogradely labeled axon terminals and retrogradely labeled cells appeared in the premotor area, in the supplementary motor area, and in area 46 on the side of injection; sites containing labeled axon terminals also contained labeled cells. In other words, the examined connections were reciprocal. In the labeled areas, labeled terminals and cells coexisted, and most formed radial columns. However, no labeling of cells and terminals was seen in the motor area (Brodmann's area 4). After injection of WGA-HRP into area 8A, labeled terminals and cells appeared predominantly in the superior premotor area (a region of the premotor area above the arcuate spur, Vogt and Vogt's upper areas 6a alpha and 6a beta), forming one, two, or three bands of label in the anteroposterior direction, whereas labeling occurred to a lesser extent in the inferior premotor area (a region of the premotor area below the arcuate spur, Vogt and Vogt's areas 4c, lower 6a alpha and 6b). In contrast, injection of WGA-HRP into area 45 resulted in the predominant labeling of the inferior premotor area with scant labeling in the superior premotor area. In the premotor area, labeled terminals were distributed over the entire cortical depth, although few were found in the lower half of layer III, and labeled cells were distributed mainly in layer III. In area 46 of the banks of the principal sulcus in the prefrontal cortex, labeled terminals were distributed in all cortical layers or over the entire cortical depth with a lower concentration in layer IV; labeled cells were found mostly in layers III and V, with a relatively high density in layer V.

Animals↗
PubMed1996

Microcircuitry of forward and feedback connections within rat visual cortex.

Visual cortex in mammals is composed of many distinct areas that are linked by reciprocal connections to form a multilevel hierarchy. Ascending information is sent via forward connections from lower to higher areas and is thought to contribute to the emergence of increasingly complex receptive field properties at higher levels. Descending signals are transmitted via feedback connections from higher to lower areas and are believed to provide information about the context in which a stimulus appears, to contribute to modulation of visual responses by attention, and to play a role in memory processes. To determine whether forward and feedback pathways in rat visual cortex constitute distinct intracortical circuits, we have studied the distribution of reciprocal corticocortical inputs to pyramidal cells and gamma-aminobutyric acid (GABA)ergic interneurons. For this purpose, we chose forward and feedback connections between primary visual cortex and the secondary extrastriate lateromedial (LM) area as a model system. Pathways were traced with the axonal marker phaseolus vulgaris-leucoagglutinin. Labeled terminals were identified in the electron microscope, and GABA immunocytochemistry was used to identify the postsynaptic dendritic shafts of GABAergic interneurons. In both pathways, inputs to pyramidal cells were directed preferentially to dendritic spines and not to shafts. In the forward pathway, 90% of labeled inputs were distributed to pyramidal cells and 10% to interneurons. This proportion was similar to that of nearby unlabeled connections in the neuropil, indicating that forward connections are not selective for pyramidal cells or interneurons. In sharp contrast, feedback connections were significantly different from the unlabeled connections and supplied almost exclusively pyramidal cells (98%). Feedback inputs to GABAergic neurons were five times weaker (2%) relative to the forward direction. These structural differences suggest that disynaptic GABAergic inhibition is much stronger in forward than in feedback pathways. Recent physiological experiments have confirmed this prediction (Shao et al. [1995] Soc. Neurosci. Abstr., 21:1274) and we, therefore, conclude that relatively small anatomical differences in the microcircuitry can have important functional consequences. It remains an open question whether generally reciprocal interareal circuits at all levels of the cortical hierarchy are organized in similar fashion.

Animals↗