Cortical hierarchy

A fundamental aspect of human experience is that it is segmented into discrete events, cortical hierarchy. This may be underpinned by transitions between distinct neural states. Using an innovative data-driven state segmentation method, we investigate how neural states are organized cortical hierarchy the cortical hierarchy and where in the cortex neural state boundaries and perceived event boundaries overlap.

Cortical information processing is structurally and functionally organized into hierarchical pathways, with primary sensory cortical regions providing modality specific information and associative cortical regions playing a more integrative role. Historically, there has been debate as to whether primary cortical regions mature earlier than associative cortical regions, or whether both primary and associative cortical regions mature simultaneously. Identifying whether primary and associative cortical regions mature hierarchically or simultaneously will not only deepen our understanding of the mechanisms that regulate brain maturation, but it will also provide fundamental insight into aspects of adolescent behavior, learning, neurodevelopmental disorders and computational models of neural processing. This mini-review article summarizes the current evidence supporting the sequential and hierarchical nature of cortical maturation, and then proposes a new cellular model underlying this process. Finally, unresolved issues associated with hierarchical cortical maturation are also addressed.

Cortical hierarchy

Hierarchical cortical organization is found in all sensory systems, in the reward system, and in the memory systems. Adjacent cortical areas in the hierarchy are connected by strong forward connections, and weaker backprojections which have synapses in cortical layer 1. There is convergence from cortical area to cortical area, in that neurons in a cortical area receive inputs from a limited region topologically of the preceding cortical area. This enables neurons to operate with the number of synapses from the preceding cortical area received by a neuron limited to in the order of 10, synapses. This is a major cortical principle of operation, for if each processing system consisted of only an input and an output cortical area, any neuron in the output area would need to receive the biologically implausible number of tens of millions of synapses to cover the whole space of the input cortical area. The convergence from cortical area to cortical area is such that after approximately at most four areas or stages of cortical processing, the convergence is sufficient to enable a single neuron at the top of the hierarchy to receive input from anywhere in the first cortical area, as illustrated in Fig. A consequence of this connectivity is that within a neocortical area, the computation is local. Consistent with this, the recurrent collaterals of pyramidal cells spread mainly with a region of 1—3 mm, and the inhibitory neurons operate within a similar extent of neocortex. One reason for the number of areas in a hierarchy being limited to approximately a maximum of four is that this keeps the computation time within reasonable limits, of approximately 20 ms per cortical area for the computation and information transmission, which is sufficient for a cortical area to be influenced by its recurrent collaterals and to fall towards a basin of attraction that reflects the previously learned constraints implemented in the strengths of the local recurrent collaterals. Sections B. Topography is often present associated with this connectivity, though in higher cortical areas the maps can become highly fragmented and local as described in Section B. The cortico-cortical backprojections are not sufficiently strong to make neurons at earlier stages in the hierarchy have the same responses as at higher stages. Instead, the cortical backprojections are used for gentle influences on earlier cortical stages, such as top-down attention, and memory recall if there is not a strong bottom-up input. Each cortical hierarchy thus operates computationally with a feedforward style of computation, in which new representations are built at each succeeding stage, in a divide and conquer approach to computation.

Figure 3 visualizes for each voxel which functional network label occurs most frequently for the searchlights overlapping that voxel.

Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Brains are composed of anatomically and functionally distinct regions performing specialized tasks, but regions do not operate in isolation.

Federal government websites often end in. The site is secure. Preview improvements coming to the PMC website in October Learn More or Try it out now. Author contribution. Hierarchy is a major organizational principle of the cortex and underscores modern computational theories of cortical function.

Cortical hierarchy

Federal government websites often end in. The site is secure. Preview improvements coming to the PMC website in October Learn More or Try it out now. Concepts shape the interpretation of facts. However, this concept has been interpreted in many different ways, which are not well aligned. This observation suggests that the concept is ill defined.

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Gunnar and C. Music and Media. Regional and Area Studies. Recent work by Chien and Honey, has shown that neural activity around an artificially introduced event boundary can be effectively modeled by ongoing information integration, which is reset by a gating mechanism, very much in line with the mechanism proposed to underlie event segmentation Kurby and Zacks, We also found a similar drop in prevalence of event boundaries across communities, supporting our previous observation that the perception of event boundaries is associated with the sharing of neural state boundaries across large parts of the cortical hierarchy. Calcium imaging movies were processed using Suite2p 70 , and regions of interest corresponding to putative cell somata were manually selected. Importantly, the authors build on this previous research and demonstrate that canonical functional networks — such as the frontoparietal network, and the 'default mode' network — feature distinct subnetworks with corresponding faster and slower timescales of pattern shifts. However, how sensory-related activity is structured to facilitate its journey through the brain, and how it interacts with ongoing cortical activity, is less well understood. Developmental and Physical Disabilities Social Work. Thus, although we can make statements about a causal relation, we cannot make any claim about the specific paths or their relative contributions. One of the important conclusions of the paper is that simultaneous neural state shifts in multiple brain regions are more likely to be experienced as boundaries. Literary Studies - World. Histed, M. Literary Studies History of the Book.

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Urban History. Quantitative Political Methodology. Oxford University Press is a department of the University of Oxford. General Anaesthesia. Long-range connectivity of mouse primary somatosensory barrel cortex. Mice became acclimatized to head fixation and relaxed in the tube after the first 1—2 sessions. Indeed, the inhibited responses increased with the strength of optogenetic stimulation number of cells targeted; Fig. Cortical microstimulation influences perceptual judgements of motion direction. We also investigated how the variability of state durations differed across the cortex. We localized S1 and S2 by performing wide-field calcium imaging during deflection of individual whiskers Fig.