Functional segregation vs. functional integration of the brain Domina Petric, MD

Functional segregation vs. functional integration individual anatomical units are sometimes tuned to different types of stimuli or stimulus features and can carry out different kinds of computations individual anatomical units show a high number of reciprocal effective connections and typically work together to process perceptual information and to produce motor output

Neural complexity A balance between the functional segregation of specialized areas and their functional integration arises naturally through the constructive and correlative properties of reentry. Neural complexity (Cn) reflects the interplay between functional segregation and integration within a neural system. Cn describes how much is more integrated the whole brain than its parts. Most intrareal and interareal neuronal pathways are reciprocal allowing for the process of reentry1.

Large-scale networks in brain Intrinsic connectivity networks (ICNs) are identified by similarities in the temporal evolution of activity in different brain areas (nodes in the network). They are most commonly extracted by functional connectivity (FC) analyses of functional magnetic resonance imaging (fMRI) data using one of two main techniques: seed-based correlation maps spatial independent component analysis (spatial ICA)

Large-scale networks in brain The default mode network (DMN) and the dorsal attention network (DAN) are the two most prominent among the commonly observed ICNs2.

Functional segregation and specialisation Functional segregation demands that cells with common functional properties are grouped together. Extrinsic connections, between cortical regions, are not continous, but occur in patches. Extrinsic connections couple different cortical areas. Intrinsic connections are confined to the cortical sheet. There is hierarchical organisation: distinction between forward and backward connections. Karl J Friston. Functional integration in the brain.

Hierarchical organisation The organisation of the visual cortices is a hierarchy of cortical levels with reciprocal extrinsic cortico-cortical connections among the constituent cortical areas (Felleman, Van Essen, 1991). The notion of a hierarchy depends upon a distinction between reciprocal forward and backward extrinsic connections. Karl J Friston. Functional integration in the brain.

Reciprocal connections Forward and backward connections show both a microstructural and functional asymmetry. Forwards connections (from a low to a high level) have sparse axonal bifurcations and are topohraphically organised. Backward connections show abundant axonal bifurcation and more diffuse topohraphy. Extrinsic connections show an orderly convergence and divergence of connections from one cortical level to the next. Backward connections are more abundant then forward connections and transcend more levels. Karl J Friston. Functional integration in the brain.

Structural plasticity The interactions between the molecular biology of gene expression, cell migration and neurogenesis in the developing brain.

Synaptic plasticity Activity dependent modelling of the pattern and strength of synaptic connections. Involves changes in the form, expression and function of synapses that endure throughout the life.

Associative plasticity Synaptic plasticity may be: transient (short-term potentiation or depression) enduring (long-term potentiation or depression) Long-term changes rely on protein synthesis, synaptic remodelling and infrastructural changes in cell processes (terminal arbours or dendritic spines). Those are calcium-dependent mechanisms. Karl J Friston. Functional integration in the brain.

Functional integration Functional integration refers to the interactions among specialised neuronal populations and how these interactions depend upon the sensorimotor or cognitive context. Functional integration is usually assessed by examining the correlations among activity in different brain areas. Explanation of the activity in one area in relation to activities elsewhere. Karl J Friston. Functional integration in the brain.

Functional connectivity Correlations between remote neurophysiological events. Effective connectivity refers explicitly to the influence that one neuronal system exerts over another (synaptic level or population level). Abbot LF, Varela JA, Karmel Sen, and Nelson SB (1997) Synaptic depression and cortical gain control Science 275:220-223

Neural activity measures5 spatial resolution temporal resolution measured phenomenon

Spatial resolution Explains across what region of brain tissue is neural activity being averaged.

Temporal resolution Explains across how much elapsed time is neural activity being averaged.

Measured phenomenon Explains what is being measured and what kind of neural activity does it correlate with.

Literature: 1) Tononi G, Sporns O, Edelman GM. A measure for brain complexity: relating functional segregation and integration in the nervous system. Proceedings of the National Academy of Sciences of the United States of America. 1994;91(11):5033-5037. 2) Matthias Mittner. Functional Integration of Large-Scale Brain Networks. Journal of Neuroscience. 27 November 2013, 33 (48) 18710-18711; DOI:10.1523/JNEUROSCI.4084-13.2013. Karl J Friston. Functional integration in the brain. Abbot LF, Varela JA, Karmel Sen, and Nelson SB (1997) Synaptic depression and cortical gain control Science 275:220-223

Literature 5) https://www.quora.com/What-are-all-of-the-different-measures-of-neural-activity-in-terms-of-their-physical-units (Paul King, fmr UC Berkeley Redwood Center for Theoretical Neuroscience)