2. Functional segregation vs. functional integration
Functional segregation
• individual anatomical
units are sometimes
tuned to
different types of
stimuli or stimulus
features and can carry
out different kinds
of computations
Functional integration
• individual anatomical units
show a high number of
reciprocal effective
connections and typically
work together to process
perceptual information and
to produce motor output
3. 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.
4. 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)
5. 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.
6. 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.
7. 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.
8. 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.
11. 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.
12. 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.
13. Functional connectivity
Abbot LF, Varela JA, Karmel Sen, and Nelson
SB (1997) Synaptic depression and cortical
gain control Science 275:220-223
18. 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
