Where does connectivity collide?

In neuroscience, connectivity is the way the regions of a brain are linked and how strongly their activity moves together. The field separates three ideas that share the word: structural connectivity, the physical wiring of nerve fibres between regions; functional connectivity, the statistical dependence between the activity of two regions whether or not they are wired directly; and effective connectivity, the directed causal influence one region exerts on another. Sporns, Tononi, and Kötter's 2005 The human connectome proposed mapping the brain's full structural wiring diagram, while Friston's 2011 Functional and effective connectivity: A review set out the statistical and causal readings. The referent is a relationship between parts of one nervous system, read off a scanner, not the openness of a whole landscape, an abstract graph, or a working radio network.[1][2]

Unit

A link between two brain regions, scaled as fibre count, correlation, or causal weight

Recovery means

Not applicable

Measured by

Traced by diffusion imaging for wiring, or by correlating fMRI or EEG time series for functional and effective coupling

In landscape ecology, connectivity is the degree to which a landscape helps or hinders the movement of organisms among patches of habitat. Taylor, Fahrig, Henein, and Merriam's 1993 Connectivity is a vital element of landscape structure argued that it is as basic to a landscape as the patches themselves. Ecologists further split it into structural connectivity, the physical arrangement and closeness of habitat, and functional connectivity, how a particular species actually moves through that arrangement, so the same ground can be well linked for a bird and cut off for a beetle. The referent is a property of habitat spread across real terrain, judged by whether animals can travel between patches, not a coupling inside a brain, a counting property of a graph, or a signal reaching a phone.[3]

Unit

A whole landscape's ease of movement between habitat patches, for a given species

Recovery means

Corridors, stepping-stone patches, and habitat restoration can raise a landscape's connectivity for target species

Measured by

Estimated from patch maps and least-cost or circuit models, and checked against tracked animal movement or gene flow

In graph theory, connectivity is a precise property of an abstract graph: whether every vertex can be reached from every other, and how many vertices or edges must be removed to break it apart. Vertex connectivity is the smallest number of nodes whose deletion disconnects the graph, and edge connectivity the smallest number of links. Menger's 1927 Zur allgemeinen Kurventheorie proved the theorem now central to the topic: the largest number of independent paths between two vertices equals the fewest elements needed to separate them. The referent is a counting invariant of a mathematical object made of dots and lines, fixed exactly for a given graph, not a biological linkage, a property of real land, or the reach of a working network.[4]

Unit

An integer for a graph: the fewest vertices or edges whose removal disconnects it

Recovery means

Not applicable

Measured by

Computed exactly from the graph by max-flow or path-counting algorithms grounded in Menger's theorem

In telecommunications and networking, connectivity is the practical ability of a network to establish and hold usable links so that nodes stay reachable and can carry traffic. Unlike the exact graph property, it depends on physical facts: transmission range, node density, interference, mobility, and fading, so it is treated as something that holds with a probability rather than a yes-or-no invariant. Bettstetter's 2002 On the minimum node degree and connectivity of a wireless multihop network asked how densely radios must be placed for the whole network to be connected with high probability. The referent is whether a real, working network can keep its links up and reach its endpoints, not the wiring of a brain, the openness of a landscape, or a pure theorem about dots and lines.[5]

Unit

A working network's ability to keep nodes reachable, often as a probability of being connected

Recovery means

Adding relays, raising transmit power, or increasing node density can restore lost network connectivity

Measured by

Assessed by the probability a deployment is connected, plus coverage and reachability under range and density models

In marine ecology, connectivity refers to the exchange of individuals among marine populations, mostly through the dispersal of larvae, which shapes how populations are replenished. This meaning comes from Cowen (2009) in Annual Review of Marine Science.[6]

Unit

Recovery means

Measured by