THE PHENOMENON OF BRAIN PLASTICITY 25two stimuli occur together, the near- simultaneous firing of cells results in
a strengthening of their connectivity, so that they are more likely to fire to-
gether again. Conversely, the connection weakens when they fire separately.
Terje Lomo at the University of Oslo later hypothesized that connections
could be strengthened for long periods of time, a process he named long-
term potentiation. Lomo and Tim Bliss (Bliss and Lomo 1973) tested the
thesis on the hippocampi of live, anesthetized rabbits in the early 1970s,
finding that stimulating a pathway with an electrode repeatedly modified its
strength for hours on end.^5 Synaptic plasticity suggests that the brain can
change and adapt as a function of learning while remaining structurally
stable. It is this sort of plasticity that animates much contemporary social
theory, in part because of the influence of Gilles Deleuze and Felix Guat-
tari (1987).^6 They were inspired by the brain’s ability to self- organize at this
micro- architectural level, to act in a probabilistic rather than fixed fashion,
as well as to connect remote areas of itself through the creation of networks
(Murphie 2010). They described synaptic plasticity in terms of the brain’s
material potential (and its capture). But while synaptic plasticity allows the
brain to modify itself micro-^ architecturally with seemingly few limits, there
remains the question of its gross organization — for example, the relative
size, density, and shape of different brain regions and the basic wiring of
neural pathways that allow the brain to receive sensory information.
The dominant view for much of the past century was that basic neural
circuitry is predetermined, unfolding automatically from a genetic blue-
print. The cells in the retina would be connected to cells in the visual cortex
at the back of the brain, for example, through intrinsically generated path-
ways that, once laid down, are permanently fixed. David Hubel and Torsten
Wiesel’s research in the 1960s and 1970s offered a striking alternative: that
the brain uses external stimuli for its wiring. In one of their famous exper-
iments on the visual cortex, they sewed one eye of a litter of kittens shut
for three months; afterward they measured cellular activity in the column
of cells in the visual cortex that would normally have received visual in-
formation from that eye. Those cells were considerably less active, and the
kittens could see almost nothing out of the eye that had previously been
occluded, even though the eye itself was perfectly normal. Hubel and Wie-
sel concluded that sensing light generates the electrical activity necessary to
complete the writing of the visual cortex. As they put it, “in early life neuro-